MicroRNA-99a Inhibits Human Hepatocellular Carcinoma Growth And Correkates With Prognosis Of Patients With Hepatocellular Carcinoma

Through our in-depth analysis carried out by the Illumina Solexa massive parallel signature sequencing, microRNA-99a (miR-99a) was found to be the sixth abundant microRNA (miRNA) in miRNome of normal human liver but markedly down-regulated in hepatocellular carcinoma (HCC). Compelling evidences have suggested the important roles of miRNAs in HCC development. However, the biological function of miR-99a deregulation in HCC remains unknown. In this study, we found that miR-99a was remarkably decreased in HCC tissues and cell lines. Importantly, lower miR-99a expression in HCC tissues significantly correlated with shorter survival of HCC patients, and miR-99a was identified to be an independent predictor for prognosis of HCC patients. Further in vivo and in vitro experiments were employed to explore the physiological significance of miR-99a disorder in HCC. Restoration of miR-99a dramatically suppressed HCC cell growth in vitro by inducing G1phase cell cycle arrest. Intratumoral injection of cholesterol-conjugated miR-99a mimics significantly inhibited tumor growth and reduced AFP level in HCC-bearing nude mice. Insulin-like growth factor1receptor (IGF-1R) and Mammalian target of rapamycin (mTOR) were further characterized as the direct targets of miR-99a. Furthermore, protein levels of IGF-1R and mTOR were found to be inversely correlated with miR-99a expression in HCC tissues. miR-99a mimics inhibited IGF-1R and mTOR pathways and subsequently suppressed expression of cell cycle related proteins including Cyclin D1in HCC cells. In conclusion, miR-99a expression is frequently downregulated in HCC tissues and correlates with prognosis of HCC patients, thus proposing miR-99a as a prospective prognosis predictor of HCC. miR-99a suppresses HCC growth by inducing cell cycle arrest via targeting IGF-1R and mTOR, suggesting miR-99a as potential tumor suppressor for HCC therapeutics.