MicroRNA-9 promotes tumor metastasis via repressing E-cadherin in esophageal squamous cell carcinoma

MicroRNAs (miRNAs) play a critical role in development and progression of cancers. Deregulation of MicroRNA-9 (miR-9) has been documented in many types of cancers but their role in the development of esophageal squamous cell carcinoma (ESCC) has not been studied. This study aimed to investigate the effect of miR-9 in esophageal cancer metastasis. The up-regulation of miR-9 was frequently detected in primary ESCC tumor tissue, which was significantly associated with clinical progression (P = 0.022), lymph node metastasis (P = 0.007) and poor overall survival (P < 0.001). Functional study demonstrated that miR-9 promoted cell migration and tumor metastasis, which were effectively inhibited when expression of miR-9 was silenced. Moreover, we demonstrated that miR-9 interacted with the 3'-untranslated region of E-cadherin and down-regulated its expression, which induced β-catenin nuclear translocation and subsequently up-regulated c-myc and CD44 expression. In addition, miR-9 induced epithelial-mesenchymal transition (EMT) in ESCC, a key event in tumor metastasis. Taken together, our study demonstrates that miR-9 plays an important role in ESCC metastasis by activating β-catenin pathway and inducing EMT via targeting E-cadherin. Our study also suggests miR-9 can be served as a new independent prognostic marker and/or as a novel potential therapeutic target for ESCC.