5-methylcytosine is present in the 5′ flanking region of ha-ras in mouse liver and increases with ageing

✍ Scribed by Jennifer L. Counts; Janice M. Kaznowski; R. Michael McClain; Jay I. Goodman

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: French
• Weight: 164 KB
• Volume: 72
• Category: Article
• ISSN: 0020-7136
• DOI: 10.1002/(sici)1097-0215(19970729)72:3<491::aid-ijc18>3.0.co;2-f

✦ Synopsis

Modifications to DNA-5-methylcytosine (5MeC) content (i.e., alterations in the level of 5MeC) constitute epigenetic events. In general, hypomethylation of a gene is necessary but not sufficient for expression, while methylated genes typically are quiescent. Ha-ras is an oncogene commonly implicated in murine liver tumorigenesis, often, though not always, involving mutation. A PCR-based approach using pre-PCR digestion with methylation-sensitive enzymes was employed to determine the 5MeC content of the 58 flanking region of this gene in (i) B6C3F 1 and C57BL/6 mouse liver from young animals (4 months old) and (ii) B6C3F 1 mouse liver from aged animals (24 months old). Two segments of the 58 flanking region of Ha-ras were examined. We demonstrate the presence of 5MeC in a portion of the 58 flanking region of Ha-ras that does not share characteristics of a CpG island, while a region that shares CpG island characteristics is primarily unmethylated. Differences in methylation status in these areas of Ha-ras were not observed between B6C3F 1 and C57BL/6 mouse livers. Increases in methylation status were observed with ageing in B6C3F 1 mouse liver. These data provide a role for methylation in regulating Ha-ras expression in mouse liver. Ha-ras in human liver has been reported to be unmethylated. There are substantial sequence differences in a key region of the 58 flanking region of Ha-ras in mice as compared to humans. These differences in DNA methylation and sequence may, in part, provide a basis for the frequent involvement of Ha-ras in mouse liver tumors and its virtual lack of involvement in human tumors.