Role of SHIP in FcgammaRIIb-mediated inhibition of Ras activation in B cells.
Previous studies by our lab and others established that co-crosslinking sIg and IgG receptor FcgammaRIIb in B cells in a feedback suppression model (negative signaling) promoted tyrosine phosphorylation of the inositol 5-phosphatase SHIP and its interaction with Shc and that these events were associated with inhibition of the Ras pathway. We therefore hypothesized a competition model in which the SH2 domain of SHIP competes with that of Grb2 for binding to phospho-Shc to inhibit the Ras pathway. Here, we provide evidence consistent with this hypothesis. First, FcgammaRIIb-deficient B cells, which do not undergo SHIP tyrosine phosphorylation nor interaction with Shc, displayed an active Ras pathway under negative signaling conditions; reconstitution of FcgammaRIIb expression restored the block in Ras. Second, under conditions of negative signaling leading to SHIP-Shc interaction in wild-type B cells, we observed a profound reduction in the activation-induced association of Grb2 to Sos. Experiments reported here and elsewhere revealed the Grb2-Sos interaction required the engagement of the Grb2 SH2 domain by phospho-Shc. Third, we demonstrated that phospho-Shc cannot concomitantly bind Grb2 and SHIP, indicating that the two proteins competed for the same phospho-tyrosine residue on Shc. These data are consistent with the proposed competition model, and further indicate that the activation induced Grb2-Sos association is rate limiting for Ras activation.
Ohio State University, Department of Microbiology and the Comprehensive Cancer Center, Columbus 43210, USA.
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Tridandapani
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Phee
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Shivakumar
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Kelley
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Coggeshall
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D001402:B-Lymphocytes / Q000276:immunology*; D051380:GRB2 Adaptor Protein; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D018448:Models, Immunological; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism; D017452:Receptors, IgG / Q000378:metabolism*; D015398:Signal Transduction; D020664:Son of Sevenless Proteins; D018631:ras Proteins / Q000378:metabolism*; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D015703:Antigens, CD; C080571:Fc gamma receptor IIB; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D008565:Membrane Proteins; D011506:Proteins; D017452:Receptors, IgG; D020664:Son of Sevenless Proteins; D010744:Phosphoric Monoester Hydrolases; C098706:INPPL1 protein, human; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D018631:ras Proteins