Thrombin induces the activation of progelatinase A in vascular endothelial cells. Physiologic regulation of angiogenesis

Thrombin Suppresses Matrix Metalloproteinase 2 Activity and Increases Tissue Inhibitor of Metalloproteinase 1 Synthesis in Cultured Human Peritoneal Mesothelial Cells

Objective

Recently, high levels of intraperitoneally generated thrombin were found in the effluent of patients treated with continuous ambulatory peritoneal dialysis (CAPD). The aim of the present study was to investigate in human peritoneal mesothelial cells (HMCs) the effect of thrombin on the activity and synthesis of matrix metalloproteinases (MMPs), which regulate the degradation of basement membrane collagen.

Methods

Cultured HMCs were isolated from omental tissue and used at confluence for the experiments. Conditioned media were obtained by incubating cells with serum-free M199 containing the relevant doses of thrombin. Activity of MMP-2 and MMP-9 were determined by an activity assay system. The antigen levels of MMPs and of the specific tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by ELISA. Northern blot analysis was applied to analyze mRNA expression of MMP-2 and TIMP-1.

Results

Incubation of HMCs with increasing doses of thrombin resulted in a concentration- and time-dependent suppression of MMP-2 activity. No changes in MMP-9 activity were seen. After a 48-hour stimulation period with thrombin (5 U/mL), MMP-2 activity decreased to 53% of that seen in control conditions. Antigen measurements revealed that this decrease was paralleled by a slight reduction in MMP-2 levels, which became significant at a thrombin dose of 5 U/mL [50.65 ± 7.5 ng/105cells (48 hours, 5 U/mL) vs 64.6 ± 10.1 ng/105cells (control)]. Under the same conditions, TIMP-1 levels were considerably increased [3.9 ± 0.46 μg/105cells (48 hours, 5 U/mL) vs 1.2 ± 0.14 μg/105cells (control)]. Hirudin (10 U/mL) completely inhibited the thrombin-induced effects on MMP-2 and TIMP-1 synthesis. These results were also reflected by Northern blot hybridization, where a slight decrease in MMP-2 and an increase in TIMP-1 mRNA expression were observed in response to thrombin.

Conclusions

Our results suggest that high thrombin levels suppress MMP-2 activity through decreased MMP-2 and increased TIMP-1 synthesis. Thus, thrombin may promote the accumulation of basement membrane collagen. In addition to fibrin formation, this mechanism may represent a further contribution by thrombin to peritoneal thickening during CAPD.

Matrix metalloproteinase-2: Not (just) a "hero" of the past

The 72-kDa type IV collagenase or gelatinase A is the second member of the matrix metalloproteinase family, MMP-2. Since the discovery of its first two substrates within components of the extracellular matrix, denatured interstitial type I collagen and native type IV collagen, the roles and various levels of regulation of MMP-2 have been intensively studied, mainly in vitro. Its (over)expression in most if not all tumors was considered a hallmark of cancer aggressiveness and boosted investigations aiming at its inhibition. Unfortunately, the enthusiasm subsided like a soufflé after clinical trial failures, mostly because of insufficient knowledge of in vivo MMP-2 activities and detrimental side effects of broad-spectrum MMP inhibition. Nowadays, MMP-2 remains a major topic of interest in research, the second in the MMP family after MMP-9. This review presents a broad overview of the major features of this protease. This knowledge is crucial to identify diagnostic or therapeutic strategies focusing on MMP-2. In this sense, recent publications and clinical trials underline the potential value of measuring circulating or tissular MMP-2 levels as diagnostic or prognostic tools, or as a useful secondary outcome for therapies against other primary targets. Direct MMP-2 inhibition has benefited from substantial progress in the design of more specific inhibitors but their in vivo application remains challenging but certainly worth the efforts it receives.

miR-181a-5p Inhibits Cancer Cell Migration and Angiogenesis via Downregulation of Matrix Metalloproteinase-14

Upregulation of matrix metalloproteinase MMP-14 (MT1-MMP) is associated with poor prognosis in cancer patients, but it is unclear how MMP-14 becomes elevated in tumors. Here, we show that miR-181a-5p is downregulated in aggressive human breast and colon cancers where its levels correlate inversely with MMP-14 expression. In clinical specimens, enhanced expression of MMP-14 was observed in cancer cells located at the invasive front of tumors where miR-181a-5p was downregulated relative to adjacent normal cells. Bioinformatics analyses defined a potential miR-181a-5p response element within the 3'-untranslated region of MMP-14 that was validated in reporter gene experiments. Ectopic miR-181a-5p reduced MMP-14 expression, whereas miR-181a-5p attenuation elevated MMP-14 expression. In support of a critical relationship between these two genes, miR-181a-5p-mediated reduction of MMP-14 levels was sufficient to decrease cancer cell migration, invasion, and activation of pro-MMP-2. Furthermore, this reduction in MMP-14 levels was sufficient to reduce in vivo invasion and angiogenesis in chick chorioallantoic membrane assays. Taken together, our results establish the regulation of MMP-14 in cancers by miR-181a-5p through a posttranscriptional mechanism, and they further suggest strategies to elevate miR-181a-5p to prevent cancer metastasis.

Multilevel regulation of matrix metalloproteinases in tissue homeostasis indicates their molecular specificity in vivo

The matrix metalloproteinases (MMPs) play a crucial role in irreversible remodeling of the extracellular matrix (ECM) in normal homeostasis and pathological states. Accumulating data from various studies strongly suggest that MMPs are tightly regulated, starting from the level of gene expression all the way to zymogen activation and endogenous inhibition, with each level controlled by multiple factors. Recent in vivo findings indicate that cell-ECM and cell-cell interactions, as well as ECM bio-active products, contribute an additional layer of regulation at all levels, indicating that individual MMP expression and activity in vivo are highly coordinated and tissue specific processes.

Repurposing the antipsychotic trifluoperazine as an antimetastasis agent

Because cancer cell invasion is a critical determinant of metastasis, targeting invasion is a viable approach to prevent metastasis. Utilizing a novel three-dimensional high-throughput invasion assay, we screened a National Cancer Institute compound library and discovered compounds demonstrating inhibitory effects on cancer cell invasion. One hit, trifluoperazine, suppresses invasion of human cancer cell lines while displaying a limited cytotoxicity profile. This inhibition is due to the interference with cancer cell migratory ability but not proteolytic activity. Treatment of cancer cells with trifluoperazine significantly reduces angiogenesis and prevents cancer cell invasion through a chorioallantoic basement membrane. Mechanistically, treatment results in decreased phosphorylated AKT (Ser(473) and Thr(308)) and β-catenin (Ser(552)). Lack of phosphorylation of Ser(552) of β-catenin prevents β-catenin nuclear relocation, resulting in decreased expression of vascular endothelial growth factor, likely mediated through dopamine receptor D2. Taken together, we demonstrated that trifluoperazine is responsible for reducing the angiogenic and invasive potential of aggressive cancer cells through dopamine receptor D2 to modulate the β-catenin pathway and propose that trifluoperazine may be used as an antimetastasis chemotherapeutic.

Inhibition of coagulation factor Xa improves myocardial function during CVB3-induced myocarditis

INTRODUCTION

Myocarditis is induced by coxsackievirus B3 (CVB3). Myocardial inflammation is tied to the activation of coagulation. Coagulation factor (F) Xa, a central player in coagulation, activates matrix metalloproteinases (MMP), which modulate the remodeling.

AIMS

In this study, we investigated the effects of pharmacological FXa inhibition on myocardial function, inflammation, and remodeling during a CVB3-induced myocarditis.

