Cells Processing High Density Lipoproteins

描述(申请人提供)：从脂蛋白颗粒(如高密度脂蛋白)中选择性地摄取胆固醇酯(CE)是一个过程，通过该过程，高密度脂蛋白核心-CE被带入细胞，而不会平行地摄取和降解高密度脂蛋白颗粒本身。它是将CES输送到啮齿动物和人类产生类固醇的组织的主要途径。清道夫受体，B类，I型(SR-BI)，是CD36超家族蛋白质中的一员，是一种真实的高密度脂蛋白受体，通过这一过程介导对高密度脂蛋白的摄取，免疫化学分析表明，它在类固醇生成细胞和肝脏中表达最丰富。我们已发表的和初步的数据表明，SR-BI蛋白的物理状态和由SR-BI表达引起的组织结构变化对选择性途径的效率有重要影响。这些数据表明，SR-BI的二聚体和高阶低聚形式与SR-BI介导的选择性高密度脂蛋白-CE转运密切相关，而且SR-BI的这些物理状态有助于细胞表面(微绒毛)通道的形成，从而进一步提高选择性途径的效率。该建议的具体目的是：1)确定SR-BI的C-末端细胞质结构域在调节SR-BI二聚体形成中的作用；2)确定SR-BI的胞外区(ECD)独立地或与C-末端结构域协同在调节SR-BI二聚化和功能中的作用；以及3)确定SR-BI相互作用的辅助蛋白(即含有PDZ结构域的蛋白质和/或与肌动蛋白细胞骨架相关的ERM家族蛋白)是否有助于SR-BI二聚体的形成和/或在SR-BI功能中发挥重要作用。推动这一提议的假设是，二聚体的形成和伴随的表面结构变化对于脂蛋白胆固醇酯通过“选择性”摄取过程的有效输送是必要的。拟议的实验将确定这在多大程度上是正确的，同时，试图确定SR-BI分子和SR-BI相互作用的辅助蛋白(PDZ、ERM和肌动蛋白)上参与二聚化过程和微绒毛通道形成的特定位点。

DESCRIPTION (provided by applicant): The selective uptake of cholesteryl ester (CE) from lipoprotein particles such as HDL is a process by which HDL core-CE is taken into cells without a parallel uptake and degradation of the HDL particle itself. It represents a major route for the delivery of CEs to steroid producing tissues of rodents and humans. Scavenger receptor, class B, type I (SR-BI), a member of the CD36 super-family of proteins, has been identified as an authentic HDL receptor that mediates-the uptake of HDL-CEs via this process, and immunochemical analyses indicate that it is expressed most abundantly in the steroidogenic cells and liver. Our published and preliminary data provide evidence that the physical state of the SR-BI protein and architectural changes in tissue induced by the expression of SR-BI .have major effects on the efficiency of the selective pathway. These data led us to suggest that the dimeric and higher order oligomeric forms of SR-BI are intimately involved in regulating SR-BI-mediated selective HDL-CE transport, and moreover, that these physical states of SR-BI contribute to the formation of cell surface (microvillar) channels to further enhance the efficiency of the selective pathway. The specific aims of this proposal are: 1) to determine the contribution of SR-BI's C-terminal cytoplasmic domain in regulating SR-BI dimer formation; 2) to determine the contribution of the extracellular domain (ECD) of SR-BI either independently, or in cooperation with C- terminal domain, in regulating SR-BI dimerization and function; and 3) to determine whether SR-BI interacting accessory proteins (i.e., PDZ domain containing proteins and/or ERM family proteins in connection with the actin cytoskeleton) contribute to SR-BI dimer formation and/or play an essential role in SR-BI function. The hypothesis which drives this proposal is that dimer formation and concomitant surface architectural changes are necessary for efficient delivery of lipoprotein cholesteryl esters via the "selective" uptake process. The experiments proposed will determine to what extent this is true, and at the same time, attempt to identify specific sites on both the SR-BI molecule and SR-BI interacting accessory proteins (PDZ, ERM, and actin proteins) which are involved in the dimerization process and in microvillar channel formation.