Induction of hyperphosphorylation and activation of the p56 lck protein tyrosine kinase by phenylarsine oxide, a phosphotyrosine phosphatase inhibitor

Abstract

The T cell protein tyrosine kinase p56 lck is implicated in thymic development and mitogenic activation of T lymphocytes, and is itself regulated by reversible tyrosine phosphorylation. When phenylarsine oxide (PAO), a membrane-permeable inhibitor of phosphotyrosine phosphatases, was added to Jurkat T leukemia or LSTRA thymoma cells, the phosphate content of p56 lck increased rapidly. The sites of increased phosphorylation were mapped to Tyr-192, Tyr-394 and Tyr-505. Hyperphosphorylated p56 lck displayed retarded mobility on SDS gels, unaltered or marginally increased cytoskeletal association, and its catalytic activity changed in a biphasic manner; during the first 10–20 min of PAO-treatment the activity increased and then it declined to very low values within 1–2 hr. Our data suggest that p56 lck contains both positive and negative regulatory sites which are constantly dephosphorylated at an unexpectedly high rate by cellular phosphotyrosine phosphatases.