title: Efflux of sphingomyelin, cholesterol, and phosphatidylcholine by ABCG1.
abstract: Cholesterol and phospholipids are essential to the body, but an excess of cholesterol or lipids is toxic and a risk factor for arteriosclerosis. ABCG1, one of the half-type ABC proteins, is thought to be involved in cholesterol homeostasis. To explore the role of ABCG1 in cholesterol homeostasis, we examined its subcellular localization and function. ABCG1 and ABCG1-K120M, a WalkerA lysine mutant, were localized to the plasma membrane in HEK293 cells stably expressing ABCG1 and formed a homodimer. A stable transformant expressing ABCG1 exhibited efflux of cholesterol and choline phospholipids in the presence of BSA, and the cholesterol efflux was enhanced by the presence of HDL, whereas cells expressing ABCG1-K120M did not, suggesting that ATP binding and/or hydrolysis is required for the efflux. Mass and TLC analyses revealed that ABCG1 and ABCA1 secrete several species of sphingomyelin (SM) and phosphatidylcholine (PC), and SMs were preferentially secreted by ABCG1, whereas PCs were preferentially secreted by ABCA1. These results suggest that ABCA1 and ABCG1 mediate the lipid efflux in different mechanisms, in which different species of phospholipids are secreted, and function coordinately in the removal of cholesterol and phospholipids from peripheral cells.
authors.affiliation: Laboratory of Cellular Biochemistry, Division of Applied Life Sciences, Kyoto University Graduate School of Agriculture, Kyoto 606-8502, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Kobayashi
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Takanezawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Hirata
authors.forename: Yuji
authors.initials: Y
authors.lastname: Shimizu
authors.forename: Keiko
authors.initials: K
authors.lastname: Misasa
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kioka
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Arai
authors.forename: Kazumitsu
authors.initials: K
authors.lastname: Ueda
authors.forename: Michinori
authors.initials: M
authors.lastname: Matsuo
mesh_terms: D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D019921:Biotinylation; D002417:Cattle; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D019281:Dimerization; D006031:Glycosylation; D006801:Humans; D008856:Microscopy, Fluorescence; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010713:Phosphatidylcholines / Q000378:metabolism*; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013109:Sphingomyelins / Q000378:metabolism*
chemical_list: C419353:ABCG1 protein, human; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D050505:Mutant Proteins; D010713:Phosphatidylcholines; D013109:Sphingomyelins; D012710:Serum Albumin, Bovine; D000255:Adenosine Triphosphate; D002784:Cholesterol