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 polymorphonucle ar leucocyte (PMN) activation we have examined the effect of the poten t tyrosine phosphatase (PTPase) inhibitor, vanadyl hydroperoxide, on P MN function. Western blotting of vanadyl hydroperoxide-treated PMN sho wed that there was a rapid dose-dependent increase in tyrosine-phospho rylated proteins. Vanadyl hydroperoxide also induced superoxide produc tion in PMN over the range 10-100 mu M, similar to the concentrations that also induced tyrosine phosphorylation. The tyrosine kinase inhibi tor erbstatin totally inhibited the respiratory burst induced by vanad yl hydroperoxide, showing that tyrosine kinase activity was necessary for superoxide production. The protein kinase C (PKC) inhibitors chele rythrine and bisidolylmaleimide inhibited the vanadyl hydroperoxide-in duced respiratory burst with an inhibitory concentration of 50% (IC50) close to that for PKC inhibition without affecting tyrosine phosphory lation. These results indicate a possible role for PKC in vanadyl hydr operoxide-mediated superoxide production, and that any PKC involvement is downstream of tyrosine phosphorylation. These results further demo nstrate that inhibition of phosphotyrosine phosphatases results in the activation of a functional response, indicating a critical role for p hosphotyrosine phosphatases in PMN stimulation.