SR-B1 Sorting Signals in HDL Metabolism

高密度脂蛋白(Hdl)是胆汁中胆固醇的主要载体 胆固醇分泌。高密度脂蛋白受体清道夫受体B-L(SR-BI)介导高密度脂蛋白摄取 胆固醇和胆固醇酯排泄到胆汁中，其表达与胆汁胆固醇相关 分泌物。SR-BI基因敲除小鼠胆汁胆固醇分泌显著减少，表明 SR-BI在这一过程中发挥了重要作用。然而，人们对其分子机制知之甚少。 其中SR-BI介导肝胆胆固醇的分泌。SR-BI在正弦和正弦上均有表达 肝内的小管膜，并经历跨细胞的小管膜。分选信号 SR-BI所需的基底侧靶向和对小管膜的跨细胞作用尚不清楚。我们 已经定义了三个可能调节肝脏SR-BI亚细胞分选从而调节SR-BI的重要因素。 依赖胆汁胆固醇分泌。其中一个因素是PDZK1，一种PDZ结构域蛋白，已被证明 与SR-BI相互作用，对维持肝脏SR-BI水平至关重要。第二个因素是基底侧向 靶向信号位于SR-BI的C-末端，第三个因子是C-BI中的胆固醇结合结构域。 SR-BI的末端跨膜区。SR-BI的C端跨膜结构域可直接结合 胆固醇，但对SR-BI介导的选择性摄取或胆固醇流出并不重要。胆固醇结合力 肝脏中的SR-BI可能在SR-BI的细胞转运中起作用。具体目标1将确定PDZK1在 SR-BI排序。我们已经建立了PDZK1基因敲除小鼠模型，并将使用这两种PDZK1缺陷小鼠 体外极化细胞模型检测PDZK1在SR-BI分选中的作用。具体目标2将划定 SR-BI的基侧靶向信号及其在体内和体内SR-BI分选中的作用 在体外以及体内胆汁胆固醇的分泌中也是如此。特定目标3将测试SR-BI的假设 胆固醇结合区在SR-BI跨细胞作用中起着重要作用。我们将测试这个结构域在胆道中的作用 体内胆固醇分泌和体外SR-BI转胞作用。这些研究将提供基本的见解 探讨SR-BI分选和胆汁胆固醇分泌的调节机制。

Plasma high density lipoprotein (HDL) is the principal carrier of plasma cholesterol for biliary cholesterol secretion. The HDL receptor Scavenger Receptor B-l (SR-BI) mediates the uptake of HDL cholesterol and cholesteryl ester for excretion into bile, and its expression correlates with biliary cholesterol secretion. SR-BI knockout mice have a significant decrease in biliary cholesterol secretion, indicating an important role of SR-BI in that process. However, little is known regarding the molecular mechanisms by which SR-BI mediates hepatobiliary secretion of cholesterol. SR-BI is expressed on both sinusoidal and canalicular membranes in liver, and undergoes transcytosisto the canalicular membrane. The sorting signals necessary for SR-BI basolateral targeting and transcytosis to the canalicular membrane are unknown. We have defined three important factors that may regulate SR-BI subcellular sorting in liver and thus SR-BI- dependent biliary cholesterol secretion. One factor is PDZK1, a PDZ domain protein that has been shown to interact with SR-BI and to be essential to maintain hepatic SR-BI levels. A second factor is a basolateral targeting signal in the C-terminus of SR-BI, and a third factor is a cholesterol binding domain in the C- terminal transmembrane domain of SR-BI. The C-terminal transmembrane domain of SR-BI can directly bind cholesterol but is not important for SR-BI-mediated selective uptake or cholesterol efflux. Cholesterol binding by SR-BI in liver may play a role in SR-BI transcytosis. Specific Aim 1 will determine the role of PDZK1 in SR-BI sorting. We have generated a PDZK1 knockout mouse model and will use both PDZK1 deficient mice and in vitro polarized cells models to examine the role of PDZK1 in SR-BI sorting. Specific Aim 2 will delimit the basolateral targeting signal of SR-BI and test the role of this sequence in SR-BI sorting in vivo and in vitro as well as in biliary cholesterol secretion in vivo. Specific Aim 3 will test the hypothesis that the SR-BI cholesterol binding domain plays a role in SR-BI transcytosis. We will test the role of this domain in biliary cholesterol secretion in vivo and SR-BI transcytosis in vitro. These studies will provide fundamental insights into the mechanisms regulating SR-BI sorting and biliary cholesterol secretion.