ASSOCIATION BETWEEN MITOGEN-ACTIVATED PROTEIN-KINASE AND THE ZETA-CHAIN OF THE T-CELL RECEPTOR (TCR) WITH THE SH2,3 DOMAIN OF P56(LCK) - DIFFERENTIAL REGULATION BY TCR CROSS-LINKING

A number of protein-tyrosine kinases have been shown to be important i n T cell activation. One such kinase, Lck, has been demonstrated genet ically to be essential for T cell receptor (TcR) signaling, and the SH 2 and SH3 (src homology 2 and 3) domains of Lck have been shown to be indispensable for T cell activation. We have sought substrates with wh ich the SH2,3 domain mould interact following T cell activation using fusion proteins containing the Lck SH2 and SH3 domains linked to gluta thione S-transferase. We demonstrate that the SH2,3 region interacts s pecifically and directly with numerous tyrosine-phosphorylated molecul es following TcR cross-linking, including constitutively with mitogen- activated protein kinase (MAPK)/extracellular-regulated kinase and ind ucibly with the zeta chain of the TcR. The interaction with MAPK/extra cellular-regulated kinase was via the SH3 domain. The interaction with the tyrosine-phosphorylated zeta chain, while phosphotyrosine-depende nt, required both the SH3 and SH2 domains. These interactions were spe cific as molecules known to be tyrosine-phosphorylated following TcR c ross-linking, phospholipase C-gamma 1 and Fyn, were not bound. Thus, w e suggest that during TcR signaling, Lck interacts with numerous molec ules, including MAPK and TcR-zeta, via its SH2,3 domain. The interacti on with MAPK mould place Lck in a position to be involved in the compl ex resulting in the activation of MAPK. In addition, the binding of Lc k to the tyrosine-phosphorylated zeta chain of the TcR would serve to strengthen the interaction of the associated CD4 and the TcR complex, leading to increased avidity for the antigen-major histocompatibility protein complex.