IFN-gamma + LPS induction of iNOS is modulated by ERK, JNK/SAPK, and p38(mapk) in a mouse macrophage cell line

Nitric oxide (NO .) produced by inducible nitric oxide synthase (iNOS) medi ates a number of important physiological and pathophysiological processes. The objective of this investigation was to examine the role of mitogen-acti vated protein kinases (MAPKs) in the regulation of iNOS and NO . by interfe ron-gamma (IFN-gamma) + lipopolysaccharide (LPS) in macrophages using speci fic inhibitors and dominant inhibitory mutant proteins of the MAPK pathways . The signaling pathway utilized by IFN-gamma in iNOS induction is well elu cidated. To study signaling pathways that are restricted to the LPS-signali ng arm, we used a subclone of the parental RAW 264.7 cell line that is unre sponsive to IFN-gamma alone with respect to iNOS induction. In this RAW 264 .7 gamma NO(-) subclone, IFN-gamma and LPS are nevertheless required for sy nergistic activation of the iNOS promoter. We found that extracellular sign al-regulated kinase (ERK) augmented and p38(mapk) inhibited IFN-gamma + LPS induction of iNOS. Dominant-negative MAPK kinase-4 inhibited iNOS promoter activation by IFN-gamma + LPS, also implicating the c-Jun NH2-terminal kin ase (JNK) pathway in mediating iNOS induction. Inhibition of the ERK pathwa y markedly reduced IFN-gamma + LPS-induced tumor necrosis factor-alpha prot ein expression, providing a possible mechanism by which ERK augments iNOS e xpression. The inhibitory effect of p38(mapk) appears more complex and may be due to the ability of p38(mapk) to inhibit LPS-induced JNK activation. T hese results indicate that the MAPKs are important regulators of iNOS-NO . expression by IFN-gamma + LPS.