TIM-3 Participates in the Invasion and Metastasis of Nasopharyngeal Carcinoma via SMAD7/SMAD2/SNAIL1 Axis-Mediated Epithelial-Mesenchymal Transition

BACKGROUND: T-cell immunoglobulin and mucin domain-containing molecule-3 (TIM-3) was originally found to negatively regulate immune response and mediate immune escape in tumors. Subsequently, an increasing body of evidence has shown that TIM-3 exerts positive functions in the development and progression of several tumors. However, the role of TIM-3 in nasopharyngeal carcinoma (NPC) remains unknown. METHODS: Data from the Cancer Genome Atlas-head and neck squamous cell carcinoma and immunohistochemistry were analyzed to compare the expression of TIM-3 in NPC and non-cancerous nasopharyngitis tissues. Cell proliferation was evaluated using the Cell counting kit-8 in vitro and xenograft experiment in nude mice in vivo. Flow cytometry was used to evaluate the cell cycle. The migration and invasion of NPC cells were assessed through wound healing and Transwell assays. In addition, Western blotting was used to analyze the expression of specific proteins. RESULTS: Higher expression of TIM-3 was detected in NPC tissues than normal nasopharyngeal tissues and positively correlated with the clinical stage and T classification; however, it was not correlated with gender, age, and N classification. Furthermore, overexpression of TIM-3 using lentiviral vectors increased the malignancy of 6-10B and CNE-2 cell lines that lowly express TIM-3, by promoting cell proliferation, migration, and invasion in vitro and in vivo. In addition, overexpression of TIM-3 was associated with upregulation of matrix metalloproteinase 9 (MMP9) and MMP2, and led to epithelial-mesenchymal transition (EMT) by increasing the levels of mesenchymal markers (ie, N-cadherin, Vimentin) and decreasing those of the epithelial marker E-cadherin. Further study showed that SMAD7 was downregulated in the TIM-3 overexpression group. Relatively, phosphorylated SMAD2 and downstream molecule SNAIL1 were also upregulated in this group. CONCLUSION: TIM-3 exerts a tumor-promoting function in NPC by mediating changes in the SMAD7/SMAD2/SNAIL1 axis. These findings provide a new idea for the study of invasion, metastasis, and treatment of NPC.