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

Mapping Extracellular Protein-Protein Interactions Using Extracellular Proximity Labeling (ePL)

Proximity labeling (PL) has given researchers the tools to explore protein-protein interactions (PPIs) in living systems; however, most PL studies are performed on intracellular targets. We have adapted the original PL method to investigate PPIs within the extracellular compartment, which we term extracellular PL (ePL). To demonstrate the utility of this modified technique, we investigated the interactome of the matrisome protein TIMP2. TIMPs are a family of multifunctional proteins that were initially defined by their ability to inhibit metalloproteinases, the major mediators of extracellular matrix (ECM) turnover. TIMP2 exhibits broad expression and is often abundant in both normal and diseased tissues. Understanding the functional transformation of matrisome regulators, such as TIMP2, during disease progression is essential for the development of ECM-targeted therapeutics. Using dual orientation fusion proteins of TIMP2 with BioID2/TurboID, we describe the TIMP2 proximal interactome (MassIVE MSV000095637). We also illustrate how the TIMP2 interactome changes in the presence of different stimuli, in different cell types, in unique culture conditions (2D vs 3D), and with different reaction kinetics, demonstrating the power of this technique versus classical PPI methods. We propose that screening of matrisome targets in disease models using ePL will reveal new therapeutic targets for further comprehensive studies.

The Continuing Saga of Tissue Inhibitor of Metalloproteinase 2: Emerging Roles in Tissue Homeostasis and Cancer Progression

Tissue inhibitors of metalloproteinases (TIMPs) are a conserved family of proteins that were originally identified as cytokine-like erythroid growth factors. Subsequently, TIMPs were characterized as endogenous inhibitors of matrixin proteinases. These proteinases are the primary mediators of extracellular matrix turnover in pathologic conditions, such as cancer invasion and metastasis. Thus, TIMPs were immediately recognized as important regulators of tissue homeostasis. However, TIMPs also demonstrate unique biological activities that are independent of metalloproteinase regulation. Although often overlooked, these non-protease-mediated TIMP functions demonstrate a variety of direct cellular effects of potential therapeutic value. TIMP2 is the most abundantly expressed TIMP family member, and ongoing studies show that its tumor suppressor activity extends beyond protease inhibition to include direct modulation of tumor, endothelial, and fibroblast cellular responses in the tumor microenvironment. Recent data suggest that TIMP2 can suppress both primary tumor growth and metastatic niche formation. TIMP2 directly interacts with cellular receptors and matrisome elements to modulate cell signaling pathways that result in reduced proliferation and migration of neoplastic, endothelial, and fibroblast cell populations. These effects result in enhanced cell adhesion and focal contact formation while reducing tumor and endothelial proliferation, migration, and epithelial-to-mesenchymal transitions. These findings are consistent with TIMP2 homeostatic functions beyond simple inhibition of metalloprotease activity. This review examines the ongoing evolution of TIMP2 function, future perspectives in TIMP research, and the therapeutic potential of TIMP2.

OUP accepted manuscript

Tissue inhibitors of metalloproteinases (TIMPs) are a conserved family of proteins that were originally identified as endogenous inhibitors of matrixin and adamalysin endopeptidase activity. The matrixins and adamalysins are the major mediators of extracellular matrix (ECM) turnover, thus making TIMPs important regulators of ECM structure and composition. Despite their high sequence identity and relative redundancy in inhibitory profiles, each TIMP possesses unique biological characteristics that are independent of their regulation of metalloproteinase activity. As our understanding of TIMP biology has evolved, distinct roles have been assigned to individual TIMPs in cancer progression. In this respect, data regarding TIMP2's role in cancer have borne conflicting reports of both tumor suppressor and, to a lesser extent, tumor promoter functions. TIMP2 is the most abundant TIMP family member, prevalent in normal and diseased mammalian tissues as a constitutively expressed protein. Despite its apparent stable expression, recent work highlights how TIMP2 is a cell stress-induced gene product and that its biological activity can be dictated by extracellular posttranslational modifications. Hence an understanding of TIMP2 molecular targets, and how its biological functions evolve in the progressing tumor microenvironment may reveal new therapeutic opportunities. In this review, we discuss the continually evolving functions of TIMP proteins, future perspectives in TIMP research, and the therapeutic utility of this family, with a particular focus on TIMP2.

