Vps33B is required for delivery of endocytosed cargo to lysosomes
Vps33B is required for delivery of endocytosed cargo to lysosomes
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DOI：
10.1111/tra.12334
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发表时间：
2015-12-01
期刊：
影响因子：
4.5
通讯作者：
Klumperman, Judith
中科院分区：
文献类型：
--
作者：
Galmes, Romain;ten Brink, Corlinda;Klumperman, Judith
溶酶体是真核细胞的主要降解区室。CORVET和HOPS系链复合物在酵母胞吞途径中的膜融合中的作用是众所周知的。酵母Vps 33 p是两种复合物的一部分，并且具有两种哺乳动物同源物：Vps 33 A和Vps 33 B。Vps 33 B是极化细胞顶端蛋白再循环所必需的，也是ARC综合征的致病基因。在这里，我们调查是否Vps 33 B也需要在降解途径。通过荧光和电子显微镜，我们表明，在HeLa细胞中的Vps 33 B耗尽导致晚期内体的数量显着增加，与溶酶体一起积累在核周区域。在这些细胞中，内吞货物的降解受损。通过电子显微镜，我们发现，内吞BSA-金到达晚期内体，但在溶酶体中减少。晚期内体数量的增加和溶酶体中内化的货物的缺乏指示晚期内体-溶酶体融合事件的缺陷，这解释了观察到的货物降解的减少。在Vps 33 A敲低后发现了相应的表型，这也导致溶酶体数量减少。我们的结论是，Vps 33 B，除了其在内体回收的作用，是所需的晚期内体-溶酶体融合事件。
Lysosomes are the main degradative compartments of eukaryotic cells. The CORVET and HOPS tethering complexes are well known for their role in membrane fusion in the yeast endocytic pathway. Yeast Vps33p is part of both complexes, and has two mammalian homologues: Vps33A and Vps33B. Vps33B is required for recycling of apical proteins in polarized cells and a causative gene for ARC syndrome. Here, we investigate whether Vps33B is also required in the degradative pathway. By fluorescence and electron microscopy we show that Vps33B depletion in HeLa cells leads to significantly increased numbers of late endosomes that together with lysosomes accumulate in the perinuclear region. Degradation of endocytosed cargo is impaired in these cells. By electron microscopy we show that endocytosed BSA-gold reaches late endosomes, but is decreased in lysosomes. The increase in late endosome numbers and the lack of internalized cargo in lysosomes are indicative for a defect in late endosomal-lysosomal fusion events, which explains the observed decrease in cargo degradation. A corresponding phenotype was found after Vps33A knock down, which in addition also resulted in decreased lysosome numbers. We conclude that Vps33B, in addition to its role in endosomal recycling, is required for late endosomal-lysosomal fusion events.