Glycosylation Broadens the Substrate Profile of Membrane Type 1 Matrix Metalloproteinase

Distinct structural basis and catalytic classification of matrix metalloproteinases and their endogenous tissue inhibitors with glycosylation issue in cellular and tissue regulation

Matrix metalloproteinase (MMP) enzymes cleave proteins on the extracellular matrix (ECM) region. MMPs are categorized as Zn2+-binding endo-proteinases. MMPs are stringently regulated in cancers, inflammatory cells and tissues. There are 29 types of MMPs as initially expressed in inactive zymogens (proMMPs) and activated by proteolysis in vertebrates including human. MMPs consist of three highly conserved parts of pro-MMP in precursor, catalytic and hemopexin domains. The MMPs are composed of systemic complexes with their endogenously expressed inhibitors of the tissue inhibitors of metalloproteinases (TIMPs). Therefore, TIMPs intrinsically control such activated MMPs, indicating the existence of self-modulation capacity. N-linked glycosylation (N-glycosylation) saves biological information than known phosphorylation, ubiquitination and acetylation. The MMPs are roughly present as membrane-merged and secreted glycoproteins. MMPs N-glycans regulate cellular behaviors, immune tolerance, and developing angiogenesis. Aberrant N-glycosylation of MMPs may cause the pathogenic properties. N-glycosylation shapes phenotypes of MMPs-producing cells during early MMPs involved in human. Additionally, issues of MMPs and TIMPs glycosylation have been described to view the importance of the glycans in their interaction with owns and other targets. Most of MMPs and 4 TIMPs are not well studied for their glycosylation and its functional roles.

Effects of Thai propolis mixed in mineral trioxide aggregate on matrix metalloproteinase-2 expression and activity in inflamed human dental pulp cells

OBJECTIVES

This study sought to determine effects of Thai propolis extract mixed in mineral trioxide aggregate (MTA) on matrix metalloproteinase-2 (MMP-2) expression and its activity in inflamed human dental pulp cells (HDPCs).

MATERIALS AND METHODS

Interleukin-1β-primed HDPCs were treated with either the eluate of MTA mixed with distilled water, of MTA mixed with 0.75 mg/ml of the propolis extract, or of Dycal®, 0.75 mg/ml of the propolis extract, or 0.2% (v/v) of chlorhexidine for 24 or 72 h. The viability of HDPCs was determined by the PrestoBlue® cytotoxic assay. HDPCs' lysates were analyzed for MMP-2 mRNA expression by RT-qPCR, while their supernatants were measured for MMP-2 activity by gelatin zymography.

RESULTS

At 24 and 72 h, a non-toxic dose of the propolis extract at 0.75 mg/ml by itself or mixed in MTA tended to reduce MMP-2 expression upregulated by MTA, while it further decreased the MMP-2 activity as compared to that of MTA mixed with distilled water. The MMP-2 activity of interleukin-1β-primed HDPCs treated with the eluate of the propolis extract mixed in MTA was significantly lower than that of interleukin-1β-primed HDPCs at 24 h (p=0.012). As a control, treatment with chlorhexidine significantly inhibited MMP-2 expression induced by MTA and MMP-2 activity enhanced by interleukin-1β (p<0.05). Treatment with Dycal® caused a significant increase in HDPC's death, resulting in a significant decrease in MMP-2 expression and activity (p<0.05).

CONCLUSIONS

MTA mixed with Thai propolis extract can reduce MMP-2 mRNA expression and activity when compared to MTA mixed with distilled water in inflamed HDPCs.

Truncated O-glycosylation in metastatic triple-negative breast cancer reveals a gene expression signature associated with extracellular matrix and proteolysis

Breast cancer (BC) is the leading cause of death by cancer in women worldwide. Triple-negative (TN) BC constitutes aggressive and highly metastatic tumors associated with shorter overall survival of patients compared to other BC subtypes. The Tn antigen, a glycoconjugated structure resulting from an incomplete O-glycosylation process, is highly expressed in different adenocarcinomas, including BC. It also favors cancer growth, immunoregulation, and metastasis in TNBC. This work describes the differentially expressed genes (DEGs) associated with BC aggressiveness and metastasis in an incomplete O-glycosylated TNBC cell model. We studied the transcriptome of a TNBC model constituted by the metastatic murine 4T1 cell line that overexpresses the Tn antigen due to a mutation in one of the steps of the O-glycosylation pathway. We analyzed and compared the results with the parental wild-type cell line and with a Tn-negative cell clone that was poorly metastatic and less aggressive than the 4T1 parental cell line. To gain insight into the generated expression data, we performed a gene set analysis. Biological processes associated with cancer development and metastasis, immune evasion, and leukocyte recruitment were highly enriched among functional terms of DEGs. Furthermore, different highly O-glycosylated protein-coding genes, such as mmp9, ecm1 and ankyrin-2, were upregulated in 4T1/Tn+ tumor cells. The altered biological processes and DEGs that promote tumor growth, invasion and immunomodulation might explain the aggressive properties of 4T1/Tn+ tumor cells. These results support the hypothesis that incomplete O-glycosylation that leads to the expression of the Tn antigen, which might regulate activity or interaction of different molecules, promotes cancer development and immunoregulation.

