Regulation of Cellular Cholesterol Homeostasis

描述(由申请人提供)：细胞脂平衡是维持双层流动性、膜的不通透性和细胞器特性所必需的。系统脂平衡失调是冠状动脉疾病和肥胖相关的II型糖尿病发病的核心。这项研究的长期目标是将细胞调节事件的知识转化为整个生物体的知识，并促进我们对这些日益广泛的疾病的理解。作为实现这一目标的第一步，我们将使用胆固醇作为模型脂质来了解细胞如何测量这些主要不可溶分子的水平，并反过来调节它们的产生。哺乳动物细胞中的胆固醇动态平衡受到反馈机制的调节，该反馈机制监测细胞膜中的胆固醇水平，并改变胆固醇供应所需基因的转录。这些基因的转录受内质网膜结合转录因子SREBP的控制，这种转录因子在固醇耗竭的细胞中通过蛋白分解而被激活并从膜上释放。为了加速甾醇动态平衡调节剂的发现，我们正在研究裂解酵母中的SREBP途径。酵母SREBP，称为Sre1，在一种新的氧感应途径中发挥作用，该途径介导细胞对低氧的适应。有趣的是，在分裂酵母中，甾醇通过一种新的机制调节Sre1的活性，而且证据还表明，Sre1的裂解是由一种独特的蛋白分解系统介导的。在这个项目中，我们将结合遗传学、分子和生物化学方法来实现以下具体目标：1)通过遗传选择来确定Sre1裂解所需的基因；2)确定Sre1裂解的机制；以及3)确定类固醇调节Sre1裂解的机制。该项目的长期目标是使用S.pombe作为遗传模型，以了解细胞如何测量不溶的、嵌入膜的胆固醇水平。人们期望这些研究将描述新的脂类感知和蛋白降解机制，从而促进我们对哺乳动物SREBP途径和真核细胞生物学的理解。

DESCRIPTION (provided by applicant): Cellular lipid homeostasis is required to maintain bilayer fluidity, membrane impermeability, and organelle identity. Disturbances in systemic lipid homeostasis lie at the core of the pathologies for both coronary artery disease and obesity related type II diabetes. The long-term goal of this research is to translate knowledge of cellular regulatory events to that of the whole organism and to advance our understanding of these increasingly widespread diseases. As a first step toward this goal, we will use cholesterol as a model lipid to understand how cells measure levels of these largely insoluble molecules and in turn modulate their production. Cholesterol homeostasis in mammalian cells is regulated by a feedback mechanism that monitors the level of cholesterol in membranes and alters transcription of genes required for cholesterol supply. Transcription of these genes is controlled by the ER membrane-bound transcription factor called SREBP that is activated and released from the membrane by proteolysis in sterol-depleted cells. To accelerate discovery of sterol homeostasis regulators, we are studying the SREBP pathway in the fission yeast Schizosaccharomyces pombe. Yeast SREBP, called Sre1, functions in a new oxygen sensing pathway that mediates adaptation of cells to low oxygen. Interestingly, sterols regulate Sre1 activity through a novel mechanism in fission yeast, and evidence also indicates that Sre1 cleavage is mediated by a unique proteolytic system. In this project, a combination of genetic, molecular, and biochemical approaches will be used to accomplish the following specific aims: 1) To identify genes required for Sre1 cleavage using a genetic selection; 2) To define the machinery for Sre1 cleavage; and 3) To define the mechanism of sterol-regulated Sre1 cleavage. The long-term goal of this project is to use S. pombe as a genetic model to understand how cells measure levels of insoluble, membrane-embedded cholesterol. The expectation is that these studies will describe new mechanisms for lipid sensing and proteolysis that will advance our understanding of the mammalia SREBP pathway and eukaryotic cell biology.