CD87, a potential therapeutic target in angiogenesis

Angiogensis, the growth of new blood vessels, is important in the pathogenesis of malignant, infectious, fibro- proliferative, and inflammatory diseases. The angiogenic response of endothelial cells towards different growth factors is accompanied by the assembly of a cell surface-bound proteolytic machinery as a prerequisite for focal invasion. Thereby, especially the urokinase / plasminogen system has been shown to play a central role in angiogenesis. We could show previously that VEGF-induced endothelial cell migration depends on the presence of the cellular urokinase receptor, uPAR, which becomes internalized and redistributed to the leading edge during endothelial cell migration. Now, our preliminary data indicate that during this process uPAR drags integrin adhesion receptors into the same endocytotic compartment, which is prerequisite for endothelial cell migration. Within the last years, uPAR / integrin interaction attracted gaining interest as a proteolytic system interacting with integrins; thereby adhesion-induced signal transduction is affected. We hypothesize that in angiogenesis, uPAR / integrin interaction is essential for redistributing adhesive and proteolytic molecules guaranteeing angiogeneic endothelial cell behavior. In this proposal we aim to investigate consequences of uPAR / integrin interaction on signal transduction in endothelial cells. Thereby, we will analyze in detail which mechanisms are responsible for uPAR-induced and integrin-dependent signal transduction in endothelial cells, and whether these effects are matrix specific. Furthermore, we aim to characterize members of the uPAR interactome (Binder-BR et al., 2007) which are required for this process. In addition, we aim to characterize the sequence of events leading to co-internalization of integrins with uPAR during endothelial cell migration. The functional relevance of our findings will be verified in well established in vitro and in vivo assays, including a tumor-angiogenesis assay. A better understanding of the complex mechanisms by which uPAR is interfering and redistributing integrin adhesion receptors in endothelial cells, thereby affecting adhesion-induced signal transduction, might provide novel and promising leads for therapeutic targets for anti-angiogenic approaches in malignant or chronic inflammatory diseases.

Angiogensis, the growth of new blood vessels, is important in the pathogenesis of malignant, infectious, fibro-proliferative, and inflammatory diseases. The angiogenic response of endothelial cells towards different growth factors is accompanied by the assembly of a cell surface-bound proteolytic machinery as a prerequisite for focal invasion. Thereby, especially the urokinase / plasminogen system has been shown to play a central role in angiogenesis. In the study supported by the Austrian Science Foundation (FWF), we demonstrated that endothelial cell migration depends on the presence of the cellular urokinase receptor, uPAR, which becomes internalized and redistributed to the leading edge during endothelial cell migration. This effect was not exclusively dependent of stimulation via the major angiogenic growth factor VEGF, but also by various other stimuli such as FGF-2, HGF, EGF or VEGF-E. Furthermore, the results obtained in this study indicate that during this process uPAR drags integrin adhesion receptors into the same endocytotic compartment, which is a prerequisite for endothelial cell migration. We demonstrated that uPAR / integrin interaction is essential for redistributing adhesive and proteolytic molecules for guaranteeing angiogenic endothelial cell behavior. The functional relevance of our findings was verified in well established in vitro and in vivo assays, including angiogenesis assays.Finally, we determined DEP-1 as an important regulator of cell density dependent regulator of uPAR expression. DEP-1, thereby, was suggested to act as an inhibitor of endothelial cell activity upon cell-cell contact formation.In summary, the project could successfully address all aims raised, thereby the results led to a better understanding of the functional role of uPAR as a central regulator in growth-factor induced angiogenesis.