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UBC Theses and Dissertations

Regulation of CYP1B1 and CYP2S1expression in extrahepatic tissues in rodents Deb, Subrata


Cytochrome P450 (CYP) enzymes play an important role in the metabolism of xenobiotics and physiological substances that are vital to the normal biological functions. It is important to understand the tissue distribution and factors that regulate the expression of CYP enzymes in hepatic and extrahepatic tissues. In the present study the regulation of two extrahepatic CYP enzymes, CYP1B1 and CYP2S1, was investigated. Rat testicular CYP1B1 protein expression is developmentally regulated and suppressed by hypophysectomy. The hormonal regulation of testicular CYP1B1 expression was examined in mouse MA-b and rat R2C Leydig tumor cells in the present study. CYPlB1 mRNA levels and protein kinase A (PKA) activity were increased 4.2-fold and 2.7-fold, respectively, after treatment of MA-b cells with luteinizing hormone (LH). Similarly, LH increased CYP1B1 protein levels by 30% in R2C cells. Treatment with a PKA activator mimicked the inductive effect of LH on CYP1B1 expression in MA-b and R2C cells. In contrast, treatment with PKA inhibitors attenuated the LH-elicited increases in CYP1B1 mRNA and protein levels and PKA activity and decreased basal CYP1B1 expression. Collectively, the results suggest that testicular CYP1B1 expression is regulated by LH through a PKA-mediated pathway. In separate experiments, estradiol benzoate decreased CYP1B1 mRNA levels in MA-b cells. Treatment of adult rats and Leydig cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin, the most potent AhR agonist, did not induce testicular CYP1B1 expression, indicating that testicular CYP1B1 is not regulated by the AhR pathway. CYP2S1 mRNA was detected in rat liver, lung, and other extrahepatic tissues. There was no sex-dependent difference in constitutive CYP2S1 mRNA expression in adult rats. Antibody against rat CYP2S1 was prepared using an antipeptide approach and was able to detect CYP2S1 protein in microsomes of rat lung, stomach and kidney. Rat CYP2S1 mRNA levels were induced in lung, stomach and jejunum by treatment with 3-methyicholanthrene (up to 3-fold) and in lung, liver and kidney by treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (up to 7-fold). However, CYP2S1 protein levels were not increased after treatment of rats with 3-methyicholanthrene, benzo[a]pyrene, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. Thus, rat CYP2S1 expression at the level of mRNA, but not protein, is sensitive to treatment by AhR agonists. The results obtained in the present study provide insight into the regulation of extrahepatic CYP1B1 and CYP2S1 by hormones and environmental pollutants. I show for the first time that CYP2S1 mRNA is expressed in most tissues whereas CYP2S1 protein has a limited tissue distribution in rats.

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