VE-CADHERIN ORCHESTRATES EPIGENETIC MODIFICATIONS AIMED AT ENDOTHELIAL STABILISATION

In healthy tissues blood vessels undergo a process known as vascular stabilisation in order to tightly control vascular permeability and ensure an optimal perfusion of the tissue. Vascular stabilisation is accomplished through endothelial cell-cell contact formation, basement membrane deposition and mural cell recruitment. Conversely, tumor vessels lack vascular stability features leading to increased interstitial fluid pressure, reduced drug delivery and easier metastatic dissemination. Vascular Endothelial (VE)-cadherin plays a crucial role in adherens junction (AJ) formation between endothelial cells (ECs) and in the regulation of vascular permeability. Given this, we sought to determine in more details how VE-cadherin promotes the expression of vascular stability genes in ECs. We found that the expression and clustering of VE-cadherin at AJs upregulates a subset of endothelial-specific genes encoding the tight junction protein claudin-5, Vascular Endothelial-Protein Tyrosine Phosphatase (VE-PTP) and von Willebrand factor (vWf). Most importantly, these genes are well-known for their key role in promoting vascular stabilisation. In the absence of VE-cadherin claudin-5, VE-PTP and vWf are repressed by the combined activity of the transcription factor Forkhead-box O1 (FoxO1), β-catenin and Polycomb Group (PcG) proteins, a family of epigenetic repressors of transcription. Here we show that FoxO1 and β-catenin interact with PcG proteins in ECs and that they work as PcG protein recruiters on claudin-5, VE-PTP and vWf promoters. Strikingly, we found also that VE-cadherin is able to sequester part of Enhancer of Zeste homolog 2 (Ezh2), a key PcG protein, out of the nucleus in a β-catenin- and p120-catenin-dependent manner. Preventing p120-dependent Ezh2 sequestration at the plasma membrane leads to the repression of claudin-5, VE-PTP and vWf, thus suggesting that the sequestered pool of Ezh2 is functionally relevant for gene expression. Since in human ovarian cancer EZH2 is often upregulated in tumor vessels, we took advantage of this condition to demonstrate that CLAUDIN-5 expression is strongly downregulated when EZH2 expression is increased. This suggests that CLAUDIN-5 undergoes an epigenetic regulation exerted by PcG proteins in vivo as well. To conclude, our findings prove for the first time that AJ organisation can influence gene expression at the epigenetic level and provide new insights into the understanding of vascular stabilisation paving the way for developing new therapies for diseases characterized by vessel instability such as cancer.