Inactivation of plasminogen activator inhibitor-1 by specific proteolysis with stromelysin-1 (MMP-3)

Matrix metalloproteinase-3 (MMP-3 or stromelysin-1) specifically hydrolyzes the Ser(337)-Ser(338) (P10-P9) and Val(341)-Ile(342) (P6-P5) peptide bonds in human plasminogen activator inhibitor-1 (PAI-1). Cleavage is completely abolished in the presence of the metal chelators EDTA or 1,10-phenanthroli ne. A stabilized active PAI-1 variant was also cleaved by MMP-3. At an enzy me/substrate ratio of 1/10 at 37 degreesC, PAI-1 protein cleavage occurred with half-lives of 27 or 14 min for active or stable PAI-1 and was associat ed with rapid loss of inhibitory activity toward tissue-type plasminogen ac tivator with half-lives of 15 or 13 min, respectively. A substrate-like var iant of PAI-1, lacking inhibitory activity but with exposed reactive site l oop, was cleaved with a half-life of 23 min, whereas latent PAI-1 in which a major part of the reactive site loop is inserted into the molecule, was r esistant to cleavage, Biospecific interaction analysis indicated comparable binding of active, stable, and substrate PAI-1 to both proMMP-3 and MMP-3 (K-A of 12-22 x 10(6) M-1), whereas binding of latent PAI-1 occurred with l ower affinity (1.7-2.3 x 10(6) M-1). Stable PAI-1 bound to vitronectin was cleaved and inactivated by MMP-3 in a manner comparable with that of free P AI-1; however, the cleaved protein did not bind to vitronectin. Cleavage an d inactivation of PAI-1 by MMP-3 may thus constitute a mechanism decreasing the antiproteolytic activity of PAI-1 and impairing the potential inhibito ry effect of vitronectin-bound PAI-1 on cell adhesion and/or migration.