T-CELL RECEPTOR (TCR) ENGAGEMENT IN APOPTOSIS-DEFECTIVE, BUT INTERLEUKIN-2 (IL-2)-PRODUCING, T-CELLS RESULTS IN IMPAIRED ZAP70 CD3-ZETA ASSOCIATION/

We have previously shown that a tyrosine to leucine replacement in the transmembrane region of T cell receptor (TCR)-beta results in a defic ient induction of CD95-L aid apoptosis upon TCR triggering in a transf ected T cell line. By contrast, interleukin (IL)-2 production and the expression of CD25 and CD69 were normally induced. Since the mutation in TCR-beta also resulted in impaired association of CD3-zeta, it was proposed that this chain is specifically required for die induction of apoptosis. We now show that the deficient induction of CD95-L and apo ptosis does not derive from a general lower production of second messe ngers, since intracellular Ca2+ fluxes and tyrosine phosphorylation of total proteins were elicited at wild-type levels. Unlike in T cell cr ones stimulated with partial agonists, both p21 and p18 forms of tyros ine-phosphorylated CD3-zeta were detected, although the overall level of tyrosine-phosphorylated CD3-zeta was low. More strikingly, inducibl e association of ZAP70 to CD3-zeta was strongly inhibited, despite a n ormal induction of ZAP70 tyrosine phosphorylation. Finally, ZAP70 was not concentrated near the plasma membrane ill the apoptosis-deficient cells. These results suggest that CD3-zeta is necessary for engagement of a specific signaling pathway leading to CD95-L expression that als o needs the recruitment of ZAP70.