Basolateral Internalization of GPI-anchored Proteins Occurs via a Clathrin-independent Flotillin-dependent Pathway in Polarized Hepatic Cells
Basolateral Internalization of GPI-anchored Proteins Occurs via a Clathrin-independent Flotillin-dependent Pathway in Polarized Hepatic Cells
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DOI：
10.1091/mbc.e09-04-0275
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发表时间：
2009-09-01
影响因子：
3.3
通讯作者：
Maurice, Michele
中科院分区：
文献类型：
--
作者：
Ait-Slimane, Tounsia;Galmes, Romain;Maurice, Michele
在极化肝细胞中，顶端驻留蛋白到达顶端胆管膜的主要途径是胞吞作用。根尖蛋白首先被分类到基底外侧膜，从基底外侧膜内化并运输到相反的表面。我们之前已经注意到，跨膜蛋白和gpi锚定蛋白以非常不同的速度到达胆管顶端。在这里，我们研究了这些差异是否可以用不同的内吞机制来解释。我们发现极化肝细胞基底外膜上两类蛋白的内吞作用是动力蛋白依赖的。然而，跨膜蛋白的内化是由网格蛋白介导的，而gpi锚定蛋白的内吞作用则不需要网格蛋白。进一步分析gpi锚定蛋白的基底外侧内吞作用表明，小窝蛋白和小GTPase cdc42是必不可少的。另外，内化的gpi锚定蛋白与flotillin-2阳性囊泡共定位，flotillin-2的下调表达抑制了gpi锚定蛋白的内吞作用。这些结果表明，肝细胞中gpi锚定蛋白的基底外侧内吞作用是通过一种不依赖网格蛋白的漂蛋白依赖途径发生的。使用不同的内吞途径可以解释，至少部分地，跨膜和gpi锚定蛋白之间的不同的胞吞率。
In polarized hepatocytes, the predominant route for apical resident proteins to reach the apical bile canalicular membrane is transcytosis. Apical proteins are first sorted to the basolateral membrane from which they are internalized and transported to the opposite surface. We have noted previously that transmembrane proteins and GPI-anchored proteins reach the apical bile canaliculi at very different rates. Here, we investigated whether these differences may be explained by the use of distinct endocytic mechanisms. We show that endocytosis of both classes of proteins at the basolateral membrane of polarized hepatic cells is dynamin dependent. However, internalization of transmembrane proteins is clathrin mediated, whereas endocytosis of GPI-anchored proteins does not require clathrin. Further analysis of basolateral endocytosis of GPI-anchored proteins showed that caveolin, as well as the small GTPase cdc42 were dispensable. Alternatively, internalized GPI-anchored proteins colocalized with flotillin-2-positive vesicles, and down-expression of flotillin-2 inhibited endocytosis of GPI-anchored proteins. These results show that basolateral endocytosis of GPI-anchored proteins in hepatic cells occurs via a clathrin-independent flotillin-dependent pathway. The use of distinct endocytic pathways may explain, at least in part, the different rates of transcytosis between transmembrane and GPI-anchored proteins.