Vascular Endothelial Growth Factor Receptor-2–Induced Initial Endothelial Cell Migration Depends on the Presence of the Urokinase Receptor

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Abstract
The angiogenic response of endothelial cells initiated by different growth factors is accompanied by assembly of cell surface–bound proteolytic machinery as a prerequisite for focal invasion. We have shown previously how the vascular endothelial growth factor (VEGF) initiates proteolysis by activation of pro-urokinase (pro-PA) via the VEGF receptor-2 (VEGFR-2). We now show that the cell surface receptor of the uPA-system, the urokinase receptor (uPAR), is redistributed to focal adhesions at the leading edge of endothelial cells in response to VEGF. VEGF165 and VEGF-E, both interacting with VEGFR-2, but not PlGF exclusively stimulating VEGFR-1, induce within minutes internalization of uPAR via an LDL receptor–like molecule, dependent on generation of active uPA and the presence of plasminogen activator inhibitor-1 (PAI-1). uPAR seems to play a pivotal role in VEGFR-2–induced endothelial cell migration because cleavage of surface uPAR impaired the migratory response of endothelial cells toward VEGF-E, but not toward PlGF.

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