title: A critical role for phosphatidylinositol (3,4,5)-trisphosphate-dependent Rac exchanger 1 in endothelial junction disruption and vascular hyperpermeability.
abstract: BACKGROUND
  The small GTPase Rac is critical to vascular endothelial functions, yet its regulation in endothelial cells remains unclear. Understanding the upstream pathway may delineate Rac activation mechanisms and its role in maintaining vascular endothelial barrier integrity.
  
  
  OBJECTIVE
  By investigating phosphatidylinositol (3,4,5)-trisphosphate-dependent Rac exchanger 1 (P-Rex1), one of the Rac-specific guanine nucleotide exchange factors previously known for G protein-coupled receptor signaling, we sought to determine whether Rac-guanine nucleotide exchange factor is nodal for signal integration and potential target for drug intervention.
  
  
  RESULTS
  Using gene deletion and small interference RNA silencing approach, we investigated the role of P-Rex1 in human lung microvascular endothelial cells. Tumor necrosis factor α (TNF-α) exposure led to disruption of endothelial junctions, and silencing P-Rex1 protected junction integrity. TNF-α stimulated Rac activation and reactive oxygen species production in a P-Rex1-dependent manner. Removal of P-Rex1 significantly reduced intercellular adhesion molecule-1 expression, polymorphonuclear leukocyte transendothelial migration, and leukocyte sequestration in TNF-α-challenged mouse lungs. The P-Rex1 knockout mice were also refractory to lung vascular hyperpermeability and edema in a lipopolysaccharide-induced sepsis model.
  
  
  CONCLUSIONS
  These results demonstrate for the first time that P-Rex1 expressed in endothelial cells is activated downstream of TNF-α, which is not a G protein-coupled receptor agonist. Our data identify P-Rex1 as a critical mediator of vascular barrier disruption. Targeting P-Rex1 may effectively protect against TNF-α- and lipopolysaccharide-induced endothelial junction disruption and vascular hyperpermeability.
authors.affiliation: Department of Pharmacology, University of Illinois College of Medicine, Chicago, IL 60612, USA.
authors.forename: Ram P
authors.initials: RP
authors.lastname: Naikawadi
authors.forename: Ni
authors.initials: N
authors.lastname: Cheng
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Vogel
authors.forename: Feng
authors.initials: F
authors.lastname: Qian
authors.forename: Dianqing
authors.initials: D
authors.lastname: Wu
authors.forename: Asrar B
authors.initials: AB
authors.lastname: Malik
authors.forename: Richard D
authors.initials: RD
authors.lastname: Ye
mesh_terms: D000818:Animals; D002199:Capillary Permeability / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D020662:Guanine Nucleotide Exchange Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D018922:HL-60 Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000633:toxicity
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C511197:PREX1 protein, mouse; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha