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Paxillin Is Involved in the Differential Regulation of Endothelial Barrier by HGF and VEGF

¹ Department of Medicine, University of Chicago, Chicago, Illinois

Correspondence and requests for reprints should be addressed to Konstantin Birukov, M.D., Ph.D., Section of Pulmonary and Critical Medicine, Department of Medicine, University of Chicago, 929 East 57th Street, CIS Bldg., W410, Chicago, IL 60637. E-mail: kbirukov{at}medicine.bsd.uchicago.edu

Circulating levels of hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) are increased during acute lung injury; however, combined effects of HGF and VEGF on pulmonary endothelial cell (EC) permeability remain to be elucidated. We have previously shown differential remodeling of focal adhesions (FA) caused by barrier-protective and barrier-disruptive mechanical and chemical stimuli. This study examined a role of FA protein paxillin in the pulmonary EC barrier responses induced by HGF and VEGF. VEGF increased, but HGF decreased, pulmonary EC permeability. These effects were accompanied by differential patterns of site-specific phosphorylation of focal adhesion kinase (FAK) and paxillin and FA redistribution. HGF antagonized random FA formation caused by VEGF challenge and promoted FA accumulation at the cell periphery. HGF attenuated VEGF-induced paxillin redistribution, FA remodeling, and endothelial permeability. SiRNA-based paxillin knockdown attenuated VEGF-induced EC permeability, myosin light chain phosphorylation, and stress fiber and paracellular gap formation. Paxillin knockdown also decreased HGF-induced EC barrier enhancement and suppressed activation of Rac and its effector PAK1. Expression of paxillin-S²⁷³ deficient on PAK1 phosphorylation site prevented HGF-induced cytoskeletal remodeling. These data show a dual role of paxillin in the HGF- and VEGF-mediated endothelial barrier regulation and suggest essential paxillin role in the modulation of Rac-Rho crosstalk. Our results also support a model of pulmonary EC barrier recovery during resolution of ALI via switch from VEGF to HGF signaling.

Key Words: paxillin • small GTPase • pulmonary endothelium • permeability • growth factors

CLINICAL RELEVANCE We show that paxillin may serve as integrator of hepatocyte growth factor (HGF)/vascular endothelial growth factor (VEGF) signaling to small GTPases regulating endothelial cell (EC) permeability. Our data support a model of pulmonary EC barrier recovery during resolution of acute lung injury via switch from VEGF to HGF signaling.