Anti-fibrotic effects of nintedanib in lung fibroblasts derived from patients with idiopathic pulmonary fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease with poor prognosis. The kinase inhibitor nintedanib specific for vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR) and fibroblast growth factor receptor (FGFR) significantly reduced the rate of decline of forced vital capacity versus placebo.

AIM

To determine the in vitro effect of nintedanib on primary human lung fibroblasts.

METHODS

Fibroblasts were isolated from lungs of IPF patients and from non-fibrotic controls. We assessed the effect of VEGF, PDGF-BB and basic FGF (bFGF) ± nintedanib on: (i) expression/activation of VEGFR, PDGFR, and FGFR, (ii) cell proliferation, secretion of (iii) matrix metalloproteinases (MMP), (iv) tissue inhibitor of metalloproteinase (TIMP), and (v) collagen.

RESULTS

IPF fibroblasts expressed higher levels of PDGFR and FGFR than controls. PDGF-BB, bFGF, and VEGF caused a pro-proliferative effect which was prevented by nintedanib. Nintedanib enhanced the expression of pro-MMP-2, and inhibited the expression of TIMP-2. Transforming growth factor-beta-induced secretion of collagens was inhibited by nintedanib.

CONCLUSION

Our data demonstrate a significant anti-fibrotic effect of nintedanib in IPF fibroblasts. This effect consists of the drug's anti-proliferative capacity, and on its effect on the extracellular matrix, the degradation of which seems to be enhanced.

NEDD9/Arf6-dependent endocytic trafficking of matrix metalloproteinase 14: a novel mechanism for blocking mesenchymal cell invasion and metastasis of breast cancer

NEDD9 is an established marker of invasive and metastatic cancers. NEDD9 downregulation has been shown to dramatically reduce cell invasion and metastasis in multiple tumors. The mechanisms by which NEDD9 regulates invasion are largely unknown. In the current study, we have found that NEDD9 is required for MMP14 enzymatic recovery/recycling through the late endosomes to enable disengagement of tissue inhibitor of matrix metalloproteinase 2 (TIMP2) and tumor invasion. Depletion of NEDD9 decreases targeting of the MMP14/TIMP2 complex to late endosomes and increases trafficking of MMP14 from early/sorting endosomes back to the surface in a small GTPase Arf6-dependent manner. NEDD9 directly binds to Arf6-GAP, ARAP3, and Arf6 effector GGA3 thereby facilitating the Arf6 inactivation required for MMP14/TIMP2 targeting to late endosomes. Re-expression of NEDD9 or a decrease in Arf6 activity is sufficient to restore MMP14 activity and the invasive properties of tumor cells. Importantly, NEDD9 inhibition by Vivo-Morpholinos, an antisense therapy, decreases primary tumor growth and metastasis in xenograft models of breast cancer. Collectively, our findings uncover a novel mechanism to control tumor cells dissemination through NEDD9/Arf6-dependent regulation of MMP14/TIMP2 trafficking, and validates NEDD9 as a clinically relevant therapeutic target to treat metastatic cancer.

Endothelial sirtuin 1 deficiency perpetrates nephrosclerosis through downregulation of matrix metalloproteinase-14: relevance to fibrosis of vascular senescence

