NOS2 regulation of NF-κB by S-nitrosylation of p65

Signal transduction in the NF-kappa B transcription factor pathway is inhibited by inducible nitric oxide synthase ( NOS2) activity, although the molecular mechanism( s) are incompletely understood. We have previously shown that nitric oxide ( NO), derived from NOS2 consequent upon cytokine stimulation, attenuates NF-kappa B p50-p65 heterodimer DNA binding and have identified the p50 monomer as a locus for inhibitory S-nitrosylation. We now show that the binding partner of p50, NF-kappa B p65, is also targeted by NO following cytokine stimulation of respiratory epithelial cells and macrophages and identify a conserved cysteine within the Rel homology domain that is the site for S-nitrosylation. S-Nitrosylation of p65 inhibits NF-kappa B-dependent gene transcription, and nuclear levels of S-nitrosylated p65 correlate with decreased DNA binding of the p50-p65 heterodimer. NOS2 regulates cytokine-induced S-nitrosylation of p65, resulting in decreased NF-kappa B binding to the NOS2 promoter, thereby inhibiting further NOS2 expression. Collectively, these findings delineate a mechanism by which NOS2 modulates NF-kappa B activity and regulates gene expression in inflammation.