INCREASED PLASMINOGEN BINDING IS ASSOCIATED WITH METASTATIC BREAST-CANCER CELLS - DIFFERENTIAL EXPRESSION OF PLASMINOGEN BINDING-PROTEINS

Overexpression of urokinase-type plasminogen activator and its recepto r correlates with metastatic capacity in breast cancer. In this study we show that the urokinase/urokinase receptor-overexpressing, metastat ic human breast cancer cell line MDA-MB-231 (1) bound significantly mo re cell-surface plasminogen in a lysine-dependent manner and(2) was ca pable of generating large amounts of plasmin compared with the non-met astatic cell lines MCF-7 and T-47D. In addition, distinct plasminogen binding proteins were detected in the plasma membranes of the cell lin es, suggesting heterogeneity of binding proteins. Plasminogen binding was analysed using a combination of dual-colour fluorescence flow cyto metry and ligand histochemistry (for comparative and cellular localiza tion of ligand binding), and fluorimetry (for Scatchard analysis). Apa rt from revealing the greater plasminogen binding capacity of MDA-MB-2 31 cells, flow cytometry and histochemistry also revealed that, in all three cell lines, non-viable or permeabilized cells bound significant ly more plasminogen in a lysine-dependent. manner than viable or non-p ermeabilized cells. Viable MDA-MB-231 cells bound plasminogen with mod erate affinity and high capacity (K-d = 1.8 mu M, receptor sites per c ell 5.0 x 10(7). Our results indicate that differences in cell surface -specific plasminogen binding capacity between cell lines may not be d etectable with binding techniques that cannot distinguish between viab le and non-viable cells.