BioProject

MicroRNAs (miRNAs) are small RNAs that regulate the expression of specific target genes. More...

MicroRNAs (miRNAs) are small RNAs that regulate the expression of specific target genes. While deregulated miRNA expression levels have been detected in many tumors, whether miRNA functional impairment is also involved in carcinogenesis remains unknown. We investigated whether deregulation of miRNA machinery components and subsequent functional impairment of miRNAs are involved in hepatocarcinogenesis. Among miRNA-containing ribonucleoprotein complex components, reduced expression of DDX20 was frequently observed in human hepatocellular carcinomas, in which enhanced NF-kB activity is closely linked to carcinogenesis. Because DDX20 normally suppresses NF-kB activity by preferentially regulating the function of the NF-kB suppressing miRNA-140, we hypothesized that impairment of miRNA-140 function may be involved in hepatocarcinogenesis. Dnmt1 was identified as a direct target of miRNA-140, and increased Dnmt1 expression in DDX20-deficient cells hypermethylated the promoters of metallothionein genes, resulting in decreased metallothionein expression leading to enhanced NF-kB activity and hepatocarcinogenesis. MiRNA-140 knockout mice were prone to hepatocarcinogenesis and showed phenomena similar to those of DDX20 deficiency, suggesting that miRNA-140 plays a central role in DDX20 deficiency–related pathogenesis. Conclusion: These results indicate that miRNA-140 acts as a liver tumor suppressor, and that impairment of miRNA-140 function due to a deficiency of DDX20, a miRNA machinery component, could lead to hepatocarcinogenesis. Overall design: Genome wide DNA methylation profiling of control and DDX20-knockdown HepG2 cells. Bisulphite converted DNA from the 2 samples were hybridised to the Illumina HumanMethylation450 BeadChip. Less...