on September 27, 2007
Published online before print September 27, 2007, doi: 10.1161/ATVBAHA.107.150482
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Submitted on June 26, 2007
Accepted on September 17, 2007
VEGF Induces Tie2 Shedding via a Phosphoinositide 3-Kinase/Akt-Dependent Pathway to Modulate Tie2 Signaling
Clarence M. Findley ;
From the Department of Pharmacology and Cancer Biology (C.M.F., C.D.K.), Duke University Medical Center and the Duke University School of Medicine (C.M.F.), Durham, NC; the Department of Medicine (C.M.F., C.D.K.), Division of Cardiovascular Medicine, Duke University Medical Center, Durham, NC; and the Department of Reproductive and Vascular Biology (M.J.C., A.A.), Institute for Biomedical Research, The Medical School, University of Birmingham, UK
* To whom correspondence should be addressed. E-mail: cdkontos{at}duke.edu.
Objective—Tie2 and its ligands, the angiopoietins (Ang), are required for embryonic and postnatal angiogenesis. Previous studies have demonstrated that Tie2 is proteolytically cleaved, resulting in the production of a 75-kDa soluble receptor fragment (sTie2). We investigated mechanisms responsible for Tie2 shedding and its effects on Tie2 signaling and endothelial cellular responses.
Methods and Results—sTie2 bound both Ang1 and Ang2 and inhibited angiopoietin-mediated Tie2 phosphorylation and antiapoptosis. In human umbilical vein endothelial cells, Tie2 shedding was both constitutive and induced by treatment with PMA or vascular endothelial growth factor (VEGF). Constitutive and VEGF-inducible Tie2 shedding were mediated by PI3K/Akt and p38 MAPK. Tie2 shedding was blocked by pharmacological inhibitors of either PI3K or Akt as well as by overexpression of the lipid phosphatase PTEN. In contrast, sTie2 shedding was enhanced by overexpression of either dominant negative PTEN, which increased Akt phosphorylation, or constitutively active, myristoylated Akt.
Conclusions—These findings demonstrate that VEGF regulates angiopoietin-Tie2 signaling by inducing proteolytic cleavage and shedding of Tie2 via a novel PI3K/Akt-dependent pathway. These results suggest a previously unrecognized mechanism by which VEGF may inhibit vascular stabilization to promote angiogenesis and vascular remodeling.
Key words: Tie2 • VEGF • phosphoinositide 3-kinase • Akt • endothelium
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