Degradomic Identification of Membrane Type 1-Matrix Metalloproteinase as an ADAMTS9 and ADAMTS20 Substrate

The secreted metalloproteases ADAMTS9 and ADAMTS20 are implicated in extracellular matrix proteolysis and primary cilium biogenesis. Here, we show that clonal gene-edited RPE-1 cells in which ADAMTS9 was inactivated, and which constitutively lack ADAMTS20 expression, have morphologic characteristics distinct from parental RPE-1 cells. To investigate underlying proteolytic mechanisms, a quantitative terminomics method, terminal amine isotopic labeling of substrates was used to compare the parental and gene-edited RPE-1 cells and their medium to identify ADAMTS9 substrates. Among differentially abundant neo-amino (N) terminal peptides arising from secreted and transmembrane proteins, a peptide with lower abundance in the medium of gene-edited cells suggested cleavage at the Tyr314-Gly315 bond in the ectodomain of the transmembrane metalloprotease membrane type 1-matrix metalloproteinase (MT1-MMP), whose mRNA was also reduced in gene-edited cells. This cleavage, occurring in the MT1-MMP hinge, that is, between the catalytic and hemopexin domains, was orthogonally validated both by lack of an MT1-MMP catalytic domain fragment in the medium of gene-edited cells and restoration of its release from the cell surface by reexpression of ADAMTS9 and ADAMTS20 and was dependent on hinge O-glycosylation. A C-terminally semitryptic MT1-MMP peptide with greater abundance in WT RPE-1 medium identified a second ADAMTS9 cleavage site in the MT1-MMP hemopexin domain. Consistent with greater retention of MT1-MMP on the surface of gene-edited cells, pro-MMP2 activation, which requires cell surface MT1-MMP, was increased. MT1-MMP knockdown in gene-edited ADAMTS9/20-deficient cells restored focal adhesions but not ciliogenesis. The findings expand the web of interacting proteases at the cell surface, suggest a role for ADAMTS9 and ADAMTS20 in regulating cell surface activity of MT1-MMP, and indicate that MT1-MMP shedding does not underlie their observed requirement in ciliogenesis.

Cytoplasmic Tail of MT1-MMP: A Hub of MT1-MMP Regulation and Function

MT1-MMP (MMP-14) is a multifunctional protease that regulates ECM degradation, activation of other proteases, and a variety of cellular processes, including migration and viability in physiological and pathological contexts. Both the localization and signal transduction capabilities of MT1-MMP are dependent on its cytoplasmic domain that constitutes the final 20 C-terminal amino acids, while the rest of the protease is extracellular. In this review, we summarize the ways in which the cytoplasmic tail is involved in regulating and enacting the functions of MT1-MMP. We also provide an overview of known interactors of the MT1-MMP cytoplasmic tail and the functional significance of these interactions, as well as further insight into the mechanisms of cellular adhesion and invasion that are regulated by the cytoplasmic tail.

Protease-dependent defects in N-cadherin processing drive PMM2-CDG pathogenesis

The genetic bases for the congenital disorders of glycosylation (CDG) continue to expand, but how glycosylation defects cause patient phenotypes remains largely unknown. Here, we combined developmental phenotyping and biochemical studies in a potentially new zebrafish model (pmm2^sa10150) of PMM2-CDG to uncover a protease-mediated pathogenic mechanism relevant to craniofacial and motility phenotypes in mutant embryos. Mutant embryos had reduced phosphomannomutase activity and modest decreases in N-glycan occupancy as detected by matrix-assisted laser desorption ionization mass spectrometry imaging. Cellular analyses of cartilage defects in pmm2^sa10150 embryos revealed a block in chondrogenesis that was associated with defective proteolytic processing, but seemingly normal N-glycosylation, of the cell adhesion molecule N-cadherin. The activities of the proconvertases and matrix metalloproteinases responsible for N-cadherin maturation were significantly altered in pmm2^sa10150 mutant embryos. Importantly, pharmacologic and genetic manipulation of proconvertase activity restored matrix metalloproteinase activity, N-cadherin processing, and cartilage pathology in pmm2^sa10150 embryos. Collectively, these studies demonstrate in CDG that targeted alterations in protease activity create a pathogenic cascade that affects the maturation of cell adhesion proteins critical for tissue development.

Membrane-type I matrix metalloproteinase (MT1-MMP), lipid metabolism and therapeutic implications

Lipids exert many essential physiological functions, such as serving as a structural component of biological membranes, storing energy, and regulating cell signal transduction. Dysregulation of lipid metabolism can lead to dyslipidemia related to various human diseases, such as obesity, diabetes, and cardiovascular disease. Therefore, lipid metabolism is strictly regulated through multiple mechanisms at different levels, including the extracellular matrix. Membrane-type I matrix metalloproteinase (MT1-MMP), a zinc-dependent endopeptidase, proteolytically cleaves extracellular matrix components, and non-matrix proteins, thereby regulating many physiological and pathophysiological processes. Emerging evidence supports the vital role of MT1-MMP in lipid metabolism. For example, MT1-MMP mediates ectodomain shedding of low-density lipoprotein receptor and increases plasma low-density lipoprotein cholesterol levels and the development of atherosclerosis. It also increases the vulnerability of atherosclerotic plaque by promoting collagen cleavage. Furthermore, it can cleave the extracellular matrix of adipocytes, affecting adipogenesis and the development of obesity. Therefore, the activity of MT1-MMP is strictly regulated by multiple mechanisms, such as autocatalytic cleavage, endocytosis and exocytosis, and post-translational modifications. Here, we summarize the latest advances in MT1-MMP, mainly focusing on its role in lipid metabolism, the molecular mechanisms regulating the function and expression of MT1-MMP, and their pharmacotherapeutic implications.

Emerging roles of MT-MMPs in embryonic development

Membrane-type matrix metalloproteinases (MT-MMPs) are cell membrane-tethered proteinases that belong to the family of the MMPs. Apart from their roles in degradation of the extracellular milieu, MT-MMPs are able to activate through proteolytic processing at the cell surface distinct molecules such as receptors, growth factors, cytokines, adhesion molecules, and other pericellular proteins. Although most of the information regarding these enzymes comes from cancer studies, our current knowledge about their contribution in distinct developmental processes occurring in the embryo is limited. In this review, we want to summarize the involvement of MT-MMPs in distinct processes during embryonic morphogenesis, including cell migration and proliferation, epithelial-mesenchymal transition, cell polarity and branching, axon growth and navigation, synapse formation, and angiogenesis. We also considered information about MT-MMP functions from studies assessed in pathological conditions and compared these data with those relevant for embryonic development.

