Inhibitors of ADP-ribosylation impair inducible nitric oxide synthase gene transcription through inhibition of NF kappa B activation.

In murine macrophages, inducible NO synthase II (iNOS or NOS-II) is induced at the transcriptional level by IFN-gamma, alone or synergistically with LPS. We investigated the possible role of reactions of ADP-ribosylation in triggering the signaling pathways involved in NOS-II gene expression. Stimulation with IFN-gamma and/or LPS of RAW 264.7 macrophages, transiently transfected with the NOS-II promoter, was inhibited by ADP-ribosylation inhibitors, indicating that they interfered with the signal(s) responsible for NOS-II gene transcription. We therefore explored the effect of these inhibitors on the activity of IRF-1 and NF kappa B transcription factors known to be involved in NOS-II induction by IFN-gamma and LPS. No effect was observed on IRF-1 activation. However, NF kappa B binding to its target sequence diminished and transfection experiments with an NF kappa B-driven reporter plasmid demonstrating that ADP-ribosylation inhibitors suppressed NF kappa B-dependent promoter activity. These results provide evidence that a step involving ADP-ribosylation is required to activate NF kappa B-mediated gene transcription.