PROTEIN-TYROSINE KINASE P72(SYK) IN FC-GAMMA-RI RECEPTOR SIGNALING

In this report we show that gamma-interferon (IFN) induces the express ion of the nonreceptor protein tyrosine kinase, p72(syk), and that cro ss-linking the Fc gamma RI receptor in IFN-differentiated U937 cells ( U937IF cells) results in the activation of syk kinase. We show that sy k is tyrosine phosphorylated (12-fold increase) after Fc gamma RI cros s-linking. In vitro kinase assays demonstrate that the specific kinase activity of syk increased eightfold after Fc gamma RI cross-linking. The activation of signal transduction through the Fc gamma RI receptor , as measured by the respiratory burst, is associated with the tyrosin e phosphorylation and catalytic activation of the syk kinase. We show that syk coprecipitates with the gamma subunit of the Fc gamma RI, Fc gamma RI gamma. The data suggest that p72(syk) is involved in signal t ransduction through the Fc gamma RI receptor, involving the Fc gamma R I gamma subunit. (C) 1994 by The American Society of Hematology.