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REGULATION OF C/EBPdelta-DEPENDENT TRANSACTIVATION BY HISTONE DEACETYLASES

N Turgeon¹, C Valiquette¹, M Blais¹, S Routhier¹, EG Seidman², C Asselin¹
¹Département d'anatomie et biologie cellulaire, Université de Sherbrooke, Sherbrooke, Quebec; ²Department of Medicine, McGill University, Montreal, Quebec

The C/EBPdelta transcription factor is involved in the positive regulation of the intestinal epithelial cell acute phase response. C/EBPdelta modulation by histone deacetylases (HDACs) during the course of inflammation remains to be determined. Our aim was to examine the effect of HDACs on C/EBPdelta-dependent regulation of haptoglobin, an acute phase protein induced in intestinal epithelial cells in response to inflammation.
METHODS: HDAC expression was determined by Western blot in IEC-6 rat intestinal epithelial cells. We analysed the interaction between C/EBPdelta and HDAC1, using GST pull-down and immunoprecipitation assays. The consequence of HDAC1 overexpression on haptoglobin induction was assessed by transient transfection and luciferase assays. We determined the presence of HDAC1 at the haptoglobin promoter and measured the extent of histone H3 and H4 acetylation by chromatin immunoprecipitation. The effect of HDAC1 silencing by shRNAs on IL-1beta-induced haptoglobin expression was assessed by Northern blot.
RESULTS: HDAC1, 3, 4, 5, 6 and 7 were expressed in IEC-6 cells. GST pull-down assays showed specific HDAC1 interactions with the transcriptional activation and the b-ZIP C/EBPdelta domains. Immunoprecipitation assays confirmed the interaction between HDAC1 and amino acids 36 to 164 of the N-terminal C/EBPdelta domain. HDAC1 overexpression decreased C/EBPdelta transcriptional activity of the haptoglobin promoter. Chromatin immunoprecipitation analysis shows a displacement of HDAC1 from the haptoglobin promoter in response to inflammatory stimuli and an increased acetylation of histone H3 and H4. HDAC1 silencing increased haptoglobin expression in epithelial intestinal cells in an IL-1beta-dependent manner.
CONCLUSION: Our results suggest that interactions between C/EBPdelta and HDAC1 negatively regulate C/EBPdelta-dependent haptoglobin expression in intestinal epithelial cells.
Supported by CIHR, CCFC, NSERC

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