THE AMINO-TERMINAL SRC HOMOLOGY-2 DOMAIN OF PHOSPHOLIPASE C-GAMMA-1 IS ESSENTIAL FOR TCR-INDUCED TYROSINE PHOSPHORYLATION OF PHOSPHOLIPASE C-GAMMA-1

TCR engagement activates phospholipase C gamma 1 (PLC gamma 1) via a t yrosine phosphorylation-dependent mechanism. PLC gamma 1 contains a pa ir of Src homology 2 (SH2) domains whose function is that of promoting protein interactions by binding phosphorylated tyrosine and adjacent amino acids, The role of the PLC gamma 1 SH2 domains in PLC gamma 1 ph osphorylation was explored by mutational analysis of an epitope-tagged protein transiently expressed in Jurkat T cells. Mutation of the amin o-terminal SH2 domain (SH2(N) domain) resulted in defective tyrosine p hosphorylation of PLC gamma 1 in response to TCR/CD3 perturbation. In addition, the PLC gamma 1 SH2(N) domain mutant failed to associate wit h Grb2 and a 36- to 38-kDa phosphoprotein (p36-38), which has previous ly been recognized to interact with PLC gamma 1, Grb2, and other molec ules involved in TCR signal transduction. Conversely, mutation of the carboxyl-terminal SH2 domain (SH2(C) domain) did not affect TCR-induce d tyrosine phosphorylation of PLC gamma 1. Furthermore, binding of p36 -38 to PLC gamma 1 was not abrogated by mutations of the SH2(C) domain . In contrast to TCR/CD3 Ligation, treatment of cells with pervanadate induced tyrosine phosphorylation of either PLC gamma 1 SH2(N) or SH2( C) domain mutants to a level comparable with that of the mild-type pro tein, indicating that pervanadate treatment induces an alternate mecha nism of PLC gamma 1 phosphorylation, These data indicate that the SH2( N) domain is required for TCR-induced PLC gamma 1 phosphorylation, pre sumably by participating in the formation of a complex that promotes t he association of PLC gamma 1 with a tyrosine kinase.