Membrane type matrix metalloproteinase 1 activates pro-gelatinase A without furin cleavage of the N-terminal domain

The emerging role of furin in neurodegenerative and neuropsychiatric diseases

Furin is an important mammalian proprotein convertase that catalyzes the proteolytic maturation of a variety of prohormones and proproteins in the secretory pathway. In the brain, the substrates of furin include the proproteins of growth factors, receptors and enzymes. Emerging evidence, such as reduced FURIN mRNA expression in the brains of Alzheimer's disease patients or schizophrenia patients, has implicated a crucial role of furin in the pathophysiology of neurodegenerative and neuropsychiatric diseases. Currently, compared to cancer and infectious diseases, the aberrant expression of furin and its pharmaceutical potentials in neurological diseases remain poorly understood. In this article, we provide an overview on the physiological roles of furin and its substrates in the brain, summarize the deregulation of furin expression and its effects in neurodegenerative and neuropsychiatric disorders, and discuss the implications and current approaches that target furin for therapeutic interventions. This review may expedite future studies to clarify the molecular mechanisms of furin deregulation and involvement in the pathogenesis of neurodegenerative and neuropsychiatric diseases, and to develop new diagnosis and treatment strategies for these diseases.

Kallikrein-Related Peptidase 14 Activates Zymogens of Membrane Type Matrix Metalloproteinases (MT-MMPs)-A CleavEx Based Analysis

Kallikrein-related peptidases (KLKs) and matrix metalloproteinases (MMPs) are secretory proteinases known to proteolytically process components of the extracellular matrix, modulating the pericellular environment in physiology and in pathologies. The interconnection between these families remains elusive. To assess the cross-activation of these families, we developed a peptide, fusion protein-based exposition system (Cleavage of exposed amino acid sequences, CleavEx) aiming at investigating the potential of KLK14 to recognize and hydrolyze proMMP sequences. Initial assessment identified ten MMP activation domain sequences which were validated by Edman degradation. The analysis revealed that membrane-type MMPs (MT-MMPs) are targeted by KLK14 for activation. Correspondingly, proMMP14-17 were investigated in vitro and found to be effectively processed by KLK14. Again, the expected neo-N-termini of the activated MT-MMPs was confirmed by Edman degradation. The effectiveness of proMMP activation was analyzed by gelatin zymography, confirming the release of fully active, mature MT-MMPs upon KLK14 treatment. Lastly, MMP14 was shown to be processed on the cell surface by KLK14 using murine fibroblasts overexpressing human MMP14. Herein, we propose KLK14-mediated selective activation of cell-membrane located MT-MMPs as an additional layer of their regulation. As both, KLKs and MT-MMPs, are implicated in cancer, their cross-activation may constitute an important factor in tumor progression and metastasis.

MMPs/TIMPs imbalances in the peripheral blood and cerebrospinal fluid are associated with the pathogenesis of HIV-1-associated neurocognitive disorders

HIV-1-associated neurocognitive disorders (HAND) continue to be a major concern in the infected population, despite the widespread use of combined antiretroviral therapy (cART). Growing evidence suggests that an imbalance between matrix metalloproteinases (MMPs) and endogenous tissue inhibitors of MMPs (TIMPs) contributes to the pathogenesis of HAND. In our present study, we examined protein levels and enzymatic activities of MMPs and TIMPs in both plasma and cerebrospinal fluid (CSF) samples from HIV-1 patients with or without HAND and HIV-1-negative controls. Imbalances between MMPs and TIMPs with distinct patterns were revealed in both the peripheral blood and CSF of HIV-1 patients, especially those with HAND. In the peripheral blood, the protein levels of MMP-2, MMP-9, TIMP-1, TIMP-2, and the enzymatic activities of MMP-2 and MMP-9 were increased in HIV-1 patients with or without HAND when compared with HIV-1-negative controls. The enzymatic activity of MMP-2, but not MMP-9, was further increased in plasma samples of HAND patients than that of HIV-1 patients without HAND. Notably, the ratio of MMP-2/TIMP-2 in plasma was significantly increased in HAND patients, not in patients without HAND. In the CSF, MMP-2 activity was increased, but the ratio of MMP-2/TIMP-2 was not altered. De novo induction and activation of MMP-9 in the CSF of HAND patients was particularly prominent. The imbalances between MMPs and TIMPs in the blood and CSF were related to the altered profiles of inflammatory cytokines/chemokines and monocyte activation in these individuals. In addition, plasma from HIV-1 patients directly induced integrity disruption of an in vitro blood-brain barrier (BBB) model, leading to increased BBB permeability and robust transmigration of monocytes/macrophages. These results indicate that imbalances between MMPs and TIMPs are involved in BBB disruption and are implicated in the pathogenesis of neurological disorders such as HAND in HIV-1 patients.

Plasminogen Improves Mouse IVF by Interactions with Inner Acrosomal Membrane-Bound MMP2 and SAMP14

Spermatozoa must penetrate the outer investments of the oocyte, the cumulus oophorus and the zona pellucida (ZP), in order for fertilization to occur. This may require exposure of enzymes on the sperm's inner acrosomal membrane (IAM), one of which is matrix metalloproteinase (MMP) 2, to factors in oviductal fluid. Plasminogen is present in oviductal fluid and activates MMP2 in somatic tissues. The objectives of this study were: 1) to examine possible interactions between plasminogen and IAM-bound plasminogen activator receptor (SAMP14) and -MMP2, 2) to demonstrate plasminogen's presence in the extracellular environment at the site of fertilization, and 3) to provide evidence that plasminogen plays a role in fertilization. Zymographs of sonicated bull and rat sperm extracts incubated with plasmin and/or plasminogen (plasmin/ogen) showed acceleration of initiation of MMP2 activity in concentrations as low as 1 μg/ml. Immunohistochemical and immunofluorescence analysis of plasmin/ogen revealed its presence in the cytoplasm of mouse ovarian and oviductal oocytes, oviductal epithelium, around the ZP, and amongst the cumulus cells. We modified the standard in vitro fertilization (IVF) approach to more closely mimic natural fertilization by reducing sperm concentration during insemination by ∼100× and also comparing cumulus-intact and denuded oocytes. In mice, addition of plasminogen in IVF medium significantly improved fertilization, while MMP2 antibody significantly inhibited sperm penetration in these conditions. IVF improvement by plasminogen was blocked by SAMP14 antibody. Furthermore, MMP2 antibody inhibition was coincident with a failure by spermatozoa to disperse the cumulus oophorus. We provide evidence that plasminogen on its own and through an MMP2-related mechanism improves the ability of oocytes to be fertilized, and demonstrate its effect in sperm penetration of oocyte investments.

A novel role of endothelium in activation of latent pro-membrane type 1 MMP and pro-MMP-2 in rat aorta

AIMS

Aortic stiffness is an independent risk factor for progression of cardiovascular diseases. Degradation of elastic fibres in aorta due to angiotensin II (ANGII)-stimulated overactivation of latent membrane type 1 matrix metalloproteinase (MT1MMP) and matrix metalloproteinase-2 (MMP2) is regarded to represent an important cause of aortic stiffness. Therefore, clarification of the causal mechanisms triggering the overactivation of these MMPs is of utmost importance. This study addresses the endothelium as a novel key activator of latent pro-MT1MMP and pro-MMP2 in rat aorta.

