Roles of StAR in Regulated Steroidogenesis

描述(申请人提供)：调节类固醇生成的一个基本事件是类固醇生成细胞对营养激素的急性反应；这种反应主要反映了胆固醇底物向线粒体膜内的胆固醇侧链裂解酶(Cyp11a)输送增加。类固醇合成急性调节蛋白(STAR)在人类先天性类脂肾上腺增生症(Lipoid CAH)和STAR基因敲除小鼠(STAR KO)中的重要作用已被揭示。STAR的作用有两种不同的模式：一种是作用于线粒体膜外膜，可能经历了促进胆固醇转移的构象变化；另一种是它将胆固醇运送到线粒体膜外膜和内膜的类固醇合成复合体之间。我们认为，前一个模型--主要基于在非类固醇生成的COS细胞中的转基因研究--反映了STAR在非类固醇生成的细胞中过度表达的异常效应。我们进一步假设，在真正的类固醇生成细胞中诱导类固醇合成将需要线粒体靶向STAR。为了解决这个问题，我们将分析来自STAR KO小鼠的永生化细胞系中的STAR功能。这些细胞系还将提供一个独特的系统，在类固醇生成细胞的背景下探索星形结构和功能的其他方面。对STAR功能提供新见解的结果将通过BAC转基因对STAR KO小鼠的转基因拯救在体内得到验证。最后，最近的研究表明，脊椎动物的大脑产生一系列类固醇衍生物--称为神经类固醇--在记忆、应激反应、癫痫阈值和焦虑等过程中发挥重要作用；我们建议培育出中枢神经系统特异的STAR KO小鼠，从而为确定STAR在神经类固醇产生中的作用提供了一个独特的机会。总而言之，这些研究将为调节类固醇生成的这一基本成分的功能提供新的见解。

DESCRIPTION (provided by applicant): An essential event in regulated steroidogenesis is the acute response of steroidogenic cells to trophic hormones; this response predominantly reflects increased delivery of cholesterol substrate to the cholesterol side-chain cleavage enzyme (Cyp11a) in the inner mitochondrial membrane. The essential role of the Steroidogenic Acute Regulatory protein (STAR) in cholesterol translocation has been revealed by humans with congenital lipoid adrenal hyperplasia (lipoid CAH) and by StAR knockout (STAR KO) mice. There are two divergent models of StAR action: that it acts at the outer mitochondrial membrane, perhaps undergoing a conformational change that facilitates cholesterol translocation, or that it shuttles cholesterol between the outer mitochondrial membrane and the steroidogenic complex in the inner membrane. We believe that the former model--based largely on transfection studies in non-steroidogenic COS cells--reflects aberrant effects of StAR over-expression in non-steroidogenic cells. We further hypothesize that induction of steroidogenesis in bona fide steroidogenic cells will require mitochondrial targeting of STAR. To address this question, we will analyze StAR function in immortalized cell lines derived from StAR KO mice. These cell lines also will provide a unique system to explore other aspects of StAR structure and function within the context of steroidogenic cells. Results that provide novel insights into StAR function will be verified in vivo by transgenic rescue of StAR KO mice via BAC transgenesis. Finally, recent studies suggest that the vertebrate brain produces a series of steroid derivatives--termed neurosteroids--that play important roles in processes such as memory, stress response, seizure threshold, and anxiety; we propose to generate CNS-specific StAR KO mice, thereby providing a unique opportunity to define the role of StAR in neurosteroid production. Collectively, these studies will provide novel insights into the function of this essential component of regulated steroidogenesis.