Oxidative Stress Triggers STAT3 Tyrosine Phosphorylation and Nuclear Translocation in Human Lymphocytes

Oxidizing agents are powerful activators of factors responsible for the transcriptional activation of cytokine-encoding genes involved in tissue injury. In this study we show evidence that STAT3 is a transcription factor whose activity is modulated by H 2 O 2 in human lymphocytes, in which endogenous catalase had previously been inhibited. H 2 O 2 -induced nuclear translocation of STAT3 to form sequence-specific DNA-bound complexes was evidenced by immunoblotting of nuclear fractions and electrophoretic mobility shift assays, and vanadate was found to strongly synergize with H 2 O 2 . Moreover, anti-STAT3 antibodies specifically precipitated a protein of 92 kDa that becomes phosphorylated on tyrosine upon lymphocyte treatment with H 2 O 2 . Phenylarsine oxide, a tyrosine phosphatase inhibitor, and genistein, a tyrosine kinase inhibitor, cooperated and cancelled, respectively, the H 2 O 2 -promoted STAT3 nuclear translocation. Evidence is also presented, using Fe 2+ /Cu 2+ ions, that ⋠OH generated from H 2 O 2 through Fenton reactions could be a candidate oxygen reactive species to directly activate STAT3. Present data suggest that H 2 O 2 and vanadate are likely to inhibit the activity of intracellular tyrosine phosphatase(s), leading to enhanced STAT3 tyrosine phosphorylation and hence its translocation to the nucleus. These results demonstrate that the DNA binding activity of STAT3 can be modulated by oxidizing agents and provide a framework to understand the effects of oxidative stress on the JAK-STAT signaling pathway.