Hypomethylation of CpG sites and c-myc gene overexpression in hepatocellular carcinomas, but not hyperplastic nodules, induced by a choline-deficient L-amino acid-defined diet in rats.
We have investigated aberrant methylation of CpG nucleotides (CpG sites) and gene expression of c-myc during hepatocarcinogenesis induced by a choline-deficient, L-amino acid-defined (CDAA) diet in rats. Male Fischer 344 rats, 6 weeks old, were continuously given a CDAA diet for 50 and 75 weeks and then killed. Macroscopically detectable nodules, which were histologically confirmed to be hyperplastic nodules (HNs) or well-differentiated hepatocellular carcinomas (HCCs), were dissected free from the surrounding tissue. Normal control liver was obtained from 6-week-old rats. Methylation of CpG sites of the c-myc gene was investigated in bisulfite-treated DNA isolated from normal liver, HNs and HCCs. All 33 cytosines in the 5'-upstream region of the c-myc gene were fully methylated in control liver and the 4 HNs. In contrast, these cytosines were completely unmethylated in 5 HCCs. Examination of the c-myc expression by reverse transcription-polymerase chain reaction (RT-PCR) analysis also showed a marked increase as compared to the low levels in normal livers and HNs. These results suggest that hypomethylation of the c-myc gene might play a critical role in malignant transformation from HN to HCC during CDAA diet-induced hepatocarcinogenesis in rats.
Tsujiuchi
T
T
Department of Oncological Pathology, Cancer Center, Nara Medical University, Kashihara.
Tsutsumi
M
M
Sasaki
Y
Y
Takahama
M
M
Konishi
Y
Y
D000596:Amino Acids / Q000009:adverse effects; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000235:genetics*; D002794:Choline / Q000009:adverse effects; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D004032:Diet; D020518:Focal Nodular Hyperplasia / Q000139:chemically induced / Q000235:genetics*; D005526:Food, Formulated / Q000009:adverse effects; D015972:Gene Expression Regulation, Neoplastic; D008113:Liver Neoplasms / Q000139:chemically induced / Q000235:genetics*; D008297:Male; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis / Q000235:genetics*; D051381:Rats; D011916:Rats, Inbred F344
D000596:Amino Acids; D016271:Proto-Oncogene Proteins c-myc; D002794:Choline