title: Involvement of Cdc42 signaling in apoA-I-induced cholesterol efflux.
abstract: Cholesterol efflux, an important mechanism by which high density lipoproteins (HDL) protect against atherosclerosis, is initiated by docking of apolipoprotein A-I (apoA-I), a major HDL protein, to specific binding sites followed by activation of ATP-binding cassette transporter A1 (ABCA1) and translocation of cholesterol from intracellular compartments to the exofacial monolayer of the plasma membrane where it is accessible to HDL. In this report, we investigated potential signal transduction pathways that may link apoA-I binding to cholesterol translocation to the plasma membrane and cholesterol efflux. By using pull-down assays we found that apoA-I substantially increased the amount of activated Cdc42, Rac1, and Rho in human fibroblasts. Moreover, apoA-I induced actin polymerization, which is known to be controlled by Rho family G proteins. Inhibition of Cdc42 and Rac1 with Clostridium difficile toxin B inhibited apoA-I-induced cholesterol efflux, whereas inhibition of Rho with Clostridium botulinum C3-exoenzyme exerted opposite effects. Adenoviral expression of a Cdc42(T17N) dominant negative mutant substantially reduced apoA-I-induced cholesterol efflux, whereas dominant negative Rac1(T17N) had no effect. We further found that two downstream effectors of Cdc42/Rac1 signaling, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK), are activated by apoA-I. Pharmacological inhibition of JNK but not p38 MAPK decreased apoA-I-induced cholesterol efflux, whereas anisomycin and hydrogen peroxide, two direct JNK activators, could partially substitute for apoA-I in its ability to induce cholesterol efflux. These results for the first time demonstrate activation of Rho family G proteins and stress kinases by apoA-I and implicate the involvement of Cdc42 and JNK in the apoA-I-induced cholesterol efflux.
authors.affiliation: Institut für Klinische Chemie und Laboratoriumsmedizin, Westfälische Wilhelms-Universität, D-48129 Münster, Germany. nofer@uni-muenster.de
authors.forename: Jerzy-Roch
authors.initials: JR
authors.lastname: Nofer
authors.forename: Renata
authors.initials: R
authors.lastname: Feuerborn
authors.forename: Bodo
authors.initials: B
authors.lastname: Levkau
authors.forename: Andrea
authors.initials: A
authors.lastname: Sokoll
authors.forename: Udo
authors.initials: U
authors.lastname: Seedorf
authors.forename: Gerd
authors.initials: G
authors.lastname: Assmann
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry; D000256:Adenoviridae / Q000235:genetics; D000841:Anisomycin / Q000494:pharmacology; D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D015153:Blotting, Western; D001905:Botulinum Toxins / Q000378:metabolism; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D005799:Genes, Dominant; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction; D012867:Skin / Q000166:cytology; D013997:Time Factors; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D054462:p21-Activated Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D000199:Actins; D016632:Apolipoprotein A-I; D001426:Bacterial Proteins; D001427:Bacterial Toxins; C031815:toxB protein, Clostridium difficile; D006153:Guanosine Diphosphate; D000841:Anisomycin; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D002784:Cholesterol; D006861:Hydrogen Peroxide; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D001905:Botulinum Toxins; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020741:rho GTP-Binding Proteins