MiR-770 promotes oral squamous cell carcinoma migration and invasion by regulating the Sirt7/Smad4 pathway

Oral squamous cell carcinoma (OSCC) is a common malignant cancer with unfavorable prognosis, and the epithelial-to-mesenchymal transition (EMT) is a critical contributor to OSCC metastasis. Recently, we have shown that sirtuin 7 (Sirt7) is associated with EMT and OSCC metastasis by acetylating small mother against decapentaplegic 4 (Smad4). Nonetheless, the mechanism of Sirt7 downregulation in OSCC cells remains unknown. This study analyzed the potential microRNAs that were predicted to regulate Sirt7 expression by online databases. We identified miR-770 as an upstream regulator of Sirt7 that targets its 3'-untranslated region. The expression of miR-770 was observed to be negatively correlated with the mRNA expression of Sirt7 in metastatic OSCC tumors, and higher miR-770 expression was correlated with poorer OSCC patient survival. Our in vitro data indicated that miR-770 promoted OSCC cell migration and invasion, and this process was dependent on Sirt7/Smad4 signaling. Furthermore, in vivo metastasis experiments indicated that miR-770 overexpression led to more prominent OSCC metastasis and downregulated Sirt7 expression. Collectively, our results revealed a new role of Sirt7 downregulation in metastatic OSCC and suggested that miR-770 is a potential target in counteracting OSCC metastasis.