| 研究実績の概要 |
Forty-two pairs of tumor and adjacent non-tumor tissues from liver cancer patients with chronic hepatitis C virus infection were evaluated for CYGB promoter methylation using Ion GeneStudio S5. Methylation frequency in tumors is significantly higher than that in non-tumor tissues at all 33 CpG sites (P = 1.02E-8) in this region. The mean of methylation index in tumor and non-tumor tissues were 43.8% and 20.5%, respectively. A subset of HCC samples was examined, CYGB mRNA and protein expression in tumor is significantly lower than that in non-tumor tissues (-60%, P < 0.05).
In vitro, high methylation frequency and no CYGB expression at RNA and protein levels were found in HCC cells (HepG2, Huh7, SNU-387, HLE) and also well-known myofibroblast LX-2 cells. In contrast, almost no methylation in human hepatic stellate cells (both primary and cell line) that correspond to positive CYGB expression.
Restoration of CYGB expression was performed in four HCC cell lines treated with 1, 3, 5, and 10 uM 5-aza-2′- deoxycytidine (DAC). Interestingly, DAC treatment time- and dose-dependently restored CYGB expression at both mRNA and protein levels in SNU-387, HLE and Huh7, and at mRNA level in HepG2 cells while DAC did not induce CYGB expression in LX-2. Notably, after inducing CYGB expression in SNU-387, removal of DAC resulted in regressing of CYGB expression at both mRNA and protein levels.
Luciferase assay data demonstrated that the CYGB promoter region spanning from -994 to -639 relative to translation start site exhibited a significant decrease in luciferase activity.
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