TYROSINE PHOSPHORYLATION OF THE CD3-EPSILON SUBUNIT OF THE T-CELL ANTIGEN RECEPTOR MEDIATES ENHANCED ASSOCIATION WITH PHOSPHATIDYLINOSITOL 3-KINASE IN JURKAT T-CELLS

T cell receptor signaling results both in T cell. proliferation and ap optosis. A key enzyme at the intersection of these downstream pathways is phosphatidylinositol 3'-kinase (PIS-kinase). In a previous report, we showed that the p85 alpha subunit of the PI 3-kinase preferentiall y associated with the CD3-zeta membrane-proximal immuno-receptor tyros ine-based activation motif of the zeta chain (zeta A-ITAM) (Exley, M., Varticovski, L., Peter, M., Sancho, J., and Terhorst, C. (1994) J. Bi ol. Chem. 269, 15140-15146). Here, we demonstrate that tyrosine phosph oryl ation of CD3-epsilon can recruit the PI 3-kinase enzyme in a T ce ll activation-dependent manner. In vivo studies with Jurkat cells stab ly transfected with a CD8-CD3-epsilon chimera (termed CD8-epsilon) sho ws that ligation of endogenous CD3-epsilon or CD8-epsilon by specific antibodies induces tyrosine phosphorylation of CD3-epsilon or CD8-epsi lon, respectively. Increased tyrosine phosphorylation correlates with increased binding of p85 alpha PI S-kinase and recruitment of PI S-kin ase enzymatic activity to CD3-epsilon or CD8-epsilon proteins. Mutagen esis studies in COS-7 cells, transiently transfected with CD8-epsilon, p85 alpha, and Fyn cDNAs in various combinations, show that both Tyr( 170) and Tyr(181) within the CD3-epsilon-ITAM are required for efficie nt binding of p85 alpha PI 3-kinase. Thus, replacement of Tyr(170) by Phe (Y170F), or Tyr(181) by Phe (Y181F) significantly reduces binding of p85 alpha PI 3-kinase, whereas it does not affect binding of Fyn. F urther in vitro experiments suggest that a direct binding of the tande m SH2 domains of p85 alpha PI 3-kinase to the two phosphorylated tyros ines in a single CD3-epsilon-ITAM may occur, The data also support a m odel in which a single CD3 subunit can recruit distinct effector molec ules by means of TCR-mediated differential ITAM phosphorylation.