The G protein βγ subunit mediates reannealing of adherens junctions to reverse endothelial permeability increase by thrombin

Abstract

The inflammatory mediator thrombin proteolytically activates protease-activated receptor (PAR1) eliciting a transient, but reversible increase in vascular permeability. PAR1-induced dissociation of Gα subunit from heterotrimeric Gq and G12/G13 proteins is known to signal the increase in endothelial permeability. However, the role of released Gβγ is unknown. We now show that impairment of Gβγ function does not affect the permeability increase induced by PAR1, but prevents reannealing of adherens junctions (AJ), thereby persistently elevating endothelial permeability. We observed that in the naive endothelium Gβ1, the predominant Gβ isoform is sequestered by receptor for activated C kinase 1 (RACK1). Thrombin induced dissociation of Gβ 1 from RACK1, resulting in Gβ 1 interaction with Fyn and focal adhesion kinase (FAK) required for FAK activation. RACK1 depletion triggered Gβ 1 activation of FAK and endothelial barrier recovery, whereas Fyn knockdown interrupted with Gβ 1-induced barrier recovery indicating RACK1 negatively regulates Gβ 1-Fyn signaling. Activated FAK associated with AJ and stimulated AJ reassembly in a Fyn-dependent manner. Fyn deletion prevented FAK activation and augmented lung vascular permeability increase induced by PAR1 agonist. Rescuing FAK activation in fyn-/- mice attenuated the rise in lung vascular permeability. Our results demonstrate that Gβ 1-mediated Fyn activation integrates FAK with AJ, preventing persistent endothelial barrier leakiness. © 2009 Knezevic et al.