Vascular endothelial growth factor (VEGF) induces rapid prourokinase (pro-uPA) activation on the surface of endothelial cells

Abstract

Vascular endothelial growth factor (VEGF) is the pivotal angiogenic growth factor activating endothelial cells to migrate, proliferate, and form capillary tubes. For an ordered endothelial cell migration, tissue invasion, and degradation of the extracellular matrix, proteolytic machinery is indispensable. Such machinery, suitable for localized proteolysis, is provided by the prourokinase-urokinase-plasmin system. Prourokinase (pro-uPA), the initial component of this system, is, however, synthesized in its inactive precursor form and as such bound to its cellular receptor uPAR. Here we identify a mechanism via which VEGF 165 interacting with its receptor VEGFR-2 rapidly induces prourokinase activation that is dependent on a change in integrin affinity, activation of matrix metalloproteinase 2 (MMP-2), and pro-uPA being bound to its surface receptor uPAR. This VEGF-induced pro-uPA activation on endothelial cells is responsible for VEGF-dependent local fibrinolytic activity and might be one of the initial steps in the angiogenic process. (Blood. 2004;103:955-962)

Emodin inhibits vascular endothelial growth factor‐A‐induced angiogenesis by blocking receptor‐2 (KDR/Flk‐1) phosphorylation

“…44 During migration, VEGF-A induces pro-uPA activation via KDR/ Flk-1, and uPAR internalization leads to increased fibrinolytic activity in endothelial cells. 45 Furthermore, increased uPAR expression by hypoxia is enhanced in migrating endothelial cells in vitro, 46 and the finding that neovascularization of transplanted tumors in vivo is inhibited by uPAR antagonists 47,48 suggests that hypoxia-stimulated uPAR expression plays an essential role in tumor metastasis as well as local invasion. In our experiments, HUVECs stimulated with VEGF-A displayed elevated levels of uPA and uPAR proteins, and emodin inhibited the VEGF-Ainduced expression of uPAR, but not of uPA.…”

Gelatinase-mediated migration and invasion of cancer cells

“…Furthermore, does activation of MMPs occur simultaneously or subsequently to integrin activation? Some studies have indicated that the activation of the proteases may occur concomitant with integrin ligand-binding and activation (Prager et al, 2003;Yan et al, 2000). Investigations with activation state-specific integrin antibodies and antibodies specific for pro-and active MMPs could shed light on this matter.…”

“…MMP-1 (trypsin-activated) yes (Crabbe et al, 1994) Pro-MMP-2 yes (Crabbe et al, 1993) Pro-MMP-9 yes yes (Fridman et al, 1995;Ray et al, 2003) Pro-MMP-13 yes (Knauper et al, 1996) Pro-TGF-β1 yes yes (Yu and Stamenkovic, 2000) Pro-TNF-α yes yes (Gearing et al, 1994) Pro-urokinase yes (Prager et al, 2003) Stromal cell derived factor (SDF)-1 yes yes (McQuibban et al, 2001) Substance P yes (Backstrom and Tokes, 1995) Troponin yes Urokinase receptor yes no (Andolfo et al, 2002) Gelatinase binding to native collagens and gelatin occurs primarily via the CBD (Allan et al, 1995), whereas other MMPs, eg. MMP-3 utilizes the C-terminal domain for collagen binding (Allan et al, 1991).…”

“…The order of events occuring on the cell surface is far from clear. Some studies show that integrin activation by antibodies or divalent cations blocks uPA and MMP-2 activation and that MMP-2 activates uPA (Prager et al, 2003;Yan et al, 2000). This suggests that uPA and MMPs are activated prior to integrin activation and remain associated to the integrins.…”

“…Many of these functions appear to be signallingdependent processes and independent on the proteolytic activity (Blasi and Carmeliet, 2002). uPA is expressed as a single chain precursor, which may be activated by many proteases including plasmin, trypsin or the gelatinases (Dano et al, 1985;Ellis, 2003;Koivunen et al, 1989;Prager et al, 2003). The single chain uPA can be cleaved either to a 52 kDa or 33 kDa active two-chain molecule.…”