Submitted June 19, 2008
Accepted October 8, 2008
Urokinase (uPA) mediates endothelial cell survival via induction of the X-linked inhibitor of apoptosis protein (XIAP)
Gerald W Prager, Judit Mihaly, Patrick M. Brunner, Yuri Koschelnick, Gunilla Hoyer-Hansen, and Bernd R. Binder*
Clinical Division of Oncology, Department of Medicine I and Cancer Center, Medical University Vienna, Vienna, Austria
Department of Vascular Biology and Thrombosis Research, Centre for Bio-Molecular Medicine and Pharmacology, Medical University of Vienna, Vienna, Austria
Finsen Laboratory, Copenhagen Biocenter, Copenhagen, Denmark
* Corresponding author; email: bernd.binder{at}meduniwien.ac.at.
The fibrinolytic system was originally implicated to assist the angiogenic process by inducing proteolysis. uPA additionally elicits a whole array of pro-angiogenic responses such as differentiation, proliferation, and migration, by inducing intracellular signal transduction. In this study we demonstrate that in endothelial cells uPA also protects against apoptosis by transcriptional upregulation and partially by mRNA stabilization of inhibitor of apoptosis proteins (IAPs), among them most prominently the X- linked inhibitor of apoptosis protein (XIAP). The anti-apoptotic activity of uPA was dependent on its protease activity, the presence of uPAR and LRP, but independent of the PI3kinase pathway, while VEGF-induced anti-apoptosis was PI3kinase dependent. uPA-induced cell survival involved phosphorylation of p21-activated kinase 1 (Pak1) and the I
B kinase alpha (IKK
) that leads to NFB p52 activation. In fact, blocking NFB activation by using the specific NFB inhibitor BAY11-7082 or by adenoviral-mediated over-expression of the NFB inhibitor IB, abolished uPA-induced cell survival as it blocked uPA-induced XIAP upregulation. Furthermore, down-regulating XIAP expression by siRNA significantly reduced uPA-dependent endothelial cell survival. This mechanism is also important for VEGF induced anti-apoptosis, because VEGF-dependent upregulation of XIAP was found defective in uPA-/- endothelial cells. This led us to conclude that uPA is part of a novel NFB-dependent cell survival pathway.
