INHIBITION OF CD4 P56LCK SIGNALING BY A DOMINANT-NEGATIVE MUTANT OF THE SHC ADAPTER PROTEIN/

T-cell antigen receptor stimulation results in phosphorylation of the SH2 containing She proteins and recruitment of the Grb2/mSos complex s uggesting that She proteins are involved in transducing T-cell activat ing signals to Ras, We have measured the effects of the isolated Shc-S H2 domain and the dominant negative Ras(N17) protein on activation of the T-cell specific transcription factor NF-AT, The isolated Shc-SH2 d omain was designed to compete with endogenous She binding to upstream tyrosine phosphorylated proteins and to interfere with coupling to reg ulators of Ras activation, We have demonstrated that both the Shc-SH2 domain and the Ras(N17) protein significantly inhibited NF-AT activati on by the CD4 coreceptor and the CD4 associated tyrosine kinase p56(lc K). Tn contrast, only the Ras(N17) protein reduced NF-AT activation by the TCR/CD3 complex, Furthermore, tyrosine kinase activity and p56(lc K) protein were found in complexes immunoprecipitated with She specifi c antisera after CD4 triggering but not after CD3 triggering, These re sults indicate that both CD4 and CD3 signal to Ras and that this signa ling is mediated by independent pathways of activation of the She adap tor protein.