A role for Shc, Grb2, and Raf-1 in FcgammaRI signal relay.
The activation of the serine/threonine kinase, Raf-1, serves to connect upstream protein tyrosine kinases to downstream signaling events. We previously reported that FcgammaRI stimulation of interferon gamma-differentiated U937 cells (termed U937IF cells) induces a mobility shift in Erk2. Herein, we report that cross-linking of FcgammaRI receptor in U937IF cells induces a marked tyrosine phosphorylation of Raf-1 (10-fold increase). Tyrosine phosphorylation of Raf-1 is induced by FcgammaRI activation and not by PMA (1 microg/ml), N-formyl-Met-Leu-Phe (1 microM), calcium ionophore (1 microM), thrombin (0.05 unit/ml), FcgammaRII, or FcgammaRIII stimulation. The kinetics of Raf-1 tyrosine phosphorylation is rapid, reaching peak levels 1-2 min after FcgammaRI activation, and the tyrosine phosphorylation of Raf-1 precedes the activation of the respiratory burst. FcgammaRI cross-linking induces the tyrosine phosphorylation of Shc; tyrosine-phosphorylated Shc binds to Grb2 forming a Shc-Grb2 complex. The data provide evidence that the FcgammaRI receptor signals via the upstream activation of nonreceptor protein tyrosine kinases, which leads to the subsequent activation of Ras family GTPases and serine/threonine kinases, Raf-1 and mitogen-activated protein kinase.
Park
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RK
Neil Bogart Memorial Laboratories, Division of Hematology-Oncology, Childrens Hospital Los Angeles and University of Southern California School of Medicine, Los Angeles, California 90027, USA.
Liu
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Y
Durden
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D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D051380:GRB2 Adaptor Protein; D006801:Humans; D007700:Kinetics; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D017452:Receptors, IgG / Q000235:genetics / Q000378:metabolism*; D016897:Respiratory Burst; D015398:Signal Transduction / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495949:Grb2 protein, mouse; D011506:Proteins; D011518:Proto-Oncogene Proteins; D017452:Receptors, IgG; D014443:Tyrosine; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1