title: The Human ABCG1 Transporter Mobilizes Plasma Membrane and Late Endosomal Non-Sphingomyelin-Associated-Cholesterol for Efflux and Esterification.
abstract: We have previously shown that GFP-tagged human ABCG1 on the plasma membrane (PM) and in late endosomes (LE) mobilizes sterol on both sides of the membrane lipid bilayer, thereby increasing cellular cholesterol efflux to lipid surfaces. In the present study, we examined ABCG1-induced changes in membrane cholesterol distribution, organization, and mobility. ABCG1-GFP expression increased the amount of mobile, non-sphingomyelin(SM)-associated cholesterol at the PM and LE, but not the amount of SM-associated-cholesterol or SM. ABCG1-mobilized non-SM-associated-cholesterol rapidly cycled between the PM and LE and effluxed from the PM to extracellular acceptors, or, relocated to intracellular sites of esterification. ABCG1 increased detergent-soluble pools of PM and LE cholesterol, generated detergent-resistant, non-SM-associated PM cholesterol, and increased resistance to both amphotericin B-induced (cholesterol-mediated) and lysenin-induced (SM-mediated) cytolysis, consistent with altered organization of both PM cholesterol and SM. ABCG1 itself resided in detergent-soluble membrane domains. We propose that PM and LE ABCG1 residing at the phase boundary between ordered (Lo) and disordered (Ld) membrane lipid domains alters SM and cholesterol organization thereby increasing cholesterol flux between Lo and Ld, and hence, the amount of cholesterol available for removal by acceptors on either side of the membrane bilayer for either efflux or esterification.
authors.affiliation: Lipoprotein Metabolism Section, Cardiovascular and Pulmonary Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. neufelde@mail.nih.gov.
authors.forename: Edward B
authors.initials: EB
authors.lastname: Neufeld
authors.affiliation: Lipid Trafficking Core, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. obrienk@nhlbi.nih.gov.
authors.forename: Katherine
authors.initials: K
authors.lastname: O'Brien
authors.affiliation: Lipid Trafficking Core, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. awalts@yahoo.com.
authors.forename: Avram D
authors.initials: AD
authors.lastname: Walts
authors.affiliation: Lipoprotein Metabolism Section, Cardiovascular and Pulmonary Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. jstonik@verizon.net.
authors.forename: John A
authors.initials: JA
authors.lastname: Stonik
authors.affiliation: NHLBI Light Microscopy Core Facility, National Institutes of Health, Bethesda, MD 20892, USA. dmalide@mail.nih.gov.
authors.forename: Daniela
authors.initials: D
authors.lastname: Malide
authors.affiliation: NHLBI Light Microscopy Core Facility, National Institutes of Health, Bethesda, MD 20892, USA. combsc@nih.gov.
authors.forename: Christian A
authors.initials: CA
authors.lastname: Combs
authors.affiliation: Lipoprotein Metabolism Section, Cardiovascular and Pulmonary Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. Alan.Remaley@nih.gov.
authors.forename: Alan T
authors.initials: AT
authors.lastname: Remaley