ACTIONS OF ESTROGEN IN MATURING GRAAFIAN FOLLICLES

描述(由申请人提供)：目前的竞争性更新扩展了我们早期的主题，即卵巢细胞中营养激素控制关键的类固醇代谢基因的特殊机制。在主要的Graafian Follide中，颗粒细胞经历了逐步的类固醇合成细胞分化，为黄体期孕酮的产生做准备。同时，膜细胞提供雌激素芳构化所需的限制性雄激素底物。雌激素和孕激素协同作用，使子宫内膜成熟，使胚泡着床，并使排卵前促性腺激素激增的时间延长。这两种性类固醇的来源都是胆固醇在摄取类固醇后转化为孕烯醇酮，并限速传递给线粒体酶。我们最近的研究证明，在体外原代培养的(猪)颗粒细胞和卵泡膜细胞中，黄体生成素和胰岛素样生长因子L对低密度脂蛋白受体和类固醇生成急性调节蛋白基因的表达具有协同作用。事实上，这两个基因都处于强大的转录控制之下。它们的产物对引导细胞摄取类固醇底物及其限速递送到内侧有丝分裂的小叶起着关键作用。相应地，我们在体内发现了低密度脂蛋白受体基因在颗粒黄体细胞中的优势表达，以及STAR基因在卵泡膜细胞中的优势表达。相应地，我们设计了它们的5‘上游调控区，并通过启动子缺失分析，已经开始定位介导黄体生成素和胰岛素样生长因子-L超相加效应的顺式作用区域。基于这一平台，我们提出了以下新的假说来解释双激素控制颗粒-黄体和卵泡膜细胞中类固醇调节基因的表达：假说(1)。黄体生成素和胰岛素样生长因子-L通过相互放大远端效应-信号通路的选定方面实现协同作用。假设(2)。黄体生成素和胰岛素样生长因子-L通过离散的顺式作用区域和相应的核反式激活蛋白上调颗粒黄体细胞低密度脂蛋白受体基因的表达。假设(3)。促黄体生成素和胰岛素样生长因子-I通过刺激不同的顺式作用DNA元件和相关的核因子，协同驱动膜细胞中STAR基因的表达。综上所述，上述两种激素控制颗粒-黄体和卵泡膜细胞中的类固醇代谢基因表达的命题应该为了解垂体促性腺激素、促黄体生成素和局部产生的生长因子--胰岛素样生长因子-L如何共同作用于调控(A)细胞内信号和(B)卵巢细胞中的基因表达提供新的见解。了解这种基本的相互作用对于合理设计替代策略以中断成熟的Graafian卵泡和黄体中正常的类固醇激素合成并挽救受损的类固醇激素合成非常重要。

DESCRIPTION (provided by applicant): The present competitive renewal extends our earlier theme of speafic mechanisms of trophic hormone control of key sterol-metabolizing genes in ovarian cells. Granulosa cells in the dominant Graafian follide undergo progressive steroidogenic cytodifferentiation in preparation for the luteal-phase production of progesterone. Concomitantly, theca cells provide limiting androgen substrate required for aromatization to estrogen. Estrogen and progesterone act coordinately to mature the endometrium for implantation of the blastocyst and time the preovulatory gonadotropin surge. Both sex steroids originate from cholesterol's conversion to pregnenolone after sterol uptake and rate-limiting delivery to mitochondnal enzymes. Our recent studies document synergistic drive by LH and the potent insulin-like growth factor, IGF-l, of expression of the low-density lipoprotein-receptor (LDL-R) and steroidogenic acute regulatory protein (StAR) genes in vitro primary cultures of (swine) granulosa and theca cells. Indeed, both genes are under strong transcriptional control. Their products are pivotal to direct the cellular uptake of sterol substrate and its rate-limiting delivery to the inner mitochrondial leaflet. Concomitantly, we could demonstrate predominant expression of the LDL-R gene in granulosa-luteal cells and of the StAR gene in theca cells in vivo Accordingly, we doned their 5'-upstream regulatory regions, and, by promoter deletional analyses, have begun to map cis-acting DNA regions mediating the supraadditive effects of LH and IGF-l. Based on this platform, we propose the following new hypotheses to explicate bihormonal control of sterol-regulatory gene expression in the granulosa-luteal and theca cell: Hypothesis (1). LH and IGF-l achieve synergism by reciprocally amplifying selected facets of distal effector-signaling pathways. Hypothesis (2). LH and IGF-l upregulate LDL-R gene expression supraadditively in the granulosa-luteal cell by way of discrete cis-acting DNA regions and corresponding nuclear transactivating proteins. Hypothesis (3). LH and IGF-I drive StAR gene expression synergistically in theca cells by stimulating distinct cis-acting DNA elements and associated transacting nuclear factors. In ensemble, the foregoing thesis of bihormonal control of sterol-metabolizing gene expression in the granulosa-luteal and theca cell should provide novel insights into how the pituitary gonadotropin, LH, and the locally produced growth factor, IGF-l, act convergently to govern (a) intracellular signaling and (b) gene expression in ovarian cells. Understanding such fundamental interactions is important to the rational design of alternative strategies to interrupt normal and rescue impaired steroidogenesis in the maturing Graafian follicle and corpus luteum.