Abstract 5179: An endothelial-mesenchymal transition of brain endothelial cells is required for metastatic extravasation

Abstract

Abstract Endothelial-mesenchymal transition (EndMT) is an embryonic program necessary for organ development. Despite being normally dormant in adult organisms, this mechanism can be reactivated during several pathological conditions, such as cancer and fibrosis. EndMT is characterized by the downregulation of the endothelial program, activation of the mesenchymal-fibrogenic program, and finally the activation of the myogenic program. Cancer progression towards metastasis follows a defined sequence of events described as the metastatic cascade. For extravasation and transendothelial migration metastatic cells interact first with endothelial cells. Yet the role of endothelial cells during the process of metastasis formation and extravasation is still unclear, and the interaction between metastatic and endothelial cells during transendothelial migration is poorly understood. Since tumor cells are well known to express TGF-β, and the compact endothelial layer undergoes a series of changes during metastatic extravasation (cell contact disruption, cytoskeletal reorganization, contractility), we hypothesized that an EndMT may be necessary for metastatic extravasation. We show that primary rat brain endothelial cells (BECs) undergo EndMT upon TGF-β1 treatment, characterized by the loss of tight and adherent junction proteins, the expression of fibronectin, β1-integrin, calponin and α-smooth muscle actin (SMA), and an increase in N-cadherin levels. B16/F10 activated conditioned medium (ACM) induced claudin-5 downregulation, fibronectin and SMA expression in BECs. Inhibition of TGF-β signaling during B16/F10 ACM stimulation using SB-431542 maintained claudin-5 levels and mitigated fibronectin and SMA expression. SB-431542 prevented SMA upregulation upon stimulation of BECs with A2058, MCF-7 and MDA-MB231 ACM. Moreover, B16/F10 ACM caused a reduction in transdendothelial electrical resistance and enhanced the number of melanoma cells adhering to the endothelial layer, both in a TGF- β dependent manner. Finally, pretreatment with TGF-β1 or B16/F10 ACM enhanced transendothelial migration of B16/F10 cells. Our results indicate that an EndMT may be necessary for metastatic transendothelial migration, and may play a relevant role during the complex phenomenon known as metastatic extravasation. Citation Format: Istvan A. Krizbai, Akos Gasparics, Peter Nagyoszi, Csilla Fazakas, Imola Wilhelm, Rita Bencs, Laszlo Rosivall, Attila Sebe. An endothelial-mesenchymal transition of brain endothelial cells is required for metastatic extravasation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5179. doi:10.1158/1538-7445.AM2015-5179