Abstract
Oral squamous cell carcinoma (OSCC) is one of the most common head and neck malignancies. Advanced stages of the disease are associated with poor survival, highlighting a need for new treatment modalities. We previously showed that the proinflammatory cytokine interleukin-18 (IL-18) has a tumor suppressive role in OSCC. Here, we investigated the effects of IL-18 on proliferation, migration, and invasion of OSCC cells ex vivo and in vitro, and in nude mouse xenografts. We report that expression of tankyrase 2 (TNKS2), β-catenin, and N-cadherin was higher in tumor cells than in normal mucosae, whereas the expression of IL-18 and E-cadherin was higher in normal than in tumor tissues. Elevated expression of IL-18 (P < 0.01) and E-cadherin (P = 0.034) was associated with tumor differentiation, whereas expression of TNKS2 (P < 0.01), β-catenin (P = 0.012), and N-cadherin (P < 0.01) was associated with tumor de-differentiation. Furthermore, compared with the vector control, IL-18 overexpression promoted tumor cell migration and invasion (P < 0.01), but inhibited growth of tumor cell xenografts (P < 0.05). At the protein level, expression levels of IL-18 (P < 0.01), TNKS2 (P = 0.045), β-catenin (P = 0.028), and N-cadherin (P = 0.068) were upregulated in tumor cells after IL-18 overexpression compared with those of the vector control mice, whereas expression levels of E-cadherin (P = 0.045) were decreased. In conclusion, our data suggest that IL-18 overexpression induces oral SCC cell invasion and metastasis by promoting the tumor cell epithelial-mesenchymal transition via the Wnt/β-catenin signaling pathway.