title: cAMP induces ABCA1 phosphorylation activity and promotes cholesterol efflux from fibroblasts.
abstract: ATP-binding cassette transporter A1 (ABCA1) plays a crucial role in apoA-I lipidation, a key step in reverse cholesterol transport. cAMP induces apoA-I binding activity and promotes cellular cholesterol efflux. We investigated the role of the cAMP/protein kinase A (PKA) dependent pathway in the regulation of cellular cholesterol efflux. Treatment of normal fibroblasts with 8-bromo-cAMP (8-Br-cAMP) increased significantly apoA-I-mediated cholesterol efflux, with specificity for apoA-I, but not for cyclodextrin. Concomitantly, 8-Br-cAMP increased ABCA1 phosphorylation in a time-dependent manner. Maximum phosphorylation was reached in <10 min, representing a 260% increase compared to basal ABCA1 phosphorylation level. Forskolin, a known cAMP regulator, increased both cellular cholesterol efflux and ABCA1 phosphorylation. In contrast, H-89 PKA inhibitor reduced cellular cholesterol efflux by 70% in a dose-dependent manner and inhibited almost completely ABCA1 phosphorylation. To determine whether naturally occurring mutants of ABCA1 may affect its phosphorylation activity, fibroblasts from subjects with familial HDL deficiency (FHD, heterozygous ABCA1 defect) and Tangier disease (TD, homozygous/compound heterozygous ABCA1 defect) were treated with 8-Br-cAMP or forskolin. Cellular cholesterol efflux and ABCA1 phosphorylation were increased in FHD but not in TD cells. Taken together, these findings provide evidence for a link between the cAMP/PKA-dependent pathway, ABCA1 phosphorylation, and apoA-I mediated cellular cholesterol efflux.
authors.affiliation: Cardiovascular Genetics Laboratory, McGill University Health Centre, Royal Victoria Hospital, Montréal, QC H3A 1A1. Faculty of Medicine, Université de Montréal, Montréal, QC H3C 3J7, Canada.
authors.forename: Bassam
authors.initials: B
authors.lastname: Haidar
authors.forename: Maxime
authors.initials: M
authors.lastname: Denis
authors.forename: Larbi
authors.initials: L
authors.lastname: Krimbou
authors.forename: Michel
authors.initials: M
authors.lastname: Marcil
authors.forename: Jacques
authors.initials: J
authors.lastname: Genest
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D009154:Mutation; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013631:Tangier Disease / Q000235:genetics / Q000378:metabolism
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D012333:RNA, Messenger; D002784:Cholesterol; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases