MAL proteolipids in apical protein delivery in epithelia

描述（由申请人提供）：极化上皮细胞的质膜（PM）在物理上是连续的，但在功能和组成上分为两个独立的区域：顶侧和基底侧。新合成的PM蛋白实现其特定但不对称分布的分子分选机制和途径正在许多极化上皮细胞类型中积极研究。新合成的顶端蛋白通过两种途径传递到顶端PM：直接或间接。使用直接途径的蛋白质直接从高尔基体网络（trans-Golgi network，TGN）递送到顶端表面，而使用间接途径的蛋白质采取更迂回的路线。它们首先从TGN递送到基底外侧域，在基底外侧域中它们通过内吞作用被取回并被胞吞到顶端表面。该提议集中于MAL 1和MAL 2蛋白脂质在调节顶端递送中的作用。MAL 1已经涉及直接途径中的分选蛋白质，并且MAL 2在间接分选中具有假定的作用。我们的长期目标是了解肝细胞（肝脏的主要上皮细胞）中调节顶端蛋白质递送的机制。与大多数简单的上皮细胞不同，肝细胞使用间接途径进行顶端蛋白质递送。我们以前已经表明，肝细胞中的间接分选需要胆固醇和鞘糖脂。因为MAL 1和MAL 2已被鉴定为两种途径中顶端PM递送的重要调节剂，并且因为它们的活性需要胆固醇和鞘糖脂，所以我们提出表征MAL蛋白脂在Aim 1的极化肝细胞和Aim 3的非极化肝细胞中顶端PM分选中起作用的机制。有趣的是，MAL 1和MAL 2的组织表达模式通常是不重叠的，表明它们参与细胞特异性转运途径。MAL 2是否赋予并调节肝细胞中顶端蛋白的间接分选？同样地，MAL 1是否在肾来源的细胞中赋予来自TGN的直接顶端靶向？我们打算在目标2中检验这一假设。确定机制调节囊泡介导的新合成的顶端居民顶端PM的交付是必要的了解如何建立和维护这个表面。这些信息将提供深入了解人类肝脏疾病和其他上皮细胞疾病的分子基础。

DESCRIPTION (provided by applicant): The plasma membrane (PM) of polarized epithelial cells is physically continuous, but functionally and compositionally divided into two separate domains: the apical and basolateral. The molecular sorting mechanisms and pathways by which newly synthesized PM proteins achieve their specific yet asymmetric distributions are actively being examined in many polarized epithelial cell types. Newly synthesized apical proteins are delivered to the apical PM by two pathways: the direct or indirect. Proteins using the direct pathway are delivered directly form the trans-Golgi network (TGN) to the apical surface whereas proteins using the indirect pathway take a more circuitous route. They are first delivered from the TGN to the basolateral domain where they are retrieved by endocytosis and transcytosed to the apical surface. This proposal focuses on the role of MAL l and MAL2 proteolipids in regulating apical delivery. MAL l has been implicated in sorting proteins in the direct pathway and MAL2 has a presumed role in indirect sorting. Our long-term goal is to understand the mechanisms regulating apical protein delivery in hepatocytes, the major epithelial cell of the liver. Unlike most simple epithelial cells, hepatocytes use the indirect pathway for apical protein delivery. We have previously shown that indirect sorting in hepatocytes requires cholesterol and glycosphingolipids. Because MAL l and MAL 2 have been identified as important regulators of apical PM delivery in both pathways and because their activity requires cholesterol and glycosphingolipids, we propose to characterize the mechanism by which the MAL proteolipids function in apical PM sorting in polarized hepatic cells in Aim 1 and in non-polarized hepatic cells in Aim 3. Interestingly, the tissue expression patterns of MAL l and MAL 2 are generally non-overlapping suggesting they participate in cell-specific transport pathways. Does MAL2 confer and regulate indirect sorting of apical proteins in hepatocytes? Likewise, does MAL l confer direct apical targeting from the TGN in kidney-derived cells? We intend to test this hypothesis in Aim 2. Identifying the mechanisms regulating the vesicle-mediated delivery of newly synthesized apical residents to the apical PM is imperative to understanding how this surface is established and maintained. Such information will provide insight into the molecular basis of human liver disease and other diseases of epithelial cells.