MicroRNA-9 inhibits the proliferation of oral squamous cell carcinoma cells by suppressing expression of CXCR4 via the Wnt/β-catenin signaling pathway

Aberrant expression of microRNAs (miRNAs) has been involved in the development and progression of malignancy. MicroRNA-9 (miR-9) has been confirmed to be underexpressed in many types of cancers. However, the relationship between miR-9 and the Wnt/beta-catenin signaling pathway in oral squamous cell carcinoma (OSCC) remains largely unknown. Here we showed that the miR-9 was underexpressed in patients with OSCC and several OSCC cell lines. Lentivirus-mediated miR-9 overexpression in highly aggressive (Tca8113 and SCC-9) tumor cells significantly inhibited proliferation of the two cell lines in vitro and in vivo. Furthermore, we found that the CXC chemokine receptor 4 (CXCR4) gene was a direct target of miR-9. RNA interference silencing of CXCR4 proved that miR-9 underexpression led to constitutive activation of beta-catenin through activation of CXCR4 expression in OSCC cells. Finally, we also analyzed the possible relationship between miR-9 and the genes downstream of the Wnt/beta-catenin pathway in OSCC development and progression. These results provide new evidence of miR-9 as a promising tumor gene therapeutic target for OSCC patients.