METHODS AND RESULTS

Using a co-culture model of rat aortic endothelial cells (ECs) and smooth muscle cells (SMCs), we found that ANGII stimulation resulted in activation of latent pro-MT1MMP and pro-MMP2 in SMCs exclusively when co-cultured with ECs (assessed with western blot and gelatin zymography, respectively). EC-specific AT1 receptor stimulation triggered endothelin-1 release and paracrine action on SMCs. Endothelin-1 increased expression and activity of pro-protein convertase furin in SMCs via endothelin receptor type A (assessed with qPCR and furin activity assay, respectively). Consequently, furin acted in two ways. First, it increased the activation of latent pro-MT1MMP and, second, it activated pro-αvβ3 integrin. Both pathways led to overactivation of latent pro-MMP2. In vitro findings in the co-culture model were fully consistent with the ex vivo findings obtained in isolated rat aorta.

CONCLUSIONS

We propose that the endothelium under ANGII stimulation acts as a novel and key activator of latent pro-MT1MMP and pro-MMP2 in SMCs of rat aorta. Therefore, endothelium may critically contribute to pathophysiology of aortic stiffness.

Identification of potent and compartment-selective small molecule furin inhibitors using cell-based assays

The proprotein convertase furin is implicated in a variety of pathogenic processes such as bacterial toxin activation, viral propagation, and cancer. Several groups have identified non-peptide compounds with high inhibitory potency against furin in vitro, although their efficacy in various cell-based assays is largely unknown. In this study we show that certain guanidinylated 2,5-dideoxystreptamine derivatives exhibit interesting ex vivo properties. Compound 1b (1,1'-(4-((2,4-diguanidino-5-(4-guanidinophenoxy)cyclohexyl)oxy)-1,3-phenylene)diguanidine) is a potent and cell-permeable inhibitor of cellular furin, since it was able to retard tumor cell migration, block release of a Golgi reporter, and protect cells against Bacillus anthracis (anthrax) and Pseudomonas aeruginosa intoxication, with no evident cell toxicity. Other compounds based on the 2,5-dideoxystreptamine scaffold, such as compound 1g (1,1'-(4,6-bis(4-guanidinophenoxy)cyclohexane-1,3-diyl)diguanidine) also efficiently protected cells against anthrax, but displayed only moderate protection against Pseudomonas exotoxin A and did not inhibit cell migration, suggesting poor cell permeability. Certain bis-guanidinophenyl ether derivatives such as 2f (1,3-bis(2,4-diguanidinophenoxy) benzene) exhibited micromolar potency against furin in vitro, low cell toxicity, and highly efficient protection against anthrax toxin; this compound only slightly inhibited intracellular furin. Thus, compounds 1g and 2f both represent potent furin inhibitors at the cell surface with low intracellular inhibitory action, and these particular compounds might therefore be of preferred therapeutic interest in the treatment of certain bacterial and viral infections.

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.

Functional interactions between matrix metalloproteinases and glycosaminoglycans

Similar to most proteinases, matrix metalloproteinases (MMP) do not recognize a consensus cleavage site. Thus, it is not surprising that, in a defined in vitro reaction, most MMPs can act on a wide range of proteins, including many extracellular matrix proteins. However, the findings obtained from in vivo studies with genetic models have demonstrated that individual MMPs act on just a few extracellular protein substrates, typically not matrix proteins. The limited, precise functions of an MMP imply that mechanisms have evolved to control the specificity of proteinase:substrate interactions. We discuss the possibility that interactions with the glycosaminoglycan chains of proteoglycans may function as allosteric regulators or accessory factors directing MMP catalysis to specific substrates. We propose that understanding how the activity of specific MMPs is confined to discreet compartments and targeted to defined substrates via interactions with other macromolecules may provide a means of blocking potentially deleterious MMP-mediated processes at the same time as sparing any beneficial functions.

Filamin A controls matrix metalloproteinase activity and regulates cell invasion in human fibrosarcoma cells

Filamins are an important family of actin-binding proteins that, in addition to bundling actin filaments, link cell surface adhesion proteins, signaling receptors and channels to the actin cytoskeleton, and serve as scaffolds for an array of intracellular signaling proteins. Filamins are known to regulate the actin cytoskeleton, act as mechanosensors that modulate tissue responses to matrix density, control cell motility and inhibit activation of integrin adhesion receptors. In this study, we extend the repertoire of filamin activities to include control of extracellular matrix (ECM) degradation. We show that knockdown of filamin increases matrix metalloproteinase (MMP) activity and induces MMP2 activation, enhancing the ability of cells to remodel the ECM and increasing their invasive potential, without significantly altering two-dimensional random cell migration. We further show that within filamin A, the actin-binding domain is necessary, but not sufficient, to suppress the ECM degradation seen in filamin-A-knockdown cells and that dimerization and integrin binding are not required. Filamin mutations are associated with neuronal migration disorders and a range of congenital malformations characterized by skeletal dysplasia and various combinations of cardiac, craniofacial and intestinal anomalies. Furthermore, in breast cancers loss of filamin A has been correlated with increased metastatic potential. Our data suggest that effects on ECM remodeling and cell invasion should be considered when attempting to provide cellular explanations for the physiological and pathological effects of altered filamin expression or filamin mutations.

Human matrix metalloproteinases: an ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.

Ukrain affects pancreas cancer cell phenotype in vitro by targeting MMP-9 and intra-/extracellular SPARC expression

BACKGROUND/AIMS

We investigated whether the anticancer drug Ukrain (UK) is able to modulate the expression of some of the key markers of tumor progression in pancreatic cell carcinoma, in order to assess its potential therapeutic effect.

METHODS

Three cell lines (HPAF-II, PL45, HPAC) were treated with UK (5, 10 and 20 μM) for 48 h, or left untreated. Secreted protein acidic and rich in cysteine (SPARC) mRNA levels were assessed by real-time PCR. Matrix metalloproteinases (MMP)-2 and -9 activity was analyzed by SDS zymography; SPARC protein levels in cell lysates and supernatants were determined by Western blot. Cell cycle was determined by flow cytometric analysis, and invasion by matrigel invasion assay.

RESULTS

UK down-regulated MMP-2 and MMP-9, suggesting that UK may decrease pancreatic cancer cell invasion, as confirmed by the matrigel invasion assay. SPARC protein down-regulation in supernatants points to an inhibition by UK of extracellular matrix remodeling in the tumor microenvironment. At the same time, SPARC mRNA and cellular protein level up-regulation suggests that UK can affect cell proliferation by cell cycle inhibition, showing a cell cycle G2/M arrest in UK-treated cells.

CONCLUSION

Our results suggest that UK modulates two major aspects involved in tumorigenesis of pancreatic cancer cells, such as extracellular matrix remodeling and cell proliferation.

Role of matrix metalloproteinase-9 dimers in cell migration: design of inhibitory peptides

Non-proteolytic activities of matrix metalloproteinases (MMPs) have recently been shown to impact cell migration, but the precise mechanism remains to be understood. We previously demonstrated that the hemopexin (PEX) domain of MMP-9 is a prerequisite for enhanced cell migration. Using a biochemical approach, we now report that dimerization of MMP-9 through the PEX domain appears necessary for MMP-9-enhanced cell migration. Following a series of substitution mutations within the MMP-9 PEX domain, blade IV was shown to be critical for homodimerization, whereas blade I was required for heterodimerization with CD44. Blade I and IV mutants showed diminished enhancement of cell migration compared with wild type MMP-9-transfected cells. Peptides mimicking motifs in the outermost strands of the first and fourth blades of the MMP-9 PEX domain were designed. These peptides efficiently blocked MMP-9 dimer formation and inhibited motility of COS-1 cells overexpressing MMP-9, HT-1080, and MDA-MB-435 cells. Using a shRNA approach, CD44 was found to be a critical molecule in MMP-9-mediated cell migration. Furthermore, an axis involving a MMP-9-CD44-EGFR signaling pathway in cell migration was identified using antibody array and specific receptor tyrosine kinase inhibitors. In conclusion, we dissected the mechanism of pro-MMP-9-enhanced cell migration and developed structure-based inhibitory peptides targeting MMP-9-mediated cell migration.

Biochemical properties of the matrix metalloproteinase NtMMP1 from Nicotiana tabacum cv. BY-2 suspension cells

A zinc-dependent matrix metalloproteinase (NtMMP1) found in the plasma membrane of Nicotiana tabacum cv. Bright Yellow 2 (BY-2) suspension cells is thought to be responsible for the degradation of recombinant proteins secreted into the culture supernatant. We have characterized the proteolytic activity of NtMMP1 by expressing a recombinant derivative lacking the C-terminal transmembrane domain in yeast. After purifying the protein by affinity chromatography, its autocatalytic activity was analyzed using monoclonal antibodies raised against its N-terminal and C-terminal portions. Both the unprocessed and processed forms of NtMMP1 displayed caseinolytic activity and N-terminal sequencing identified an autocatalytic cleavage site within the sequence motif HFSFFP, which is similar to the corresponding sequences of the human matrix metalloproteinases stromelysin-1 (MMP-3) and stromelysin-2 (MMP-10). Unlike all other matrix metalloproteinases investigated so far, NtMMP1 contains a disulfide bond within its propeptide thus rendering the proenzyme catalytically active. Kinetic analysis of NtMMP1 with a synthetic substrate revealed a K(m) of 10.55 +/- 0.9 microM, a k(cat) of 0.6 +/- 0.01 s(-1) and maximum activity at pH 7.5. We found that NtMMP1 degrades Desmodus rotundus salivary plasminogen activator alpha 1 (DSPAalpha1), a biopharmaceutical protein, that has proven difficult to produce in tobacco BY-2 cells. This provides a likely explanation for the frequent instability of secreted recombinant biopharmaceuticals produced in plant suspension cell cultures. Our data suggest new avenues that can be explored to improve the production of pharmaceutical proteins in plants and plant cells.

Physiology and pathophysiology of matrix metalloproteases

Matrix metalloproteases (MMPs) comprise a family of enzymes that cleave protein substrates based on a conserved mechanism involving activation of an active site-bound water molecule by a Zn(2+) ion. Although the catalytic domain of MMPs is structurally highly similar, there are many differences with respect to substrate specificity, cellular and tissue localization, membrane binding and regulation that make this a very versatile family of enzymes with a multitude of physiological functions, many of which are still not fully understood. Essentially, all members of the MMP family have been linked to disease development, notably to cancer metastasis, chronic inflammation and the ensuing tissue damage as well as to neurological disorders. This has stimulated a flurry of studies into MMP inhibitors as therapeutic agents, as well as into measuring MMP levels as diagnostic or prognostic markers. As with most protein families, deciphering the function(s) of MMPs is difficult, as they can modify many proteins. Which of these reactions are physiologically or pathophysiologically relevant is often not clear, although studies on knockout animals, human genetic and epigenetic, as well as biochemical studies using natural or synthetic inhibitors have provided insight to a great extent. In this review, we will give an overview of 23 members of the human MMP family and describe functions, linkages to disease and structural and mechanistic features. MMPs can be grouped into soluble (including matrilysins) and membrane-anchored species. We adhere to the 'MMP nomenclature' and provide the reader with reference to the many, often diverse, names for this enzyme family in the introduction.

Pleiotropic roles of matrix metalloproteinases in tumor angiogenesis: contrasting, overlapping and compensatory functions

A number of extensive reviews are available discussing the roles of MMPs in various aspects of cancer progression from benign tumor formation to overt cancer present with deadly metastases. This review will focus specifically on the evidence functionally linking the MMPs and tumor-induced angiogenesis in various in vivo models. Emphasis has been placed on the cellular origin of the MMPs in tumor tissue, the requirement of proMMP activation and the resulting proteolytic activity for the induction and progression of tumor angiogenesis, and the pleiotropic roles for some of the MMPs. The functional mechanisms of the angiogenic MMPs are discussed as well as their catalytic detection in complex biological systems. In addition, the contribution of active MMPs to metastatic spread and establishment of secondary metastasis will be discussed in view of the findings indicating that MMPs are involved in the preparation of pre-metastatic niches. Finally, the most recent evidence, indicating the pro-metastatic consequences of anti-angiogenic therapies employing MMP inhibitors will be presented as examples highlighting possible outcomes of interfering with the pleiotropic nature of the MMP functionality.

Membrane type-1 matrix metalloprotease-independent activation of pro-matrix metalloprotease-2 by proprotein convertases

Matrix metalloprotease-2 is implicated in many biological processes and degrades extracellular and non-extracellular matrix molecules. Matrix metalloprotease-2 maintains a latent state through a cysteine-zinc ion pairing which, when disrupted, results in full enzyme activation. This pairing can be disrupted by a conformational change or cleavage within the propeptide. The best known activation mechanism for pro-matrix metalloprotease-2 occurs via cleavage of the propeptide by membrane type-1 matrix metalloprotease. However, significant residual activation of pro-matrix metalloprotease-2 is seen in membrane type-1 matrix metalloprotease knockout mice and in fibroblasts treated with metalloprotease inhibitors. These findings indicate the presence of a membrane type-1 matrix metalloprotease-independent activation mechanism for pro-matrix metalloprotease-2 in vivo, which prompted us to explore an alternative activation mechanism for pro-matrix metalloprotese-2. In this study, we demonstrate membrane type-1 matrix metalloprotease-independent propeptide processing of matrix metalloprotease-2 in HEK293F and various tumor cell lines, and show that proprotein convertases can mediate the processing intracellularly as well as extracellularly. Furthermore, processed matrix metalloprotease-2 exhibits enzymatic activity that is enhanced by intermolecular autolytic cleavage. Thus, our experimental data, taken together with the broad expression of proprotein convertases, suggest that the proprotein convertase-mediated processing may be a general activation mechanism for pro-matrix metalloprotease-2 in vivo.

Targeting a metalloprotease-PAR1 signaling system with cell-penetrating pepducins inhibits angiogenesis, ascites, and progression of ovarian cancer

Gene chip and proteomic analyses of tumors and stromal tissue has led to the identification of dozens of candidate tumor and host components potentially involved in tumor-stromal interactions, angiogenesis, and progression of invasive disease. In particular, matrix metalloproteases (MMP) have emerged as important biomarkers and prognostic factors for invasive and metastatic cancers. From an initial screen of benign versus malignant patient fluids, we delineated a metalloprotease cascade comprising MMP-14, MMP-9, and MMP-1 that culminates in activation of PAR1, a G protein-coupled protease-activated receptor up-regulated in diverse cancers. In xenograft models of advanced peritoneal ovarian cancer, PAR1-dependent angiogenesis, ascites formation, and metastasis were effectively inhibited by i.p. administration of cell-penetrating pepducins based on the intracellular loops of PAR1. These data provide an in vivo proof-of-concept that targeting the metalloprotease-PAR1 signaling system may be a novel therapeutic approach in the treatment of ovarian cancer.

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.

A small-molecule furin inhibitor inhibits cancer cell motility and invasiveness

Furin, a member the proprotein convertase (PC) family, processes inactive precursor proteins to functional proteins within the Golgi/trans-Golgi network secretory pathway. Furin and other PC family members (furin/PCs) activate proteins vital to proper physiological functioning, including growth factors and hormones, receptors, plasma proteins, and matrix metalloproteases (MMPs). Additionally, the expression and activity of furin/PC are necessary for processing substrates important for cell transformation and tumor progression, metastasis, and angiogenesis. Furin processing of the remodeling protease membrane type-1 matrix metalloproteinase (MT1-MMP) enhances cellular motility and invasiveness, contributing to aggression and metastatic potential cancer cells. Whereas overexpression and activity of furin/PC exacerbate the cancer phenotype, inhibition of its activity decreases or nullifies furin/PC-mediated effects, and thus, inhibition of furin may be a viable route to cancer therapy. Recently, we identified a small-molecule inhibitor of furin, named B3, by high-throughput screening with a K(i) and IC(50) of 12 microM. Here, we show that this cell-permeable, small-molecule compound inhibits furin-mediated cleavage of proMT1-MMP, resulting in decreased MMP-2 activation and cell motility in CHO cells expressing proMT1-MMP. Additionally, this molecule inhibited proMT1-MMP processing, complete MMP-2 maturation, and invasiveness of human fibrosarcoma cells (HT1080).

Activation of protease-activated receptor1 mediates induction of matrix metalloproteinase-9 by thrombin in rat primary astrocytes

Thrombin plays an important role in diverse neurological processes such as proliferation, cell migration, differentiation and neuroinflammation. In this study, we investigated the effect of thrombin on matrix metalloprotease-9 (MMP-9) expression in rat primary astrocytes. Thrombin (1-10U/ml) induced a significant increase in MMP-9 activity as measured by gelatin zymography. Thrombin also increased MMP-9 mRNA expression. Among three isotypes of thrombin receptor, i.e. protease-activated receptor (PAR)-1, -3 and -4, PAR1 agonist (1-100muM) but not PAR3 and PAR4 agonist induced MMP-9 expression. Inhibition of thrombin-induced MMP-9 production by SCH 79797 (10-50nM), a selective PAR1 receptor antagonist, confirmed that PAR1 is a main receptor for thrombin-induced MMP-9 expression. In astrocytes, thrombin activated Erk1/2, and it was inhibited by PD98059. In this study, thrombin-induced MMP-9 expression was inhibited by PD98059. PAR1 agonist activated Erk1/2 and PD98059 inhibited PAR1 agonist-induced MMP-9 expression. MMP-9 promoter reporter assay confirmed the positive effect of ERK1/2 on MMP-9 expression. These results suggest that the activation of PAR1 mediates thrombin-induced MMP-9 expression through the regulation of Erk1/2.

Leukocyte cell surface proteinases: regulation of expression, functions, and mechanisms of surface localization

A number of proteinases are expressed on the surface of leukocytes including members of the serine, metallo-, and cysteine proteinase superfamilies. Some proteinases are anchored to the plasma membrane of leukocytes by a transmembrane domain or a glycosyl phosphatidyl inositol (GPI) anchor. Other proteinases bind with high affinity to classical receptors, or with lower affinity to integrins, proteoglycans, or other leukocyte surface molecules. Leukocyte surface levels of proteinases are regulated by: (1) cytokines, chemokines, bacterial products, and growth factors which stimulate synthesis and/or release of proteinases by cells; (2) the availability of surface binding sites for proteinases; and/or (3) internalization or shedding of surface-bound proteinases. The binding of proteinases to leukocyte surfaces serves many functions including: (1) concentrating the activity of proteinases to the immediate pericellular environment; (2) facilitating pro-enzyme activation; (3) increasing proteinase stability and retention in the extracellular space; (4) regulating leukocyte function by proteinases signaling through cell surface binding sites or other surface proteins; and (5) protecting proteinases from inhibition by extracellular proteinase inhibitors. There is strong evidence that membrane-associated proteinases on leukocytes play critical roles in wound healing, inflammation, extracellular matrix remodeling, fibrinolysis, and coagulation. This review will outline the biology of membrane-associated proteinases expressed by leukocytes and their roles in physiologic and pathologic processes.

Control of matrix metalloproteinase catalytic activity

As their name implies, MMPs were first described as proteases that degrade extracellular matrix proteins, such as collagens, elastin, proteoglycans, and laminins. However, studies of MMP function in vivo have revealed that these proteinases act on a variety of extracellular protein substrates, often to activate latent forms of effector proteins, such as antimicrobial peptides and cytokines, or to alter protein function, such as shedding of cell-surface proteins. Because their substrates are diverse, MMPs are involved in variety of homeostatic functions, such as bone remodeling, wound healing, and several aspects of immunity. However, MMPs are also involved in a number of pathological processes, such as tumor progression, fibrosis, chronic inflammation, tissue destruction, and more. A key step in regulating MMP proteolysis is the conversion of the zymogen into an active proteinase. Several proMMPs are activated in the secretion pathway by furin proprotein convertases, but for most the activation mechanisms are largely not known. In this review, we discuss both authentic and potential mechanisms of proMMP activation.

Vasogenic edema due to tight junction disruption by matrix metalloproteinases in cerebral ischemia

Cerebral ischemia causes cell swelling and breakdown of the blood-brain barrier (BBB). Cytotoxic edema results from energy failure, and vasogenic edema occurs when the blood vessels are damaged. Proteases and free radicals are the end result of a molecular injury cascade. Matrix metalloproteinases (MMPs) are a gene family of extracellular matrix-degrading enzymes that disrupt the BBB. Tight junction proteins (TJPs), occludin and claudin-5, which form the endothelial barrier, are vulnerable to attack by MMPs. Basal lamina proteins, such as fibronectin, laminin, and heparan sulfate, are also degraded by MMPs. Reperfusion injury leads to a biphasic opening of the BBB, with the early opening occurring several hours after the onset of reperfusion due to activation of the constitutive enzyme gelatinase A (MMP-2). This initial opening is transient and followed 24 to 48 hours later by more intense damage to the blood vessel, which is associated with the expression and activation of gelatinase B (MMP-9) and stromelysin-1 (MMP-3). Synthetic MMP inhibitors restore the early integrity of the BBB but are ineffective in the later opening. Because these inhibitors block MMPs involved in angiogenesis and neurogenesis, they also slow recovery. The challenge is to identify agents that will protect the BBB, blocking vasogenic edema without interfering with recovery.

The Study of a Patient's Immune System May Prove to be a Useful Noninvasive Tool for Stage Classification in Colon Cancer

Therapy, and, therefore, prognosis, is strictly related to cancer stage, and hence, screening tests that can contribute to the early classification of disease stage represent a step forward in treatment. Unfortunately, few prognostic indices are available, especially noninvasive ones. Our study of the physiological network of the immune response, however, leads us to believe that it may well be possible to define immunological indices for the classification of cancer stage using blood parameters. In this paper, we show how the study of a patient's immune system can be used as a noninvasive tool for early-stage classification.

