Caveolae structure and function

描述（由申请人提供）：小窝是在大多数细胞表面发现的众所周知的膜结构域，部分由瓶状形态定义，细胞质表面的丝状外壳由小窝蛋白和相对于周围膜的高浓度胆固醇组成。小泡参与一种独特的内吞活动，能够将分子携带到细胞质、特殊的内体室和内质网。该结构域对致病性病毒和细菌的感染也至关重要。既然小泡途径被更好地定义了，重要的问题就出现了：内陷、出芽和运输的机制，小泡如何实现其独特的蛋白质和脂质组成，以及提供结构性脂质（如胆固醇）的机制。本建议概述了解决这三个问题的项目。第一个项目重点研究小泡内化的机制。我们已经确定了一个新的驻留小窝蛋白家族，该家族似乎通过将PKC的不同亚型与小窝蛋白-1和内化机制联系起来来调节内化机制。实验计划确定这些小窝蛋白适配器如何调节内化并识别相关分子。小囊含有一组独特的蛋白质，包括酪氨酸激酶受体和GPI锚定蛋白。在目标2中，我们将研究三种控制蛋白质定位到小泡的潜在机制。我们将探索的一种机制是基于最近的发现，即由胆固醇和鞘脂组成的脂质外壳包围的蛋白质被小泡特异性保留。最近我们发现PDGF刺激了PDGFRB在小囊中的泛素化，因此我们计划通过实验来确定泛素化在控制PDGFRB从小囊中退出中的作用。此外，我们将确定蛋白质在小泡中的保留是否由膜外和膜内蛋白质水解控制。第三个目标将集中在确定向小泡提供胆固醇的机制，以及细胞用来感知小泡中胆固醇的数量和调节输送的机制。这些研究将集中在与维持小窝胆固醇有关的三种蛋白质上：小窝蛋白、胆固醇传感分子SR-BI和胆固醇调节支架蛋白OSBP。更好地了解基本的小泡生物学可能会导致治疗人类疾病的新策略。

DESCRIPTION (provided by applicant): Caveolae are well-known membrane domains found on the surface of most cells that are defined in part by a flask-shaped morphology, a filamentous coat on the cytoplasmic surface composed of caveolin and a high concentration of cholesterol relative to surrounding membrane. Caveolae engage in a distinctive endocytic activity capable of carrying molecules to the cytoplasm, to special endosomal compartments and to the ER. This domain is also critical for infection by pathogenic viruses and bacteria. Now that the caveolae pathway is better defined, important questions arise about the mechanism of invagination, budding and traffic, how caveolae achieve their unique protein and lipid composition, and the machinery involved in supplying structural lipids like cholesterol. This proposal outlines projects to address these three issues. The first project focuses on the mechanism of caveolae internalization. We have identified a new family of resident caveolae proteins that appear to regulate the internalization machinery by linking different isoforms of PKC to caveolin-1 and the internalization machinery. Experiments are planned to define how these caveolin adapters regulate internalization and identify the molecules involved. Caveolae contain a unique set of proteins that includes tyrosine kinase receptors and GPI anchored proteins. In aim 2, we will look at three potential mechanisms for controlling the localization of proteins to caveolae. One mechanism we will explore is based on recent findings that proteins surrounded by a lipid shell composed of cholesterol and sphingolipid are specifically retained by caveolae. Recently we found that PDGF stimulates the ubiquitination of PDGFRB in caveolae, so experiments are planned to determine the role of ubiquitination in controlling the exit of PDGFRB from caveolae. In addition, we will determine if retention of proteins in caveolae is controlled by extramembrane and intramembrane proteolysis. The third aim will focus on identifying the machinery that supplies cholesterol to caveolae and the mechanism cells use to sense the amount of cholesterol in caveolae and regulate delivery. These studies will focus on three proteins that have been implicated in maintaining caveolae cholesterol: caveolin, the cholesterol sensing molecule SR-BI and the cholesterol-regulated scaffolding protein OSBP. A better understanding of basic caveolae biology may lead to new strategies for treating human disease.