Molecular mechanism of Rac1 regulation of endothelial permeability (1095.4)

Abstract

The RhoGTPase Rac1 plays 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. Here using photo‐activatable (PA)‐Rac1 and VE‐cadherin‐Dendra2 reporter, we studied Rac1‐mediated VE‐cadherin dynamics. We observed that activation of Rac1 reduced VE‐cadherin dissociation from AJs but had no effect on VE‐cadherin association. The net result of Rac1 activation was to promote steady‐state accumulation of VE‐cadherin at AJs by increasing the affinity of VE‐cadherin homotypic interaction. Inhibition of VE‐cadherin‐mediated adhesion with a peptide that prevents formation of VE‐cadherin‐trans interaction abolished Rac1‐mediated effect on VE‐cadherin kinetics, suggesting that stabilization of trans interaction is required for Rac1 to re‐anneal the AJ barrier. Importantly, Rac1 counterbalanced RhoA activity and decreased the mechanical tension applied to VE‐cadherin adhesion as measured using FRET biosensor. Similar to Rac1 activation, inhibition of Rho kinase (ROCK) at AJs, by un‐caging ROCK inhibitor in UV‐dependent manner, led to accumulation of VE‐cadherin at AJs via stabilization of VE‐cadherin‐trans interaction. Our findings elucidate the important molecular functions of Rac1 in promoting AJ re‐annealing through stabilizing VE‐cadherin‐trans interaction.Grant Funding Source: Supported by AHA 13PRE14670018 and NIH R01 HL045638‐24