title: HGF attenuates thrombin-induced endothelial permeability by Tiam1-mediated activation of the Rac pathway and by Tiam1/Rac-dependent inhibition of the Rho pathway.
abstract: Reorganization of the endothelial cell (EC) cytoskeleton and cell adhesive complexes provides a structural basis for increased vascular permeability implicated in the pathogenesis of many diseases, including asthma, sepsis, and acute respiratory distress syndrome (ARDS). We have recently described the barrier-protective effects of hepatocyte growth factor (HGF) on the human pulmonary EC. In the present study, we explored the involvement of Rac-GTPase and Rac-specific nucleotide exchange factor Tiam1 in the mechanisms of EC barrier protection by HGF. HGF protected EC monolayers from thrombin-induced hyperpermeability, disruption of intercellular junctions, and formation of stress fibers and paracellular gaps by inhibiting thrombin-induced activation of Rho GTPase, Rho association with nucleotide exchange factor p115-RhoGEF, and myosin light chain phosphorylation, which was opposed by stimulation of Rac-dependent signaling. The pharmacological Rac inhibitor or silencing RNA (siRNA) based depletion of either Rac or Tiam1 significantly attenuated HGF-induced peripheral translocation of Rac effector cortactin, cortical actin ring formation, and EC barrier enhancement. Moreover, Tiam1 knockdown using the siRNA approach, attenuated the protective effect of HGF against thrombin-induced activation of Rho signaling, monolayer disruption, and EC hyperpermeability. This study demonstrates the Tiam1/Rac-dependent mechanism of HGF-induced EC barrier protection and provides novel mechanistic insights into regulation of EC permeability via dynamic interactions between Rho- and Tiam1/Rac-mediated pathways.
authors.affiliation: Section of Pulmonary and Critical Medicine, Department of Medicine, University of Chicago, 929 East 57th St., CIS Bldg., W410, Chicago, IL 60637, USA. abirukov@medicine.bsd.uchicago.edu
authors.forename: Anna A
authors.initials: AA
authors.lastname: Birukova
authors.forename: Elena
authors.initials: E
authors.lastname: Alekseeva
authors.forename: Arsen
authors.initials: A
authors.lastname: Mikaelyan
authors.forename: Konstantin G
authors.initials: KG
authors.lastname: Birukov
mesh_terms: D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D017097:Electric Impedance; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D020662:Guanine Nucleotide Exchange Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006490:Hemostatics / Q000494:pharmacology; D017228:Hepatocyte Growth Factor / Q000494:pharmacology*; D006801:Humans; D015151:Immunoblotting; D021381:Protein Transport; D011651:Pulmonary Artery / Q000166:cytology / Q000378:metabolism; D034741:RNA, Small Interfering; D064067:Rho Guanine Nucleotide Exchange Factors; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D013917:Thrombin / Q000494:pharmacology*; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C576600:ARHGEF1 protein, human; D020662:Guanine Nucleotide Exchange Factors; D006490:Hemostatics; D034741:RNA, Small Interfering; D064067:Rho Guanine Nucleotide Exchange Factors; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C087334:TIAM1 protein, human; D017228:Hepatocyte Growth Factor; D013917:Thrombin; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins