Endothelial integrity is dependent on intercellular adherens junctions formed by complexes of Vascular Endothelial (VE) cadherin and catenins. VE cadherin is a single-chain transmembrane protein that forms homophilic intercellular interactions specific to endothelial cells (EC) and mediates EC adhesion. In epithelial cells, E cadherin similarly anchors intercellular junctions, and down-regulation of E cadherin induces tumor invasion. During extravasation, cancer cells induce EC dissociation and loss of VE cadherin. While TWIST and SNAIL are transcriptional repressors of the E cadherin promoter, very little is known about TWIST and SNAIL regulation of VE-cadherin. In this study, we explored the hypothesis that TWIST and SNAIL upregulation in EC represses the VE cadherin promoter and disrupts EC integrity. In our study, human dermal microvessel endothelial cells (HDMEC) exposed to 24 hr conditioned media from SKBr-3 and MCF-7 breast cancer cells showed decreased expression of VE cadherin and upregulation of TWIST and SNAIL proteins by Western blot and qPCR. Using a Luciferase reporter construct, decreased VE cadherin promoter activity was seen in 293-T cells transfected with SNAIL cDNA. Further, Western blot data showed activated AKT and ERK/MAPK pathways in ECs exposed to conditioned media from SKBr-3 and MCF-7 cells. Blockade of AKT and ERK/MAPK pathways abrogated both VE cadherin down-regulation and SNAIL and TWIST upregulation. Taken together our results suggest that tumor released factors upregulate TWIST and SNAIL in HDMEC by AKT and ERK/MAPK kinase dependent pathways. These transcriptional repressors down-regulate the VE cadherin promoter leading to loss of VE cadherin in EC. Further, loss of VE cadherin disrupts EC integrity, facilitating tumor extravasation and metastataic progression. Optimizing EC stabilization to support EC barrier function may provide a “firewall” that may work synergistically with anti-angiogenic therapies.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA