5-aza-2'-deoxycitydine induces demethylation and up-regulates transcription of p16INK4A gene in human gastric cancer cell lines

Background To investigate the effects of DNA methylation on the expression of tumor-associated genes and the cell cycle in human gastric cancer cells. Methods Two gastric cancer cell lines (MKN-45 and HGC-27) were treated with DNA methyltransferase (DNMT) inhibitor,5-aza-2’-deoxycytidine (5-aza-dC). The expressions of p16 INK4A,p21 WAF1,p53 , p73 ,c-Ha-ras and c-myc genes mRNA were detected by using reverse transcription PCR (RT-PCR). DNA methylation status of p16 INK4A gene promoter was assayed by bisulfite modification and sequencing. The cell cycle was analyzed by using flow cytometry (FCM). Results 5-aza-dC induced the demethylation of p16 INK4A gene promoter. The expression of p16 INK4A mRNA was obviously up-regulated by treatment with 10 μmol/L (MKN-45 cells) or 5 μmol/L (HGC-27 cells) of 5-aza-dC for 24 hours. However,5-aza-dC treatment failed to regulate the expressions of p21 WAF1,p53 , p73 ,c-Ha-ras and c-myc genes in MKN-45 and HGC-27 cells. Furthermore,5-aza-dC induced the cell cycle arrest in G1 phase in HGC-27 cell,but not in MKN-45 cell. Conclusions DNA methylation regulates the transcription of p16 INK4A but not p21 WAF1 and proto-oncogenes in human gastric cancer cell lines MKN-45 and HGC-27.