Exploring the role(s) of oncogenic microRNAs in hepatocellular carcinoma

Abstract

Small non-coding RNA known as microRNA (miRNAs) were considered to be superfluous genomic material for years. Recently, miRNAs have been shown to have regulatory roles in important cellular functions involved in carcinogenesis. This study describes a miRNA signature for human primary Hepatitis B Virus positive human Hepatocellular Carcinoma (HCC). The miR-17-92 polycistron and miR-21 were among the most highly up-regulated miRNAs in HCC compared to normal liver. A finding confirmed by Northern blot analysis in both human and woodchuck tumors. Additionally, the level of thesis miRNAs was also found to be increased in cirrhotic liver.;In vitro antisense oligonucleotide knockdown models were used to evaluate the role(s) of these miRNAs in the preservation of a malignant phenotype. Reduction of the miR-17-92 polycistron or miR-21 levels significantly decreased proliferation. Additionally, knockdown of the miR-17-92 polycistron led to an increased percentage of cells in G1 phase of the cell cycle and expression of E2F1. Anchorage-independent growth was also suppressed upon reduction of the expression of either of the miR-17-92 polycistron or miR-21.;The anti-apoptotic potential of these miRNA was addressed through evaluation of Caspae-3 levels. Loss of miR-21 induced Caspase-3 levels; however loss of the miR-17-92 polycistron did not. Evaluation of known apoptosis associated miR-21 targets revealed that the tumor suppressors PTEN and PDCD4 were both elevated after miR-21 knockdown. Therefore, these findings support the hypothesis that over-expression of these miRNAs supports a malignant phenotype.;Bioinformatic analysis indicated a role for miR-21 in metastasis. Loss of tumor suppressor RhoB is associated with more aggressive tumors, changes in cell shape, migration and adhesion. This study demonstrates that miR-21 represses RhoB expression by directly binding its 3 'UTR. Using three functional assays, we demonstrated that loss of miR-21 causes a reduction in migration, invasion and cell elongation in vitro. The changes in migration and cell elongation can be mimicked by over expression of RhoB. Therefore, we conclude that miR-21 repression of RhoB promotes multiple components of the metastatic phenotype.