title: Lipid raft-dependent and -independent signaling through HLA-DR molecules.
abstract: Lipid rafts are plasma membrane microdomains that are highly enriched in signaling molecules and that act as signal transduction platforms for many immune receptors. The involvement of these microdomains in HLA-DR-induced signaling is less well defined. We examined the constitutive presence of HLA-DR molecules in lipid rafts, their possible recruitment into these microdomains, and the role of these microdomains in HLA-DR-induced responses. We detected significant amounts of HLA-DR molecules in the lipid rafts of EBV(+) and EBV(-) B cell lines, monocytic cell lines, transfected HeLa cells, tonsillar B cells, and human monocytes. Localization of HLA-DR in these microdomains was unaffected by the deletion of the cytoplasmic domain of both the alpha and beta chains. Ligation of HLA-DR with a bivalent, but not a monovalent, ligand resulted in rapid tyrosine phosphorylation of many substrates, especially Lyn, and activation of ERK1/2 MAP kinase. However, the treatment failed to induce further recruitment of HLA-DR molecules into lipid rafts. The HLA-DR-induced signaling events were accompanied by the induction of cell-cell adhesion that could be inhibited by PTK and Lyn but not ERK1/2 inhibitors. Disruption of lipid rafts by methyl-beta-cyclodextrin (MbetaCD) resulted in the loss of membrane raft association with HLA-DR molecules, inhibition of HLA-DR-mediated protein tyrosine phosphorylation and cell-cell adhesion. MbetaCD did not affect the activation of ERK1/2, which was absent from lipid rafts. These results indicate that although all the HLA-DR-induced events studied are dependent on HLA-DR dimerization, some require the presence of HLA-DR molecules in lipid rafts, whereas others do not.
authors.affiliation: Centre de Recherche en Rhumatologie et Immunologie, (CHUL), Département de Médecine, Université Laval, Quebec City, Quebec G1V 4G2, Canada.
authors.forename: Marlene
authors.initials: M
authors.lastname: Bouillon
authors.forename: Youssef
authors.initials: Y
authors.lastname: El Fakhry
authors.forename: Julie
authors.initials: J
authors.lastname: Girouard
authors.forename: Hayssam
authors.initials: H
authors.lastname: Khalil
authors.forename: Jacques
authors.initials: J
authors.lastname: Thibodeau
authors.forename: Walid
authors.initials: W
authors.lastname: Mourad
mesh_terms: D000911:Antibodies, Monoclonal / Q000378:metabolism; D015153:Blotting, Western; D002448:Cell Adhesion; D002460:Cell Line; D002784:Cholesterol / Q000494:pharmacology; D003505:Cyclodextrins / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D019281:Dimerization; D005434:Flow Cytometry; D006684:HLA-DR Antigens / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008024:Ligands; D050356:Lipid Metabolism; D020935:MAP Kinase Signaling System; D021962:Membrane Microdomains / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009000:Monocytes / Q000378:metabolism; D014066:Palatine Tonsil / Q000166:cytology; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D047392:beta-Cyclodextrins; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D003505:Cyclodextrins; D006684:HLA-DR Antigens; D008024:Ligands; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D014443:Tyrosine; D002784:Cholesterol; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases