INTERFERON-GAMMA MODULATES THE LIPOPOLYSACCHARIDE-INDUCED EXPRESSION OF AP-1 AND NF-KAPPA-B AT THE MESSENGER-RNA AND PROTEIN LEVEL IN HUMANMONOCYTES

Interferon-gamma (IFN-gamma) modulates the expression of several cytok ines by human monocytes at the transcriptional level. In view of these findings, we analyzed the effects of IFN-gamma on the expression of d ifferent transcription factors in activated human monocytes. Priming o f human monocytes with IFN-gamma resulted in the downregulation of c-f os and c-jun mRNA in response to stimulation with lipopolysaccharide ( LPS) compared to the effects of LPS alone. Not only was this effect ob served at the mRNA level, but activator protein-1 (AP-1) DNA binding c apacity was affected as well. A strong reduction was observed in the L PS-induced DNA-binding activity of AP-1 in the presence of IFN-gamma. LPS-stimulated monocytes showed an increased expression of p105 mRNA, the precursor of the p50 subunit of the transcription factor nuclear f actor-kappa B (NF-kappa B), while no effect was noticed on the express ion of p65 mRNA. In contrast, IFN-gamma priming did not affect the exp ression of p105 transcripts but enhanced the expression of p65 mRNA (t wo-fold). Priming with IFN-gamma followed by LPS stimulation resulted in a further increase in the expression of p65 mRNA. This was due to a n increase in the half-life of p65 mRNA (75 vs. 150 minutes). Electrop horetic mobility shift assays (EMSAs) demonstrated that unstimulated m onocytes predominantly expressed p50 NF-kappa B. Stimulation with LPS or IFN-gamma resulted in the expression of p50 and p65 subunits, while the combination of IFN-gamma plus LPS caused a further increase in th e expression of NF-kappa B. With Western blotting, it was shown that n uclear extracts from monocytes contained p50 and p65 protein in respon se to LPS and IFN-gamma stimulation. However, the combined stimulation did not result in enhanced p50 and p65 protein expression. The effect s of IFN-gamma on the transcription factors were specific, since no ch ange was observed in the expression of NF-IL-6 or I kappa B alpha, the inhibitor of NF-kappa B. We conclude that the effects of IFN-gamma on the expression of the transcription factors AP-1 and NF-kappa B may b e important for the modulatory effects of IFN-gamma on the cytokine ex pression in activated human monocytes.