THE LCK SH2 PHOSPHOTYROSINE BINDING-SITE IS CRITICAL FOR EFFICIENT TCR-INDUCED PROCESSIVE TYROSINE PHOSPHORYLATION OF THE ZETA-CHAIN AND IL-2 PRODUCTION

The lymphocyte-specific tyrosine kinase Lck is essential for TCR-media ted signal transduction. This is in part due to its enzymatic activity as a tyrosine kinase responsible for TCR-induced tyrosine phosphoryla tion of zeta and CD3 receptor subunits. In addition to its catalytic d omain, the Lck protein contains SH3 and SH2 domains capable of associa ting with other signaling molecules. It has been proposed that phospho tyrosine binding by the Lck SH2 domain may enhance substrate tyrosine phosphorylation by facilitating the processive phosphorylation of mult iple sites within the TCR complex, Alternatively or additionally, it m ay function in adapter activity for facilitating required protein-prot ein interactions. Previous experiments demonstrate that overexpression of a constitutively activated form of Lck (F505) in the BI-141 T cell hybridoma leads to the Lck kinase activity-dependent enhancement of T CR-mediated signals, Here we demonstrate that mutation of amino acids important for SH2 phosphotyrosine binding significantly compromises th e ability of F505 to enhance TCR-mediated protein tyrosine phosphoryla tion and Ag-induced IL-2 production in BI-141. Examination of the effe cts of TCR-regulated phosphorylation of the Lck substrate zeta provide s in vivo evidence for a role for the Lck SH2 domain in the processive phosphorylation of a multiply phosphorylated substrate.