A critical role for the membrane-type 1 matrix metalloproteinase in collagen phagocytosis

Degradation of collagen is important for the physiological remodeling of connective tissues during growth and development as well as in wound healing, inflammatory diseases, and cancer cell invasion. In remodeling adult tissues, degradation of collagen occurs primarily through a phagocytic pathway. However, although various steps in the phagocytic pathway have been characterized, the enzyme required to initially fragment collagen fibrils for subsequent phagocytosis has not been identified. We have used laser confocal microscopy, transmission electron microscopy, and biochemical assays to show that human fibroblasts initiate degradation of collagen through the collagenase activity of the membrane-bound metalloproteinase MT1-MMP. Degradation of natural and reconstituted collagen substrates correlated with the expression of MT1-MMP, which was localized at sites of collagen cleavage at the surface of the cells and also within the cells, whereas collagen degradation was abrogated when MT1-MMP expression was blocked by small interfering RNA treatment. In contrast to MT1-MMP, the gelatinolytic activity of MMP-2 was not required for collagen phagocytosis. These studies demonstrate a pivotal role of catalytically active MT1-MMP in preparing collagen fibrils for phagocytic degradation.

Selective regulation of MMP and TIMP mRNA levels in tree shrew sclera during minus lens compensation and recovery

PURPOSE

In juvenile tree shrews, a minus-power lens placed in front of the eye produces increased axial elongation and a myopic shift in refractive state that compensates for the power of the lens. Scleral tissue remodeling and modulation of the mechanical properties of the sclera occur during lens compensation. In this study, the time course of changes in scleral mRNA levels of three MMPs and three TIMPs during compensation for a minus lens and during recovery was investigated, to determine which, if any, are temporally associated with changes in the mechanical properties of the sclera and the axial elongation rate.

METHODS

Competitive RT-PCR was used to measure the levels of mRNA for MT1-MMP, MMP-2, MMP-3, TIMP-1, TIMP-2, and TIMP-3 in the scleras of tree shrews that had received either 1, 2, 4, or 11 days of monocular -5-D lens treatment, or 11 days of -5-D lens treatment followed by 2 or 4 days of recovery.

RESULTS

Relative to their control eyes, treated eye MT1-MMP and MMP-2 mRNA levels were significantly higher, and TIMP-3 levels were lower by 1 to 4 days of minus lens treatment. These differential effects were absent by 11 days of treatment when the treated eyes had compensated for the lens. The levels of all three TIMPs spiked upward in both eyes after 2 days of recovery. The differential changes in MT1-MMP, MMP-2, and TIMP-3 mRNA levels were all restricted to the treated eye and were temporally associated with the differential changes in axial elongation, refractive state, and the previously measured changes in creep rate.

CONCLUSIONS

The observed changes in MT1-MMP, MMP-2, TIMP-2, and TIMP-3 mRNA are consistent with visually modulated MT1-MMP activation of MMP-2 and with MT1-MMP degradation of scleral extracellular matrix components. These data constitute further evidence that visual signals modulate gene expression of selected MMPs and TIMPs to control scleral remodeling, the mechanical properties of the sclera, axial elongation, and refractive state.

Membrane type-matrix metalloproteinases and tumor progression

Matrix metalloproteinases (MMPs) are a family of zinc endopeptidases that process growth factors, growth factor binding proteins, cell surface proteins, degrade extracellular matrix (ECM) components and thereby play a central role in tissue remodeling and tumor progression. Membrane-type matrix metalloproteinases (MT-MMPs) are a recently discovered subgroup of intrinsic plasma membrane proteins. Their functions have been extended from pericellular proteolysis and control of cell migration to cell signaling, control of cell proliferation and regulation of multiple stages of tumor progression including growth and angiogenesis. This review sheds light on the new functions of MT-MMPs and their inhibitors in tumor development and angiogenesis, and presents recent investigations that document their influence on various cell functions.

Cyclic mechanical strain-induced proliferation and migration of human airway smooth muscle cells: role of EMMPRIN and MMPs

Airway smooth muscle (ASM) proliferation and migration are major components of airway remodeling in asthma. Asthmatic airways are exposed to mechanical strain, which contributes to their remodeling. Matrix metalloproteinase (MMP) plays an important role in remodeling. In the present study, we examined if the mechanical strain of human ASM (HASM) cells contributes to their proliferation and migration and the role of MMPs in this process. HASM were exposed to mechanical strain using the FlexCell system. HASM cell proliferation, migration and MMP release, activation, and expression were assessed. Our results show that cyclic strain increased the proliferation and migration of HASM; cyclic strain increased release and activation of MMP-1, -2, and -3 and membrane type 1-MMP; MMP release was preceded by an increase in extracellular MMP inducer; Prinomastat [a MMP inhibitor (MMPI)] significantly decreased cyclic strain-induced proliferation and migration of HASM; and the strain-induced increase in the release of MMPs was accompanied by an increase in tenascin-C release. In conclusion, cyclic mechanical strain plays an important role in HASM cell proliferation and migration. This increase in proliferation and migration is through an increase in MMP release and activation. Pharmacological MMPIs should be considered in the pursuit of therapeutic options for airway remodeling in asthma.

Furin Directly Cleaves proMMP-2 in the trans-Golgi Network Resulting in a Nonfunctioning Proteinase

Proprotein convertases play an important role in tumorigenesis and invasiveness. Here, we report that a dibasic amino acid convertase, furin, directly cleaves proMMP-2 within the trans-Golgi network leading to an inactive form of matrix metalloproteinase-2 (MMP-2). Co-transfection of COS-1 cells with both proMMP-2 and furin cDNAs resulted in the cleavage of the N-terminal propeptide of proMMP-2. The molecular mass of cleaved MMP-2 (63 kDa), detected in both cell lysates and conditioned medium, is between the intermediate and fully activated forms of MMP-2 induced by membrane type 1-MMP. Furin-cleaved MMP-2 does not possess proteolytic activity as examined in a cell-free assay. Treatment of transfected cells with a furin inhibitor resulted in a dose-dependent inhibition of proMMP-2 cleavage; recombinant tissue inhibitor of metalloproteinase-2, which binds to the active site of membrane type 1-MMP, had no inhibitory effect. Site-directed mutagenesis of amino acids in the furin consensus recognition motif of proMMP-2(R69KPR72) prevented propeptide cleavage, thereby identifying the scissile bond and characterizing the basic amino acids required for cleavage. Other experimental observations were consistent with intracellular furin cleavage of proMMP-2 in the trans-Golgi network. The furin cleavage site in other proMMPs was examined. MMP-3, which contains the RXXR furin consensus sequence, was cleaved in furin co-transfected cells, whereas MMP-1, which lacks an RXXR consensus sequence, was not cleaved. In conclusion, we report the novel observation that furin can directly cleave the RXXR amino acid sequence in the propeptide domain of proMMP-2 leading to inactivation of the enzyme.

Paradigmatic identification of MMP-2 and MT1-MMP activation systems in cardiac fibroblasts cultured as a monolayer

Activations of MMP-2 and membrane type 1-matrix metalloproteinase (MT1-MMP) have been correlated with cell migration, a key cellular event in the wound healing and tissue remodeling. We have previously demonstrated furin-dependent MMP-2 and MT1-MMP activations induced by type I collagen in cardiac fibroblasts. To understand mechanistic aspects of the regulation of MMP-2 and MT1-MMP activations by potential non-matrix factor(s) in cardiac fibroblasts, in the present study, we examined the effects of various agents including concanavalin A (ConA), a proteolytic phenotype-producing agent. We showed that treatment of cells with ConA activated pro-MMP-2, and that this activation concurred with elevated levels of cellular MT1-MMP and TIMP-2. The presence of active MT1-MMP and 43 and 36 kDa processed forms of MT1-MMP in a fraction of intracellular proteins prepared from ConA-treated cells suggests the possible internalization of differential forms of MT1-MMP. The appearance of 36 kDa processed form of MT1-MMP in conditioned media prepared from ConA-treated cells indicates the possible extracellular release of the further processed MT1-MMP fragment. Inhibition of furin in ConA-treated cells attenuated pro-MT1-MMP processing and the cellular TIMP-2 level, plus it reduced cell-released active MMP-2 in a time-dependent manner. These results suggest the involvement of furin in the ConA-induced activations of MT1-MMP and MMP-2. Furthermore, the existence of furin inhibitor-insensitive pro- and active MMP-2 species associated with ConA-treated cells implies that a mechanism independent of furin may perhaps account for the binding of the MMP-2 species to the cells. Supplementary material for this article can be found at http://www.mrw.interscience.wiley.com/suppmat/0730-2312/suppmat/94/suppmat_guo.tif.