METHODS AND RESULTS

Immune cells and matrix proteins were detected by immunohistochemistry. The expression of cytokines was measured by real-time PCR and the activity of MMP-2 by zymography. Left ventricular function was analyzed using microconductance pressure catheter. Treatment with the FXa inhibitor fondaparinux led to an improved left ventricular function in CVB3-induced mice compared to saline-treated controls (dPdtmax: fondaparinux 4632 ± 499.6 vs. saline 3131 ± 374.0 [mmHg/s], P = 0.0503; SV: fondaparinux 33.19 ± 4.893 vs. saline 19.32 ± 2.236 [μL], P < 0.118; CO: fondaparinux 15124 ± 2183 vs. saline 8088 ± 1035 [μL/min], P < 0.05). Therapy with fondaparinux reduced the activity of MMP-2 (fondaparinux 1.208 ± 0.1247 vs. saline 1.565 ± 0.05476, P < 0.05). The collagen type I/III ratio as well as the expression of TIMP-1 was comparable in both infection groups postinfectionem (p.i.), despite an increased infiltration of macrophages into the hearts of mice treated with fondaparinux 8 days p.i. (CD68+: fondaparinux 494.2 ± 64.73 vs. saline 306.9 ± 43.73 [cells/mm(2) ], P < 0.05). Anti-inflammatory CD206-positive M2-type macrophages were increased in the infected hearts after fondaparinux treatment (CD206+: fondaparinux 182.1 ± 18.18 vs. saline 111.6 ± 21.07 [cells/mm(2) ], P < 0.05), whereas CD80-positive M1-type macrophages were comparable in both groups.

CONCLUSION

In conclusion, selective inhibition of FXa improves the left ventricular function during CVB3-induced myocarditis and seems to be associated with an improved myocardial remodeling.

Immunohistochemical correlation of matrix metalloproteinase-2 and tissue inhibitors of metalloproteinase-2 in tobacco associated epithelial dysplasia

Aim. To study the immunohistochemical expression of matrix metalloproteinase and tissue inhibitors of matrix metalloproteinase-2 in different histological grades of tobacco associated epithelial dysplasia and correlate the association between these proteases. Potentially malignant oral disorders (PMODs) progressing to oral cancer are related to the severity of epithelial dysplasia. Methods. A retrospective immunohistochemical study was carried out on 30 clinically and histologically proven cases of leukoplakia with dysplasia and 10 cases of normal buccal mucosa using anti-MMP-2 and anti-TIMP-2 monoclonal antibodies. Results. Mann Whitney U test, for comparing the expression of both MMP-2 and TIMP-2 in normal mucosa with dysplasia, was highly significant (P < 0.001). Kruskal-Wallis test to compare the median score of MMP-2 and TIMP-2 in different grades of dysplasia showed statistical significance (P < 0.001), and a Spearman's correlation between MMP-2 and TIMP-2 through different grades of dysplasia and cells observed showed positive correlation. Conclusion. Concomitant increase in the expression of both MMP-2 and TIMP-2 suggested that the activation of MMP-2 is dependent on TIMP-2 acting as a cofactor. Changes in TIMP-2 levels are considered important because they directly affect the level of MMP-2 activity.

Red ginseng extract reduced metastasis of colon cancer cells in vitro and in vivo

This study investigated the effect of red ginseng extract on metastasis of colon cancer cells in vitro and in vivo. Wound healing migration, cell motility, invasion, and activity, protein expression, and mRNA expression of matrix metalloproteinases (MMPs) were examined in SW480 human colon cancer cells. SW480 cells were cultured with or without 100 μg/L PMA in the absence or presence of various concentrations (100, 200, or 300 μg/mL) of red ginseng extract. Red ginseng extract treatment caused significant suppression of cell motility and invasion (p<0.05) in SW480 cells. Red ginseng extract inhibited MMP-2 and MMP-9 activity and their protein and mRNA expression in a dose-dependent manner (p<0.05) in SW480 cells. For experimental metastasis, BALB/c mice were injected intravenously with CT-26 mouse colon cancer cells in the tail vein, and were orally administered various concentrations (0, 75, 150, or 300 mg/kg body weight) of red ginseng extract for 3 weeks. Numbers of pulmonary nodules were significantly decreased in mice that were fed red ginseng extract (p<0.05). Plasma MMP-2 and MMP-9 activity significantly decreased in response to treatment with red ginseng extract in mice (p<0.05). These data suggest that red ginseng extract may be useful for prevention of cancer invasion and metastasis through inhibition of MMP-2 and MMP-9 pathways.

Matrix metalloproteinase-2 as a target for head and neck cancer therapy

INTRODUCTION

Matrix metalloproteinase (MMP)-2 is a zinc-dependent proteinase that is capable of cleaving all extracellular matrix (ECM) substrates. Degradation of the matrix is a key event in the progression, invasion, and metastasis of potentially malignant and malignant lesions of the head and neck. Therefore, blocking MMP-2 expression or activity may present a promising strategy for anticancer treatment.

AREAS COVERED

Current understanding of the molecular mechanisms that govern MMP-2 regulation and its tumorigenic effects, and that are involved in the initiation and progression of head and neck cancers, in particular the emerging role of MMP-2 in cell migration, which is a prerequisite for tumor metastasis. MMP-2 gene polymorphisms, cellular substrates, and interacting proteins are summarized. The current state of drugs that target this enzyme, either alone or in combination with other targeted agents are also discussed.

EXPERT OPINION

MMP-2 has long been a drug target. The current status of MMP-2 inhibitors as anticancer agents and their failure in the clinic is discussed in light of new data on the MMP-2s role as a cell surface transducer - data that may lead to the design and development of novel, MMP-2-targeting inhibitors.

Kuguacin J, a triterpeniod from Momordica charantia leaf, modulates the progression of androgen-independent human prostate cancer cell line, PC3

In this study, we focused on the in vitro effects of Kuguacin J (KuJ), a purified component of bitter melon (Momordica charantia) leaf extract (BMLE), on the androgen-independent human prostate cancer cell line PC3 and the in vivo effect of dietary BMLE on prostate carcinogenesis using a PC3-xenograph model. KuJ exerted a strong growth-inhibitory effect on PC3 cells. Growth inhibition was mainly through G1-arrest: KuJ markedly decreased the levels of cyclins (D1 and E), cyclin-dependent kinases (Cdk2 and Cdk4) and proliferating cell nuclear antigen. Interestingly, KuJ also dramatically decreased the levels of survivin expressed by PC3 cells. In addition, KuJ exerted anti-invasive effects on PC3 cells, significantly inhibiting migration and invasion: KuJ inhibited secretion of the active forms of MMP-2, MMP-9 and uPA by PC3 cells. In addition, KuJ treatment significantly decreased the expression of membrane type 1-MMP (MT1-MMP) by PC3 cells. In vivo, 1% and 5% BMLE in the diet resulted in 63% and 57% inhibition of PC3 xenograft growth without adverse effect on host body weight. Our results suggest that KuJ is a promising new candidate chemopreventive and chemotherapeutic agent for prostate cancer.

Immobilization of the irreversible thrombin inhibitor D-Phe-Pro-Arg-chloromethylketone: a concept for hemocompatible surfaces?

The irreversible thrombin inhibitor D-Phe-Pro-Arg-chloromethylketone (PPACK) was covalently immobilized to PEGylated polymer thin films at its primary alpha-amino group. Activity assays and capture of radioconjugated thrombin reveal that the PPACK-decorated surfaces could bind thrombin forming up to 30% of a monolayer density. Back-calculation of this high thrombin-inhibiting capacity indicated that the surface immobilization of the inhibitor was still associated with more than two orders of magnitude of loss of activity; increasing activity was observed at higher surface densities. PPACK-containing polymer films almost duplicated the plasma coagulation time when compared with the reference substrate without inhibitor. In whole blood, however, the anticoagulant properties were below those previously found for benzamidine-type reversible thrombin inhibitors; in addition, the surface exhibited inflammatory properties. It is concluded that immobilized reversible thrombin inhibitors are more effective by passivating higher amounts of thrombin in a cooperative action with antithrombin III.

