Coupling of GTP-binding to the T cell receptor (TCR) zeta-chain with TCR-mediated signal transduction.

The zeta-subunit of the TCR binds GTP and is a well characterized substrate for a TCR-activated tyrosine kinase. To examine the possible coupling of GTP-binding to zeta with TCR-mediated signal transduction, a mutant (termed J32-3.2) of the T cell line Jurkat (J32) was used. Anti-TCR/CD3 stimulation of the TCR/CD3+ J32-3.2 cells resulted in a weak stimulation of both the phosphatidyl inositol and tyrosine kinase signal transduction pathways, as measured by changes in the level of free intracellular calcium, tyrosine phosphorylation of TCR-zeta, CD3-epsilon and ZAP-70, p56lck, or p59fyn tyrosine kinase activity and IL-2 gene activation. The impaired responsiveness of J32-3.2 cells to anti-TCR/CD3 mAb correlated with a low basal level of GTP-binding to zeta. Furthermore, in J32-3.2 cells TCR activation by antibody ligation caused a weaker increase in GTP-binding to the zeta-chain, as compared with that of wild-type J32 cells, which indicates for the first time that GTP-binding to zeta can be modulated by extracellular signals and suggest that the role of GTP-binding to zeta is to couple the TCR to intracellular signal transduction mechanisms.