Transient vs. prolonged histone hyperacetylation: effects on colon cancer cell growth, differentiation, and apoptosis

The role of histone hyperacetylation in regard to growth, differentiation, and apoptosis in colon cancer cells was assessed in an in vitro model syste m. HT-29 cells were grown in +/-10% fetal bovine serum with either 5 mM sod ium butyrate or 0.3 muM trichostatin A [single dose (T) or 3 doses 8 h apar t (TR)] for 24 h. Serum-starved HT-29 cells were further treated with epide rmal growth factor or insulin-like growth factor I for an additional 24 h. Apoptosis was quantified with propidium iodide and characterized by electro n microscopy. Northern blot analyses were performed with cDNA probes specif ic for intestinal alkaline phosphatase, Na-K-2Cl cotransporter, the cell cy cle inhibitor p21, and the actin control. Flow cytometric analysis revealed a time-dependent growth suppression along with early induction of p21 mRNA in the butyrate, T, and TR groups. Histone hyperacetylation, assessed by a cid-urea-triton gel electrophoresis, was transient in the T group but persi sted for up to 24 h in the butyrate and TR groups. Induction of apoptosis, growth factor unresponsiveness, and differentiation occurred in the butyrat e- and TR-treated cells but not those treated with a single dose of trichos tatin A. Thus transient hyperacetylation of histones is sufficient to induc e p21 expression and produce cellular growth arrest, but prolonged histone hyperacetylation is required for induction of the programs of differentiati on, apoptosis, and growth factor unresponsiveness.