Sialic acid removal by trans-sialidase modulates MMP-2 activity during Trypanosoma cruzi infection

Matrix metalloproteinases (MMPs) not only play a relevant role in homeostatic processes but are also involved in several pathological mechanisms associated with infectious diseases. As their clinical relevance in Chagas disease has recently been highlighted, we studied the modulation of circulating MMPs by Trypanosoma cruzi infection. We found that virulent parasites from Discrete Typing Units (DTU) VI induced higher proMMP-2 and MMP-2 activity in blood, whereas both low (DTU I) and high virulence parasites induced a significant decrease in proMMP-9 plasma activity. Moreover, trans-sialidase, a relevant T. cruzi virulence factor, is involved in MMP-2 activity modulation both in vivo and in vitro. It removes α2,3-linked sialyl residues from cell surface glycoconjugates, which then triggers the PKC/MEK/ERK signaling pathway. Additionally, bacterial sialidases specific for this sialyl residue linkage displayed similar MMP modulation profiles and triggered the same signaling pathways. This novel pathogenic mechanism, dependent on sialic acid removal by the neuraminidase activity of trans-sialidase, can be exploited by different pathogens expressing sialidases with similar specificity. Thus, here we present a new pathogen strategy through the regulation of the MMP network.

A common SNP risk variant MT1-MMP causative for Dupuytren's disease has a specific defect in collagenolytic activity

Dupuytren's Disease (DD) is a common fibroproliferative disease of the palmar fascia. We previously identified a causal association with a non-synonymous variant (rs1042704, p.D273N) in MMP14 (encoding MT1-MMP). In this study, we investigated the functional consequences of this variant, and demonstrated that the variant MT1-MMP (MT1-N273) exhibits only 17% of cell surface collagenolytic activity compared to the ancestral enzyme (MT1-D273). Cells expressing both MT1-D273 and MT1-N273 in a 1:1 ratio, mimicking the heterozygous state, possess 38% of the collagenolytic activity compared to the cells expressing MT1-D273, suggesting that MT1-N273 acts in a dominant negative manner. Consistent with the above observation, patient-derived DD myofibroblasts with the alternate allele demonstrated around 30% of full collagenolytic activity detected in ancestral G/G genotype cells, regardless of the heterozygous (G/A) or homozygous (A/A) state. Small angle X-ray scattering analysis of purified soluble Fc-fusion enzymes allowed us to construct a 3D-molecular envelope of MT1-D273 and MT1-N273, and demonstrate altered flexibility and conformation of the ectodomains due to D273 to N substitution. Taking together, rs1042704 significantly reduces collagen catabolism in tissue, which tips the balance of homeostasis of collagen in tissue, contributing to the fibrotic phenotype of DD. Since around 30% of the worldwide population have at least one copy of the low collagenolytic alternate allele, further investigation of rs1042704 across multiple pathologies is needed.

Mechanism and Inhibition of Matrix Metalloproteinases

Matrix metalloproteinases hydrolyze proteins and glycoproteins forming the extracellular matrix, cytokines and growth factors released in the extracellular space, and membrane-bound receptors on the outer cell membrane. The pathological relevance of MMPs has prompted the structural and functional characterization of these enzymes and the development of synthetic inhibitors as possible drug candidates. Recent studies have provided a better understanding of the substrate preference of the different members of the family, and structural data on the mechanism by which these enzymes hydrolyze the substrates. Here, we report the recent advancements in the understanding of the mechanism of collagenolysis and elastolysis, and we discuss the perspectives of new therapeutic strategies for targeting MMPs.

Post-Translational Modification-Dependent Activity of Matrix Metalloproteinases

Due to their capacity to process different proteins of the extracellular matrix (ECM), matrix metalloproteinases (MMPs) were initially described as a family of secreted proteases, functioning as main ECM regulators. However, through proteolytic processing of various biomolecules, MMPs also modulate intra- and extracellular pathways and networks. Thereby, they are functionally implicated in the regulation of multiple physiological and pathological processes. Consequently, MMP activity is tightly regulated through a combination of epigenetic, transcriptional, and post-transcriptional control of gene expression, proteolytic activation, post-translational modifications (PTMs), and extracellular inhibition. In addition, MMPs, their substrates and ECM binding partners are frequently modified by PTMs, which suggests an important role of PTMs in modulating the pleiotropic activities of these proteases. This review summarizes the recent progress towards understanding the role of PTMs (glycosylation, phosphorylation, glycosaminoglycans) on the activity of several members of the MMP family.

The Expanding Role of MT1-MMP in Cancer Progression

For over 20 years, membrane type 1 matrix metalloproteinase (MT1-MMP) has been recognized as a key component in cancer progression. Initially, the primary roles assigned to MT1-MMP were the activation of proMMP-2 and degradation of fibrillar collagen. Proteomics has revealed a great array of MT1-MMP substrates, and MT1-MMP selective inhibitors have allowed for a more complete mapping of MT1-MMP biological functions. MT1-MMP has extensive sheddase activities, is both a positive and negative regulator of angiogenesis, can act intracellularly and as a transcription factor, and modulates immune responses. We presently examine the multi-faceted role of MT1-MMP in cancer, with a consideration of how the diversity of MT1-MMP behaviors impacts the application of MT1-MMP inhibitors.

Fine-Tuning Limited Proteolysis: A Major Role for Regulated Site-Specific O-Glycosylation

Limited proteolytic processing is an essential and ubiquitous post-translational modification (PTM) affecting secreted proteins; failure to regulate the process is often associated with disease. Glycosylation is also a ubiquitous protein PTM and site-specific O-glycosylation in close proximity to sites of proteolysis can regulate and direct the activity of proprotein convertases, a disintegrin and metalloproteinases (ADAMs), and metalloproteinases affecting the activation or inactivation of many classes of proteins, including G-protein-coupled receptors (GPCRs). Here, we summarize the emerging data that suggest O-glycosylation to be a key regulator of limited proteolysis, and highlight the potential for crosstalk between multiple PTMs.

