Plasminogen Activator Inhibitor‐1 shows metal dependent stabilization

Abstract

Plasminogen activator inhibitor‐1 (PAI‐1) is the major inhibitor of both urokinase (uPA) and tissue plasminogen activator (tPA). PAI‐1 forms a stable complex with these proteases in a suicide fashion. The active conformation of PAI‐1 is metastable and spontaneously converts to a latent form with a half‐life of 1.1 hours at 370C. The half‐life of the active conformation is extended to 1.5 hours when PAI‐1 is bound to the plasma protein vitronectin. However, we have evidence that this stabilization is metal dependent. Our collaborators have shown that human PAI‐1 (hPAI‐1) binds to immobilized metal affinity media charged with Mn, Co, Ni, Cu, or Zn. In this study, we measured the functional effects of metals on hPAI‐1 to determine the relevance of the hPAI‐1/metal interaction. hPAI‐1 was mixed with metal chloride in the absence or presence of added vitronectin. The decay in the amount of active PAI‐1 was measured over time by mixing it with tPA, and then measuring the amount of active/free tPA. Our results show that Mg, Ca, and Mn show modest increases in the life span of hPAI‐1 with and without vitronectin; however, Fe, Co, Ni, and Cu dramatically destabilize hPAI‐1 in the absence of vitronectin while Co, Ni, and Cu show a large stabilizing effect on hPAI‐1 in the presence of vitronectin.