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.