ACTIVATION AND TYROSINE PHOSPHORYLATION OF P72(SYK) AS WELL AS CALCIUM MOBILIZATION AFTER HYDROGEN-PEROXIDE STIMULATION IN PERIPHERAL-BLOODLYMPHOCYTES

To determine the regulatory role of p72(syk) in lymphocyte activation, peripheral blood lymphocytes were treated with 10 mM hydrogen peroxid e, Hydrogen peroxide induced a rapid elevation of p72(syk) activity (4 -6-fold) and a dramatic increase in tyrosine phosphorylation of a numb er of cellular proteins, including phospholipase C gamma 1 (PLC gamma 1) and p72(syk). Monoclonal antibodies to PLC gamma 1 co-precipitated p72(syk) from hydrogen peroxide-stimulated cell lysates, but not from unstimulated cell lysates. Furthermore, we observed a rise in intracel lular Ca2+, corresponding to the combination of extracellular Ca2+ inf lux and the release from intracellular Ca2+ stores, Extracellular Ca2 influx was necessary for the sustenance of p72(syk) activity, but not for the initiation of p72(syk) activation induced by hydrogen peroxid e. Taken together, these data suggested that one possible role of p72( syk) was to activate PLC gamma 1, at least in part through tyrosine ph osphorylation, and then to trigger calcium mobilization in pig periphe ral blood lymphocytes in response to hydrogen peroxide stimulation.