Department of Medicine and Clinical Science, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8558, Japan.
Biochem Biophys Res Commun. 2013 May 3;434(2):401-6. doi: 10.1016/j.bbrc.2013.04.002. Epub 2013 Apr 9.
Estrogen is known to play a pivotal role in granulosa cell responses to follicle-stimulating hormone (FSH) that is critical for the establishment of dominant follicles and subsequent ovulation in mammals. Thus, elucidating the cellular and molecular mechanisms that regulate FSH activity is important to understand female fertility. We previously discovered that the oocyte is required for estrogen to exert its positive effects on FSH activity in rat granulosa cells. This finding supports the new concept that estrogen action in granulosa cells is mediated by the oocyte. In the current study, we explored the underlying mechanism. In the presence of oocytes, estrogens enhanced FSH-induced increases in aromatase, steroidogenic acute regulatory protein and FSH receptor mRNA expression as well as cAMP production. However, as forskolin did not mimic FSH activity this indicated that coexistence of estrogen/oocytes increases FSH activity at a site upstream of adenylate cyclase in granulosa cells. We therefore sought a possible involvement of the autoregulatory molecules for FSH receptor, G protein-coupled receptor kinases (GRKs) and ß-arrestins in enhancing FSH activity in response to the estrogen/oocyte co-treatment in granulosa cells. Among the seven known GRK and two ß-arrestin molecules, we found that estrogens with oocytes suppressed FSH-induced GRK-6 mRNA expression. Consistent with this finding, transfecting granulosa cells with small interfering RNA of GRK-6 significantly increased FSH induction of aromatase mRNA, suggesting that endogenous GRK-6 plays an inhibitory role in FSH-induced aromatase mRNA expression. Consequently, these findings strongly suggest that GRK-6 is involved in the mechanism by which estrogen and oocytes synergistically augment FSH activity in granulosa cells.
雌激素被认为在颗粒细胞对卵泡刺激素 (FSH) 的反应中起着关键作用，这对于哺乳动物优势卵泡的建立和随后的排卵至关重要。因此，阐明调节 FSH 活性的细胞和分子机制对于理解女性生育能力很重要。我们之前发现，卵母细胞是雌激素对大鼠颗粒细胞中 FSH 活性发挥正向作用所必需的。这一发现支持了雌激素在颗粒细胞中的作用是通过卵母细胞介导的新概念。在本研究中，我们探讨了潜在的机制。在卵母细胞存在的情况下，雌激素增强了 FSH 诱导的芳香化酶、类固醇急性调节蛋白和 FSH 受体 mRNA 表达以及 cAMP 产生。然而，由于 forskolin不能模拟 FSH 活性，这表明雌激素/卵母细胞共存会增加颗粒细胞中环磷酸腺苷酶上游的 FSH 活性。因此，我们寻求 FSH 受体的自调节分子，G 蛋白偶联受体激酶 (GRKs) 和β-抑制蛋白，在雌激素/卵母细胞共处理增强颗粒细胞中 FSH 活性的可能参与。在七种已知的 GRK 和两种β-抑制蛋白中，我们发现雌激素与卵母细胞一起抑制 FSH 诱导的 GRK-6 mRNA 表达。这一发现与以下发现一致：用 GRK-6 的小干扰 RNA 转染颗粒细胞显著增加了 FSH 诱导的芳香化酶 mRNA，表明内源性 GRK-6 在 FSH 诱导的芳香化酶 mRNA 表达中发挥抑制作用。因此，这些发现强烈表明，GRK-6 参与了雌激素和卵母细胞协同增强颗粒细胞中 FSH 活性的机制。
