Double-stranded RNA-induced inducible nitric-oxide synthase expression and interleukin-1 release by murine macrophages requires NF-κB activation

Abstract

The effects of double-stranded RNA (synthetic polyinosinic- polycytidylic acid; poly(I-C)) on macrophage expression of inducible nitric- oxide synthase (iNOS), production of nitric oxide, and release of interleukin-1 (IL-1) were investigated. Individually, poly(I-C), interferon- γ (IFN-γ), and lipopolysaccharide (LPS) stimulate nitrite production and iNOS expression by RAW 264.7 cells. In combination, the effects of poly(I-C) + IFN-γ are additive, while poly(I-C) does not further potentiate LPS- induced nitrite production. These results suggest that poly(I-C) and LPS may stimulate iNOS expression by similar signaling pathways, which may be independent of pathways activated by IFN-γ. LPS-induced iNOS expression is associated with the activation of NF-κB. We show that inhibition of NF-κB by pyrrolidinedithiocarbamate prevents poly(I-C) + IFN-γ-, poly(I-C) + LPS- , and LPS-induced iNOS expression, nitrite production and IκB degradation by RAW 264.7 cells. The effects of poly(I-C) on iNOS expression appear to be cell-type specific. Poly(I-C), alone or in combination with IFN-γ, does not stimulate, nor does poly(I-C) potentiate, IL-1-induced nitrite production by rat insulinoma RINm5F cells. In addition, we show that the combination of poly(I-C) + IFN-γ stimulates iNOS expression, nitrite production, IκB degradation, and the release of IL-1 by primary mouse macrophages, and these effects are prevented by pyrrolidinedithiocarbamate. These findings indicate that double-stranded RNA, in the presence of IFN-γ, is a potent activator of macrophages, stimulating iNOS expression, nitrite production, and IL-1 release by a mechanism which requires the activation of NF-κB.