Interleukin-lβ induces migration of rat arterial smooth muscle cells through a mechanism involving increased matrix metalloproteinase-2 activity

BACKGROUND

Interleukin-lβ (IL-lβ) is associated with vascular smooth muscle cell (VSMC) migration during neointimal formation following arterial injury, of which matrix metalloproteinase-2 (MMP-2) may have an important role. We investigated whether IL-lβ stimulated migration and MMP-2 production in VSMC, and, if so, whether migration correlated with MMP-2 activity.

MATERIALS AND METHODS

Modified Boyden chamber assay quantified cultured rat aorta VSMC migration. Methyl-thiazolyl-tetrazolium assay assessed cell growth. Gelatin zymography and Western blotting determined MMP-2 activity and protein levels, respectively.

RESULTS

IL-lβ (0.1 - 10 ng/mL) induced migration of VSMC in a concentration-dependent manner without cell proliferation. VSMC released increasing levels of active MMP-2 in a dose-response fashion at IL-1β 1-10 ng/mL (P < 0.05) while significantly increased levels of latent MMP-2 (pro-MMP-2) were attained more gradually (10 ng/mL, P < 0.05). There was a dose-dependent increase in the ratio of active MMP-2 to pro-MMP-2 in response to IL-1β (1-10 ng/mL, P < 0.05), suggesting extracellular activation of pro-MMP-2. Protein levels on Western blot paralleled enzyme activity, with the synthesis of more active MMP-2 than pro-MMP-2 in response to IL-1β. IL-lβ-stimulated VSMC migration was significantly attenuated by both the pan-selective MMP inhibitor GM6001 and cis-9-octadecenoyl-N-hydroxylamide, a MMP-2-selective inhibitor.

CONCLUSIONS

IL-lβ increases MMP-2 activity in VSMC through increased protein synthesis and activation of pro-MMP-2. VSMC migration induced by IL-lβ requires active MMP-2. IL-lβ may play a role in arterial remodeling following injury.

Matrix metalloproteinase-10 is upregulated by thrombin in endothelial cells and increased in patients with enhanced thrombin generation

OBJECTIVE

Thrombin is a multifunctional serine protease that promotes vascular proinflammatory responses whose effect on endothelial MMP-10 expression has not previously been evaluated.

METHODS AND RESULTS

Thrombin induced endothelial MMP-10 mRNA and protein levels, through a protease-activated receptor-1 (PAR-1)-dependent mechanism, in a dose- and time-dependent manner. This effect was mimicked by a PAR-1 agonist peptide (TRAP-1) and antagonized by an anti-PAR-1 blocking antibody. MMP-10 induction was dependent on extracellular regulated kinase1/2 (ERK1/2) and c-jun N-terminal kinase (JNK) pathways. By serial deletion analysis, site-directed mutagenesis and electrophoretic mobility shift assay an AP-1 site in the proximal region of MMP-10 promoter was found to be critical for thrombin-induced MMP-10 transcriptional activity. Thrombin and TRAP-1 upregulated MMP-10 in murine endothelial cells in culture and in vivo in mouse aorta. This effect of thrombin was not observed in PAR-1-deficient mice. Interestingly, circulating MMP-10 levels (P<0.01) were augmented in patients with endothelial activation associated with high (disseminated intravascular coagulation) and moderate (previous acute myocardial infarction) systemic thrombin generation.

CONCLUSIONS

Thrombin induces MMP-10 through a PAR-1-dependent mechanism mediated by ERK1/2, JNK, and AP-1 activation. Endothelial MMP-10 upregulation could be regarded as a new proinflammatory effect of thrombin whose pathological consequences in thrombin-related disorders and plaque stability deserve further investigation.

Matrix metalloproteinase-2 and myocardial oxidative stress injury: beyond the matrix

Matrix metalloproteinase (MMP)-2 belongs to a family of zinc-dependent proteases which are best known for their ability to proteolyse extracellular matrix proteins throughout the body, including the cardiovascular system. Increased MMP-2 activity has been demonstrated in myocardial ischaemia and reperfusion injury and the progression to congestive heart failure, with most evidence to date for its role in cardiac remodelling. Recent evidence, however, shows that MMP-2 also co-localizes with and proteolyses specific protein targets within the cardiomyocyte to cause acute, reversible contractile dysfunction, challenging the conventional wisdom on the 'extracellular matrix only' actions of this enzyme. In this review, we discuss the recent upsurge in MMP-2 research with regards to its activation by non-proteolytic pathways in the setting of enhanced oxidative stress in the heart. We will focus on the consequences of intracellular actions of MMP-2 within the cardiomyocyte and its regulation at several levels including its expression, post-translational modifications, and regulation by endogenous tissue inhibitors of metalloproteinases, caveolin, and small molecule MMP inhibitors. MMP-2 is emerging as an important signalling protease implicated in the proteolytic regulation of various intracellular proteins in myocardial oxidative stress injury.

Inflammation and melanoma metastasis

Metastatic melanoma is extremely refractory to existing chemotherapeutic drugs and bioimmune adjuvant therapies, and the life span of patients with metastatic melanoma is often measured in months. Understanding the mechanisms responsible for the development of tumor metastasis is critical for finding successful curative measures. An expending amount of data reveal the importance of inflammatory microenvironment and stroma in cancer initiation and progression, which brings new directions and approaches to cancer treatment. This review will summarize current data on the role of the tumor microenvironment in shaping the metastatic phenotype of melanoma.

ProMMP-2: TIMP-1 complexes identified in plasma of healthy individuals

Activation of MMPs in tissues is an important component of tissue injury. Based on earlier reports that (latent) proMMP-2 is incapable of forming a complex with TIMP-1, we reasoned that the identification of MMP-2:TIMP-1 complexes in blood might serve as a surrogate marker ("smoking gun") of MMP-2 activation in tissues. Using specific antibodies, we developed a sensitive and specific assay to detect MMP-2:TIMP-1 complexes. We were perplexed to find that approximate 40% of plasma specimens from healthy individuals had detectable levels of the MMP-2:TIMP-1 complexes. Employing recombinant TIMP-1 bound Sepharose beads and Western blots, we demonstrated binding between recombinant proMMP-2 and TIMP-1 proteins. Recombinant MMP-2 lacking the catalytic domain also bound to TIMP-1 coated beads. These data are consistent with TIMP-1 binding to the hemopexin or hinge domain of proMMP-2. The explanation for the presence of plasma proMMP-2:TIMP-1 complexes in selected healthy individuals remains to be determined. In contrast to our immunoassay and bead-binding experiments, proMMP-2 failed to bind to immobilized TIMP-1 employing surface plasmon resonance technology. Additional studies are needed to clarify these contrasting results.

Targeting melanoma growth and metastasis with systemic delivery of liposome-incorporated protease-activated receptor-1 small interfering RNA

The thrombin receptor [protease-activated receptor-1 (PAR-1)] is overexpressed in highly metastatic melanoma cell lines and in patients with metastatic lesions. Activation of PAR-1 leads to cell signaling and up-regulation of genes involved in adhesion, invasion, and angiogenesis. Herein, we stably silence PAR-1 through the use of lentiviral short hairpin RNA and found significant decreases in both tumor growth (P < 0.01) and metastasis (P < 0.001) of highly metastatic melanoma cell lines in vivo. The use of viruses for therapy is not ideal as it can induce toxic immune responses and possible gene alterations following viral integration. Therefore, we also used systemic delivery of PAR-1 small interfering RNA (siRNA) incorporated into neutral liposomes [1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC)] to decrease melanoma growth and metastasis in vivo. Significant decreases in tumor growth, weight, and metastatic lung colonies (P < 0.001 for all) were found in mice treated with PAR-1 siRNA-DOPC. The in vivo effects of PAR-1 on invasion and angiogenesis were analyzed via immunohistochemistry. Concomitant decreases in vascular endothelial growth factor, interleukin-8, and matrix metalloproteinase-2 expression levels, as well as decreased blood vessel density (CD31), were found in tumor samples from PAR-1 siRNA-treated mice, suggesting that PAR-1 is a regulator of melanoma cell growth and metastasis by affecting angiogenic and invasive factors. We propose that siRNA incorporated into DOPC nanoparticles could be delivered systemically and used as a new modality for melanoma treatment.

