Involvement of clathrin and AP-2 in the trafficking of MHC class II molecules to antigen-processing compartments
Involvement of clathrin and AP-2 in the trafficking of MHC class II molecules to antigen-processing compartments
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DOI：
10.1073/pnas.0502206102
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发表时间：
2005-05-31
影响因子：
11.1
通讯作者：
Bonifacino, JS
中科院分区：
文献类型：
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作者：
McCormick, PJ;Martina, JA;Bonifacino, JS
主要组织相容性复合物II类（MHC-II）分子由两条多态性链α和β组成，其在内质网中与不变链Ii组装。组装的MHC-II复合物被转运到高尔基体复合物，然后转运到晚期内体/溶酶体，在那里Ii被降解，α β受体结合来自外源抗原的肽。MHC-II分子靶向这些区室是由Ii胞质结构域中的两个基于二亮氨酸的信号介导的。这些信号在体外与两种衔接蛋白（AP）复合物AP-1和AP-2结合，AP-1和AP-2是参与囊泡形成和货物分选的网格蛋白外壳的组分。然而，这些蛋白在MHC-II分子运输中的生理作用仍有待解决。在这里，我们报告使用RNA干扰检查网格蛋白和四个AP复合物（AP-1，AP-2，AP-3和AP-4）在体内MHC-II分子运输的参与。我们发现，网格蛋白或AP-2的消耗导致细胞表面上Ii表达增加> 10倍，并且伴随着Ii定位于内体/溶酶体囊泡的减少。此外，网格蛋白或AP-2的消耗延迟了Ii的降解，并降低了负载肽的α β二聚体的表面表达。相比之下，AP-1、AP-3或AP-4的耗尽几乎没有影响。这些发现表明网格蛋白和AP-2参与体内MHC-II分子运输。由于AP-2仅与质膜相关，因此这些结果还表明，大量MHC-II分子通过细胞表面运输至内体-溶酶体系统。
Major histocompatibility complex class II (MHC-II) molecules are composed of two polymorphic chains, alpha and beta, which assemble with an invariant chain, Ii, in the endoplasmic reticulum. The assembled MHC-II complexes are transported to the Golgi complex and then to late endosomes/lysosomes, where Ii is degraded and alpha beta climers bind peptides derived from exogenous antigens. Targeting of MHC-II molecules to these compartments is mediated by two dileucine-based signals in the cytoplasmic domain of Ii. These signals bind in vitro to two adaptor protein (AP) complexes, AP-1 and AP-2, which are components of clathrin coats involved in vesicle formation and cargo sorting. The physiological roles of these proteins in MHC-II molecule trafficking, however, remain to be addressed. Here, we report the use of RNA interference to examine the involvement of clathrin and four AP complexes (AP-1, AP-2, AP-3, and AP-4) in MHC-II molecule trafficking in vivo. We found that depletion of clathrin or AP-2 caused > 10-fold increases in Ii expression on the cell surface and a concomitant decrease in Ii localization to endosomal/lysosomal vesicles. in addition, depletion of clathrin or AP-2 delayed the degradation of Ii and reduced the surface expression of peptide-loaded alpha beta dinners. In contrast, depletion of AP-1, AP-3, or AP-4 had little or no effect. These findings demonstrate that clathrin and AP-2 participate in MHC-II molecule trafficking in vivo. Because AP-2 is only associated with the plasma membrane, these results also indicate that a significant pool of MHC-II molecules traffic to the endosomal-lysosomal system by means of the cell surface.