Department of Molecular Genetics and Microbiology, University of New Mexico, Albuquerque, NM 87131.
Autophagy, Inflammation, and Metabolism Center of Biomedical Research Excellence, University of New Mexico, Albuquerque, NM 87131.
Mol Biol Cell. 2022 Aug 1;33(9):ar81. doi: 10.1091/mbc.E21-11-0595-T. Epub 2022 Jun 2.
Lysosomes receive extracellular and intracellular cholesterol and redistribute it throughout the cell. Cholesterol egress from lysosomes is critical for cholesterol homeostasis, and its failure underlies the pathogenesis of genetic disorders such as Niemann-Pick C (NPC) disease. Here we report that the BLOC one-related complex (BORC)-ARL8-homotypic fusion and protein sorting (HOPS) ensemble is required for egress of free cholesterol from lysosomes and for storage of esterified cholesterol in lipid droplets. Depletion of BORC, ARL8, or HOPS does not alter the localization of the lysosomal transmembrane cholesterol transporter NPC1 to degradative compartments but decreases the association of the luminal transporter NPC2 and increases NPC2 secretion. BORC-ARL8-HOPS depletion also increases lysosomal degradation of cation-independent (CI)-mannose 6-phosphate (M6P) receptor (MPR), which normally sorts NPC2 to the endosomal-lysosomal system and then is recycled to the trans-Golgi network. These defects likely result from impaired HOPS-dependent fusion of endosomal-lysosomal organelles and an uncharacterized function of HOPS in CI-MPR recycling. Our study demonstrates that the BORC-ARL8-HOPS ensemble is required for cholesterol egress from lysosomes by enabling CI-MPR-dependent trafficking of NPC2 to the endosomal-lysosomal system.
溶酶体接收细胞外和细胞内的胆固醇，并将其重新分配到整个细胞中。胆固醇从溶酶体中流出对于胆固醇的动态平衡至关重要，其功能的失败是尼曼-皮克 C（NPC）疾病等遗传疾病发病的基础。在这里，我们报告说，BLOC one-related complex（BORC）-ARL8-homotypic fusion and protein sorting（HOPS）综合体对于游离胆固醇从溶酶体中流出以及酯化胆固醇在脂滴中的储存是必需的。BORC、ARL8 或 HOPS 的耗竭不会改变溶酶体跨膜胆固醇转运蛋白 NPC1 到降解区室的定位，但会降低腔转运蛋白 NPC2 的关联并增加 NPC2 的分泌。BORC-ARL8-HOPS 耗竭还会增加溶酶体对阳离子非依赖性（CI）-甘露糖 6-磷酸（M6P）受体（MPR）的降解，MPR 通常将 NPC2 分拣到内体-溶酶体系统，然后再循环到反式高尔基体网络。这些缺陷可能是由于 HOPS 依赖性内体-溶酶体细胞器融合受损以及 HOPS 在 CI-MPR 回收中的未表征功能所致。我们的研究表明，BORC-ARL8-HOPS 综合体对于胆固醇从溶酶体中流出是必需的，因为它允许 NPC2 依赖 CI-MPR 进行内体-溶酶体系统的运输。