Organelle Specific O-Glycosylation Drives MMP14 Activation, Tumor Growth, and Metastasis

Cancers grow within tissues through molecular mechanisms still unclear. Invasiveness correlates with perturbed O-glycosylation, a covalent modification of cell-surface proteins. Here, we show that, in human and mouse liver cancers, initiation of O-glycosylation by the GALNT glycosyl-transferases increases and shifts from the Golgi to the endoplasmic reticulum (ER). In a mouse liver cancer model, expressing an ER-targeted GALNT1 (ER-G1) massively increased tumor expansion, with median survival reduced from 23 to 10 weeks. In vitro cell growth was unaffected, but ER-G1 strongly enabled matrix degradation and tissue invasion. Unlike its Golgi-localized counterpart, ER-G1 glycosylates the matrix metalloproteinase MMP14, a process required for tumor expansion. Together, our results indicate that GALNTs strongly promote liver tumor growth after relocating to the ER.

RNA interference-mediated silencing of ppGalNAc-T1 and ppGalNAc-T2 inhibits invasion and increases chemosensitivity potentially by reducing terminal α2,3 sialylation and MMP14 expression in triple‑negative breast cancer cells

Glycopeptide-preferring polypeptide N-acetylgalactosamine transferase (ppGalNAc‑T) is a key enzyme that initiates the formation of the first GalNAc monosaccharide to polypeptides at Thr/Ser residues by O‑linked glycosylation. In order to investigate the effects of ppGalNAc‑T1 and ppGalNAc‑T2 on the initiation of O‑glycosylation, siRNA‑ppGalNAc‑T1 (si‑T1) and siRNA‑ppGalNAc‑T2 (si‑T2) were transfected into highly‑invasive estrogen receptor‑negative MDA‑MB‑231 cells to inhibit O‑glycosylation. Downregulation of ppGalNAc‑T1 demonstrated a significant reduction in the number of terminal α2,3 sialic acids, when compared to cells transfected with si‑T2 or si‑T1/T2. This downregulation led to a decrease in the invasion capabilities of the breast carcinoma cells, as well as enhanced chemosensitivity, which was the result antineoplastic drug effects. In addition, immunoprecipitation assays demonstrated that downregulation of ppGalNAc‑T1 led to a reduction in the number of terminal α2,3 sialic acids on O‑linked glycans of the matrix metalloproteinase‑14 (MMP14) glycoprotein. Furthermore, MMP14 and vascular endothelial growth factor were downregulated in the si‑T1 groups when compared with the si‑T2 and si‑T1/T2 groups. In conclusion, the results of the present study suggest that ppGalNAc‑T1 may serve a pivotal role in the initiation of O‑glycosylation, which may lead to a low density of α2,3 sialic acids on O‑linked glycans of MMP14 when downregulated. Glycosylation serves a significant role in regulating the sensitivity of MMP14 to self‑proteolysis, which ultimately decreases the invasion capabilities of breast cancer cells. The results of the present study may be useful in establishing the function of ppGalNAc‑T1 during breast cancer invasion and metastasis.

Glycosylation of matrix metalloproteases and tissue inhibitors: present state, challenges and opportunities

Current knowledge about the glycosylation of matrix metalloproteinases (MMPs) and the inhibitors of metalloproteinases (TIMPs) is reviewed. Whereas structural and functional aspects of the glycobiology of many MMPs is unknown, research on MMP-9 and MMP-14 glycosylation reveals important functional implications, such as altered inhibitor binding and cellular localization. This, together with the fact that MMPs contain conserved and many potential attachment sites for N-linked and O-linked oligosaccharides, proves the need for further studies on MMP glycobiology.

Matrix metalloproteases (MMPs) are crucial components of a complex and dynamic network of proteases. With a wide range of potential substrates, their production and activity are tightly controlled by a combination of signalling events, zymogen activation, post-translational modifications and extracellular inhibition. Slight imbalances may result in the initiation or progression of specific disease states, such as cancer and pathological inflammation. As glycosylation modifies the structures and functions of glycoproteins and many MMPs contain N- or O-linked oligosaccharides, we examine, compare and evaluate the evidence for whether glycosylation affects MMP catalytic activity and other functions. It is interesting that the catalytic sites of MMPs do not contain O-linked glycans, but instead possess a conserved N-linked glycosylation site. Both N- and O-linked oligosaccharides, attached to specific protein domains, endow these domains with novel functions such as the binding to lectins, cell-surface receptors and tissue inhibitors of metalloproteases (TIMPs). Validated glycobiological data on N- and O-linked oligosaccharides of gelatinase B/MMP-9 and on O-linked structures of membrane-type 1 MMP/MMP-14 indicate that in-depth research of other MMPs may yield important insights, e.g. about subcellular localizations and functions within macromolecular complexes.

Effects of Glycosylation on the Enzymatic Activity and Mechanisms of Proteases

Posttranslational modifications are an important feature of most proteases in higher organisms, such as the conversion of inactive zymogens into active proteases. To date, little information is available on the role of glycosylation and functional implications for secreted proteases. Besides a stabilizing effect and protection against proteolysis, several proteases show a significant influence of glycosylation on the catalytic activity. Glycans can alter the substrate recognition, the specificity and binding affinity, as well as the turnover rates. However, there is currently no known general pattern, since glycosylation can have both stimulating and inhibiting effects on activity. Thus, a comparative analysis of individual cases with sufficient enzyme kinetic and structural data is a first approach to describe mechanistic principles that govern the effects of glycosylation on the function of proteases. The understanding of glycan functions becomes highly significant in proteomic and glycomic studies, which demonstrated that cancer-associated proteases, such as kallikrein-related peptidase 3, exhibit strongly altered glycosylation patterns in pathological cases. Such findings can contribute to a variety of future biomedical applications.