Role of the hemopexin domain of matrix metalloproteinases in cell migration

The biological functions of matrix metalloproteinases (MMPs) extend beyond extracellular matrix degradation. Non-proteolytic activities of MMPs are just beginning to be understood. Herein, we evaluated the role of proMMPs in cell migration. Employing a Transwell chamber migration assay, we demonstrated that transfection of COS-1 cells with various proMMP cDNAs resulted in enhancement of cell migration. Latent MMP-2 and MMP-9 enhanced cell migration to a greater extent than latent MMP-1, -3, -11 and -28. To examine if proteolytic activity is required for MMP-enhanced cell migration, three experimental approaches, including fluorogenic substrate degradation assay, transfection of cells with catalytically inactive mutant MMP cDNAs, and addition of hydroxamic acid-derived MMP inhibitors, were employed. We demonstrated that the proteolytic activities of MMPs are not required for MMP-induced cell migration. To explore the mechanism underlying MMP-enhanced cell migration, structure-function relationship of MMP-9 on cell migration was evaluated. By using a domain swapping approach, we demonstrated that the hemopexin domain of proMMP-9 plays an important role in cell migration when examined by a transwell chamber assay and by a phagokinetic migration assay. TIMP-1, which interacts with the hemopexin domain of proMMP-9, inhibited cell migration, whereas TIMP-2 had no effect. Employing small molecular inhibitors, MAPK and PI3K pathways were found to be involved in MMP-9-mediated cell migration. In conclusion, we demonstrated that MMPs utilize a non-proteolytic mechanism to enhance epithelial cell migration. We propose that hemopexin homodimer formation is required for the full cell migratory function of proMMP-9.

Thrombin mediates mitogenesis and survival of human endothelial cells through distinct mechanisms

Thrombin has been reported to play a pivotal role in the initiation of angiogenesis by indirectly regulating and organizing a network of angiogenic molecules. In addition, it has been proposed that thrombin can directly activate endothelial cell proliferation. However, in this report it was shown that thrombin is a poor growth factor for human endothelial cells, and its modest mitogenic activity is mediated indirectly by the release of heparin-binding epidermal growth factor, subsequent to proteinase-activated receptor 1 (PAR1) activation. On the other hand, it was demonstrated that thrombin is a potent anti-apoptotic factor for endothelial cells, pointing to a novel role of thrombin in vascular protection. Analysis by annexin V-propidium iodide double staining revealed that thrombin, specifically, promoted survival of serum-starved endothelial cells in a concentration-dependent manner. In contrast to its mitogenic effect, the anti-apoptotic effect of thrombin was largely independent of its catalytic activity and was mediated through interaction with alphanubeta3 and alpha5beta1 integrins, whereas the involvement of PAR1 was limited. These results provide new insights in understanding the role of thrombin in endothelial cell signaling and vascular biology.

Emerging roles of PAR-1 and PAFR in melanoma metastasis

Melanoma growth, angiogenesis and metastatic progression are strongly promoted by the inflammatory tumor microenvironment due to high levels of cytokine and chemokine secretion by the recruited inflammatory and stromal cells. In addition, platelets and molecular components of procoagulant pathways have been recently emerging as critical players of tumor growth and metastasis. In particular, thrombin, through the activity of its receptor protease-activated receptor-1 (PAR-1), regulates tumor cell adhesion to platelets and endothelial cells, stimulates tumor angiogenesis, and promotes tumor growth and metastasis. Notably, in many tumor types including melanoma, PAR-1 expression directly correlates with their metastatic phenotype and is directly responsible for the expression of interleukin-8, matrix metalloproteinase-2 (MMP-2), vascular endothelial growth factor, platelet-derived growth factor, and integrins. Another proinflammatory receptor–ligand pair, platelet-activating factor (PAF) and its receptor (PAFR), have been shown to act as important modulators of tumor cell adhesion to endothelial cells, angiogenesis, tumor growth and metastasis. PAF is a bioactive lipid produced by a variety of cells from membrane glycerophospholipids in the same reaction that releases arachidonic acid, and can be secreted by platelets, inflammatory cells, keratinocytes and endothelial cells. We have demonstrated that in metastatic melanoma cells, PAF stimulates the phosphorylation of cyclic adenosine monophosphate response element-binding protein (CREB) and activating transcription factor 1 (ATF-1), which results in overexpression of MMP-2 and membrane type 1-MMP (membrane type 1-MMP). Since only metastatic melanoma cells overexpress CREB/ATF-1, we propose that metastatic melanoma cells are better equipped than their non-metastatic counterparts to respond to PAF within the tumor microenvironment. The evidence supporting the hypothesis that the two G-protein coupled receptors, PAR-1 and PAFR, contribute to the acquisition of the metastatic phenotype of melanoma is presented and discussed.

Thrombin induces tumor invasion through the induction and association of matrix metalloproteinase-9 and beta1-integrin on the cell surface

The procoagulatory serine protease, thrombin, is known to induce invasion and metastasis in various cancers, but the mechanisms by which it promotes tumorigenesis are poorly understood. Because the 92-kDa gelatinase (MMP-9) is a known mediator of tumor cell invasion, we sought to determine whether and how thrombin regulates MMP-9. The thrombin receptor, PAR-1, and MMP-9 are expressed in osteosarcomas, as determined by immunohistochemistry. Stimulation of U2-OS osteosarcoma cells with thrombin and a thrombin receptor-activating peptide induced pro-MMP-9 secretion as well as cell surface-associated pro-MMP-9 expression and proteolytic activity. This was paralleled by an increase in MMP-9 mRNA and MMP-9 promoter activity. Thrombin-induced invasion of U2-OS cells through Matrigel was mediated by the phosphatidylinositol 3-kinase signaling pathway and could be inhibited with an MMP-9 antibody. The stimulation of MMP-9 by thrombin was paralleled by an increase in beta1-integrin mRNA and beta1-integrin expression on the cell surface, which was also mediated by phosphatidylinositol 3-kinase and was required for invasion. Thrombin activation induced and co-localized both beta1-integrin and pro-MMP-9 on the cell membrane, as evidenced by co-immunoprecipitation, confocal microscopy, and a protein binding assay. The thrombin-mediated association of these two proteins, as well as thrombin-mediated invasion of U2-OS cells, could be blocked with a cyclic peptide and with an antibody preventing binding of the MMP-9 hemopexin domain to beta1-integrin. These results suggest that thrombin induces expression and association of beta1-integrin with MMP-9 and that the cell surface localization of the protease by the integrin promotes tumor cell invasion.

Acute actions and novel targets of matrix metalloproteinases in the heart and vasculature

Matrix metalloproteinases (MMPs) have been shown to play significant roles in a number of physiological as well as pathological processes. Best known to proteolyse components of the extracellular matrix, MMPs have recently been discovered to also target a growing list of proteins apart from these, both inside and outside the cell. MMPs have also been traditionally thought of as enzymes involved in chronic processes such as angiogenesis, remodelling and atherosclerosis on a days-week time-scale. However they are now understood to also act acutely in response to oxidative stress on a minutes time-scale on non-extracellular matrix substrates. This review focuses on the acute actions and both extracellular and intracellular targets of two prominent MMP family members, MMP-2 and -9, in cardiovascular diseases including ischaemia/reperfusion injury, inflammatory heart disease, septic shock and pre-eclampsia. Also discussed are various ways of regulating MMP activity, including post-translational mechanisms, the endogenous tissue inhibitors of metalloproteinases and pharmacological inhibitors. A comprehensive understanding of MMP biology is necessary for the development of novel pharmacological therapies to combat the impact of cardiovascular disease.

