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Ligand-independent activation of steroid hormone receptors by gonadotropin-releasing hormone Chen, Junling 2010

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Ligand-independent activation of steroid hormone receptors by gonadotropin-releasing hormone by Junling Chen Bachelor of Medicine, Xi’an Medical University, 1993 Master of Science, University of Edinburgh, 2000  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY in The Faculty of Graduate Studies (Reproductive and Developmental Sciences)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) November, 2010 © Junling Chen, 2010  Abstract Nuclear receptors including estrogen receptors (ERs) and progesterone receptors (PRs) are activated by their ligands as well as by signaling pathways in response to peptide hormones and growth factors. In gonadotrophs, gonadotropin releasing hormones (GnRHs) act via the GnRH receptor (GnRHR). Both GnRH-I and GnRH-II activate an estrogen response element (ERE)-driven luciferase reporter gene in Lf3T2 mouse pituitary cells, and GnRH-I is more potent in this regard. The ERc is phosphorylated at Ser’ 18 in the nucleus and at Ser 167 in both nucleus and cytoplasm after GnRI-I treatments, and this coincides with increased ERct binding to its co-activator, the P300/CBP-associated factor (PCAF). Most importantly, both GnRH subtypes robustly up-regulate expression of the immediate early response gene, Fosb, while co-treatment with ERa siRNA or PCAF siRNA attenuates this effect. This appears to occur at the transcriptional level because co-recruitment of ERa and PCAF to an ERE within the endogenous Fosb promoter is increased by GnRH treatments, as shown by chromatin immunoprecipitation assays. Furthermore, cross-talk between GnRH-I and PR accentuates gonadotropin production. GnRH-I activates a progesterone response element (PRE)-driven luciferase reporter gene and gonadotropin a subunit (Gsua) gene expression in two mouse gonadotroph cell lines, aT3-1 and L13T2. Up-regulation of the PRE-luciferase reporter gene by GnRH-I is attenuated by pre-treatment with protein kinase A (H89) and protein kinase C (GF109203X) inhibitors, while only GF109203X inhibits GnRH-1-induced Gsua mRNA levels. In both cell lines within the same time-frame, knockdown of PR levels by siRNA reduces GnRH-I activation of Gsua mRNA levels by approximately 40%. Both GnRH-I and GnRH-II also increase mouse Gnrhr-luciferase promoter activity and this is significantly reduced by knockdown of PR in L3T2 cells. We conclude that the effects of GnRH-I on Fosb  11  and Gsua expression, as well as mouse Gnrhr promoter activity in mouse gonadotrophs are mediated by ligand-independent activation of ERc and PR. These ligand-independent effects of GnRHs on steroid hormone receptor function may influence the magnitude of changes in the expression of specific genes in the pituitary during the mouse estrous cycle, which in this context may serve as a model in the human menstrual cycle.  111  Preface  1. A version of chapter 2 has been published. Chen J, An BS, Cheng L, Hammond GL, Leung PC 2009 Gonadotropin-releasing hormone-mediated phosphorylation of estrogen receptor-alpha contributes to Fosb expression in mouse gonadotrophs. Endocrinology 150:4583-4593.  Contributions  An BS and I designed and performed the experiments. I drafted the manuscript. Leung PC, Hammond GL and Cheng L were responsible for supervision of this work. Hammond GL and Leung PC critically revised the manuscript. All authors read and approved the final manuscript.  Presentations  Third Annual Scientific Meeting of Chinese Society of Reproductive Medicine, Chinese Medical Association. Guangzhou, China. February 2009. Oral presentation. Gonadotropin releasing hormone-mediated phosphorylation of the estrogen receptor alpha induces expression of the early response gene Fosb in mouse pituitary cells. Chen J, An BS, Cheng L, Hammond GL, Leung PC.  CIHR Research Poster Competition at the Canadian Student Health Research Forum. Winnipeg. June 2009. Poster presentation. Gonadotropin-releasing hormone-mediated phosphorylation of estrogen receptor-alpha contributes to Fosb expression in mouse gonadotrophs. Chen J, An BS, Cheng L, Hammond GL, Leung PC. CIHR-IHDCYH Scientific Forum and Poster Session. UBC. May 2010. Poster presentation. Gonadotropin-releasing hormone-mediated phosphorylation of estrogen receptor-alpha contributes to Fosb expression in mouse gonadotrophs. Chen J, An BS, Cheng L, Hammond GL, Leung PC.  2. A version of chapter 3 has been published. Chen J, An BS, So WK, Cheng L, Hammond GL, Leung PC 2010 Gonadotropin-releasing hormone-I-mediated activation of progesterone  iv  receptor contributes to gonadotropin alpha-subunit expression in mouse gonadotrophs. Endocrinology 151:1204-1211.  Contributions  An BS, So WK and I participated in the design and performance of the study, as well as the discussion of the results. I drafted the manuscript. Leung PC, Hammond GL and Cheng L were responsible for supervision of this work. Hammond GL and Leung PC critically revised the manuscript. All authors read and approved the final manuscript. An BS and I contributed equally.  Presentation The  th 4  Annual Conference of the Chinese Society of Reproductive Medicine and the  St 1  China-Association of Southeast Asian Nations Forum in Reproductive Medicine. Nanning, China. February 2010. Oral presentation. Lignd-independent activation of progesterone  receptor contributes to the self-priming effect of gonadotropin releasing hormone-I in the pituitary. Chen J, An BS, So WK, Cheng L, Hammond GL, Leung PC.  V  Table of Contents Abstract  .  ii  Preface  iv  Table of Contents  vi  List of Figures  ix  List of Abbreviations  xi  Acknowledgements  xiii  Chapter 1 Introduction  1  1.1 Overview  1  1.2 GnRH and the GnRH receptor  3  1.2.1 GnRH-I and GnRH-II  3  1.2.2 GnRI-1 receptor  8  1.2.3 Signal transduction mechanism of type I GnRHR  10  1.2.4 Regulation of type I GnRHR  12  1.3 Estrogen receptor a  13  1.3.1 Estrogen receptor  13  1.3.2 ERE-dependent genomic actions  16  1.3.3 ERE-independent genomic actions  17  1.3.4 ERa. phosphorylation  18  1.3.5 Nuclear coactivators  19  1.3.6 Ligand-independent activation of ER  21  1.4 Progesterone receptor  23  1.4.1 Progesterone receptor  23  1.4.2 Ligand-dependent activation of PR  25  1.4.3 PR phosphorylation  26  1.4.4 Ligand-independent activation of PR  26  1.5AP-1  30  1.6 Hypothesis and objectives  34  Chapter 2 GnRH-mediated phosphorylation of estrogen receptor a contributes to Fosb expression in mouse gonadotrophs  43  vi  2.1 Introduction  .43  2.2 Materials and methods  44  2.2.1 Cells and cell culture  44  2.2.2 Plasmid and ERE-luciferase reporter gene assays  45  2.2.3 Nuclear extraction, immunoblotting and immunoprecipitation  46  2.2.4 Real-time RT-PCR  47  2.2.5 Chromatin immunoprecipitation (ChIP)  48  2.2.6 Data analysis  49  2.3 Results  49  2.3.1 GnRH-I and GnRH-II rapidly and transiently activate ERa in L13T2 cells 49 2.3.2 GnRHR is required for GnRH-mediated ERE-luciferase activation  50  2.3.3 GnRH treatments affect ERa phosphorylation and promote ERa interactions with PCAF  51  2.3.4 GnRH treatments promote the co-recruitment of ERa and PCAF to the Fosb promoter ERE  52  2.3.5 GnRH treatments increase Fshb expression  54  2.4 Discussion  54  Chapter 3 GnRJ-I-I-mediated activation of progesterone receptor contributes to Gsua expression in mouse gonadotrophs  74  3.1 Introduction  74  3.2 Materials and methods  76  3.2.1 Cells and cell culture  76  3.2.2 Plasmids, siRNA and transient transfection assay  76  3.2.3 Immunoblotting  77  3.2.4 Real-time RT-PCR  77  3.2.5 Data analysis  78  3.3 Results 3.3.1 GnRH-I rapidly and transiently activates PR in aT3-l and L13T2 cells  78 ....  78  3.3.2 GnRI-I-I enhances Gsua gene expression in aT3-1 and L3T2 cells  79  3.3.3 Activation of PR and its effects on Gsua expression involves PKC  80  VII  3.3.4 GnRH-I-induced Gsua gene expression requires PR 3.4 Discussion  80 81  Chapter 4 Cross-talk between GnRH and PR in the induction of Gnrhr in mouse gonadotrophs  94  4.1 Introduction  94  4.2 Materials and methods  96  4.2.1 Cells and cell culture  96  4.2.2 Plasmids, siRNA and transient transfection assay  97  4.2.3 Immunoblotting  98  4.2.4 Real-time RT-PCR  98  4.2.5 Data analysis  98  4.3 Results  99  4.3.1 GnRI-I-I and GnRH-II transiently activate mouse Gnrhr in L13T2 cells....99 4.3.2 GnR}I-I rapidly and transiently activates the AP-1 luciferase gene in L13T2 and aT3-1 cells 4.3.3 GnRH-I-induced mouse Gnrhr promoter activity requires PR 4.4 Discussion Chapter 5 Conclusion and future work 5.1 Physiological relevance of the experimental conditions design  99 100 100 110 111  5.2 GnRH activates specific signaling pathways in the transactivation of ERcL and PR  112  5.3 GnRH-I has more robust effects than GnRH-II in mouse gonadotrophs  113  5.4 Single mutations (S118A or S167A) of ERa phosphorylation sites are not sufficient to affect Fosb protein Levels  114  5.5 PCAF regulates gene expression in the pituitary after interactions with ERa.. 116 5.6 GnRH-I activates PR in a ligand-independent manner to induce Gsua expression 117 5.7 The physiological importance of transactivation of ERa and PR by GnRI-1-I.. 119 References  127  viii  List of Figures Figure 1. 1 Hypothalamic-pituitary-gonadal axis  36  Figure 1. 2 Genomic structures of human GnRH-I and GnRH-II genes  37  Figure 1. 3 Genomic structures of human and mouse GnRI-IR type I genes  38  Figure 1. 4 Structural organization of human ERcL and ER  39  Figure 1. 5 Schematic representation of ER phosphorylation sites  40  Figure 1. 6 Structural organization of the human PR-A and PR-B isoforms  41  Figure 1. 7 Schematic representation of human PR phosphorylation sites  42  Figure 2.1 Effects of GnRH-I or GnRH-II on the trans-activation of an ERE-reporter gene in L13T2 cells Figure 2.2 GnRHR mediates the activation of ERE by GnRH-I and GnRH-II  60 62  Figure 2.3 Regulation of ERa phosphorylation at Ser’ 18 and Ser’ by GnRH-I or GnRH-II. 67 64  Figure 2.4 Interactions between ERa and PCAF after GnRH-I or GnRH-II treatments and effects on the transcription activity of ERa  66  Figure 2.5 The induction of Fosb gene expression and co-recruitment of ERa and PCAF to an ERE within the Fosb promoter after GnRH treatments  69  Figure 2.6 Increased expression of Fshb in L13T2 cells after treatments with GnRI-I subtypes  72  Figure 2.7 GnRH-mediated phosphorylation of ERa contributes to Fosb expression in mouse gonadotrophs  73  Figure 3.1 GnRH-I activates the PR in aT3-1 and LT2 cells  86  Figure 3.2 GnRH-I enhances Gsua gene expression in aT3-1 and L13T2 cells  87  Figure 3.3 PKA and PKC inhibitors reduce GnRH-I induced PRE-luciferase reporter gene activity in ctT3-1 and LPT2 cells  89  Figure 3.4 PKC inhibitors reduce GnRH-I induced increases in Gsua mRNA levels in ctT3-I and L13T2 cells Figure 3.5 GnRH-I-modulated Gsua gene expression requires the PR  90 92  Figure 3.6 GnRI-I-I-mediated activation of PR contributes to Gsua expression in mouse  ix  gonadotrophs  Figure 4.1 GnRH-I and GnRH-II activate mouse Gnrhr in L13T2 cells  .93  104  Figure 4.2 GnRH-I and GnRH-II have no effects on mouse Gnrhr-luciferase promoter activity in the aT3-1 cell line Figure 4.3 GnRH-I and GnRH-II activate AP-1 luciferase activity in L13T2 cells  105 106  Figure 4.4 GnRH-I rapidly and transiently activates AP-1 luciferase activity in aT3-1 cells  Figure 4.5 GnRH-I-induced mouse Gnrhr promoter activity requires PR  107 108  Figure 4.6 Cross-talk between GnRH-I and PR in the induction of Gnrhr promoter activity in mouse gonadotrophs  109  Figure 5. 1 Effects of mutation of Ser” 8 and Ser’ 67 on GnRH-I and GnRI-I-II induced Fosb protein levels  123  Figure 5. 2 Effects on Fosb mRNA levels by different concentration of GnRH-I and GnRH-II Figure 5. 3 Transactivation of ERcL and PR by GnRI-I-I in mouse gonadotrophs  124 125  Figure 5. 4 The physiological importance of Fosb, Gsua and Gnrhr in human menstrual cycle and mouse estrous cycle  126  x  List of Abbreviations AF  Transactivation function  AP-l  Activator protein-i  Bp  Base pair(s)  cAMP  Cyclic adenosine 5’-monophosphate  CBP  cAMP response element-binding protein-binding protein  CDK  Cyclin-dependent kinase  C/EBP13  CCAAT/enhancer binding protein 13  ChIP  Chromatin immunoprecipitation  Cpm  Counts per minute  CREB  CAMP-response element binding protein  DBD  DNA binding domain  2 E  Estradiol  EGF  Epidermal growth factor  Egri  Early growth response I  ER  Estrogen receptor  ERE  Estrogen-response element  ERK  Extracellular signal regulated protein kinase  FBS  Fetal bovine serum  FSH  Follicle stumulating hormone  FSHB  FSH beta  GAP  Gonadotropin-releasing hormone-associated peptide  GAPDH  Glyceraldehyde-3-phosphate dehydrogenase  GnRH  Gonadotropin-releasing hormone  GnRHR  GnRH receptor  GPCR  G protein-coupled receptor  GSUa  Gonadotropin a subunit  GR  Glucocorticoid receptor  GRIP-i  Glucocorticoid receptor interacting protein I  hCG  Human chorionic gonadotropin  Hsp  Heat shock protein  xi  IGF-I  Insulin-like growth factor I  INK  c-Jun N-terminal protein kinase  Kb  Kilo base pairs  LBD  Ligand binding domain  LH  Luteinizing hormone  LHB  LH beta  MAPK  Mitogen-activated protein kinase  M-MLV  Moloney murine leukemia virus  NFKB  Nuclear factor KB  P4  Progesterone  PCAF  P300/CBP-associated factor  P13K  Phosphatidylinositol 3-kinase  PKA  Protein kinase A  PKC  Protein kinase C  PR  Progesterone receptor  PRE  Progesterone-response element  RARIRXR  Retinoic acid receptor/retinoid X receptor  RSK  Ribosomal S6 kinase  RSV  Rous sarcoma virus  SRC  Steroid receptor coactivator  STAT  Signal transducer and activator of transcription  TGFct  Transforming growth factor alpha  TM  Transmembrane helices  UTR  Untranslated regions  xli  Acknowledgements First of all, I would like to express my sincere respect and deep appreciation to my supervisor, Dr. Peter C.K. Leung, for providing me the great opportunity and his supervision throughout my PhD study. I register my heartfelt gratitude to Dr. Geoffrey L. Hammond, my co-supervisor, for his constructive guidance, invaluable advice and constant encouragement for my research. I am appreciated to my supervisory committee member, Drs. Anthony Perks and Anthony Cheung for all the direction and criticisms. I sincerely thank Professor Linan Cheng, for her continuous suggestions and support for my study and career.  I am grateful to Dr. Christian Klausen for his advice and comments. I would acknowledge our senior program assistant, Ms Roshni Nair, for her patience and facilitation. I thank the Strategic Training Initiative in Research in the Reproductive Health Sciences and the Interdisciplinary Women’s Reproductive Health Research Training Program for providing me scholarship during my study.  Special thanks go to my outstanding laboratory colleagues. Their intelligence, assistance, enthusiasm, and friendship have provided both critical feedback and great enjoyment to me during my study.  I am greatly indebted to my family for their unlimited love, understanding, and support for my career.  XIII  Chapter 1 Introduction 1.1 Overview  In the reproductive system, numerous hormones and signaling pathways interact to regulate the hypothalamic-pituitary-gonadal axis. One of the master hormones in this regard is gonadotropin releasing hormone-I (GnRI-I-I), which is released from neurons within the hypothalamus in a pulsatile manner. The main target of hypothalamic GnRH-I is the anterior pituitary. After binding to the GnRH receptor (GnRHR) on the surface of gonadotrophs, GnRH-I promotes the production and release of follicle stimulating hormone (FSH) and luteinizing hormone (LH). These gonadotropins are members of the glycoprotein hormone family which comprise a common gonadotropin a subunit (GSUa) and unique 13 subunits (1). The gonadotropins play a essential role in folliculogenesis, steroidogenesis, and ovulation in the gonads (2-4). Steroid hormones from the gonads, including estradiol (E ) and 2 progesterone (P4), in turn feedback at the level of the hypothalamus and pituitary to modulate the expression and secretion of GnRH and the gonadotropins (Figure 1.1) (5). Changes in plasma hormone levels during the human menstrual cycle, which is commonly divided into the follicular phase, ovulation, and the luteal phase, are the result of a highly synchronized regulation of the hypothalamic-pituitary-ovary axis. Between the luteal and follicular phase transition, there is a small increase in serum FSH concentrations 2-4 days before the inception of the menstruation (6). In the early follicular phase the FSH level maintains improved until the midfollicular phase, during which decreases to a basal level (7). The dominant follicle is selected in this period. The intercycle FSH rise is regulated by a considerable reduction in the plasma E 2 and P4 levels during the late luteal phase (8); this  decline also reduces the negative feedback effect of these steroid hormones in the early and midluteal phase. The rise of plasma FSH concentrations in the transition from the luteal to follicular phase causes a cohort of ovarian follicles to develop. Usually only one follicle in which the granulosa cells with the lowest FSH threshold and the highest sensitivity to FSH becomes the first in the cohort to secrete E 2 (9). The E 2 concentration then feeds back to repress FSH secretion via the hypothalamic-pituitary axis. Therefore, FSH levels decline to a concentration insufficient to sustain the development of other follicles with relatively higher FSH thresholds. E 2 negatively feeds back on GnRI-I-I and LH secretion during most phases of the menstrual cycle (10), but E 2 is also the principal regulator that provides the positive feedback required to sensitize the pituitary to GnRH. This positive feedback is essential for triggering the LH surge by E 2 when a certain plasma level is achieved and maintains for a particular duration (11, 12). Although the extent to which P4 participates in the positive feedback effect before ovulation is less clear, studies have indicated that the GnRI-I self-priming effect and the onset of LH surge prompted by E 2 depend on the activation of progesterone receptor (PR) in ovariectomized Pr knockout mice administered with E 2 (13). The LH surge results in the resumption of meiosis of the oocyte, ovulation and granulosa cell Luteinization. In the luteal phase, the elevated P4 level induces the production of E . The 2 augmented plasma level of P4 first inhibits the pulsatile secretion of GnRH-I and LH and then precludes the elevated E 2 plasma levels induced GnRH-I and LH surges (14-18). Consequently, the levels of FSH and LH decrease quickly over time, and the corpus luteum subsequently undergoes atrophy. With the decrease levels of P4, menstruation occurs and the next cycle begins (19). Mouse and humans share certain similarities in their reproductive systems, including the  2  hormone synthesis and release from the hypothalamic-pituitary-gonadal axis. One significant difference is that mouse has an estrous cycle of 4 days, which is divided into diestrus, proestrus, estrus and metestrus phase. In the proestrus phase, there is an estrogen peak, followed by a progesterone, FSH and LH surge. Ovulation occurs during the estrus phase. Steroid hormone receptors are of critical importance in the reproductive system. In addition to being activated by their ligands, steroid hormone receptors, including estrogen receptor (ER) and PR, are activated by growth factors as well as by GnRH-I. Ligand-independent activation of ERa and PR by GnRH has been found in mouse gonadotrophs. As observed in mouse aT3-1 pituitary cells, GnRH-I works in concert with E 2 to influence the timing and/or magnitude of the ERa-mediated effects on gene expression (20); but the detailed mechanisms remain elusive. Furthermore, GSUa protein levels are impacted by the ligand-independent activation of PR by GnRH-I and GnRH-II in the aT3-1 cell line (21). More direct evidence that the transactivation of PR by GnRH-I contributes to Gsua gene expression is lacking. In addition, it is not known whether cross talk between GnRH and PR contributes to the expression of other genes in the pituitary, such as the Gnrhr which possesses a PRE and AP-l binding site in its promoter. In this project, the molecular mechanisms responsible for the ligand-independent activation of ERa and PR by GnRH have been studied, especially in relation to induction of their endogenous genes.  1.2 GnRH and the GnRH receptor  1.2.1 GnRII-I and GnRH-II  There are more than 20 naturally occurring GnRHs sharing 10-50% amino acid identity  3  across vertebrate species. The majority of vertebrates contain minimum two, but normally three GnRH subtypes, which vary in the amino acid sequence, tissue localization, and embryonic derivation (3, 22). On the basis of evidence from high performance liquid chromatography (23), immunohistochemistry (24-26), northern blots (27), and in situ hybridization (28), at least two GnRH subtypes, GnRH-I and GnRH-II have been ascertained in the central nervous system in mammals. The preprohormone encoded by GnRHs comprises a signal sequence, a ten-amino acid GnRH peptide, a conserved proteolytic site (Gly-Lys-Arg), followed by a GnRH-associated peptide (GAP) (29). GnRH-I is preserved all over the evolution from invertebrates to vertebrates, as demonstrated by the 60% of shared identity between tunicates and mammals (30). The human GnRH-I gene is pinpointed on chromosome 8pll .2-p2l (31) and comprises four exons disconnected by three introns. The genomic structures have been intensively studied and reviewed (Figure 1.2) (32-34). Exon 1 of the gene contains a 61 base pairs (bp) 5 ‘-untranslated region (UTR), which is represented in the mRNA expressed in the brain.  Exon 2 codes the signal sequence, followed by the ten amino acid GnRH peptide, the conserved proteolytic site (Gly-Lys-Arg), and the beginning eleven GAP residues. Exon 3 encodes the subsequent thirty-two GAP residues. The last exon codes for the rest GAP residues, the translation stop codon, and the complete 3 ‘-UTR (32, 35). The amino acid sequence  of  mammalian  GnRI-I-I  is  as  follows:  pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2 (36, 37). In human brain, GnRH-I neurons are located in the preoptic area and basal hypothalamus. Other regions in the brain have also been identified including the septal region, anterior olfactory area, the cortical and medial amygdaloid nuclei (38). Immunocytochemical studies have found the localization of GnRH-I fibers in the median eminence and infundibular stalk.  