Bilayer Membrane Modulation of Membrane Type 1 Matrix Metalloproteinase (MT1-MMP) Structure and Proteolytic Activity

Cell surface proteolysis is an integral yet poorly understood physiological process. The present study has examined how the pericellular collagenase membrane-type 1 matrix metalloproteinase (MT1-MMP) and membrane-mimicking environments interplay in substrate binding and processing. NMR derived structural models indicate that MT1-MMP transiently associates with bicelles and cells through distinct residues in blades III and IV of its hemopexin-like domain, while binding of collagen-like triple-helices occurs within blades I and II of this domain. Examination of simultaneous membrane interaction and triple-helix binding revealed a possible regulation of proteolysis due to steric effects of the membrane. At bicelle concentrations of 1%, enzymatic activity towards triple-helices was increased 1.5-fold. A single mutation in the putative membrane interaction region of MT1-MMP (Ser466Pro) resulted in lower enzyme activation by bicelles. An initial structural framework has thus been developed to define the role(s) of cell membranes in modulating proteolysis.

EMMPRIN-mediated induction of uterine and vascular matrix metalloproteinases during pregnancy and in response to estrogen and progesterone

Pregnancy is associated with uteroplacental and vascular remodeling in order to adapt for the growing fetus and the hemodynamic changes in the maternal circulation. We have previously shown upregulation of uterine matrix metalloproteinases (MMPs) during pregnancy. Whether pregnancy-associated changes in MMPs are localized to the uterus or are generalized in feto-placental and maternal circulation is unclear. Also, the mechanisms causing the changes in uteroplacental and vascular MMPs during pregnancy are unclear. MMPs expression, activity and tissue distribution were measured in uterus, placenta and aorta of virgin, mid-pregnant (mid-Preg) and late pregnant (late-Preg) rats. Western blots and gelatin zymography revealed increases in MMP-2 and -9 in uterus and aorta of late-Preg compared with virgin and mid-Preg rats. In contrast, MMP-2 and -9 were decreased in placenta of late-Preg versus mid-Preg rats. Extracellular MMP inducer (EMMPRIN) was increased in uterus and aorta of pregnant rats, but was less in placenta of late-Preg than mid-Preg rats. Prolonged treatment of uterus or aorta of virgin rats with 17β-estradiol and progesterone increased the amount of EMMPRIN, MMP-2 and -9, and the sex hormone-induced increases in MMPs were prevented by EMMPRIN neutralizing antibody. Immunohistochemistry revealed that MMP-2 and -9 and EMMPRIN increased in uterus and aorta of pregnant rats, but decreased in placenta of late-Preg versus mid-Preg rats. Thus pregnancy-associated upregulation of uterine MMPs is paralleled by increased vascular MMPs, and both are mediated by EMMPRIN and induced by estrogen and progesterone, suggesting similar role of MMPs in uterine and vascular tissue remodeling and function during pregnancy. The decreased MMPs and EMMPRIN in placenta of late-Preg rats suggests reduced role of MMPs in feto-placental circulation during late pregnancy.

Axonal growth towards Xenopus skin in vitro is mediated by matrix metalloproteinase activity

We have previously demonstrated that the growth of peripheral nervous system axons is strongly attracted towards limb buds and skin explants in vitro. Here, we show that directed axonal growth towards skin explants of Xenopus laevis in matrigel is associated with expression of matrix metalloproteinase (MMP)-18 and also other MMPs, and that this long-range neurotropic activity is inhibited by the broad-spectrum MMP inhibitors BB-94 and GM6001. We also show that forced expression of MMP-18 in COS-7 cell aggregates enhances axonal growth from Xenopus dorsal root ganglia explants. Nidogen is the target of MMPs released by cultured skin in matrigel, whereas other components remain intact. Our results suggest a novel link between MMP activity and extracellular matrix breakdown in the control of axonal growth.

Concanavalin-A-induced autophagy biomarkers requires membrane type-1 matrix metalloproteinase intracellular signaling in glioblastoma cells

Pre-clinical trials for cancer therapeutics support the anti-neoplastic properties of the lectin from Canavalia ensiformis (Concanavalin-A, ConA) in targeting apoptosis and autophagy in a variety of cancer cells. Given that membrane type-1 matrix metalloproteinase (MT1-MMP), a plasma membrane-anchored matrix metalloproteinase, is a glycoprotein strongly expressed in radioresistant and chemoresistant glioblastoma that mediates pro-apoptotic signalling in brain cancer cells, we investigated whether MT1-MMP could also signal autophagy. Among the four lectins tested, we found that the mannopyranoside/glucopyranoside-binding ConA, which is also well documented to trigger MT1-MMP expression, increases autophagic acidic vacuoles formation as demonstrated by Acridine Orange cell staining. Although siRNA-mediated MT1-MMP gene silencing effectively reversed ConA-induced autophagy, inhibition of the MT1-MMP extracellular catalytic function with Actinonin or Ilomastat did not. Conversely, direct overexpression of the recombinant Wt-MT1-MMP protein triggered proMMP-2 activation and green fluorescent protein-microtubule-associated protein light chain 3 puncta indicative of autophagosomes formation, while deletion of MT1-MMP's cytoplasmic domain disabled such autophagy induction. ConA-treated U87 cells also showed an upregulation of BNIP3 and of autophagy-related gene members autophagy-related protein 3, autophagy-related protein 12 and autophagy-related protein 16-like 1, where respective inductions were reversed when MT1-MMP gene expression was silenced. Altogether, we provide molecular evidence supporting the pro-autophagic mechanism of action of ConA in glioblastoma cells. We also highlight new signal transduction functions of MT1-MMP within apoptotic and autophagic pathways that often characterize cancer cell responses to chemotherapeutic drugs.

