Using Illumina Infinium HumanMethylation 450K BeadChip to explore genome-wide DNA methylation profiles in a human hepatocellular carcinoma cell line

Aberrant DNA methylation is the most common type of epigenetic alteration and is associated with many types of cancer. Although previous studies have provided a few novel DNA methylation markers in hepatocellular carcinoma (HCC), specific DNA methylation patterns and comparisons of the aberrant alterations in methylation between HCC and normal liver cell lines have not yet been reported. Therefore, in the present study the Illumina Infinium HumanMethylation 450K BeadChip was employed to identify the genome-wide aberrant DNA methylation profiles of Huh7 and L02 cells. Following Bonferroni adjustment, 102,254 differentially methylated CpG sites (covering 26,511 genes) were detected between Huh7 and L02 cells. Of those CpG sites, 62,702 (61.3%) sites were hypermethylated (covering 12,665 genes) and 39,552 (38.7%) sites were hypomethylated (covering 13,846 genes). The results of the present study indicated that 40.3% of the CpG sites were in CpG island regions, 20.7% were in CpG shores and 8.8% were in shelf regions. A total of 57.3% hypermethylated CpG sites and 39.4% of the hypomethylated CpG sites had a |β-Difference| ≥50%. Within the significant differentially methylated CpG sites, 490 genes were located within 598 differentially methylated regions. Gene Ontology enrichment analysis revealed that 2,107 differentially methylated genes were associated with ‘biological process’, 13,351 differentially methylated genes were associated with ‘molecular function’, and 18,041 differentially methylated genes were associated with ‘cellular component’. Kyoto Encyclopedia of Genes and Genomes pathway-based analysis revealed 43 signaling pathways that were associated with 5,195 differentially methylated genes. These results demonstrated that aberrant DNA methylation may be a key and common event underlying the tumorigenesis of Huh7 cells. The present study also identified many subsets of hypo- or hyper-methylated CpG sites, genes and signaling pathways, which have an importance in the occurrence and development of HCC.