Sirtuin 1 (SIRT1) depletion in vascular endothelial cells mediates endothelial dysfunction and premature senescence in diverse cardiovascular and renal diseases. However, the molecular mechanisms underlying these pathologic effects remain unclear. Here, we examined the phenotype of a mouse model of vascular senescence created by genetically ablating exon 4 of Sirt1 in endothelial cells (Sirt1(endo-/-)). Under basal conditions, Sirt1(endo-/-) mice showed impaired endothelium-dependent vasorelaxation and angiogenesis, and fibrosis occurred spontaneously at low levels at an early age. In contrast, induction of nephrotoxic stress (acute and chronic folic acid-induced nephropathy) in Sirt1(endo-/-) mice resulted in robust acute renal functional deterioration followed by an exaggerated fibrotic response compared with control animals. Additional studies identified matrix metalloproteinase-14 (MMP-14) as a target of SIRT1. In the kidneys of Sirt1(endo-/-) mice, impaired angiogenesis, reduced matrilytic activity, and retention of the profibrotic cleavage substrates tissue transglutaminase and endoglin accompanied MMP-14 suppression. Furthermore, restoration of MMP-14 expression in SIRT1-depeleted mice improved angiogenic and matrilytic functions of the endothelium, prevented renal dysfunction, and attenuated nephrosclerosis. Our findings establish a novel mechanistic molecular link between endothelial SIRT1 depletion, downregulation of MMP-14, and the development of nephrosclerosis.

Evaluation of gelatinases, tissue inhibitor of matrix metalloproteinase-2, and myeloperoxidase protein in healthy and inflamed human dental pulp tissue

INTRODUCTION

The aim of this study was to compare the gelatinolytic activity of matrix metalloproteinase (MMP)-2 and MMP-9 and the expression of tissue inhibitor of matrix metalloproteinase (TIMP)-2 and myeloperoxidase protein (MPO) in clinically healthy human pulp and inflamed pulp tissue specimens.

METHODS

Twenty dental pulps clinically diagnosed as inflammatory tissues and 20 healthy pulp tissues from enclosed third molars were harvested and evaluated. The gelatinolytic activity for MMP-2 and MMP-9 was assessed by using the zymography technique, TIMP-2 gene expression was evaluated using the enzyme-linked immunosorbent assay, and MPO was determined using the MPO assay.

RESULTS

Data showed increased levels of MMP-9, active MMP-2, TIMP-2, and MPO in inflammatory pulp tissues compared with healthy tissues (P < .05). No statistical difference could be observed for pro-MMP-2 (P > .05).

CONCLUSIONS

Although all samples were associated with MMP-2 expression, the active form of this MMP was observed only in inflamed pulps. Inflamed pulps showed an up-regulation of MMP-9, TIMP-2, and MPO.

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.

Caveolin-1 modulates the ability of Ewing's sarcoma to metastasize

Metastasis is the final stage of tumor progression and is thought to be responsible for up to 90% of deaths associated with solid tumors. Caveolin-1 (CAV1) regulates multiple cancer-associated processes related to malignant tumor progression. In the present study, we tested the hypothesis that CAV1 modulates the metastatic ability of cells from the Ewing's sarcoma family of tumors (ESFT). First, we analyzed the expression of CAV1 by immunostaining a tissue microarray containing 43 paraffin-embedded ESFT tumors with known EWS translocations. Even though no evidence was found for a significant association between CAV1 expression and stage, size or tumor site, all metastatic samples (10 of 10) had significantly high CAV1 expression, suggesting that high CAV1 content could positively contribute to enhance ESFT metastasis. To determine the effect of CAV1 on the migratory and invasive capabilities of ESFT cells, we knocked down CAV1 expression in TC252 and A673 cells by stably transfecting a previously validated shRNA construct. In vitro, migration and invasion assays showed that for both cell lines, CAV1 knocked-down cells migrated and invaded significantly less (P ≤ 0.01) than control cells. Moreover, control A673 cells introduced into BALB/c nude mice by tail vein injection strongly colonized the lungs. In contrast, animals injected with CAV1 knocked-down cells showed either no incidence of metastasis or developed lung metastases after a significant delay (P < 0.0001). Finally, we show that the molecular mechanisms by which CAV1 carries out its key role in regulating ESFT metastasis involve matrix metalloproteinase production and activation as well as the control of the expression of SPARC, a known determinant of lung colonization.

Matrix invasion by tumour cells: a focus on MT1-MMP trafficking to invadopodia

When migrating away from a primary tumour, cancer cells interact with and remodel the extracellular matrix (ECM). Matrix metalloproteinases (MMPs), and in particular the transmembrane MT1-MMP (also known as MMP-14), are key enzymes in tumour-cell invasion. Results from recent in vitro studies highlight that MT1-MMP is implicated both in the breaching of basement membranes by tumour cells and in cell invasion through interstitial type-I collagen tissues. Remarkably, MT1-MMP accumulates at invadopodia, which are specialized ECM-degrading membrane protrusions of invasive cells. Here we review current knowledge about MT1-MMP trafficking and its importance for the regulation of protease activity at invadopodia. In invasive cells, endocytosis of MT1-MMP by clathrin- and caveolae-dependent pathways can be counteracted by several mechanisms, which leads to protease stabilization at the cell surface and increased pericellular degradation of the matrix. Furthermore, the recent identification of cellular components that control delivery of MT1-MMP to invadopodia brings new insight into mechanisms of cancer-cell invasion and reveals potential pharmacological targets.

Indian hedgehog promotes the migration of rat activated pancreatic stellate cells by increasing membrane type-1 matrix metalloproteinase on the plasma membrane

Indian hedgehog (Ihh) is a member of hedgehog peptides family that exerts diverse effects on multiple cellular functions. Since Ihh expression is elevated in the pancreas of chronic pancreatitis patients, Ihh has been assumed to participate in the chronic pancreatic injury, especially in pancreatic fibrosis. However, its function in pancreatic fibrosis is still unknown. We thus examined Ihh effects on rat activated pancreatic stellate cells (PSCs) that play a central role in pancreatic fibrosis. Activated PSCs express both patched-1 and smoothened that are essential components of hedgehog receptor system. Ihh did not alter the PSC expression of collagen-1 or alpha-smooth muscle actin, a parameter of PSC transformation, or did not change PSC proliferation. However, Ihh enhanced PSC migration in both chemotactic and chemokinetic manners. Furthermore, Ihh increased the amount of membrane-type 1 matrix metalloproteinase (MT1-MMP) and altered its localization on the plasma membrane, which plays a stimulatory role in cellular migration. In addition, tissue inhibitor of metalloproteinase-2 (TIMP-2) attenuated Ihh-stimulated PSC migration. Since most hedgehog intracellular signals are mediated by Gli-1 transcription factor, we investigated its contribution to Ihh-enhancement of PSC migration. Ihh induced Gli-1 nuclear accumulation in PSCs, indicating that Ihh stimulates Gli-1-dependent signaling pathway in PSCs. Unexpectedly, however, adenovirus-mediated Gli-1 overexpression blocked the Ihh enhancement of both MT1-MMP localization on the plasma membrane and PSC migration. Furthermore, reduction of Gli-1 expression with RNA interference augmented Ihh-stimulated PSC migration. These data indicate that Ihh promotes PSC migration by enhancing MT1-MMP localization on the plasma membrane but is negatively regulated by Gli-1.

Molecular dissection of the structural machinery underlying the tissue-invasive activity of membrane type-1 matrix metalloproteinase

Membrane type-1 matrix metalloproteinase (MT1-MMP) drives cell invasion through three-dimensional (3-D) extracellular matrix (ECM) barriers dominated by type I collagen or fibrin. Based largely on analyses of its impact on cell function under two-dimensional culture conditions, MT1-MMP is categorized as a multifunctional molecule with 1) a structurally distinct, N-terminal catalytic domain; 2) a C-terminal hemopexin domain that regulates substrate recognition as well as conformation; and 3) a type I transmembrane domain whose cytosolic tail controls protease trafficking and signaling cascades. The MT1-MMP domains that subserve cell trafficking through 3-D ECM barriers in vitro or in vivo, however, remain largely undefined. Herein, we demonstrate that collagen-invasive activity is not confined strictly to the catalytic, hemopexin, transmembrane, or cytosolic domain sequences of MT1-MMP. Indeed, even a secreted collagenase supports invasion when tethered to the cell surface in the absence of the MT1-MMP hemopexin, transmembrane, and cytosolic tail domains. By contrast, the ability of MT1-MMP to support fibrin-invasive activity diverges from collagenolytic potential, and alternatively, it requires the specific participation of MT-MMP catalytic and hemopexin domains. Hence, the tissue-invasive properties of MT1-MMP are unexpectedly embedded within distinct, but parsimonious, sequences that serve to tether the requisite matrix-degradative activity to the surface of migrating cells.

