Background & Aims: microRNAs (miRNAs) are short noncoding RNAs that regulate gene expression negatively. Although a role for aberrant miRNA expression in cancer has been postulated, the pathophysiologic role and relevance of aberrantly expressed miRNA to tumor biology has not been established. Methods: We evaluated the expression of miRNA in human hepatocellular cancer (HCC) by expression profiling, and defined a target gene and biologically functional effect of an up-regulated miRNA. Results: miR-21 was noted to be highly overexpressed in HCC tumors and cell lines in expression profiling studies using a miRNA microarray. Inhibition of miR-21 in cultured HCC cells increased expression of the phosphatase and tensin homolog (PTEN) tumor suppressor, and decreased tumor cell proliferation, migration, and invasion. In contrast-enhanced miR-21 expression by transfection with precursor miR-21 increased tumor cell proliferation, migration, and invasion. Moreover, an increase in cell migration was observed in normal human hepatocytes transfected with precursor miR-21. PTEN was shown to be a direct target of miR-21, and to contribute to miR-21 effects on cell invasion. Modulation of miR-21 altered focal adhesion kinase phosphorylation and expression of matrix metalloproteases 2 and 9, both downstream mediators of PTEN involved in cell migration and invasion. Conclusions: Aberrant expression of miR-21 can contribute to HCC growth and spread by modulating PTEN expression and PTEN-dependent pathways involved in mediating phenotypic characteristics of cancer cells such as cell growth, migration, and invasion.
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