A c-Myc/miR-17-5p feedback loop regulates metastasis and invasion of hepatocellular carcinoma

The molecular mechanisms that control metastasis of hepatocellular cancer (HCC) are still poorly understood. It has been determined that microRNA (miRNA) expression has tissue and cell specific, and decreased expression of specific miRNA could induce tumor genesis or metastasis. In this study, we identified that miR-17-5p was expressed lower in high metastatic capability HCC cell lines HCCLM3 and MHCC97H than low metastatic HCC cell line HepG2 by real-time (RT)-PCR. Restoration of miR-17-5p could significantly repress the invasiveness and metastasis of MHCC97H cell line. Furthermore, we validated c-Myc as a downstream and functional target of miR-17-5p using luciferase reporter assay. Immunohistochemical assay revealed that the expression of c-Myc protein levels was significantly increased in cancerous tissues compared with para-tumor tissues. After clinical data analysis, we observed that the higher level of c-Myc was significantly associated with a reduced overall survival (p = 0.0209). Consistent with previous research, we also demonstrated that c-Myc could upregulate the expression of miR-17-5p. Taken together, our data indicated that there is a regulatory feedback loop between miR-17-5p and c-Myc, in which miR-17-5p could suppress some of the distinguishing features, invasion, and metastasis, of oncogenic c-Myc in HCC cells, and meanwhile, miR-17-5p is upregulated by c-Myc role as a transcription factor, although further studies are still needed.