The inactive 44-kDa processed form of membrane type 1 matrix metalloproteinase (MT1-MMP) enhances proteolytic activity via regulation of endocytosis of active MT1-MMP

Membrane type 1 (MT1) matrix metalloproteinase (MMP-14) is a membrane-tethered MMP considered to be a major mediator of pericellular proteolysis. MT1-MMP is regulated by a complex array of mechanisms, including processing and endocytosis that determine the pool of active proteases on the plasma membrane. Autocatalytic processing of active MT1-MMP generates an inactive membrane-tethered 44-kDa product (44-MT1) lacking the catalytic domain. This form preserves all other enzyme domains and is retained at the cell surface. Paradoxically, accumulation of the 44-kDa form has been associated with increased enzymatic activity. Here we report that expression of a recombinant 44-MT1 (Gly(285)-Val(582)) in HT1080 fibrosarcoma cells results in enhanced pro-MMP-2 activation, proliferation within a three-dimensional collagen I matrix, and tumor growth and lung metastasis in mice. Stimulation of pro-MMP-2 activation and growth in collagen I was also observed in other cell systems. Expression of 44-MT1 in HT1080 cells is associated with a delay in the rate of active MT1-MMP endocytosis resulting in higher levels of active enzyme at the cell surface. Consistently, deletion of the cytosolic domain obliterates the stimulatory effects of 44-MT1 on MT1-MMP activity. In contrast, deletion of the hinge turns the 44-MT1 form into a negative regulator of enzyme function in vitro and in vivo, suggesting a key role for the hinge region in the functional relationship between active and processed MT1-MMP. Together, these results suggest a novel role for the 44-kDa form of MT1-MMP generated during autocatalytic processing in maintaining the pool of active enzyme at the cell surface.

Rapid expression and activation of MMP-2 and MMP-9 upon exposure of human breast cancer cells (MCF-7) to fibronectin in serum free medium

Interactions between tumour cells and the extracellular matrix (ECM) strongly influence tumour development, affecting cell survival, proliferation and migration. Many of these interactions are mediated through a family of cell surface receptors named integrins. Fibronectin and its integrin receptors play important roles in tumour development. The alpha5beta 1 integrin interacts with the central cell adhesive region of fibronectin and requires both the RGD and synergy sites for maximal binding. Matrix metalloproteinases (MMPs) are a family of zinc dependent endopeptidases. They are capable of digesting the different components of the ECM and basement membrane. The ECM gives structural support to cells and plays a central role in cell adhesion, differentiation, proliferation and migration. Binding of ECM to integrins modulates expression and activity of the different MMPs. Our experimental findings demonstrate that cultivation of human breast cancer cells, MCF-7, in serum free medium in the presence of fibronectin upregulates the activity of MMP-2 and MMP-9. Blocking of alpha5beta 1 integrin with anti-alpha5 monoclonal antibody inhibits the fibronectin-induced MMP activation response appreciably. This strongly indicates alpha5beta 1 mediated signalling events in activation of MMP-2 and MMP-9. Phosphorylation of FAK and PI-3 kinase and the nuclear translocation of ERK and NF-kappaB upon fibronectin binding demonstrate possible participation of the FAK/PI-3K/ERK signalling pathways in the regulation of MMP-2 activity.

MT1-MMP down-regulates the glucose 6-phosphate transporter expression in marrow stromal cells: a molecular link between pro-MMP-2 activation, chemotaxis, and cell survival

