Effects of DNA methylation on expression of tumor suppressor genes and proto-oncogene in human colon cancer cell lines

Abstract

Aim: To investigate the effects of DNA methylation on the expression of tumor suppressor genes and proto-oncogene in human colon cancer cell lines. Methods: Three colon cancer cell lines (HT-29, SW1116 and Colo-320) treated with different concentrations of DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine (5-aza-dC) were used to induce DNA demethylation. The expressions of p16INK4A, p21WAF1, APC and c-myc genes were observed by using RT-PCR. The methylation status of p16INK4A promoter in HT-29 cells was also determined by methylation-specific PCR (MSP). Results: Weak expressions of p16INK4A and APC in the three colon cancer cells were detected, and p21WAF1 expression was not found in SW1116 and Colo-320 cells before treatment. After treatment of 1 μmol/L but not 10 μmol/L of 5-aza-dC, the methylation level of p16INK4A gene promoter decreased significantly, and the hypomethylation led to the up-regulation of p16INK4A gene transcription in HT-29 cells. In the cell lines of SW1116 and Colo-320, p16INK4A and APC mRNA expressions were obviously enhanced after treatment of either 10 μmol/L or 5 μmol/L 5-aza-dC for 24 h. However, no evidence was found that methylation regulated the expression of p21WAF1 and c-myc genes in human colon cancer cell lines. Conclusion: Expression of p16INK4A and APC genes is regulated by DNA methylation in three human colon cancer cell lines.