Plasminogen activator inhibitor type-2 (PAI-2) is a nonconventional serine protease inhibitor (serpin) with unique and tantalizing properties that is generally considered to be an authentic and physiological inhibitor of uro-kinase. However, the fact that only a small percentage of PAI-2 is secreted has been a long-standing argument for alternative roles for this serpin. Indeed, PAI-2 has been shown to have a number of intracellular roles: it can alter gene expression, influence the rate of cell proliferation and differ-entiation, and inhibit apoptosis in a manner independent of urokinase inhi-bition. .
