PAI-3 Background Information PAI-1, PAI-2 and PAI-3 (plasminogen activator inhibitor-1, -2 and -3) are members of the serpin serine proteinase inhibitor family. PAI-1 and PAI-2 regulate uPA (urokinase-type plasminogen activator) and TPA (tissue plasminogen activator), resulting in the inhibition of proteolytic activity. Members of the serpin family generally complex with their target proteinases, then disassociate slowly into cleaved species that fold into stable inactive forms. PAI-1 can fold into the inactive state without cleavage resulting in the latent form of PAI-1. Activity can be restored to the latent form of PAI-1 through denaturation and renaturation. PAI-2 occurs in secreted and cytosolic forms through facultative polypeptide translocation. PAI-3 inhibits plasminogen activators as well as activated protein C. PAI-3 is secreted in plasma, but is also expressed in liver.
