Interaction of NPC2 protein with Lysobisphosphatidic Acid is required for normal endolysosomal cholesterol trafficking

Abstract

1 2 Unesterified cholesterol accumulation in the late endosomal/lysosomal (LE/LY) compartment is the 3 cellular hallmark of Niemann-Pick C (NPC) disease, caused by defects in the genes encoding NPC1 or 4 NPC2. We previously reported the dramatic stimulation of NPC2 cholesterol transport rates by the 5 LE/LY phospholipid lysobisphosphatidic acid (LBPA) and in these studies sought to determine their 6 functional relationship in normal LE/LY cholesterol egress. Here we demonstrate that NPC2 interacts 7 directly with LBPA and identify the NPC2 hydrophobic knob domain as the site of interaction. Using its 8 precursor phosphatidylglycerol (PG), we show that PG-induced LBPA enrichment results in clearance of 9 accumulated cholesterol from NPC1-deficient cells but is ineffective in cells lacking functional NPC2. 10Together these studies reveal a heretofore unknown aspect of intracellular cholesterol trafficking, in 11 which NPC2 and LBPA function together in an obligate step of sterol egress from the LE/LY 12 compartment, which appears to be independent of NPC1. 13 egress pathway of membrane-impermeable species utilized by the NPC1 and NPC2 proteins (Goldman & 46 Krise, 2010). It has also been shown that overexpression of ABCA1 reversed lysosomal cholesterol 47