REGULATION OF TYROSINE PHOSPHORYLATION IN ISOLATED T-CELL MEMBRANE BYINHIBITION OF PROTEIN-TYROSINE PHOSPHATASES

Jurkat T cells activated by the phosphotyrosine phosphatase inhibitors H2O2 or vanadate were found to have a similar pattern of tyrosine pho sphorylation when compared with T cells stimulated by anti-CD3 Ab cros s-linking, suggesting that protein tyrosine phosphatase (PTP) inhibito rs affect the early steps of TCR signaling. To study the role of PTPs in the most proximal membrane events of tyrosine phosphorylation, subc ellular fractions of T cells were treated with the PTP inhibitors in t he presence of ATP, In the membrane fraction, tyrosine phosphorylation of Lck, Fyn, and CD3 zeta can be induced by PTP inhibitors, but not b y anti-CD3, Detailed characterization of this cell-free system showed that the pattern and the order of induced tyrosine phosphorylation is similar to that induced in intact cells, Upon removal of the PTP inhib itor, the tyrosine-phosphorylated proteins, including Lck, Fyn, Syk, Z ap70, and CD3 zeta, are rapidly dephosphorylated. Preliminary characte rizations indicate that a PTP distinct from CD45, SHP1, and SHP2 is pr esent in T cell membranes and the inhibition of this get unidentified PTP is most likely responsible for the Lck-dependent tyrosine phosphor ylation triggered by PTP inhibitors.