Interleukin-33-nuclear factor-κB-CCL2 signaling pathway promotes progression of esophageal squamous cell carcinoma by directing regulatory T cells

Esophageal cancer is currently one of the most fatal cancers. However, there is no effective treatment. Increasing evidence suggests that interleukin (IL)-33 has a significant role in tumor progression and metastasis. Currently, the underlying cellular and molecular mechanism of IL-33 in promoting esophageal squamous cell carcinoma (ESCC) remains unclear. In this study, we investigated whether IL-33 could induce the epithelial-mesenchymal transition (EMT) in ESCC. Interleukin-33 expression was examined in ESCC and corresponding adjacent normal tissues by immunohistochemistry and quantitative real-time PCR experiments. Elevated IL-33 levels were observed in ESCC tissues. Further in vitro experiments were undertaken to elucidate the effect of IL-33 on migration and invasion in KYSE-450 and Eca-109 esophageal cancer cells. Knockdown of IL-33 decreased the metastasis and invasion capacity in esophageal cancer cells, whereas IL-33 overexpression showed the opposite effect. We then screened CCL2 which is a downstream molecule of IL-33, and proved that IL-33 could promote tumor development and metastasis by recruiting regulatory T cells (Tregs) through CCL2, and IL-33 regulated the expression of CCL2 through transforming growth factor-beta in Treg cells. Knockdown of IL-33 decreased the development of human ESCC xenografts in BALB/c nude mice. Collectively, we found that the IL-33/nuclear factor-kappa B/CCL2 pathway played an essential role in human ESCC progress. Hence, IL-33 should be considered as an effective therapy target for ESCC.