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Induction of neuronal apoptosis inhibitory protein expression in response to androgen deprivation by NF-κB in prostate cancer cells Chiu, Helen Hoi-Lun

Abstract

Androgen deprivation therapy is an efficacious treatment for advanced prostate cancer (CaP) by inducing apoptosis of prostate cells. Despite the initial effectiveness of this systemic therapy, the cancer will inevitably recur and progress to an androgen-independent stage. The molecular mechanism by which some CaP cells may bypass the cell death induced by androgen deprivation is unclear. Emerging studies have highlighted the role of the inhibitor of apoptosis protein (lAP) family members in conferring an enhanced ability of malignant cells to survive in conditions normally resulting in cell death. Therefore, we explored levels of expression of these anti-apoptotic proteins in CaP cells in response to androgen deprivation. Levels of neuronal apoptosis inhibitory protein (NAIP) mRNA were significantly increased in response to castration of hosts. The increase in NAIP mRNA levels in response to androgen deprivation was further confirmed in an in vitro system. Nuclear factor (NF)-κB, for which constitutive activity has been implicated in CaP, is suspected to play a role in the expression of lAPs. Using a NF-κB luciferase reporter construct, we demonstrated that the transcriptional activity of NF-κB was inhibited by androgen. In vitro, nuclear localization of NF-κB correlated with the DNA-binding activity of NF-κB as determined by electrophoretic mobility shift assay in human CaP cell lines with different androgen requirement and androgen receptor status. However, in vivo, the DNA-binding activity of NF-κB was independent from its protein levels in the nucleus. Importantly, elevated expression of NAIP correlated to the increased DNA-binding activity of NF-κB in vivo in response to castration of the hosts. To determine if the transcription of NAIP was directly regulated by NF-κB, subsequent characterization of three κB-like sites in the regulatory regions of the NAIP locus led us to confirm the physiological relevance of the κB-like site within the second intron of the gene locus using chromatin immunoprecipitation assay. Our observations suggest that transcription of NAIP may be regulated by NF-κB via regulatory element(s) in the NAIP locus in response to androgen deprivation. Thus, this study underlines a plausible mechanism by which some CaP cells may acquire the ability to resist apoptosis in androgen-deprived conditions.

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