Oxidative stress triggers STAT3 tyrosine phosphorylation and nuclear translocation in human lymphocytes

Oxidizing agents are powerful activators of factors responsible for the tra nscriptional activation of cytokine-encoding genes involved in tissue injur y. In this study we show evidence that STAT3 is a transcription factor whos e activity is modulated by H2O2 in human lymphocytes, in which endogenous c atalase had previously been inhibited. H2O2-induced nuclear translocation o f STAT3 to form sequence-specific DNA-bound complexes was evidenced by immu noblotting of nuclear fractions and electrophoretic mobility shift assays, and vanadate was found to strongly synergize with H2O2. Moreover, anti-STAT 3 antibodies specifically precipitated a protein of 92 kDa that becomes pho sphorylated on tyrosine upon lymphocyte treatment with H2O2. Phenylarsine o xide, a tyrosine phosphatase inhibitor, and genistein, a tyrosine kinase in hibitor, cooperated and cancelled, respectively, the H2O2-promoted STAT3 nu clear translocation, Evidence is also presented, using Fe2+/Cu2+ ions, that 'OH generated from H2O2 through Fenton reactions could be a candidate oxyg en reactive species to directly activate STAT3, Present data suggest that H 2O2 and vanadate are likely to inhibit the activity of intracellular tyrosi ne phosphatase(s), leading to enhanced STAT3 tyrosine phosphorylation and h ence its translocation to the nucleus, These results demonstrate that the D NA binding activity of STAT3 can be modulated by oxidizing agents and provi de a framework to understand the effects of oxidative stress on the JAK-STA T signaling pathway.