Urokinase Receptor (uPAR)-Dependent Integrin Redistribution Represents a Central Mechanism for Growth Factor Induced Endothelial Cell Migration

Abstract 2119

Tumor angiogenesis is induced when the net balance of pro- and antiangiogenic molecules is tipped in favor of angiogenesis, the so called ‘angiogenic switch’. Recently, we described a mechanism how VEGF induces pro-urokinase (pro-uPA) activation, which led to uPAR-complex formation and internalization of beta-1 integrins into the endosomal compartment via LDLR-proteins such as ApoER2 or VLDLR. Thereby, uPAR plays a central role for VEGF-induced endothelial cell migration.

Here, we describe that uPAR-induced integrin internalization and redistribution to the leading edge is not only limited to VEGF-induced endothelial cell migration, but plays a central role for others angiogenic growth factors such as fibroblast growth factor-2 (FGF-2), hepatocyte growth factor (HGF) as well as epidermal growth factor (EGF). Furthermore, we found that a hitherto undescribed binding site on domain 3 of uPAR for direct LDLR-protein interaction is required and sufficient for uPAR-dependent integrin redistribution. Interference with the uPAR/integrin internalization either by the Receptor Associated Protein (RAP) or a specific LDLR-binding site mimicking peptide (P1), the migratory response of endothelial cells towards the growth factors VEGF, HGF, FGF-2, or EGF was almost blocked (20.24% ± 4.56%). Consistently, expression of a mutated uPAR lacking interaction site for LDLR-proteins in uPAR-/- endothelial cells via a retroviral construct led to reduced invasive response towards angiogenic growth factors in vitro as well as in a Matrigel plug in vivo assay.

From these data we conclude that uPAR/LDLR-protein interaction represents a central molecule in growth factor-induced endothelial cell behavior, which might open a new avenue for therapeutic intervention.