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      Early Signaling by Vascular Endothelial Growth Factor and Placental Growth Factor in Human Bone Marrow-Derived Endothelial Cells Is Mediated by Superoxide

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          Aims: We investigated the role of superoxide O<sub>2</sub><sup>–</sup> during the initiation of vascular endothelial growth factor (VEGF)- and placental growth factor (PlGF)-mediated signal transduction in bone marrow-derived endothelial cells. Methods: BMhTERT cells were treated with VEGF or PlGF in the presence or absence of antioxidants. The signaling pathways downstream were analyzed by immunoprecipitation and Western blotting. Superoxide and reactive oxygen species (ROS) were measured using Superluminol or 2′,7′-dichlorofluorescein fluorescence measurements. Results: We show here that VEGF and PlGF generate extracellular and intracellular O<sub>2</sub><sup>–</sup> that regulates their downstream signaling transduction pathways. Indeed, the extracellular O<sub>2</sub><sup>–</sup> generated treatment of endothelial cells (using hypoxanthine/xanthine oxidase) was sufficient to initiate receptor phosphorylation of VEGF receptor 2. The PlGF treatment of endothelial cells increased the generation of intracellular ROS in an extracellular O<sub>2</sub><sup>–</sup> dependent manner. Quenching of intracellular ROS by resveratrol inhibits PlGF- and VEGF-dependent induction of MAP kinase phosphorylation. Additionally, we found that the interaction of VEGF and PlGF with their specific receptors generates O<sub>2</sub><sup>–</sup> in a cell-free system. Endothelial cells treated with VEGF stop proliferation in the presence of extracellular catalase, superoxide dismutase or peroxiredoxin IV. Conclusion: Our studies underscore the role of O<sub>2</sub><sup>–</sup> as a critical regulator of VEGF and PlGF signal transduction initiation in endothelial cells.

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          Most cited references 24

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          Identification of the KDR tyrosine kinase as a receptor for vascular endothelial cell growth factor.

          Vascular endothelial cell growth factor (VEGF), also known as vascular permeability factor, is an endothelial cell mitogen which stimulates angiogenesis. Here we report that a previously identified receptor tyrosine kinase gene, KDR, encodes a receptor for VEGF. Expression of KDR in CMT-3 (cells which do not contain receptors for VEGF) allows for saturable 125I-VEGF binding with high affinity (KD = 75 pM). Affinity cross-linking of 125I-VEGF to KDR-transfected CMT-3 cells results in specific labeling of two proteins of M(r) = 195 and 235 kDa. The KDR receptor tyrosine kinase shares structural similarities with a recently reported receptor for VEGF, flt, in a manner reminiscent of the similarities between the alpha and beta forms of the PDGF receptors.
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            VEGF-receptor signal transduction.

            The vascular endothelial growth factor (VEGF) family of ligands and receptors has been the focus of attention in vascular biology for more than a decade. There is now a consensus that the VEGFs are crucial for vascular development and neovascularization in physiological and pathological processes in both embryo and adult. This has facilitated a rapid transition to their use in clinical applications, for example, administration of VEGF ligands to enhance vascularization of ischaemic tissues and, conversely, inhibitors of VEGF-receptor function in anti-angiogenic therapy. More recent data indicate essential roles for the VEGFs in haematopoietic cell function and in lymphangiogenesis.
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              Reactive oxygen species as downstream mediators of angiogenic signaling by vascular endothelial growth factor receptor-2/KDR.

              Recent evidence shows the involvement of reactive oxygen species (ROS) in the mitogenic cascade initiated by the tyrosine kinase receptors of several growth factor peptides. We have asked whether also the vascular endothelial growth factor (VEGF) utilizes ROS as messenger intermediates downstream of the VEGF receptor-2 (VEGFR-2)/KDR receptor given that the proliferation of endothelial cells during neoangiogenesis is physiologically regulated by oxygen and likely by its derivative species. In porcine aortic endothelial cells stably expressing human KDR, receptor activation by VEGF is followed by a rapid increase in the intracellular generation of hydrogen peroxide as revealed by the peroxide-sensitive probe dichlorofluorescein diacetate. Genetic and pharmacological studies suggest that such oxidant burst requires as upstream events the activation of phosphatidylinositol 3-kinase and the small GTPase Rac-1 and is likely initiated by lipoxygenases. Interestingly, ROS generation in response to VEGF is not blocked but rather potentiated by endothelial nitric-oxide synthase inhibitors diphenyleneiodonium and N(G)methyl-l-arginine, ruling out the possibility of nitric oxide being the oxidant species here detected in VEGF-stimulated cells. Inhibition of KDR-dependent generation of ROS attenuates early signaling events including receptor autophosphorylation and binding to a phospholipase C-gamma-glutathione S-transferase fusion protein. Moreover, catalase, the lipoxygenase inhibitor nordihydroguaiaretic acid, the synthetic ROS scavenger EUK-134, and phosphatidylinositol 3-kinase inhibitor wortmannin all reduce ERK phosphorylation in response to VEGF, and antioxidants prevent VEGF-dependent mitogenesis. Finally, cell culture and stimulation in a nearly anoxic environment mimic the effect of ROS scavenger on receptor and ERK phosphorylation, reinforcing the idea that ROS are necessary components of the mitogenic signaling cascade initiated by KDR. These data identify ROS as a new class of intracellular angiogenic mediators and may represent a potential premise for new antioxidant-based antiangiogenic therapies.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                October 2009
                30 June 2009
                : 46
                : 6
                : 601-608
                aDepartment of Biological Sciences, SUNY College at Old Westbury, Old Westbury, N.Y., bDepartment of Anatomy and Cell Biology, State University of New York, Downstate Medical Center, and cDepartment of Medicine, Memorial Sloan-Kettering Cancer Center, New York, N.Y., USA
                226228 J Vasc Res 2009;46:601–608
                © 2009 S. Karger AG, Basel

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                Page count
                Figures: 4, References: 29, Pages: 8
                Research Paper


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