Zhao Kexin, Ridgway Neale D
Departments of Pediatrics and Biochemistry & Molecular Biology, Atlantic Research Centre, Dalhousie University, Box 15000, Halifax, NS B3H 4R2, Canada.
Departments of Pediatrics and Biochemistry & Molecular Biology, Atlantic Research Centre, Dalhousie University, Box 15000, Halifax, NS B3H 4R2, Canada.
Cell Rep. 2017 May 30;19(9):1807-1818. doi: 10.1016/j.celrep.2017.05.028.
Lipoprotein cholesterol is delivered to the limiting membrane of late endosomes/lysosomes (LELs) by Niemann-Pick C1 (NPC1). However, the mechanism of cholesterol transport from LELs to the endoplasmic reticulum (ER) is poorly characterized. We report that oxysterol-binding protein-related protein 1L (ORP1L) is necessary for this stage of cholesterol export. CRISPR-mediated knockout of ORP1L in HeLa and HEK293 cells reduced esterification of cholesterol to the level in NPC1 knockout cells, and it increased the expression of sterol-regulated genes and de novo cholesterol synthesis, indicative of a block in cholesterol transport to the ER. In the absence of this transport pathway, cholesterol-enriched LELs accumulated in the Golgi/perinuclear region. Cholesterol delivery to the ER required the sterol-, phosphatidylinositol 4-phosphate-, and vesicle-associated membrane protein-associated protein (VAP)-binding activities of ORP1L, as well as NPC1 expression. These results suggest that ORP1L-dependent membrane contacts between LELs and the ER coordinate cholesterol transfer with the retrograde movement of endo-lysosomal vesicles.
脂蛋白胆固醇通过尼曼-匹克C1（NPC1）被转运至晚期内体/溶酶体（LEL）的界膜。然而，胆固醇从LEL转运至内质网（ER）的机制目前仍不清楚。我们报告称，氧甾醇结合蛋白相关蛋白1L（ORP1L）是胆固醇输出这一阶段所必需的。通过CRISPR技术敲除HeLa和HEK293细胞中的ORP1L，会使胆固醇酯化水平降至NPC1敲除细胞中的水平，并增加固醇调节基因的表达和胆固醇的从头合成，这表明胆固醇向ER的转运受阻。在缺乏这种转运途径的情况下，富含胆固醇的LEL会在高尔基体/核周区域积累。胆固醇向ER的转运需要ORP1L的固醇、磷脂酰肌醇4-磷酸和囊泡相关膜蛋白相关蛋白（VAP）结合活性，以及NPC1的表达。这些结果表明，LEL与ER之间依赖ORP1L的膜接触将胆固醇转运与内溶酶体囊泡的逆行运动协调起来。
