LIGATION OF THE T-CELL ANTIGEN RECEPTOR (TCR) INDUCES ASSOCIATION OF HSOS1, ZAP-70, PHOSPHOLIPASE C-GAMMA-1, AND OTHER PHOSPHOPROTEINS WITH GRB2 AND THE ZETA-CHAIN OF THE TCR

Signaling by the T-cell antigen receptor (TCR) involves both phospholipase C (PLC)-gamma 1 and p21(ras) activation. While failing to induce Shc/Grb2 association, ligation of the TCR/CDS receptor in Jurkat T-cells induced hSos1-Grb2 complexes. In addition to hSos1, Grb2 participates in the formation of a tyrosine phosphoprotein complex that includes 145-, 95-, 70-, 54-, and 36-38 kDa proteins. p145 was identified as PLC-gamma 1 and p70 as the protein tyrosine kinase, ZAP-70. Although of the same molecular weight, p95 was not recognized by an antiserum to p95 Vav. The SH2 domains of Grb2 and PLC-gamma 2 were required for the formation of this protein complex. In anti-CD3-treated cells, Grb2 redistributed from the cytosol to a particulate cell compartment along with p36/p38, ZAP-70, and PLC-gamma 1. Part of the Grb2 complex associated with the particulate compartment could be extracted with Nonidet P-40, while the rest was Nonidet P-40 insoluble. In both the detergent-soluble and -insoluble fractions, Grb2 coimmunoprecipitated with the zeta chain of the TCR. Taken together, these results indicate that anti-CDS induces Grb2-hSos1-PLC-gamma 1-p36/p38-ZAP70 complexes, which localize in the vicinity of TCR-zeta.