Inhibition of Cancer Cell Urokinase Plasminogen Activator by Its Specific Inhibitor PAI-2 and Subsequent Effects on Extracellular Matrix Degradation

Isotopically labeled ([3H]serine, [3H]proline, and (35S sulfate) subendothelial cell basement membranes were used to determine the role of urokinase plasminogen activator (uPA) and its specific inhibitor plasminogen activator inhibitor 2 (PAI-2) in colon cancer cell extracellular matrix degradation. Recombinant PAI-2 irreversibly inhibited low and high molecular weight purified human uPA in addition to both colon cancer cell-associated and secreted uPA, particularly if pro-uPA had been preactivated. Two selected lines (COL0394 and LI M1215) preferentially degraded differently labeled matrices in a time- and plasminogen-depend-ent manner. This process was inhibitable by PAI-2 in the medium at levels which suggested that some degree of “shielding” of cell surface uPA from inhibitor occurred. The ability of PAI-2 to regulate the invasive phenotype of cells which express cell surface or receptor-bound uPA is discussed.