title: Role of Syk in Fc gamma receptor-coupled tyrosine phosphorylation of Cbl in a manner susceptible to inhibition by protein kinase C.
abstract: Fcgamma receptors (FcgammaR) of guinea pig neutrophils were ligated and anti-Cbl immunoprecipitates prepared therefrom were assayed for the associated protein tyrosine kinase activity, which increased upon ligation of FcgammaR. The increases were overcome upon activation of cellular protein kinase C by simultaneous addition of phorbol 12-myristate 13-acetate (PMA) to the ligated cells. Syk proved to be the most important tyrosine kinase bound to Cbl that served as the major substrate; essentially no tyrosine phosphorylation occurred in the anti-Cbl immunoprecipitates prepared from the cell lysate that had been depleted of Syk by prior immunoprecipitation with anti-Syk antibodies. Exposure of the (32)P-labeled cells to PMA resulted in phosphorylation of cellular Cbl on serine residues. Thus, protein kinase C-induced serine phosphorylation of Cbl suppressed its tyrosine phosphorylation by Syk as a result of tyrosine kinase inhibition by unknown mechanisms, leading to inhibition of Cbl-mediated signaling such as phosphatidylinositol 3-kinase activation.
authors.affiliation: The Ui Laboratory Institute of Physical and Chemical Research, Wako-shi, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hazeki
authors.forename: O
authors.initials: O
authors.lastname: Hazeki
authors.forename: T
authors.initials: T
authors.lastname: Matsuo
authors.forename: T
authors.initials: T
authors.lastname: Seya
authors.forename: T
authors.initials: T
authors.lastname: Yamashita
authors.forename: S
authors.initials: S
authors.lastname: Nagasawa
authors.forename: H
authors.initials: H
authors.lastname: Band
authors.forename: M
authors.initials: M
authors.lastname: Ui
mesh_terms: D000818:Animals; D004792:Enzyme Precursors / Q000037:antagonists & inhibitors* / Q000502:physiology*; D006168:Guinea Pigs; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology*; D050721:Proto-Oncogene Proteins c-cbl; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D017452:Receptors, IgG / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D000072377:Syk Kinase; D013755:Tetradecanoylphorbol Acetate / Q000031:analogs & derivatives / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases
chemical_list: D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; D017452:Receptors, IgG; D012694:Serine; C016658:phorbolol myristate acetate; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D011493:Protein Kinase C; C067419:CBL protein, human; D013755:Tetradecanoylphorbol Acetate