Bone marrow-derived stromal cells (BMSC) are avidly recruited by experimental vascularizing tumors, which implies that they must respond to tumor-derived growth factor cues. In fact, BMSC chemotaxis and cell survival are regulated, in part, by the membrane type-1 matrix metalloproteinase (MT1-MMP), an MMP also involved in pro-MMP-2 activation and in degradation of the extracellular matrix (ECM). Given that impaired chemotaxis was recently observed in bone marrow cells isolated from a glucose 6-phosphate transporter-deficient (G6PT-/-) mouse model, we sought to investigate the potential MT1-MMP/G6PT signaling axis in BMSC. We show that MT1-MMP-mediated activation of pro-MMP-2 by concanavalin A (ConA) correlated with an increase in the sub-G1 cell cycle phase as well as with cell necrosis, indicative of a decrease in BMSC survival. BMSC isolated from Egr-1-/- mouse or MT1-MMP gene silencing in BMSC with small interfering RNA (siMT1-MMP) antagonized both the ConA-mediated activation of pro-MMP-2 and the induction of cell necrosis. Overexpression of recombinant full-length MT1-MMP triggered necrosis and this was signaled through the cytoplasmic domain of MT1-MMP. ConA inhibited both the gene and protein expression of G6PT, while overexpression of recombinant G6PT inhibited MT1-MMP-mediated pro-MMP-2 activation but could not rescue BMSC from ConA-induced cell necrosis. Cell chemotaxis in response to the tumorigenic growth factor sphingosine 1-phosphate was significantly abrogated in siMT1-MMP BMSC and in chlorogenic acid-treated BMSC. Altogether, we provide evidence for an MT1-MMP/G6PT signaling axis that regulates BMSC survival, ECM degradation, and mobilization. This may lead to optimized clinical applications that use BMSC as a platform for the systemic delivery of therapeutic or anti-cancer recombinant proteins in vivo.

Hypoxia stimulates breast carcinoma cell invasion through MT1-MMP and MMP-2 activation

The process of cancer cell invasion involves degradation of the extracellular matrix (ECM) by proteases, integrin adhesion and cell motility. The role of ECM degrading proteases on the hypoxia-induced invasion of breast carcinoma cells was investigated. Hypoxia markedly increased the invasion capacity of MDA-MB-231 and MDA-MB-435 breast carcinoma cell lines. Matrix metalloproteinase (MMP) inhibitors blocked the hypoxia-induced invasion, whereas other protease inhibitors had no effect. Antibodies or siRNAs blocking either membrane type-1 MMP (MT1-MMP) or MMP-2 were effective in reducing the hypoxia-induced invasion. Serum-free reconstitution experiments confirmed the involvement of the MT1-MMP/MMP-2/tissue inhibitor of metalloproteinase-2 complex in this hypoxia-induced response. Overexpression of MT1-MMP in a poorly invasive breast cancer cell line, T47-D, promoted hypoxia-induced invasion and MMP-2 activation. Cell surface accumulation and activation of MT1-MMP without apparent regulation at the mRNA or protein levels indicated a post-translational adaptive response to hypoxia. Inhibition of the small GTPase RhoA eliminated the hypoxia-induced invasion and blocked the localization of MT1-MMP to the plasma membrane. Zymographic and molecular analysis of human breast tumors showed a strong correlation between hypoxic microenvironments and MMP-2 activation without changes in MT1-MMP expression. Our studies suggest that hypoxic tumor microenvironments promote breast cancer invasion through an MT1-MMP-dependent mechanism.

Cardiac morphogenesis: matrix metalloproteinase coordination of cellular mechanisms underlying heart tube formation and directionality of looping

During heart organogenesis, the spatiotemporal organization of the extracellular matrix (ECM) undergoes significant remodeling. Because matrix metalloproteinases (MMPs) are known to be key regulators of cell-matrix interactions, we analyzed the role(s) of MMPs, and specifically MMP-2, in early heart development. Both MMP-2 neutralizing antibody and the broad-spectrum MMP inhibitor Ilomastat in a temporal manner, when applied between chick embryonic stages 5 (primitive streak stage) to stage 12 ( approximately 16-somites), produced severe heart tube defects. Exposure to the MMP inhibitor at stage 5 produced various degrees of cardia bifida. At the seven-somite stage, MMP-2/Ilomastat inhibition caused a shift in normal left-right patterning of cell proliferation within the dorsal mesocardium and mesoderm of the anterior heart field that correlated with a change in looping direction. MMP inhibition at the 10- to 12-somite stage resulted in an arrest of heart tube bending by inhibiting the breakdown of the dorsal mesocardial ECM. The experimental observations suggest that MMP activity regulates the coordination of early heart organogenesis by affecting ventral closure of the heart and gut tubes, asymmetric cell proliferation in the dorsal mesocardium to drive looping direction, and ECM degradation within the dorsal mesocardium allowing looping to proceed toward completion.

