Abstract
cAMP significantly inhibits IL-1β+IFNγ-induced iNOS gene expression in hepatocytes, but the signaling pathways responsible for the effect are not known. PKA inhibitors, H89, PKI, and KT5720, had no effect on the recovery of the inhibitory effects of cAMP on cytokine-induced hepatocyte iNOS expression and activity. The JNK inhibitor, SP 600125, effectively reversed the inhibitory effects of cAMP on iNOS expression and significantly increased iNOS promoter activity. A cAMP analogue, dbcAMP, significantly induced JNK signaling and increased AP-1 binding activity in hepatocytes. The JNK activator, anisomycin, inhibited iNOS expression and transcription in hepatocytes as well as AP-1 binding activity; and SP600125 reversed this effect of anisomycin. Overexpression of c-Jun in hepatocytes inhibited IL-1β+IFNγ-induced nitrite accumulation and iNOS promoter activity while dominant negative c-Jun partially reversed the inhibitory effects of cAMP on nitrite accumulation. We conclude that JNK signaling plays an important role in the inhibitory effects of cAMP on IL-1β+IFNγ-induced iNOS gene expression in cultured hepatocytes.
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