Heterotrimeric G proteins, focal adhesion kinase, and endothelial barrier function

Abstract

Ligands by binding to G protein coupled receptors (GPCRs) stimulate dissociation of heterotrimeric G proteins into Gα and Gβγ subunits. Released Gα and Gβγ subunits induce discrete signaling cues that differentially regulate focal adhesion kinase (FAK) activity and endothelial barrier function. Activation of G proteins downstream of receptors such as protease activated receptor 1 (PAR1) and histamine receptors rapidly increases endothelial permeability which reverses naturally within the following one to two hours. However, activation of G proteins coupled to the sphingosine-1-phosphate receptor 1 (S1P1) signal cues that enhance basal barrier endothelial function and restore endothelial barrier function following the increase in endothelial permeability by edemagenic agents. Intriguingly, both PAR1 and S1P1 activation stimulates FAK activity, which associates with alteration in endothelial barrier function by these agonists. In this review, we focus on the role of the G protein subunits downstream of PAR1 and S1P1 in regulating FAK activity and endothelial barrier function.

Role of Tyr143 phosphorylation of S1PR1 in downregulating endothelial cell surface S1PR1 expression and responsiveness

“…This finding demonstrates the central role of Y143 phosphorylation in regulating cell surface S1PR1 expression, and thereby the ability of endothelial cells to respond to S1P. S1PR1 functions through the heterotrimeric Gi protein pathway and downstream activation of the monomeric Rho GTPase Rac1 (Garcia et al, 2001;Lee et al, 2000;Mehta et al, 2005;Thennes and Mehta, 2012). The mechanisms by which Y143 phosphorylation of S1PR1 downregulates cell surface expression of the receptor remain unknown.…”

“…S1PR1 expressed in endothelial cells regulates angiogenesis (Argraves et al, 2010), contributes to the mechanism of vascular inflammation Peng et al, 2004) and reseals the endothelial cell barrier by mediating the assembly of adherens junctions Tauseef et al, 2008). S1PR1 functions in endothelial cells through interaction with heterotrimeric Gi proteins and downstream activation of the monomeric Rho GTPase Rac1 (Garcia et al, 2001;Lee et al, 2000;Mehta et al, 2005;Thennes and Mehta, 2012).…”

Novel regulators of endothelial barrier function

“…FAK has a long list of interacting partners. Some of these proteins include the cytoplasmic domain of the ␤-subunit of integrins, band 4.1 containing proteins -ezrin, radixin, moesin-homology domain (FERM domain), N-WASP, pp60Src, and pp59fyn, growth factor receptor-bound protein 2 (Grb2), Arf (ADP ribosylation factor), GAP containing SH3, Ankyrin repeats and PH domain (ASAP1), and p130 Crk-associated substrate (p130Cas), vinculin, talin, paxillin, 190RhoGEF, and GTPase regulator associated with FAK (GRAF) (50,87,108,139). Several studies showed that FAK through N-WASP and p120-catenin interacts with AJs and reanneals them by dampening endothelial contraction (65,75,88,118).…”

A critical role for Lyn kinase in strengthening endothelial integrity and barrier function

“…Focal adhesion kinase (FAK), which regulates focal adhesion formation and turnover, is a major determinant of vessel wall permeability. 16 Interestingly, FAK appears to be involved in both increasing or decreasing in endothelial permeability elicited by stimulation with the protease activated receptor 1 or the sphingosine-1-phosphate receptor 1, respectively. 16 FAK can be phosphorylated by SFKs at multiple sites, including tyrosine 576/577 and 925.…”

“…16 Interestingly, FAK appears to be involved in both increasing or decreasing in endothelial permeability elicited by stimulation with the protease activated receptor 1 or the sphingosine-1-phosphate receptor 1, respectively. 16 FAK can be phosphorylated by SFKs at multiple sites, including tyrosine 576/577 and 925. 17,18 It is not clear whether the distinct roles of FAK in the regulation of endothelial barrier are due to differential FAK phosphorylation by different kinases.…”