Epithelial–mesenchymal transition of ovarian tumor cells induces an angiogenic monocyte cell population

Vasculogenesis, or recruitment of progenitors able to differentiate into endothelial-like cells, may provide an important contribution to neovessel formation in tumors. However, the factors involved in the vasculogenic process and in particular the role of the epithelial–mesenchymal transition of tumor cells have not yet been investigated. We found a CD14+/KDR+ angiogenic monocyte population in undifferentiated ovarian tumors, significantly increased in the corresponding tumor metastasis. In vitro, monocyte differentiation into CD14+/KDR+ cells was induced by conditioned media from the primary ovarian tumor cells expressing a mesenchymal phenotype. In contrast, the ovarian tumor cell line SKOV3 expressing an epithelial phenotype was unable to stimulate the differentiation of monocytes into CD14+/KDR+ cells. When an epithelial–mesenchymal transition was induced in SKOV3, they acquired this differentiative ability. Moreover, after mesenchymal transition pleiotrophin expression by SKOV3 was increased and conversely its blockade significantly reduced monocyte differentiation. The obtained CD14+/KDR+ cell population showed the expression of endothelial markers, increased the formation of capillary-like structures by endothelial cells and promoted the migration of ovarian tumor cells in vitro. In conclusion, we showed that the epithelial–mesenchymal transition of ovarian tumor cells induced differentiation of monocytes into the pro-angiogenic CD14+/KDR+ population and thus it may provide a tumor microenvironment that favours vasculogenesis and metastatization of the ovarian cancer.