Interleukin 1-induced cyclooxygenase and nitric oxide synthase gene expression in the rat dorsal root ganglia is modulated by antioxidants

Abstract

Interleukin 1β induced both nitric oxide synthase 2 (NOS-2) and cyclooxygenase 2 (COX-2) gene expression in dorsal root ganglion explant culture with increased NOS-2 and COX-2 activities, and corresponding increases in the production of nitric oxide and prostaglandin E 2. The proinflammatory cytokine also increased 8-isoprostaglandin F 2α concentration, an index of oxidant stress-mediated production of lipid hydroperoxides/reactive oxygen species. The signaling mechanisms by which interleukin 1β regulates NOS-2 and COX-2 genes remain obscure. Reactive oxygen species play an important role in inflammatory processes as mediators of injury, and potentially as intracellular signaling molecules in interleukin 1β-mediated regulation of gene expression. The effects of antioxidants that act by different mechanisms on interleukin 1β-mediated NOS-2 and COX-2 gene expression were studied in rat dorsal root ganglion explants. The oxidant scavenger pyrrolidine dithiocarbamate abolished interleukin 1β-induced NOS-2 mRNA accumulation and decreased nitric oxide production in a concentration-dependent manner, thus indicating that this antioxidant decreased either the transcription of NOS-2 gene or the stability of NOS-2 mRNA. In contrast, pyrrolidine dithiocarbamate significantly inhibited COX-2 gene expression at the posttranscriptional level, since pyrrolidine dithiocarbamate did not affect interleukin 1β-induced COX-2 mRNA transcripts but inhibited COX-2 protein expression and prostaglandin E 2 production. Rotenone, another antioxidant that attenuates reactive oxygen species production by inhibiting the mitochondrial electron transport system, failed to inhibit interleukin 1β-induced NOS-2 and COX-2 mRNA-encoding transcripts. However, rotenone inhibited NOS-2 and COX-2 proteins and associated nitric oxide and prostaglandin E 2 production, respectively, suggesting a posttranscriptional target for interleukin 1β-mediated regulation of NOS-2 and COX-2 gene expression. Furthermore, both pyrrolidine dithiocarbamate and rotenone also decreased interleukin 1β-induced 8-isoprostaglandin F 2α production. These results indicate that not only transcriptional regulation, but also posttranscriptional events are involved in a redox-sensitive regulation of interleukin 1β-induced NOS-2 and COX-2 gene expression in the dorsal root ganglia. Overall, interleukin 1β-induced oxidant stress appears to regulate NOS-2 and COX-2 gene expression primarily at the level of protein translation. By implicating reactive oxygen species production in interleukin-1β receptor-activated molecular signaling in the dorsal root ganglia, our data suggest a possible novel target for intervention in cytokine-mediated inflammatory processes.