4  They are also detectable in substantial projections to the neurohypophysis (39, 40). GnRH-I mRNA is localized in the normal pituitary and in several types of pituitary adenomas (41, 42). In humans and other vertebrates, GnRH-I represents a fundamental neuroendocrine connection between the central nervous system and the reproductive system. Alterations in the frequency and amplitude of GnRH-I release from the hypothalamus in response to variations in steroid hormones sequentially alter the synthesis and secretion of both FSH and LH (43). Generally, rapid GnRH pulses, which occur in the follicular phase, favor LH secretion, and slow GnRH pulses, which occur in the luteal phase, favor FSH secretion. LH is released in a pulsatile manner, and every episode is consistent with one GnRH-I pulse. In contrast, the release pattern of FSH possesses both pulsatile and constitutive constituents, with approximately two-thirds of the total pulses successfully matching the GnRH-I pulses as observed in sheep (44). Other than its well-documented endocrine function, GnRH-I is also a potential autocrine and paracrine factor in several tissues outside of pituitary including the ovary, uterus and placenta (45-48). Since the discovery of GnRI-I-I, several GnRH-I agonists with enhanced biological potency, and GnRH-I antagonists have been discovered and comprehensively investigated (49). Some regimens have been applied for the treatment of several gynecological endocrine diseases and in controlled ovarian hyperstimulation for assisted reproductive techniques (50, 51). GnRH-II is the most conserved GnRH subtype because it is found in members of every vertebrate class (52-55) and shares 100% identity between birds and mammals (31). Initially discovered in chicken and commonly known as GnRH-II, the gene for human GnRH-II is discovered on chromosome 20pl3 by fluorescence in situ hybridization (27) and comprises four exons interrupted by three introns (Figure 1.2) (34). Compared to GnRH-I (5.1 kilo base  5  pairs (kb)), the human GnRH-II gene is notably small (2.1 kb) due to the comparatively  shorter introns. The length of the individual preprohormone elements of the two subtypes of GnRH in human is comparable, with the exception that GnRH-II has a 50% longer GAP compared to GnRH-I. A comparable discrepancy in the GAP has been found in tree shrew, indicating that this might be a feature among GnRH-II precursors in some mammals (35, 36, 56, 57). The sequence of GnRH-II is pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2, and  it only varies from that of GnRH-I at positions 5, 7, and 8 (27, 36). GnRH-II localizes among the reproductive system and other systems. The most important difference in the tissue distribution of the two GnRH subtypes is that the expression of GnRH-II is at considerably excessive levels outside the brain (27). In the human central nervous system, immunopositive GnR}I-II signals occur in the midbrain and limbic structures, where they have a crucial function in the behavioral aspects of reproduction (58, 59). Comparing with GnRH-I, GnRH-II is more efficient in accelerating reproductive  behavior in female sparrow (60), although its mechanism of action is unknown. In certain human neuronal cell lines, both expression of GnRH-I and GnRH-II is validated at the mRNA and protein levels, but there is approximately ten- to one hundred-fold higher amount of GnRH-I than that of GnRI-I-II (61). In monkeys, similar to GnRH-I, GnRH-II also localizes to the supraoptic, paraventricular, arcuate nucleus and pituitary stalk area (28, 62), where it regulates gonadotropin secretion. In rhesus monkeys, GnRH-II effectively stimulates gonadotropin release in vivo, a step mediated via the type I GnRI-IR; specifically, treatment with GnRH-II elevates plasma LH concentrations. Although a single treatment of GnRH-II fails to affect plasma FSH concentrations, a significant increase is achieved after repeated exposures. Antide, a type I GnR}IR antagonist, completely blocks GnRH-II-induced LH release (59). Furthermore, in male sheep, GnRH-II prefers FSH release (63). Both GnRH-I  6  and GnRH-II have also been localized in the pituitary of various teleost fish species in which they regulate gonadotropins and growth hormone (36). In the ram, treatments with two type I GnRHR-specific antagonists block GnRH-II-stimulated gonadotropin secretion; however, the concurrent treatment with GnRH-II fails to change GnRH-I-stimulated LH release (64). Thus, whether GnRH-I and GnRH-II elicit different effects on gonadotropin synthesis and secretion remains elusive, but this may be related to their different patterns of pulsatile secretion, concentration or the effects on intracellular signaling pathways (65). Compared to GnRH-I, GnRH-II is less vulnerable to peptidase and more stable, which improves its tissue bioavailability. Such characteristics have important implications for GnRH-II functions, particularly in hormone regulation of the reproductive system, and may result in the clarification of innovative paracrine physiological functions of GnRH-II (66). Currently, there is a lack of information on GnRH-II secretion profiles. Further studies are required to assess the effects of different GnRH subtypes on the induction of gonadotropin subunit genes, as well as other genes that are essential for pituitary function. GnRH-II has also been identified in other reproductive tissues including the endometrium (67), ovarian surface epithelial cells (68), granulosa cells (69), breast tissue (70), as well as ovarian epithelial and breast tumors (68, 70). In addition, GnRH-II plays an important role in ovarian function and implantation in humans. It is uncertain whether in these tissues the responsiveness induced by GnRH-II is significantly different from that elicited by GnRH-I. In addition to the reproductive tissues, GnRH-II mRNA has been localized in human kidney, bone marrow, and prostate. Compared with the central nervous system, kidney contains around 30-fold higher GnRH-II mRNA levels, and the prostate and bone marrow possess approximately 4-fold higher levels (27).  7  1.2.2 GnRH receptor  GnRHR belongs to the G protein-coupled receptor (GPCR) family, the structures of which are characterized by seven transmembrane helices associated with continuous intracellular and extracellular loops, as well as an external N-terminal domain. The external domains and the transmembrane regions create the area for the binding of the ligand, and the intracellular fractions are responsible for communications with intracellular G proteins, as well as other regulatory proteins (71, 72). The mammalian genome contains two subtypes of GnRHRs, type I and type II GnRHR, located on chromosome 4 and 1 in human, respectively.  The type I GnRHR genes from the human (73), mouse (74), rat (75), pig (76) and sheep (77) have been characterized, and exhibit extensive sequence similarity in the coding areas. Their structural organization consists of 3 exons interrupted by 2 introns which have been extensively studied and reviewed (Figure 1.3) (34, 78). Although the borders between exon and intron are preserved among different species, the sizes of the introns, the length and sequence of the 5 ‘-and 3 ‘-UTRs are different in the genes. The first exon codes type I GnRHR amino-terminal domain, transmembrane helices (TM) I to 3 and the first section of TM 4. The second exon contains the other section of TM 4 and TM 5. The third exon consists of TM 6 and 7 (79). The type II GnRHR gene exhibits the similar exon and intron construction as type I GnRHR, with the exception that the third exon encodes an intracellular carboxyl terminal tail, which is deficient in type I GnRHR. In the second exon of the human type II GnRHR gene, a premature stop codon (UAA) is identified which indicates products of  this gene are unfunctional. A second locus possessing a pseudogene for human type II GnRHR is localized on chromosome 14. The chimpanzee type II GnRHR gene also contains a premature stop codon (58). A fully functional type II GnRHR gene, however, is ascertained in  8  other mammalian genomes including lower primates, for instance, the marmoset monkey (63), African green monkey and rhesus monkey (80). In nonprimate mammals, the type II GnRHR gene potentially encodes functional protein in pigs and dogs, whereas not in cows and sheep. In mouse genome, there is no type II Gnrhr gene (65), whereas rat genome contains a gene remnant (81). Thus in the following content Gnrhr refers to type I Gnrhr in mouse. Since there is no functional type II GnRHR protein in the mouse or human, both GnRH-I and GnRH-II function through the type I GnRI-IR in these species (58). The intracellular tail in many GPCRs has a fundamental regulatory function in ligand-stimulated receptor signaling, desensitisation, and trafficking (82). Noticeably, comparing with other GPCR members, the type I GnRHR is special due to its total lack of a cytoplasmic carboxyl terminal tail (54, 83-86), and it does not exhibit rapid desensitisation (87). In the human type I GnRHR, several amino acid residues have been ascertained to have important function. In particular, in the third cytoplasmic loop Ala is vital for G protein coupling and GnRHR internalization (88). Some other amino acids have been found to be responsible for binding of the ligand (89-93). The species-specific Lys residue is a significant determinant of expression and internalization (94). The mammalian type I GnRHR has approximately ten-fold binding affinity for GnRH-I other than GnRH-II (95). On the other hand, the type II GnRHR has around four hundred-fold preference for GnRH-II comparing with GnRH-I (63, 80, 96). The distribution of immunoreactive type I GnRHR has been studied in normal pituitary and human pituitary tumors. In normal anterior pituitary, type I GnRHR is localized in gonadotrophs, thyrotrophs and somatotrophs. It is co-localized with GSUa, FSH beta (FSHB) and LH beta (LHB) in gonadotrophs, thyroid-stimulating hormone beta in thyrotrophs, and growth hormone in somatotrophs (97). In accordance with its mRNA expression profile in  9  pituitary tumors, immunoreactive type I GnRHR has been detected in adenomas derived gonadotrophs and somatotrophs (42, 97). In the pituitary, the type I GnRHR cascade has been comprehensively studied due to the importance of GnRH-I in the modulation of synthesis and secretion of LH and FSH. The requirement for type I GnRHR in the regulation of gonadotrophin is highlighted by the fact that in the human, type I GnRHR mutations cause hypogonadotrophic hypogonadism which has the clinical symptoms of sexual development delay, apulsatile or low levels of gonadotrophin, and low levels of steroid hormone (3, 98). This mutation results in majority mislocalised GnRHR proteins, that display changed membrane trafficking (99) and endoplasmic reticulum preservation, which may be restored to function by pharmacological chaperones (100). Apart from the pituitary, the localization of type I GnRHR mRNA has been identified in other normal tissues as well as malignant cells outside of brain, including ovary, uterus, breast, placenta and prostate (101). GnRH-I and GnRH-II exhibit other functions after binding with GnRHR such as inhibition of cell proliferation in some cell types, including cancer cells (86, 102-109).  1.2.3 Signal transduction mechanism of type I GnRIIR  In the anterior pituitary, following binding to the receptor, GnRH-I activates the protein kinase A (PKA), protein kinase C (PKC), mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (P13 K) signaling pathways; all of these pathways are indirectly involved in regulating gonadotropin subunit genes via mechanisms that are not well defined (110-116). Binding of GnRH-I to the type I GnRHR causes the coupling of the Gaq/1 1 proteins and subsequently stimulation of phospholipase Cf3 (117). This hydrolyzes  10  phosphatidylinositol 4,5-bisphosphate to diacyiglycerol and (1,4,5) inositol trisphosphate that, in turn, activates conventional PKC isoforms and mobilizes cytoplasmic calcium, respectively. In terms of PKC isoforms, u and f311 have been discovered in gonadotroph cells (118-12 1). GnRH-I also activates PKC-dependent and -independent MAPK cascades that influence gene expression (115, 122-126). Type I GnRHR signaling activates four kinase cascades, containing the extracellular signal regulated protein kinase (ERK) (122, 123, 125, 127-131), the c-Jun N-terminal protein kinase (INK) (4, 115, 129, 132, 133), p 38 MAPK (123), and the big MAPK (115); these subsequently induce expression of several genes. The activation of ERKs by GnRH-I has been widely recognized. In cT3-1 cells, the GnRH-I pulse pattern affects the responsiveness of ERKs to GnRH-I such that continuous exposure of GnRH-I stimulates short-term ERK activity, while pulsatile GnRH-I results in prolonged activation of ERK activity (128). Stimulation of ERK takes place mainly through PKC pathway in uT3-1 cell line (129, 133). In L13T2 cells, the binding of type I GnRHR by GnRI-I-I leads to activation of ERK and induction of c-fos, Gsua, Lhb, and Fshb gene expression (113, 115, 121, 134). The INK signaling cascade is another fundamental MAPK signaling participated in GnRI-{-I pathway in the aT3-1 pituitary cells. GnRH-I treatment results in a significant enhancement in INK signaling, surpassing the sequential activation of PKC, c-Src, CDC42 (Rac), and MEKK1 (115, 129). A iNK cascade regulates both basal and GnRH-I-increased rat Lhb promoter activity (115, 132). Nevertheless, other reports have indicated that iNK activation is mainly PKC-independent and mediated by elevated intracellular calcium (132, 133). The PKC-independent pathways may due to the distinct circumstances under which the PKC-dependent pathway is changed. In the fish, tilapia, GnRH-I also regulates LH and FSH secretion through divergent signaling via receptor binding. In this species, the expression of  11  the gsua and lhb subunit mRNAs is increased by ERK activation, while the induction offshb is mediated by the cyclic adenosine 5’-monophosphate (cAMP)-PKA signaling cascades (135). Another study has found that P13K is engaged in the negative adjustment of the Gsua and Fshb subunit gene expression and the cell proliferation in LPT2 cells (116).  1.2.4 Regulation of type I GnRBR  The sensitivity of GnRH-I in gonadotrophs relies on the amount of GnRHR on the surface of the cells, and this is partially regulated at the transcriptional step (136, 137). Several hormones including GnRH-I itself (123, 138-141), melatonin (142), steroid hormones (143-145), activin (31), human chorionic gonadotropin (hCG) (146, 147), intracellular signaling pathways (84, 148, 149) and transcription factors (150-152) regulate mammalian type I GnRHR transcription in different tissues from various species. In the pituitary, GnRH-I robustly regulates type I Gnrhr expression in the way that lower dosages of GnRH-I increase Gnrhr expression, while higher dosages decrease Gnrhr levels in rodents (140, 141). The frequencies of GnRH-I pulse influence the degree of increase, and highest enhancement is reached at a thirty-minute frequency in rat primary pituitary cells (153). In uT3-1 cells, the stimulation of MAPK signalings by GnRI-1-1 influences type I Gnrhr gene expression. Activation of the INK pathway by GnRH-I stimulates activator protein-i (AP- 1), which interacts with the AP-1 element in the type I Gnrhr promoter and enhances endogenous type I Gnrhr gene expression (4). It has been discovered that GnRH-I has a biphasic effect on type I GnRHR expression in human cells such as granulosa luteal cells, normal ovarian surface epithelium, ovarian cancer, and peripheral blood mononuclear cells (69, 124, 154, 155). Inhibition of type I GnRHR mRNA levels by GnRH-II irrespective of the concentration used has been reported in human granulosa luteal cells (69).  12  The steroid hormone P4 directly inhibits type I GnRHR expression in the pituitary (156). Intriguingly, P4 displays a dual function in regulating human type I GnRHR gene transcription such that it suppresses the type I GnRHR promoter in gonadotrophs but has stimulatory effects in placental cells (157). Due to the critical significance of GnRHRs in reproductive system and the prevalent usage of GnRH analogues and antagonist in endocrinology and malignant therapy, it is fundamental to clarify both the physiological and therapeutic roles of GnRH and its receptor. In summary, GnRH-I and GnRH-II regulate the synthesis and secretion of gonadotropin in the pituitary after binding with their receptor, type I GnRI-IR, both in mouse and humans. GnRI-I activates several signaling pathways, which are indispensable for the gonadotropin subunit genes expression. The functions of GnRH depend on the amount of type I GnRHR at the gonadotroph cell surface, and this is regulated by several hormones and factors including the GnRH and P4.  1.3 Estrogen receptor ct  1.3.1 Estrogen receptor Estrogens modulate many physiological functions including cell growth, development, and tissue-specific gene expression in the reproductive, skeletal and central nervous systems. Estrogens are a group of compounds and the major estrogens in human are 2 E estriol, and , estrone. Among them, E 2 is the most important physiological ligand of the ER. E 2 is produced primarily by follicles and the corpus luteum in the ovaries. In the menstrual cycle, under the stimulation of FSH and LH, there are systematic changes in the level of E 2 with  13  one surge occurring at 24-36 hours before ovulation and the other during the middle luteal phase. Feedback regulation of the hypothalamus and pituitary by estrogen is especially essential during the menstrual cycle. In the physiology and pathophysiology of many tissues, E 2 exerts critical roles by interacting with ER, which belongs to nuclear receptor superfamily. EReL and ER are two recognized subtypes of ER, which are coded by different genes and distinguished in construction, function, and tissue localization (84, 158, 159). In humans, the ERc gene has been mapped to chromosomal locus 6q25.1 (160), whereas ER gene is located on 14q22-24 (161). Both ER subtypes are composed of six domains. In details, the N-terminal A/B domain exhibits 17% amino acid sequence identity between ERc and ER. ERuc contains a ligand-independent transactivation function 1 (AF-1) in this region. The central C region is the DNA-binding domain (DBD), and it possesses two zinc finger structures crucial for connecting to estrogen response elements (EREs) in DNA sequences. This structure is considered to be the hallmark of the nuclear receptor superfamily (162, 163). In addition, the DBD mediates receptor dimerization. Given their highly conserved amino acid similarity (96%) within domain C, ERct and ERI3 should bind to the same ERE. The D domain possesses a nuclear localization signal. There are several functions in the carboxyl-terminal ElF domain involving binding to the ligand, dimerization, as well as ligand-dependent  transactivation function 2 (AF-2), comprising a shallow hydrophobic groove made up by residues among helices H3, H4, H5, and H12 where the coactivators LXXLL receptor interaction domain operates (L is leucine and X is any amino acid) (Figure 1.4) (164, 165). The ligand binding domains (LDB5) of the ERa and ERP have high homology, especially the amino acid residues which directly contact with the ligand or consist of the ligand binding cavity (166). Therefore E 2 and several other ligands bind to ERa and ER with similar  14  affinity. However, due to the relatively small ligand binding cavity in ERa, a number of ligands exhibit receptor-selective affinity and exert different biological response (161, 167). The tissue distribution profiles of the two types of ER indicate that they may have similar but also unique roles in E 2 action in vivo. ERa is primarily located in the pituitary, uterus, mammary gland, testis, liver, kidney, heart, and skeletal muscles. ERI3 is present in the ovary and prostate. The gonad, thyroid, adrenals, and various regions of the brain have relatively similar levels of ERa and ER/i mRNA. However, the cellular distribution of ERa and ER/i mRNA differs within the tissues that coexpress both subtypes of ER (168). Characterization of mice lacking either Era, Er/i, or both have shed light on the function of 2 involves each ER subtype (168). The physiological importance of ERa after binding with E maintenance of the hypothalamic-pituitary axis, bone mineral density, glucose metabolism, cardiovascular function, mating behavior, and the development of mammary gland. By contrast, ERI3 is responsible for the regulating ovulation, several aspects of mating behavior, and the immune system. The two subtypes also have different intrinsic mechanistic properties such that ER can function as an inhibitor of ERa and reduces the strength of E 2 acting via ERa (169). Both sexes of Era knockout mice are infertile, and while male Er/i knockout mice are fertile, the females are subfertile. Female mice that lack ERa have a hypoplastic uterus, a condition that is insensitive to E , donor embryos do not implant, immature follicles are 2 present in the ovary and they do not ovulate. On the other hand, female Er/i knockout mice have a normal response to E 2 in the uterus and can support pregnancy. The appearance of the Er/i knockout mouse ovary is normal but it exhibits reduced ovulation (168). In the anterior pituitary, E 2 binding can be localized within the gonadotroph, lactotrope, somatotrope, and thyrotrope cells. The rodent pituitary contains three forms of ER, including the predominant ERa, the truncated pituitary-specific form of ERa called TERP, and ERI3. In  15  both normal rodent primary cells and several cell lines including pituitary uT3-1 cells, only ERc and TERP proteins are expressed at noteworthy levels, whereas the expression of ERI3 in the pituitary is extremely low (5, 170-173). Furthermore, mice with a disrupted Era gene have compromised pituitary function, whereas Er/3 knockout mice appear to have normal pituitary function (174, 175). Thus, the response of gonadotroph cells to E 2 is primarily mediated by ERCL.  1.3.2 ERE-dependent genomic actions The main genomic effect of E 2 occurs via the ERE-dependent E -ER signaling pathway. 2 Binding of E 2 to the ER permits the receptor to separate from heat shock proteins (hsps) and promotes ER dimerization to form homodimers or heterodimers (159, 176, 177). Subsequently the ER accumulates at various permutations of a palindromic DNA sequence, 5 ‘-GGTCAnnnTGACC, which is the so-called consensus ERE with three central nonspecific nucleotides. Natural EREs lose affinity for ER with an increase in the number of nucleotides deviating from the consensus sequence, especially when the changes occur in both bisects of the ERE palindrome (178). In the human genome, however, most E 2 target genes possess non-palindromic EREs (179). The requisite sequences for imperfect EREs have been identified in vitro (180). The two ER subtypes are assumed to bind to EREs in an identical approach because both ERa and ERI3 communicate with the same nucleotides in the consensus ERE (181). The ER-ERE complex recruits coregulatory proteins, thus affecting chromatin remodeling and/or providing a bridge to other transcription factors that mediate assembly of the transcriptional machinery (182).  16  1.3.3 ERE-independent genomic actions  It is evident that ER not only regulates genes that contain EREs but also influences the expression of those that do not, and this enables ER to regulate a broader range of genes. These genes normally possess binding sites for a variety of heterogeneous transcription factors, including AP-1, Sp-1, and nuclear factor KB (NFKB) which interact with ER through protein-protein binding. The ERcL-AP- 1 protein (Fos and Jun) interaction increases the transcription of genes such as ovalbumin (183), insulin-like growth factor I (IGF-I) (184), collagenase (185) and cyclin Dl (186, 187). Activation of the ERot-AP-1 complexes induced by E 2 requires the AF-2 domain of ERcL, which binds p160 to form a multiprotein (176, 188). A direct connection between ERa and c-Jun is necessary for ERa/AP-1 action. Moreover, the coactivator glucocorticoid receptor interacting protein 1 (GRIP-i) forms a triple complex with c-Jun and ERa which stabilizes the ERa/c-Jun complex (188). The interaction between ERa and Sp- 1 regulates several genes that contain GC-rich promoter sequences, including E2F 1 (189), low-density lipoprotein receptor (190), c-fos (191), and cyclin Dl (192). The actions of ER at Sp-1 binding sites rely on the ligand, the cell type, and the receptor subtype. Although both ERa and ER form complexes with Sp-1, only ERa induces consensus Sp-1 element-linked reporter gene activity; ER by contrast exhibits minimal or decreased basal reporter gene activity. Additionally, it has been shown that the AF-1 domain of ERa is critical for ERa/Sp-1-mediated transactivation (193). Other than AP- 1 and Sp- 1, the interactions of ERa with two other transcription factors, NFiB and CCAAT/enhancer binding protein f3 (C/EBPf3), decrease interleukin-6 gene expression (194). In terms of ERE-independent genomic actions, ERs do not interact directly  17  with DNA but act by tethering other transcription factors. However, in this context, the DBD of the ERs is also crucial for proper protein-protein interactions and for the recruitment of coregulator proteins to the promoter region (130, 183-186, 194, 195).  1.3.4 ERa phosphorylation Activation of ERct by its ligand is associated with increases in overall receptor phosphorylation and this regulates certain receptor functions. Eight phosphorylation sites , Ser’° 4 , Ser’ 6 , and 18 have been identified within the human ERct. Four of these sites (Ser’° ) are located in the A/B domain, one is in C domain (Ser 67 Ser’ ), and the other three sites 236 , threonine 305 (Ser 311 and tyrosine ) are found within the LBD (Figure 1.5) (196). Among 537 them, Ser” 8 and Ser’ 67 are the major E -inducible phosphorylation sites in ERoS isolated from 2 different cell lines (197-203). Phosphorylation of the serine residues modulates the down-regulation of ERo by the ubiquitin-proteasome pathway (204); its nuclear localization (205), and transcriptional activity (198, 199). ERa phosphorylation at Ser” 8 is detected after transfection of human ERa into COS-1 cells. Mutation of this serine to alanine causes a significant reduction in transcriptional activation by ERa of reporter genes containing an ERE (199). In contrast, another study has determined that the Si 1 8A-ERa mutation alone can not significantly abolish E 2 stimulated transcriptional activity when compared to the wild-type ERa. Oniy the combined mutation of three of the amino-terminal phosphorylation , Ser’° 4 6 and Ser ) to alanine residues significantly reduces the ERa 118 sites (Ser’° transcriptional activity, highlighting the importance of multiple phosphorylation of these amino acids for full receptor function (198). Tyrosine 537 is located immediately amino-terminal to the AF-2 activation helix and is conserved in the ERa sequence of every species (206). It is regarded as a basal phosphorylation site (197).  