Detection of the heterogeneous O-glycosylation profile of MT1-MMP expressed in cancer cells by a simple MALDI-MS method

Background

Glycosylation is an important and universal post-translational modification for many proteins, and regulates protein functions. However, simple and rapid methods to analyze glycans on individual proteins have not been available until recently.

Methods/Principal Findings

A new technique to analyze glycopeptides in a highly sensitive manner by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) using the liquid matrix 3AQ/CHCA was developed recently and we optimized this technique to analyze a small amount of transmembrane protein separated by SDS-PAGE. We used the MALDI-MS method to evaluate glycosylation status of membrane-type 1 matrix metalloproteinase (MT1-MMP). O-glycosylation of MT1-MMP is reported to modulate its protease activity and thereby to affect cancer cell invasion. MT1-MMP expressed in human fibrosarcoma HT1080 cells was immunoprecipitated and resolved by SDS-PAGE. After in-gel tryptic digestion of the protein, a single droplet of the digest was applied directly to the liquid matrix on a MALDI target plate. Concentration of hydrophilic glycopeptides within the central area occurred due to gradual evaporation of the sample solution, whereas nonglycosylated hydrophobic peptides remained at the periphery. This specific separation and concentration of the glycopeptides enabled comprehensive analysis of the MT1-MMP O-glycosylation.

Conclusions/Significance

We demonstrate, for the first time, heterogeneous O-glycosylation profile of a protein by a whole protein analysis using MALDI-MS. Since cancer cells are reported to have altered glycosylation of proteins, this easy-to-use method for glycopeptide analysis opens up the possibility to identify specific glycosylation patterns of proteins that can be used as new biomarkers for malignant tumors.

Classically activated macrophages use stable microtubules for matrix metalloproteinase-9 (MMP-9) secretion

As major effector cells of the innate immune response, macrophages must adeptly migrate from blood to infected tissues. Endothelial transmigration is accomplished by matrix metalloproteinase (MMP)-induced degradation of basement membrane and extracellular matrix components. The classical activation of macrophages with LPS and IFN-γ causes enhanced microtubule (MT) stabilization and secretion of MMPs. Macrophages up-regulate MMP-9 expression and secretion upon immunological challenge and require its activity for migration during the inflammatory response. However, the dynamics of MMP-9 production and intracellular distribution as well as the mechanisms responsible for its trafficking are unknown. Using immunofluorescent imaging, we localized intracellular MMP-9 to small Golgi-derived cytoplasmic vesicles that contained calreticulin and protein-disulfide isomerase in activated RAW 264.7 macrophages. We demonstrated vesicular organelles of MMP-9 aligned along stable subsets of MTs and showed that selective modulation of MT dynamics contributes to the enhanced trafficking of MMP-9 extracellularly. We found a Rab3D-dependent association of MMP-9 vesicles with the molecular motor kinesin, whose association with the MT network was greatly enhanced after macrophage activation. Finally, we implicated kinesin 5B and 3B isoforms in the effective trafficking of MMP-9 extracellularly.

Glycosylation of Twisted Gastrulation is Required for BMP Binding and Activity during Craniofacial Development

Twisted gastrulation (TWSG1) is a conserved, secreted glycoprotein that modulates signaling of bone morphogenetic proteins (BMPs) in the extracellular space. Deletion of exon 4 of mouse Twsg1 (mTwsg1) is associated with significant craniofacial defects. However, little is understood about the biochemical properties of the corresponding region of the protein. We have uncovered a significant role for exon 4 sequences as encoding the only two glycosylation sites of the mTWSG1 protein. Deletion of the entire exon 4 or mutation of both glycosylation sites within exon 4 abolishes glycosylation of mTWSG1. Importantly, we find that constructs with mutated glycosylation sites have significantly reduced BMP binding activity. We further show that glycosylation and activity of TWSG1 recombinant proteins vary markedly by cellular source. Non-glycosylated mTWSG1 made in E. coli has both reduced affinity for BMPs, as shown by surface plasmon resonance analysis, and reduced BMP inhibitory activity in a mandibular explant culture system compared to glycosylated proteins made in insect cells or murine myeloma cells. This study highlights an essential role for glycosylation in Twisted gastrulation action.

Characterization of the dimerization interface of membrane type 4 (MT4)-matrix metalloproteinase

MT4-MMP (MMP17) belongs to a unique subset of membrane type-matrix metalloproteinases that are anchored to the cell surface via a glycosylphosphatidylinositol moiety. However, little is known about its biochemical properties. Here, we report that MT4-MMP is displayed on the cell surface as a mixed population of monomeric, dimeric, and oligomeric forms. Sucrose gradient fractionation demonstrated that these forms of MT4-MMP are all present in lipid rafts. Mutational and computational analyses revealed that Cys(564), which is present within the stem region, mediates MT4-MMP homodimerization by forming a disulfide bond. Substitution of Cys(564) results in a more rapid MT4-MMP turnover, when compared with the wild-type enzyme, consistent with a role for dimerization in protein stability. Expression of MT4-MMP in Madin-Darby canine kidney cells enhanced cell migration and invasion of Matrigel, a process that requires catalytic activity. However, a serine substitution at Cys(564) did not reduce MT4-MMP-stimulated cell invasion of Matrigel suggesting that homodimerization is not required for this process. Deglycosylation studies showed that MT4-MMP is modified by N-glycosylation. Moreover, inhibition of N-glycosylation by tunicamycin diminished the extent of MT4-MMP dimerization suggesting that N-glycans may confer stability to the dimeric form. Taken together, the data presented here provide a new insight into the characteristics of MT4-MMP and highlight the common and distinct properties of the glycosylphosphatidylinositol-anchored membrane type-matrix metalloproteinases.

