Activation and tyrosine phosphorylation of p72^syk as well as calcium mobilization after hydrogen peroxide stimulation in peripheral blood lymphocytes

To determine the regulatory role of p72syk in lymphocyte activation, peripheral blood lymphocytes were treated with 10 mM hydrogen peroxide. Hydrogen peroxide induced a rapid elevation of p72syk activity (4-6-fold) and a dramatic increase in tyrosine phosphorylation of a number of cellular proteins, including phospholipase C gamma 1 (PLC gamma 1) and p72syk. Monoclonal antibodies to PLC gamma 1 co-precipitated p72syk from hydrogen peroxide-stimulated cell lysates, but not from unstimulated cell lysates. Furthermore, we observed a rise in intracellular Ca2+, corresponding to the combination of extracellular Ca2+ influx and the release from intracellular Ca2+ stores. Extracellular Ca2+ influx was necessary for the sustenance of p72syk activity, but not for the initiation of p72syk activation induced by hydrogen peroxide. Taken together, these data suggested that one possible role of p72syk was to activate PLC gamma 1, at least in part through tyrosine phosphorylation, and then to trigger calcium mobilization in pig peripheral blood lymphocytes in response to hydrogen peroxide stimulation.