Tyrosine phosphatase antagonist-induced activation of the neutrophil NADPH oxidase: a possible role for protein kinase C.

To investigate the role of tyrosine phosphorylation in polymorphonuclear leucocyte (PMN) activation we have examined the effect of the potent tyrosine phosphatase (PTPase) inhibitor, vanadyl hydroperoxide, on PMN function. Western blotting of vanadyl hydroperoxide-treated PMN showed that there was a rapid dose-dependent increase in tyrosine-phosphorylated proteins. Vanadyl hydroperoxide also induced superoxide production in PMN over the range 10-100 microM, similar to the concentrations that also induced tyrosine phosphorylation. The tyrosine kinase inhibitor erbstatin totally inhibited the respiratory burst induced by vandyl hydroperoxide, showing that tyrosine kinase activity was necessary for superoxide production. The protein kinase C (PKC) inhibitors chelerythrine and bisidolylmaleimide inhibited the vanadyl hydroperoxide-induced respiratory burst with an inhibitory concentration of 50% (IC50) close to that for PKC inhibition without affecting tyrosine phosphorylation. These results indicate a possible role for PKC in vanadyl hydroperoxide-mediated superoxide production, and that any PKC involvement is downstream of tyrosine phosphorylation. These results further demonstrate that inhibition of phosphotyrosine phosphatases results in the activation of a functional response, indicating a critical role for phosphotyrosine phosphatases in PMN stimulation.