Downregulation of miR‐122 in the rodent and human hepatocellular carcinomas

MicroRNAs (miRs) are conserved small non‐coding RNAs that negatively regulate gene expression. The miR profiles are markedly altered in cancers and some of them have a causal role in tumorigenesis. Here, we report changes in miR expression profile in hepatocellular carcinomas (HCCs) developed in male Fisher rats‐fed folic acid, methionine, and choline‐deficient (FMD) diet. Comparison of the miR profile by microarray analysis showed altered expression of some miRs in hepatomas compared to the livers from age‐matched rats on the normal diet. While let‐7a, miR‐21, miR‐23, miR‐130, miR‐190, and miR‐17‐92 family of genes was upregulated, miR‐122, an abundant liver‐specific miR, was downregulated in the tumors. The decrease in hepatic miR‐122 was a tumor‐specific event because it did not occur in the rats switched to the folate and methyl‐adequate diet after 36 weeks on deficient diet, which did not lead to hepatocarcinogenesis. miR‐122 was also silent in a transplanted rat hepatoma. Extrapolation of this study to human primary HCCs revealed that miR‐122 expression was significantly (P = 0.013) reduced in 10 out of 20 tumors compared to the pair‐matched control tissues. These findings suggest that the downregulation of miR‐122 is associated with hepatocarcinogenesis and could be a potential biomarker for liver cancers. J. Cell. Biochem. 99: 671–678, 2006. © 2006 Wiley‐Liss, Inc.

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