In gastric cancer, increasing numbers of genes have been reported to be silenced by aberrant methylation. However, global analysis of epigenetic inactivation in cancer cells has rarely been performed. For screening the genes upregulated by the demethylating agent 5-aza-2'-deoxycytidine (DAC), cDNA microarray analysis (AceGene(R), containing 30,000 genes) was performed using gastric cancer cell lines (AGS, MKN74, MKN1, MKN45 and Kato3) treated with DAC. The candidate upregulated genes were confirmed by real-time PCR, and the methylation status of 5'CpG islands was determined by bisulfite DNA sequencing or methylation-specific PCR. Among the upregulated genes considered to have CpG island in their promoter regions, we selected 5 genes (BCL2L10, DKK1, DNAJD1, GAGED2 and NMU) that exhibited a greater than 3-fold increase in at least 2 cell lines. Of these, we could determine the methylation status of 5'CpG islands of BCL2L10, DKK1 and DNAJD1. 5'CpG of BCL2L10 and DNAJD1 was hypermethylated in 4 of 5 gastric cancer cell lines, whereas 5'CpG of DKK1 was hypermethylated in only 1 cell line. MSP analysis for BCL2L10 revealed that the CpG island was demethylated after DAC treatment. In addition, we observed that overexpression of BCL2L10 could promote apoptosis and growth-inhibitory effect in gastric cancer cell lines. In conclusion, some of the genes upregulated by DAC treatment may be transcriptionally repressed by promoter hypermethylation. These genes might be related to gastric carcinogenesis. In particular, the suppression of BCL2L10, which could induce apoptosis and inhibit proliferation of cancer cells, might be one of the underlying mechanisms for gastric carcinogenesis.
Copyright 2006 Wiley-Liss, Inc.