PLENARY 2: ISFT Prize Lecture 23

fir; THE UROKINASE RECEPTOR The characterization of the nPA/nPA receotor interaction rewaled the “V

Q&h. J.-D, roleofthenoncatalyticAdrainoftheenz;me.Importantly,thebaund

Department of Morphology, University of Geneva Medical School, enzyrneretainedactivltyandtcmainedexposuIonthecetlsnrfacefornp

Geneva, Switzerland to several hnnrs. Receptor+ont~I nPA was nnt praected from PA inhibitors (PAW. but rec&or4mund uPA/PAl complexes were found to be clear& by. &docyto& from the cell sm%ce.~Cells placed in a

Extracelhdar proteolysis is catalyzed by enzymatic cascades involving wcreted enzymes of the serine- aod metall- families. A precise spa&-temporal control of enzyme activities is likely to be important tbr physiological extmcelhdar proteolysis. While transcriptional modulation of protease genes and specific pmtease inhibitors participate in tbis amtxul, the loc&zation of the enzymes in the extmcelhdar milieu is also one critical &erminant of their biological function. Binding of secreted etuytnes to compnncnts of extraceUnIar matrices or to cell swfaces could direct their activity to selected regions of the cellular e&moment. One of the extmcellolar prote3lytic cascades expnxed by a large variety of oell types, in cnnditions of cell migration and tissue remodeling for instance, is the plasminogen activator (PA)/plasmin system In ew aimed at exploring cell biological aspects of the PA/p&ntin system, we &served the specific binding of the nrokin;se- type PA @PA) to the plasma membmne of a number of different cell types, and proposed that tbis binding was to a high affinity cell surface receptor that could focus UPA activity to the close rnicro+nvironment of the cell.

cbemotactic gradient were observed to nzdisbiie their UPA receptors to the leading edge. plasma membmnee.xpressionoftheuPAxxxptorwds modulated upon exposure of cells to certain cytokines and other agonists.Boththe~ofreccp(orsand~raffin~fortheLil4and were fbuod to wry. Increased levels of cell sort& UPA activity on migrating endotbelial cells, for instance, resulted from increa& pmdnction ofbnth UPA and UPA receptor. TbeseobserwtionssuggestthattbeuF’Areceptoranddserve,inan autocrine or paracrine way, to direct proteolysis to discrete regions of the peri-cellular matrix, in an appqwiate am6goration to participate in the enzymatic events required for cell migration. Work by others has suggested additional, or alternative, possiilitie$ i.e. that binding of UPA to its recqtor could provide a signal for cell proliferation or ditfaentiation. Taken together, these findings iodicate tbat the UPA nxptor may play an important part in the modulation of interactions between ceils and their enviromnent.

66 STRUCTURE, FUNCTION, LOCALIZATION AND REGULATION OF THE UPA RECEPTOR, uPAR. Francesco Blasi, Massimo Conese, Francesca Fazioli, Alexandra Grebe, Paola Lirnongi, Massimo Resnati, Leena Riittinen, Nicolai Sidenius, Emilia Soravia, Daniela Talarico, Tambet Teesalu,. Simona Valcamonica. Dipartimento dr Genetica and DIBIT, H.S. Raffaele. University of Milano, via Olgettina 60, 20132 Milan, Italy.

The urokinase receptor (uPAR) provides a site for pro-uPA activation and hence for control of all UPA functions: olasmin oroduction. latent TGF-I3 and oro-HGF activation,’ mitagenesis and adhesion-promotion. uPAR can efficiently internalize uPA:serpin (PAI-1, PAI- and PN-1) complexes, but much less efficiently active, free uPA. Internalization depends on the interaction of the uPAR-bound uPA:serpin complex with the trans- membrane receptor for o.2-macroglobulin (a2-MR) (Nykiier et al., JBC, 262, 14543, 1992).The nature of the ligand, i.e. free UPA vs. uPA:serpin also affects cell surface location of uPAR. Unlike free UPA, uPA:serpins trap uPAR in a PI-PLC resistant, submembrane form that is internalized and recycled. Internalization of uPA:serpin complexes can also be regulated. Phorbol ester PMA

inhibits uPA:PAI-1 internalization by U937 cells by causing a decrease of a2-MR. A similar effect is observed when the leukemia-specific chimeric transcription factor PML- RARa is expressed in U937 cells. The recent discovery that PAI- is one of the most informative prognostic markers in most types of cancer stresses the importance of uPA:serpins internalization in cancer invasiveness. In this respect the spatial distribution of the various actors in the uPA:serpin internalization (i.e. UPA, PAI-1, uPAR and a2-MR) during embryo implantation, interestingly shows important similarities to tumors. The synthesis of individual molecules is restricted at discrete regional areas and this results in the physical separation between areas of uPA activity vs. areas of uPA:PAI-1 clearance. The stromal contribution to the uPA/uPAR/PAI system in invading cancer (Pyke et al., Am. J. Path. 1991, 138, 1059-1067, and others) finds therefore its counterpart in physiology. During embryo implantation, mother and embryo concur to form areas of different physiological functions by coordinating the expression of several genes.

67 THE UROKINASE RECEPTOR. PROTEIN STRUCTURE AND uPAR and uPA are consistently expressed at invasive foci in many ROLE IN PLASMINOGEN ACTIVATION AND CANCER types of human cancer. Often one or both these molecules are INVASION expressed by non-malignant stromal cells such as macrophages or K.Dans, N.Behrendt, N.Briinner, V.Ellis, J.Grnndahl-Hansen, tibroblasts, indicating that these cells actively contribute to the BSNielsen, H.Pappot, M.Ploug, CPyke, JRomer, and H.Solberg. invasive process. This active stromal cell participation ill cancer Finsen Laboratory, Rigshospitalet, Strandboulevarden 49, DK-2 100 invasion represents a new paradigm that may provide a framework Copenhagen, Denmark. for a better understanding of some basic phenomena in tumor

biology and also have important implications for development of Degradation of the extracellular matrix during cancer in- new treatment strategies. In addition the resent results in uPAR

vasion is accomplished by a combination of proteolytic enzyme research have several other clinical implications. High levels of systems, inchrding generation of plasmin catalyzed by the urokiuase- uPAR in breast and lung cancer tissue are, like high uPA and PAI- 1 type plasminogen activator (uPA). A specific receptor for uPA levels, associated with poor prognosis, and interference with the (uPAR) binds the enzyme to cell surfaces. uPAR is synthesized as uPA/uPAR interaction represents a promising new approach for a 3 13 amino acid residue polypeptide that is carboxy-terminally anti-invasive therapy. processed and attached to the membrane by a glycosyl- phosphatidylinositol anchor. It consists of three homologous sequence repeats, the aminoterminal one of which constitutes the uPA binding domain, Concomitant binding of uPA to uPAR and of plasminogen to unidentified binding sites at cell surfaces strongly enhances plasminogen activation and surfaces of uPAR expressing cells thus appear to be preferential sites for plasminogen activation.