Quantitative Analysis of Melanocytic Tissue Array Reveals Inverse Correlation between Activator Protein-2α and Protease-Activated Receptor-1 Expression during Melanoma Progression

The identification of molecular markers of melanoma progression is needed to more accurately stage and identify treatments for patients with malignant melanoma. Previously, we demonstrated that loss of the activator protein-2alpha (AP-2alpha) expression results in overexpression of the protease-activated receptor-1 (PAR-1) in human melanoma cell lines. Here, we used a tissue microarray platform that consisted of 64 melanocytic lesions, including dysplastic nevi (N=21), primary melanoma (N=20), and metastatic melanoma (N=23). We analyzed the expression of AP-2 and PAR-1 simultaneously by immunofluorescent microscopy with an automated quantification laser scanning cytometer. AP-2 was highly expressed in normal cutaneous melanocytes and dysplastic nevi but not in melanoma metastases. We observed a significantly higher number of AP-2-positive cells in the dysplastic nevi (P=0.0013) and primary melanoma (P=0.0023) compared to the metastatic melanoma. In contrast, we observed a significantly higher percentage of PAR-1-positive cells in the metastatic melanoma compared to dysplastic nevi (P=0.0072) and primary melanoma (P=0.0138). Increased expression of PAR-1 in metastatic melanomas contributes to tumor progression by modulating expression of genes, such as IL-8, matrix metalloproteinase-2, vascular endothelial growth factor, platelet-derived growth factor, and integrins. These findings support our hypothesis that loss of AP-2 is a crucial event in the progression of human melanoma and contributes to the acquisition of the metastatic phenotype via upregulation of PAR-1.

Thrombomodulin enhances the invasive activity of mouse mammary tumor cells

Thrombomodulin (TM) is a thrombin receptor on the surface of endothelial cells that converts thrombin from a procoagulant to an anticoagulant. Thrombin promotes invasion by various tumor cells, and positive or negative correlations are found between the expression of TM and tumorigenesis in some patients. In this study, we used an invasion assay to investigate the effect of TM on the invasive activity of a mouse mammary tumor cell line, MMT cells, and the effects of TM were compared with those of thrombin as a positive control. In the presence of 1% fetal calf serum (FCS), TM significantly stimulated MMT cell invasion in a dose-dependent manner, resulting in an approximately 3-fold increase at 1-10 pg/ml over the untreated control. Thrombin also caused a similar degree of stimulation at 50 ng/ml. Since thrombin activity was detected in the components of the assay system, an invasion assay was also performed in a thrombin-activity-depleted assay system constructed to eliminate the effect of thrombin activity; TM (10 pg/ml) plus thrombin (1 pg/ml) stimulated invasion by approximately 3.5-fold in this assay system. Hirudin, a specific thrombin inhibitor, inhibited stimulation by TM as well as by thrombin in both the presence and absence of 1% FCS. Investigations of the effects of TM on proliferation, adhesion and chemotaxis to clarify the mechanism of stimulation by TM revealed that TM does not affect proliferation or adhesion in the presence of 1% FCS, but stimulates chemotaxis by approximately 2.3-fold. Similar results were obtained in experiments using thrombin. TM (10 pg/ml) plus thrombin (1 pg/ml), on the other hand, stimulated chemotaxis by approximately 2.3-fold in the thrombin-activity-depleted assay system. Binding studies using [125I]-thrombin revealed that the cells have specific saturable binding sites for thrombin. These results show that TM stimulates the invasive activity of MMT cells, probably by acting as a cofactor for the thrombin-stimulated invasion of the cells via its receptor and lowering the effective concentration of thrombin. The findings also indicate that the stimulation of invasive activity in the presence of 1% FCS and in the thrombin-activity-depleted assay system may mainly be mediated by the stimulation of chemotaxis.

Activation of gelatinases by fibrin is PA/plasmin system-dependent in human glomerular endothelial cells

Evidence suggests that fibrin deposit is related to severity of glomerulonephropathy. Fibrin is considered to play an active role beyond a haemostatic plug or temporary matrix in response to injury. We have reported that fibrin induced specific morphological changes and up-regulated intercellular adhesion molecule-1 expression of glomerular endothelial cells (GECs). Changes of gelatinases activity have been implicated playing a prominent role in glomerular diseases involving matrix turnover. This study examined whether overlying fibrin influences the expression of gelatinase A and B in cultured human GECs and mechanism underlying the activation. No gelatinase activity was detectable in supernatant of cultured GECs; however, physiological concentration of fibrin (0.5-2.0 mg/ml) induced a dramatic expression of activated MMP-2 and MMP-9 at both mRNA and protein level in a dose and time dependent manner. Increased mRNA level of membrane-type 1 matrix metalloproteinases (MT1-MMPs) was also found. Interestingly, we observed that fibrin also induced the expression of tissue type plasminogen activator (tPA), urokinase type plasminogen activator (uPA) and plasminogen activator inhibitor-1 by casein zymographic and reverse zymographic analysis. Fibrin plate assay revealed the net activity was PA predominant. Serine protease inhibitor aprotinin blocked the conversion of pro-gelatinase A and B to their active forms. The results demonstrate that overlying fibrin increased the secretion of gelatinase A and B from GECs. PA/plasmin proteolytic pathways contributed to the activation of gelatinases.

Differential transcriptional activation of matrix metalloproteinase-2 and membrane type-1 matrix metalloproteinase by experimental deep venous thrombosis and thrombin

OBJECTIVE

Resolution of deep venous thrombosis (DVT) is involved in the pathogenesis of postthrombotic syndrome. Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that are critical in angiogenesis and tissue remodeling. We hypothesized that MMP-2 and its membrane-bound activator membrane type-1 matrix metalloproteinase (MT1-MMP) expression would be expressed and activated during the resolution of DVT.

METHODS

DVT was generated by caval ligation in wild-type and MMP-2 transgenic reporter mice. Ligated and sham-operated (control) cavae were analyzed for MMP-2 transcription (beta-galactosidase activity in MMP-2 reporter mice) and MT1-MMP mRNA by real-time polymerase chain reaction. MMP-2 activity was determined by zymography, and immunohistochemical staining for beta-galactosidase and MT1-MMP protein was used to localize expression. Human umbilical vascular endothelial cells (HUVEC) were treated with 10 U/mL thrombin and MMP-2 and MT1-MMP mRNA levels and MMP-2 activity was determined.

RESULTS

MMP-2 activity increased 71% (n = 5, P < .05) at day 8 in ligated vs control cavae by zymography. beta-galactosidase activity showed a 1.2-fold (n = 8, P < .05) and 1.7-fold (n = 8, P < .05) induction in MMP-2 transcription at day 3 and day 8, respectively. No significant MT1-MMP gene induction was seen at day 3 in ligated vs control cavae, but MT1-MMP mRNA was upregulated 2.5-fold (n = 8, P < .05) in ligated cavae at day 8. Immunohistochemical staining localized MMP-2 and MT1-MMP expression to the vein wall and cellular infiltrates of the thrombus. Thrombin-treated HUVEC showed differential responses of MMP-2 and MT1-MMP. Zymography of conditioned media and cell lysates illustrated a 220% (152.6 +/- 8.6 vs 69.445 +/- 5.46 pixels/unit area, n = 5, P < .05) and 150% (74.1 +/- 7.3 vs 49.2 +/- 5.7 pixels/unit area, n = 5, P < .05) increases in MMP-2 activity respectively. MMP-2 mRNA levels were downregulated 30% (0.48 +/- 0.023 vs 0.63 +/- 0.035 copies of MMP-2 mRNA/copy GAPDH, n = 5, P < .05), whereas MT1-MMP message was upregulated 250% (0.147 +/- 0.009 vs 0.059 +/- 0.005 copies of MT1-MMP mRNA/copy GAPDH, n = 5, P < .05).