Matrix metalloproteinase-2 (MMP-2) and MMP-9 in pulmonary pathology

The lung is affected by a variety of disease processes that can lead to considerable morbidity and mortality. As the lung is the only organ for respiration and gas exchange, the structural and functional integrity of the lung is of primary importance. Various pathological processes affect the extracellular matrix (ECM) of the lung in an adverse manner, causing destruction of tissue integrity followed by tissue remodeling, which together impair normal pulmonary function. Matrix metalloproteinases (MMPs) are neutral proteinases that are involved in the breakdown and remodeling of the ECM under a variety of physiological and pathological conditions. MMP-2 and MMP-9, collectively known as the gelatinases, are particularly important in the pathogenesis of inflammatory, infectious, and neoplastic diseases in many organs including the lung. This review examines the expression of MMP-2 and MMP-9 in disease of the lung and discusses the role these gelatinases may play in disease progression.

Furin-Like Proprotein Convertases Are Central Regulators of the Membrane Type Matrix Metalloproteinase–Pro-Matrix Metalloproteinase-2 Proteolytic Cascade in Atherosclerosis

BACKGROUND

Accumulation of macrophages and their in situ expression of matrix metalloproteinases (MMPs) are important determinants of plaque stability. Activation of membrane-bound MT1-MMP, the major activator of pro-MMP-2, requires intracellular endoproteolytic cleavage of its precursor protein. This type of activation typically requires suitable furin-like proprotein convertases (PCs), specifically furin and PC5. The present study was done to investigate the function of MT1-MMP as well as furin-like PCs in mononuclear inflammatory cells.

METHODS AND RESULTS

Macrophage differentiation of human monocytic THP-1 cells was accompanied by increased expression of furin, PC5, and MT1-MMP. Some pro-MMP-2 activation was found in macrophages, but pro-MMP-2 level or activation was not enhanced after stimulation with the proinflammatory mediators tumor necrosis factor-alpha or lipopolysaccharide. However, culturing of macrophages in conditioned medium from serum-starved vascular smooth muscle cells, which constitutively secrete pro-MMP-2, resulted in a strong pro-MMP-2 activation. Inhibition of furin-like PCs with the specific pharmacological inhibitor decanoyl-RVKR-chloromethylketone (dec-CMK) inhibited MT1-MMP activation in macrophages. Dec-CMK or furin-specific small interfering RNA significantly inhibited macrophage MT1-MMP-dependent activation of vascular smooth muscle cell-derived pro-MMP-2. Flow cytometry demonstrated that human circulating monocytes express furin and PC5, and MT1-MMP and immunohistochemistry revealed their colocalization in macrophages in advanced human atherosclerotic lesions.

CONCLUSIONS

Furin-like PCs (furin and PC5) play a central role in a MT-MMP-MMP-2 proteolytic cascade, involving provision of macrophage MT1-MMP for the activation of pro-MMP-2 synthesized by other cells. Furin and PC5 are expressed in human peripheral blood mononuclear cells and colocalize with MT1-MMP in macrophages in the atherosclerotic plaque, supporting the hypothesis that they are potential targets in atherosclerosis.

Mutational and structural analyses of the hinge region of membrane type 1-matrix metalloproteinase and enzyme processing

