HGF attenuates thrombin-induced endothelial permeability by Tiam1-mediated activation of the Rac pathway and by Tiam1/Rac-dependent inhibition of the Rho pathway

• Published in: The FASEB journal 2007-09, Vol.21 (11), p.2776-2786
• Main Authors: Birukova, Anna A, Alekseeva, Elena, Mikaelyan, Arsen, Birukov, Konstantin G
• Format: Article
• Language: English
• Subjects: Cell Membrane Permeability; Cells, Cultured; Electric Impedance; Endothelial Cells - cytology; Endothelial Cells - metabolism; Fluorescent Antibody Technique; Guanine Nucleotide Exchange Factors - antagonists & inhibitors; Guanine Nucleotide Exchange Factors - genetics; Guanine Nucleotide Exchange Factors - metabolism; Hemostatics - pharmacology; Hepatocyte Growth Factor - pharmacology; Humans; Immunoblotting; Protein Transport; Pulmonary Artery - cytology; Pulmonary Artery - metabolism; rac GTP-Binding Proteins - antagonists & inhibitors; rac GTP-Binding Proteins - genetics; rac GTP-Binding Proteins - metabolism; rho GTP-Binding Proteins - genetics; rho GTP-Binding Proteins - metabolism; Rho Guanine Nucleotide Exchange Factors; RNA, Small Interfering; T-Lymphoma Invasion and Metastasis-inducing Protein 1; Thrombin - pharmacology
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fj.06-7660com

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. --Birukova, A., Alekseeva, E., Mikaelyan, A., and Birukov, K. G. HGF attenuates thrombin-induced endothelial permeability by Tiam1-mediated activation of the Rac pathway and by Tiam1/Rac-dependent inhibition of the Rho pathway.