title: The AAA ATPase VPS4/SKD1 regulates endosomal cholesterol trafficking independently of ESCRT-III.
abstract: The exit of low-density lipoprotein derived cholesterol (LDL-C) from late endosomes (LE)/lysosomes (Ly) is mediated by Niemann-Pick C1 (NPC1), a multipass integral membrane protein on the limiting membranes of LE/Ly, and by NPC2, a cholesterol-binding protein in the lumen of LE/Ly. NPC2 delivers cholesterol to the N-terminal domain of NPC1, which is believed to insert cholesterol into the limiting membrane for subsequent transport to other subcellular organelles. Few cytoplasmic factors have been identified to govern cholesterol efflux from LE/Ly, and much less is known about the underlying molecular mechanisms. Here we establish VPS4, an AAA ATPase that has a well-established role in disassembling the ESCRT (endosomal sorting complex required for transport)-III polymer, as an important regulator of endosomal cholesterol transport. Knocking down VPS4 in HeLa cells resulted in prominent accumulation of LDL-C in LE/Ly, and disrupted cholesterol homeostatic responses at the endoplasmic reticulum. The level and localization of NPC1 and NPC2 appeared to be normal in VPS4 knockdown cells. Importantly, depleting any of the ESCRT-III components did not exert a significant effect on endosomal cholesterol transport. Our results thus identify an important cytoplasmic regulator of endosomal cholesterol trafficking and represent the first functional separation of VPS4 from ESCRT-III.
authors.affiliation: School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW, 2052, Australia.
authors.forename: Ximing
authors.initials: X
authors.lastname: Du
authors.forename: Abdulla S
authors.initials: AS
authors.lastname: Kazim
authors.forename: Ian W
authors.initials: IW
authors.lastname: Dawes
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Brown
authors.forename: Hongyuan
authors.initials: H
authors.lastname: Yang
mesh_terms: D000074183:ATPases Associated with Diverse Cellular Activities; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D008078:Cholesterol, LDL / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D006367:HeLa Cells; D006706:Homeostasis; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008247:Lysosomes / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D000077296:Niemann-Pick C1 Protein; D021381:Protein Transport; D034741:RNA, Small Interfering; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D008078:Cholesterol, LDL; D056827:Endosomal Sorting Complexes Required for Transport; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; C104585:NPC2 protein, human; D000077296:Niemann-Pick C1 Protein; D034741:RNA, Small Interfering; D033921:Vesicular Transport Proteins; D000251:Adenosine Triphosphatases; D000074183:ATPases Associated with Diverse Cellular Activities; C490304:VPS4B protein, human