The topology of plasminogen binding and activation on the surface of humanbreast cancer cells

The urokinase-dependent activation of plasminogen by breast cancer cells pl ays an important role in metastasis. We have previously shown that the meta static breast cancer cell line MDA-MB-231 over-expresses urokinase and bind s and efficiently activates plasminogen at the cell surface compared to non -metastatic cells, The aim of this study was to further characterise plasmi nogen binding and determine the topology of cell surface-bound plasminogen in terms of its potential for activation. The lysine-dependent binding of p lasminogen at 4 degreesC to MDA-MB-231 cells was stable and resulted in an activation-susceptible conformation of plasminogen. Topologically, a fracti on of bound plasminogen was co-localised with urokinase on the surfaces of MDA-MB-231 cells where it could be activated to plasmin. At 37 degreesC pla smin was rapidly lost from the cell surface. Apart from actin, other candid ate plasminogen receptors were either not expressed or did not co-localise with plasminogen at the cell surface. Thus, based on co-localisation with u rokinase, plasminogen binding is partitioned into two functional pools on t he surface of MDA-MB-231 cells. In conclusion, these results shed further l ight on the functional organisation of the plasminogen activation cascade o n the surface of a metastatic cancer cell. (C) 2001 Cancer Research Campaig n.