Role of Src in the modulation of multiple adaptor proteins in FcαRI oxidant signaling

Cross-linking of Fc receptors for IgA, Fc alpha R (CD89), on monocytes/macrophages is known to enhance phagocytic activity and generation of oxygen free radicals. We provide evidence here that the Fc alpha R signals through the gamma subunit of Fc epsilon RI in U937 cells differentiated with interferon gamma (IFN gamma). Our results provide the first evidence that Fc alpha R-mediated signals modulate a multimolecular adaptor protein complex containing Grb2, She, SHIP, CrkL, Cbl, and SLP-76. Cross-linking of Fc alpha RI using anti-Fc alpha RI induces the phosphorylation of the gamma subunit as detected by mobility retardation on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Stimulation of Fc alpha RI induced the tyrosine phosphorylation of She and increased the association of Grb2 with She and CrkL. Grb2 associates constitutively with Sos, and the latter undergoes mobility shift upon Fc alpha RI stimulation. The complex adapter proteins, Cbl and SLP-76, are physically associated in myeloid cells and both proteins undergo tyrosine phosphorylation upon Fc alpha R stimulation. These data indicate that the stimulation of Fc alpha R results in the modulation of adaptor complexes containing tyrosine-phosphorylated Cbl, Shc, SHIP, Grb2, and Crkl. Experiments performed with the Src kinase inhibitor, PP1, provide the first evidence that Src kinase activation is required for Fc alpha RI-induced production of superoxide anions and provide insight into the mechanism for Fc alpha R-mediated activation of downstream oxidant signaling in myeloid cells. (C) 1999 by The American Society of Hematology.