Angiopoietin-1 prevents VEGF-induced endothelial permeability by sequestering Src through mDia

Vascular endothelial growth factor (VEGF) and Angiopoietin 1 (Ang1) are both potent proangiogenic factors, but, whereas VEGF causes vascular permeability, Ang1 stabilizes blood vessels and protects them from VEGF-induced plasma leakage. The antivascular permeability mechanisms deployed by Ang1 are still undefined. Here, we demonstrate that Ang1 halts the ability of VEGF to induce the phosphorylation-dependent redistribution of the adhesion molecule VE-cadherin, thereby rescuing the endothelial barrier function. Ang1 inhibits the activation of Src by VEGF, the most upstream component of the pathway linking VEGF receptors to VE-cadherin internalization. Indeed, Ang1 promotes the activation of mDia through RhoA, resulting in the association of mDia with Src. This ultimately deprives VEGF receptors of an essential molecule required for promoting the disruption of endothelial cell-cell contacts and paracellular permeability.