title: Tyrosine kinase and CD45 tyrosine phosphatase activity mediate p21ras activation in B cells stimulated through the antigen receptor.
abstract: Cross-linking of the Ag receptor (AgR) induces intracellular signaling events in B cells, such as p21ras activation, that lead to their proliferation and differentiation. This event is accompanied by the tyrosine phosphorylation of the p21ras-associated GTPase-activating protein p120 ras.GAP, raising the possibility that AgR-stimulated p21ras activity is regulated by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPases) in B cells. To test this possibility, we examined the effects of PTK and PTPase inhibitors on protein tyrosine phosphorylation and p21ras activation induced by AgR cross-linking in TNP-specific TA3 7.9 murine B lymphoma cells. Although AgR-induced protein tyrosine phosphorylation was inhibited by the PTK inhibitors genistein and herbimycin A, it was enhanced by exposure to the PTPase inhibitor phenylarsine oxide (PAO). Cross-linking of the AgR by Ag or F(ab')2 anti-IgM induced a rapid (within 5 min) two- to threefold increase in p21ras activation in 7.9 B cells. Interestingly, a second peak of p21ras activation was evident at approximately 40 min after stimulation. Genistein and herbimycin A and PAO each blocked AgR-stimulated p21ras activation. Similarly, Ag-induced p21ras activation was inhibited by pretreatment of 7.9 B cells with an anti-CD45 mAb (detects the 220-kDa B cell isoform of CD45). Moreover, p21ras activation was induced by Ag and F(ab')2 anti-IgM in CD45+ but not CD45- J558L microns 3 B cells. These data indicate that p21ras activation induced by AgR cross-linking in B cells is regulated by both PTK and CD45 PTPase activities.
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: M J
authors.initials: MJ
authors.lastname: Rapoport
authors.forename: A
authors.initials: A
authors.lastname: Harwood
authors.forename: J C
authors.initials: JC
authors.lastname: Cambier
authors.forename: T L
authors.initials: TL
authors.lastname: Delovitch
mesh_terms: D000818:Animals; D000941:Antigens / Q000276:immunology; D001402:B-Lymphocytes / Q000502:physiology*; D002460:Cell Line; D004789:Enzyme Activation; D017493:Leukocyte Common Antigens / Q000378:metabolism*; D051379:Mice; D010047:Ovalbumin / Q000276:immunology; D019000:Phosphotyrosine; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000502:physiology
chemical_list: D000941:Antigens; D011947:Receptors, Antigen, B-Cell; D019000:Phosphotyrosine; D014443:Tyrosine; D010047:Ovalbumin; D011505:Protein-Tyrosine Kinases; D017493:Leukocyte Common Antigens; D017027:Protein Tyrosine Phosphatases; D016283:Proto-Oncogene Proteins p21(ras)