TIM-3 promotes the metastasis of esophageal squamous cell carcinoma by targeting epithelial-mesenchymal transition via the Akt/GSK-3/Snail signaling pathway

T-cell immunoglobulin and mucin domain-containing protein-3 (TIM-3), a negative regulator of antitumor immune response, has been demonstrated to be involved in the onset and progression of several types of malignancies. The present study aimed to determine whether and how TIM-3 plays such a role in esophageal squamous cell carcinoma (ESCC). TIM-3 expression was analyzed by immunohistochemistry and real-time fluorescence quantitative PCR (qRT-PCR) in ESCC and matched adjacent normal tissues. Functional experiments in vitro were performed to elucidate the effect of TIM-3 knockdown on the proliferation, apoptosis, migration, invasion and epithelial-mesenchymal transition (EMT) in Eca109 and TE-1 cell lines. Our data revealed that TIM-3 expression was significantly elevated at both the mRNA and protein levels in ESCC tissues compared with the levels in the matched adjacent normal tissues (both P<0.001). TIM-3 expression was significantly associated with lymph node metastasis (P=0.008), tumor-node-metastasis (TNM) stage (P=0.042) and depth of tumor invasion (P=0.042). In addition, we observed a strong correlation between high TIM-3 expression and a worse overall survival of ESCC patients (P=0.001). Functional study demonstrated that TIM-3 knockdown markedly inhibited proliferation, migration and invasion of ESCC cell lines without affecting apoptosis. In addition, TIM-3 depletion was associated with downregulation of matrix metalloproteinase (MMP)-9 and upregulation of tissue inhibitor of metalloproteinase (TIMP)-1, and with reversion of EMT, as reflected by higher levels of the epithelial marker E-cadherin and lower levels of the mesenchymal markers N-cadherin and vimentin. Further study found that TIM-3 depletion suppressed the signaling pathway involving p-Akt, p-GSK-3 and Snail. Taken together, these results suggest that TIM-3 is a novel therapeutic target and prognostic biomarker for ESCC and promotes metastasis of ESCC by inducing EMT via, at least partially, the Akt/GSK-3/Snail signaling pathway.