EMK1 in kidney and hepatic epithelial cell polarity

描述（申请人提供）：丝氨酸/苏氨酸激酶Par-1的直向同源物，Par-1是C.线虫单细胞胚胎中的微管蛋白（MT）在许多系统中被鉴定为微管调节蛋白。我们已经确定，哺乳动物PAR 1同源EMK 1促进肾脏（MDCK）和肝脏（WIFB）上皮细胞中的非中心体，顶端基底外侧MT阵列的发展，在他们正在经历极化。MT组织的这种变化对于上皮管腔的产生是必不可少的，这可能是因为MT在管腔蛋白的极化靶向中的关键作用。肾和肝上皮细胞在它们的管腔极性和它们用于靶向管腔蛋白的机制方面不同。肾细胞（例如MDCK）产生顶腔并将蛋白质直接从高尔基体靶向顶表面，而肝细胞在细胞-细胞接触位点（胆小管）处形成腔并通过经由基底外侧结构域的转胞吞作用靶向其腔标志物蛋白。我们已经最终证明，EMK 1过表达诱导MDCK细胞中细胞间腔和间接顶端靶向模式的出现。因此，EMK 1是第一个被指定为调节肝和柱状上皮表型之间的发育分支决定的蛋白质。该提案的目标是1。深入了解EMK 1在上皮MT和管腔组织中作用的信号传导机制; 2.阐明EMK 1介导的顶端蛋白运输途径的差异，导致肾上皮细胞和肝细胞中不同的管腔极性。

DESCRIPTION (provided by applicant): Orthologues of the serine/threonine kinase Par-1, a polarity determinant in the C. elegans one-cell embryo, have been identified as microtubule (MT)-regulating proteins in several systems. We have established that the mammalian PAR1-homologue EMK1 promotes the development of a non-centrosomal, apico-basolateral MT-array in kidney (MDCK) and hepatic (WIFB) epithelial cells at the time they are undergoing polarization. This change in MT-organization is essential for the generation of epithelial lumina, likely because of a key role of MTs in polarized targeting of luminal proteins. Kidney and liver epithelial cells differ in their lumen polarity and in the mechanisms they use to target luminal proteins. Kidney cells (e.g.MDCK) generate apical lumina and target proteins directly from the Golgi to the apical surface while hepatocytes form lumina at cell-cell contact sites (bile canaliculi) and target their luminal markers proteins by transcytosis via the basolateral domain. We have conclusively demonstrated that EMK1 -overexpression induced the appearance of intercellular lumina and an indirect apical targeting mode in MDCK cells. Thus, EMK1 is the first protein assigned the role of regulating the developmental branching decision between the hepatic and columnar epithelial phenotypes. The goals of this proposal are 1. to gain insight into the signaling mechanisms that underlie the role of the EMK1 in epithelial MT- and lumen organization and 2. to elucidate the EMK1 -mediated differences in the apical protein trafficking pathways that contribute to different lumen polarity in kidney epithelia and hepatocytes.