Role for Src kinases in FcRI oxidant signaling in myeloid cells. The Src family kinase inhibitor, PP1, was used to determine the role of Src kinases in phosphorylation of Shc, Shc-adaptor protein interactions, and FcR-induced superoxide response. Shc was immunoprecipitated from resting (lane 2) or FcRI-stimulated U937IF cells (lanes 3 through 6). U937IF cells were preincubated at 37°C with 1 μmol/L PP1 (lane 4), 5 μmol/L PP1 (lane 5), or 10 μmol/L PP1 (lane 6). Lanes 1 through 3 represent immunoprecipitations performed on U937IF cells treated with DMSO (D) at 5 μg/mL. Lane 7 represents a whole cell lysate of U937IF cells. Lane 1 represents a preimmune immunoprecipitation. Membranes were probed with (A) antiphosphotyrosine antibody, (B) anti-Sos immunoblot, (C) anti-SHIP immunoblot, (D) anti-Shc immunoblot, or (E) anti-Grb2 immunoblot. (F) Effects of PP1 on FcRI-induced respiratory burst response. Data shown are the means and the standard deviation of triplicate samples in each experimental group (see legend).