The influence of type 2 diabetes mellitus on the expression of inflammatory mediators and tissue inhibitor of metalloproteinases-2 in human chronic periodontitis

PURPOSE

The purpose of this study was to compare and quantify the expression of C-reactive protein (CRP), matrix metalloproteinase (MMP)-14, and tissue inhibitor of metalloproteinases (TIMP)-2 in gingival tissues of patients with chronic periodontitis accompanied with inflammatory reaction related to alveolar bone resorption with or without type 2 diabetes mellitus (DM).

METHODS

Twelve patients with type 2 DM and chronic periodontitis (group 3), twelve patients with chronic periodontitis (group 2), and twelve healthy individuals (group 1) were included in the study. Gingival tissue biopsies were collected from each patient and from healthy individuals at the time of periodontal surgery (including surgical crown lengthening) or tooth extraction. The concentrations of cytokines were determined by a western blot analysis.

RESULTS

The expression levels of CRP and MMP-14 increased in group 2 and 3, and they were highest in group 3. The expressions of TIMP-2 also increased in group 2 and 3.

CONCLUSIONS

This study demonstrated that the expression levels of CRP, MMP-14, and TIMP-2 might be inflammatory markers in periodontal inflamed tissue. It can be assumed that CRP, MMP-14, and TIMP-2 may be partly involved in the progression of periodontal inflammation associated to type 2 DM.

The dimer interface of the membrane type 1 matrix metalloproteinase hemopexin domain: crystal structure and biological functions

Homodimerization is an essential step for membrane type 1 matrix metalloproteinase (MT1-MMP) to activate proMMP-2 and to degrade collagen on the cell surface. To uncover the molecular basis of the hemopexin (Hpx) domain-driven dimerization of MT1-MMP, a crystal structure of the Hpx domain was solved at 1.7 Å resolution. Two interactions were identified as potential biological dimer interfaces in the crystal structure, and mutagenesis studies revealed that the biological dimer possesses a symmetrical interaction where blades II and III of molecule A interact with blades III and II of molecule B. The mutations of amino acids involved in the interaction weakened the dimer interaction of Hpx domains in solution, and incorporation of these mutations into the full-length enzyme significantly inhibited dimer-dependent functions on the cell surface, including proMMP-2 activation, collagen degradation, and invasion into the three-dimensional collagen matrix, whereas dimer-independent functions, including gelatin film degradation and two-dimensional cell migration, were not affected. These results shed light on the structural basis of MT1-MMP dimerization that is crucial to promote cellular invasion.

Posttranslational regulation of membrane type 1-matrix metalloproteinase (MT1-MMP) in mouse PTEN null prostate cancer cells: Enhanced surface expression and differential O-glycosylation of MT1-MMP

Membrane type 1 (MT1)-matrix metalloproteinase (MT1-MMP) is a membrane-tethered MMP that has been shown to play a key role in promoting cancer cell invasion. MT1-MMP is highly expressed in bone metastasis of prostate cancer (PC) patients and promotes intraosseous tumor growth of PC cells in mice. The majority of metastatic prostate cancers harbor loss-of-function mutations or deletions of the tumor suppressor PTEN (phosphatase and tensin homologue deleted on chromosome ten). However, the role of PTEN inactivation in MT1-MMP expression in PC cells has not been examined. In this study, prostate epithelial cell lines derived from mice that are either heterozygous (PTEN(+/-)) or homozygous (PTEN(-/-)) for PTEN deletion or harboring a wild-type PTEN (PTEN(+/+)) were used to investigate the expression of MT1-MMP. We found that biallelic loss of PTEN is associated with posttranslational regulation of MT1-MMP protein in mouse PC cells. PTEN(-/-) PC cells display higher levels of MT1-MMP at the cell surface when compared to PTEN(+/+) and PTEN(+/-) cells and consequently exhibited enhanced migratory and collagen-invasive activities. MT1-MMP displayed by PTEN(-/-) cells is differentially O-glycosylated and exhibits a slow rate of turnover. MT1-MMP expression in PTEN(-/-) cells is under control of the PI3K/AKT signaling pathway, as determined using pharmacological inhibitors. Interestingly, rapamycin, an mTOR inhibitor, upregulates MT1-MMP expression in PTEN(+/+) cells via PI3K activity. Collectively, these data in a mouse prostate cell system uncover for the first time a novel and complex relationship between PTEN loss-mediated PI3K/AKT activation and posttranslational regulation of MT1-MMP, which may play a role in PC progression.

Navigating ECM barriers at the invasive front: the cancer cell-stroma interface

A seminal event in cancer progression is the ability of the neoplastic cell to mobilize the necessary machinery to breach surrounding extracellular matrix barriers while orchestrating a host stromal response that ultimately supports tissue-invasive and metastatic processes. With over 500 proteolytic enzymes identified in the human genome, interconnecting webs of protease-dependent and protease-independent processes have been postulated to drive the cancer cell invasion program via schemes of daunting complexity. Increasingly, however, a body of evidence has begun to emerge that supports a unifying model wherein a small group of membrane-tethered enzymes, termed the membrane-type matrix metalloproteinases (MT-MMPs), plays a dominant role in regulating cancer cell, as well as stromal cell, traffic through the extracellular matrix barriers assembled by host tissues in vivo. Understanding the mechanisms that underlie the regulation and function of these metalloenzymes as host cell populations traverse the dynamic extracellular matrix assembled during neoplastic states should provide new and testable theories regarding cancer invasion and metastasis.

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.