18  1.3.5 Nuclear coactivators  The recruitment of coactivators to ERa allows the resulting complex to bridge the receptor to the general transcription machinery, leading to chromatin structure remodeling, and thereby facilitating gene expression (207). Several ERa co-activators have been identified including members of the P160 or steroid receptor coactivator (SRC) family, P300, cAMP  response  element-binding  protein-binding  protein  (CBP),  and  the  P300/CBP-associated factor (PCAF) (178, 182). The SRC family members of proteins are composed of ligand-dependent coactivators that enhance the transcriptional activation of several nuclear receptors such as ER and PR (182). This family is divided into three classes based on their sequence homology: SRC-1/NcoA-1 belongs to class I; TIF2/glucocorticoid receptor-interacting protein /NCoA-2 fits in class II, and pCIP/activator of thyroid and retinoic acid receptor/amplified in breast cancer 1/SRC-3 is a class III coactivator (208). Recruitment of SRC to the ER depends on the integrity of helix 12 with the carboxy-terminal region of the ER. Upon ligand binding, repositioning of helix 12 of the ER forms a hydrophobic cleft acting as “a charged clamp” to interact with LXXLL motifs in the coactivators (209-211). It has also been reported that SRC- 1 enhance transcriptional activation of ERa through both AF- 1 and AF-2, acting synergistically to achieve receptor full activity (212). CBP, and its homologue P300, are another class of coactivators that exhibit histone acetylase activity. They were first identified as nuclear proteins that functionally interact with the cAMP response element binding protein (CREB) and the viral adenovirus oncoprotein E1A, respectively. Subsequently they were suggested to potentiate activation of the thyroid hormone receptor, the glucocorticoid receptor (GR) and the ER (213, 214). Purified P300 is  19  found to significantly enhance ligand-dependent ER actions on a chromatin template, suggesting a role for the histone acetyltransferase activity of P300 in chromatin remodeling (215). Although CBP/P300 directly interacts with nuclear receptors through the LXXLL motifs in CBP/P300 and the LBD of the nuclear receptors (214), this somehow appears to be dispensable for transcriptional activation in vitro (216). Instead, P300/CBP is indirectly recruited to nuclear receptor target genes by the SRC coactivators, which serve as an assembly point for multimeric activation complexes (217). Both CBP and P300 have also been associated with the regulation of a large numbers of transcription factors (218). Competition for limiting levels of these proteins within a cell results in cross-talk between different signaling pathways, suggesting that CBP/P300 proteins are key mediators of signal integration (219). PCAF is the first mammalian histone acetyltransferase found original from sequence homology to the yeast Gcn5p protein (220). Chromatin is composed of nucleosomal core particles in which DNA is wrapped around histone octamers containing histones H3 and H4 heterotetramer and two heterodimers of H2A and H2B. In each of the core histones, there is a lysine rich N-terminal tail, the majority of which can be acetylated in transcriptionally active chromatin. Recombinant PCAF generally acetylates lysine 14 of H3 and lysine 8 of H4 (220, 221). PCAF also functions as a transcriptional coactivator, thus contributing to transcriptional activation by chromatin structure remodeling in GR, ER and the retinoic acid receptor/retinoid X receptor (RAR/RXR). PCAF contains an extended amino terminus that interacts with other coactivators such as CBP/P300 and members of SRC family to form a multiprotein (213, 222, 223). It is interesting that though CBP is compulsory for the roles of several transcription factors, the function of PCAF and SRC appears to be more specific. The DNA-bound transcription factors can determine recruitment of CBP, PCAF and SRC. In  20  addition, signal cascades probably participate in the regulation of the complex assembly (223, 224). Many studies have reported that steroid hormone receptors are activated and bind to specific regions in the promoters of target genes, and this occurs with the recruitment of certain coactivators to increase the target gene expression. However, how this occurs in the context of gonadotropin subunit gene expression in the pituitary function remains unclear.  1.3.6 Ligand-independent activation of ER It was originally thought that steroid hormone receptors were only activated by their own ligands. However, ligand-independent activation of a steroid hormone receptor has been found to occur in response to signaling pathways from membrane regulatory molecules including growth factors, cAMP, dopamine, cytokines, and other regulators. The activation of steroid hormone receptors by other factors instead of their own ligands represents a prime function by which membrane receptors and steroid hormone receptors cross-talk at the level of the gene transcription, and is a mechanism by which the cellular environment modulates the functions of steroid hormone receptors as transcriptional regulators (225). Numerous studies have reported that epidermal growth factor (EGF), transforming growth factor alpha (TGFcc), IGF-1, heregulin, insulin, act through several signaling pathways to transcriptionally activate genes whose promoters contain a consensus ERE in an ER-dependent manner (201, 226-23 1). For instance, EGF mimics estrogenic effects in ovariectomized mice, resulting in increased uterine and vaginal cell proliferation (232). The inhibitory effects of ICI 164,384 on EGF-stimulated cell proliferation are observed in wild-type mice but not in Era knockout mice, suggesting an association of EGF signaling with the ligand-independent activation of the ERa (233). In addition, growth factor-activated  21  ERcL transcriptional activity is dependent on the phosphorylation state of ERcL. EGF or IGF activates ERK1/2, which mediates phosphorylation of ERo at Ser , leading to the 8 ligand-independent transactivation of ERoS (226, 234). A 90 kDa ribosomal S6 kinase (RSK) is an ERK substrate and a mediator of the ERK signaling pathway. EGF or phorbol myristate activates RSK, causing specific phosphorylation of ERut at Ser’ 67 (235). PKA overexpression has been linked to improved proliferation in normal breast samples, breast malignant transformation, poor prognosis in breast tumor, as well as antiestrogen resistance (236). Up-regulation of PKA activity induces the ligand-independent activation of ERx (201, 226, 237) and increases receptor phosphorylation (198, 238-240). The ligand-independent and ERE-dependent activation of the other subtype of ER, ERf3, is also induced by forskolin and 3-isobutyl-1-methylxanthine, resulting in increases in intracellular cAMP in transient transfections of Hela cells (237). AKT is a serine/threonine protein kinase that is a downstream target of P13K. P13K and AKT activate human ERut in the absence of E 2 (241, 242). Cyclins are subunits of cyclin-dependent kinase (CDK) complexes, which regulate cell cycle progression. Cyclin Dl is overexpressed at a significant level in human breast cancers together with expression of ERct. Overexpression of cyclin Dl stimulates ERcc transcriptional functions in the absence of 2 (243, 244). The cyclin A/CDK2 complex phosphorylates ERu at Ser’° E 4 and Ser’° , and 6 these modifications potentiate the transcriptional activity of ERc in a ligand-independent manner (245). Furthermore, cyclin Dl also interactes with PCAF to facilitate the association between PCAF and the ERa. Overexpression of PCAF potentiates cyclin Dl -stimulated ERa activity in a dose-dependent manner (246), suggesting the importance of this coactivator. In the pituitary, the ligand-independent activation of ERa contributes to gene expression. In ctT3-1 gonadotroph cells, cAMP stimulates ERa in a ligand-independent manner via  22  PKA-dependent pathways. Because several physiological factors stimulate cAMP levels in the pituitary, cAMP can influence ERa activity in the pituitary in vivo (5). GnRH-I also stimulates an ERE-promoter activity in the same cell line (20). However, the molecular mechanisms responsible for this, and whether the ligand-independent activation of ERa by GnRH-I might modulate the expression of relevant endogenous genes in the pituitary remain unclear.  1.4 Progesterone receptor  1.4.1 Progesterone receptor  Pogesterone (P4) is critical in the regulation of mammary gland development, ovulation, blastocyst implantation, epithelial cell proliferation, uterus contractility, and reproductive behavior (247, 248). In the neuroendocrine system, P4 exerts negative feedback effects on both hypothalamic GnRH release and pituitary gonadotropin production (249, 250), which include homeostatic suppression of pulsatile GnRH secretion (251), as well as the pre-ovulatory GnRI-I and gonadotropin surges (252). The main regulation of female reproduction by P4 depends on the binding and activation of PR, which is another member of the nuclear receptor superfamily. The two main isoforms of PR are a full length PR-B and an amino-terminally truncated PR-A, lacking the first 164 amino acids of PR-B. The two isoforms are attained from the transcription of a same gene from two specific promoters and a translation start at two substitute AUG initiation codons (253). Both PR isoforms have three major functional domains (Figure 1.6) (254). The amino-terminal transactivation domain is poorly conserved and contains a functionally important AF-1 region. Apart from AF-1, PR-B  23  also possesses an AF-3 region that is responsible for the recruitment of coactivators to the receptor, and which modulates target gene activation and promoter specificity (255, 256). An inhibitory domain, which recruits transcriptional corepressors,  is  located  in the  amino-terminal transactivation domain (257). The DBD is composed of about 66-68 amino acids. The LBD contains a ligand-dependent AF-2, which is requisite for hormone-dependent enrollment of coactivators. The occurrence of PR-A and PR-B is conserved in several vertebrate species comprising humans and rodents (258). The two PR isoforms are usually coexpressed in normal cells in vivo; however, the ratios of the isoforms differ in reproductive tissues as a result of development (259) and hormonal levels (260), as well as during carcinogenesis (261). In the brain of E -treated rhesus macaques, the hypothalamus expresses a high level of PR-B, but 2 the pituitary contains an excess of PR-A (262). PR-A is found to be the predominant isoform in the LPT2 cell line, or pituitary cells from ovariectomizeci rats or mice. There is a relatively lower level of PR in the LPT2 cell line compared to the primary pituitary cells, and it is unaffected by E 2 alone or with P4 treatment (263). Regarding other tissues, the PR-A and PR-B levels and their ratio vary extensively during the menstrual cycle in the human endometrium (264, 265). Overexpression of PR-B is associated with advanced endometrial, cervical, and ovarian malignancy (266, 267). The PR-A and PR-B isoforms have dissimilar transactivational properties which are particular to the cell type and the target gene promoters. Generally in a diversity of cell types, the PR-B isoform is a strong transcriptional activator of some PR-dependent promoters, whereas PR-A is inactive. Furthermore, the PR-A isoform represses the transcription of PR-B, ER, the androgen receptor,  GR, and the  mineralocorticoid receptor when the receptors are co-expressed in cultured cells (255, 268, 269). In addition, the PR-B and PR-A isoforms have effect on different target genes  24  expression; for instance, of 94 P4-regulated genes in breast cancer cell lines, approximately 70% are uniquely regulated by PR-B, 4% are regulated by PR-A and not by PR-B, and 26% are regulated by both PR isoforms (270). The Pr knockout mice model has provided extensive substantiation for the essential roles of PR subtypes in female reproduction. More specifically, both Pr-a and Pr-b knockout female mice display impaired gonadotropin regulation and pregnancy-associated mammary gland morphogenesis, anovulation, and uterine dysfunction (13, 27 1-273). Specifically, Pr-a knockout mice have irregular uterine and ovarian function, whereas the defeat of Pr-b result in flawed mammary gland development during pregnancy (274, 275).  1.4.2 Ligand-dependent activation of PR The function of intracellular PR as a ligand-activated transcription factor is well characterized and is similar to that of ER (276). In the absence of P4, PRs form complexes with a number of chaperone molecules containing hsp9o, hsp7o, hsp40, Hop, and p23. The associations are required for the accurate protein folding and creation of stable complexes for competent binding ligand (277). Following P4 binding, the PRs exhibit conformational changes leading to hsp dissociation, receptor phosphorylation, dimerization, nuclear translocation, binding to progesterone response elements (PREs) with a specific sequence as 5’-AGAACAnnnTGTTCT, and subsequent gene transcription (278). If expressed in equal ratios, the PR-A and PR-B proteins dimerize to form the three distinct dimer types, A:A or B:B homodimers or A:B heterodimers, that bind DNA. The presence of the specific AF-3 domain of PR-B in these complexes contains differential transactivation properties, which may influence the entire repertoire of physiological responses to P4 (114, 279, 280). Similar to ER, PR may alternatively control genes expression by tethering to other  25  transcription factors including AP-1, SP-1, or the signal transducer and activator of transcription (STAT) (270, 28 1-283). All of these regulation routes contribute to the biological response to P4.  1.4.3 PR phosphorylation  The role of PR phosphorylation is still elusive; it may be responsible for the modulation of ligand-dependent (284) and ligand-independent (285, 286) hormone sensitivity, nuclear localization, receptor turnover, interaction with co-regulators, and transcriptional activities. Fourteen PR phosphorylation sites have been identified (Figure 1.7) (287, 288). Of these sites, serines 102, 294, 345 and 400 can be phosphorylated by the ligand (289, 290). The phosphorylation of serines at positions 81, 162, 190, 294 and 400 seem to occur in a ligand-independent manner (289).  1.4.4 Ligand-independent activation of PR O’Malley’s group published the pioneering study on the ligand-independent activation of the nuclear receptor family, where cellular phosphorylation pathways were first discovered to activate PR in the absence of a ligand (291). Next, they reported that dopamine activated PR in both cultured cells and living animals by acting on its own Dl membrane receptor (292, 293). Later studies have demonstrated that several growth factors and kinases phosphorylate specific serine sites and activate the PR, a process with physiological significance. For instance, in neuroendocrine cells, the ligand-independent activation of PR in response to dopamine is found to mediate sexual behavior in rodents (272, 293). In breast cancer cells EGF strongly activates MAPK, thus inducing PR phosphorylation at 5er 294 and its rapid nuclear accumulation, and mutation of Ser 294 to Ala (S294A) abolishes EGF-mediated  26  translocation (294). In addition, heregulin, an EGF family member, also stimulates the MAPK signaling pathway and induces PR phosphorylation at Ser , nuclear translocation, 294 DNA binding, and transcriptional activity in a ligand-independent manner in T47D breast cancer cells (285, 294). Casein kinase II and MAPK phosphorylate PR at Ser ’ (295) and 8 294 (284, 296), respectively. Cyclin A/CDK2 complexes phosphorylate eight of the 14 sites Ser in vitro; these include serines 25, 162, 190, 213, 400, 554, 676, and Thr ° (286, 289, 297), 43  although only 5 of them including serines 162, 190, 213, 400 and 676, have been confirmed to be phosphorylated in vivo (286, 289, 295, 297). CDK2 is also shown to enhance the translocation of phosphorylated PR at Ser ° to the nucleus. Overexpression of CDK2 40 increases PR transcriptional activity with or without treatment with progestin. The ligand-independent transactivation of PR is specifically blocked by the mutation of Ser ° to 40 alanine (S400A) (286), suggesting that CDK2 regulates unliganded PR by stimulating Ser ° 40 phosphorylation. In addition to the ligand-independent transcriptional activity of PR by growth factors, the cross-talk between GnRH-I and PR, which is believed to play an imperative role in the GnRI-I-I self-priming effect, has been reported in rodent pituitary cells. The self-priming effect of GnRI-I-I is one of the fundamental pathways involved in the GnRH-I-induced release of gonadotropin; this effect is defined as increased gonadotropin secretion from gonadotrophs in response to a second stimulation by GnRH-I (298, 299). This pathway markedly potentiates the pituitary responsiveness to GnRH-I. Numerous animal studies have suggested that such amplifying effects of serial GnRH-I pulses are crucial to the genesis of the preovulatory LH surge at the mid-point of the menstrual cycle. Interestingly, the administration of a pulse of GnRH-I to primary rat pituitary cells cultured with E 2 potentiates the LH secretion in response to subsequent GnRH-I pulses, and this is blocked by a PR  27  antagonist, RU488. Similarly, forskolin increases the response to a pulse of GnRH-I in rat pituitary cells; this is also reduced by RU488 in the absence of P4 (250). Furthermore, P4, GnRI-I-I, or 8-bromo-CAMP induce CAT activity in the pituitary cells transfected with the PRE-Elb-CAT plasmid.  CAT activity  is blocked by RU488,  suggesting that a  GnRH-I-triggered signaling cascade transactivates PR in a ligand-independent manner (300). The GnRH-I seif-potentiation is shown to depend on PR in experiments using Pr knockout mice that lack either isoform a or b of the Pr. Wild-type mice exhibit a robust GnRH-I self-priming effect. In contrast, Pr knockout mice receiving two GnRH-I pulses present no additional increase in plasma LH levels, suggesting that the activation of PR is essential for the existence of the GnRH-I self-priming effect (13). Pituitary cells from ovariectomized wild-type or Pr knockout mice challenged with hourly pulses of GnRH-I achieve similar results. The cells from Pr knockout mice exhibit a blunted GnRH-I self-priming response (301). Data from our laboratory have provided further evidence of the cross-talk between GnRI-I and PR in mouse pituitary cells. More specifically, GnRI-1-I and GnRI-I-II activate a PRE-luciferase reporter gene in a ligand-independent manner through the PKC and PKA signaling pathways; the effect of GnRH-I is more profound than that of GnRH-II. GnRH-I and GnRH-II also phosphorylate PR at 5er 294 and induce PR translocation to the nucleus. Furthermore, interactions between PR and SRC-3 increase after GnRH treatment. Most importantly, GnRFI-I and GnRH-II induce the assembly of PR and SRC-3 to the PREs of the  luciferase reporter gene, as well as the Gsua subunit gene promoter. These effects rely on GnRHR since knockdown of GnRHR using siRNA reduces activation of PR by GnRH (21).  More recently, our laboratory has shown that GnRH-I increases Fshb through the ligand-independent activation of PR in LT2 cells. GnRI-I-I stimulates PRE-luciferase  28  reporter gene activity and Fshb mRNA levels; GnRH-I is more effective than GnRH-II. While this is attenuated by PKA and PKC inhibitors, PR phosphorylation at Ser 249 is only blocked by inhibition of PKC. In addition, treatment with GnRH-I increases the interaction between PR and SRC-3; this interaction is believed to be imperative for the induction of Fshb by GnRH-I because transfection of SRC-3 siRNA markedly reduces the GnRH-I effect. Importantly, knocking down PR by using siRNA significantly reduces the GnRH-I activation of a PRE-luciferase reporter gene and Fshb mRNA levels. ChIP assays also demonstrate that GnRH-I induces binding of PR to the PRE within the promoter of Fshb (302). From these studies it is concluded that the effects of GnRH on Gsua and Fshb gene expression depend, at least in part, on the transactivation of PR in a ligand-independent manner. This is mediated by PR phosphorylation, nuclear translocation and loading of PR and SRC-3 at the PRE within the promoters of Gsua and Fshb. Throughout the human menstrual cycle and mouse estrous cycle, the gonadotropins are coordinately and differentially regulated in essentially the same way. The physiological importance of induction of Gsua by GnRH through the cross-talk with PR is proposed as the normal mechanism of the preovulatory LH surge (21, 299). The routes for GnRH-I self priming require the PR and serve as functional pathway to ensure the LH surge. Apart from this, GnRH-I is suggested to activate the PR in the absence of P4 and to promote the accumulation of Fshb gene expression in L13T2 cells. This contributes to the differential regulation of gondotropin gene expression during the luteal-follicular transition and leads to the selection of dominant follicles. There are still several issues that remain uncertain in relation to the ligand-independent activation of PR by GnRH, and its effects on Gsua gene expression. Although GnRH-I treatment increases the assembly of PR and SRC-3 to the PRE in the promoter of Gsua, and promotes GSU protein levels (21), direct evidence for the  29  GnRH-I dependent induction of the Gsua gene through PR is lacking. Furthermore, the induction of Gsua gene expression by GnRH-I involving the transactivation of PR was only previously studied in ctT3-l cells. Further research is needed to demonstrate that the induction of Gsua gene expression is mediated by the cross-talk between GnRH and PR also occurs in other pituitary cell lines, such as LT2 cells, which are more representative of mature pituitary gonadotrophs.  1.5 AP-1  The AP- 1 proteins are basic leucine zipper transcription factors which comprise c-Jun, JunB, JunD, c-Fos, Fosb, Fra-1 and Fra-2; the members of this family are early response genes which can be stimulated by several extracellular subjects compassing UV irradiation, oxidative stress, steroid hormones, as well as growth factors (118, 303). AP- 1 proteins attach to particular promoter areas, otherwise known as 1 2-O-tetradecanoylphorbol 13-acetate response elements, to regulate several genes expression which participate in cell growth, differentiation and metastasis (304). Increased AP-1 levels often result in the amplification of target gene expression. AP- 1 activity can be regulated at several levels, for instance, AP- 1 dimer formation, transcription and posttranslation issues, as well as communication with accessory proteins (305). In terms of the structure, AP-1 members are similar to other transcription factors which possess transactivation domains, DNA binding domains, and leucine zippers which form dimerization areas to allow the creation of effective transcriptional items (303). The Jun family members generate dimers among themselves to be active in transcription. However, the Fos family members do not form stable dimers but bind to the Jun members to form heterodimers.  30  Although all types of Fos-Jun and Jun-Jun dimers bind the consensus AP- 1 binding site in the promoters of target genes, functional assays have revealed some discrepancies in their binding ability and stability to unique AP-l sites, as well as transcriptional activation. Typically, the binding of heterodimers of Fos-Jun to DNA is more stable than homodimers (306). In addition, c-Jun dimers are the strongest with respect to target gene expression as compared to the JunB or JunD homodimers (307). Heterodimers consisting of Fosb are more stable than those composed of Fra-1 or c-Fos binding to DNA (308). Due to differences in c-Jun to JunB ratios, AP-1 dimers stimulate either cellular growth or differentiation in keratinocytes (309) and serve as activators or inhibitors of cell death in erythroid cells (310). The essential function of AP-l in malignancy has been broadly studied. It has been found that c-Jun and c-Fos are involved in oncogenic transformation (311, 312). Increase of Fra-1 at least in part involves in the proliferation of estrogen-independent breast cancer cells (313). The regulation of AP-1 activity by retinoic acid partially mediates anti-carcinogenesis in AP-1-luciferase transgenic mouse (314). Experimentally manipulated deficiencies in individual AP-1 proteins in mice or cultured cells provide a more precise technique to ascertain the physiological roles. Fibroblasts obtained from lacking both c-los and Fosb mice display diminished cell growth. Mice with both c-fos and Fosb deletions are approximately one third smaller than their wild-type siblings or the corresponding single mutants (315). Unlike a deficiency in one of the Fos members, deletion of one individual Jun protein in fibroblasts results in considerable alteration of cell growth. The c-jun mutation induces a dramatic increase in cell cycle transit time, the most rigorous flaws which cause fibroblasts only have one or two cell division rounds before they display a growth arrest phenotype in culture (120, 316, 317). The importance of AP-1 in the pituitary has been confirmed by several studies.  31  Administration of GnRH-I stimulates transcription of the early response genes, including Fosb, c-Fos, and c-Jun either in cultured cells or in hypogonadotropic animals (318-321). Furthermore, the induction of the Fshb gene by GnRH-I involves the transcription factor AP-1. In aT3-1 and HeLa cells transfected with mouse Gnrhr, GnRH-I increases the AP-l binding activity. Mutation of putative AP-l sites in the Fshb promoter reduces GnRH-I induction of Fshb in heterologous HeLa cells (322). In the ovine FSHI3 promoter, purified c-Jun protein binds to putative AP-1 sites (323). In mouse L13T2 gonadotroph cells, regulation of the mouse Fshb promoter by GnRH-I is mediated, at least in part, by the induction of multiple AP-1 subtypes. These subtypes integrate to a site consisting of a half-site of the AP-1 consensus binding sequence that overlaps the element binding to the basal transcription factor NF-Y. GnRH-I stimulates the interaction of NF-Y and AP- 1, as well as the co-occupation to this site in vivo (324). In Lf3T2 cells transfected with a human FSHB promoter reporter construct, GnRI-I-I stimulates FSHB promoter activity in a concentrationand time-dependent manner, via the ERK1/2 and p38 signaling pathways. GnRI-I-I also induces the synthesis of AP-1 proteins, including Fosb, c-Fos, JunB, and c-Jun, as well as AP-1 complex formation. AP-1 binds to a conserved cis-element in the transcriptional initiation site of the FSHB promoter. There is also the other site that localizes more proximally  with  lower  affinity.  