Small GTP-binding protein Rac is an essential mediator of vascular endothelial growth factor-induced endothelial fenestrations and vascular permeability.
BACKGROUND
Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) induces both angiogenesis and vascular permeability. Although its angiogenic activity has been well characterized, the signaling pathways of VEGF-induced permeability remain poorly understood.


RESULTS
Using the mouse corneal micropocket assay, Miles assay, and a combination of cytochemical, electron microscopic, and biochemical assays, we demonstrate that VEGF-induced vascular leakage partly can be separated from its angiogenic activity. VEGF but not FGF-2 induced capillaries with a highly fenestrated endothelium, a feature linked with increased vascular permeability. A cell-permeable Rac antagonist (TAT-RacN17) converted VEGF-induced, leaky vascular plexuses into well-defined vascular networks. In addition, this Rac mutant blocked formation of VEGF-induced endothelial fenestrations and vascular permeability but only partially inhibited angiogenesis. Studies on endothelial cell cultures further revealed that VEGF stimulated phosphorylation of VEGF receptor-2 (VEGFR-2), leading to activation of Rac as well as increased phosphorylation of phospholipase Cgamma (PLCgamma), protein kinase B (Akt), endothelial nitric oxide synthase (eNOS), and extracellular regulated kinase (Erk1/2). We further found that phosphatidylinositol-3-OH kinase (PI3K) acted upstream of Rac and Akt-eNOS in VEGF/VEGFR-2 signaling.


CONCLUSIONS
Our findings indicate that the small GTP-binding protein Rac is a key component in mediation of VEGF-induced vascular permeability but less so in neovascularization. This may have conceptual implications for applying Rac antagonists in treatment and prevention of VEGF-induced vascular leakage and edema in connection with ischemic disorders.
Eriksson
Anna
A
Microbiology and Tumor Biology Center, Karolinska Institute, Stockholm, Sweden.
Cao
Renhai
R
Roy
Joy
J
Tritsaris
Katerina
K
Wahlestedt
Claes
C
Dissing
Steen
S
Thyberg
Johan
J
Cao
Yihai
Y
D000818:Animals; D002196:Capillaries / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D002199:Capillary Permeability / Q000187:drug effects; D002478:Cells, Cultured; D003315:Cornea / Q000033:anatomy & histology / Q000098:blood supply / Q000187:drug effects; D016228:Endothelial Growth Factors / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure*; D005260:Female; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D008222:Lymphokines / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018919:Neovascularization, Physiologic; D015398:Signal Transduction; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020744:rac GTP-Binding Proteins / Q000502:physiology*
D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D016222:Fibroblast Growth Factor 2; D020744:rac GTP-Binding Proteins