ABSTRACT
Plasminogen activator inhibitor 1 (PAI-1) is a fast-acting inhibitor of tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), the activators of plasminogen and hence fi brinolysis. It is mainly produced by the endothelium, but also secreted by other tissue types, such as adipose tissue. It is a serine protease inhibitor (serpin) protein. Like other serpins, PAI-1 reacts with its cognate proteases to form 1:1 enzyme-inhibitor complexes that are enzymatically inactive. PAI-1 also inhibits the activity of matrix metalloproteinases, which play a crucial role in invasion of malignant cells across the basal lamina.
