Casanova J E, Mishumi Y, Ikehara Y, Hubbard A L, Mostov K E
Department of Anatomy, University of California School of Medicine, San Francisco 94143.
J Biol Chem. 1991 Dec 25;266(36):24428-32.
In Madin-Darby canine kidney (MDCK) cells, apical and basolateral membrane proteins are segregated from each other in the trans-Golgi network (TGN) and are transported to the appropriate membrane domain via separate vesicle populations. In hepatocytes, however, all plasma membrane proteins are delivered basolaterally. Apical proteins are then selectively retrieved and reach the apical surface by transcytosis. The sorting of apical proteins in different cell types may be the result of differences in the cellular sorting machinery, or alternatively, due to expression of cell-specific sorting signals on the proteins themselves. To test this directly, we have stably expressed cDNA encoding an apical protein from rat liver, dipeptidylpeptidase IV (DPPIV), in MDCK cells. We found that approximately 90% of the exogenous DPPIV is expressed on the apical cell surface at steady state. Furthermore, we demonstrate that this distribution is primarily due to vectorial transport from the TGN to the apical plasma membrane. The small pool of mis-sorted DPPIV that appears basolaterally is slowly endocytosed (t1/2 approximately 60 min) and is subsequently transcytosed. These data are consistent with the notion that both hepatocytes and MDCK cells are capable of correctly sorting rat liver DPPIV, but that this sorting occurs at different sites in the two cell types.
在犬肾Madin-Darby（MDCK）细胞中，顶膜蛋白和基底外侧膜蛋白在反式高尔基体网络（TGN）中彼此分离，并通过不同的囊泡群体被转运到相应的膜结构域。然而，在肝细胞中，所有质膜蛋白都被输送到基底外侧。然后，顶端蛋白被选择性回收，并通过转胞吞作用到达顶端表面。不同细胞类型中顶端蛋白的分选可能是细胞分选机制差异的结果，或者是由于蛋白质自身上细胞特异性分选信号的表达。为了直接验证这一点，我们在MDCK细胞中稳定表达了编码大鼠肝脏顶端蛋白二肽基肽酶IV（DPPIV）的cDNA。我们发现，在稳态下，大约90%的外源性DPPIV表达在细胞顶端表面。此外，我们证明这种分布主要是由于从TGN到顶端质膜的定向转运。少量错误分选到基底外侧的DPPIV会被缓慢内吞（半衰期约60分钟），随后进行转胞吞作用。这些数据与肝细胞和MDCK细胞都能够正确分选大鼠肝脏DPPIV的观点一致，但这种分选在两种细胞类型中的发生位点不同。
