title: ABCA1 mediates concurrent cholesterol and phospholipid efflux to apolipoprotein A-I.
abstract: Prior studies provide data supporting the notion that ATP binding cassette transporter A1 (ABCA1) promotes lipid efflux to extracellular acceptors in a two-step process: first, ABCA1 mediates phospholipid efflux to an apolipoprotein, and second, this apolipoprotein-phospholipid complex accepts free cholesterol in an ABCA1-independent manner. In the current study using RAW264.7 cells, ABCA1-mediated free cholesterol and phospholipid efflux to apolipoprotein A-I (apoA-I) were tightly coupled to each other both temporally and after treatment with ABCA1 inhibitors. The time course and temperature dependence of ABCA1-mediated lipid efflux to apoA-I support a role for endocytosis in this process. Cyclodextrin treatment of RAW264.7 cells partially inhibited 8Br-cAMP-induced efflux of free cholesterol and phospholipid to apoA-I. ABCA1-expressing cells are more sensitive to cell damage by high-dose cyclodextrin and vanadate, leading to increased lactate dehydrogenase leakage and phospholipid release even in the absence of the acceptor apoA-I. Finally, we could not reproduce a two-step effect on lipid efflux using conditioned medium from ABCA1-expressing cells pretreated with cyclodextrin.
authors.affiliation: Department of Cell Biology NC10, The Cleveland Clinic Foundation, Cleveland, OH 44195, USA. smithj@lerner.ccf.org
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Smith
authors.forename: Wilfried
authors.initials: W
authors.lastname: Le Goff
authors.forename: Megan
authors.initials: M
authors.lastname: Settle
authors.forename: Gregory
authors.initials: G
authors.lastname: Brubaker
authors.forename: Christine
authors.initials: C
authors.lastname: Waelde
authors.forename: Andrew
authors.initials: A
authors.lastname: Horwitz
authors.forename: Michael N
authors.initials: MN
authors.lastname: Oda
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D003505:Cyclodextrins / Q000494:pharmacology; D004705:Endocytosis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D051379:Mice; D010743:Phospholipids / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D003505:Cyclodextrins; D004791:Enzyme Inhibitors; D010743:Phospholipids; D014638:Vanadates; D002784:Cholesterol