Activation of Rac1 at adherens junctions promotes VE‐cadherin trans interaction

Abstract

The monomeric RhoGTPases Rac1, Cdc42, and RhoA play a critical role in regulating endothelial junctional permeability; however, the causal relationship between Rac1 activity at adherens junctions (AJs) and stability of Vascular Endothelial (VE)‐cadherin adhesion, the main adhesive complex of AJs, is not well understood. Utilizing a photo‐activatable Rac1 probe (PA‐Rac1) as a tool to control the spatial and temporal activity of Rac1 we demonstrated that photo‐activation of PA‐Rac1 at the level of AJs induced VE‐cadherin accumulation at a rate constant of 0.36 ± 0.22 min−1 in human dermal microvascular endothelial cells. Pretreatment of cells with inhibitory peptide (SP) that binds to a VE‐cadherin extracellular 1 module and prevents trans interaction abolished PA‐Rac1 effect, suggesting that Rac1 stabilizes VE‐cadherin adhesion. Consistently, PA‐Rac1 activation decreased the dissociation rate of wt‐VE‐cadherin, but not adhesion‐defective Trp2Ala and Trp4Ala mutant, from AJs as demonstrated by dynamics of photo‐switchable protein Dendra2‐tagged VE‐cadherin. In addition, PA‐Rac1 activation at AJs decreased mechanical tension across VE‐cadherin adhesion, which was directly measured using VE‐cadherin FRET‐based tension biosensor. These data cumulatively demonstrate that Rac1 signaling stabilizes VE‐cadherin trans interaction and AJ integrity by reducing tension across cell‐cell junction.