Khatter Divya, Raina Vivek B, Dwivedi Devashish, Sindhwani Aastha, Bahl Surbhi, Sharma Mahak
Department of Biological Sciences, Indian Institute of Science Education and Research-Mohali (IISERM), India.
Department of Biological Sciences, Indian Institute of Science Education and Research-Mohali (IISERM), India
J Cell Sci. 2015 May 1;128(9):1746-61. doi: 10.1242/jcs.162651. Epub 2015 Apr 23.
The homotypic fusion and protein sorting (HOPS) complex is a multi-subunit complex conserved from yeast to mammals that regulates late endosome and lysosome fusion. However, little is known about how the HOPS complex is recruited to lysosomes in mammalian cells. Here, we report that the small GTPase Arl8b, but not Rab7 (also known as RAB7A), is essential for membrane localization of the human (h)Vps41 subunit of the HOPS complex. Assembly of the core HOPS subunits to Arl8b- and hVps41-positive lysosomes is guided by their subunit-subunit interactions. RNA interference (RNAi)-mediated depletion of hVps41 resulted in the impaired degradation of EGFR that was rescued upon expression of wild-type but not an Arl8b-binding-defective mutant of hVps41, suggesting that Arl8b-dependent lysosomal localization of hVps41 is required for its endocytic function. Furthermore, we have also identified that the Arl8b effector SKIP (also known as PLEKHM2) interacts with and recruits HOPS subunits to Arl8b and kinesin-positive peripheral lysosomes. Accordingly, RNAi-mediated depletion of SKIP impaired lysosomal trafficking and degradation of EGFR. These findings reveal that Arl8b regulates the association of the human HOPS complex with lysosomal membranes, which is crucial for the function of this tethering complex in endocytic degradation.
同型融合与蛋白分选（HOPS）复合体是一种从酵母到哺乳动物都保守的多亚基复合体，它调节晚期内体和溶酶体的融合。然而，关于HOPS复合体如何在哺乳动物细胞中被招募到溶酶体，人们知之甚少。在这里，我们报告小GTP酶Arl8b而非Rab7（也称为RAB7A）对于HOPS复合体的人（h）Vps41亚基的膜定位至关重要。核心HOPS亚基与Arl8b和hVps41阳性溶酶体的组装是由它们的亚基-亚基相互作用引导的。RNA干扰（RNAi）介导的hVps41缺失导致表皮生长因子受体（EGFR）降解受损，而野生型而非hVps41的Arl8b结合缺陷突变体的表达可挽救这种情况，这表明hVps41依赖Arl8b的溶酶体定位是其胞吞功能所必需的。此外，我们还确定Arl8b效应器SKIP（也称为PLEKHM2）与HOPS亚基相互作用并将其招募到Arl8b和驱动蛋白阳性的外周溶酶体。相应地，RNAi介导的SKIP缺失损害了溶酶体运输和EGFR的降解。这些发现揭示了Arl8b调节人HOPS复合体与溶酶体膜的结合，这对于该拴系复合体在胞吞降解中的功能至关重要。