Lipopolysaccharide induces matrix metalloproteinase-9 expression via a mitochondrial reactive oxygen species-p38 kinase-activator protein-1 pathway in Raw 264.7 cells

We have identified a novel signaling pathway that leads to expression of matrix metalloproteinase-9 (MMP-9) in murine macrophages in response to the bacterial endotoxin, LPS. We showed that p38 kinase was essential for this induction and observed that LPS-induced MMP-9 expression was sensitive to rottlerin, a putative protein kinase Cdelta (PKCdelta) inhibitor. However neither infection with a retrovirus expressing a dominant negative mutant of PKCdelta nor down-regulation of PKCdelta by prolonged PMA treatment affected MMP-9 expression, thus excluding involvement of PKCdelta. Interestingly, LPS-induced MMP-9 expression and p38 kinase phosphorylation were shown to be suppressed by the antioxidant N-acetylcysteine and the flavoenzyme inhibitor diphenyleneiodonium chloride, but not by pyrrolidine dithiocarbamate, an NF-kappaB inhibitor. In addition, LPS was found to induce the production of mitochondrial reactive oxygen species (ROS) and this effect was rottlerin-sensitive, suggesting an inhibitory effect of rottlerin on mitochondrial ROS. LPS-induced MMP-9 expression and p38 kinase phosphorylation were also inhibited by rotenone, a specific inhibitor of mitochondrial complex I, supporting the role of mitochondrial ROS in LPS signaling to MMP-9. Finally, we showed that the ROS-p38 kinase cascade targets the transcription factor AP-1. Taken together, our findings identify a ROS-p38 kinase-AP-1 cascade as a novel pathway mediating LPS signaling to MMP-9 expression in macrophages.

The possible role of matrix metalloproteinase (MMP)-2 and MMP-9 in cancer, e.g. acute leukemia

In the past decades, a lot of effort has been put in identifying the role of matrix metalloproteinases (MMPs) in cancer. The main role of MMPs in angiogenesis, tumor growth and metastasis is degradation of extracellular matrix (ECM) and release and/or activation of growth factors through their degradative activity. The degradative activity finally results in cancer progression. MMP-inhibitors (MMPIs) have already been designed and tested, based on the degradative role of MMPs in cancer progression. First clinical trials with MMPIs have been performed with disappointing results, showing that in order to use MMP-inhibition the mechanisms underlying MMP-expression in cancer have to be further elucidated. This paper reviews the mechanisms of MMPs on molecular and cellular level and discusses the role for MMPs and MMP-inhibition in cancer with special focus on acute leukemia.

Intracellular processing and activation of membrane type 1 matrix metalloprotease depends on its partitioning into lipid domains

The integral membrane type 1 matrix metalloprotease (MT1-MMP) is a pivotal protease in a number of physiological and pathological processes and confers both non-tumorigenic and tumorigenic cell lines with a specific growth advantage in a three-dimensional matrix. Here we show that, in a melanoma cell line, the majority (80%) of MT1-MMP is sorted to detergent-resistant membrane fractions; however, it is only the detergent-soluble fraction (20%) of MT1-MMP that undergoes intracellular processing to the mature form. Also, this processed MT1-MMP is the sole form responsible for ECM degradation in vitro. Finally, furin-dependent processing of MT1-MMP is shown to occur intracellularly after exit from the Golgi apparatus and prior to its arrival at the plasma membrane. It is thus proposed that the association of MT1-MMP with different membrane subdomains might be crucial in the control of its different activities: for instance in cell migration and invasion and other less defined ones such as MT1-MMP-dependent signaling pathways.

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.

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.

The 'Abtropfung phenomenon' revisited: Dermal nevus cells from congenital nevi cannot activate matrix metalloproteinase 2 (MMP-2)

Since Unna's Abtropfung hypothesis, the process of migration of nevus cells in the dermis remains unknown. To investigate its mechanisms, we studied the role of gelatinases in dermal nevus cells obtained from congenital pigmented nevi, which are major actors in the remodeling of basement membrane proteins. Our previous studies have shown that dermal nevus cells express pro-matrix metalloproteinase (MMP)-2 exclusively and cannot return to the dermis when seeded together with keratinocytes on top of the dermis in a skin reconstruction model. To examine why MMP-2 was not in its active form, we used Western blot to study the expression of members of the MMP-2 activation pathway (membrane type 1-MMP and tissue inhibitor of metalloproteinase-2), which proved to be normally expressed. To induce the dermal passage of nevus cells artificially, we also tried to activate gelatinases with phorbol-12-myristate-13-acetate and epidermal growth factor, using epidermis reconstructed with nevus cells. No migration in the dermis could be triggered. We conclude that the absence of active MMP-2 is due to a functional blockade of its activation pathway and may prevent dermal nevus cells from reaching the dermal compartment in skin reconstructs. Furthermore, our findings reinforce the concept that dermal nevus cells originating from congenital nevi are in a quiescent status.

Membrane-type 1 matrix metalloproteinase: a key enzyme for tumor invasion

Matrix metalloproteinases (MMPs) are believed to play a pivotal role in malignant behavior of cancer cells such as rapid tumor growth, invasion, and metastasis by degrading extracellular matrix (ECM). Different types of synthetic inhibitors against MMPs (MMPIs) were developed as candidates for anti-cancer therapeutics and so far clinical trials had led to no significant success. However, this does not diminish the importance of MMPs in the malignancy of cells. Details about MMPs, specifically when and how they take part in the development of cancer are necessary for more advanced application of MMPIs. In this paper, we summarize recent knowledge about membrane-type 1 matrix metalloproteinase (MT1-MMP) which is expressed on cancer cell surface as an invasion-promoting proteinase. By localizing at the leading edge of invasive cancer cells, MT1-MMP degrades components of the tissue barriers. One of the major targets is type I collagen, the most abundant ECM component. Although MT1-MMP itself cannot degrade type IV collagen in the basement membrane, it binds to and activates proMMP-2, one of the type IV collagenases. However, degradation of the ECM is not the sole function of MT1-MMP. MT1-MMP also regulates cell-ECM interaction by processing cell adhesion molecules such as CD44 and integrin alphav chain, and eventually promotes cell migration as well. In addition to the transcriptional regulation, invasion-promoting activity of the MT1-MMP is also strictly monitored at the post-translational level. Precise knowledge about the regulation will give us insight to develop new methods for treating invasive cancer patients.

