Protein C inhibitor, a serpin with functions in- and outside vascular biology

Human protein C inhibitor (PCI), a serpin-type protease inhibitor originally described as an inhibitor of activated protein C, has broad protease reactivity. In addition to its activities within the blood clotting and fibrinolytic cascades, it seems to participate in several biological processes including reproduction and tumor growth. This review summarizes the current understanding of PCI function, regulation, and potential biological role.