Matrix metalloproteinases and cellular fibrinolytic activity.
Several molecular interactions between the matrix metalloproteinase (MMP) and the plasminogen/plasmin (fibrinolytic) system may affect cellular fibrinolysis. MMP-3 (stromelysin-1) specifically hydrolyzes urokinase (u-PA), yielding a 17 kD NH2-terminal fragment containing the functionally intact receptor (u-PAR)-binding sequence and a 32 kD COOH-terminal fragment containing the intact serine proteinase domain. MMP-3 generates an angiostatin-like fragment (containing kringles 1-4 with the cellular binding domains) from plasminogen. Treatment with MMP-3 of monocytoid THP-1 cells saturated with bound plasminogen, resulted in a dose-dependent reduction of the amount of u-PA-activatible plasminogen. Treatment with MMP-3 of cell-bound u-PA, in contrast, did not alter cell-associated u-PA activity. These data thus indicate that MMP-3 may downregulate cell-associated plasmin activity by decreasing the amount of activatible plasminogen, without affecting cell-bound u-PA activity. MMP-3 also specifically interacts with the main inhibitors of the fibrinolytic system. Thus, MMP-3 specifically hydrolyzes human alpha2-antiplasmin (alpha2-AP), the main physiological plasmin inhibitor. alpha2-AP cleaved by MMP-3 no longer forms a stable complex with plasmin and no longer interacts with plasminogen. Cleavage and inactivation of alpha2-AP by MMP-3 may constitute a mechanism favoring local plasmin-mediated proteolysis. Furthermore, MMP-3 specifically hydrolyzes and inactivates human plasminogen activator inhibitor-1 (PAI-1). Stable PAI-1 bound to vitronectin is cleaved and inactivated by MMP-3 in a comparable manner as free PAI-1; the cleaved protein, however, does not bind to vitronectin. Cleavage and inactivation of PAI-1 by MMP-3 may thus constitute a mechanism decreasing the antiproteolytic activity of PAI-1 and impairing the potential inhibitory effect of vitronectin-bound PAI-1 on cell adhesion and/or migration. These molecular interactions of MMP-3 with enzymes, substrates and inhibitors of the fibrinolytic system may thus play a role in the regulation of (cellular) fibrinolysis. Furthermore, the temporal and topographic expression pattern of MMP components, as well as studies in gene-deficient mice, suggest a functional role in neointima formation after vascular injury.
Lijnen
H Roger
HR
Center for Molecular and Vascular Biology, University of Leuven, Campus Gasthuisberg, O&N, Herestraat 49, B-3000 Leuven, Belgium. roger.lijnen@med.kuleuven.ac.be
D000818:Animals; D002465:Cell Movement; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005342:Fibrinolysis; D006801:Humans; D006868:Hydrolysis; D019278:Matrix Metalloproteinase 3 / Q000378:metabolism*; D020782:Matrix Metalloproteinases / Q000378:metabolism*; D008954:Models, Biological; D009130:Muscle, Smooth / Q000166:cytology; D010958:Plasminogen / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism; D017434:Protein Structure, Tertiary; D019096:Vitronectin / Q000378:metabolism; D000979:alpha-2-Antiplasmin / Q000378:metabolism
D017395:Plasminogen Activator Inhibitor 1; D019096:Vitronectin; D000979:alpha-2-Antiplasmin; D010958:Plasminogen; D020782:Matrix Metalloproteinases; D019278:Matrix Metalloproteinase 3