CONCLUSIONS

Resolution of DVT is associated with increased MMP-2 transcription and activity as well as MT1-MMP expression. Thrombin may mediate the increase in MT1-MMP noted in DVT. This is the first article studying MMP-2 and MT1-MMP transcription in DVT. These findings add DVT resolution to the class of inflammatory and fibrotic disorders in which transcriptional activation of the MT1-MMP/MMP-2 genes occurs and identify a potential therapeutic target to modulate this clinically relevant process.

CLINICAL RELEVANCE

Postthrombotic syndrome remains a significant clinical problem after deep venous thrombosis (DVT), but the cellular and molecular mechanisms involved in thrombus resolution and vein wall fibrosis remain undefined. Matrix metalloproteinase (MMP) enzymes are critical to cell migration and matrix breakdown. We identify gene transcription and activity of two MMP isoforms, MMP-2 and MMP-14 (membrane type MMP 1, MT1-MMP) in the resolution phase of experimental DVT and in thrombin-treated endothelial cells. These studies define new proteases potentially important to resolution of DVT and development of postthrombotic syndrome.

The MMP-9 expression determined the efficacy of postoperative adjuvant chemotherapy using oral fluoropyrimidines in stage II or III colorectal cancer

BACKGROUND

The aim of this study was to determine any correlation between the efficacy of postoperative adjuvant chemotherapy using oral fluoropyrimidines and the matrix metalloproteinase 9 (MMP-9) expression in primary colorectal cancer tissues.

PATIENTS AND METHODS

The data on 307 patients with colorectal cancer at stage II or III, who underwent potentially curative resection with lymphadenectomy, were reviewed. Of these, 188 received postoperative administration of oral fluoropyrimidines such as UFT and 5'-DFUR (chemotherapy group), while the other 119 patients underwent surgery alone (surgery-alone group). Immunostaining for MMP-9 was performed using surgical specimens of all 307 primary tumors and 18 recurrent tumors.

RESULTS

Overall, MMP-9 was positively expressed in the primary tumor in 44% of patients. Multivariate analysis revealed that the MMP-9 expression was a worse prognostic factor with a second highest hazard ratio for recurrence. The disease-free survival rate in the chemotherapy group was significantly higher than that in the surgery-alone group. However, no significant difference in disease-free survival rate between the two groups was found in patients with a tumor positive for MMP-9. There was a strong positive correlation of MMP-9 expression between the primary tumors and the recurrent liver or lung tumors.

CONCLUSIONS

The efficacy of postoperative adjuvant chemotherapy using oral fluoropyrimidines such as UFT and 5'-DFUR may not be as great for patients with a tumor positive for MMP-9 having a greater risk to postoperative recurrence.

Membrane independent activation of fibroblast proMMP-2 by snake venom: novel roles for venom proteinases

ProMMP-2 activation by Bothrops asper venom was investigated in mouse gastrocnemius muscle, mammalian cell culture and a cell-free system. Zymography revealed an increment of latent and activated forms of MMP-2 in muscle homogenates 1-3 days after venom injection. To clarify if venom can induce expression and activation of MMP-2, independently of the inflammatory response, venom was added to cultured human fibroblasts, endothelial and skeletal muscle cells, which expressed proMMP-2 constitutively. Venom activated proMMP-2 without promoting its expression. Venom also activated and degraded proMMP-2 in supernatants collected from fibroblast cultures, indicating that cells are not required for this activation. Pretreatment with EDTA increased MMP-2 activation and reduced degradation. Venom serine proteinases activated proMMP-2, whereas BaP1, a P-I metalloproteinase, predominantly degraded the latent and active forms of MMP-2. Moreover, pretreatment of conditioned medium with serine proteinase inhibitors greatly reduced the venom-induced activation, suggesting that venom proteinases activate MMP-2 via a serine proteinase secreted by fibroblasts. Venom also directly activated and degraded purified proMMP-2, albeit requiring a high concentration. Thus, B. asper venom proteinases activate and degrade proMMP-2 without inducing its synthesis. Serine proteinases play a dominant role in the activation, whereas metalloproteinases predominantly degrade MMP-2. Activation of proMMP-2 by snake venom proteinases, independently of the MT1-MMP/TIMP-2 pathway, extracellular matrix degradation or apoptosis, represents a novel mechanism in human fibroblasts.

Thrombin and Its Protease-Activated Receptor-1 (PAR1) Participate in the Endothelial–Mesenchymal Transdifferentiation Process

The serine protease thrombin, independently of its participation in hemostasis and thrombosis, has been involved in tissue repair and remodeling, embryogenesis, angiogenesis, and development and progression of atherosclerosis. Many of these functions appear to be mediated by specific thrombin receptors, particularly the protease-activated receptor-1 (PAR1). In this study, we investigated whether both thrombin and PAR1 were present in the aortic wall of chicken embryos at days 11 and 12 of development. We found that PAR1 was limited to some cells of the intimal thickening and the inner media, whereas thrombin appeared distributed across the aortic wall. We also investigated whether PAR1 was present during endothelial-mesenchymal transdifferentiation (EMT) in vitro. A moderate immunoreactivity was detected in the monolayer of endothelial cells. In contrast, a strong cytoplasmic immunoreactivity was observed in the detaching and migrating cells and those that had acquired mesenchymal characteristics. This PAR1 expression was confirmed by flow cytometry. In this study, the addition of thrombin to arrested endothelial cell cultures was assessed. We found that thrombin stimulated endothelial cell spreading and migration, as no migrating cells were observed in serum-free medium (SFM) condition. Immunolocalization of PAR1 in the thrombin-treated cultures showed strong cytoplasmic immunoreactivity in the monolayers and in spreading and migrating cells, whereas in the SFM condition undetectable PAR1 immunoreactivity was observed. Flow cytometry of these cultures revealed an elevated expression of PAR1 in the presence of thrombin, in contrast to that detected in SFM and complete medium. These data indicate that both thrombin and PAR1 are involved in the remodeling of the aortic wall and intimal thickening formation, and in the endothelial-mesenchymal transdifferentiation process.

A paradoxical pro-apoptotic effect of thrombin on smooth muscle cells

Whereas thrombin (below 10 nM) is a potent mitogen, recent studies report that exposure to higher doses of thrombin could lead to apoptosis of neurons and tumor cells. Our results show that prolonged exposure (> or = 24 h) to thrombin (50-100 nM) exerts a pro-apoptotic effect on cultured vascular smooth muscle cells (VSMCs). This phenomenon depends on thrombin serine-protease activity but is independent of PAR-1 and -4 activation and subsequent signaling. The parallel occurrence of cell retraction and cleavage of fibronectin suggests that thrombin-induced apoptosis is consecutive to pericellular proteolysis. These data point to a new potential action of thrombin in the cardiovascular system.

Limited processing of pro-matrix metalloprotease-2 (gelatinase A) overexpressed by transfection in PC-3 human prostate tumor cells: association with restricted cell surface localization of membrane-type matrix metalloproteinase-1

The expression and activation of matrix metalloproteinases (MMPs) by tumor cells is correlated with progression to invasive and metastatic status. The purpose of this study was to examine the role of increased MMP-2 (gelatinase A) expression in prostate cancer progression utilizing human prostate PC-3 cancer cells that overexpress MMP-2 using gene transfection. PC-3 cells were transfected with pCR-3 vector only and pCR-3 MMP-2 plasmids employing the LipofectAMINE method, and stable transfectants were selected with G418. The expression of MMP-2, tissue inhibitor of metalloproteinase-2 (TIMP-2), and membrane-type MMP 1 (MT1-MMP) in PC-3 parental and transfected cells under serum-free conditions was determined by zymography, immunoblotting, immunofluorescent microscopy, Northern blotting, and/or reverse transcriptase-polymerase chain reaction (RT-PCR). MMP-2 transfected cells produced primarily the proenzyme form of MMP-2; the parental and vector control transfected PC-3 cells did not express any MMP-2 that was detectable by the methods we employed. Treatment of PC-3 MMP-2 transfected cells with Concanavalin A (Con A), in contrast to HT-1080 cells, processed only a small amount of the secreted 72-kd proenzyme to a 62-kd intermediate and a cell-associated 59-kd active form. The low level of secreted pro-MMP-2 processing induced by Con A was inhibited by serine protease inhibitors and was unaffected by cyclic adenosine monophosphate (cAMP). Immunoblotting showed that these cells produced abundant TIMP-2 and lower amounts of MT1-MMP in comparison with Con A-responding HT-1080 cells. HT-1080 cells respond to Con A by translocating MT1-MMP from intracellular localization sites to the plasma membrane, an effect not observed in PC-3 cells. The molecular basis for the low level of processing of pro-MMP-2 by PC-3 cells may be due to an overabundance of TIMP-2 and/or a low level of cell surface active MT1-MMP.

