TEMPORAL REGULATION OF NONTRANSMEMBRANE PROTEIN-TYROSINE KINASE ENZYME-ACTIVITY FOLLOWING T-CELL ANTIGEN RECEPTOR ENGAGEMENT

We evaluated in Jurkat T cells the time-dependent re sponses of Fyn, L ck, Syk, and Zap following antibody-mediated cross-linking of the T ce ll antigen receptor. Our results show that the protein kinase activiti es of Fyn and Lck were activated within seconds of receptor cross-link ing. Fyn activity, as measured by autophosphorylation and tyrosine pho sphorylation of an exogenous substrate, was maximal 5 s to 1 min follo wing receptor cross-linking. Lck was also found to be activated within 5 s of antigen receptor cross-linking but differed from Fyn in that L ck activity was elevated for at least 30 min. Syk and Zap protein kina se activities were found to peak between 5 and 10 min following recept or crosslinking, returning to approximately basal activity levels by 6 0 min. The protein kinase activities of both Syk and Zap were found to parallel their reactivity in immunoblotting experiments with anti-pho sphotyrosine antibodies. Both Syk and Zap were found to associate with the tyrosine-phosphorylated zeta subunit of the T cell antigen recept or. These observations imply that T cell antigen receptor signal trans duction involves the activation of multiple members of at least two di fferent families of non-transmembrane protein tyrosine kinases.