Hormonal regulation of LDL receptor trafficking

本研究将阐明外囊复合体和肌动蛋白动力学在脂蛋白代谢及其胰岛素调控中的作用。我们的初步数据显示，胰岛素刺激肝细胞中LDL受体的再循环，从而增加LPL进入细胞的输送。我们假设胰岛素通过两种途径控制肝细胞小GTPase RalA的活性，包括其GAP蛋白的磷酸化和抑制，以及其GEF蛋白的募集。一旦被激活，RalA可以与靶向胞囊复合物的组分相互作用，导致含有LDLR的胞囊胞泡在基底外侧质膜的离散区域捆绑在一起，这些区域富含融合所需的机制。我们还假设胰岛素调节皮质肌动蛋白的动态以促进LDLR的内吞作用。我们将评估：i)胞囊复合物及其调节因子RalGAP、ralgef和RalA在肝细胞极化LDLR胞囊分泌中的作用；ii)皮质肌动蛋白细胞骨架变化在LDLR内吞作用中的作用；Iii)这些肝脏信号和运输事件与整体脂蛋白代谢的生理相关性。这些新的想法和方法将阐明控制这些贩运路线的关键因素，并可能最终对肥胖和2型糖尿病中血脂异常的分子机制产生有价值的见解。

This proposal will elucidate the function of the exocyst complex and actin dynamics in lipoprotein metabolism and its regulation by insulin. Our preliminary data reveal that insulin stimulates the recycling of the LDL Receptor in hepatocytes to increase the delivery of LPL into cells. We hypothesize that insulin controls the activity of the small GTPase RalA in hepatocytes by two pathways involving phosphorylation and inhibition of its GAP protein, and recruitment of its GEF protein. Once activated, RalA can interact with components of the targeting exocyst complex, resulting in the tethering of exocytotic vesicles containing the LDLR at discrete regions of the basolateral plasma membrane that are enriched in machinery required for fusion. We also hypothesize that insulin regulates the dynamics of cortical actin to propel LDLR endocytosis. We will evaluate: i) the role of the exocyst complex, and its regulators RalGAP, RalGEFs and RalA in the regulation of polarized LDLR exocytosis in hepatocytes; ii) the role of changes in the cortical actin cytoskeleton in governing LDLR endocytosis; iii) the physiological relevance of these hepatic signaling and trafficking events to overall lipoprotein metabolism. These new ideas and approaches will elucidate the key elements in control of these trafficking itineraries, and may ultimately generate valuable insights into the molecular mechanisms underlying dyslipidemia in obesity and Type 2 diabetes.