Involvement of metalloprotease-2 in the development of human brain microvessels

The involvement of the metalloprotease-2 (MMP-2) in vessel development was investigated in the human telencephalon by double immunoreactions with antibodies to the enzyme, latent (proMMP-2) and active (aMMP-2) forms, and an antibody against collagen type IV, a constitutive component of the extracellular matrix (ECM) of the vessel basal lamina. MMP-2 is expressed in both 12- and 18-week telencephalic vessels, the proenzyme being mainly localised in endothelial cells and the active form prevailing in alpha-actin-reactive periendothelial cells identified as pericytes. Endothelial cells intensely positive for aMMP-2 were revealed in some microvessels and appeared locally associated with discontinuities of the collagen basal lamina. No detectable expression of MMP-2 was observed in perivascular glial processes revealed by vimentin/glial fibrillary acidic protein immunostainings. Double immunoreactions performed to further investigate telencephalon angiogenesis have demonstrated that both the endothelial cells and pericytes strongly express vascular endothelial growth factor (VEGF). Taken together, the results indicate that MMP-2 is largely involved in human brain angiogenesis and suggest that endothelial cells and pericytes tightly interplay in both angiogenesis mechanisms, by ECM proteolysis, and angiogenesis regulation, by local (autocrine/juxtacrine) VEGF action.

Red wine polyphenolic compounds strongly inhibit pro-matrix metalloproteinase-2 expression and its activation in response to thrombin via direct inhibition of membrane type 1-matrix metalloproteinase in vascular smooth muscle cells

BACKGROUND

Regular consumption of moderate amounts of red wine is associated with a reduced risk of coronary disease. Matrix metalloproteinases (MMPs) that participate in extracellular matrix degradation have been involved in atherosclerotic plaque growth and instability. The present study examined whether red wine polyphenolic compounds (RWPCs) inhibit activation of MMP-2, a major gelatinase, in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Expression of pro-MMP-2 was assessed by Western and Northern blot analyses; MMP-2 activity was assessed by zymography and cell invasion by a modified Boyden's chamber assay. High levels of pro-MMP-2 and low levels of MMP-2 activity were found in conditioned medium from unstimulated VSMCs. Thrombin induced cell-associated pro-MMP-2 protein expression and MMP-2 activity in conditioned medium of VSMCs. The stimulatory effect of thrombin on MMP-2 activation was prevented by RWPCs in a concentration-dependent and reversible manner. Thrombin markedly increased cell-associated membrane type 1 (MT1)-MMP activity, the physiological activator of pro-MMP-2, and this response was not affected by RWPCs. However, addition of RWPCs directly to MT1-MMP abolished its metalloproteinase activity in a reversible manner. Finally, matrix invasion of VSMCs was stimulated by thrombin, and this response was prevented by RWPCs as efficiently as a broad-spectrum MMP inhibitor.

CONCLUSIONS

The present findings demonstrate that RWPCs effectively inhibit thrombin-induced matrix invasion of VSMCs, most likely by preventing the expression and activation of MMP-2 via direct inhibition of MT1-MMP activity. The inhibitory effect of RWPCs on the activation of pro-MMP-2 and matrix degradation might contribute to their beneficial effects on the cardiovascular system.

Clinical implications of matrix metalloproteinases

Matrix metalloproteinases (MMPs) are a family of neutral proteinases that are important for normal development, wound healing, and a wide variety of pathological processes, including the spread of metastatic cancer cells, arthritic destruction of joints, atherosclerosis, pulmonary fibrosis, emphysema and neuroinflammation. In the central nervous system (CNS), MMPs have been shown to degrade components of the basal lamina, leading to disruption of the blood brain barrier and to contribute to the neuroinflammatory responses in many neurological diseases. Inhibition of MMPs have been shown to prevent progression of these diseases. Currently, certain MMP inhibitors have entered into clinical trials. A goal to the future should be to design selective synthetic inhibitors of MMPs that have minimum side effects. MMP inhibitors are designed in such a way that these can not only bind at the active site of the proteinases but also to have the characteristics to bind to other sites of MMPs which might be a promising route for therapy. To name a few: catechins, a component isolated from green tea; and Novastal, derived from extracts of shark cartilage are currently in clinical trials for the treatment of MMP-mediated diseases.

Distinct Roles for the Catalytic and Hemopexin Domains of Membrane Type 1-Matrix Metalloproteinase in Substrate Degradation and Cell Migration

Substrate degradation and cell migration are key steps in cancer metastasis. Membrane-type 1-matrix metalloproteinase (MT1-MMP) has been linked with these processes. Using the fluorescein isothiocyanate (FITC)-labeled fibronectin degradation assay combined with the phagokinetic cell migration assay, structure-function relationships of MT1-MMP were studied. Our data indicate that MT1-MMP initiates substrate degradation and enhances cell migration; cell migration occurs as a concurrent but independent event. Using recombinant DNA approaches, we demonstrated that the hemopexin-like domain and a nonenzymatic component of the catalytic domain of MT1-MMP are essential for MT1-MMP-mediated cell migration. Because the cytoplasmic domain of MT1-MMP was not required for MT1-MMP-mediated fibronectin degradation and cell migration, it is proposed that cross-talk between the hemopexin domain of MT1-MMP and adjacent cell surface molecules is responsible for outside-in signaling. Employing cDNAs encoding dominant negative mutations, we demonstrated that Rac1 participates in the MT1-MMP signal transduction pathway. These data demonstrated that each domain of MT1-MMP plays a distinct role in substrate degradation and cell migration.

TIMP-2 is released as an intact molecule following binding to MT1-MMP on the cell surface

Binding of tissue inhibitor of metalloproteinase-2 (TIMP-2) to pro-MMP-2 and mature membrane type-1 MMP (MT1-MMP) on the cell surface is required for activation of MMP-2. It has been reported that following binding to cell surface receptors, TIMP-2 undergoes endocytosis and extensive degradation in lysosomes. The purpose of this study was to reexamine the fate of TIMP-2 following binding to transfected HT1080 cell surface MT1-MMP at 4 degrees C. Following 37 degrees C incubation, 125I-TIMP-2 release, endocytosis, and degradation were characterized under varying conditions. More than 85% of the total 125I-TIMP-2 bound to cells was released as intact functional molecules; <15% was degraded. Transfection of HT1080 cells with dominant negative mutant dynamin cDNA resulted in delayed endocytosis and release of 125I-TIMP-2 from cells. Pharmacologic agents that induce clustering of cell surface receptors (concanavalin A) and interfere with endosomal/lysosomal function (bafilomycin A(1)) resulted in enhanced binding of 125I-TIMP-2 to cell surface receptors. Abrogation of activation of proMT1-MMP with a furin inhibitor prevented binding and endocytosis of 125I-TIMP-2. Biotinylation of cell surface MT1-MMP followed by Western blotting confirmed the presence of mature MT1-MMP on the cell surface and degraded MT1-MMP in the intracellular compartment. In conclusion, these studies demonstrate that TIMP-2 is released from cells primarily as an intact functional molecule following binding to MT1-MMP on the cell surface.

