Tiam1 and Rac1 are required for platelet-activating factor-induced endothelial junctional disassembly and increase in vascular permeability

J Biol Chem. 2009 Feb 20;284(8):5381-94. doi: 10.1074/jbc.M808958200. Epub 2008 Dec 17.


It is known that platelet-activating factor (PAF) induces severe endothelial barrier leakiness, but the signaling mechanisms remain unclear. Here, using a wide range of biochemical and morphological approaches applied in both mouse models and cultured endothelial cells, we addressed the mechanisms of PAF-induced disruption of interendothelial junctions (IEJs) and of increased endothelial permeability. The formation of interendothelial gaps filled with filopodia and lamellipodia is the cellular event responsible for the disruption of endothelial barrier. We observed that PAF ligation of its receptor induced the activation of the Rho GTPase Rac1. Following PAF exposure, both Rac1 and its guanine nucleotide exchange factor Tiam1 were found associated with a membrane fraction from which they co-immunoprecipitated with PAF receptor. In the same time frame with Tiam1-Rac1 translocation, the junctional proteins ZO-1 and VE-cadherin were relocated from the IEJs, and formation of numerous interendothelial gaps was recorded. Notably, the response was independent of myosin light chain phosphorylation and thus distinct from other mediators, such as histamine and thrombin. The changes in actin status are driven by the PAF-induced localized actin polymerization as a consequence of Rac1 translocation and activation. Tiam1 was required for the activation of Rac1, actin polymerization, relocation of junctional associated proteins, and disruption of IEJs. Thus, PAF-induced IEJ disruption and increased endothelial permeability requires the activation of a Tiam1-Rac1 signaling module, suggesting a novel therapeutic target against increased vascular permeability associated with inflammatory diseases.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism
  • Animals
  • Antigens, CD / metabolism
  • Cadherins / metabolism
  • Capillary Permeability / drug effects
  • Capillary Permeability / physiology*
  • Cells, Cultured
  • Endothelial Cells / cytology
  • Endothelial Cells / metabolism*
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Humans
  • Intercellular Junctions / metabolism*
  • Membrane Proteins / metabolism
  • Mice
  • Myosin Light Chains / metabolism
  • Neuropeptides / metabolism*
  • Phosphoproteins / metabolism
  • Phosphorylation / drug effects
  • Phosphorylation / physiology
  • Platelet Activating Factor / metabolism
  • Platelet Activating Factor / pharmacology*
  • Platelet Membrane Glycoproteins / agonists
  • Platelet Membrane Glycoproteins / metabolism
  • Protein Transport / drug effects
  • Protein Transport / physiology
  • Receptors, G-Protein-Coupled / agonists
  • Receptors, G-Protein-Coupled / metabolism
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • T-Lymphoma Invasion and Metastasis-inducing Protein 1
  • Zonula Occludens-1 Protein
  • rac GTP-Binding Proteins / metabolism*
  • rac1 GTP-Binding Protein / metabolism*


  • Actins
  • Antigens, CD
  • Cadherins
  • Guanine Nucleotide Exchange Factors
  • Membrane Proteins
  • Myosin Light Chains
  • Neuropeptides
  • Phosphoproteins
  • Platelet Activating Factor
  • Platelet Membrane Glycoproteins
  • RAC1 protein, human
  • Rac1 protein, mouse
  • Receptors, G-Protein-Coupled
  • T-Lymphoma Invasion and Metastasis-inducing Protein 1
  • TIAM1 protein, human
  • TJP1 protein, human
  • Tiam1 protein, mouse
  • Tjp1 protein, mouse
  • Zonula Occludens-1 Protein
  • cadherin 5
  • platelet activating factor receptor
  • rac GTP-Binding Proteins
  • rac1 GTP-Binding Protein