Synergy Between Deacetylase Inhibitors and IL-1β in Activation of the Serum Amyloid A2 Gene Promoter

Abstract

Butyrate (NaBu) regulates intestinal inflammatory gene expression in part through inhibition of deacetylase activity, but the exact mechanisms involved remain to be determined. In this study, we showed by Northern blot a synergistic induction of the acute phase protein gene SAA2 with a combination of deacetylase inhibitors(Trichostatin A or NaBu) and IL-1β in the colon carcinoma cell line Caco-2. While the NF-κB DNA-binding site was essential for SAA2 regulation by IL-1β and deacetylase inhibitors, the C/EBP DNA-binding site modulated SAA2 expression levels, as assessed by transient transfection assays and mutagenesis studies. NaBu was sufficient to induce SAA2 expression after transient treatment with IL-1β and, conversely, IL-1β induced SAA2 after transient treatment with NaBu. These data suggest that pretreatment with either NaBu or IL-1β predisposes the SAA2 promoter to further stimulation. Indeed, both NaBu and IL-1β led to increased recruitment of NF-κB p65, C/EBPβ, and C/EBPδ, and decreased NF-κB p50 and C/EBPα DNA-binding to the proximal SAA2 promoter, as assessed by chromatin immunoprecipitation assays. Interestingly, while IL-1β, in contrast to NaBu, induced histone H4 acetylation, addition of IL-1β and NaBu increased histone H4 acetylation and both C/EBPβ and NF-κB p65 DNA-binding. Therefore, these results suggest that NaBu and IL- 1β mediate SAA2 synergistic induction by establishing and maintaining similar and complementary chromatin modifications and transcription factor recruitment as well. In addition to global effects, NaBu specifically regulate gene expression, as exemplified by SAA2.