Endothelium-dependent epithelial-mesenchymal transition of tumor cells: Exclusive roles of transforming growth factor β1 and β2

Background: Induction of epithelial-mesenchymal transition (EMT) is essential for the metastasis of tumor cells and maintaining their sternness. 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 alpha-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 beta (TGF beta) antibodies were used to neutralize TGF beta(1), TGF beta(2) and TGF beta(3). Expression and release of TGF beta 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 TGF beta(1) and TGF beta(2) proteins and much lower level of TGF beta(3) protein. Conditioned medium from these endothelial cells contained TGF beta(1) and TGF beta(2), but TGF beta(3) could not be detected. Neutralizing antibody against each of TGF beta(1) or TGF beta(2) did not reverse endothelium-dependent EMT, but simultaneous neutralization of both TGF beta(1) and TGF beta(2) completely abolished it. Conclusions: Endothelial cells may play a role in the induction and maintenance of EMT in tumor cells by constitutively releasing TGF beta(1) and TGF beta(2). General significance: The present results provide a novel strategy of the inhibition of tumor metastasis by targeting vascular endothelium. (c) 2013 Elsevier B.V. All rights reserved.