Disturbance of DNA methylation patterns in the early phase of hepatocarcinogenesis induced by a choline‐deficient L‐amino acid‐defined diet in rats

The authors investigated the DNA methylation patterns of the E‐cadherin, Connexin 26 (Cx26), Rassf1a and c‐fos genes in the early phase of rat hepatocarcinogenesis induced by a choline‐deficient L‐amino acid‐defined (CDAA) diet. Six‐week‐old F344 male rats were continuously fed with the CDAA diet, and three animals were then killed at each of 4 and 8 days and 3 weeks. Genomic DNA was extracted from livers for assessment of methylation status in the 5′ upstream regions of E‐cadherin, Cx26, Rassf1a and c‐fos genes by bisulfite sequencing, compared with normal livers. The livers of rats fed the CDAA diet for 4 and 8 days and 3 weeks were methylated in E‐cadherin, Cx26 and Rassf1a genes, while normal livers were all unmethylated. In contrast, normal livers were highly methylated in c‐fos gene. Although the livers at 4 days were weakly methylated, those at 8 days and 3 weeks were markedly unmethylated. Methylation patterns of CpG sites in E‐cadherin, Cx26 and Rassf1a were sparse and the methylation was not associated with gene repression. These results indicate that gene‐specific DNA methylation patterns were found in livers of rats after short‐term feeding of the CDAA diet, suggesting gene‐specific hypermethylation might be involved in the early phase of rat hepatocarcinogenesis induced by the CDAA diet. (Cancer Sci 2007; 98: 1318–1322)