Rappaport M S, Smith E P
Division of Endocrinology, Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA.
Biol Reprod. 1996 Feb;54(2):446-52. doi: 10.1095/biolreprod54.2.446.
Sertoli cells in the testis and granulosa cells in the ovary convert androgen to estrogen under the primary control of FSH. Insulin-like growth factor I (IGF-I) markedly augments FSH-stimulated estrogen production in the rat granulosa cell. In this study we examined the regulation of aromatase by FSH and characterized the effects of IGF-I on FSH-induced estrogen production by Sertoli cells cultured from the testes of 16-day-old rats. FSH stimulated aromatization of androstenedione in Sertoli cell culture and achieved maximal effectiveness by 12 h of treatment. Analysis of aromatase mRNA by reverse transcription-polymerase chain reaction indicated a marked induction by FSH within 3 h of treatment that was dependent on FSH concentration. IGF-I inhibited FSH-stimulated aromatization dose-dependently; inhibition was approximately 50% by 6 h of cotreatment (p < 0.01). IGF-I was ineffective if added more than 3 h after addition of FSH. Aromatase mRNA was reduced by IGF-I (37 +/- 12%, p < 0.01), coincident with the decrease in estrogen production. To further address the mechanism of IGF-I inhibition, potential interactions with the cAMP and protein kinase C (PKC) signaling pathways were examined. IGF-I inhibited aromatase activity induced by dibutyryl cAMP and inhibited FSH-stimulated estrogen production in the presence of 3-isobutyl-1-methylxanthine, suggesting that IGF-I action was independent of cAMP production. Phorbol-12-myristate-13-acetate (PMA) and IGF-I were additive in their inhibition of FSH. However, down-regulation of PKC prevented PMA inhibition of FSH but not inhibition by IGF-I. We conclude that IGF-I specifically inhibits FSH-induced aromatization in the Sertoli cell in marked contrast to the effects of IGF-I on rat granulosa cells. Although IGF-I and PMA both inhibit aromatase induction, the independence of the IGF-I effect from PKC down-regulation suggests that the initial action of IGF-I is independent of PKC. As IGF-I treatment similarly alters FSH stimulation of both estrogen production and aromatase mRNA, it is likely that the effect of IGF-I on estrogen production in the Sertoli cell is a result, at least in part, of a decrease in aromatase mRNA.
睾丸中的支持细胞和卵巢中的颗粒细胞在促卵泡激素（FSH）的主要调控下将雄激素转化为雌激素。胰岛素样生长因子I（IGF-I）可显著增强FSH刺激的大鼠颗粒细胞雌激素生成。在本研究中，我们检测了FSH对芳香化酶的调控，并描述了IGF-I对从16日龄大鼠睾丸培养的支持细胞中FSH诱导的雌激素生成的影响。FSH刺激支持细胞培养物中雄烯二酮的芳香化，并在处理12小时后达到最大效果。通过逆转录-聚合酶链反应分析芳香化酶mRNA表明，处理3小时内FSH可显著诱导其表达，且这种诱导依赖于FSH浓度。IGF-I剂量依赖性地抑制FSH刺激的芳香化；共同处理6小时后抑制率约为50%（p<0.01）。如果在添加FSH后3小时以上添加IGF-I则无效。IGF-I使芳香化酶mRNA减少（37±12%，p<0.01），这与雌激素生成的减少相一致。为了进一步探讨IGF-I抑制的机制，研究了其与环磷酸腺苷（cAMP）和蛋白激酶C（PKC）信号通路的潜在相互作用。IGF-I抑制二丁酰cAMP诱导的芳香化酶活性，并在存在3-异丁基-1-甲基黄嘌呤的情况下抑制FSH刺激的雌激素生成，这表明IGF-I的作用独立于cAMP生成。佛波酯-12-肉豆蔻酸酯-13-乙酸酯（PMA）和IGF-I对FSH的抑制作用具有相加性。然而，PKC的下调可阻止PMA对FSH的抑制，但不能阻止IGF-I对FSH的抑制。我们得出结论，与IGF-I对大鼠颗粒细胞的作用形成显著对比的是，IGF-I特异性抑制支持细胞中FSH诱导的芳香化。尽管IGF-I和PMA均抑制芳香化酶的诱导，但IGF-I的作用独立于PKC下调，这表明IGF-I的初始作用独立于PKC。由于IGF-I处理同样改变了FSH对雌激素生成和芳香化酶mRNA的刺激，因此IGF-I对支持细胞中雌激素生成的影响可能至少部分是芳香化酶mRNA减少的结果。
