title: Membrane microdomains modulate oligomeric ABCA1 function: impact on apoAI-mediated lipid removal and phosphatidylcholine biosynthesis.
abstract: Recent studies have identified an ABCA1-dependent, phosphatidylcholine-rich microdomain, called the "high-capacity binding site" (HCBS), that binds apoA-I and plays a pivotal role in apoA-I lipidation. Here, using sucrose gradient fractionation, we obtained evidence that both ABCA1 and [¹²⁵I]apoA-I associated with the HCBS were found localized to nonraft microdomains. Interestingly, phosphatidylcholine (PtdCho) was selectively removed from nonraft domains by apoA-I, whereas sphingomyelin and cholesterol were desorbed from both detergent-resistant membranes and nonraft domains. The modulatory role of cholesterol on apoA-I binding to ABCA1/HCBS was also examined. Loading cells with cholesterol resulted in a drastic reduction in apoA-I binding. Conversely, depletion of membrane cholesterol by methyl-β-cyclodextrin treatment resulted in a significant increase in apoA-I binding. Finally, we obtained evidence that apoA-I interaction with ABCA1 promoted the activation and gene expression of key enzymes in the PtdCho biosynthesis pathway. Taken together, these results provide strong evidence that the partitioning of ABCA1/HCBS to nonraft domains plays a pivotal role in the selective desorption of PtdCho molecules by apoA-I, allowing an optimal environment for cholesterol release and regeneration of the PtdCho-containing HCBS. This process may have important implications in preventing and treating atherosclerotic cardiovascular disease.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, McGill University Health Center/Royal Victoria Hospital, Montréal, Québec, H3A 1A1, Canada. jacques.genest@muhc.mcgill.ca
authors.forename: Iulia
authors.initials: I
authors.lastname: Iatan
authors.forename: Dana
authors.initials: D
authors.lastname: Bailey
authors.forename: Isabelle
authors.initials: I
authors.lastname: Ruel
authors.forename: Anouar
authors.initials: A
authors.lastname: Hafiane
authors.forename: Steven
authors.initials: S
authors.lastname: Campbell
authors.forename: Larbi
authors.initials: L
authors.lastname: Krimbou
authors.forename: Jacques
authors.initials: J
authors.lastname: Genest
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism*; D001665:Binding Sites; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D006224:Cricetinae; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000096:biosynthesis* / Q000378:metabolism*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D021381:Protein Transport
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D010713:Phosphatidylcholines; D002784:Cholesterol