MicroRNA-504 functions as a tumor suppressor in oral squamous cell carcinoma through inhibiting cell proliferation, migration and invasion by targeting CDK6

MicroRNA (miRNA), as tumor suppressor or oncogene, is involved in the regulation of tumor development. However, the role of miRNA in human oral squamous cell carcinoma (OSCC) is less well understood. In our previous studies, we have successfully established a Chinese hamster oral squamous cell carcinoma animal model and constructed a miRNA differential expression profile, and screened out the abnormal expressed gene (miR-504). The purpose of this study was to investigate the regulatory mechanism of miR-504 in human OSCC cells and to elucidate its new target genes. CCK-8 assay, colony formation assay, transwell migration and invasion assay were used to test the cell proliferation, cell growth, cell migration and cell invasion abilities of the miR-504 mimics group, respectively. Flow cytometry was used to detect the apoptotic ability. In order to verify the direct target of miR-504, we used the dual luciferase reporting system for detection. The expressions of RNA and proteins were detected by qRT-PCR and western blotting. The results of our study showed that miR-504 expression was down-regulated in OSCC animal tissue samples. In human OSCC cell lines, miR-504 over-expression significantly inhibited cell proliferation, migration and invasion. The dual luciferase reporting system confirmed that CDK6 was a direct target of miR-504 and that miR-504 expression inhibited CDK6 expression. In addition, the over-expression of miR-504 in OSCC cells could significantly inhibit the expression of cell cycle-related proteins (E2F1, Cyclin D1), but the expression of p21 was significantly increased. The results of this study suggest that miR-504 may be a new therapeutic target for OSCC.