Mutations  of  these  cis-elements  reduce  the  GnRH-I-stimulated FSHB promoter activity; undoubtedly, the interruption of the site with higher affinity is more effective. A dominant-negative Fos protein restrains the GnRFJ-I-stimulated FSHB transcriptional activity in a concentration-dependent manner, confirming the central role of endogenous AP-1 proteins (325). The involvement of AP- 1 in the induction of Gnrhr by GnRH-I and glucocorticoids has been recognized. GnRH-I induces Gnrhr mRNA levels in primary rat pituitary cells (139). In  32  the aT3-1 and LT2 cell lines, GnRH-I stimulates endogenous Gnrhr mRNA levels and a mouse Gnrhr-luciferase promoter activity (123, 326-328). An AP-1-binding site is the critical promoter element in the regulation of the mouse Gnrhr by GnRH-I in LT3-1 cells (326). In addition to GnRH-I, glucocorticoids have also been shown to induce Gnrhr gene expression in GnRH-deficient rodents pituitary cells (329). In L13T2 cells, dexamethasone alone upregulates both the expression of an endogenous Gnrhr gene and that of a transfected mouse Gnrhr promoter-reporter construct (327, 330). These results are further confirmed in the somatolactotrope GGH3 cell line, where glucocorticoids strengthens the mouse Gnrhr promoter activity (143). Importantly, an AP-1 site in the mouse Gnrhr promoter is required for this up-regulation by glucocorticoids, indicating that the GR combines with AP- 1 proteins to increase transcription of the mouse Gnrhr gene (331, 332). A more recent study has indicated a rapid nongenomic and genomic cross-talk machinery between the GnRNR and GR signaling pathways in LPT2 cells. GnRH-I and dexamethasone increase both the mouse Gnrhr promoter activity and endogenous Gnrhr gene expression, which requires GR. ChIP and immunofluorescence analyses indicate that both GnRH-I and dexamethasone enhance the mouse Gnrhr gene through nuclear localization and connection of the GR with the AP-1 binding site on the mouse Gnrhr promoter. Furthermore, GnRH and dexamethasone synergistically activate the endogenous Gnrhr promoter via a mechanism involving the recruitment of SRC-1 to the AP-l region in the promoter of Gnrhr (333). These studies provide evidence that AP-1 proteins are necessary for Gnrhr gene expression and that this involves protein-protein interactions between AP- 1 and GR. Taken together, the available data suggest that AP- I plays important roles in the pituitary. GnRH-I rapidly induces the expression of several AP-1 family genes, including mouse Fosb (318), which contains an ERE in its promoter (334). As indicated previously, GnRH-I also  33  increases the activity of a ERE-luciferase reporter gene in mouse pituitary ctT3- 1 cells (20). It is unclear whether GnRH-I stimulates Fosb via the ligand-independent activation of ERx, and contributes to Fshb expression. Intriguingly, other than the GR (333), GnRH-I and GnRH-II activate PR in a ligand-independent manner (21, 302). GnRH-I also increases Gnrhr gene expression and a mouse Gnrhr-luciferase reporter gene activity (333). As confirmed by previous studies and using the bioinformatic analysis tool, Genomatix (http://www.genomatix.de/en/index.html), the mouse Gnrhr is composed of a PRE and an AP-1 binding site in the promoter (326, 333). But whether induction of Gnrhr by GnRH is mediated by ligand-independent activation of PR and ER in the pituitary remains unclear.  1.6 Hypothesis and objectives  This project sets out to address the hypothesis that ligand-independent activation of ERo and PR by GnRH involves in target genes expression in mouse gonadotrophs. In this project, we have re-examined the cross-talk between ER&PR and the GnRH-mediated signaling pathways that regulate the activation and expression of specific genes in mouse LT2 and/or ctT3-1 pituitary cells.  Objective 1. In Chapter 2, I tested the hypothesis that GnRH-mediated phosphorylation of the ERa contributes to Fosb expression in mouse gonadotrophs in 5 sets of experiments: 1) The activation of ERa by GnRH-I and GnRH-II in LPT2 cells was investigated. 2) The requirement of GnRHR for GnRH-mediated ERE-luciferase was examined. 3) The phosphorylation of ERa and promotion of ERa interactions with its coactivators by GnRH-I and GnRH-II were evaluated.  34  4) The co-recruitment of ERri and PCAF to the Fosb promoter ERE after GnRI-I treatments was verified. 5) Whether GnRH treatments increased Fshb expression was measured.  Objective 2. In Chapter 3, I investigated whether the GnRI-I-I-mediated activation of PR contributes to Gsua expression in mouse gonadotrophs in 4 sets of experiments: 1) The activation of PR by GnRH-I in uT3-l and Lf3T2 cells was tested. 2) The stimulation of Gsua gene expression by GnRH-I in oT3-1 and L13T2 cells was evaluated. 3) The involvement of PKC during the activation of PR and its effects on Gsua expression was elucidated. 4) The induction of Gsua gene expression by GnRH-I requires PR was examined.  Objective 3. In Chapter 4, I inspected the cross-talk between GnRH and PR in the induction of Gnrhr in mouse gonadotrophs in 4 sets of experiments: 1) The ability of GnRH-I and GnR}I-II to activate a mouse Gnrhr-luciferase promoter in L13T2 and aT3-l cells was measured. 2) The ability of GnRH-I and GnRH-I1 to activate AP-I-Luciferase gene in LPT2 and aT3-l cells was evaluated. 3) The requirement for the PR in GnRH-I-induced mouse Gnrhr promoter activity was tested.  35  +1-  Hypothalamus GnRH  AJtJ\. +1-  Pituitary  4  FSH,LH  , P4 2 E  Figure 1. 1 Hypothalamic-pituitary-gonadal axis. , estradiol; FSH, follicle stumulating hormone; GnRH, gonadotropin-releasing hormone; 2 E  LH, luteinizing hormone; P4, progesterone;  +,  positive feedback;  -,  negative feedback; (1fIJ\,  pulsatile secretion.  36  869bp  2.lkp  1.5kp  Human GnRH-I 142.bp  6lbp 741bp  2Olbp  96bp 844bp  lO9bp  Human GnRH-II l6lhp  44bp  Exon 2  Exon 1  D 5-UTR Q  Signal sequence  6Obp  158bp  Exon 4  Exon 3  • GnR}I  GAP  Q Y-UTR  Figure 1. 2 Genomic structures of human GnRH-I and GnRH-II genes. Two forms of GnRH, termed GnRH-I and GnRH-II, have been identified in humans. Their genes consist of 4 exons (boxes) interrupted by 3 introns (thin lines). The encoded preprohormones contain a signal sequence, a GnRI-I decapeptide, a conserved GKR cleavage site,  and  subsequently  a  GAP.  bp,  base  pairs;  GAP,  gonadotropin-releasing  hormone-associated peptide; GnRH, gonadotropin-releasing hormone; kp, kilo base pairs; UTR, untranslated regions. Modified from Cheng CK and Leung Pc, 2005 (34).  37  Exonl  Exon:3  Exon2  Human  1  Mouse  328  241 bp  522 bp —15 kb  3’-UTR  —5 kb  Figure 1. 3 Genomic structures of human and mouse GnRHR type I genes.  In human and mouse the genes coding for the type I GnRH receptor are composed of three exons separated by two introns. In human, exon 1 consists of the 5’-UTR and encodes the first 3 TM domains and a part of the fourth TM domain. Exon 2 codes the remainder of the fourth TM domain, the fifth TM domain, and part of the third intracellular ioop. Exon 3 consists of the rest of the open reading frame and contains the 3’-UTR. bp, base pairs; GnRHR, GnRH receptor; kb, kilo base pairs; TM, transmembrane helices; UTR, untranslated regions. Modified from Cheng CK and Leung Pc, 2005; and Hapgood JP et a!, 2005 (34, 78).  38  ERc  DBD  ] 2 NE{  LBD  I—COOH  AF-1  I  ER  I  I  }C00H  AF-2 AJE  CD  E  F  Figure 1. 4 Structural organization of human ERu and ER. Both ER subtypes share a highly conserved DBD and moderately conserved LDB. The ligand-dependent transcriptional activities are mediated through AF-2 in both subtypes. ERct contains a constitutive AF-1 in the N terminus. AF, transactivation function; DBD, DNA binding domain; ER, estrogen receptor; LBD, ligand binding domain. Modified from Hall JM and McDonnell DP, 2005 (165).  39  CDK2/cycin A MAPK AKT PKA PKA P38cz/SAPK2a Src  1  ER S104/106/118  S167  S236  S305 T311  C  D  Y537 E  F  Figure 1. 5 Schematic representation of ER phosphorylation sites. Eight phosphorylation sites have been identified within the human ERL. Four of these sites , Ser 6 , Ser’° 104 (Ser ) are located in the A/B domain, one is in C domain (Ser 67 , and Ser’ 118 ), 236 and the other three sites (Ser ) are found within the E domain. 537 , threonine 305 ’ and tyrosine 31 CDK, cyclin-dependent kinase; ER, estrogen receptor; MAPK, mitogen-activated protein kinase; PKA, protein kinase A; S104/106/118, Ser’° , Ser’ 4 06 and Ser” ; S167, Ser’ 8 ; S236, 67 ; S305, Ser 236 Ser ; SAPK, stress-activated protein kinase; T311, threonine 305 ; T537, 311 . Modified from Al-Dhaheri MH and Rowan BG 2006 (196). 537 tyrosine  40  AF-3  AF-1  PR-B M{ F 1f 2  AF-2  TDBDII  1  f  I—CO0H 923  DIM  AF-1  AF-2  —  PR-A  [  LBD  M12—J]D1  JDBDII  f  166  LBD  T  I—COOH 923  AF-2 CD  F DIM  Figure 1. 6 Structural organization of the human PR-A and PR-B isoforms. Numbers stand for the amino acid position in each protein. AF, transactivation function; DBD, DNA binding domain; DIM, sequences important for receptor dimerization; ID, inhibitory domain; LBD, ligand binding domain; PR, progesterone receptor. Modified from Mulac-Jericevic B and Conneely OM, 2004 (254).  41  PR-B  I  PR-A  I  DBD  Io*+***I**®o***I  LBD  1*1  AF-1  I AF-2  o  MAPK consensus sites (20, 294, 345) • CaseinKinaselisite (81) * CDK2 sites (25, 162, 190, 213, 400, 430, 554, 676) * Unknown kinases (102, 130, 294) Hormone-dependent sites: 102, 294, 345, 400 Basal sites: 81, 162, 190, 400  Figure 1. 7 Schematic representation of human PR phosphorylation sites. There are totally 13 serine residues and 1 threonine residue in human PR which represent basal and ligand-induced phosphorylation sites. MAPK, casein kinase II, and CDK2 can also phosphorylate PR. AF, transactivation function; CDK, cyclin-dependent kinase; DBD, DNA binding domain; LBD, ligand binding domain; MAPK, mitogen-activated protein kinase; PR, progesterone receptor. Modified from Lange CA, 2004 and Lange CA, 2008 (287, 288)  42  Chapter 2 GnRII-mediated phosphorylation of estrogen receptor a contributes to Fosb expression in mouse gonadotrophs’ 2.1 Introduction In the pituitary, numerous hormones and signaling cascades intersect to control the reproductive system. Critically important in this regard is GnRH-I which is released into the hypophyseal portal system in a pulsatile manner to stimulate the biosynthesis and secretion of FSH and LH (30, 54, 335, 336). A second GnRH subtype, GnRH-II, displays a different spatial pattern of expression and has specific functions in other reproductive tissues, such as the placenta and ovary (34, 337). The mammalian genome also contains two distinct GnRH receptor genes (type I and type II GnRHR), but type 11 GnRHR has never been found to be expressed in the mouse or human, and GnRH-I and GnRH-II function through the type I GnRHR in these species (81). After binding to its receptor, GnRH-I activates the PKA, PKC, P13K and MAPK signaling pathways, which are all indirectly involved in regulating gonadotropin subunit genes (110-114, 116, 338). The pulsatile binding of GnRH-I to the type I GnRHR on pituitary gonadotrophs also induces the expression of immediate early response genes, including AP- 1 which comprises either Jun/Jun homodimers or Jun/Fos heterodimers. In mouse LT2 pituitary cells, GnRH-I stimulates the production of AP-1 components via the MAPK signaling pathway (324, 325, 339), and subsequently up-regulates Fshb promoter activity (322, 325). Feedback regulation of pituitary gonadotropin production by estrogen is also essential for controlling reproductive cycles. E 2 is the most important physiological ligand of the ERcc, A version of this chapter has been published. Chen J, An BS, Cheng L, Hammond GL, Leung PC 2009 Gonadotropin-releasing hormone-mediated phosphorylation of estrogen receptor-alpha contributes to fosB expression in mouse gonadotrophs. Endocrinology 150:4583-4593  43  and it promotes ERa dimerization and binding to EREs that are often located in the promoters of estrogen sensitive genes (176, 340). When ERa binds to an ERE (178) it recruits co-regulatory proteins that influence chromatin remodeling and/or provide a bridge to other transcription factors that mediate assembly of the transcriptional machinery (182). Several ERct co-activators have been identified, including members of the P160 or SRC family, P300, CBP proteins, and PCAF (178, 182). In addition to this classical genomic mechanism of ligand-induced activation of ERa, its transcriptional activity can be influenced by signaling pathways that alter its phosphorylation status (20, 197, 198, 201, 226). These signaling pathways are normally triggered by growth factors and peptide hormones, such as GnRH-I, and they work in concert with E 2 to influence the timing and/or magnitude of the ERa-mediated effects on gene expression, as observed in mouse aT3-1 pituitary cells (20). However, since the latter immortalized mouse gonadotrophs are considered developmentally immature and do not express the gondotropin 3 subunit genes (341), we have re-examined the cross-talk between E 2 and GnRI-I-mediated signaling pathways that regulate ERa activation of gene expression in mouse L13T2 pituitary cells, because they express both Fshb and Lhb subunit genes (342, 343). In particular, our experiments set out to define the molecular mechanisms that mediate the rapid ERa-dependent responses to GnRH in these pituitary cells.  2.2 Materials and methods  2.2.1 Cells and cell culture  The mouse gonadotroph-derived L13T2 (342) cell line was generously provided by Dr.  44  P.L. Melon (Department of Reproductive Medicine, University of California, San Diego, CA) and maintained in monolayer cultures in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal bovine serum (FBS), 100 U/ml penicillin G, and 0.1 mg/mI streptomycin (Invitrogen, Burlington, ON) in humidified 5% C0 , 95% air at 37 C. The cells were 2 passaged when they reached about 90% confluence using a trypsin/EDTA solution (0.05% trypsin, 0.5 mM EDTA), and kept in phenol-red free medium and charcoal-treated FBS for 4 days before experiments.  2.2.2 Plasmid and ERE-luciferase reporter gene assays  The pERE-tk-Luc reporter plasmid containing two copies of a consensus ERE was kindly provided by Dr. J. Larry Jameson (Northwestern University Medical Schol, Chicago, IL, USA), and prepared for transfections using Qiagen Plasmid Maxi Kits (Qiagen, Mississauga, ON). Transient transfections of the pERE-tk-Luc were performed using FuGENE 6.0 (Roche Diagnostics, Quebec, QC) together with a Rous sarcoma virus (RSV)-lacZ plasmid to correct for transfection efficiencies. One day before transfection, 12x i0 L13T2 cells were seeded in six-well plates. One microgram of pERE-tk-Luc and 0.5j.tg of RSV-lacZ were dissolved in I OOp.l culture medium containing 3il of FuGENE 6.0 without serum. The DNA mixture was incubated for 25 mm at room temperature and then applied to the cells. After set times of culture (1  -  48 h), cellular lysates were obtained after addition of  150111 reporter lysis buffer (Promega Corp., San Luis Obispo, CA), and assayed for luciferase activity using a Lumat LB 9507 luminometer (EG&G, Berthold, Germany). 13-Galactosidase activity was also measured using the -Ga1actosidase Enzyme Assay System (Promega Corp.) to  normalize  for transfection  efficiencies.  Promoter  activity  was  calculated  as  luciferase/-galactosidase activity. To knock-down the cell levels of specific proteins,  45  indicated amounts of siRNAs (ERa, GnRHR or PCAF from Qiagen) were co-transfected together with pERE-tk-Luc and RSV-lacZ using FuGENE 6.0.  2.2.3 Nuclear extraction, immunoblotting and immunoprecipitation  Cells seeded in 10cm dishes were washed with cold PBS and harvested with 1 ml 10 mM Hepes, pH 7.9, 10 mM KC1, 10 mM EDTA, 1 mM dithiothreitol, 40 jil/ml 10% IGEPAL (Nonidet P40 Substitute), and 10 jil/ml protein inhibitor cocktail. Cell lysates were placed in an orbital rocker for 15 mill at 4 C. After centrifugation (14,000 g at 4 C for 5 mm), the supernatant cytoplasmic protein was collected. Nuclear pellets were obtained and re-suspended in 20 mM Hepes, pH 7.9, 0.4 mM NaCI, 1 mM EDTA, 50% glycerol, 1 mM dithiothreitol, and 10 il/ml protein inhibitor cocktail (Sigma. St. Louis, MO); mixed in an orbital rocker for 2 h at 4 C, and then centrifuged (14,000 g at 4 C for 5 mm) to obtain nuclear protein extracts. The protein content was determined using a Bradford assay (Bio-Rad Laboratories, Mississauga, ON), and 40 jil aliquots were resolved by  10% SDS-PAGE and  electrotransferred to a Hybond-C membrane (Amersham Biosciences, Morgan, ON). After blocking, the membranes were incubated (overnight 4 C) with specific antibodies against: phospho-ERa (Ser’ ), phosphor-ERa (Ser’ 18 ) (Cell Signaling Technology, Inc., Pickering, 67 ON), ERa, Fosb, 13-actin (Santa Cruz Biotechnology, Santa Cruz, CA), or type I GnRHR (Lab Vision Corporation, Montreal, QC). Horseradish peroxidase-conjugated secondary antibodies were then incubated with the membranes. After washing, immunoblots were examined using the ECL chemiluminescent system (Amersham Pharmacia Biotech, Piscataway, NJ) followed by exposure to Kodak X-Omat film. Nuclear protein extracts were incubated with ERa antibody (10 ug/ml), followed by  46  addition of the antibody capture affinity ligand included in an immunoprecipitation kit (Upstate, Lake Placid, NY) for 1 h at room temperature. The immunoprecipitated proteins were then subjected to 8% SDS-PAGE and western blotting using appropriate antibodies (SRC-1, catalogue number 05-522, glucocorticoid receptor-interacting protein-i (SRC-2), catalogue number 06-986, activator of thyroid and retinoic acid receptor! amplified in breast cancer 1 (SRC-3), catalogue number 05-490: Upstate; P300, catalogue number sc-585, CBP, catalogue number sc-121 1, PCAF, catalogue number sc-8999: Santa Cruz Biotechnology). After incubation with secondary antibodies, the immunoreactive proteins on western blots were detected, as described above.  2.2.4 Real-time RT-PCR Total RNA was extracted from cell cultures using Trizol (Invitrogen, Burlington, Canada). The RNA concentration was measured based on absorbance at 260 nm. The isolated RNA was reverse transcribed into first-strand cDNA using Moloney murine leukemia virus (M-MLV) reverse transcriptase (Promega BioSciences, San Luis Obispo, CA, USA). The primers used for SYBR Green real-time RT-PCR were designed using Primer Express Software v2.0 (PerkinElmer Applied Biosystems, Foster City, CA), and were as follows:  Egr-1  mRNA  (sense,  5’-GAGCGAACAACCCTATGAGC  5’-AGGCCACTGACTAGGCTGAA);  Fosb  and  mRNA  antisense, (sense,  5’-GAGGGAGCTGACAGATCGAC and antisense, 5’-TTCCTTAGCGGATGTTGACC); Annexin  AS  mRNA  (sense,  5’-GAAGCCCTCACGACTCTACG  5’-TATCCCCCACCACATCATCT);  Lhb  5’-GGCCGCAGAGAATGAGTTCT  and  CTCGGACCATGCTAGGACAGTAG);  Fshb  mRNA antisense, mRNA  and  antisense, (sense,  5’(sense,  47  5’-CCCAGCTCGGCCCAATA and antisense, 5’-GCAATCTTACGGTCTCGTATACCA); and  glyceraldehyde-3-phosphate  5’-CATGGCCTTCCGTGTTCCTA  dehydrogenase and  antisense,  (Gapdh)  mRNA  (sense,  5’-GCGGCACGTCAGATCCA).  Real-time PCR was performed using the ABI prism 7000 Sequence Detection System (PerkinElmer Applied Biosystems) equipped with a 96-well optical reaction plate. The reactions were set up in a 20 p1 reaction mixture containing 10 p1 SYBR Green PCR Master Mix (PerkinElmer Applied Biosystems), 4 j.tl of eDNA template and 6 jil of primer mixture (2 jiM). Real time PCR conditions were 50 C for 2 mm, 95 C for 10 mm, followed by 40 cycles of 95 C for 15 sec and 60 C for 1 mm. All experiments were run in duplicate, and mRNA levels were normalized against the amount of Gapdh mRNA.  2.2.5 Chromatin immunoprecipitation (ChIP) All reagents, buffers and supplies were provided in a ChIPITTM kit (Active Motif, Inc., Carlsbad, CA) and described previously (344). Briefly, the Lf3T2 cells were cross-linked with 1% formaldehyde for 10 mill at room temperature. The cells were treated with glycine Stop-Fix solution, re-suspended in lysis buffer, and incubated on ice for 30 mm. Then the cells were homogenized and nuclei were re-suspended in shearing buffer, and applied to ultrasonic disruption situations optimized before the experiments to generate 100-400 bp DNA fragments. The chromatin was pre-cleared with Protein G beads and 1 jig of the following antibodies were added: negative control IgG anti-ERa and anti-PCAF. Protein G beads were then supplied to the antibody/chromatin incubation mixtures. After several times of washing, elution buffer was used to remove antibody bound protein!DNA complexes from the beads. The samples then were incubated with NaC1 and RNase at 65 C for 4 h to reverse cross-links and remove RNA. The samples were treated with proteinase K for 2 h at 42 C and  48  the DNA was purified using gel exclusion columns. The purified DNA was subjected to PCR amplification (1 cycle of 94 C for 3 mm; 40 cycles of 94 C for 20 sec; 64 C for 30 sec and 72 C for 30 sec) of the Fosb promoter region that contains a known ERE (334) using forward (5’-AGGAGGCCCCTGGATTACATC) and reverse (5’-GTACCACCTTTGGCCTGGAA) primers. As an input control, 10% of each chromatin preparation was used in a parallel PCR reaction. The PCR products were resolved by 2% agarose gel electrophoresis and visualized after ethidium bromide staining.  2.2.6 Data analysis For transfection assays, data are shown as the mean  ±  SEM of at least three independent  experiments. Data were analyzed by one-way ANOVA and the GraphPad Prism 4 statistical software (GraphPad Software, Inc., San Diego, CA), and p<O.O5 was considered statistically significant.  2.3 Results  2.3.1 GnRH-I and GnRII-II rapidly and transiently activate ERz in LPT2 cells When L13T2 cells containing an ERE-luciferase reporter plasmid were treated with 100 nM GnRH-I or GnRH-II, we observed rapid but transient increases in luciferase activity which peaked at 12 h, with GnRH-I being more potent than GnRI-I-II (Figure 2.1A). In contrast to the robust 12 and 7 fold responses obtained after 12 h treatment with GnRH-I and GnRH-II, respectively, we observed only a 2-3 fold induction of the ERE-luciferase reporter activity after cells were treated with 100 nM E , which occurred within 6 h and was 2  49  maintained at this level for 48 h (Figure 2.1 B). In dose response assays, in which cells were treated with 0.1 nM to I iiM GnRH-I or GnRH-II, maximum increases in ERE-luciferase reporter activity were seen with lOnM GnRH-I and 100 nM GnRH-II (Figure 2.1C), while the 2 fold response in cells treated with 10 pM E 2 was not increased at higher E 2 concentrations up to 100 nM (data not shown). Since ERo is the predominant ER subtype in LT2 cells, we used an siRNA to knock down the amounts of ERu in these cells, and observed about a 50% reduction in ERct levels by western blotting (see upper panel of Figure 2.1 D). When these ERa siRNA-treated cells were treated for 6 h with 100 nM GnRI-1-1 or GnRH-II in the absence of E , the response of 2 an ERE-luciferase reporter gene was also about half that observed in control cells (Figure 2.TD). Moreover, we observed a significant (p<O.O5) reduction in the modest increase in ERE-luciferase reporter gene activity in ERa siRNA-treated cells exposed to 100 nM E 2 for 6 h (Figure 2.1D). Although activation of the ERE-luciferase reporter gene by both GnRH subtypes in LT2 cells is very much more robust than the response obtained after E 2 treatment, we wished to determine whether co-treatments with E 2 and the GnRH subtypes might act synergistically. The results of this experiment, however, indicate that E 2 does not further enhance the transient responses obtained after treatment with either GnRH subtype over and above that expected after E treatment alone (Figure 2.1E and 2.1F). 2  2.3.2 GnRIIR is required for GnRH-mediated ERE-luciferase activation  To verify that the activation of the ERE-luciferase reporter gene by GnRH-I and GnRH-II is mediated by the GnRHR, L13T2 cells were co-treated with its antagonist, antide. This almost completely blocked the induction of luciferase activity by both GnRH subtypes,  50  while co-treatment with an ER antagonist, ICI 182,780, did not (Figure 2.2A). By contrast, activation of the ERE-luciferase reporter gene by E 2 was attenuated by ICI 182,780 under the  same conditions (Figure 2.2A). To further confirm that the GnRHR is required for GnRH-induced activation of the ERE-luciferase reporter gene, we used an s1RNA to knock-down GnRHR levels in LT2 cells, and checked this by western blotting (upper panel of Figure 2.2B). This siRNA treatment resulted in a> 50% reduction in the ERE-reporter gene activation by both GnRH subtypes, but did not influence the 2 -E dependent activation of the reporter gene (Figure 2.2B), thus confirming that the GnRI-IR specifically mediates the ligand-independent activation of the ERE-luciferase reporter gene by both forms of GnRH in L3T2 cells.  