Semaphorin 3A elevates endothelial cell permeability through PP2A inactivation.

VE-cadherin-mediated cell-cell junction weakening increases paracellular permeability in response to both angiogenic and inflammatory stimuli. Although Semaphorin 3A has emerged as one of the few known anti-angiogenic factors to exhibit pro-permeability activity, little is known about how it triggers vascular leakage. Here we report that Semaphorin 3A induced VE-cadherin serine phosphorylation and internalisation, cell-cell junction destabilisation, and loss of barrier integrity in brain endothelial cells. In addition, high-grade glioma-isolated tumour-initiating cells were found to secrete Semaphorin 3A, which promoted brain endothelial monolayer permeability. From a mechanistic standpoint, Semaphorin 3A impinged upon the basal activity of the serine phosphatase PP2A and disrupted PP2A interaction with VE-cadherin, leading to cell-cell junction disorganization and increased permeability. Accordingly, both pharmacological inhibition and siRNA-based knockdown of PP2A mimicked Semaphorin 3A effects on VE-cadherin. Hence, local Semaphorin 3A production impacts on the PP2A/VE-cadherin equilibrium and contributes to elevated vascular permeability.