Mobilization of rate-endosomal cholesterol is inhibited by Rab guanine nucleotide dissociation inhibitor

Cholesterol entering cells in low-density lipoproteins (LDL) via receptor-m ediated endocytosis is transported to organelles of the late endocytic path way for degradation of the lipoprotein particles, The fate of the free chol esterol released remains poorly understood, however. Recent observations su ggest that late-endosomal cholesterol sequestration is regulated by the dyn amics of lysobisphosphatidic acid (LBPA) rich membranes [1], Genetic studie s have pinpointed a protein, Niemann-Pick C-1 (NPC-1), that is required for the mobilization of late-endosomal/lysosomal cholesterol by an unknown mec hanism [2], Here, we report the removal of accumulated cholesterol by overe xpression of the NPC-1 protein in NPC-l-deficient fibroblasts from patients with Niemann-Pick disease, and in normal fibroblasts upon release of a pro gesterone-induced block of cholesterol transport. We show that late-endosom al/lysosomal cholesterol mobilization is specifically inhibited by microinj ection of Rab GDP-dissociation inhibitor (Rab GDI). Moreover, clearance of the cholesterol deposits by NPC-1 in patients' fibroblasts is accompanied b y the redistribution of LBPA and of a lysosomal hydrolase that utilizes the mannose-6-phosphate receptor. Our results reveal, for the first time, the involvement of a specific molecular component of the membrane-trafficking m achinery in cholesterol transport and the coupling of late-endosomal choles terol egress to the trafficking of other lipid and protein cargo.