Plasminogen activator expression and matrix degradation.

The plasminogen activator (PA)-plasmin system is discussed in respect to the major interacting proteins. The various mechanisms controlling this system are described including physical properties of the reactants, molecules affecting PA synthesis, and receptors. Data is presented showing that for cell invasion to take place not only must the PA-plasmin system be operative but also specific metalloproteases must be activated. Indirect evidence indicates that this activation occurs through the action of the PA-plasmin system.