Plasminogen Activators (Urokinase) Mediate Neovascularization: Possible Role in Tumor Angiogenesis

Abstract

Most malignant solid tumors induce the growth of new capillaries from the vascular bed by tumor angiogenesis, and dormant tumors can grow only if new capillaries are induced and penetrate into the tumor. 2 Since many human tumors produce a plasminogen activator (PA) immunochemically and biochemically identical to urokinase (the PA produced by the kidney and excreted in urine), highly purified preparations of both high and low M r urokinase have been examined for their potential to mediate neovascularization. This was of interest since PA activity has been correlated with various aspects of malignant transformation, tumor invasion, and tumor metastasis. 3 " 6 We report that homogeneously purified high molecular weight (HMW) and low molecular weight (LMW) urokinase can cause angiogenesis when angiogenic capacity was evaluated in the rabbit cornea assay. 8 The enzymatic activity of the urokinase preparations were assayed by multiple methods, including plasminogen-dependent fibrinolysis of iodinated fibrin and fluorometric determinations on a fluorogenic substrate: CBZ-Gly-Gly-Argamino methyl coumarin. 5,7,9 Purity of the enzymes employed was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. 5-7 HMW urokinase mediated angiogenesis in eight of ten experiments, whereas LMW urokinase mediated neovascularization in six of ten experiments. In control experiments it was observed that 3 H diisopropylfluorophosphate ( 3 H-DFP) labeled preparations of pure HMW and LMW urokinase failed to mediate neovascularization. It was demonstrated that 3 H-DFP-labeled urokinase preparations were inhibited in their enzymatic activity by greater than 98%. In addition, SDS-PAGE autoradiography demonstrated that 3 H-DFP was incorporated into both HMW and LMW urokinase and showed complete coincidence with Coomassie blue stained counterpart lanes in the same gels.It is therefore concluded that LMW and HMW urokinase directly, or indirectly, mediated neovascularization in the rabbit cornea and that the active site of the enzyme is required for this activity. Preliminary experiments have also suggested that tissue plasminogen activator also mediated neovascularization.It therefore appears that an important regulatory neutral serine protease that contributes to both normal degradative thrombolysis and pathologic tumor invasion and metastasis may contribute to neovascularization. During the course of our studies, an additional group of investigators simultaneously observed that LMW urokinase causes vascularization of the cornea. 1 REFERENCES 1. Berman M, S Winthrop, D Ausprunk, et al: Plasminogen activator (urokinase) causes vascularization of the cornea.

Expression and localization of 72 kDa type IV collagenase (MMP-2) in human malignant gliomas in vivo

“…In addition, tumor cells induce neovascularization in vivo [36], and increased vascularity is one of the characteristic features of glioblastomas. During the formation of new blood vessels, endothelial cells degrade basement membrane and ECM and migrate into surrounding tissues, a process that is thought to be facilitated by increased production of proteolytic enzymes from the endothelial cells [37]. In our immunohistochemical studies it was shown that MMP-2 is localized within endothelial cells of blood vessels of malignant astrocytomas, suggesting a role for MMPs in angiogenesis of brain tumors.…”

Piperine is a potent inhibitor of nuclear factor-κB (NF-κB), c-Fos, CREB, ATF-2 and proinflammatory cytokine gene expression in B16F-10 melanoma cells

“…It is also noticed that molecular events associated with those that take place during tumor invasion including growth control, regulation of motility and matrix degradation by proteolytic enzymes [43]. Several experimental observations suggest that MMPs are not only breaking down the physical barrier of extracellular matrix but also modulating the growth factors and cytokines stored in the extracellular matrix which may promote the neoplastic progression [44].…”

Novel Bi- and Trifunctional Inhibitors of Tumor-Associated Proteolytic Systems

“…Upon ligand binding (such as pro-uPA, uPA or ATF), uPAR undergoes either a conformational change or Introduction 10 demonstrated to play a role in endothelial cell migration and differentiation. uPA itself had a proangiogenic effect, when assayed in the rabbit cornea or on chicken chorioallantoic membrane (Berman et al, 1982;Goldfarb et al, 1986;Rabatti et al, 1999). Studies in PAI-1 null mice have revealed an absolute requirement for PAI-1 in tumor-induced angiogenesis.…”