Excessive activation of IL-33/ST2 in cancer-associated fibroblasts promotes invasion and metastasis in ovarian cancer

Ovarian cancer is highly prevalent and has high mortality rates due to metastasis and relapse. The cross communication between cancer-associated fibroblasts (CAFs) and cancer-associated macrophages (CAMs) in the ovarian tumor microenvironment leads to cancer cell invasion and metastasis. However, the role of overproduction of IL-33/ST2 in the CAFs of ovarian cancer is still unclear. The expression of IL-33, ST2, apoptosis-related proteins and epithelial-mesenchymal transition (EMT) markers was measured by western blotting. Primary normal fibroblasts and CAFs from ovarian cancerous tissue were isolated and cultured in vitro, and the medium was used to stimulate blood-derived monocytes. Flow cytometry analysis was used to detect the frequency of M2-like macrophages in blood-derived monocytes from patients with ovarian cancer. Cell invasion were evaluated using Transwell assays. A xenograft model was used to study tumor growth in ST2-knockout and wild-type NOD-SCID mice. The results demonstrated higher expression of IL-33 and ST2 in carcinoma tissues compared with in para-carcinoma tissues, and there was a survival improvement associated with elevated IL-33. IL-33 and culture supernatants from CAFs, rather than normal ovarian fibroblasts, led to a higher expression of M2 macrophage marker genes in human blood-derived monocytes. Invasion and migration were aggravated in COC1 cells co-cultured with CAF-induced CAMs, and the EMT marker genes were upregulated. It was reported that EMT marker genes were downregulated and tumor volumes were significantly reduced in ST2-deficient mice. Overall, the IL-33/ST2 axis in ovarian cancer might integrate IL-33-expressing CAFs with M2 type-like CAMs, which aggravated invasion and metastasis by promoting EMT.