Stimulatory effects of the protein tyrosine phosphatase inhibitor, pervanadate, on T-cell activation events

Ligation of the multimeric T-cell antigen receptor complex (TCR) triggers a pleiotropic cellular activation response that includes lymphokine secretion, cell-cycle progression, and ultimately, T-cell proliferation. The earliest detectable biochemical event triggered by TCR cross-linkage is the tyrosine phosphorylation of specific intracellular proteins, which, in turn, propagate receptor-mediated signals into the cytoplasm and nucleus. In this study, we have examined the effects of pervanadate, a powerful inhibitor of protein tyrosine phosphatases (PTP), on the activation state of the human leukemic T-cell line, Jurkat. Treatment of Jurkat cells with pervanadate rapidly induced a series of proximal T-cell activation events that closely resembled those induced by TCR-dependent stimuli. Moreover, pervanadate treatment, like TCR cross-linkage, stimulated interleukin-2 production in wild-type Jurkat cells, indicating that the biochemical events initiated by this TCR-independent stimulus were sufficient to induce lymphokine gene expression. Exposure of intact cells to pervanadate also stimulated the in vitro catalytic activities of both p59fyn and p56lck, src family kinases strongly implicated in TCR-mediated signaling. The stimulatory effects of pervanadate on protein tyrosine kinase-mediated signaling events were accompanied by a marked inhibition of CD45-associated PTP activity. However, the ability of pervanadate to stimulate tyrosine phosphorylation in CD45-negative Jurkat cells suggests that PTPs other than CD45 are important intracellular targets for pervanadate. These studies demonstrate that inhibition of PTP activities in Jurkat cells leads to a T-cell activation response that is remarkably similar to that induced by TCR crosslinkage.