Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Mol Biol Cell. 2011 Sep;22(17):3218-30. doi: 10.1091/mbc.E10-11-0874. Epub 2011 Jul 14.
Following endocytosis, internalized plasma membrane proteins can be recycled back to the cell surface or trafficked to late endosomes/lysosomes for degradation. Here we report on the trafficking of multiple proteins that enter cells by clathrin-independent endocytosis (CIE) and determine that a set of proteins (CD44, CD98, and CD147) found primarily in recycling tubules largely failed to reach late endosomes in HeLa cells, whereas other CIE cargo proteins, including major histocompatibility complex class I protein (MHCI), trafficked to both early endosome antigen 1 (EEA1) and late endosomal compartments in addition to recycling tubules. Expression of the membrane-associated RING-CH 8 (MARCH8) E3 ubiquitin ligase completely shifted the trafficking of CD44 and CD98 proteins away from recycling tubules to EEA1 compartments and late endosomes, resulting in reduced surface levels. Cargo affected by MARCH expression, including CD44, CD98, and MHCI, still entered cells by CIE, suggesting that the routing of ubiquitinated cargo occurs after endocytosis. MARCH8 expression led to direct ubiquitination of CD98 and routing of CD98 to late endosomes/lysosomes.
内吞作用后，内化的质膜蛋白可以被重新循环到质膜表面，或者被运输到晚期内体/溶酶体进行降解。在这里，我们报告了多种通过网格蛋白非依赖的内吞作用（CIE）进入细胞的蛋白质的运输情况，并确定一组主要存在于再循环小管中的蛋白质（CD44、CD98 和 CD147）主要未能到达 HeLa 细胞中的晚期内体，而其他 CIE 货物蛋白，包括主要组织相容性复合体 I 类蛋白（MHCI），除了再循环小管外，还运输到早期内体抗原 1（EEA1）和晚期内体区室。膜相关环指蛋白 8（MARCH8）E3 泛素连接酶的表达完全将 CD44 和 CD98 蛋白的运输从再循环小管转移到 EEA1 区室和晚期内体，导致表面水平降低。受 MARCH 表达影响的货物，包括 CD44、CD98 和 MHCI，仍然通过 CIE 进入细胞，这表明泛素化货物的路由发生在内吞作用之后。MARCH8 表达导致 CD98 的直接泛素化，并将 CD98 路由到晚期内体/溶酶体。
