CpG island hypermethylation and repetitive DNA hypomethylation in premalignant lesion of extrahepatic cholangiocarcinoma

Abstract

Biliary intraepithelial neoplasia (BilIN) is the premalignant lesion of extrahepatic cholangiocarcinoma (EHC), and there are no published data regarding epigenetic changes throughout disease progression from normal biliary epithelia to BilIN to EHC. The objective of this study was to identify the occurrence of CpG island hypermethylation and repetitive DNA hypomethylation in BilIN. A total of 50 EHCs, 31 BilINs, and 31 normal cystic duct samples were analyzed for their methylation status in seven genes and two repetitive DNA elements. The number of methylated genes increased with disease progression (normal bile duct, 0.6; BilIN, 2.0; EHC, 3.6; P < 0.001). The methylation level of examined genes was significantly higher in BilIN than in normal samples (TMEFF2, HOXA1, NEUROG1, and RUNX3, P < 0.05) and in EHC than in BilIN samples (TMEFF2, HOXA1, NEUROG1, RUNX3, RASSF1A, and APC, P < 0.05). Long interspersed nucleotide element-1 (LINE-1) and juxtacentromeric satellite 2 (SAT2) methylation levels were markedly lower in EHC than in normal duct and BilIN samples, and BilIN samples showed a decrease of SAT2 methylation levels but no decrease of LINE-1 methylation levels compared to normal samples. These findings suggest that most of cancer-specific CpG island hypermethylation occur in the stage of BilIN and that CpG island hypermethylation seems to occur earlier than repetitive DNA element hypomethylation.

Hypomethylation of Alu repetitive elements in esophageal mucosa, and its potential contribution to the epigenetic field for cancerization

“…Although the presence of global hypomethylation is considered to be a universal phenomenon across various types of cancers [14,[29][30][31], this is the first report on its presence in ESCCs and provides a fundamental piece of information. Also, it was striking that hypomethylation of Alu, but not LINE1, was present in non-cancerous background mucosae of ESCC patients.…”

DNA methylation profile during multistage progression of pulmonary adenocarcinomas

“…By aberrant promoter hypermethylation, transcription of the promoter regions of tumor suppressor genes is repressed leading to gene silencing. Subsets of CpG island loci are hypermethylated in premalignant or in situ neoplastic lesions, including extrahepatic biliary intraepithelial neoplasia [32], colon adenomas [33], gastric adenomas [34], pancreatic intraepithelial neoplasia [35], and prostatic intraepithelial neoplasia [36], although the methylation frequencies or methylation levels at each locus are generally lower in premalignant lesions than in their malignant counterparts.…”

DNA methylation changes in ex-adenoma carcinoma of the large intestine

“…Epithelial malignancies which develop through multistep carcinogenesis have demonstrated a stepwise increase of CpG island hypermethylation and a stepwise decrease of methylation levels in repetitive DNA elements with the progression of the lesion along multistep carcinogenesis, including hepatocellular carcinoma [30], gastric cancer [31], prostate cancer [32], and extrahepatic cholangiocarcinoma [33]. In contrast with these malignancies, colorectal cancers in the present study showed neither further increase of promoter CpG island hypermethylation compared with those of colon adenomas nor further decrease of LINE-1 and ALU methylation levels compared with those of colon adenomas.…”