title: Identification of a 52-kDa molecule (p52) coprecipitated with the Ig receptor-related MB-1 protein that is inducibly phosphorylated by the stimulation with phorbol myristate acetate.
abstract: Triggering of the Ig receptor (IgR) induces the activation in multiple intracellular signal transduction reactions including protein tyrosine phosphorylation, activation of phospholipase C, increased inositoltriphosphate, increased diacylglycerol, intracellular Ca2+ mobilization, and activation of protein kinase C. The IgR-complex, composed of mu-chain, L chain, Ig-alpha (MB-1), and Ig-beta (B29) proteins, is a functional unit both for expression of IgR and for signal transduction into cells, possibly by physical association with the down-stream functional molecules. An important functional motif ((D or E)-X7-(D or E)-Y-X3-L-X7-Y-X2-(L or I)) in the cytoplasmic domain of MB-1 molecule was shown to bind with several phosphoprotein components including src-type tyrosine kinases and phosphatidylinositol-3 kinase. To further study the functional components, we analyzed the phosphoprotein molecules coprecipitated with MB-1 protein. We found that a 52-kDa protein is coprecipitated with MB-1 protein and is inducibly phosphorylated by the stimulation with PMA. A rat mAb, prepared by immunizing the 52-kDa protein purified from SDS-PAGE, could detect the similar 52-kDa phosphoprotein (p52) expressed on the cell surface. In comparison with the 52-kDa protein in the immunoprecipitate of MB-1, the p52 migrated to the same position on 2-D gel electrophoresis (nonequilibrium pH gradient gel electrophoresis/SDS-PAGE). An in vitro kinase reaction analysis demonstrated that the p52 is tightly associated with the tyrosine kinase molecule(s), one of which is an 80-kDa protein containing an apparent autophosphorylation activity. These molecules would provide the informations of the down-stream molecules in the cascade reactions of the IgR-mediated signal transduction.
authors.affiliation: Department of Immunology, School of Life Science, Faculty of Medicine, Tottori University, Yonago, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kuwahara
authors.forename: T
authors.initials: T
authors.lastname: Matsuo
authors.forename: J
authors.initials: J
authors.lastname: Nomura
authors.forename: H
authors.initials: H
authors.lastname: Igarashi
authors.forename: M
authors.initials: M
authors.lastname: Kimoto
authors.forename: S
authors.initials: S
authors.lastname: Inui
authors.forename: N
authors.initials: N
authors.lastname: Sakaguchi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D015703:Antigens, CD; D051925:CD79 Antigens; D008562:Membrane Glycoproteins / Q000032:analysis / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011947:Receptors, Antigen, B-Cell / Q000032:analysis / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D051925:CD79 Antigens; C497882:Cd79a protein, mouse; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell; D011505:Protein-Tyrosine Kinases; D013755:Tetradecanoylphorbol Acetate