Marwaha Rituraj, Arya Subhash B, Jagga Divya, Kaur Harmeet, Tuli Amit, Sharma Mahak
Department of Biological Sciences, Indian Institute of Science Education and Research, Mohali, Punjab 140306, India.
Division of Cell Biology and Immunology, Council of Scientific and Industrial Research, Institute of Microbial Technology, Chandigarh 160036, India.
J Cell Biol. 2017 Apr 3;216(4):1051-1070. doi: 10.1083/jcb.201607085. Epub 2017 Mar 21.
Endocytic, autophagic, and phagocytic vesicles move on microtubule tracks to fuse with lysosomes. Small GTPases, such as Rab7 and Arl8b, recruit their downstream effectors to mediate this transport and fusion. However, the potential cross talk between these two GTPases is unclear. Here, we show that the Rab7 effector PLEKHM1 simultaneously binds Rab7 and Arl8b, bringing about clustering and fusion of late endosomes and lysosomes. We show that the N-terminal RUN domain of PLEKHM1 is necessary and sufficient for interaction with Arl8b and its subsequent localization to lysosomes. Notably, we also demonstrate that Arl8b mediates recruitment of HOPS complex to PLEKHM1-positive vesicle contact sites. Consequently, Arl8b binding to PLEKHM1 is required for its function in delivery and, therefore, degradation of endocytic and autophagic cargo in lysosomes. Finally, we also show that PLEKHM1 competes with SKIP for Arl8b binding, which dictates lysosome positioning. These findings suggest that Arl8b, along with its effectors, orchestrates lysosomal transport and fusion.
内吞小泡、自噬小泡和吞噬小泡沿着微管轨道移动，与溶酶体融合。小GTP酶，如Rab7和Arl8b，招募其下游效应物来介导这种运输和融合。然而，这两种GTP酶之间潜在的相互作用尚不清楚。在这里，我们表明Rab7效应物PLEKHM1同时结合Rab7和Arl8b，导致晚期内体和溶酶体的聚集和融合。我们表明，PLEKHM1的N端RUN结构域对于与Arl8b的相互作用及其随后定位于溶酶体是必要且充分的。值得注意的是，我们还证明Arl8b介导HOPS复合物募集到PLEKHM1阳性的小泡接触位点。因此，Arl8b与PLEKHM1的结合是其在溶酶体中递送并因此降解内吞和自噬货物功能所必需的。最后，我们还表明PLEKHM1与SKIP竞争Arl8b的结合，这决定了溶酶体的定位。这些发现表明，Arl8b与其效应物一起协调溶酶体的运输和融合。
