A TYROSINE-PHOSPHORYLATED 110-120-KDA PROTEIN ASSOCIATES WITH THE C-TERMINAL SH2 DOMAIN OF PHOSPHOTYROSINE PHOSPHATASE-1D IN T-CELL RECEPTOR-STIMULATED T-CELLS

The role of cytosolic phosphotyrosine phosphatases (PTPase) in T cell receptor (TCR)-mediated signaling was investigated. PTPase activity wa s detected in a purified immunocomplex comprising aggregated TCR from the cell surface of Jurkat T cells. Since TCR aggregation results in p hosphorylation of critical immunoreceptor tyrosine-based activation mo ths (ITAM) in the TCR zeta chain, a doubly tyrosine-phosphorylated syn thetic peptide containing the membrane-proximal zeta chain ITAM (zeta p ITAM) was used to characterize TCR zeta-associated PTPases. PTPase a ctivity was detected in stable association with zeta p ITAM and the SH 2 domain-containing PTPase PTP-1D (Syp, SH-PTP2) was identified in thi s complex. TCR stimulation resulted in increased total PTPase activity and PTP-1D protein in zeta p ITAM precipitates. TCR stimulation did n ot result in the tyrosine phosphorylation of PTP-1D but caused the rap id and transient tyrosine phosphorylation of a 110-120-kDa protein whi ch associated selectively with the C-terminal SH2 domain of PTP-1D. Th is currently unidentified phosphotyrosine protein may be involved in l ocalizing PTP-1D to the TCR following receptor stimulation.