Vicinal dithiol-binding agent, phenylarsine oxide, inhibits inducible nitric-oxide synthase gene expression at a step of nuclear factor-kappa B DNA binding in hepatocytes

Inflammatory cytokine interleukin 1 beta induces inducible nitric-oxide syn thase (iNOS) mRNA and its protein, which are followed by increasing the pro duction of nitric oxide, in primary cultures of rat hepatocytes. Nuclear fa ctor-kappa B (NF-kappa B), an important transcription factor for iNOS gene expression, is also activated and translocated to the nucleus. In the prese nt study, we found that vicinal dithiol-binding agent, phenylarsine oxide ( PAO), inhibited the induction of iNOS protein and mRNA as well as the relea se of nitrite (nitric oxide metabolite) into the culture medium. Simultaneo us addition of a vicinal dithiol compound, 2,3-dimercaptopropanol, with PAO completely abolished these inhibitions. PAO could not prevent either degra dation of an inhibitory protein, I kappa B, of NF-kappa B or translocation of NF-kappa B to the nucleus, However, electrophoretic mobility shift assay demonstrated that PAO decreased the interaction between NF-kappa B and its binding consensus oligonucleotide. Transfection experiments with iNOS prom oter-luciferase construct revealed that PAO inhibited NF-kappa B binding to DNA These results indicate that PAO inhibits iNOS gene expression at a ste p of NF-kappa B binding to DNA by modifying its vicinal dithiol moiety, whi ch may play a crucial role for the iNOS regulation in hepatocytes.