Membrane type 1 (MT1)-matrix metalloproteinase (MMP) is a major mediator of collagen degradation in the pericellular space in both physiological and pathological conditions. Previous evidence has shown that on the cell surface, active MT1-MMP undergoes autocatalytic processing to a major membrane-tethered 44-kDa product lacking the catalytic domain and displaying Gly285 at its N terminus, which is at the beginning of the hinge domain. However, the importance of this site and the hinge region in MT1-MMP processing is unknown. In the current study, we generated mutations and deletions in the hinge of MT1-MMP and followed their effect on processing. These studies established Gly284-Gly285 as the main cleavage site involved in the formation of the 44-kDa species. However, alterations at this site did not prevent processing. Instead, they forced downstream cleavages within the stretch of residues flanked by Gln296 and Ser304 in the hinge region, as determined by the processing profile of various hinge deletion mutants. Also, replacement of the hinge of MT1-MMP with the longer MT3-MMP hinge did not prevent processing of MT1-MMP. Molecular dynamic studies using a computational model of MT1-MMP revealed that the hinge region is a highly motile element that undergoes significant motion in the highly exposed loop formed by Pro295-Arg302 consistent with being a prime target for proteolysis, in agreement with the mutational data. These studies suggest that the hinge of MT1-MMP evolved to facilitate processing, a promiscuous but compulsory event in the destiny of MT1-MMP, which may play a key role in the control of pericellular proteolysis.

Low density lipoprotein receptor-related protein mediates endocytic clearance of pro-MMP-2.TIMP-2 complex through a thrombospondin-independent mechanism

The low density lipoprotein receptor-related protein (LRP) mediates the endocytic clearance of various proteinases and proteinase.inhibitor complexes, including thrombospondin (TSP)-dependent endocytosis of matrix metalloproteinase (MMP)-2 (or gelatinase A), a key effector of extracellular matrix remodeling and cancer progression. However, the zymogen of MMP-2 (pro-MMP-2) mostly occurs in tissues as a complex with the tissue inhibitor of MMPs (TIMP-2). Here we show that clearance of the pro-MMP-2.TIMP-2 complex is also mediated by LRP, because addition of receptor-associated protein (RAP), a natural LRP ligand antagonist, inhibited endocytosis and lysosomal degradation of (125)I-pro-MMP-2.TIMP-2. Both TIMP-2 and the pro-MMP-2 collagen-binding domain independently competed for endocytosis of (125)I-pro-MMP-2.TIMP-2 complex. Surface plasmon resonance studies indicated that pro-MMP-2, TIMP-2, and pro-MMP-2.TIMP-2 directly interact with LRP in the absence of TSP. LRP-mediated endocytic clearance of (125)I-pro-MMP-2 was inhibited by anti-TSP antibodies and accelerated upon complexing with TSP-1, but these treatments had no effect on (125)I-pro-MMP-2.TIMP-2 uptake. This implies that mechanisms of clearance by LRP of pro-MMP-2 and pro-MMP-2.TIMP-2 complex are different. Interestingly, RAP did not inhibit binding of (125)I-pro-MMP-2.TIMP-2 to the cell surface. We conclude that clearance of pro-MMP-2.TIMP-2 complex is a TSP-independent two-step process, involving (i) initial binding to the cell membrane in a RAP-insensitive manner and (ii) subsequent LRP-dependent (RAP-sensitive) internalization and degradation.

Involvement of syntaxin 4 in the transport of membrane-type 1 matrix metalloproteinase to the plasma membrane in human gastric epithelial cells

Membrane-type 1 matrix metalloproteinase (MT1-MMP) localized on the plasma membrane plays a central role in various normal biological responses including tissue remodeling, wound heeling, and angiogenesis and in cancer cell invasion and metastasis, by functioning as a collagenase and activating other matrix metalloproteinases. In order to elucidate the molecular mechanism of the MT1-MMP targeted localization on the plasma membrane, we examined the participation of syntaxin proteins in MT1-MMP intracellular transport to the plasma membrane in human gastric epithelial AGS cells. Western blotting showed that syntaxin 3 and 4 proteins, which are known to function in intracellular transport towards the plasma membrane, were expressed in AGS cells. Immunocytochemistry revealed that transient transfection of AGS cells with dominant-negative mutant syntaxin 4 decreased plasma membrane MT1-MMP expression. In contrast, transient transfection with either dominant-negative mutant syntaxin 3 or 7 did not affect MT1-MMP localization on the plasma membrane. Cell surface biotinylation assay and Matrigel chamber assay demonstrated that stable transfection with dominant-negative mutant syntaxin 4 decreased the amount of MT1-MMP on the plasma membranes and inhibited the cell invasiveness. We suggest that syntaxin 4 is involved in the intracellular transport of MT1-MMP toward the plasma membrane.