Abstract
Ovarian estradiol (E2) production is regulated by complex interaction of different hormones, such as gonadotropins, steroids, and growth factors. Despite the key role of 17 beta-hydroxysteroid dehydrogenase (17HSD) in E2 biosynthesis, little is known about its regulation in the ovary. Recently, we have characterized the structure of rat 17HSD type 1 and demonstrated that its expression is regulated by gonadotropins and diethylstilbestrol (DES) in rat ovary in vivo. In the present study, the hormonal regulation of 17HSD type 1, and the expression of cytochrome P450 aromatase were examined in parallel in cultured granulosa cells obtained from DES-primed immature rats. Under these conditions, the cells show high expression of 17HSD type 1. Both the enzyme activity and 17HSD type 1 messenger RNA expression in these cells decreased over 2 days of culture in serum-free medium. However, recombinant FSH (recFSH) partially prevented the decreases in enzyme activity and messenger RNA expression in a dose-dependent manner. This effect appears to be mediated by a cAMP-dependent pathway. In contrast to recFSH, neither estrogens (DES or E2) nor androgens (testosterone or dihydrotestosterone) alone affected expression of the enzyme in the cultured cells. However, both estrogens and androgens clearly enhanced the effect of recFSH on 17HSD type 1 expression and 17HSD activity in a dose-dependent manner. Among the growth factors, epidermal growth factor (EGF) has previously been shown to decrease the expression of cytochrome P450 aromatase and E2 biosynthesis in granulosa cells. In the present study, we found that treatment with EGF caused a marked decrease in the effect of recFSH on 17HSD type 1 expression and 17HSD activity. The fact that 17HSD type 1 expression and 17HSD activity always behaved in parallel suggests that 17HSD type 1 is the major 17HSD enzyme involved in estradiol biosynthesis in rat granulosa cells. In conclusion, these data indicate that expression of 17HSD type 1 in rat granulosa cells is under multihormonal regulation. The enzyme is regulated by FSH, via cAMP, and the effect of FSH is modulated by estrogens, androgens, and EGF.
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