Perini Enrico D, Schaefer Ramona, Stöter Martin, Kalaidzidis Yannis, Zerial Marino
Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307, Dresden, Germany.
Traffic. 2014 Dec;15(12):1366-89. doi: 10.1111/tra.12232. Epub 2014 Nov 6.
Early endosomes are organized in a network of vesicles shaped by cycles of fusion, fission, and conversion to late endosomes. In yeast, endosome fusion and conversion are regulated, among others, by CORVET, a hexameric protein complex. In the mammalian endocytic system, distinct subpopulations of early endosomes labelled by the Rab5 effectors APPL1 and EEA1 are present. Here, the function of mammalian CORVET with respect to these endosomal subpopulations was investigated. Tgfbrap1 as CORVET-specific subunit and functional ortholog of Vps3p was identified, demonstrating that it is differentially distributed between APPL1 and EEA1 endosomes. Surprisingly, depletion of CORVET-specific subunits caused fragmentation of APPL1-positive endosomes but not EEA1 endosomes in vivo. These and in vitro data suggest that CORVET plays a role in endosome fusion independently of EEA1. Depletion of CORVET subunits caused accumulation of large EEA1 endosomes indicative of another role in the conversion of EEA1 endosomes into late endosomes. In addition, depletion of CORVET-specific subunits caused alterations in transport depending on both the type of cargo and the specific endosomal subpopulation. These results demonstrate that CORVET plays distinct roles at multiple stages in the mammalian endocytic pathway.
早期内体通过融合、裂变以及向晚期内体转化的循环过程，形成了一个囊泡网络。在酵母中，内体融合和转化受到多种因素的调控，其中包括CORVET，一种六聚体蛋白复合物。在哺乳动物的内吞系统中，存在由Rab5效应器APPL1和EEA1标记的不同亚群的早期内体。在此，研究了哺乳动物CORVET在这些内体亚群方面的功能。鉴定出Tgfbrap1作为CORVET特异性亚基和Vps3p的功能直系同源物，表明它在APPL1和EEA1内体之间存在差异分布。令人惊讶的是，在体内，CORVET特异性亚基的缺失导致APPL1阳性内体碎片化，但EEA1内体没有。这些以及体外数据表明，CORVET在不依赖EEA1的内体融合中发挥作用。CORVET亚基的缺失导致大型EEA1内体积累，这表明CORVET在EEA1内体向晚期内体的转化中还有另一个作用。此外，CORVET特异性亚基的缺失根据货物类型和特定内体亚群导致运输改变。这些结果表明，CORVET在哺乳动物内吞途径的多个阶段发挥着不同的作用。
