AbstractBackgroundChromodomain helicase DNA binding protein 5 (CHD5) has recently been identified as a potent tumour suppressor by acting as a master regulator of a tumour‐suppressive network. Its inactivation resulted from aberrant methylation in the promoter occurs in several types of human malignancy and is associated with malignant tumour behaviour. In human hepatocellular carcinoma (HCC), CHD5 gene expression, methylation status and tumour‐suppressive function have not been elucidated.AimsIn this study, we focused on the epigenetic modification and tumour‐suppressive mechanism of CHD5 gene in HCC.MethodsCHD5 expression in nine HCC cell lines and 30 pairs of HCC specimens and adjacent non‐cancerous tissues were analysed by quantitative reverse transcription PCR and Western blotting. Methylation‐specific sequencing and methylation‐specific PCR were performed to examine DNA methylation status of the CHD5 promoter in HCC cell lines and samples. The effect of CHD5 restoration on proliferation, colony formation, senescence, apoptosis and tumourigenicity were examined.ResultsCHD5 expression was sinificantly down‐regulated in HCC cell lines and tissues examined, and the −841 to −470 region of CHD5 promoter was hypermethylated in these samples. Treatment with DNA methyltransferase inhibitor 5‐aza‐2‐deoxycytidine resulted in a striking regional demethylation of the −841 to −470 region of CHD5 promoter and an increase in CHD5 expression. The restoration of CHD5 expression inhibited tumour cell proliferation, colony formation and tumourigenicity and caused cellular senescence.ConclusionsOur findings demonstrate that CHD5 is a potential tumour suppressor gene epigenetically silenced in HCC.