Membrane type-1 matrix metalloproteinase functions as a proprotein self-convertase. Expression of the latent zymogen in Pichia pastoris, autolytic activation, and the peptide sequence of the cleavage forms

An understanding of the regulatory mechanisms that control the activity of membrane type-1 matrix metalloproteinase (MT1-MMP), a key proteinase in tumor cell invasion, is essential for the design of potent and safe anti-cancer therapies. A unique proteolytic pathway regulates MT1-MMP at cancer cell surfaces. The abundance of proteolytic enzymes in cancer cells makes it difficult to identify the autocatalytic events in this pathway. To identify these events, a soluble form of MT1-MMP, lacking the C-terminal transmembrane and cytoplasmic domains, was expressed in Pichia pastoris. Following secretion, the latent zymogen and active enzyme were each purified from media by fast protein liquid chromatography. Trace amounts of active MT1-MMP induced activation of the zymogen and its self-proteolysis. This autocatalytic processing generated six main forms of MT1-MMP, each of which was subjected to the N-terminal microsequencing to identify the cleavage sites. Our data indicate that MT1-MMP functions as a self-convertase and is capable of cleaving its own prodomain at the furin cleavage motif RRKR downward arrow Y(112), thus autocatalytically generating the mature MT1-MMP enzyme with an N terminus starting at Tyr(112). The mature enzyme undergoes further autocatalysis to the two distinct intermediates (N terminus at Trp(119) and at Asn(130)) and, next, to the three inactive ectodomain forms (N terminus at Thr(222), at Gly(284), and at Thr(299)). These findings provide, for the first time, a structural basis for understanding the unconventional mechanisms of MT1-MMP activation and regulation. Finally, our data strongly imply that MT1-MMP is a likely substitute for the general proprotein convertase activity of furin-like proteinases, especially in furin-deficient cancer cells.

Induction of matrix metalloproteinase-9 (MMP-9) in lipopolysaccharide-stimulated primary astrocytes is mediated by extracellular signal-regulated protein kinase 1/2 (Erk1/2)

In the present study, we investigated whether the activation of protein kinase C (PKC) and extracellular signal-regulated kinase 1/2 (Erk1/2) are involved in the induction of MMP-9 in lipopolysaccharide (LPS)-stimulated primary astrocytes. The expression of MMP-9 but not MMP-2 was increased by LPS. LPS treatment induced activation of Erk1/2 within 30 min, which was dose-dependently inhibited by PD98059, a specific inhibitor of the Erk kinase (MEK). In this condition, PD98059 blocked the increase in MMP-9 protein and mRNA level as well as gelatin-digesting activity. Inhibition of PKC activity blocked the LPS-induced activation of Erk1/2 as well as MMP-9 expression. In addition, activation of PKC by phorbol myristoyl acetate (PMA) activated Erk1/2 with concomitant increase in MMP-9 production. Moreover, treatment of PD98059 dose-dependently decreased the PMA-induced MMP-9 expression. The results from the present study suggest that induction of MMP-9 by LPS in rat primary astrocytes is mediated, at least in part, by the sequential activation of PKC and Erk1/2. The Erk1/2-mediated MMP-9 induction may provide insights into the regulation of MMP-9 production in CNS, which may occur in vivo in pathological situations such as CNS inflammation.

The cell surface: the stage for matrix metalloproteinase regulation of migration

Matrix metalloproteinases are important for the turnover of extracellular matrix in tissue. Recent studies have expanded their roles well beyond extracellular matrix degradation - they also cleave many growth factors, cytokines and cell adhesion molecules in the extracellular milieu, modulating their functions irreversibly. In particular, some matrix metalloproteinases that associate with the cell surface have arisen as intriguing regulators of cellular functions, including migration.

Ovarian tissue remodeling: role of matrix metalloproteinases and their inhibitors

Follicular formation, growth or atresia, and ovulation as well as luteal formation and subsequent regression are dependent upon cyclical remodeling of the extracellular matrix (ECM). The proteinaceous and nonproteinaceous components of the ECM provide the tissue specific, extracellular architecture to which cells attach. Furthermore, the ECM modulates cellular activities through cellular surface receptors and serves as a reservoir for specific growth factors, cytokines, and binding proteins. The ability of the ECM to direct the proliferation, differentiation and function of cells implicates ECM remodeling in normal ovarian function. Specific components of the ECM are cleaved by matrix metalloproteinases (MMPs) whose activities are specifically inhibited by tissue inhibitors of metalloproteinases (TIMPs). MMPs are zinc- and calcium-dependent enzymes that collectively degrade proteinaceous components of the ECM. Controlled turnover of ECM by MMPs and TIMPs may be essential for creating and (or) preserving microenvironments conducive to follicular and luteal function and is likely dependent upon the ratio of enzyme to inhibitor. To date, most studies have focused upon correlating ovarian expression of MMPs and TIMPs with various stages of the reproductive cycle. From these studies, many potential key regulators of ovarian ECM remodeling have been identified. This review presents evidence for the involvement of MMPs and TIMPs in ECM remodeling associated with follicular and luteal function.

Membrane-type matrix metalloproteinases (MT-MMPs): expression and function during glioma invasion

Membrane-type MMPs (MT-MMPs) constitute a growing subclass of recently identified matrix metalloproteinases (MMPs). In addition to the highly conserved MMP functional domains, the MT-MMPs have additional insertion sequences (IS) that confer unique functional roles. While most of the MMPs are secreted, the MT-MMPs are membrane associated and a number of these have cytoplasmic domains which may be important in cellular signaling. This membrane localization leads to focal areas of receptor recruitment and subsequent activity, thereby enhancing pericellular proteolysis in specific areas of contact within the brain interstitium. MT1-MMP is the best-characterized MT-MMP, the measure against which subsequently cloned homologues are compared. MT1-MMP activates proMMP2 via its interaction with TIMP2, which serves as an intermolecular bridge for proMMP2 binding to MT-MMPs. In addition to activation of proMMP2, MT-MMPs display intrinsic proteolytic activity towards extracellular matrix molecules (ECM), which is independent of MMP2 activation. The increased expression levels of several members of the MMP family have been shown to correlate with high-grade gliomas, including MTI-MMP. Despite improvements in the diagnosis and treatment of patients with glial tumors, they remain the most common and least curable brain cancer in adults. The ability of glioma cells to infiltrate surrounding brain tissue, and ultimately escape current therapeutic modalities, could potentially be minimized using anti-invasive therapies. Proteolysis is a necessary part of the invasion process, within which the MT-MMPs appear to play a central role. The development of pharmaceutical approaches that target expression and regulation of MT-MMPs may prove beneficial in targeting invading glioma cells.

Regulation of membrane type-matrix metalloproteinases

Pericellular proteolysis is a hallmark of tumor cell metastasis. The membrane type (MT)-matrix metalloproteinases (MMPs) constitute a distinctive group of membrane-bound MMPs that are central mediators of surface proteolytic events that regulate tumor cell motility, metastasis and angiogenesis. As membrane-tethered proteases, the MT-MMPs exhibit unique regulatory mechanisms and interactions with metalloproteinase inhibitors and other relevant molecules. This review will focus on new emerging information on the mechanisms that regulate MT-MMP processing, activity and inhibition, and their significance for enzyme function in the tumor microenvironment.

