Background-Sodium butyrate, a product of colonic bacterial fermentation, is able to inhibit cell proliferation and to stimulate cell diVerentiation of colonic epithelial cell lines. It has been proposed that these cellular eVects could be linked to its ability to cause hyperacetylation of histone through the inhibition of histone deacetylase. Aim-To analyse the molecular mechanisms of butyrate action on cell proliferation/diVerentiation and to compare them with those of trichostatin A, a well known inhibitor of histone deacetylase. Methods-HT-29 cells were grown in the absence or presence of butyrate or trichostatin A. Cell proliferation and cell cycle distribution were studied after DNA staining by crystal violet and propidium iodide respectively. Cell cycle regulatory proteins were studied by western blot and reverse transcription-polymerase chain reaction. Cell diVerentiation was followed by measuring brush border enzyme activities. Histone acetylation was studied by acid/urea/Triton acrylamide gel electrophoresis. Results-Butyrate blocked cells mainly in the G 1 phase of the cell cycle, whereas trichostatin A was inhibitory in both G 1 and G 2 phases. Butyrate inhibited the mRNA expression of cyclin D1 without aVecting its protein expression and stimulated the protein expression of cyclin D3 without aVecting its mRNA expression. Trichostatin A showed similar eVects on cyclin D1 and D3. Butyrate and trichostatin A stimulated p21 expression both at the mRNA and protein levels, whereas their eVects on the expression of cyclin dependent kinases were slightly diVerent. Moreover, butyrate strongly stimulated the activity of alkaline phosphatase and dipeptidyl peptidase IV, whereas trichostatin A had no eVect. Finally, a six hour exposure to butyrate or trichostatin A induced histone H4 hyperacetylation. At 15 and 24 hours, histone H4 remained hyperacetylated in the presence of butyrate, whereas it returned to control levels in the presence of trichostatin A. Conclusions-The data may explain how butyrate acts on cell proliferation/ diVerentiation, and they show that trichostatin A does not reproduce every eVect of butyrate, mainly because of its shorter half life. (Gut 2000;46:507-514)

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