[Regulation of histone acetylation on the expression of cell cycle-associated genes in human colon cancer cell lines].

OBJECTIVE

To investigate the effects of histone acetylation on the expression of p21(WAF1) and p16(INK4A) genes in two human colon cancer cell lines.

METHODS

Two colon cancer cell lines (SW1116 and Colo-320) were treated with the DNA methyltransferase (DNMT) inhibitor, 5-aza-2'-deoxycytidine (5-aza-dC) and/or the histone deacetylase (HDAC) inhibitor, trichostatin A (TSA) or sodium butyrate (NaBu). The cell cycle distribution was studied by flow cytometry (FCM). The expression of p21(WAF1) and p16(INK4A) genes mRNA was detected by real-time RT-PCR. The level of acetylated histones in chromatin associated with the p21(WAF1) and p16(INK4A) genes was examined by chromatin immunoprecipitation (ChIP) assay.

RESULTS

TSA or NaBu blocked cells mainly in the G(1) phase, whereas 5-aza-dC treatment failed to affect cell cycle distribution. Expression of p16(INK4A) was detected slightly and p21(WAF1) was not expression in SW1116 and Colo-320 cells before treatment. In SW1116 and Colo-320 cells, the expression of p16(INK4A) gene was markedly increased after treatment of 5-aza-dC, although 5-aza-dC treatment did not activate the expression of p21(WAF1) gene. Treatment of TSA and NaBu resulted in the significant over-expression of p21(WAF1) in these two cell lines and induced an accumulation of acetylate histones H3 and H4 in chromatin associated with p21(WAF1) gene.

CONCLUSION

In these two human colon cancer cell lines, HDAC inhibitors stimulate the p21(WAF1) gene expression by selectively increasing the degree of acetylation of the gene-associated histones, and induce a G(1) cell cycle arrest. The expression of the p16(INK4A) gene is regulated by DNA methylation.