VE‐PTP Functions as a Scaffold to Stabilize the AJ and Endothelial Barrier

Abstract

Vascular Endothelial Protein Tyrosine Phosphatase (VE‐PTP) is an endothelial‐specific phosphatase that dephosphorylates multiple proteins including Vascular Endothelial (VE)‐cadherin, the main adhesive protein of adherens junctions (AJ). VE‐PTP‐mediated dephosphorylaiton of VE‐cadherin is required for reassembly of VE‐cadherin junctions and restoration of endothelial barrier function after humoral or mechanical stress. The role of VE‐PTP in regulation of VE‐cadherin adhesion complexes under basal conditions, however, remains unknown. VE‐cadherin establishes adhesion events through trans‐interaction with opposing VE‐cadherin molecules at AJs. In resting endothelial monolayers, VE‐cadherin undergoes continues exchange between junctional and cytosolic pools due to VE‐ cadherin recruitment to and internalization from AJs. Using VE‐cadherin tagged with the photoconvertable protein Dendra2, we have demonstrated that VE‐PTP controls stability of VE‐cadherin junctions in a phosphatase‐independent manner. Overexpression of wild‐type or phosphatase “dead” VE‐PTP mutant similarly decreased the VE‐cadherin internalization rate without having any effect on VE‐cadherin recruitment rate. Consistent with these data, depletion of VE‐PTP increased VE‐cadherin internalization rate from AJs as compared to control cells suggesting that VE‐PTP stabilizes AJs in resting endothelial monolayers. Interestingly, treatment of cells with VE‐PTP phosphatase inhibitor had no effect on VE‐cadherin kinetics, further indicating a specific role of VE‐PTP in regulating stability of AJs independent of Aniopoetin‐1/Tie2 signaling. The phosphatase‐independent role of VE‐PTP was further investigated by elucidating VE‐PTP binding partners through mass spectrometry analysis. We found that VE‐PTP binds to GEF‐H1, a RhoA GEF, and inhibits RhoA activity at AJs. Knockdown of GEF‐H1 reduced both RhoA activity at AJs and tension across VE‐cadherin adhesion in VE‐PTP knockdown cells. These events coincided with restoration of VE‐cadherin kinetics at AJs suggesting that VE‐PTP stabilizes VE‐cadherin junctions via inhibition of RhoA and intracellular tension. Our data, for the first time, describe the scaffold function of VE‐PTP at AJs in the mechanism of AJ stabilization.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.