Objective: We attempted to identify tumor-related genes whose expression is affected by DNA methylation and that participate in the determination of the biological characteristics of human cancers. Methods and materials: We used the differential display method in ten 5-azacytidine-treated human cancer cell lines. Timedependent induction of mRNA expression of Wip1, TROP2, B4-2 protein, BRCA-2 region transcription unit CG005, cofilin, ROCK, CD44, and interferon-inducible protein 6-16 was observed during 5-azacytidine treatment. We then evaluated the mRNA expression of these genes in 26 stomach and 32 colorectal cancers and 44 hepatocellular carcinomas (HCCs) and in the corresponding non-cancerous tissues. Results: Significantly reduced mRNA expression of Wip1, B4-2, and cofilin in stomach cancers, of Wip1, B4-2, BRCA-2 region transcription unit CG005, cofilin, and ROCK in colorectal cancers, and of TROP2, B4-2, and BRCA-2 region transcription unit CG005 in HCCs, was observed in comparison with the corresponding non-cancerous tissues, whereas overexpression of TROP2 was detected in colorectal cancers. Reduced expression of Wip1 and BRCA-2 region transcription unit CG005 was significantly correlated with poorer differentiation of HCCs, and mRNA expression of these genes was significantly reduced in HCCs associated with portal vein involvement compared with HCCs without such involvement. Expression of TROP2 mRNA was significantly higher in chronically diseased liver from HCC patients compared with histologically normal liver, but was reduced in progressed HCCs. Reduced expression of B4-2 protein was observed in association with hepatitis B virus infection of HCC patients. Conclusions: These data suggest that DNA methylation may play a role in human multistage carcinogenesis through direct or indirect regulation of multiple tumor-related genes.
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