Bernath V A, Muro A F, Vitullo A D, Bley M A, Barañao J L, Kornblihtt A R
Instituto de Investigaciones en Ingeniería Genética y Biología Molecular (INGEBI-CONICET), Buenos Aires, Argentina.
J Biol Chem. 1990 Oct 25;265(30):18219-26.
The main role of the ovarian granulosa cells is to nurse the oocyte and to produce estradiol and progesterone upon stimulation by gonadotropins. In fact, follicle-stimulating hormone (FSH) and luteinizing hormone control the expression of several genes during granulosa cell differentiation via cyclic AMP-dependent phosphorylations. Cyclic AMP stimulates transcription of genes that carry the cAMP-responsive element (CRE,5'TGACGTCA3') in their promoters. The fibronectin (FN) gene contains one CRE sequence at position -170. However, gonadotropins and cAMP inhibit FN gene expression in granulosa cells. To study the mechanism of the inhibition we developed a bovine granulosa cell line (BGC-1) that synthesizes estradiol in response to FSH and in which FSH and dibutyryl cAMP specifically decrease FN synthesis and its mRNA levels. The inhibitory effect (a) is not due to an alteration in FN mRNA stability, (b) requires upstream sequences other than CRE, located between positions -510 and -223, that are able to bind granulosa cell nuclear proteins, (c) is entirely dependent on the synthesis of intermediate proteins induced and or phosphorylated by cAMP, and (d) effectively suppresses the CRE-dependent transcriptional activation.
卵巢颗粒细胞的主要作用是滋养卵母细胞，并在促性腺激素刺激下产生雌二醇和孕酮。事实上，促卵泡激素（FSH）和黄体生成素通过环磷酸腺苷（cAMP）依赖性磷酸化作用，在颗粒细胞分化过程中控制多个基因的表达。环磷酸腺苷刺激启动子中携带cAMP反应元件（CRE，5'TGACGTCA3'）的基因转录。纤连蛋白（FN）基因在 -170 位置含有一个CRE序列。然而，促性腺激素和环磷酸腺苷会抑制颗粒细胞中FN基因的表达。为了研究这种抑制机制，我们建立了一种牛颗粒细胞系（BGC-1），该细胞系能响应促卵泡激素合成雌二醇，并且促卵泡激素和二丁酰环磷酸腺苷会特异性降低FN的合成及其mRNA水平。这种抑制作用（a）不是由于FN mRNA稳定性的改变，（b）需要位于 -510 和 -223 位置之间、除CRE之外的上游序列，这些序列能够结合颗粒细胞核蛋白，（c）完全依赖于由环磷酸腺苷诱导和/或磷酸化的中间蛋白的合成，并且（d）有效地抑制了CRE依赖性转录激活。
