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Like most metalloproteases, matrix metalloprotease 2 (MMP-2) is synthesized as a zymogen. MMP-2 propeptide plays a role in inhibition of catalytic activity through a cysteine-zinc ion pairing, disruption of which results in full enzyme activation. A variety of proteases have been shown to be involved in the activation of pro-MMP-2, including metalloproteases and serine proteases. In the previous study we showed that MMP-2 activation occurred via specific cleavages of the propeptide by thrombin followed by intermolecular autoproteolytic processing for full enzymatic activity. Thrombin also degraded MMP-2, but this degradation was reduced greatly under cell-associated conditions with a concomitant increase in activation, prompting us to elucidate the molecular mechanisms underlying thrombin-mediated MMP-2 activation. In the present study we demonstrate that heparan sulfate is essential for thrombin-mediated activation of pro-MMP-2. Binding of heparan sulfate to thrombin is primarily responsible for this activation process, presumably through conformational changes at the active site. Furthermore, interaction of MMP-2 with exosites 1 and 2 of thrombin is crucial for thrombin-mediated MMP-2 degradation, and inhibition of this interaction by heparan sulfate or hirudin fragment results in a decrease in MMP-2 degradation. Finally, we demonstrated interaction between exosite 1 and hemopexin-like domain of MMP-2, suggesting a regulatory role of hemopexin-like domain in MMP-2 degradation. Taken together, our experimental data suggest a novel regulatory mechanism of thrombin-dependent MMP-2 enzymatic activity by heparan sulfate proteoglycans. Matrix metalloprotease 2 (MMP-2)3 is widely expressed and is closely associated with diverse biological processes through the degradation of extracellular and non-extracellular matrix molecules (1, 2). Its activity is regulated at multiple levels including gene expression, compartmentalization, zymogen activation, and enzyme inactivation by extracellular inhibitors such as tissue inhibitors of metalloproteases (TIMPs) (1). Like most metalloproteases, MMP-2 is synthesized as a zymogen that is activated by conformational change (3) or proteolytic cleavage of the propeptide. Propeptides of protease zymogens have been shown to have important functions in the inhibition of catalytic activity (4); thus, removal of the propeptide is an important prerequisite for enzymatic activity. A variety of proteases have been shown to be involved in the activation of pro-MMP-2, including metalloproteases (e.g. MMP-7 and MT-MMPs) (5-10), serine proteases (e.g. thrombin, factor Xa, activated protein C, and plasmin) (11-14), and a cysteine protease (legumain) (15).Thrombin is involved in the coagulation cascade and multiple cellular processes, including mitogenesis of fibroblasts, lymphocytes, mesenchymal cells, and smooth muscle cells, via proteolytic activation of protease activated receptors (16 -20). It also plays a role in cell migration and invasion through MMP-2 activation (21, 22).Thrombin-mediated...

Matrix metalloprotease (MMP)-2 plays a key role in many biological and pathological processes related to cell migration, invasion, and mitogenesis. MMP-2 is synthesized as a zymogen that is activated through either a conformational change or proteolysis of the propeptide. Several activating enzymes for pro-MMP-2 have been proposed, including metalloproteases and serine proteases. The mechanism of pro-MMP-2 activation by metalloproteases is well established, and the most studied activation mechanism involves cleavage of the propeptide by membrane type 1-MMP (MT1-MMP). In contrast, serine protease activation has not been thoroughly studied, although studies suggest that MT1-MMP may be involved in activation by thrombin and plasmin. Here, we demonstrate that factor Xa mediates MT1-MMP-independent processing of pro-MMP-2 in vascular smooth muscle cells and endothelial cells. Factor Xa and thrombin directly cleaved the propeptide on the carboxyl terminal sides of the Arg 98 and Arg 101 residues, whereas plasmin only cleaved the propeptide downstream of Arg 101 . Moreover, processed MMP-2 showed enzymatic activity that was enhanced by intermolecular autoproteolytic processing at the Asn 109 -Tyr peptide bond. In addition to its role in activation, factor Xa rapidly degraded MMP-2, thereby restricting excessive MMP-2 activity. Thrombin also degraded MMP-2, but the degradation was reduced greatly under cell-associated conditions, resulting in an increase in processed MMP-2. Overall, factor Xa and thrombin regulate MMP-2 enzymatic activity through its activation and degradation. Thus, the net enzymatic activity results from a balance between MMP-2 activation and degradation. Matrix metalloprotease (MMP)3 -2 is a member of the zincdependent endopeptidase family, which comprises 24 enzymes (1). MMP-2 plays a key role in many biological and pathological processes, including organ growth, endometrial cycling, wound healing, bone remodeling, tumor invasion, and metastasis (2). This enzyme functions through proteolysis of non-structural extracellular molecules and components of the basement membrane, including type IV collagen, fibronectin, elastin, laminin, aggrecan, and fibrillin (3).Like most MMPs, MMP-2 is synthesized as a zymogen that is activated by conformational change (4) or proteolysis within the propeptide, which may involve membrane type MMPs (MT-MMPs) (5-9). The most studied activation mechanism for pro-MMP-2 is cleavage of the propeptide by MT1-MMP, which requires cooperative activity between MT1-MMP and tissue inhibitor of metalloprotease (TIMP)-2 (5, 10 -12). Serine proteases, such as thrombin, factor Xa, activated protein C, and plasmin as well as the cysteine protease legumain are all known activators of pro-MMP-2 (13-17). (25,26). Both proteases can also elicit endothelial cell and SMC migration through pro-MMP-2 activation and subsequent extracellular matrix degradation (13,27,28). However, despite studies suggesting that MT1-MMP is involved in thrombin-mediated activation of pro-MMP-2, a detailed mechanism...

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Factor Xa has been reported to elicit smooth muscle cell proliferation via autocrine release of platelet-derived growth factor. However, this study has shown that factor Xa-induced mitogenesis of rat aortic smooth muscle cell is independent of platelet-derived growth factor. We also could not observe any platelet-derived growth factor isoforms in the cultured medium of factor Xastimulated cells. Our finding that the cultured medium of factor Xa-stimulated cells strongly induces rat aortic smooth muscle cell mitogenesis in the absence of factor Xa activity led us to explore the existence of a novel autocrine pathway. The autocrine growth factor was purified from the cultured medium and was identified to be epiregulin. Recombinant epiregulin was also able to induce the mitogenesis. The secretion of epiregulin from factor Xa-stimulated rat aortic smooth muscle cell required mRNA expression and protein synthesis of the growth factor. The mitogenic effect of factor Xa on rat aortic smooth muscle cell was significantly reduced by anti-epiregulin antibody or by antisense oligodeoxynucleotide to epiregulin. Several lines of experimental evidence clearly indicate that the autocrine production of epiregulin, an epidermal growth factor-related ligand, is induced in the factor Xa-stimulated mitogenic process of rat aortic smooth muscle cell.