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

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Abstract
The role of cytosolic phosphotyrosine phosphatases (PTPase) in T cell receptor (TCR)-mediated signaling was investigated. PTPase activity was detected in a purified immunocomplex comprising aggregated TCR from the cell surface of Jurkat T cells. Since TCR aggregation results in phosphorylation of critical immunoreceptor tyrosine-based activation motifs (ITAM) in the TCR ζ chain, a doubly tyrosine-phosphorylated synthetic peptide containing the membrane-proximal ζ chain ITAM (ζp ITAM) was used to characterize TCR ζ-associated PTPases. PTPase activity was detected in stable association with ζp ITAM and the SH2 domain-containing PTPase PTP-1D (Syp, SH-PTP2) was identified in this complex. TCR stimulation resulted in increased total PTPase activity and PTP-1D protein in ζp ITAM precipitates. TCR stimulation did not result in the tyrosine phosphorylation of PTP-1D but caused the rapid and transient tyrosine phosphorylation of a 110–120-kDa protein which associated selectively with the C-terminal SH2 domain of PTP-1D. This currently unidentified phosphotyrosine protein may be involved in localizing PTP-1D to the TCR following receptor stimulation.