Triggering of Peritoneal Macrophages with IFN-α/β Attenuates the Expression of Inducible Nitric Oxide Synthase Through a Decrease in NF-κB Activation

Abstract

Abstract Triggering peritoneal macrophages with IFN-γ and a low concentration of LPS induced the expression of the inducible form of nitric oxide synthase (iNOS). This process was significantly inhibited when IFN-α/β was added during the initial 2 h after the start of IFN-γ/LPS activation. Evaluation of the transcriptional activity using run-on assays indicated that IFN-α/β inhibited the transcription of iNOS. Transfection experiments using a 1.7-kb promoter sequence corresponding to the 5′ flanking region of the murine iNOS gene showed decreased promoter activity in the presence of type I IFNs. Analysis of the transcription factors that participate in iNOS expression revealed a marked decrease of NF-κB activation, a nuclear factor required for the transcription of this gene. The degradation of IκBα and IκBβ, which is required for the translocation of NF-κB to the nucleus, was inhibited in the presence of IFN-α/β. However, the activity of other transcription factors such as IFN regulatory factor 1, which is involved in the expression of iNOS in response to IFN-γ, was not affected by IFN-α/β stimulation. These results suggest that in the presence of IFN-α/β, the activity of the iNOS promoter is impaired, and this attenuated nitric oxide synthase expression could be important in pathophysiologic situations in which secretion of type I IFNs occurs.