Hepatocellular carcinoma (HCC) is a highly invasive tumor with frequent intrahepatic or pulmonary metastasis, which is the main reason for high recurrence and poor survival of HCC after liver resection. However, the mechanisms for metastasis remain incompletely clear. Given that microRNAs (miRNAs) are implicated in HCC progression, we explored a potential role of miRNAs in metastasis by performing miRNA expression profiling in three subtypes of HCC with different metastatic potentials. We discovered miR-331-3p as one of most significantly overexpressed miRNAs and highly associated with metastasis of HCC. Increased expression of miR-331-3p was correlated with poor long-term survival of HCC. We provided both in vivo and in vitro evidence demonstrating that miR-331-3p promoted proliferation and metastasis of HCC cells. Using an integrated approach, we uncovered that PH domain and leucine-rich repeat protein phosphatase (PHLPP) was a novel target of miR-331-3p. Indeed, the miR-331-3p-mediated effects were antagonized by reexpression of PHLPP or mimicked by silencing of PHLPP. We further showed that miR-331-3p-mediated inhibition of PHLPP resulted in stimulation of protein kinase B (AKT) and subsequent epithelial mesenchymal transition (EMT). Finally, inhibition of miR-331-3p through a jetPEI-mediated delivery of anti-miR-331-3p vector resulted in marked inhibition of proliferation and metastasis of HCC in xenograft mice.
Conclusion: miR-331-3p promotes proliferation and EMT-mediated metastasis of HCC through suppression of PHLPP-mediated dephosphorylation of AKT. Our work implicates miR-331-3p as a potential prognostic biomarker and a novel therapeutic target.
© 2014 by the American Association for the Study of Liver Diseases.