title: Regulation of BCR- and PKC/Ca(2+)-mediated activation of the Raf1/MEK/MAPK pathway by protein-tyrosine kinase and -tyrosine phosphatase activities.
abstract: Ligation of the B cell Ag receptor (BCR) activates a protein-tyrosine kinase (PTK) and CD45 protein-tyrosine phosphatase (PTPase)-dependent signaling cascade that results in the activation of Ras. This pathway of Ras activation can operate independently of protein kinase C (PKC) activity. Activation of Ras may lead to two distinct Ras-dependent pathways involving either a Raf1/MEK/MAPK module or a MEKK/SEK/SAPK module; however, it is unclear as to how Ras controls the independent activation of either of these pathways. We have used genistein and phenylarsine oxide (PAO) as inhibitors of PTK and PTPase, respectively, to investigate whether they regulate the BCR- and Ca2+/PKC-dependent activation of the Ras/Raf1/MEK/MAPK module. Assays of phosphotransferase activities conducted with Ag (TNP6-OVA)-specific 7.9 murine B lymphoma cells demonstrated that BCR-mediated stimulation of the Raf1/MEK/MAPK module is controlled by PTK and PTPase activities. An elevation in [Ca2+]i was required to optimally activate Raf1 and MEK through the BCR. However, when signaling through the BCR was bypassed by direct stimulation of the Raf1/MEK/MAPK module via a rise in [Ca2+]i and phorbol ester-induced PKC activation, the phosphotransferase activities of Raf1, MEK and MAPK were still regulated in a PTK-dependent manner that was also partially sensitive to the PTPase inhibitor PAO. Thus, at least two alternate routes, i.e. a BCR/PTK/Ras-dependent route and another PKC/Ca(2+)-dependent route, may converge at the level of Raf1 for activation of the Raf1/MEK/MAPK module in B cells.
authors.affiliation: Banting and Best Department of Medical Research, University of Toronto, Ontario, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Kawauchi
authors.forename: A H
authors.initials: AH
authors.lastname: Lazarus
authors.forename: J S
authors.initials: JS
authors.lastname: Sanghera
authors.forename: G L
authors.initials: GL
authors.lastname: Man
authors.forename: S L
authors.initials: SL
authors.lastname: Pelech
authors.forename: T L
authors.initials: TL
authors.lastname: Delovitch
mesh_terms: D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D008024:Ligands; D048369:MAP Kinase Kinase 1; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D011493:Protein Kinase C / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism* / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism* / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000888:Antibodies, Anti-Idiotypic; D007075:Immunoglobulin M; D008024:Ligands; D011518:Proto-Oncogene Proteins; D011947:Receptors, Antigen, B-Cell; C044203:anti-IgM; D015759:Ionomycin; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D017027:Protein Tyrosine Phosphatases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium