In view of our previous findings that tumor cell-derived macrophage migration inhibitory factor (MIF) increased macrophage-mediated ovarian cancer cell invasiveness in vitro, we investigated the wider significance of ovarian cancer cell-derived MIF for tumor growth, metastasis, and angiogenesis. We found that MIF is expressed in borderline and malignant ovarian tumors, and active MIF is found in malignant ascitic fluid. We next investigated the expression and function of MIF in a syngeneic ovarian cancer model. Stable knockdown of MIF in the murine ovarian cancer cell line ID8 decreased in vivo tumor burden and overall survival. Tumors arising from MIF knockdown cells had decreased proliferation and significantly increased apoptosis. This was associated with an increased phosphorylation of p53 and reduced Akt phosphorylation. MIF knockdown led to a changed cytokine profile in the ascitic microenvironment; tumor necrosis factor-alpha, interleukin-6 (IL-6), and IL-10 expression were all significantly decreased. Accompanying this decrease in cytokine expression was a significant decrease in macrophage infiltration into ascites. Additionally, MIF knockdown reduced the expression of proangiogenic cytokines vascular endothelial growth factor and keratinocyte chemoattractant (KC) and reduced the amount of endothelial cells in the malignant ascites. We conclude that autocrine production of MIF by ovarian cancer cells stimulates other cytokines, chemokines, and angiogenic factors that may promote colonization of the peritoneum and neovascularization of tumor deposits.
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