title: Niemann-Pick Type C2 protein contributes to the transport of endosomal cholesterol to mitochondria without interacting with NPC1.
abstract: Mitochondrial cholesterol is maintained within a narrow range to regulate steroid and oxysterol synthesis and to ensure mitochondrial function. Mitochondria acquire cholesterol through several pathways from different cellular pools. Here we have characterized mitochondrial import of endosomal cholesterol using Chinese hamster ovary cells expressing a CYP11A1 fusion protein that converts cholesterol to pregnenolone at the mitochondrial inner membrane. RNA interference-mediated depletion of the voltage-dependent anion channel 1 in the mitochondrial outer membrane or of Niemann-Pick Type C2 (NPC2) in the endosome lumen decreased arrival of cholesterol at the mitochondrial inner membrane. Expression of NPC2 mutants unable to transfer cholesterol to NPC1 still restored mitochondrial cholesterol import in NPC2-depleted cells. Transport assays in semi-permeabilized cells showed nonvesicular cholesterol trafficking directly from endosomes to mitochondria that did not require cytosolic transport proteins but that was reduced in the absence of NPC2. Our findings indicate that NPC2 delivers cholesterol to the perimeter membrane of late endosomes, where it becomes available for transport to mitochondria without requiring NPC1.
authors.affiliation: Department of Biochemistry and Molecular Biology,  Dalhousie University, Halifax, Nova Scotia, B3H 4R2,  Canada.
authors.forename: Barry E
authors.initials: BE
authors.lastname: Kennedy
authors.forename: Mark
authors.initials: M
authors.lastname: Charman
authors.forename: Barbara
authors.initials: B
authors.lastname: Karten
mesh_terms: D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism; D011992:Endosomes / Q000737:chemistry* / Q000378:metabolism; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins / Q000172:deficiency / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000737:chemistry / Q000378:metabolism; D000077296:Niemann-Pick C1 Protein; D033921:Vesicular Transport Proteins; D050995:Voltage-Dependent Anion Channel 1 / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; C104585:NPC2 protein, human; D000077296:Niemann-Pick C1 Protein; C494762:VDAC1 protein, human; D033921:Vesicular Transport Proteins; D002784:Cholesterol; D050995:Voltage-Dependent Anion Channel 1