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Identification of potential target sites on the urokinase-receptor for use in antagonist-based anti-cancer therapy

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Abstract:

During cancer invasion and metastasis the breakdown of extracellular matrix is mediated by several proteolytic enzyme systems including the plasminogen activation system. In this system plasminogen is activated to its active counterpart plasmin by urokinase-type plasminogen activator (uPA). The uPA-receptor (uPAR) is a GPI-anchored membrane glycoprotein, which focuses uPA at the cell surface, and via the interaction with other ligands such as the extracellular matrix protein vitronectin (Vn) and certain integrins the receptor also modulates cell adhesion and migration. Increased levels of uPAR expression is often found in the invasive areas of various human cancers and correlates with poor prognosis, and this receptor has therefore for more than a decade been recognized as a potential target for the development of new anti-invasive cancer therapies.

We have recently solved the 3-dimensional structure of uPAR in complex with a competitive peptide antagonist of the uPA-uPAR interaction [1], and this structural information was later extended to include a complex with the amino-terminal fragment of uPA (ATF) by Huai et al., [2]. The three homologous domains of uPAR is assembled into a “croissant-like” structure with a large deep central cavity capable of binding either the peptide antagonist or the receptor binding module of ATF, thus leaving the external surface accessible for other protein interactions. We have furthermore identified the functional binding epitopes on uPAR for uPA and Vn by using a comprehensive alanine-scanning library of 244 purified single-site uPAR-mutants, which has enabled us to propose a model for the tri-molecular complex of ATF-uPAR-Vn [3,4]. The functional epitopes for several competitive and non-competitive inhibitory monoclonal antibodies directed against uPAR have likewise also been determined [5,6].

In conclusion, our data provide new structural and functional informations at the molecular level about several biological important binding sites on uPAR. This new insight may potentially direct the future rational development and design of specific uPAR-antagonists for use in uPAR-targeted cancer therapy.

1. Llinas, P., M. H. Le Du, H. Gårdsvoll, K. Danø, M. Ploug, B. Gilquin, E. A. Stura and A. Menez (2005). Crystal structure of the human urokinase plasminogen activator receptor bound to an antagonist peptide. The EMBO journal, 24, 1655–1663.

2. Huai, Q., A. P. Mazar, A. Kuo, G. C. Parry, D. E. Shaw, J. Callahan, Y. Li, C. Yuan, C. Bian, L. Chen, B. Furie, B. C. Furie, D. B. Cines, and M. Huang (2006). Structure of human urokinase plasminogen activator in complex with its receptor. Science, 311, 656–659.

3. Gårdsvoll, H., B. Gilquin, M. H. Le Du, A. Menez, T. J. D. Jørgensen, and M. Ploug (2006). Characterization of the functional epitope on uPAR for uPA. Complete alanine scanning mutagenesis of uPAR supplemented by chemical crosslinking. Journal of Biological Chemistry, 281, 19260–19272.

4. Gårdsvoll, H. and M. Ploug (2007). Mapping of the vitronectin binding site on the urokinase receptor. Involvement of a composite interface of domain I and the flanking interdomain linker region. Journal of Biological Chemistry, 282, 13561–13572.

5. Gårdsvoll, H., K. Danø and M. Ploug (1999). Mapping part of the functional epitope for ligand-binding on the receptor for urokinase-type plasminogen activator by site-directed mutagenesis. Journal of Biological Chemistry, 274, 37995–38003.

6. Ploug, M. (2003) Structure-function relationships in the interaction between the urokinase-type plasminogen activator and its receptor. Current Pharmaceutical Design, 9, 1499–1528.

Document Type: Abstract

DOI: http://dx.doi.org/10.1111/j.1600-0463.2008.001165_29.x

Publication date: May 1, 2008

mksg/apm/2008/00000116/00000005/art00039
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