Salazar G, Craige B, Styers M L, Newell-Litwa K A, Doucette M M, Wainer B H, Falcon-Perez J M, Dell'Angelica E C, Peden A A, Werner E, Faundez V
Department of Cell Biology, Emory University, Atlanta, GA 30322, USA.
Mol Biol Cell. 2006 Sep;17(9):4014-26. doi: 10.1091/mbc.e06-02-0103. Epub 2006 Jun 7.
Mutational analyses have revealed many genes that are required for proper biogenesis of lysosomes and lysosome-related organelles. The proteins encoded by these genes assemble into five distinct complexes (AP-3, BLOC-1-3, and HOPS) that either sort membrane proteins or interact with SNAREs. Several of these seemingly distinct complexes cause similar phenotypic defects when they are rendered defective by mutation, but the underlying cellular mechanism is not understood. Here, we show that the BLOC-1 complex resides on microvesicles that also contain AP-3 subunits and membrane proteins that are known AP-3 cargoes. Mouse mutants that cause BLOC-1 or AP-3 deficiencies affected the targeting of LAMP1, phosphatidylinositol-4-kinase type II alpha, and VAMP7-TI. VAMP7-TI is an R-SNARE involved in vesicle fusion with late endosomes/lysosomes, and its cellular levels were selectively decreased in cells that were either AP-3- or BLOC-1-deficient. Furthermore, BLOC-1 deficiency selectively altered the subcellular distribution of VAMP7-TI cognate SNAREs. These results indicate that the BLOC-1 and AP-3 protein complexes affect the targeting of SNARE and non-SNARE AP-3 cargoes and suggest a function of the BLOC-1 complex in membrane protein sorting.
突变分析已经揭示了许多对于溶酶体和溶酶体相关细胞器的正常生物发生所必需的基因。这些基因编码的蛋白质组装成五个不同的复合物（AP-3、BLOC-1-3和HOPS），它们要么对膜蛋白进行分类，要么与SNARE相互作用。当这些看似不同的复合物中的几个因突变而功能缺陷时，会导致相似的表型缺陷，但潜在的细胞机制尚不清楚。在这里，我们表明BLOC-1复合物存在于微泡上，这些微泡还含有AP-3亚基和已知的AP-3货物膜蛋白。导致BLOC-1或AP-3缺陷的小鼠突变体影响了LAMP1、磷脂酰肌醇-4-激酶IIα型和VAMP7-TI的靶向。VAMP7-TI是一种参与囊泡与晚期内体/溶酶体融合的R-SNARE，在AP-3或BLOC-1缺陷的细胞中其细胞水平选择性降低。此外，BLOC-1缺陷选择性地改变了VAMP7-TI同源SNARE的亚细胞分布。这些结果表明BLOC-1和AP-3蛋白复合物影响SNARE和非SNARE AP-3货物的靶向，并提示BLOC-1复合物在膜蛋白分类中的功能。
