F-2(PMP)(2)-TAM-ZETA(3), A NOVEL COMPETITIVE INHIBITOR OF THE BINDINGOF ZAP-70 TO THE T-CELL ANTIGEN RECEPTOR, BLOCKS EARLY T-CELL SIGNALING

Signaling by the T cell antigen receptor (TCR) is mediated by 17-resid ue tyrosine-based activation motifs (TAM) present in the cytoplasmic t ails of the TCR zeta and CD3 chains. TAMs become tyrosine-phosphorylat ed upon TCR stimulation, creating a high affinity binding site for the tandem SH2 domains of ZAP-70. In permeabilized T cells, the associati on of TCR and ZAP-70 was inhibited by a protein tyrosine phosphatase ( PTPase)resistant TAM peptide analog, in which difluorophosphonomethyl phenylalanyl (F(2)Pmp) residues replaced phosphotyrosine. Inhibition o f this association prevented TCR-stimulated tyrosine phosphorylation o f ZAP-70 and reduced ZAP-70 kinase activity to basal levels. The reduc tion in ZAP-70 activity coincided with reduced tyrosine phosphorylatio n of a number of substrates. Such PTPase-resistant peptides, capable o f disrupting SH2 domain-mediated protein-protein interactions, should prove useful in further dissection of multiple signaling pathways and may serve as models for rationally designed chemotherapeutic agents fo r the treatment of autoimmune and neoplastic disorders.