F₂(Pmp)₂-TAMζ₃, a novel competitive inhibitor of the binding of 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-residue tyrosine-based activation motifs (TAM) present in the cytoplasmic tails of the TCRζ and CD3 chains. TAMs become tyrosine-phosphorylated upon TCR stimulation, creating a high affinity binding site for the tandem SH2 domains of ZAP-70. In permeabilized T cells, the association of TCR and ZAP-70 was inhibited by a protein tyrosine phosphatase (PTPase)-resistant TAM peptide analog, in which difluorophosphonomethyl phenylalanyl (F₂Pmp) residues replaced phosphotyrosine. Inhibition of this association prevented TCR- stimulated tyrosine phosphorylation of ZAP-70 and reduced ZAP-70 kinase activity to basal levels. The reduction in ZAP-70 activity coincided with reduced tyrosine phosphorylation of a number of substrates. Such PTPase- resistant peptides, capable of 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 for the treatment of autoimmune and neoplastic disorders.