Functional activation of the T-cell antigen receptor induces tyrosine phosphorylation of phospholipase C-γ1
Stimulation of the T-cell antigen receptor (TCR), which itself is not a protein-tyrosine kinase (PTK), activates a PTK and phospholipase C (PLC). Using the human T-cell leukemic line Jurkat and normal peripheral blood lymphocytes, we demonstrate that stimulation of the TCR specifically induces the recovery of PLC activity in eluates from anti-phosphotyrosine immunoprecipitates. Stimulation of the human muscarinic receptor, subtype 1, when expressed in Jurkat activates PLC through a guanine nucleotide binding protein but does not induce the recovery of PLC activity in eluates from anti-phosphotyrosine immunoprecipitates. Western blot analysis reveals that PLC-gamma 1 is tyrosine-phosphorylated in response to TCR stimulation. Nearly all of the PLC activity recovered in eluates from anti-phosphotyrosine immunoprecipitates was depleted by anti-PLC-gamma 1 antibodies. Stimulation of the TCR on mutants derived from Jurkat that are defective in TCR-induced PLC activation results in markedly reduced, if any, PLC activity recovered in phosphotyrosine immunoprecipitates and in no detectable PLC-gamma 1 tyrosine phosphorylation. Thus, the TCR functions like PTK growth factor receptors, but through an indirect interaction, to induce tyrosine phosphorylation of PLC-gamma 1. Since other studies have implicated two members of the src family of PTKs in TCR-mediated signal transduction, our findings suggest that the induction of tyrosine phosphorylation of PLC-gamma 1 by a mechanism involving a src-like kinase may be the means by which the TCR regulates PLC activity in T cells.