2.3.3 GnRH treatments affect ERi phosphorylation and promote ERa interactions with PCAF  In several different cell lines, treatments with E 2 and agents that stimulate various signal transduction pathways result in the phosphorylation of ERc at Ser” 8 and/or Ser’ 67 (197-199, 201, 226). To determine which of these phosphorylation sites are regulated by GnRH in the nucleus and cytoplasm of L13T2 cells, antibodies that recognize ERec at Ser” 8 and Ser’ 67 were used in western blotting experiments. This demonstrated that GnRI-I-I or GnRH-1I treatments result in rapid and transient increases in ERa phosphorylation at Ser” 8 in the nucleus (Figure 2.3A and 2.3B), while phosphorylation of ERa at Ser 118 was not observed after GnRH or E 2  treatments in the cytoplasm (Figure 2.3D and 2.3E). On the other hand, both GrRH subtypes induce phosphorylation of ERa at Ser’ 67 in the nucleus and cytoplasm, and were more effective than E 2 (Figure 2.3A, 2.3C, 2.3D and 2.3F). To study the signaling pathways induced by GnRH-I or GnRH-II in terms of the phosphorylation of ERa, cells were  51  pre-treated with inhibitors of PKA (H89), PKC (GF 1 09203X), P13K (LY 294002) or MAPK (PD 98059) prior to treatment with the GnRH subtypes. This experiment shows that after treatments with either GnRH subtypes, phosphorylation of ERa at Ser 118 is reduced by PKC, P13K or MAPK inhibitors but not by the PKA inhibitor, while all four inhibitors attenuate the phosphorylation of ERa at Ser’ 67 (Figure 2.3G). We then examined whether GnRFI treatments promote the association of ERa with specific coactivators in L13T2 cells by immunoprecipitation of ERa complexes with an ERa antibody, and identification of interacting co-activators by western blotting. While we were unable to identif’ any increase in the co-immunopreciptation of ERa with SRC-1, SRC-2, SRC-3, CBP or P300 after the cells were treated with GnRH subtypes, both GnRH-I and GnRH-II increased interaction of the ERa with PCAF by almost 2 fold (Figure 2.4A). Since our data showed that both GnRH subtypes stimulate recruitment of PCAF by ERa, a PCAF s1RNA was used to further explore whether PCAF is an essential component of the ERa-dependent activation of the ERE-luciferase reporter gene by GnRI-I subtypes. A western blot demonstrated that the siRNA treatment decreased cellular PCAF levels (upper panel of Figure 2.4B), and resulted in significant reductions in reporter gene activation by GnRH-I or GnRI-I-II (Figure 2.4B).  2.3.4 GnRH treatments promote the co-recruitment of ERa and PCAF to the Fosb promoter ERE It is known that GnRH treatments induce the expression of several genes that contain EREs in their promoters, including the early growth response gene I (Egr-J), Fosb, annexin AS, and Lhb genes (318, 334, 345). When we examined the expression of these genes by real-time RT-PCR after GnRH treatments, we observed rapid (within 30 mm) and transient  52  (lost by 6 h) increases in the expression of Fosb (Figure 2.5A upper panel) and egr-1 (not shown). By contrast, the annexin A5 mRNA level increased progressively until 12 h, after which it decreased rapidly, and there was no increase in Lhb mRNA at all (not shown). In addition, GnRH treatments increased Fosb protein levels within 3-6 h (Figure 2.5A). When the cells were co-treated with E 2 and the GnRH subtypes, E 2 does not further influence the transient responses of Fosb mRNA levels obtained after treatment with either GnRH subtype (Figure 2.5B). When LT2 cells were pre-treated as above with an ERa siRNA, this again reduced ERa levels (as seen in Figure 2.ID upper panel) and attenuated the stimulation of Fosb expression after GnRH treatments (Figure 2.5C), while there was no effect on Egr-1 and annexin A5 mRNA levels (not shown). When the cells were pre-treated with an PCAF siRNA which reduced PCAF levels (as seen in Figure 2.4B upper panel), this also attenuated the stimulation of Fosb expression after GnRH treatments (Figure 2.5C). To further define the signaling pathways involved in the induction of Fosb by GnRH-I or GnRH-II, cells were pre-treated with inhibitors of PKA, PKC, P13K or MAPK prior to treatment with the GnRI—1 subtypes, and we then compared the fold inductions of Fosb mRNA and Fosb protein levels. The results show that only PKA and PKC inhibitors significantly attenuate the increases in Fosb mRNA and Fosb protein levels in response to GnRH-I or GnRH-II (Figure 2.5D). We next used a ChIP assay to determine whether the GnRH-mediated induction of endogenous Fosb gene expression requires the assembly of ERa and PCAF at the ERE within its promoter region (334). This indicated that both GnRH-I and GnRH-II treatments cause rapid (within 1 h) recruitment of ERa to the Fosb promoter ERE, and this occurred in concert with the recruitment of PCAF at the same site within 1 h after GnRH-I treatment and by 3 h after GnRI-I-II treatment (Figure 2.5E).  53  2.3.5 GnRU treatments increase Fshb expression The most important physiological function of gonadotrophs is to synthesize gonadotropin under the regulation of GnRH. An AP-l half-site within the Fshb promoter binds AP-l after GnRH-I treatment and is required for the maximal induction of Fshb mRNA levels (324). We therefore examined the changes in Fshb mRNA levels in LPT2 cells by real-time RT-PCR after GnRH treatments, and this revealed transient (lost by 24 h) increases in the expression of Fshb after both GnRH-I and GnRH-II treatments (Figure 2.6A). To assess which signaling pathways might be involved in the induction of Fshb expression by GnRH-I or GnRI-1-II, cells were pre-treated with inhibitors of PKA, PKC, P13K or MAPK prior to treatment with the GnRH subtypes, and we then compared the fold inductions of Fshb mRNA levels. The results indicate that only PKA and PKC inhibitors significantly attenuate the increases in Fshb mRNA levels in response to GnRH-1 or GnRH-II (Figure 2.6B).  2.4 Discussion In gonadotrophs, signaling pathways that mediate the actions of GnRH and steroid hormones converge to regulate the expression of gonadotropin genes. It has been shown in aT3-1 cells that cAMP (5) and GnRH-I (20) both stimulate ERE-containing promoters in an estrogen-independent manner, but these cells do not express the gonadotropin 13 subunit genes. We have therefore used the mouse pituitary Lf3T2 cell line, because it expresses both gonadotropin  13 subunit genes and is considered to be a developmentally mature pituitary cell  line (342, 343). Our studies show that ERc is activated by both GnRH subtypes in these cells,  54  and that GnRH-I is consistently more potent than GnRH-II in this regard. Most importantly, when compared to other previous studies using xT3-l cells, we have now explored the molecular signaling pathways involved in the apparent ligand-independent activation of ERa in LT2 cells. As observed in aT3-l cells (5), we found that GnRH treatments of Lf3T2 cells are much more effective in increasing the expression of an ERE reporter gene, when compared to . In this context, a maximum response was obtained with 10 nM 2 equimolar amounts of E GnRH-I, which approximates the concentration of GnRH-I in the pituitary. However, GnRH-II was also maximally effective at 100 nM, and this difference in the effectiveness of these two GnRH subtypes has also been observed previously in monkey and rat pituitary cells (346), and attributed to the fact that the type 1 GnRH receptor binds GnRH- 1 better than GnRH-II (65). It is widely appreciated that phosphorylation of ERa regulates its ligand binding activity, nuclear translocation, dimerization, and ability to regulate transcription (196, 325, 347). It is also known that ligand binding increases the phosphorylation of ERa at Ser” 8 which increases the ERE-binding affinity of the receptor (197), and that substitution of Ser” 8 with alanine reduces its transcriptional activity (198, 199). Other studies have shown that the ligand-independent activation of nuclear hormone receptors, including ERa, involves a change in their phosphorylation status. For instance, activation of PKA or PKC signal transduction pathways leads to an increase in phosphorylation of ERa when it is transiently expressed in COS-1 cells (198), while cAMP treatments of HeLa and COS-1 cells results in phosphorylation of ERa via PKA or MAPK pathways (240, 348). In addition, treatments of cancer cells with growth factors, such as EGF, result in the phosphorylation of specific serine residues in the AF- I domains of both ERa and ERI3, which are crucial to their transcriptional  55  responses (234, 348-350). Subsequent studies have indicated that growth factors activate the MAPK pathway which in turn phosphorylates the 5er 118 residue of ERa (226, 234). It has also been shown that Ser 167 of ERa can be phosphorylated in vitro by MAPK and AKT (197, 241, 242, 351). Our treatments of L3T2 cells with either GnRH subtype resulted in significant increases in the amounts of phosphorylated ERa at Ser’ 67 in both nucleus and cytoplasm, as well as the amount of phosphorylated ERa at Ser” 8 in the nucleus. Interestingly, within the same 1-12 h time-frame, 2 E treatments did not enhance phosphorylation of ERa at Ser , and this may explain why the E 167 -dependent activation of 2 ERa was much less effect in these pituitary cells than observed after treatments with the GnRJ-I subtypes. It is also known that phosphorylation of ERa influences the recruitment of its co-activators, resulting in enhanced transcriptional activation (234, 350, 352) through histone modifications and recruitment of the basal transcriptional machinery (353). The binding of ligands by ERa is known to alter its affinity for co-activators, but co-activators are also recruited to nuclear receptors in a ligand-independent manner, in response to other stimuli. For instance, we have previously reported that SRC-3 is required for PR transactivation of the gonadotropin a-subunit in aT3-1 cells after treatment with GnRH subtypes (21). We therefore examined whether ERa interacts with various co-activator proteins in LT2 cells after 1-6 h stimulation with GnRH, and found a specific increase in ERa interaction with PCAF within this time-frame. It is known that PCAF interacts with multiple receptors including RXR-RAR heterodimers, ERa, AR and GR, and that its recruitment by these nuclear hormone receptors plays a key role in their transcriptional properties (222, 354). To demonstrate that PCAF plays a role in GnRH-induced, ERa-mediated transcription in LT2 cells, we knocked down  56  PCAF levels by using an siRNA approach, and found that a reduction in cellular PCAF levels by about 50% reduces the ability of both GnRH subtypes to trigger ERE-luciferase reporter gene expression, as well as Fosb mRNA levels. Although the physiological importance of ligand-independent activation of ERct remains unclear, the magnitude of the responses we observe are remarkable and suggest that they must have some impact on the gonadotrophs which are exposed to large pulsatile fluctuations in the GnRH-I levels in the hypophyseal portal system. It is therefore of interest that GnRH- 1 treatments of LT2 cells increase Fshb gene expression (330), because others have shown that the Fshb gene in L13T2 cells is regulated by the AP-1 transcription factor complex: a heterodimer of fos and jun family members, the relative levels of which influence the activity AP-1 as a transcription factor (355, 356). It has been shown that an AP-1 half-site within the Fshb promoter is occupied by AP- 1 following GnRH-I treatment, and that this is essential for the maximal induction of FshB mRNA levels by GnRH-I in these cells (324). Moreover, GnRH-I has been found to stimulate AP-1 complex formation and Fosb synthesis, and that a dominant-negative FOS protein dose-dependently inhibited GnRH-I stimulated human FSHB transcription (325). Although little is known about the regulation of Fosb by estrogens, an ERE has been located within the Fosb promoter (334), and we therefore explored the possibility that the GnRH effects on increasing Fosb expression in L13T2 cells are mediated via the ligand-independent activation of ERct. As reported previously (318, 324, 325, 330), we observed a very robust and rapid (within 30 mm) increase in Fosb mRNA levels after GnRH treatments, and found that this effect could be attenuated by an siRNA-mediated reduction in ERL levels. Unlike the effect of GnRH treatment on ERE-reporter gene expression, which appears to be mediated by multiple signaling pathways (PKA, PKC, P13K and MAPK, data not shown), the rapid induction of Fosb gene expression by both GnR}I  57  subtypes seems to involve only PKA and PKC signaling pathways, and this may due to the differences in the ERE/chromatin context of the endogenous Fosb gene promoter versus the ERE-driven luciferase reporter gene construct. We have also found that the induction of Fshb gene expression by both GnRH subtypes is only attenuated by PKA and PKC inhibitors. More importantly, although E 2 and GnRH treatments both result in the co-recruitment of ERcL and PCAF to the Fosb promoter ERE, the binding of ERa and PCAF at this site is much more prolonged after treatment with the GnRH-I when compared to 2 E Moreover, the . recruitment of ERa and PCAF to the Fosb promoter ERE occurs more rapidly and is much more prolonged after GnRH-I treatment than after GnRH-II treatment. In conclusion, our results demonstrate that GnRH-mediated phosphorylation of ERa in mouse LT2 pituitary cells results in its rapid association with PCAF, and that co-recruitment of ERa and PCAF to an ERE within the Fosb promoter likely enhances its transcriptional activation, which in turn is known to activate other genes in pituitary cells including the Fshb subunit gene (Figure 2.7). In a physiological context, the ligand-independent activation of ERa by GnRH in pituitary cells may be most important under conditions when estrogen levels are low and GnRI-I pulse amplitude is high, such as during the luteal/follicular transition phase of the menstrual cycle.  58  ____  A  D ERcL___  =  p-actin Cul  GnRH-I  GnRH-I  10  I  L1 LI  1  3  6  12  24  2  nflflnOhA  o*/  48(h)  E  B 2 EtOH DE  GnRH-I  +nRH4 2 E  150 .5  F. LI II  1  3  6  12  24  48 (h)  C  6  12  24  (h)  F GnRH-I  GnRH-I  4nRH-I 2 E  GnRH-II  10  T  nift, 0mM mU  lOnU  .  1 T  >  T  lOOnM l iM 1  6  12  24  59  Figure 2.1 Effects of GnRH-I or GnRH-II on the trans-activation of an ERE-reporter gene in LT2 cells. A-C, the ERE-luciferase reporter gene together with a (RSV)-lacZ plasmid were transiently transfected into L13T2 cells by FuGENE 6.0. The cells were either treated with 100 nM GnRI-I-I, GnRH-II (A) or 100 nM E 2 (B) over a 48 h time course, or with 0.1 nM to 1 tM GnRH-I or GnRI-I-II for 6 h (C). The cell lysates were assayed for luciferase activity and measurements of f3-galactosidase activity as a control for transfection efficiency. D, Lf3T2 cells were co-transfected with the ERE-luciferase reporter gene and a (RSV)-lacZ plasmid, with control siRNA (si-ctrl) or an siRNA for ERa (si-ERa). The efficiency of the siRNA was tested by immunoblotting for ERa (upper panel). After treatment with 100 nM GnRH-I, GnR}1-II, or E , the cell lysates were assayed for luciferase activity and measurements of 2 -galactosidase activity as a control for transfection efficiency. E and F, the ERE-luciferase reporter gene together with a (RSV)-lacZ plasmid were transiently transfected into L13T2 cells by FuGENE 6.0. The cells were treated with 100 nM GnRH-I (E) or GnRH-II (F) with or without E2 for 6, 12 and 24 h. The cell lysates were assayed for luciferase activity and measurements of -galactosidase activity as a control for transfection efficiency. Results of at least three  independent experiments are expressed as mean ± SEM luciferase  activity/-galactosidase activity (i.e., relative luciferase activity) in A and B or fold change in C, D, E and F.  *:  p<0.O5 or  **:  p<0.Oi compared to untreated control (Ctrl) in A and C, and  the untreated control value set at I in C, D, E and F. D,  *:  p<O.05 compared to the respective  treatment after transfection with control s1RNA (si-ctrl).  60  I  G)  (a  -I  (a  6;  *  *  ERE pronter activity (fold change)  IC rj  + I  1+  +  + +  + I  + I  I  I  I  I  I  I  + I  I  +  + +  I  +  I  I  +  I  I  I  I  I  I  I  I  + I  +  I  I  I  I  I  I  I  m +  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  +  I  +  I  I  I  I  I  I  I  ‘ii  3*  )*II  ) 3:  ]  0  H  I  I  i-f  0  UI  .  ERE promoter activity (fold change) I  UI  Figure 2.2 GnRHR mediates the activation of ERE by GnRH-I and GnRH-II. A, the ERE-luciferase reporter gene and a (RSV)-lacZ plasmid were transiently transfected into LT2 cells. The cells were treated with 100 nM GnRH-I, or GnRH-II alone, or together with antide (type I GnRHR antagonist), or ICI 182,780 (Id, ER antagonist) for 6 h. B, LJ3T2 cells were cotransfected with the ERE luciferase reporter gene and a (RSV)-lacZ plasmid, with control siRNA (si-ctrl) or an siRNA for GnRHR (si-GnRHR). The efficiency of the siRNA was tested by immunoblotting for GnRHR (upper panel). After treatment with 100 nM GnRH-I, GnRH-II, or E 2 for 6 h, the cell lysates were collected for luciferase assay and measurements of -galactosidase activity as a control for transfection efficiency. Results are expressed as mean ± SEM fold change in ERE promoter activity expressed as luciferase activity/-galactosidase activity of at least three independent experiments. A, versus  treatment without antide.  *:  P<0.05  versus  . B, 2 E  *:  p<0.O5  versus  * *:  p<O.Ol  the respective  treatment after transfection with control siRNA.  62  n’  ?nni  V  r,  V  +  +  +  I  +  I  +  +  I  I  +  +  I  +  +  +  +  11co  +  +  I  =-  +  I  +  +  +  +  “C,  0  ;  :;  :  ;ç  N  a  a  ‘a  a  N  a a  ‘a  a  I-I H  I—i  ç  P Ieele 11 Fold iwt. In P.eR&P  a a N  ‘a  a  a  ‘a a  a  N  a  a  bl  a  Fold dise h p.ER&*Pll* eYeIe  N  0  0  = II  I  a,  0  ‘-I  U  = a  na,  m  a  Ac  V In  a  a  a  Q  C,  0  9  C  0  Ii  II’  N  a a  ‘a  N  a a  ‘a  a  H.’ Fl.’  Fold d,.im In p.!R&mr*t IeeIe  a  a  ‘a  a  ‘a  a  N  a  a  ‘a  a  Fold dme hi p.!R&*thht I..I.  o  N  0  = a-  nLI  P.1  9  I  o  I=  a,  0  QJ  fl  ¶  fl1  =  C,  a M  Wr  a  C’  a  I  V  Figure 2.3 Regulation of ERa phosphorylation at Ser” 8 and Ser 167 by GnRH-I or GnRH-II. The Lf3T2 cells were treated with 100 nM GnRH-I, GnRH-1I, or E 2 for 1, 3, 6 and 12 h. Equal amounts of nuclear (A, B, C) or cytoplasmic lysates (D, E, F) were electrophoresed on SDS-l0% gels, and western blotted to nitrocellulose for detection with antibodies specific for 18 phosphor-ERa ’ 5 phosphor-ERcL , or ERa. Control (Ctrl) represents untreated cells. A, 67 D, western blots are representative data from three independent experiments. B, C, E, F, relative pixel intensity of protein bands from western blots for ERa phosphorylation at Ser” 8 or Ser’ . Data are presented as the mean ± SEM of three independent experiments. 67 versus  *:  p<0.O5  untreated control value set at 1. G the cells were also treated with 100 n M GnRH-I,  GnRI-I-II for 1 h alone, or after pre-treatment with lOp.M H89 (PKA inhibitor), lO iM 1 GF109203X (GF, PKC inhibitor), 50pM LY294002 (LY, P13K inhibitor) or 50j.tM PD98059 (PD, MAPK inhibitor). Equal amounts of cell lysates were electrophoresed on SDS-10% gels, and western blotted to nitrocellulose for detection with antibodies  specific for  , phosphor-ERa’ 58 phosphor-ERa , or ERa. Immunoblots shown are representative of 67 three independent experiments.  64  a  ml  S  4*  0  J  :i ]  ]  0  M I  ô I I  II  I-i  I  activity  ERE promoter (fold change) 0 I  IL;  II  -TI  w Fold change In PCAF levele  I  C)  U  .1  C)  U  fl  0  >0  •D  W  0 $3  00 C.)  U)  CoOl  $3  ‘.3  a  a $3  tt3  a  0  I  z  6)  I  z  6)  Figure 2.4 Interactions between ERct and PCAF after GnRH-I or GnRH-II treatments and effects on the transcription activity of ERL. A, LT2 cells were treated with 100 nM GnRH-I or GnRH-II for increasing lengths of time, and nuclear lysates were  immunoprecipitated  using an anti-ERa antibody.  The  immunoprecipitates were then probed with anti-SRC- 1, SRC-2, SRC-3, CBP, P300 or PCAF antibodies. The nuclear lysates (Nucleus) were also probed with the individual antibodies as an input control for the immunoprecipitations. The western blot shown is representative of three independent experiments (upper panel). Relative pixel intensity of protein bands from western blots of PCAF from ERa immunoprecipitation experiments are presented as the mean ± SEM of three independent experiments (lower panel). B, L13T2 cells were cotransfected with the ERE-luciferase reporter gene and a (RSV)-lacZ plasmid, with control siRNA (si-ctrl) or an siRNA for PCAF (si-PCAF). The efficiency of the siRNA was tested by immunoblotting for PCAF (upper panel). After treatment with 100 nM GnRH-I, GnRH-II, or , the cell lysates were assayed for luciferase activity and measurements of -galactosidase 2 E activity as a control for transfection efficiency. Results are expressed as mean ± SEM fold change in ERE promoter activity expressed as Luciferase activity/f3-galactosidase activity of at least three independent experiments. A, *:  p<O.O5  versus  *:  p<O.05  versus  untreated control value set at 1. B,  the respective treatment after transfection with control siRNA.  66  a 0 0  0  *1  (e6uqo pioj) ‘NW HOdvN.U  0  2  C,  N  N  U) 0 U.  -r  (e6tqo piq)  a  C  C  C  0  C,  I 0  0  (e6uBqo Pi)  C  E CtrI  15C  GnRH41  GnRH-I 1  3  6  3  6  GnRHI  Q  1  1  3(h)  ERx  z  PCAF  E  Input IgG  1’x fl-C <C 0  ..L..fl  E IL  GnRH4  2 E  >  d ‘U  si-dTI  s-ERo C C £ 0  0  0  z E  I  i  136  136  13(h)  Om a-C <C  jZ  o5  E J  GIiH4  GrdH-I  .  Ii 0 GnRH4 GnRH-l  +--+-+-  H89  -  GF LY PD  -+--+-  +-.+..+--+.+ -+++  +++-  -  +  -++  136 GnRH4  GnRH-II H89 GF LY PD  -  +-  -  -+--+..+--+--+ --  -  -4.-  -4-  -+.-  136  13(h)  +-  +++ +++ +++. +++  Fosb  actin  68  Figure 2.5 The induction of Fosb gene expression and co-recruitment of ERa and PCAF to an ERE within the Fosb promoter after GnRH treatments. A, LT2 cells were either untreated or treated with 100 nM GnRH-I, GnRH-11 or E 2 for 5, 15, 30, 60, 180 and 360 mm. Total RNA was extracted and reverse transcribed into first-strand eDNA. The levels of Fosb mRNA were measured by real-time RT-PCR (upper panel). The LI3T2 cells were either untreated or treated with 100 nM GnRH-I, GnRI-l-I1 or E 2 for 1, 3, 6, or 12 h. Equal amounts of cell lysates were electrophoresed on SDS-10% gels, and western blotted to nitrocellulose for detection with antibodies specific for Fosb (lower panel). Control (Ctrl) represents untreated cells. Data of real-time RT-PCR are presented as the mean ± SEM of three independent experiments. Immunoblots shown are representative of three independent experiments.  *:  p<O.O5 versus untreated control value set at 1. B, L13T2 cells  were treated with 100 nM GnRH-I (upper panel) or GnRI-I-II (lower panel) with or without E2 for 30, 60 and 180 mill. Total RNA was extracted and reverse transcribed into first-strand eDNA. The levels of Fosb mRNA were measured by real-time RT-PCR. Data of real-time RT-PCR are presented as the mean ± SEM of three independent experiments. C, LT2 cells were transfected with control siRNA (si-ctrl), siRNA for ERa (si-ERa) or PCAF (si-PCAF). After treated with 100 nM GnRH-I or GnRI-1-II for 1 h, total RNA was extracted and reverse transcribed into first-strand cDNA. The levels of Fosb mRNA were measured by real-time RT-PCR. Data of real-time RT-PCR are presented as the mean ± SEM of three independent experiments.  *:  p<O.OS versus the respective treatment after transfection with control siRNA  (si-ctrl). D, L13T2 cells were treated with 100 n M GnRH-I, GnRH-II for 1 h alone, or after pre-treatment with lOji.M H89, lOjiM GF109203X (GF), 5OjiM LY294002 (LY) or 5OjiM PD98059 (PD). Total RNA was extracted and reverse transcribed into first-strand eDNA. The levels of Fosb mRNA were measured by real-time RT-PCR. The cells were also treated with 100 n M GnRH-I, GnRH-II for 3 h alone, or after pre-treatment with H89, GF109203X, LY294002 or PD98059. Equal amounts of cell lysates were electrophoresed on SDS-10% gels, and western blotted to nitrocellulose for detection with antibodies specific for Fosb. Data of real-time RT-PCR are presented as the mean ± SEM of three independent experiments. Immunoblots shown are representative of three independent experiments.  *:  P<0.05 versus treatment without inhibitor. E, LT2 cells were treated with 100 nM GnRH-I, GnRH-II, or E 2 for 1, 3, or 6 h and the nuclear proteins were then cross-linked. Sheared  69  chromatin was immuno-precipitated (IP) with ERcL and PCAF antibodies, and recovered chromatin was subjected to PCR analysis using primers spanning an ERE within the Fosb promoter. Non-specific IgG was used in all ChIP reactions as a control. An ethidium bromide-stained gel of PCR products showed a representative of ChIP analysis (upper panel). Relative pixel intensity of PCR products bands for ERa and PCAF are presented as the mean ± SEM fold change of three independent experiments (lower panel).  *:  p<O.O5  versus  untreated control set as 1.  70  SI.  CD  0 -r I CD  0  CI  41  c.  S!;::  Ii  —i____ sH______  4  (e&sqo pjoj) W2 fl*W*flU Pd  (N ‘S  (C  C’,  ‘S  ‘C  I  CO  I  H  I  I  • +  +  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  + +  +  I  I  I  I  +  +  +  4  I  I  •  I  I  I I  +  I  I I  •  I  .4 +  +  4. +  + +  I  I  I  I  I  •‘  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  ‘I’  I  C  I  0  H_____ I  N  II.  C C  C C  C  H______  I  (e&mqopoj)  (C  CD CD lCD ..J 0.  I—  Figure 2.6 Increased expression of Fshb in Lj3T2 cells after treatments with GnRH subtypes. A, L13T2 cells were either untreated or treated with 100 nM GnRH-I, GnRH-II or E 2 for 1, 3, 6, 12 and 24 h. Total RNA was extracted and reverse transcribed into first-strand cDNA. The levels of Fshb mRNA were measured by real-time RT-PCR. Data of real-time RT-PCR are presented as the mean ± SEM of three independent experiments.  *:  p<O.05  versus untreated  control value set at 1. B, LJ3T2 cells were treated with 100 n M GnRH-I, GnRH-II for 12 h alone, or after pre-treatment with lOjiM H89, lO iM GF109203X (GF), 5OjiM LY294002 (LY) 1 or 5OjiM PD98059 (PD). Total RNA was extracted and reverse transcribed into first-strand cDNA. The levels of Fshb mRNA were measured by real-time RT-PCR. Data of real-time RT-PCR are presented as the mean ± SEM of three independent experiments.  *:  P<0.05  versus treatment without inhibitor.  72  GnRH-I GnRH-II  PCAF  I  Fosb  Fshb  {  Figure 2.7 GnRH-mediated phosphorylation of ERa contributes to Fosb expression in mouse  gonadotrophs After binding with GnRHR, GnRH-I and GnRH-II active PKA and PKC signaling pathways and mediate phosphorylation of ERa in mouse LT2 pituitary cells. These result in ERa rapid association with PCAF, and that co-recruitment of ERa and PCAF to an ERE within the Fosb promoter likely enhances its transcriptional activation, which in turn is known to activate other genes in pituitary cells including the Fshb subunit gene. ER, estrogen receptor; ERE,  estrogen-response  element;  FSH,  follicle  stumulating  hormone;  GnRH,  gonadotropin-releasing hormone; GnRHR, GnRI-T receptor; PCAF, P300/CBP-associated factor; PKA, protein kinase A; PKC, protein kinase C.  73  Chapter 3 GnRII-I-mediated activation of progesterone receptor contributes to Gsua expression in mouse gonadotrophs 2 3.1 Introduction  The  hypothalamic-pituitary-gonadal axis  is important for maintaining normal  reproductive function. GnRH is secreted in a pulsatile manner from neurons in the hypothalamus into the hypophyseal portal system (13). After binding to the GnRH receptor on the surface of gonadotrophs in the anterior pituitary, GnRH controls synthesis and secretion of FSH and LH, which consist of a common GSUu and a unique f3 subunit (1), and which play a systematic role in gametogenesis, folliculogenesis and steroidogenesis in the gonads (2, 4, 357). Subsequently, steroid hormones, including E 2 and P4, feed back to regulate expression and secretion of GnRH and gonadotropin at the level of the hypothalamus and pituitary (5). The function of intracellular PRs as ligand-activated transcription factors is well characterized (278). There are two main isoforms of PR, a full length PR-B and N-terminally-truncated PR-A; the two isoforms are derived by the transcription of a single gene from two different promoters (253). Following P4 binding, PRs exhibit conformational changes leading to phosphorylation, dimerization, nuclear translocation, binding to PREs, and subsequent gene transcription (278). Apart from being activated by their ligands, steroid hormone receptors, including PRs, are also activated after phosphorylation in a ligand-independent manner by peptide growth factors including EGF and heregulin (285, 286). 2  A version of this chapter has been published. Chen J, An BS, So WK, Cheng L, Hammond GL, Leung PC 2010 Gonadotropin-releasing hormone-I-mediated activation of progesterone receptor contributes to gonadotropin alpha-subunit expression in mouse gonadotrophs. Endocrinology 151:1204-1211  74  Cross-talk between GnRH and PR occurs in rodent pituitary cells and is believed to play an important role in the GnRH self-priming effect (21, 250, 358, 359), which is defined as increased gonadotropin secretion from gonadotrophs in response to a second stimulation by GnRH (299). As a powerful servo-mechanism, this potentiates the pituitary responsiveness to GnRH-I severalfold. In rat primary anterior pituitary cells cultured in the absence of P4, the PR antagonist RU486 inhibits GnRH self-priming and prevents cAMP augmentation of GnRH-stimulated LH secretion. This is consistent with the fact that a GnRH-stimulated PKA cascade acts, in part, through transcriptional activation of PR (250). This GnRH seif-potentiation appears to depend on PR, as it is completely absent in PR knock-out mice (13). Therefore, it is suggested that after binding to its receptor on gonadotrophs, GnRH prompts signaling pathways and activates PR in a ligand-independent manner (300), which mediates the GnRI-I self-priming effect. However, the mechanisms of PR involvement in GnR}I self-priming, which results in the abrupt and exponential increase in pituitary responsiveness at the time of the LH surge, remain unclear. We have previously demonstrated that GnRI-I-I activates a PRE-luciferase reporter gene in mouse aT3-1 pituitary cells through PKA and PKC transduction pathways. Furthermore, the binding of PR and its coactivator SRC-3 to the PRE in the murine Gsua promoter is enhanced by GnRH-I, and is coincident with an increase in GSUc protein levels, indicating that the influence of GnRH-I on the common Gsua gene expression depends on the PR (21). In this study, we have utilized L13T2 mouse pituitary cells that express both gonadotropin genes and the Gsua gene, and are considered more mature gonadotrophs, as well as aT3-1 cells to provide further direct evidence that induction of Gsua by GnRH-I depends on the ligand-independent activation of PR.  75  3.2 Materials and methods  3.2.1 Cells and cell culture The mouse gonadotroph-derived aT3-1 (341) and LT2 (342) cell lines were generously  provided by Dr. P.L. Melon (Department of Reproductive Medicine, University of California, San Diego, CA) and maintained in monolayer cultures in Dulbecco’s modified Eagle’s medium supplemented with 10% FBS, 100 U/mI penicillin G, and 0.1 mglml streptomycin (Invitrogen, Burlington, ON) in humidified 5% CO, 95% air at 37 C. The cells were passaged when they reached about 90% confluence, using a trypsin/EDTA solution (0.05% trypsin, 0.5 mM EDTA). Cells were kept in phenol-red free medium containing charcoal-treated FBS for four days prior to experiments.  3.2.2 Plasmids, siRNA and transient transfection assay  A PRE-luciferase reporter plasmid containing two copies of a consensus progesterone responsive element (PRE) upstream of the thymidine kinase promoter was provided by Dr. D. P. McDonnell (Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC). The siRNAs for PR were obtained from Qiagen Inc. (Mississauga, ON, Canada), together with a nonspecific siRNA (si-ctrl) that was used as a negative control. Transient transfections of the PRE-luciferase reporter gene or siRNA were performed using FuGENE 6.0 (Roche Diagnostics, Quebec, QC) together with a Rous sarcoma virus (RSV)-lacZ plasmids to correct for transfection efficiencies. One day before transfection, cLT3-1 and LT2 cells were seeded in six-well plates. One microgram of PRE-luciferase reporter gene and 0.5 tg of RSV-lacZ were applied to the cells. After set times of culture (0-24 h), cellular lysates were obtained after addition of 150 p1 reporter lysis buffer (Promega  76  Corp., San Luis Obispo, CA) and were assayed for luciferase activity using a Lumat LB 9507 luminometer (EG&G, Berthold, Germany). f3-Galactosidase activity was also measured using a f3-galactosidase enzyme assay system (Promega Corp.) to normalize for transfection efficiencies. Promoter activity was calculated as luciferase/f3-galactosidase activity.  3.2.3 Immunoblotting The protein content of cell lysates was determined using a Bradford assay (Bio-Rad Laboratories, Mississauga, ON); 20 jil aliquots were resolved by 10% SDS-PAGE and electrotransferred to a Hybond-C membrane (Amersham Biosciences, Morgan, ON). After blocking, the membranes were incubated (overnight 4 C) with specific antibodies against PR A/B  and  actin  (Santa  Cruz  Biotechnology,  Santa  Cruz,  CA).  Horseradish  peroxidase-conjugated secondary antibodies were then incubated with the membranes. After washing, immunoblots were examined using the ECL chemiluminescent system (Amersham Pharmacia Biotech, Piscataway, NJ) followed by exposure to Kodak X-Omat film.  3.2.4 Real-time RT-PCR Total RNA was extracted from cell cultures using Trizol (Invitrogen, Burlington, Canada). The RNA concentration was measured based on absorbance at 260 nm. Isolated RNA was reverse transcribed into first-strand eDNA using M-MLV reverse transcriptase (Promega Corp.). The primers used for SYBR Green real-time RT-PCR were designed using Primer Express Software v2.0 (PerkinElmer Applied Biosystems, Foster City, CA). The primers for Gsua mRNA were: sense, 5’- TGTTGCTTCTCCAGGGCATAT and antisense, 5’- TGGAACCAGCATTGTCTTCTTG. The primers for Gapdh mRNA were: sense, 5 ‘-CATGGCCTTCCGTGTTCCTA and antisense, 5 ‘-GCGGCACGTCAGATCCA. Real-time  77  PCR was performed using an ABI prism 7000 Sequence Detection System (PerkinElmer Applied Biosystems). Reactions were set up using SYBR Green PCR Master Mix (PerkinElmer Applied Biosystems). Relative quantification of Gsua mRNA levels was performed using the comparative cycle threshold method with GAPDH as an endogenous control and with the formula  3.2.5 Data analysis Data are presented as the mean  ±  SEM of at least three independent experiments. Data  were analyzed by one-way ANOVA followed by Tukey’s test by using the GraphPad Prism 4 statistical software (GraphPad Software, Inc., San Diego, CA); p<0.05 was considered statistically significant.  3.3 Results  3.3.1 GnRH-I rapidly and transiently activates PR in tT3-1 and LPT2 cells The basal levels of PR-B are higher in LT2 cells than in aT3-1 cells, whereas the latter cells contain much higher levels of ERcL (Figure 3.1A). Induction of PR expression by E , 2 which has synergistic effects with P4 on PR-mediated transcription, has been documented in many cell lines including those of pituitary origin (21, 263). In our experiments, we cultured cT3-1 and LPT2 cells in the presence of 0.2 nM E 2 for 2 days before treatment with GnRH-I or GnRH-II, and induction of PR was only observed in c(f3-1 cells (Figure 3.1B). After transfection of a PRE-luciferase reporter gene, 10 nM GnRH-I alone increased luciferase levels only at 8h in ctT3-1 cells. With the inclusion of E , luciferase activity 2  78  increased with a peak at 8h, and then declined (Figure 3.1 C). In Lf3T2 cells, GnRH-I transiently increased luciferase levels, which peaked at 8 h. However, there was no apparent difference in PRE-luciferase promoter activity in these cells after pretreatment with E 2 (Figure 3.ID). This finding may be due to the induction of PR by E 2 in ctT3-l cells but not in L13T2 cells (Figure 3.1 B). In dose-response assays in which cells were treated with 0.1 nM to 1 IIM GnRH-I, maximum increases in PRE-luciferase reporter activity were seen at 10 nM 1 pM GnRH-I in ctT3-1 cells (Figure 3.IE) and at 1 nM  -  -  1 jiM GnRH-I in Lf3T2 cells  (Figure 3.1F). Moreover, there was a >3-fold change in PRE-luciferase reporter activity when the LT2 cells were treated with 0.1 nM GnRH-1. Based on the results of this experiment, we used 10 nM in the following studies. Since our data and a previous study (21) showed that both GnRH subtypes and P4 activate a PRE-luciferase reporter gene, we wished to determine whether co-treatment with P4 and the GnRH subtypes might result in a synergistic effect. The results of this experiment indicate that in cJ3-1 cells, P4 further increased the response after GnRH-I, but not GnRH-II, treatment (Figure 3.1G). In LT2 cells, in contrast, there was no synergistic effect between P4 and either GnRH subtype (Figure 3.1H).  3.3.2 GuRU-I enhances Gsua gene expression in aT3-1 and LPT2 cells  Employing real-time RT-PCR to interrogate the effect of GnRH-I on Gsua gene expression, we found that GnRH-I increased Gsua mRNA accumulation, which reached its highest level at 24 h in both cell lines, while E 2 did not further enhance the GnRH-I effect (Figure 3.2A and 3.2B). The influence of GnRH-1 on Gsua mRNA levels in both cell lines at 24 h was greater than that observed after treatment with the same concentration (10 nM) of GnRH-II (Figure 3.2C and 3.2D). It should also be noted that, under these conditions, the  79  co-administration of P4 with either GnRH-I or GnRH-II did not result in any additive effects on Gsua mRNA levels in either cell line (Figure 3.2C and 3.2D).  3.3.3 Activation of PR and its effects on Gsua expression involves PKC  Since PR can be phosphorylated at Ser249 upon activation of PKA and PKC signaling pathways by GnRH-I in both T3-1 (21) and Lf3T2 cells (360), we pretreated cells with inhibitors of PKA (H89) or PKC (GF109203X) prior to treatment with GnRH-I, and compared the subsequent induction of PRE-luciferase reporter gene activities. The results show that both H89 and GF109203X significantly attenuated the activation of the PRE-luciferase reporter gene in response to GnRH-I in both cell lines (Figure 3.3A and 3.3B). To explore whether the activation of PR by GnRH-I is mediated by the GnRHR, both cell lines were pretreated with its antagonist, antide. Antide significantly blocked the induction of PRE-luciferase reporter activity by GnRH-I, while pre-treatment with a PR antagonist, RU486, did not (Figure 3.3A and 3.3B). In order to study the signaling transduction pathways involved in the GnRH-I stimulated accumulation of Gsua transcripts in these cell lines, LT3-1 and L13T2 cells were pretreated with PKA or PKC inhibitors and then challenged with GnRH-I. The results show that only GF109203X had inhibitory effects on GnRH-I-induced Gsua expression, while H89 did not (Figure 3.4A and 3.4B). As in the PRE-luciferase reporter gene study, antide abolished induction of Gsua by GnRH-I, while RU486 had no influence (Figure 3.4A and 3.4B). 3.3.4 GnRII-I-induced Gsua gene expression requires PR  In the next set of experiments, we used an siRNA approach to assess the role of PR in  80  GnRH-I-modulated Gsua gene expression in ctT3-1 and LI3T2 cells. When the PR levels in xT3-1 cells were knocked-down using two PR siRNAs separately (Figure 3.5A upper panel), approximate 40% reductions in GnRH-I stimulated Gsua mRNA levels were observed (Figure 3.5A). Similar results were obtained when PR levels were knocked-down using a PR siRNA in LT2 cells (Figure 3.5B). These data suggest that downstream signaling events involving PR are required for the GnRH-I induction of Gsua gene expression.  3.4 Discussion The development of immortalized mouse pituitary gonadotrophs, including aT3-1 and LT2 cells, has provided the opportunity to analyze mechanisms of regulation of the gonadotropin genes by GnRH-I and steroid hormones (341, 342). In particular, the immortalized L3T2 cell line expresses many markers of a mature gonadotroph, rendering it more physiologically relevant to in vivo systems (5, 23, 343, 361, 362). Our previous study using ctT3-1 cells demonstrated that, coincident with an increase in GSUa protein levels, GnRH-I increases assembly of SRC-3 and PR at the PRE in the Gsua promoter, leading to the conclusion that the induction of Gsua gene transcription by GnRH-I occurs at least partially through the ligand-independent activation of PR (21). In this study, we have found that induction of Gsua gene expression by GnRH-I can be significantly attenuated by PR siRNA, thus providing direct evidence that transactivation of PR is important for GnRH-I effects on the common gonadotropin o subunit gene, which involves PKC signaling (Figrue. 3.6). The GnRH self-priming effect involves the PR (300). Although E 2 treatment leads to increases in PR levels in primary rat and mouse pituitary cells, and thereby contributes to the  81  robust GnRH self-priming effect, E 2 pre-incubation does not influence PR levels in Lf3T2 cells (263). In the present study, we confirmed this but found that E 2 increases PR levels in aT3-lcells. Since ERcL levels are much higher in cLT3-lcells compared with L13T2 cells, we also conducted a dose response experiment of E 2 on PR expresssion in L3T2 cells. However, 0.2 nM  -  1 tM E 2 did not increase PR levels in LPT2 cells (data now shown). Thus, the more  mature L13T2 gonadotroph cells differ in this regard as compared to ccT3-lcells. The failure of 2 treatment to induce a significant increase in PR expression in L13T2 cells may be due to E differences in basal PR levels or their state of differentiation. Moreover, the different induction of PR by E 2 in the two cell lines may explain why GnRH-I and P4 synergize to activate a PRE-luciferase reporter gene in cT3-1 cells, but not in LT2 cells. Consistent with the activation of the PRE-luciferase gene, we found that GnRH-I treatment of both cell lines leads to an increase in Gsua mRNA levels at 24 h. In contrast to the additive effect of P4 on GnRH-I-induced PRE promoter activity in aT3-1 cells, there is no further enhancement of Gsua mRNA levels when the cells are co-treated with GnRH-I and P4. These data indicate that while GnRH-I induces Gsua expression, P4 cannot influence Gsua expression in a ligand-dependent manner despite the fact that it increases the expression of a PRE-luciferase reporter gene. Pulsatile secretion of GnRH-I regulates pituitary gonadotropin production. In the current study, we used a relatively low dose of GnRH-I which more closely resembles its physiological concentration in the pituitary (363, 364). Although the distinguishing feature of GnR}I-II is its wide distribution in extrahypothalamic regions of the brain and outside the nervous system, it is also present in preoptic and medio-basal hypothalamic areas (65). In agreement with previous data obtained in gonadotrophs (21), GnRI-I-II exerts somewhat milder effects on a PRE-luciferase reporter gene and Gsua mRNA levels compared with the  82  same dose of GnRI-1-I. In pituitary gonadotrophs, binding of GnRH-I to its G protein-coupled receptor (GnRHR) initiates the PKC signaling pathway to stimulate transcription of the Gsua subunit gene (110). Our results show that PKC and possibly PKA signaling pathways are important for GnRH-I activation of the PRE-luciferase reporter gene. However, only PKC signaling mediates the increase in levels of Gsua mRNA by GnRH-I treatment in these two cell lines. Our previous studies have shown that phosphorylation of PR at Ser 249 occurs in response to GnRH-I in both aT3-1 and L13T2 cells (21, 302), and that only PKC influences the phosphorylation of PR at the same site in LPT2 cells (302). Thus, in terms of downstream signals triggered by the GnRFIR, PKC induces PR phosphorylation and a subsequent increase in endogenous Gsua expression.  Cross-talk between PR and GnRH-I is associated with a GnRH-I self-priming system in transfected anterior pituitary cells in the presence of E 2 (250, 299, 300), and this depends on the presence of PR (13). Our previous study also suggested that activation of GnRI-IR by GnRH-I and GnRH-II in ctT3-1 cells prompts PKA and PKC signaling pathways, which activate PR in a ligand-independent manner and ultimately induce the loading of PR and SRC-3 onto PRE in the Gsua promoter. To provide further direct evidence that PR activation is involved in the induction of Gsua expression by GnRI-I-I, we knocked down PR protein levels using siRNAs. This reduction in PR levels resulted in an approximately 40% reduction of GnRH-I-induced Gsua mRNA levels. Supporting the concept that PR is required for GnRH-I-induced Gsua expression, there is a PRE sequence within the mouse Gsua promoter, which sequesters PR in association with SRC-3 (21). In terms of Gsua gene expression in the pituitary cells, our results therefore indicate that GnRH-I induces Gsua by transactivation of PR in the absence of its own ligand, P4.  83  The gonadotropins are coordinately and differentially regulated throughout the menstrual cycle. During the follicular phase, circulating E 2 levels increase gradually. At midcycle, there is an LH surge that induces resumption of meiosis, ovulation and luteinization. Although the LH surge has been intensively studied, the basis for the triggering of LH remains unclear. Apart from positive feedback of E , the self-priming effect of GnRH-I plays a fundamental 2 role in triggering the ovulatory gonadotrophin surge in mammals, including humans (299). Together with our previous results (21, 302), the present results show that ligand-independent activation of PR by GnRH-I is involved in Gsua and Fshb gene expression and suggest that this is important for the mid-cycle increase of gonadotropin release. Moreover, our results using aT3-1 and LT2 cells indicate that GnRH-I activates PR in a ligand-independent manner and promotes the accumulation of Gsua mRNA, and this likely contributes to the self-priming effect of GnRH-I during the follicular phase of the menstrual cycle.  84  )  .h  Q  on  ?  —  00  PR promoter activity (Fold change) ? ?  1H  3  0  PR promoter activity (fold change)  x  ‘4  “.  0  1•  b  0 -  —  Ii  PR iromoter activity (fold change)  0  PR promoter activity (Fold change)  -n  m -  F--i-  00  PR promoter activity (reid change)  F-’  —  00  PR promoter activity (fold change)  ci  C)  I  w  III  Figure 3.1 GnRH-I activates the PR in aT3-1 and LPT2 cells. A, basal levels of PR (PR-B and PR-A) and ERo in ctT3-l and Lf3T2 cells were determined by western blotting. B, after 2 days incubation in the absence or presence of 0.2 nM E , the 2 levels of PR (PR-B and PR-A) and actin were determined by western blotting in ctT3-l and LT2 cells. C-H, the PRE-luciferase reporter gene, together with a (RSV)-lacZ plasmids, was transiently transfected into aT3-1 (C, E and G) and L13T2 cells (D, F and H) by FuGENE 6.0. The cells were either pretreated with or without 0.2 nM E 2 for 48 h and then challenged with 10 nM GnRH-I over a 24 h time course (C and D), or treated with 0.1 nM to 1 jiM GnRH-I for 8 h (E and F), or were incubated with 0.2 nM E 2 and then treated with 10 nM GnRH-I or GnRH-II with or without 100 nM P4 for 8 h (G and H). Cell lysates were assayed for luciferase activity and measurements of -galactosidase activity were made as a control for transfection efficiency. Results of at least three independent experiments are expressed as mean ± SEM fold change of PRE promoter activity. C-F,  *:  p<0.05 compared to GnRH-I  treatment in the absence of E 2 at 0 h in C and D, or compared to untreated control value set at 1 in E and F. C, #: p<0.05 compared to GnRH-I treatment in the absence of E 2 at 8 h. G,  *:  p<0.05 compared to the respective treatment without P4.  86  A  B  5  C  C Q  2 E  *  ii  C  E *1  0  01  0  4  8  24  (h) uT3-1  C  mr1 f t l 0  4  8  24  (h) LP12  D  Clii  GnRK4  GnRH-I  LU4  Clii  GnRH-I  GnRH-I  LP12  Figure 3.2 GnRH-I enhances Gsua gene expression in xT3-1 and L13T2 cells. A and B, after 2 days incubation in the absence or presence of 0.2 nM E , aT3-1 and L13T2 2 cells were treated with 10 nM GnRH-I over a 24 h time course and the chronological changes of Gsua mRNA levels were monitored by real-time PCR. C and D, after 2 days incubation with 0.2 nM E , 100 nM P4 was co-treated with 10 nM GnRH-I or GnRH-II for 24 h, 2 followed by real-time PCR to monitor the expression levels of Gsua. Results are expressed as mean ± SEM (i.e., Gsua mRNA level) of three independent experiments.  *:  P<0.05 compared  to GnRH-I treatment in the absence of E 2 at 0 h.  87  44,  PRE proncter aIvIty (fold ch,ge) +0  I**  PRE proncter atlvlty (fold change)  Figure 3.3 PKA and PKC inhibitors reduce GnRH-I induced PRE-luciferase reporter gene activity in aT3-1 and LPT2 cells. A and B, PRE-luciferase reporter genes, together with a (RSV)-lacZ plasmids, were transiently transfected into ctT3-1 (A) and LT2 (B) cells. After 2 days incubation in the presence of 0.2 nM E , the cells were either treated with 10 nM GnRH-I alone or pre-treated 2 with 10 jiM H89 (PKA inhibitor), 10 jiM GF (GF109203X, PKC inhibitor), 10 nM antide, or I jiM RU486 over a 8 h time course. Cell lysates were assayed for luciferase activity and measurements of -galactosidase activity were taken as a control for transfection efficiency. Results are expressed as mean ± SEM fold change of PRE promoter activity of three independent experiments.  *:  P<0.05 compared to GnRH-I treatment alone.  89  A  S.  !:  I  flrinn — c,9.F__  1  zT3-1  GnRH-I  B  I  —  #,ffj  L3T2  ‘ GnRH-I  Figure 3.4 PKC inhibitors reduce GnRI-I-I induced increases in Gsua mRNA levels in cT3-1  and Lf3T2 cells. A and B, after 2 days incubation in the presence of 0.2 nM E , the cells were treated with 10 2 nM GnRH-I alone, or pre-treated with 10 pM H89 (PKA inhibitor), 10 jiM OF (GF109203X, PKC inhibitor), 10 nM antide, or 1 jiM RU486 over a 24 h time course. Total RNA was isolated and subjected to real-time PCR to determine the Gsua mRNA level. Results are expressed as mean ± SEM (i.e., Gsua mRNA level) of three independent experiments.  *:  P<0.05 compared to GnRH-I treatment alone.  90  A CfrI  si-ctil si-PRI si-PR2  PR-B PR-A 3-actin  5  si-ctrl si-PRI si-PR2  4  *  I  3  E 2 I 0  I  I  -j  GnRH-I  #  zT3-1  B CtrI  si-ctrl  si-PRI  PR-B PR-A 13-actin  4  *  si-PRI si-CM  I E  2 I  I  I CtrI  I GnRH-I  LpT2  91  Figure 3.5 GnRH-I-modulated Gsua gene expression requires the PR. A and B, uT3- 1 (A) and Lf3T2 (B) cells were transfected with 150 nM control siRNA (si-ctrl) or siRNAs for PR (si-PR1 and si-PR2 in aT3-1 cells, si-PR1 in LPT2 cells) for 48 h. The efficiency of the siRNAs was tested by immunoblotting (upper panel of A and B). To determine the role of PR in GnRH-I regulated Gsua mRNA levels, transient transfection was performed using the above conditions and total RNA after GnRH-I treatment was isolated and subjected to real-time PCR. Results are expressed as mean ± SEM (i.e., Gsua mRNA level) of three independent experiments.  *:  P<0.05 compared to cells transfected with an  siRNA control (si-ctrl). #: P<0.05 compared to cells transfected with an siRNA control and followed by GnRH-I treatment.  92  GnRH-I  SRC3  I  Gsuo  I  GnRH-I self-priming effect  Figure 3.6 GnRH-I-mediated activation of PR contributes to Gsua expression in mouse gonadotrophs After binding with GnRHR, GnRH-I actives PKC signaling pathway and mediates phosphorylation of PR in mouse pituitary cells. These result in PR association with SRC-3, and that co-recruitment of PR and SRC-3 to a PRE within the Gsua promoter likely enhances its transcriptional activation, which is known to contribute to GnRH-I self priming effect. The induction of Gsua by GnRH-I is significantly reduced by knockdown of PR using an siRNA approach. GnRH, gonadotropin-releasing hormone; GnRHR, GnRH receptor; GSUct, gonadotropin a subunit; PR, progesterone receptor; PRE, progesterone-response element; PKC, protein kinase C; SRC-3, steroid receptor coactivator.  93  Chapter 4 Cross-talk between GnRH and PR in the induction of Gnrhr in mouse gonadotrophs 4.1 Introduction GnRH-I plays a vital role in the regulation of mammalian reproductive function. The responsiveness of the pituitary to GnRI-I-I relies on the amounts of GnRHR on the cell surface. Pituitary Gnrhr gene expression is dynamically modulated by GnRI-1-1 pulses and concentration in rat: the highest expression level of Gnrhr in the pituitary has been reported to be associated with a 30 mm GnRH-I pulse frequency, which leads the optimum synthesis and release of LH, while lower expression of Gnrhr is observed with a 2 h GnRH-I pulse frequency, which is related to optimum synthesis and release of FSH (138, 365). Continuous exposure to high concentrations of GnRH-I results in down-regulation of Gnrhr mRNA levels (49). The difference in the Gnrhr mRNA levels influenced by high and low frequency GnRH-I pulses is approximately 2-3 fold (139). In mouse gonadotroph ccT3-1 cells, the response of Gnrhr to GnRH-I seems controversial. One study has observed that GnRH-I increases mouse Gnrhr promoter activity in a reporter gene assay (326). However, other studies find no changes in Gnrhr mRNA levels in response to continuous exposure to GnRH-I (366), or time- and concentration-dependent decreases in the levels of Gnrhr mRNA in response to GnRI-I-I (367). The disparity among these studies may be due to the difference of cell culture conditions and the duration of GnRH stimulation. In terms of the mechanisms involved in the regulation of Gnrhr by GnRH-I treatments, deletion, mutation and functional transfection studies in the murine ciT3-1 cell line have shown that the responsiveness of the mouse Gnrhr gene to GnRH-I is localized to  94  two distinct DNA elements including an AP-1 binding site, which appears to be necessary and sufficient to mediate a full GnRH-I response. In this regard, GnRH-I rapidly induces a member of the Fos/Jun heterodimer to form complexes with AP-1 binding site, and this is found to involve the PKC signal transduction pathway (326). The PR is a member of the steroid hormone receptor superfamily. It has two main isoforms obtained from the transcription of an individual gene from two separate promoters, a full length PR-B, and N-terminally-truncated PR-A lacking the first 164 amino acids of PR-B. Ligand activation of PR is well characterized (276). In general, PRs are complexed with hsp in the absence of the ligand. After binding with P4, PRs exhibit conformational changes leading to hsp dissociation, receptor phosphorylation, dimerization, loading to PRE, and induce subsequent gene transcription (278). On the other hand, PR may alternatively change gene expression by tethering to other transcription factors such as AP-1, SP-1, or STAT (270, 28 1-283). Ligand-independent activation of PR and glucocorticoid receptor (GR) by GnRH-I has been identified in gonadotrophs. In rodent pituitary cells, cross-talk between GnRH-I and PR is believed to play a role in the GnRH-I self-priming effect (21, 250, 358, 359), which serves to induce the preovulatory LH surge. The GnRH-I self-priming effect depends on PR, as it is completely absent in Pr knock-out mice (13). Previous data in our laboratory have indicated that in xT3-1 and L13T2 cells, GnRH-I activates PR in a ligand-independent manner and promotes the accumulation of Gsua mRNA (21, 368). This likely contributes to the self-priming effect of GnRH-I during the follicular phase of the menstrual cycle and also the proestrus phase of mouse estrous cycle. Furthermore, GnRH-I also activates PR and promotes the accumulation of Fshb mRNA in L3T2 cells. This is suggested to contribute to the enhancement of FSH levels during the luteal to follicular phase transition, which is  95  important for the selection and maturation of dominant follicles (302). In LT2 cells, transactivation of GR by GnRI-I-I contributes to Gnrhr expression. GnRH-I and dexamethasone increase mouse Gnrhr promoter activity via an AP- 1 site, and also induce endogenous mouse Gnrhr mRNA expression. GR is required because knocking down endogenous GR levels by siRNA reduces both the dexamethasone and GnRH-I effects. In addition, GnRH-I and dexamethasone up-regulate GR nuclear translocation, and ChIP assays demonstrate that GnRI-I-I and dexamethasone enhance the interaction of the GR with the AP-1 binding site on the mouse Gnrhr promoter (333). The murine Gnrhr promoter contains an AP-1 binding site (326, 333). We confirmed this by using the bioinformatic analysis tool, Genomatix, and also found a potential PRE in the promoter. Since GnRH-I activates luciferase reporter genes under the control of PRE and AP-1 binding sites in mouse gonadotrophs (21, 302, 333, 368), and there is cross-talk between GnRH-I and PR (21, 302, 368), we set out to determine whether the ligand-independent activation of PR by GnRH-I contributes to the induction of mouse Gnrhr gene using mouse pituitary cell lines.  4.2 Materials and methods  4.2.1 Cells and cell culture  The mouse gonadotroph-derived cLT3-1 (341) and L13T2 (342) cell lines were kindly provided by Dr. P.L. Melon (Department of Reproductive Medicine, University of California, San Diego, CA) and maintained in monolayer cultures in Dulbecco’s modified Eagle’s medium supplemented with 10% FBS, 100 U/ml penicillin G, and 0.1 mg/mI streptomycin  96  (Invitrogen, Burlington, ON) in humidified 5% C0 , 95% air at 37 C. The cells were 2 passaged when they grew approximately 90% confluence, utilizing a trypsin/EDTA solution  (0.05% trypsin, 0.5 mM EDTA). Cells were maintained in phenol-red free medium containing charcoal-treated FBS for four days prior to experiments.  4.2.2 Plasmids, s1RNA and transient transfection assay A fusion construct prepared by ligation of the 1.2-kb 5’-flanking region of the mouse  Gnrhr gene (designated -1164/+62 bp) into the luciferase reporter plasmid, pXP2, was generously provided by Dr. U. B. Kaiser (Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts) (326, 369). The pAP1-luciferase plasmid which contains seven copies of a consensus AP-1 site was obtained from Stratagene (La Jolla, CA). The siRNAs for PR and a nonspecific siRNA (negative control, si-ctrl) were obtained from Qiagen Inc. (Mississauga, ON, Canada). Transient transfections of the mouse Gnrhr-luciferase, pAP 1 -luciferase reporter genes, or siRNA were performed using Lipofectamine 2000 (Invitrogen, Burlington, ON) together with a RSV-lacZ plasmids to correct for transfection efficiencies. After seeding in six-well plates for 24 h, the cells were transfected with 1 tg of mouse Gnrhr-luciferase, or pAP 1-luciferase reporter genes, together with 0.5 tg of RSV-lacZ. After set times of culture, cellular lysates were obtained by adding 150 jil reporter lysis buffer (Promega Corp., San Luis Obispo, CA) which were assayed for luciferase activity using a Lumat LB 9507  luminometer (EG&G, Berthold, Germany). 13-Galactosidase activity was also examined using a -galactosidase enzyme assay system (Promega Corp.) to normalize for transfection efficiencies. Promoter activity was calculated as luciferase/f3-galactosidase activity.  97  4.2.3 Immunoblotting Equal amounts of protein were resolved by 10% SDS-PAGE and transferred to polyvinylidene difluoride membranes. After blocking, the membranes were incubated overnight at 4 C with specific antibodies against PR A/B and actin (Santa Cruz Biotechnology, Santa Cruz, CA). Horseradish peroxidase-conjugated secondary antibodies were incubated with the membranes. After washing, immunoblots were examined using the ECL chemiluminescent system (Amersham Pharmacia Biotech, Piscataway, NJ) followed by exposure to Kodak X-Omat film.  4.2.4 Real-time RT-PCR Total RNA was extracted from cell cultures using Trizol (Invitrogen, Burlington, Canada). The RNA concentration was calculated based on absorbance at 260 nm. Isolated RNA was reverse transcribed into first-strand eDNA using M-MLV reverse transcriptase (Promega  Corp.).  The  primers  for  mouse  Gnrhr  mRNA  were:  sense,  5’-  TCTTCTCGCAATGTGTGACC and antisense, 5’-TAGCGAATGCGACTGTCATC. The primers for Gapdh mRNA were: sense, 5’-CATGGCCTTCCGTGTTCCTA and antisense, 5’-GCGGCACGTCAGATCCA. Real-time PCR was performed using an ABI prism 7000 Sequence Detection System (PerkinElmer Applied Biosystems). Reactions were set up using SYBR Green PCR Master Mix (PerkinElmer Applied Biosystems). Relative quantification of mouse Gnrhr mRNA levels was performed using the comparative cycle threshold method with GAPDH as an endogenous control and with the formula  4.2.5 Data analysis Data are presented as the mean  ±  SEM of at least three independent experiments. Data  98  were analyzed by one-way ANOVA followed by Tukey’s test by using the GraphPad Prism 4 statistical software (GraphPad Software, Inc., San Diego, CA). Statistical significance was defined as p<O.O5.  4.3 Results  4.3.1 GnRII-I and GnRII-II transiently activate mouse Gnrhr in LT2 cells After transfection of a mouse Gnrhr promoter-luciferase reporter gene, 100 nM GnRH-I and GnRH-II transiently increase luciferase levels by approximately 4 and 2.5 fold, respectively, during 6-12 h in Lf3T2 cells. There is no apparent difference in the luciferase reporter gene activity after treatment with 100 nM P4 in L13T2 cells (Figure 4.1). In the mouse gonadotroph ccT3-1 cell line, 100 nM GnRH-1, GnRH-II or P4 has no effects on mouse Gnrhr promoter-luciferase reporter gene (Figure 4.2).  4.3.2 GnRfl-I rapidly and transiently activates the AP-1 luciferase gene in LT2 and aT3-1 cells We first checked the mouse Gnrhr promoter sequence by using the Genomatix program. In accordance with a previous study (326, 333), there is an AP-1 binding site at -338 to -327 bp. We also found a potential PRE in the promoter of Gnrhr at -232 to -213 bp. Our previous data have indicated that GnRH-I and GnRH-II enhance PRE-luciferase reporter gene activity in both the L13T2 and ccT3-1 cell lines (21, 302, 368). To examine whether GnRH treatments influence the transcriptional activity of AP- 1, LT2 cells were transfected with a synthetic AP-1-luciferase reporter gene. When cells are treated with 100 nM GnRH-I or GnRH-II, approximately 300 and 150 folds increases,  99  respectively, in luciferase activity are observed. The much greater response of the AP- 1 -luciferase reporter gene after treatments with GnRH-I and GnRH-II, compared with that of untreated cells, reflects the presence of seven AP-l sites in the AP-1-luciferase construct, when compared to only one in the Gnrhr promoter. In contrast to the results observed with GnRH-I and GnRH-II, treatment with P4 does not increase the transcriptional activity of the AP-l-luciferase reporter gene, compared with vehicle control in L13T2 cells (Figure 4.3). Similarly, when LT3-1 cells are transfected with the AP-1-luciferase reporter gene, and then treated with GnRH-I, luciferase activity is significantly increased during 6-24 h and reaches its highest level at 12 h, when it is approximately 3.5 fold higher than the control. However, treatments with GnRH-II and P4 do not enhance the AP-1-luciferase reporter gene activity in ctT3-1 cells (Figure 4.4).  4.3.3 GnRH-I-induced mouse Gnrhr promoter activity requires PR In the next set of experiments, we used a siRNA approach to assess the role of PR in GnRH-I-modulated mouse Gnrhr promoter activity in Lf3T2 cells. When the PR levels in L13T2 cells are knocked down by a PR siRNA (Figure 4.5 upper panel), significant reductions in both GnRH-I and GnRH-II stimulated mouse Gnrhr promoter-luciferase gene activity are observed (Figure 4.5). These suggest that downstream signaling events involving PR are required for the GnRH-I and GnRH-II induction of mouse Gnrhr promoter activity.  4.4 Discussion  During the human menstrual cycle and mouse estrous cycle, the biosynthesis and secretion of gonadotropins from the pituitary gonadotrophs are tightly regulated as evidenced  100  by predictable and reproducible alterations in circulating levels. This relies primarily on GnRI-I pulse amplitude and frequency, which fluctuates during the rodent estrous cycle and the human menstrual cycle. The responsiveness of pituitary gonadotrophs to GnRH-I correlates directly with variations in GnRHR concentrations on the cell surface which is partially mediated at the level of gene expression (136, 137). In this study, we have found that both GnRH-I and GnRH-II increase mouse Gnrhr promoter activity and this may be due to the activation of PR (Figure 4. 6). In the future, we will further verify whether GnRH-I and GnRH-II increase endogenous mouse Gnrhr mRNA, and whether these effects depend on the transactivation of PR by using a s1RNA approach. Since our previous data indicate that GnRH-I treatment causes phosphorylation of the PR at Ser 249 through activating PKC signaling pathways, we hypothesize that PKC signaling involves in the induction of mouse Gnrhr gene expression. Because SRC-3 has been found to assemble to the PRE in the promoter of Gsua in xT3-1 cells (21), it will be important to determine whether this or other coactivators bind to PR by co-immunoprecipitation. Assembly of the PR to the PRE on a transfected mouse Gnrhr promoter, as well as the endogenous mouse Gnrhr promoter will be assessed by ChIP assays. Our previous data have indicated that transactivation of ERa by GnRH-I and GnRH-II increases Fosb expression (370). Further studies are required to determine whether Fosb and Jun family proteins are recruited to AP-1 binding site in the promoter of Gnrhr. The concentration of GnRHR in the pituitary is regulated by several hormonal factors, most notably by its own ligand. The effects of GnRHR by GnRH-I are cell and species specific. Homologous activation of the mouse Gnrhr promoter by GnRH-I involves an AP-1 binding site (123, 326), but previous data from our laboratory have indicated that treatment with GnRH-I results in a concentration- and time-dependent repression of human type I  101  GnRHR promoter activity in ctT3-1 cells, which is mediated by the PKC signaling cascade.  Subsequent studies have indicated that mutation of an AP-1-like motif abolishes the sensitivity of the promoter to GnRH-I, and electrophoretic mobility shift assays reveal that GnRH-I stimulated c-Fos DNA binding activity in the AP-1-like binding motif is responsible for the downregulation of the human type I GnRHR gene transcription (371). In the current study, we have found that GnRH-I and GnRH-II transiently enhance mouse Gnrhr promoter activity in L13T2 cells, but not in aT3-1 cells. It is not known if the different experimental paradigms or mechanisms account for differences in the gene responsiveness to GnRH-I in the human and rodent gonadotrophs. However, disparities in Gnrhr promoter activities in the two mouse gonadotroph cell lines may be due to differences in their developmental differentiation. The dynamic changes in GnRHR levels in pituitary gonadotrophs during the estrous cycle (372-374) or after gonadectomy (139, 375) strongly implicate steroid hormones in the regulation of Gnrhr gene expression. In cLT3-1 cells, P4 represses human type I GnRHR promoter activity in concentration- and time-dependent manners, while P4 stimulates the human type I GnRHR promoter in JEG-3 cells. Moreover, mutation of an imperfect PRE in the human type I GnRHR promoter attenuates the P4 effect on its transcriptional activity (157). Overexpression of two human PR isoforms also indicates that PR-B is a fundamental modulator in mediating the down-regulatory effect of P4 in this context. However, in JEG-3 cells the two PR isoforms have differential roles such that PR-B stimulates while PR-A inhibits the activity of the human type I GnRHR promoter (157). We have found that P4 has no effect on mouse Gnrhr promoter activity in the mouse gonadotroph cell lines, indicating that ligand-dependent activation of PR in mouse gonadotrophs may not be involved in mouse Gnrhr expression.  102  A few studies suggest that ligand-independent activation of the PR occurs in mouse pituitary cells (21, 302, 368). Steroid receptors other than PR can also be activated in a ligand-independent manner. For instance, growth factors and GnRH subtypes transactivate the ERc via specific signaling pathways and phosphorylation of ERa at SerNS and Ser’ 67 (226, 370). A recent study has found that after GnRH-I binding with GnRHR, cross talk occurs with the GR, inducing GR phosphorylation at 5er 234 via PKC and MAPK signaling, resulting nuclear translocation and transactivation of a glucocorticoid response element in mouse LPT2 cells (333). By using siRNA technology in the current study, we have first indicated that the PR is required for transcriptional regulation of mouse Gnrhr promoter activity. We also searched the human GnRHR promoter using a bioinformatic approach, and in accordance with a previous study (157), we have found that it contains AP-l and PR binding sites. Whether activation the PR by GnRH and subsequent loading of the PR at PRE and/or AP- 1 binding site occur in the human pituitary which regulates GnRHR gene expression require further study. In conclusion, we demonstrate for the first time that GnRH-I and GnRH-II increase mouse Gnrhr promoter activity via ligand independent activation of the PR in L13T2 cells (Figure 4. 6). Because GnRH-I regulates many genes in gonadotrophs, this represents a mechanism by which the activation of PR by GnRH-I may modulate the expression of several GnRH-I and PR target genes. The induction of Gnrhr expression by the GnRH-mediated activation of the PR may be involved in the self-priming effect of GnRH-I before the LH surge. It may also have broader physiological implications because GnRHR and PR are widely expressed in many extrapituitary tissues.  103  A GnRH-I E•  CtrI  GnRH-II  2.c0  3  12  6  24  (h)  LpT2  B EtOH •0  ,.  4 P  2.0  o o h..  D  1.5 1.0  0  05 u-u  6  12  (Ii) LPT2  Figure 4.1 GnRI-I-I and GnRH-II activate mouse Gnrhr in LT2 cells.  The mouse Gnrhr promoter-luciferase reporter gene together with a (RSV)-lacZ plasmid were transiently transfected into L13T2 cells using Lipofectamine 2000. The cells were either treated with 100 nM GnRH-I, GnRH-II (A) or 100 nM P4(B) over a 24 h time course. The cell lysates were assayed for luciferase activity and measurements of f3-galactosidase activity as a control. Results are shown as mean ± SEM fold change in mouse Gnrhr promoter activity expressed as Luciferase activity/f3-galactosidase activity of three independent experiments.  *:  p<O.O5 compared to untreated control value set at 1  (Ctrl).  104  A  GnRH-I :J GnRH-I  Cirl  24  (tip aT3-1  B  EtOH  >.  D  4 P  2.0 C) I4-  o  Q  -=  I- .  6  12  (h)  r-j  Figure 4.2 GnRH-I and GnRH-II have no effects on mouse Gnrhr-luciferase promoter activity in the aT3-1 cell line. The mouse Gnrhr promoter-luciferase reporter gene together with a (RSV)-lacZ plasmid were transiently transfected into xT3-1cells using Lipofectamine 2000. The cells were either treated with 100 nM GnRH-I, GnRH-II (A) or 100 nM P4(B) over a 24 h time course. The cell lysates were assayed for luciferase activity and measurements of -galactosidase activity as a control. Results are shown as mean ± SEM fold change in mouse Gnrhr promoter activity expressed as luciferase activity/f3-galactosidase activity of three independent experiments.  105  A J CtrI IEI GnRH-I J GnRH-II 400 >. .  *  n  *  300  *  200•  fl  3  6  B EtOH  1*  fl  II  100  II 12  H 24  (Ii)  L12  0  2.0 11.1.5 1.0•  :::____  6  12  (h)LT2  Figure 4.3 GnRH-I and GnRH-II activate AP-! luciferase activity in LIEIT2 cells.  The luciferase reporter gene under the control of a promoter containing seven AP-1 binding sites together with a (RSV)-lacZ plasmid was transiently transfected into LPT2 cells by Lipofectamine 2000. The cells were either treated with 100 nM GnRH-I, GnRH-II (A) or 100 nM P4(B) over a 24 h time course. The cell lysates were assayed for luciferase activity and measurements of -galactosidase activity as a control. Results are shown as mean ± SEM fold change in AP- 1 promoter activity expressed as luciferase activity/-galactosidase activity of three independent experiments.  *:  p<O.05 compared to untreated control value set  at 1 (Ctrl).  106  A  ZI CtrI ZI GnRH-I c::J GnRH-II  3  6  12  24  (h)aT3-1  B  Z1 EtOH  ZI  4 P  ‘S  o..  0  •0 0  6  12  (h) aT3-1  Figure 4.4 GnRH-I rapidly and transiently activates AP-1 luciferase activity in cT3-1 cells.  The luciferase reporter gene under the control of a promoter containing seven AP-1 binding sites together with a (RSV)-lacZ plasmid  was  transiently transfected into ctT3-1 cells by  Lipofectamine 2000. The cells were either treated with 100 nM GnRH-I, GnRH-II (A) or 100 nM P4(B) over a 24 h time course. The cell lysates were assayed for luciferase activity and measurements of -galactosidase activity as a control. Results are shown as mean ± SEM fold change in AP- 1 promoter activity expressed as luciferase activity/3-ga1actosidase activity of three independent experiments.  *:  p<O.O5 compared to untreated control value set  at I (Ctrl).  107  CtrI  si-ctrl  si-PRI  PR-B PR-A 13-actin  >  4-.  >  (ZI si-PR  0  si-ctrl  *  I  0’-•4-.0 *  C)  ‘I  (5 0 (0  CtrI  GnRH-I  LT2  GnRH-II  Figure 4.5 GnRFI-I-induced mouse Gnrhr promoter activity requires PR. L13T2 cells were cotransfected with the mouse Gnrhr promoter-luciferase reporter gene and a (RSV)-lacZ plasmid, with control siRNA (si-ctrl) or an siRNA for PR (si-PR). The efficiency of the siRNA  was  tested by immunoblotting for PR (upper panel). After treatment with 100  nM GnRH-I or GnRH-II for 6 h, the cell lysates were collected for luciferase assay and measurements of -galactosidase activity as a control. Results are shown as mean ± SEM fold  change  in  mouse  Gnrhr  promoter  activity  expressed  activity/-galactosidase activity of three independent experiments.  *:  as  luciferase  P<0.05 compared to  cells transfected with an siRNA control (si-ctrl). #: P<0.05 compared to cells transfected with an siRNA control and followed by the respective treatment.  108  GnRH-I  Fosb  ?  * , * *  **  4  (Jun jFe;b)  Gnrhr  Figure 4.6 Cross-talk between GnRH-I and PR in the induction of Gnrhr promoter activity in mouse gonadotrophs. After binding with GnRI-IR, GnRH-I stimulates PR phosphorylation, loading to the PRE, and induces Gnrhr expression. On the other hand, GnRH-I also activates ERc after stimulating PKA and PKC signaling pathways and increases Fosb expression. Whether Fosb and Jun family protein form heterodimer and load to AP- 1 binding site to increase Gnrhr expression need  further  study.  AP- 1,  activator  protein-I;  ER,  estrogen  receptor;  GnRH,  gonadotropin-releasing hormone; GnRI-IR, GnRH receptor; PKA, protein kinase A; PKC, protein kinase C; PR, progesterone receptor; PRE, Progesterone-response element.  