Endothelium-dependent epithelial-mesenchymal transition of tumor cells: exclusive roles of transforming growth factor ß1 and ß2.

ABSTRACT

BACKGROUND: Induction of epithelial-mesenchymal transition (EMT) is essential for the metastasis of tumor cells and maintaining their stemness. This study aimed to examine whether endothelial cells, which are most closely located to tumor cells in vivo, play a role in inducing EMT in tumor cells or not. METHODS: Concentrated culture medium of bovine aortic endothelial cells (BAECs) was applied to tumor cell lines (A549 and PANC-1) and epithelial cell line (NMuMg). Cadherin conversion, expressions of α-smooth muscle actin and ZO-1, actin fiber formation and cell migration were examined as hallmarks of the induction of EMT in these cell lines. Transforming growth factor ß (TGFß) antibodies were used to neutralize TGFß1, TGFß2 and TGFß3. Expression and release of TGFß proteins in BAECs as well as in porcine and human endothelial cells were assessed by Western blotting and ELISA, respectively. RESULTS: Conditioned medium of BAEC induced EMT in the examined cell lines. All endothelial cells from various species and locations expressed TGFß1 and TGFß2 proteins and much lower level of TGFß3 protein. Conditioned medium from these endothelial cells contained TGFß1 and TGFß2, but TGFß3 could not be detected. Neutralizing antibody against each of TGFß1 or TGFß2 did not reverse endothelium-dependent EMT, but simultaneous neutralization of both TGFß1 and TGFß2 completely abolished it. CONCLUSIONS: Endothelial cells may play a role in the induction and maintenance of EMT in tumor cells by constitutively releasing TGFß1 and TGFß2. GENERAL SIGNIFICANCE: The present results provide a novel strategy of the inhibition of tumor metastasis by targeting vascular endothelium.