Integrated analyses of DNA methylation and hydroxymethylation reveal tumor suppressive roles of ECM1, ATF5 and EOMES in human hepatocellular carcinoma. Homo sapiens

The newly discovered 5-hydroxymethylcytosine (5hmC) may complicate previous observations of abnormal cytosine methylation statuses used for the identification of new tumor suppressor gene candidates relevant to human hepatocarcinogenesis. The simultaneous detection of 5mC and 5hmC will stimulate the discovery of aberrantly methylated genes with increased accuracy in human hepatocellular carcinoma (HCC). Here, we performed a newly developed single-base high-throughput sequencing approach (hydroxymethylation and methylation Sensitive Tag sequencing, HMST-seq) to synchronously measure these two modifications in HCC samples. After identifying the differentially methylated and hydroxymethylated genes in HCC, we integrated the DNA copy-number alterations as determined using array-based comparative genomic hybridization (aCGH) data with gene expression to identify genes potentially silenced by promoter hypermethylation. As a result, we report a high enrichment of genes with epigenetic aberrations in cancer signaling pathways. Six genes were selected as tumor suppressor gene (TSG) candidates, among which, ECM1, ATF5 and EOMES were confirmed to have potential anti-cancer function via siRNA experiments. Overall design: To fully examine 5mC and 5hmC status in HCC, we used a newly developed single-base high-throughput sequencing approach (hydroxymethylation and methylation sensitive tag sequencing, HMST-seq) to synchronously measure these two modifications in HCC samples and their adjacent non-cancerous liver tissues (non-HCCs).