Dexamethasone inhibits IL-1 beta gene expression in LPS-stimulated RAW 264.7 cells by blocking NF-kappa B/Rel and AP-1 activation

In the present study, the mechanism by which dexamethasone (DEX) inhibited IL-1 beta gene expression in bacterial lipopolysaccharide (LPS)-activated R AW 264.7 cells was investigated. The decrease in LPS-induced IL-1 beta mRNA expression was demonstrated by quantitative reverse transcription polymera se chain reaction (RT-PCR). Since the promoter in IL-1 beta gene contains b inding motifs for NF-kappa B/Rel, AP-1, NF-IL6, and CREB/ATF, which appear to be important in LPS-mediated IL-1 beta induction, the effects of DEX on the activation of these transcription factors were examined. Treatment of D EX to RAW 264.7 cells induced a dose-related inhibition of NF-kappa B/Rel a nd AP-1 in chloramphenicol acetyltransferase activity, while neither NF-IL6 nor CREB/ATF activation was affected by DEX. Treatment of RAW 264.7 cells with DEX inhibited DNA binding of NF-kappa B/Rel and AP-1 proteins to their cognate DNA sites as measured by electrophoretic mobility shift assay (EMS A). DEX treatment caused a significant reduction in nuclear c-rel, p65, and p50 protein contents, and these decreases were paralleled by the accumulat ion of cytoplasmic c-rel, p65, and p50. DEX treatment of RAW 264.7 cells di d not inhibit the nuclear translocation of c-jun and c-fos. We found that t he inhibition of IL-1 beta production by DEX is not related to p38, which i s important in the IL-1 beta induction. These results suggest that DEX may inhibit IL-1 beta gene expression by a mechanism involving the blocking of LPS-induced NF-kappa B/Rel and AP-1 activation. (C) 2000 Elsevier Science B .V. All rights reserved.