Cells Processing High Density Lipoproteins

从脂蛋白颗粒如HDL中选择性摄取胆固醇酯（CE）是一个过程， HDL核心-CE被吸收到细胞中，而没有HDL颗粒本身的平行吸收和降解。它 代表将CE递送至啮齿动物和人类的类固醇产生组织的主要途径。 清道夫受体，B类，I型（SR-BI），CD 36蛋白超家族的成员，已经被研究。 被鉴定为通过该过程介导HDL-CE摄取的真实HDL受体，和 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。 我们发表的和初步的数据提供了证据，表明SR-BI蛋白的物理状态和 由SR-BI表达诱导的组织结构变化对免疫治疗的效率有重要影响。 选择性途径这些数据使我们认为SR-BI的二聚体和更高级的寡聚体形式 密切参与调节SR-BI介导的选择性HDL-CE转运，而且，这些 SR-BI的物理状态有助于细胞表面（微绒毛）通道的形成，以进一步增强 选择性路径的效率。该提案的具体目标是：1）确定 SR-BI的C-末端胞质结构域在调节SR-BI二聚体形成中的贡献; 2）确定 SR-BI的胞外结构域（ECD）独立地或与C- 末端结构域，在调节SR-BI二聚化和功能;和3）确定SR-BI是否 相互作用的辅助蛋白（即，细胞中含有PDZ结构域的蛋白和/或ERM家族蛋白 与肌动蛋白细胞骨架的连接）有助于SR-BI二聚体的形成和/或在 SR-BI功能。驱动这一提议的假设是，二聚体形成和伴随的表面 结构变化对于脂蛋白胆固醇酯通过“选择性” 吸收过程。所提出的实验将确定这在多大程度上是正确的，同时， 试图鉴定SR-BI分子和SR-BI相互作用辅助蛋白（PDZ， ERM和肌动蛋白），其参与二聚化过程和微绒毛通道形成。

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.