SR-B1 Sorting Signals in HDL Metabolism

血浆高密度脂蛋白（HDL）是胆固醇的主要载体， 胆固醇分泌HDL受体清道夫受体B-I（SR-BI）介导HDL的摄取 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基因敲除小鼠的胆汁胆固醇分泌显著减少，这表明 SR-BI在此过程中重要作用。然而，关于细胞凋亡的分子机制知之甚少。 其中SR-BI介导胆固醇的肝胆分泌。SR-BI在正弦曲线和 肝内小管膜，并经胞吞进入小管膜。排序信号 SR-BI基底外侧靶向和转胞吞至小管膜所必需的细胞因子是未知的。我们 已经确定了三个重要的因素，可以调节SR-BI亚细胞分选在肝脏，因此SR-BI- 依赖胆汁胆固醇分泌。其中一个因子是PDZK 1，这是一种PDZ结构域蛋白， 与SR-BI相互作用，并对维持肝脏SR-BI水平至关重要。第二个因素是基底外侧 第三因子是SR-BI的C-末端中的胆固醇结合结构域， SR-BI的末端跨膜结构域。SR-BI的C-末端跨膜结构域可以直接结合 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 可能在SR-BI转胞吞作用中起一定作用。具体目标1将决定PDZK 1在以下方面的作用： SR-BI排序。我们已经建立了PDZK 1基因敲除小鼠模型，并将使用两种PDZK 1缺陷小鼠 和体外极化细胞模型以检查PDZK 1在SR-BI分选中的作用。具体目标2将界定 SR-BI的基底外侧靶向信号，并测试该序列在体内SR-BI分选中的作用以及在 体外以及体内胆汁胆固醇分泌。具体目标3将检验SR-BI 胆固醇结合结构域在SR-BI转胞吞作用中起作用。我们将测试这个结构域在胆道疾病中的作用。 体内胆固醇分泌和体外SR-BI转胞吞作用。这些研究将提供基本的见解 调节SR-BI分选和胆汁胆固醇分泌的机制。

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.