Résumé
Previous studies have implicated acetylases and deacetylases in regulating the transcriptional activity of NF-κB. Here, we show that inhibitors of deacetylases such as trichostatin A (TSA) and sodium butyrate (NaBut) potentiated TNF-induced expression of several natural NF-κB-driven promoters. This transcriptional synergism observed between TNF and TSA (or NaBut) required intact κB sites in all promoters tested and was biologically relevant as demonstrated by RNase protection on two instances of endogenous NF-κB-regulated gene transcription. Importantly, TSA prolonged both TNF-induced DNA-binding activity and the presence of NF-κB in the nucleus. We showed that the p65 subunit of NF-κB was acetylated in vivo. However, this acetylation was weak, suggesting that other mechanisms could be implicated in the potentiated binding and transactivation activities of NF-κB after TNF plus TSA versus TNF treatment. Western blot and immunofluorescence confocal microscopy experiments revealed a delay in the cytoplasmic reappearance of the IκBα inhibitor that correlated temporally with the prolonged intranuclear binding and presence of NF-κB. This delay was due neither to a defect in IκBα mRNA production nor to a nuclear retention of IκBα but was rather due to a persistent proteasome-mediated degradation of IκBα. A prolongation of IκB kinase activity could explain, at least partially, the delayed IκBα cytoplasmic reappearance observed in presence of TNF plus TSA.