Free radical stimulation of tyrosine kinase and phosphatase activity in human peripheral blood mononuclear cells

Human lymphocytes were challenged with reactive oxygen species (ROS) generated by xanthine/xanthine oxidase leading to an increase in tyrosine phosphorylation, together with an increase in tyrosine phosphatase activity. In the presence of 50 microM vanadate and xanthine/xanthine oxidase, tyrosine phosphatase activity was inhibited and a marked increase in tyrosine phosphorylation was observed. The addition of catalase abolished the increase in tyrosine phosphorylation while the addition of superoxide dismutase had no effect. This suggests that vanadate together with hydrogen peroxide derived from xanthine/xanthine oxidase activity, interact to produce an agent that is an effective inhibitor of tyrosine phosphatase activity. When human lymphocytes were challenged with xanthine/xanthine oxidase in the presence of 50 microM CuCl2, an increase in both tyrosine phosphatase and kinase activity was observed. Cupric ions inhibited xanthine oxidase activity by 84%; neither superoxide or hydroxyl radicals could be detected, but traces of hydrogen peroxide were detected in the medium. We conclude that unbound metals can interact with ROS and readily influence signalling mechanisms in human lymphocytes.