Matrix metalloproteinase (2, 9, and 14) expression, localization, and activity in ovine corpora lutea throughout the estrous cycle

Members of the matrix metalloproteinase (MMP) family collectively degrade extracellular matrix (ECM) and help regulate luteal function. The objectives of these experiments were to characterize the mRNA expression, localization, and activity of MMPs 2, 9, and 14 in ovine corpora lutea (CL). Ovine CL were collected on Days 2, 4, 10, and 15 of the estrous cycle (Day 0 = estrus). Messenger RNA transcripts for MMPs 2 and 14 were detected using Northern analysis; however, expression of MMP-9 was undetectable. Expression of MMP-14 mRNA (membrane type-1 MMP) was increased (P < 0.05) on Day 4; whereas, expression of MMP-2 mRNA was highest (P < 0.05) on Day 10, which corresponded to the observed increases in gelatinolytic activity in luteal homogenates as measured by a fluroscein-labeled gelatin substrate assay. MMP 2 and 9 proteins were localized predominantly to large luteal cells (LLCs), whereas MMP-14 was localized primarily to cells other than LLCs as demonstrated by immunohistochemistry. Immunolocalization of MMP-2 to putative endothelial cells was also observed on Day 15. Localization of MMP activity was determined using in situ zymography. Luteal tissues contained gelatinolytic activity primarily localized pericellularly to various cell types, including LLCs. These results support the hypothesis that ECM remodeling occurs throughout the luteal phase and may help potentiate cellular migration, differentiation, angiogenesis, and growth factor bioavailability.

A conserved sequence within the propeptide domain of membrane type 1 matrix metalloproteinase is critical for function as an intramolecular chaperone

The propeptide domain of secreted matrix metalloproteinases (MMPs) is responsible for maintaining the latency of these proteinases. Recently, the propeptide domain of the prototype membrane type matrix metalloproteinase (MT1-MMP) was demonstrated to act as an intramolecular chaperone (Cao, J., Hymowitz, M., Conner, C., Bahou, W. F., and Zucker, S. (2000) J. Biol. Chem. 275, 29648-29653). In the current study, the role of an unique four-amino acid sequence in the propeptide domain of MT1-MMP was examined. The sequence (42)YGYL(45) is conserved in the propeptide domain of all six members of the MT-MMP subfamily, but not in secreted MMPs. Mutant MT1-MMP cDNAs coding for alanine substitutions (single and double amino acid sequences) in this conserved propeptide region were transfected into COS-1 cells deficient in endogenous MT1-MMP. As demonstrated by immunofluorescence, mutant MT1-MMP protein was synthesized and displayed on the plasma membrane of transfected cells. Alanine substitutions within the (42)YGYL(45) sequence proved to be detrimental for enzyme function in terms of activation of proMMP-2 and binding TIMP-2 to the cell surface (MT1-MMP serves as a cell surface receptor for TIMP-2). In contrast to wild-type MT1-MMP-transfected cells, mutant MT1-MMP-transfected cells were incapable of degrading and migrating on a fibronectin substrate. These data indicate that the conserved (42)YGYL(45) sequence within the propeptide domain of MT-MMPs is required for intramolecular chaperone function of these intrinsic membrane proteinases.

Lefty contributes to the remodeling of extracellular matrix by inhibition of connective tissue growth factor and collagen mRNA expression and increased proteolytic activity in a fibrosarcoma model

Homeostasis of the extracellular matrix (ECM) of tissues is regulated by controlling deposition and degradation of ECM proteins. The breakdown of ECM is essential in blastocyst implantation and embryonic development, tissue morphogenesis, menstrual shedding, bone formation, tissue resorption after delivery, and tumor growth and invasion. TGF-beta family members are one of the classes of proteins that actively participate in the homeostasis of ECM. Here, we report on the effect of lefty, a novel member of the TGF-beta family, on the homeostasis of extracellular matrix in a fibrosarcoma model. Fibroblastic cells forced to express lefty by retroviral transduction lost their ability to deposit collagen in vivo. This event was associated with down-regulation of the steady-state level of connective tissue growth factor that induces collagen type I mRNA. In addition, lefty transduction significantly decreased collagen type I mRNA expression and simultaneously increased collagenolytic, gelatinolytic, elastolytic, and caseinolytic activities in vivo by the transduced fibroblasts. These findings provide a new insight on the actions of lefty and suggest that this cytokine plays an active role in remodeling of the extracellular matrix in vivo.

Membrane-type matrix metalloproteinase-1 and -3 activity in primate smooth muscle cells

Membrane-type matrix metalloproteinases-1 and -3 (MT1- and MT3-MMPs) are expressed by activated smooth muscle cells (SMCs) both in vitro and in vivo (19). To define their functions in SMCs, we transduced MT1- and MT3-MMP cDNAs into baboon SMCs by using adenoviral vectors. Overexpression of MT1-MMP increased the conversion of proMMP-2 to the intermediate and active forms. In contrast, in MT3-MMP-overexpressing cells, MMP-2 was activated partially. Immunoblot analyses revealed that MT1-MMP protein was present in the SMCs and accumulated in the presence of the synthetic MMP inhibitor, BB94, or tissue inhibitor of metalloproteinase-2 (TIMP-2). However, MT3-MMP protein was detectable only when BB94, but not TIMP-2, was present. Zymographic analyses showed that MT3-MMP had much stronger casein- and gelatin-degrading activities than did MT1-MMP. Furthermore, when MT3-MMP and MT1-MMP were coexpressed, MT1-MMP degradation was enhanced; this result supports the possibility that MT3-MMP can degrade MT1-MMP. SMCs overexpressing either MT1- or MT3-MMP exhibited altered morphology, without changing their proliferation. This alteration was prevented by BB94 addition. The cells, which underwent this change, showed reduced adhesion to both collagen and fibronectin and increased migration in a Boyden chamber. The present study demonstrates that MT1- and MT3-MMPs have different enzymatic activities but may nevertheless affect SMC function in the same way.

Mutation analysis of membrane type-1 matrix metalloproteinase (MT1-MMP). The role of the cytoplasmic tail Cys(574), the active site Glu(240), and furin cleavage motifs in oligomerization, processing, and self-proteolysis of MT1-MMP expressed in breast carcinoma cells

Membrane type-1 matrix metalloproteinase (MT1-MMP) is a key enzyme in the activation pathway of matrix prometalloproteinase-2 (pro-MMP-2). Both activation and autocatalytic maturation of pro-MMP-2 in trans suggest that MT1-MMP should exist as oligomers on the cell surface. To better understand the functions of MT1-MMP, we designed mutants with substitutions in the active site (E240A), the cytoplasmic tail (C574A), and the RRXR furin cleavage motifs (R89A, ARAA, and R89A/ARAA) of the enzyme. The mutants were expressed in MCF7 breast carcinoma cells that are deficient in both MMP-2 and MT1-MMP. Our results supported the existence of MT1-MMP oligomers and demonstrated that a disulfide bridge involving the Cys(574) of the enzyme's cytoplasmic tail covalently links MT1-MMP monomers on the MCF7 cell surface. The presence of MT1-MMP oligomers also was shown for the enzyme naturally expressed in HT1080 fibrosarcoma cells. The single (R89A and ARAA) and double (R89A/ARAA) furin cleavage site mutants of MT1-MMP were processed in MCF7 cells into the mature proteinase capable of activating pro-MMP-2 and stimulating cell locomotion. This suggested that furin cleavage is not a prerequisite for the conversion of pro-MT1-MMP into the functionally active enzyme. A hydroxamate class inhibitor (GM6001, or Ilomastat) blocked activation of MT1-MMP in MCF7 cells but not in HT1080 cells. This implied that a matrixin-like proteinase sensitive to hydroxamates could be involved in a furin-independent, alternative pathway of MT1-MMP activation in breast carcinoma cells. The expression of the wild type MT1-MMP enhanced cell invasion and migration, indicating a direct involvement of this enzyme in cell locomotion. In contrast, both the C574A and E240A mutations render MT1-MMP inefficient in stimulating cell migration and invasion. In addition, the C574A mutation negatively affected cell adhesion, thereby indicating critical interactions involving the cytosolic part of MT1-MMP and the intracellular milieu.