109  Chapter 5 Conclusion and future work The molecular events and mechanisms that control the dynamic flux of the hypothalamic-pituitary-gonadal axis are of particular physiological significance. Some of these mechanisms involve GnRH-I, a decapeptide that mediates reproductive competence through the stimulation of gonadotropin synthesis and secretion from pituitary gonadotrophs. Many GnRH-I agonists and antagonists have been developed for a variety of remedies in assisted reproductive technologies, gynecological diseases, and cancer treatment. Cross-talk between GnRH and steroid hormone receptors has been recognized from previous studies (20, 21, 302, 333). In this project, we have studied specific mechanisms and provide further evidence that GnRH activates both ERx and PR in a ligand-independent manner in mouse gonadotrophs. In the LT2 cell line, we have found that both GnRH-I and GnRH-II activate the ERE-luciferase reporter gene, and that GnRH-I is consistently more potent in this regard. In addition, GnRH-I and GnRH-II phosphorylate ERct at Ser 118 in the nucleus and at Ser’ 67 in both nucleus and cytoplasm, and enhance ERa binding to its coactivator PCAF. Most importantly, this transactivation of ERa by GnRH-I and GnRI-I-II are involved in the rapid and transient induction of the immediate early response gene, Fosb, since co-treatment with ERa siRNA or PCAF siRNA attenuates this induction, and GnRH-I and GnRH-II induce the assembly of ERa and PCAF to an ERE within the Fosb promoter. We have also found that GnRH-I activates a PRE-luciferase reporter gene and endogenous Gsua gene expression in both the aT3-1 and Lf3T2 pituitary cell lines. PKA and PKC inhibitors attenuate the GnRH-I induced up-regulation of the PRE-luciferase reporter gene in both cell lines, while only the PKC inhibitor significantly reduces the GnRH-I  110  stimulated increase in Gsua mRNA levels. Knockdowning endogenous PR levels using an siRNA approach also significantly reduces the GnRH-I activation of Gsua mRNA levels, and this provides direct evidence that the activation of PR by GnRH-I contributes to Gsua expression. Furthermore, both GnRH-I and GnRH-II promote the mouse Gnrhr-luciferase promoter activity in LT2 cells. This is due to the activation of the PR, because a PR siRNA significantly reduces both the GnRI-I-I and GnRH-II effects on mouse Gnrhr promoter activity. We therefore conclude that the induction of Fosb and Gsua expression, as well as Gnrhr promoter activity by GnRH-I in mouse gonadotrophs is mediated by the ligand-independent activation of ERa and PR, respectively.  5.1 Physiological relevance of the experimental conditions design  Primary pituitary cell cultures contain only about 5% gonadotrophs and are difficult to manipulate in vitro. Currently there are no human gonadotroph cell lines available. The development of immortalized mouse pituitary gonadotroph cell lines, including aT3-1 and LT2 cells, has allowed analyses of the mechanisms regulating gonadotropin genes by GnRH and nuclear receptors within a single population of gonadotroph cells. Both ctT3- 1 and L13T2 cell lines were derived from transgenic mice pituitary tumors (341, 342). The aT3-1 cell line only expresses Gsua gene but not the gonadotropin f3 subunit gene, and they represent gonadotrophs present at mouse embryonic day 13.5, and are therefore regarded as relatively immature. The gonadotroph-derived L13T2 cell line expresses both the common Gsua subunit gene and the unique 13 subunit gene , as observed in mouse gonadotrophs by embryonic day 17.5, rendering it more physiologically relevant to in vivo systems in mature animals (5, 23, 343, 361, 362, 376).  111  We assessed the relative transfection efficiencies by using siGLO transfection indicator or an EGFP expression vector in cT3-l and L13T2 cells before the transfection experiments. The transfection efficiencies after 48 hours for siRNA were evaluated by the fluorescence signal and were approximately 70% in ctT3-1, and approximately 60% in Lf3T2 cells. The transfection efficiencies for DNA were similar to siRNA in both cell lines (data not shown). From these pilot studies we have modified the transfection conditions such as cell confluence and transfection duration in these two cell lines, which we believe represent ideal models for the study of cross talk between GnRH and steroid hormone receptors.  5.2 GnRH activates specific signaling pathways in the transactivation of ERa and PR  The type I GnRHR is a special type of G protein-coupled receptor that primarily uses the Gq protein for its downstream cascades, and this activates multiple signaling pathways that in turn regulate the transcription of several genes including the gonadotropin subunit genes. Elucidating the coordination of different GnRH-induced signaling pathways is of considerable interest in understanding the mechanism of action of GnRH in the pituitary. In our studies, we have found that inhibitors of the PKA, PKC, P13K and MAPK signaling cascades significantly reduce the induction of an ERE-reporter gene by GnRH-I and GnRFI-II (data not shown). Only inhibitors of PKA and PKC signaling reduce the rapid and transient activation of Fosb gene expression by both GnRH subtypes in Lf3T2 cells. The GnRH-I induction of a PRE-luciferase reporter gene also involves the PKC and PKA signaling pathways. Interestingly, only the PKC inhibitor significantly impairs the increase of Gsua mRNA levels by GnRH-I treatment in both the aT3-1 and LT2 cells. Previous studies in our laboratory have indicated that the PKC inhibitor, OF 1 09203X, decreases the GnRH-I  112  mediated phosphorylation of the PR at Ser 249 in both the ctT3-l and L13T2 cells (302). This may explain why only the PKC inhibitor attenuates enhancement of Gsua mRNA levels by GnRH-I. Normally inhibitor studies are used to define the specificity of signaling cascades, and for this purpose a number of inhibitors of specific pathways are frequently examined to provide confidence that particular signaling pathways are involved. Only single inhibitors of PKC, PKA, as well as single antagonists of type I GnRHR and PR signaling were used in my studies of the cross talk between GnRH-I and PR. This is because PKC signaling in GnRH-I induced Gsua expression has been well-documented previously, and PKA signaling did not mediate the effects of GnRH-I on Gsua mRNA levels in my studies. Thus, the use of multiple inhibitors was considered unnecessary. In addition to the use of RU486 and antide, which are well-know antagonists of the PR and type I GnRHR, respectively, we also used siRNA to knock down PR levels and this resulted in a significant reduction of Gsua levels after GnRH-I treatment. In an earlier study, we also used an siRNA to knock down endogenous GnRHR levels in ccT3-l cells, and this significantly reduced GnRH-I enhanced PRE-luciferase reporter gene activity compared to control cells with normal levels of Gnrhr (302).  5.3 GnRH-I has more robust effects than GnRH-II in mouse gonadotrophs Both GnRH-I and GnRH-II perform their functions by binding the same receptor in  mouse, i.e., GnRHR. The physiological importance of GnRH-II remains largely unknown in the pituitary. Although our results have shown that the effects of GnRH-I and GnRH-II are similar in most experiments, we routinely tested both GnRH subtypes in terms of the  113  ligand-independent activation of ERct to increase our level of confidence that GnRH-I consistently has more robust effects on all the GnRHR-mediated responses we have studied. The induction of an ERE-luciferase reporter gene by GnRH-I is greater compared to that mediated by GnR}1-II, as shown in Figure 2.IA. However, in Figure 2.IC, the magnitude of the induction at 100 nM of each ligand is comparable. This difference is due to the relatively large error bars in Figure 2.1A, but in both experiments the induction of the ERE-luciferase reporter gene by 100 nM GnRH-I or GnRH-1I is significant. In a dose-dependent experiment, a maximum response is obtained with 10 nM GnRH-I and 100 nM GnRH-II. In studies of the ligand-independent activation of ERx by GnRH-I and GnRH-II, we utilized the same concentration of GnRH-I and GnRI-I-II, i.e., 100 nM. We have confirmed that GnRI-I-I has stronger effects than GnRH-II on the ligand-independent activation of ERG, as well as of PR in the previous study (21). Therefore, in a subsequent study of how the cross-talk between GnRI-I and PR might influence Gsua mRNA levels, we only tested GnRH-I. Based on the dose-dependent study, we utilized a low dose of GnRH-I, i.e., 10 nM, which more closely represents its physiological concentration in the pituitary (377).  5.4 Single mutations (S118A or S167A) of ERa phosphorylation sites are not sufficient to affect Fosb protein levels  The phosphorylation of ERCL is induced by its ligand and by other factors that influence its nuclear translocation, dimerization, and transcriptional activity. In this project, we have ascertained that treatments of LT2 cells with either GnRH-I or GnRH-II stimulate the phosphorylation of ERa at Ser’ 67 in both the nucleus and cytoplasm, as well as the phosphorylation of ERa at Ser” 8 in the nucleus. However, E 2 does not significantly increase  114  the phosphorylation of ERa at Ser’ . We next tried to study whether phosphorylation at these 67 two sides was important for the induction of the endogenous Fosb gene by substituting alanine for the serine residues by site-directed mutagenesis. After 24-72 h transfection of the wild-type ERa, or the ERa Si! 8A or Si 67A mutant into LT2 cells, western blot analysis shows a dramatic increase in ERa levels (Figure 5.1). Surprisingly, when treated with either GnRH-I or GnRI-I-II, the S118A or S167A ERa mutants do not significantly affect Fosb levels compared to the cells transfected with the wild-type ERa (Figure 5.1). We then determined the lowest concentrations of GnRH-I and GnRH-II that induced Fosh mRNA levels by real-time PCR. The results show that 1 nM of GriRH-I and 10 nM of GnRH-II significantly increase the Fosb mRNA levels (Figure 5.2). However, when the cells are treated with lower concentrations of GnRH-I or GnRH-II (1 nM and 10 nM, respectively), the Si 1 8A or Si 67A ERa mutants still have no effect on Fosb mRNA levels compared to the wild-type ERa (data not shown). This lack of effect may be masked by the basal levels of ERa in LT2 cells which are sufficient to induce endogenous Fosb gene expression by GnRH. Furthermore, although Ser” 67 are the most common phosphorylation sites 8 and Ser’ of ERa, other sites may still be required for GnRH-induced Fosb expression in mouse gonadotrophs. However, we have not studied other phosphorylation sites due to the unavailability of antibodies. Further investigations to assess the importance of other phosphorylation sites using site-directed mutagenesis therefore need to be conducted. It can also be assumed that the phosphorylation of only one site within ERa will not influence Fosb gene expression by GnRH, and to confirm this both phosphorylation sites may need to be mutated.  115  5.5 PCAF regulates gene expression in the pituitary after interactions with ERL.  Nuclear receptor coactivators are necessary for the proficient transcriptional modulation by nuclear receptors (378, 379). The importance of these coactivators has been noted in several diseases, such as cancer and some neurological disorders (380). The enrollment of coactivators is a rate-limiting step in the steroid receptor-induced gene transcription in in vitro studies (378, 381), and coactivator acetylation, methylation, phosphorylation and chromatin remodeling influence nuclear receptor mediated transcriptional activities (378). PCAF belongs to the Gcn5 related N-acetyl transferase superfamily of acetyltransferases and has high similarity with GCN5 over the whole sequence (220). The mechanisms underlying the ligand-dependent and -independent activation of ERa together with the loading of coactivators at specific promoter sequences to induce target gene expression at the pituitary level remain largely unknown. In this project, GnRH-1 and GnRH-II rapidly increase the ligand-independent activation of ERa in LT2 cells, as well as binding of ERa and PCAF to the ERE in the promoter of the Fosb gene. To our knowledge, this is the first time that PCAF has been shown to participate in gene expression in the pituitary after assembly with ERa. Additionally, we have obtained evidence that both GnRH-I and GnRH-II stimulate the assembly of ERa and PCAF to the ERE in a transfected luciferase reporter gene construct (data not shown). The full transcriptional activity of nuclear receptors depends, at least in part, on the recruitment of coactivators. Whether PCAF action involves the activation of other genes after binding with ERa to the ERE in the gene promoter, and the overall importance of this nuclear receptor coactivator in the pituitary require further studies.  116  5.6 GnRB-I activates PR in a ligand-independent manner to induce Gsua expression  The PR can be activated by both ligand-dependent or ligand-independent mechanisms, and these mechanisms are not mutually exclusive, and mostly likely act in synergy in most cases. In this study we focus on the ligand-independent activation of PR by GnRH-I and its role in the regulation of Gsua expression and mouse Gnrhr promoter activity in ctT3-1 and L13T2 cells. In both cell lines, the PR can be activated in a ligand-independent manner by GnRH-I. The self-priming effect of GnRH-I is a powerful servo-mechanism that amplifies the pituitary responsiveness to GnRI-I-I by several fold. This coordinates the increased pulses of GnRH-I into the hypophysial portal system with increased pituitary LH secretion so that both GnRI-I-I and LH simultaneously reach a peak just before ovulation. Animal studies have indicated that such potentiating effects of serial GnRH-I stimulation are critical to generating the preovulatory LH surge during folliculogenesis (250). A human study among healthy postmenopausal women examined the kinetic characteristics of gonadotropin release in response to pulses of exogenous GnRH-I and has found that the self-priming effects of GnRI—I-I exist in the human (382). PR plays a central role in the preovulatory LH surge at the midcycle, and Pr knockout mice provide a model for analyzing cellular pathways participating in this function (13). Together with previous data (21), we have provide direct evidence that after binding with type I GnRHR, GnRH-I at a physiological concentration prompts the PKC signaling cascade and then activates PR in the absence of the ligand; this activation induces Gsua mRNA levels after loading to the promoter PRE together with SRC-3. This mechanism likely enhances the self-priming effect of GnRH-I during the follicular phase of the human menstrual cycle and the proestrus phase of the mouse estrous  117  cycle. In experiments designed to knockdown the levels of specific endogenous gene products by using siRNA, it is better to utilize two siRNAs directed against the sequence of interest in addition to the control siRNA, in order to authenticate the response. We used a second siRNA for PR in xT3-1 cells. Both siRNAs significantly reduce PR levels and are equally effective in reducing GnRH-I stimulated Gsua mRNA levels. However, we were not able to successfully knock down PR levels with the second siRNA in Lf3T2 cells, and we were therefore not able to evaluate its effects in Lf3T2 cells. Furthermore, there are two isoforms of PR, PR-A and PR-B. So far it is still not known whether the ligand-independent activation of PR by GnRH-I relies on PR-A, PR-B, or both. This may require further study by applying specific siRNA for either PRA or PRB. In addition to the PR knockdown experiments, our findings could be strengthened if PR overexpression is also performed in the presence or absence of GnRH-I. We have since tried to overexpress PR-A and PR-B in both cell lines using an hPR B plasmid provided by Dr. P. Chambon (Institut National de la Sante et de la Recherche Médicale, University Louis Pasteur, Paris, France), and a pOP 13-hPR A plasmid from Dr. Graham (University of Sydney Westmead Hospital, Sydney, Australia). However, we have been unable to attain significant over-expression of human PR-A and PR-B in these cell lines. However, since the siRNA-mediated knockdown of PR significantly reduces Gsucz mRNA levels stimulated by GnRH-I in both aT3-1 and LPT2 cells, and our previous data have shown that GnRH-I increases assembly of SRC-3 and PR at the PRE in the Gsua promoter (21), we believe our current results provide sufficient evidence that PR is crucial for GnRH-I effects on the gonadotropin a subunit gene. We have not attempted to mutate the PRE in the Gsua promoter, which would provide  118  important insight into the role of PR in the transactivation of Gsua by GnRI-1-1. Nonetheless, our previous ChIP assay data have indicated that GnRH-I increases loading of SRC-3 and PR at the PRE in the Gsua promoter. We have since examined the Gsua promoter sequence amplified in the ChIP assay using the Genomatix program, and found no other non-PRE elements that are known to interact with PR, such as AP-l sites and Spi sites (data not shown). In addition, we show in this study that the stimulation of Gsua gene expression by GnRH-I can be significantly attenuated by PR siRNA. Together, these data provide direct evidence that activation of PR is critical for GnRH-I effects on the Gsua gene.  5.7 The physiological importance of transactivation of ERct and PR by GnRH-I The significance of growth factors and peptide hormones in the induction of ERa and PR transcriptional activity is still far from being fully understood. One possible explanation is that peptide hormone receptors are maintained at relatively high levels where steroid hormone receptor levels are low, such as in the pituitary. Furthermore, signaling cascades initiated by growth factors and peptide hormones may modulate the transcriptional activity of ligand-occupied nuclear receptors and increase the magnitude of target gene expression. It remains unclear whether the target genes activated by the steroid hormone receptors in response to growth factors and peptide hormones or steroid hormone are identical; it is also unclear whether these genes are preferentially or selectively regulated by a specific pathway (383). The GnRH agonists and antagonists have been widely utilized in in vitro fertilization and treatment of carcinoma, including endometrial and breast cancer. A better understanding of the molecular mechanisms underlying the ligand-independent activation of ERa and PR by GnRH will improve our assessment of the physiological function of GnRH and the nuclear  119  receptors, as well as the therapeutic side effects of GnRH agonists. The gonadotropins are regulated in a concert with GnRH, steroid hormones and other factors throughout the mouse estrous cycle and human menstrual cycle. During the luteal/follicular transition phase, circulating steroid hormone levels are relatively low. However, during the late follicular phase, increased E 2 levels reach a threshold for a period of time before inducing the LH surge. Our results are the first to demonstrate that in mouse L13T2 pituitary cells, GnRH mediates the phosphorylation of ERct and the co-recruitment of ERa and PCAF to an ERE within the Fosb promoter, which enhanced the transcriptional activation. This mechanism likely activates the Fshb subunit gene in pituitary cells. The ligand-independent activation of ERa by GnRH in pituitary cells may be most important under conditions when the GnRH pulse amplitude is high, such as during the transition from luteal to follicular phase of the human menstrual cycle and the proestrus phase of the mouse estrous cycle. Together with previous data from our laboratory (21), we have provided direct evidence that in aT3-l and L13T2 cells, GnRH-I activates PR in a ligand-independent manner and promotes the accumulation of Gsua mRNA, and this likely contributes to the self-priming effect of GnRH-I during the follicular phase of the human menstrual cycle and the proestrus phase of the mouse estrous cycle. Furthermore, the cross-talk between GnRH and PR has been studied in the context of a mouse Gnrhr reporter-luciferase reporter gene in LT2 cells, indicating that the mechanism of transactivation of PR by GnRH also influences other genes containing PRE. It is also possible that this may be a mechanism of action in the self-priming effect of GnRH-I. Further studies are required to determine whether the activation of PR by GnRH can induce endogenous mouse Gnrhr expression, and if the stimulation of Fosb influences Gnrhr expression (Figure 5.3 and 5.4). GnRH-I induces the ligand-independent activation of both  120  ERx and PR to mediate the expression of specific genes in mouse gonadotrophs; the genes are important in a certain period during the human menstrual cycle and mouse estrous cycle. It needs further evaluation that the activation of ERc and PR by GnRH is involved in other gene alterations in the pituitary. Apart from this, physiologically GnRH is released in a pulsatile manner from the hypothalamus. In the current project I have only tested the effects of continuous concentration of GnRH. More detailed studies of GnRH pulse frequency and/or amplitude, or the effects of other intercellular stimuli on the selective activation of ERL or PR are required.  121  a  -F’  I  I  I  I  I  I  + + I  •  I  I  I  ÷  +  +  I  I  I  I  I  I  I  +  +  i  +  I  I  I  I  i  .J.  I  +  I  I  +  I  +  i  +  I  I  ÷  +  I  I  +  I  +  I  +  I  I  +  I  —  +  —  ::  I  >p  Ct,ct, c aam ca CD  a  It  -4  rrn  Lb  Lb  Figure 5. 1 Effects of mutation of Ser’ 67 on GnRH-I and GnRH-II induced Fosb 18 and Ser’  protein levels. A, L13T2 cells were transfected with a vector control (Vec ctrl), wild-type ERo (ERa), mutant S1I8A or S167A ERa for 24, 48 and 72 h. Equal amounts of cell lysates were electrophoresed on SDS-10% gels, and western blotted to nitrocellulose for detection with antibodies specific for ERa. Control (Ctrl) represents untransfected cells. MCF-7 cells were utilized as positive control. B, LPT2 cells were transfected with a vector control (Vec ctrl), wild-type ERa (ERa), mutant S 11 8A or SI 67A ERa for 24 h and then treated with 100 n M GnRFI-I or GnRH-II for 3 h. Equal amounts of cell lysates were electrophoresed on SDS-10% gels, and western blotted to nitrocellulose for detection with antibodies specific for Fosb.  123  GnRH-I  GnRH-U *  E  1*  ,  *  *  0-c  4o, *  LL  o  —  0mM  —  —  lOnM  mM  —  —  —  lOOnM  Figure 5. 2 Effects on Fosb mRNA levels by different concentration of GnRH-I and GnRH-II. L13T2 cells were either untreated or treated with 0.1-100 nM GnRH-I or GnRH-II for 1 h. Total RNA was extracted and reverse transcribed into first-strand cDNA. The levels of Fosb mRNA were measured by real-time RT-PCR. Data of real-time RT-PCR are presented as the mean ± SEM of three independent experiments.  *:  p<O.05 versus untreated control value set  at 1.  124  __ _____  GnRH4  PR siRNA  PKC  R1  !jI•_AF I  SRC.3  I  1 Fosb  Gsucr  I  Fshbl  •:M’,i I  I  I Gnrhr  GnRH-I self.pnmiiq effect  Figure 5. 3 Transactivation of ERa and PR by GnRH-I in mouse gonadotrophs. In mouse LT2 pituitary cells, GnRH-i actives PKA and PKC signaling pathways which mediate the phosphorylation of ERa. Then ERa and PCAF are recruited to an ERE within the  Fosb promoter to enhance its transcriptional activation. This mechanism likely activates the Fshb  subunit gene in pituitary cells.  In addition,  GnRH-I activates PR in a  ligand-independent manner through the PKC signaling pathway. It promotes the binding of PR and coactivators to PREs in the Gsua and Gnrhr promoters, resulting in increased Gsua mRNA levels and Gnrhr promoter activity. These likely contribute to the self-priming effect of GnRH-I. Whether Fosb and Jun form a heterodimer and load at an AP-1 binding site to increase Gnrhr expression needs to be confirmed. AP- 1, activator protein-i; ERa, estrogen receptor; ERE, estrogen-response element; FSH, follicle stumulating hormone; GnRI-I, gonadotropin-releasing hormone; GnRHR, GnRH receptor; GSUa, gonadotropin a subunit; PCAF, P300/CBP-associated factor; PKA, protein kinase A; PKC, protein kinase C. PR, progesterone receptor; PRE, progesterone-response element; SRC-3, steroid receptor coactivator.  125  Gsua t  Fosb t  nr t 1 Gni  Fspb t  V  GnRH-l self-priming effect  —I  V  FSH t  .4—  I’  A.  I  I  / I  / ‘  —  /  —  /  Mouse esirous cycle  LH —  —  —  2 E P4  Figure 5. 4 The physiological importance of Fosb, Gsua and Gnrhr in human menstrual  cycle and mouse estrous cycle. Fosb, Gsua and Gnrhr are important for the cyclic hormonal changes during the human menstrual cycle and mouse estrous cycle. The induction of Fosb is crucial for Fshb gene expression which enhances FSH levels. This may be most important under conditions when the GnRH pulse amplitude is high, such as during the luteal/follicular transition phase of the human menstrual cycle, and proestrus phase in mouse estrous cycle. In addition, the accumulation of Gsua and Gnrhr mRNA levels likely contributes to the self-priming effect of GnRH-I, which is important to the LII surge in human menstrual cycle and mouse estrous cycle. Whether stimulation of Fosb involves in Gnrhr expression needs further study. , estradiol; FSH, follicle stumulating hormone; GnRH, gonadotropin-releasing hormone; 2 E Gnrhr, GnRH receptor; GSU, gonadotropin c subunit; LH, luteinizing hormone; P4, progesterone.  126  References  1.  Chudoba K, Jablonska J, Nowicki B 1981 Studies on transferrins of blood serum as selection criteria for animals in breeding herds. Archivum immunologiae et therapiae experimentalis 29:465-473  2.  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