Silencing of microRNA-122 is an early event during hepatocarcinogenesis from non-alcoholic steatohepatitis.
Bottom Line: Expression of miR-122 in non-tumor LC at the age of 18 weeks was significantly lower than that in LC at the age of 12 weeks.Expression of miR-122 was further decreased in HCCs relative to non-tumor LC at the age of 18 weeks.DNA methylation analysis revealed that silencing of miR-122 was not mediated by DNA hypermethylation of the promoter region.
Affiliation: Division of Pharmacotherapeutics, Keio University Faculty of Pharmacy, Tokyo, Japan.Show MeSH
Related in: MedlinePlus
Mentions: To reveal the molecular mechanism underlying regulation of miR-122, we analyzed the DNA methylation status of the miR-122 promoter region, which contains a TATA-box, a CCAAT-box, and DR-1 and DR-2 elements21 (Fig.5a). We carried out the promoter assay using fragments of the human miR-122 promoter with or without the DR-1 and DR-2 elements (Fig.5b). Plasmids with or without Sss I CpG methylase treatment were used to cotransfect HepG2 cells with the Renilla luciferase expression vector. Forty-eight hours after transfection, luciferase activities were measured. The relative luciferase activity of the construct containing the DR-1 and DR-2 elements was significantly higher than that of the construct lacking these elements (*P < 0.01, Fig.5b). After treatment with CpG methylase, the relative luciferase activities were significantly decreased in the constructs both with and without the DR-1 and DR-2 elements (**P < 0.005, Fig.5b). These results indicate that the DR-1 and DR-2 elements in the miR-122 promoter are essential for regulation of miR-122 expression and that DNA methylation around the DR-1 and DR-2 elements suppress miR-122 expression.
Affiliation: Division of Pharmacotherapeutics, Keio University Faculty of Pharmacy, Tokyo, Japan.