Expression and Regulation of Cytochrome P450 17a-Hydroxylase Messenger Ribonucleic Acid Levels and Androstenedione Production in Hen Granulosa Cells'

Studies were conducted to evaluate the expression and regulation of cytochrome P450 17a-hydroxylase (P450 17a-OH) mRNA levels and androstenedione production in 6-8-mm-diameter follicle granulosa cells from the domestic hen. Although P450 17a-OH mRNA was detected within granulosa cells from follicles at all stages of development (3-12-mm and preovulatory follicles), 8-12-fold higher levels were found in small, less developed follicles (3-12 mm in diameter) compared to the three largest follicles within the preovulatory hierarchy (F3 to F, follicles). By comparison, P450 17a-OH mRNA levels were 25-89-fold higher in theca tissue compared to the granulosa layer at comparable stages of development. Despite detection of P450 17a-OH mRNA in granulosa cells from 6-8-mm follicles, androstenedione production was low to nondetectable when cells were cultured in the presence of exogenous progesterone (10 ng/ml). Treatment with FSH increased levels of P450 17a-OH mRNA (by 6-fold after 16 h of treatment) and induced androstenedione production in cultured granulosa cells; these actions were mimicked by the cAMP analog, 8-bromo-cAMP. By contrast, addition of the growth factors transforming growth factor a (TGFa), epidermal growth factor (EGF), and basic fibroblast growth factor (bFGF) completely suppressed the stimulatory effects of FSH on both mRNA levels and androstenedione production, while insulin-like growth factor I (IGF-I) inhibited only androstenedione production. We conclude that in the granulosa layer of developing ( 12 mm) hen follicles the expression of P450 17a-OH mRNA does not directly reflect P450 17a-OH enzyme activity. Moreover, P450 17a-OH mRNA levels dramatically decrease in granulosa cells fro