| Butyric acid is one of the short chain fatty acids produced by microbial fermentation in the colon and is a well known histone deacetylase inhibitor. It suppresses cell growth, and induces differentiation and apoptosis in many cancer cell lines. The objective of the study was to assess whether the effect of sodium butyrate (NaB) on cell growth differed by p53 status of the cells. Four human colorectal adenocarcinoma cell lines were used: HT29 (p53 point mutation), Caco2 (p53 truncation), LS513 (p53 wild type) and Lovo (p53 wild type). NaB significantly inhibited cell growth independently of p53. The protein and mRNA level of the cell cycle inhibitor, p21WAF1/CIP1 , were elevated by NaB independently of p53, and the elevation of p21 mRNA level was due to an increase in transcription and not due to an increase in mRNA stability.; Another objective was to study the mechanism by which butyrate induces p21. Using the DNase I hypersensitivity assay, NaB was found not to alter the configuration of chromatin in the region of the p21 gene. Using the chromatin immunoprecipitation (ChIP) assay, acetylation of histone H3 was observed at the proximal region, but not at the distal region of the promoter within 30 min of NaB exposure, and acetylation extended to the distal region between 30 min and 2hr. By contrast, histone H4 was acetylated within 30 min at both the proximal and distal regions. Other modifications of histone H3 were not observed. Thus, chromatin modification by histone acetylation increases the potential for recruiting transcription factors onto the p21 promoter. Using the ChIP assay, ZBP89 and Sp1 were shown to be recruited onto the promoter within 30 min of NaB exposure. GCN5, a member of the HAT family, was transiently associated with the promoter.; To study if alteration of HDAC1 and/or p300/CBP activity can alter p21 gene transcription, cells were treated with protein phosphatase inhibitor (OA) or kinase inhibitor (H7). OA increased p21 mRNA without NaB; whereas H7 abolished the induction of p21 mRNA by NaB without abolishing acetylation of histone H3 and H4. This suggests that acetylation of histones is not sufficient for NaB to exert antiproliferative effects. |