Zymogen activation and characterization of a major gelatin-cleavage activity localized to the sea urchin extraembryonic matrix

The hyaline layer (HL) is an apically located extracellular matrix (ECM) which surrounds the sea urchin embryo from the time of fertilization until metamorphosis occurs. While gelatin-cleavage activities were absent from freshly prepared hyaline layers, a dynamic pattern of activities developed in layers incubated at 15 or 37 degrees C in Millipore-filtered sea water (MFSW). Cleavage activities at 90, 55, 41, and 32 kDa were evident following incubation at either temperature. The activation pathway leading to the appearance of these species was examined to determine the minimum salt conditions required for processing and to establish precursor-product relationships. In both qualitative and quantitative assays, the purified 55 kDa gelatinase activity was inhibited by 1,10-phenanthroline (a zinc-specific chelator) and ethylenebis (oxyethylenenitrilo) tetraacetic acid (EGTA). Calcium reconstituted the activity of the EGTA-inhibited enzyme with an apparent dissociation constant (calcium) of 1.2 mM. Developmental substrate gel analysis was performed using various stage embryos. The 55 and 32 kDa species comigrated with gelatin-cleavage activities present in sea urchin embryos. Collectively, the results reported here document a zymogen activation pathway which generates a 55 kDa, gelatin-cleaving activity within the extraembryonic HL. This species displayed characteristics of the matrix metalloproteinase class of ECM modifying enzymes.

Loss of activator protein-2alpha results in overexpression of protease-activated receptor-1 and correlates with the malignant phenotype of human melanoma

Increasing evidence implicates the protease-activated receptor-1 (PAR-1) as a contributor to tumor invasion and metastasis of human melanoma. Here we demonstrate that the metastatic potential of human melanoma cells correlates with overexpression of PAR-1. We also provide evidence that an inverse correlation exists between the expression of activator protein-2alpha (AP-2) and the expression of PAR-1 in human melanoma cells. Reexpression of AP-2 in WM266-4 melanoma cells, which are AP-2-negative, resulted in decreased mRNA and protein expression of PAR-1. The promoter of the PAR-1 gene contains multiple putative consensus elements for the transcription factors AP-2 and specificity protein 1 (Sp1). Chromatin immunoprecipitation analysis of the PAR-1 promoter regions bp -365 to -329 (complex 1) and bp -206 to -180 (complex 2) demonstrated that Sp1 was predominantly bound to the PAR-1 promoter in metastatic cells, whereas AP-2 was bound to the PAR-1 promoter in nonmetastatic cells. In vitro analysis of complex 1 demonstrated that AP-2 and Sp1 bound to this region in a mutually exclusive manner. Transfection experiments with full-length and progressive deletions of the PAR-1 promoter luciferase constructs demonstrated that metastatic melanoma cells had increased PAR-1 promoter activity compared with low and nonmetastatic melanoma cells. Our data show that exogenous AP-2 expression decreased promoter activity, whereas transient expression of Sp1 further increased expression of the reporter gene. Mutational analysis of complex 1 within PAR-1 luciferase constructs further demonstrated that the regulation of PAR-1 was mediated through interactions with AP-2 and Sp1. Our data suggest that loss of AP-2 in metastatic cells alters the AP-2/Sp1 ratio, resulting in overexpression of PAR-1. Taken together, our results provide strong evidence that loss of AP-2 correlates with overexpression of PAR-1, which in turn contributes to the acquisition of the malignant phenotype of human melanoma.

Type I collagen-induced MMP-2 activation coincides with up-regulation of membrane type 1-matrix metalloproteinase and TIMP-2 in cardiac fibroblasts

Migration of cardiac fibroblasts is implicated in infarct healing and ventricular remodeling. Activation of matrix metalloproteinases induced by three-dimensional type I collagen, the principal component of the myocardial interstitium, is hypothesized to be essential for this migration. By utilizing primary cultures of cardiac fibroblasts and collagen lattice models, we demonstrated that type I collagen induced MMP-2 activation, and cells undergoing a change from isometric tension to mechanical unloading were associated with increased levels of total and active MMP-2 species. The collagen-induced MMP-2 activation coincided with up-regulated cellular levels of both membrane type 1-matrix metalloproteinase (MT1-MMP) and TIMP-2. A fraction of cellular membrane prepared from cells embedded in the collagen lattice containing active MT1-MMP and TIMP-2 was capable of activating pro-MMP-2, and exogenous TIMP-2 had a biphasic effect on this membrane-mediated MMP-2 activation. Interestingly, the presence of 43-kDa MT1-MMP species in a fraction of intracellular soluble proteins prepared from monolayer cells but not cells embedded in the lattices indicates that MT1-MMP metabolizes differently under the two different culture conditions. Treatment of cells embedded in the lattice with furin inhibitor attenuated pro-MT1-MMP processing and MMP-2 activation and impeded cell migration and invasion. These results suggest that the migration and invasion of cardiac fibroblasts is furin-dependent and that the active species of MT1-MMP and MMP-2 may be involved in both events.

Thrombin up-regulates tissue factor pathway inhibitor-2 synthesis through a cyclooxygenase-2-dependent, epidermal growth factor receptor-independent mechanism

The serine proteinase inhibitor tissue factor pathway inhibitor-2 (TFPI-2) inhibits the tissue factor-factor VIIa complex and thereby impairs factor Xa and subsequently thrombin generation. Here we show that thrombin itself up-regulates TFPI-2 mRNA and protein expression in human liver myofibroblasts, a cell type shown to express high levels of TFPI-2 (Neaud, V., Hisaka, T., Monvoisin, A., Bedin, C., Balabaud, C., Foster, D. C., Desmoulière, A., Kisiel, W., and Rosenbaum, J. (2000) J. Biol. Chem. 275, 35565-35569). This effect required thrombin catalytic activity, as shown by its abolition with hirudin. Although the thrombin effect could be mimicked by agonists of both protease-activated receptor (PAR)-1 and PAR-4, it was largely blocked by a PAR-1 blocking antibody. Transactivation of the epidermal growth factor (EGF) receptor has been reported as a common event in thrombin signaling. However, thrombin did not detectably transactivate the EGF receptor in liver myofibroblasts, and blocking the EGF receptor did not affect TFPI-2 induction. On the other hand, thrombin increased the expression of cyclooxygenase-2 (COX-2) mRNA via a MAPK-dependent pathway, and a specific COX-2 inhibitor abolished the effect of thrombin on TFPI-2 expression. Thus, thrombin, through PAR-1 signaling, up-regulates the synthesis of TFPI-2 via a MAPK/COX-2-dependent pathway. The up-regulation of TFPI-2 expression by thrombin could in turn down-regulate thrombin generation and contribute to limit blood coagulation.

Protease-activated receptors 1 and 4 mediate thrombin signaling in endothelial cells

Defining the relative importance of protease-activated receptors (PARs) for thrombin signaling in mouse endothelial cells is critical for a basic understanding of thrombin signaling in these cells and for the rational use of knockout mice to probe the roles of thrombin's actions on endothelial cells in vivo. We examined thrombin- and PAR agonist-induced increases in cytoplasmic calcium, phosphoinositide hydrolysis, extracellular signal-regulated kinase (ERK) phosphorylation, and gene expression in endothelial cells from wild-type and PAR-deficient mice. PAR1 and PAR4 agonists triggered responses in wild-type but not in Par1-/- and Par4-/- endothelial cells, respectively. Calcium imaging confirmed that a substantial fraction of individual endothelial cells responded to both agonists. Compared with wild-type cells, Par1-/- endothelial cells showed markedly decreased responses to low concentrations of thrombin, and cells that lacked both PAR1 and PAR4 showed no responses to even high concentrations of thrombin. Similar results were obtained when endothelial-dependent vasorelaxation of freshly isolated mouse aorta was used as an index of signaling in native endothelial cells. Thus PAR1 is the major thrombin receptor in mouse endothelial cells, but PAR4 also contributes. These receptors serve at least partially redundant roles in endothelial cells in vitro and in vivo and together are necessary for the thrombin responses measured.