title: Carboxyl terminus of apolipoprotein A-I (ApoA-I) is necessary for the transport of lipid-free ApoA-I but not prelipidated ApoA-I particles through aortic endothelial cells.
abstract: High density lipoproteins (HDL) and apolipoprotein A-I (apoA-I) must leave the circulation and pass the endothelium to exert their atheroprotective actions in the arterial wall. We previously demonstrated that the transendothelial transport of apoA-I involves ATP-binding cassette transporter (ABC) A1 and re-secretion of lipidated particles. Transendothelial transport of HDL is modulated by ABCG1 and the scavenger receptor BI (SR-BI). We hypothesize that apoA-I transport is started by the ABCA1-mediated generation of a lipidated particle which is then transported by ABCA1-independent pathways. To test this hypothesis we analyzed the endothelial binding and transport properties of initially lipid-free as well as prelipidated apoA-I mutants. Lipid-free apoA-I mutants with a defective carboxyl-terminal domain showed an 80% decreased specific binding and 90% decreased specific transport by aortic endothelial cells. After prior cell-free lipidation of the mutants, the resulting HDL-like particles were transported through endothelial cells by an ABCG1- and SR-BI-dependent process. ApoA-I mutants with deletions of either the amino terminus or both the amino and carboxyl termini showed dramatic increases in nonspecific binding but no specific binding or transport. Prior cell-free lipidation did not rescue these anomalies. Our findings of stringent structure-function relationships underline the specificity of transendothelial apoA-I transport and suggest that lipidation of initially lipid-free apoA-I is necessary but not sufficient for specific transendothelial transport. Our data also support the model of a two-step process for the transendothelial transport of apoA-I in which apoA-I is initially lipidated by ABCA1 and then further processed by ABCA1-independent mechanisms.
authors.affiliation: From the Institute of Clinical Chemistry, University Hospital of Zurich, 8091 Zurich, Switzerland,; the Competence Center for Systems Physiology and Metabolic Diseases, ETH and University of Zurich, 8091 Zurich, Switzerland.
authors.forename: Pascale M
authors.initials: PM
authors.lastname: Ohnsorg
authors.affiliation: From the Institute of Clinical Chemistry, University Hospital of Zurich, 8091 Zurich, Switzerland,; the Center for Integrative Human Physiology, University of Zurich, 8091 Zurich, Switzerland.
authors.forename: Lucia
authors.initials: L
authors.lastname: Rohrer
authors.affiliation: From the Institute of Clinical Chemistry, University Hospital of Zurich, 8091 Zurich, Switzerland,; the Center for Integrative Human Physiology, University of Zurich, 8091 Zurich, Switzerland.
authors.forename: Damir
authors.initials: D
authors.lastname: Perisa
authors.affiliation: Molecular Genetics, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts 02118,; the Department of Biochemistry, Division of Basic Sciences, Institute of Molecular Biology and Biotechnology, University of Crete Medical School, 71201 Crete, Greece.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kateifides
authors.affiliation: the National Centre of Scientific Research "Demokritos," Institute of Biology, 15310 Athens, Greece, and.
authors.forename: Angeliki
authors.initials: A
authors.lastname: Chroni
authors.affiliation: the Department of Biochemistry, Division of Basic Sciences, Institute of Molecular Biology and Biotechnology, University of Crete Medical School, 71201 Crete, Greece.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Kardassis
authors.affiliation: Molecular Genetics, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts 02118,; the Department of Biochemistry, Division of Basic Sciences, Institute of Molecular Biology and Biotechnology, University of Crete Medical School, 71201 Crete, Greece.
authors.forename: Vassilis I
authors.initials: VI
authors.lastname: Zannis
authors.affiliation: From the Institute of Clinical Chemistry, University Hospital of Zurich, 8091 Zurich, Switzerland,; the Competence Center for Systems Physiology and Metabolic Diseases, ETH and University of Zurich, 8091 Zurich, Switzerland,; the Center for Integrative Human Physiology, University of Zurich, 8091 Zurich, Switzerland,. Electronic address: arnold.voneckardstein@usz.ch.
authors.forename: Arnold
authors.initials: A
authors.lastname: von Eckardstein
mesh_terms: D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D009154:Mutation; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology; D051122:Scavenger Receptors, Class B / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: C419353:ABCG1 protein, human; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; C495124:SCARB1 protein, human; D051122:Scavenger Receptors, Class B