EMK1 in kidney and hepatic epithelial cell polarity

描述(由申请人提供)：丝氨酸/苏氨酸激酶PAR-1的同源基因是线虫单细胞胚胎中的一个极性决定因素，已在几个系统中被鉴定为微管(MT)调节蛋白。我们已经证实，哺乳动物的PAR1同源物EMK1在肾(MDCK)和肝(WIFB)上皮细胞极化时促进了非中心体、尖基外侧MT阵列的发育。MT组织的这种变化对上皮腔蛋白的产生是必不可少的，可能是因为MTS在腔蛋白的极化靶向中起着关键作用。肾和肝上皮细胞的管腔极性不同，它们用来靶向管腔蛋白的机制也不同。肾细胞(如MDCK)直接从高尔基体到心尖表面产生管腔和靶蛋白，而肝细胞在细胞-细胞接触部位(胆小管)形成管腔，并通过基底侧域跨细胞作用靶向其管腔标记蛋白。我们已经证实，EMK1的过表达诱导了MDCK细胞中细胞间腔的出现和间接的顶端靶向模式。因此，EMK1是第一个被指定为调节肝脏和柱状上皮表型之间的发育分支决定的蛋白质。本研究的目的是：1.深入了解EMK1在上皮MT-和管腔组织中所起作用的信号机制；2.阐明EMK1介导的顶端蛋白转运途径的差异，从而导致肾上皮和肝细胞管腔的不同极性。

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.