Redox modulation of NO-dependent induction of interleukin 8 gene in monocytic U937 cells

We have examined the effects of various antioxidants and inhibitors of redox-sensitive signal transduction pathways on induction of interleukin 8 (IL-8) gene by NO in monocytic U937 cells. We have observed that nitrosoglutathione or another NO-generating compound spermine NONOate caused significant accumulation of IL-8 mRNA. Pretreatment of cells with pyrrolidine dithiocarbamate or with antioxidants, which scavenge hydroxyl radical, dimethyl sulfoxide (DMSO), or dimetylthiourea (DMTU) completely abrogated NO-dependent induction of IL-8 gene expression. The transcriptional activation of IL-8 gene was not affected by sodium formate or sodium salicylate, suggesting that suppression of the IL-8 gene induction is specific to the class of hydroxyl radical scavenger used. Furthermore, we have shown that IL-8 induction was not inhibited by catalase and the iron chelator deferoxamine, indicating that the inhibitory actions of DMSO and DMTU are not related to scavenging of reactive oxygen species produced from hydrogen peroxide in the iron-catalyzed reactions. Finally, we have not observed any significant inhibition of NO-dependent IL-8 gene induction by superoxide scavengers such as N-acetyl cysteine, uric acid, and superoxide dismutase. Therefore, it seems likely that in U937 cells, hydroxyl radicals or species with reactivity similar to hydroxyl radicals contribute to NO-mediated IL-8 gene induction.