The undecided serpin

Abstract

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 urokinase. 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 differentiation, and inhibit apoptosis in a manner independent of urokinase inhibition. Despite these recent advances in defining the intracellular function of PAI‐2, it still remains one of the most mysterious and enigmatic members of the serpin superfamily.