Endothelial Permeability Sealed with a Kinase

John F. Foley

Science Signaling, AAAS, Washington, DC 20005, USA

Disruption of adherens junctions between endothelial cells, which are dependent on cadherins, or of adhesive interactions between these cells and the extracellular matrix, which are dependent on focal adhesion kinase (FAK), gives rise to increased endothelial permeability. Such loss of barrier function is associated with a number of inflammatory conditions, including acute respiratory distress syndrome. Noting that the binding of thrombin to protease-activating receptor 1 (PAR1), a G protein–coupled receptor, leads to a transient increase in endothelial permeability that depends on the subunits of the G_q and G₁₂ families of heterotrimeric G proteins, Knezevic et al. investigated a role for β subunits in this process. Knockdown of Gβ₁ by small interfering RNA (siRNA) or inhibition of Gβ activity did not impair thrombin-induced permeability of monolayers of human endothelial cells in culture but did prevent the recovery response that was observed in monolayers of control cells. Thrombin stimulated the phosphorylation (and activation) of FAK, which was dependent on Gβ and Fyn, a member of the Src family of tyrosine kinases. Gβ, Fyn, and FAK formed a complex in cells stimulated with thrombin, and Fyn was required for the phosphorylation of FAK and for the recovery of barrier function. Treatment of mice with the PAR1-activating peptide TFLLRN led to microvascular permeability in the lung, which was exacerbated in fyn^–/– mice. TFLLRN stimulated the phosphorylation of FAK and its recruitment to adherens junctions of endothelial cells in the lungs of wild-type but not fyn^–/– mice. A mutant of FAK that mimicked phosphorylated FAK rescued barrier integrity in lung microvessels of fyn^–/– mice. Together, these data suggest that the Gβ-dependent activation of Fyn triggers the FAK-dependent reversal of thrombin-induced endothelial permeability.

N. Knezevic, M. Tauseef, T. Thennes, D. Mehta, The G protein β subunit mediates reannealing of adherens junctions to reverse endothelial permeability increase by thrombin. J. Exp. Med. 206, 2761–2777 (2009). [Abstract] [Full Text]