Wessels H P, Geffen I, Spiess M
Department of Biochemistry, University of Basel, Switzerland.
J Biol Chem. 1989 Jan 5;264(1):17-20.
Different mechanisms for polarized sorting of apical and basolateral plasma membrane proteins appear to be operative in different cell types. In hepatocytes, all proteins are first transported to the basolateral surface, where sorting (probably signal-mediated) of apical proteins then takes place. In contrast, in Madin-Darby canine kidney (MDCK) cells, proteins are directly transported from the trans-Golgi network to their appropriate plasma membrane domain. In order to study the differences in the sorting requirements of the two cell types, we have expressed a hepatocyte-specific basolateral membrane protein, the asialoglycoprotein receptor H1, in MDCK cells. H1 was found to be specifically transported to the basolateral domain also in this heterologous system, suggesting that either the same basolateral targeting signal is operative in both cell types or, more likely, that basolateral transport occurs "by default," i.e. without the requirement for a sorting signal.
不同细胞类型中，顶端和基底外侧质膜蛋白的极化分选似乎存在不同机制。在肝细胞中，所有蛋白质首先被转运至基底外侧表面，随后顶端蛋白在此处进行分选（可能是信号介导的）。相比之下，在犬肾细胞（MDCK）中，蛋白质直接从反式高尔基体网络转运至其合适的质膜结构域。为研究这两种细胞类型在分选需求上的差异，我们在MDCK细胞中表达了一种肝细胞特异性基底外侧膜蛋白——去唾液酸糖蛋白受体H1。在这个异源系统中，H1也被特异性转运至基底外侧结构域，这表明要么两种细胞类型中存在相同的基底外侧靶向信号，要么更有可能的是，基底外侧转运是“默认发生”的，即不需要分选信号。