Two distinct localization patterns of testis-specific serine protease 1 (TESSP1) in the seminiferous tubules of the mouse testis

Mouse Tesspl has been shown to be a testis-specific gene that may contribute to spermatogenesis. In this report, we raised a specific antibody against TESSP1 to assess its biological role. Western blotting detected testicular TESSP1 in all postnatal developmental stages of the mouse. Experiments using the testes of W/W(V) mice, which lack germ cells, indicated TESSP1 expression in Sertoli cells and Leydig cells. In immunofluorescence staining of the wild-type mouse testis, dot-like signals for TESSP1 were observed in the adluminal compartment of the seminiferous tubules, while diffused signals were found in the basal compartment. Generally, the dot-like and diffused signals overlapped with the trans-Golgi network marker RAB6 and the transmembrane protein CADHERIN 2, respectively. Some TESSP1 staining was also observed in association with interstitial Leydig cells of the testis. The results of this study suggest that TESSP1 is predominantly localized in the plasma membrane of spermatogonia and Sertoli cells in the basal compartment, but exhibits an intracellular localization, presumably in the Golgi apparatus, of spermatocytes and spermatids in the adluminal compartment of the seminiferous tubules. The expression of TESSP1 in both germ cells and somatic cells and alteration in its cellular localization in the germ cells during spermatogenesis indicate that it may have a unique role in the testis.

Epidermal growth factor receptor-mediated membrane type 1 matrix metalloproteinase endocytosis regulates the transition between invasive versus expansive growth of ovarian carcinoma cells in three-dimensional collagen

The epidermal growth factor receptor (EGFR) is overexpressed in ovarian carcinomas and promotes cellular responses that contribute to ovarian cancer pathobiology. In addition to modulation of mitogenic and motogenic behavior, emerging data identify EGFR activation as a novel mechanism for rapid modification of the cell surface proteome. The transmembrane collagenase membrane type 1 matrix metalloproteinase (MT1-MMP, MMP-14) is a major contributor to pericelluar proteolysis in the ovarian carcinoma microenvironment and is subjected to extensive posttranslational regulation. In the present study, the contribution of EGFR activation to control of MT1-MMP cell surface dynamics was investigated. Unstimulated ovarian cancer cells display caveolar colocalization of EGFR and MT1-MMP, whereas EGFR activation prompts internalization via distinct endocytic pathways. EGF treatment results in phosphorylation of the MT1-MMP cytoplasmic tail, and cells expressing a tyrosine mutated form of MT1-MMP (MT1-MMP-Y(573)F) exhibit defective MT1-MMP internalization. As a result of sustained cell surface MT1-MMP activity, a phenotypic epithelial-mesenchymal transition is observed, characterized by enhanced migration and collagen invasion, whereas growth within three-dimensional collagen gels is inhibited. These data support an EGFR-dependent mechanism for regulation of the transition between invasive and expansive growth of ovarian carcinoma cells via modulation of MT1-MMP cell surface dynamics.

Modulation of the membrane type 1 matrix metalloproteinase cytoplasmic tail enhances tumor cell invasion and proliferation in three-dimensional collagen matrices

Increasing evidence suggests that the cytoplasmic tail of membrane type 1 matrix metalloproteinase (MT1-MMP) is subject to phosphorylation and that this modification may influence its enzymatic activity at the cell surface. In this study, phosphorylated MT1-MMP is detected using a phospho-specific antibody recognizing a protein kinase C consensus sequence (phospho-TXR), and a MT1-MMP tail peptide is phosphorylated by exogenous protein kinase C. To characterize the potential role of cytoplasmic residue Thr(567) in these processes, mutants that mimic a state of either constitutive (T567E) or defective phosphorylation (T567A) were expressed and analyzed for their functional effects on MT1-MMP activity and cellular behavior. Phospho-mimetic mutants of Thr(567) exhibit enhanced matrix invasion as well as more extensive growth within a three-dimensional type I collagen matrix. Together, these findings suggest that MT1-MMP surface action is regulated by phosphorylation at cytoplasmic tail residue Thr(567) and that this modification plays a critical role in processes that are linked to tumor progression.

Structural and functional bases for allosteric control of MMP activities: can it pave the path for selective inhibition?

The zinc-dependent matrix metalloproteinases (MMPs) belong to a large family of structurally homologous enzymes. These enzymes are involved in a wide variety of biological processes ranging from physiological cell proliferation and differentiation to pathological states associated with tumor metastasis, inflammation, tissue degeneration, and cell death. Controlling the enzymatic activity of specific individual MMPs by antagonist molecules is highly desirable, first, for studying their individual roles, and second as potential therapeutic agents. However, blocking the enzymatic activity with synthetic small inhibitors appears to be an extremely difficult task. Thus, this is an unmet need presumably due to the high structural homology between MMP catalytic domains. Recent reports have recognized a potential role for exosite or allosteric protein regions, distinct from the extended catalytic pocket, in mediating MMP activation and substrate hydrolysis. This raises the possibility that MMP enzymatic and non-enzymatic activities may be modified via antagonist molecules targeted to such allosteric sites or to alternative enzyme domains. In this review, we discuss the structural and functional bases for potential allosteric control of MMPs and highlight potential alternative enzyme domains as targets for designing highly selective MMP inhibitors.

Compact spheroid formation by ovarian cancer cells is associated with contractile behavior and an invasive phenotype

Ovarian cancer cells are present in malignant ascites both as individual cells and as multicellular spheroid aggregates. Although spheroid formation affords protection of cancer cells against some chemotherapeutic agents, it has not been established whether a relationship exists between invasive behavior and predisposition to spheroid formation. Aspects of spheroid formation, including cell-matrix adhesion, remodeling and contractility are characteristic myofibroblast-like behaviors associated with fibrosis that contribute to tumor growth and dissemination. We explored the possibility that cell behaviors that promote spheroid formation also facilitate invasion. Our analysis of 6 human ovarian cancer cell lines indicated that ovarian cancer cells possessing myofibroblast-like properties formed compact spheroids and invaded 3D matrices. These cells readily contracted collagen I gels, possessed a spindle-like morphology, and had elevated expression of genes associated with the TGFbeta-mediated fibrotic response and/or beta1 integrin function, including fibronectin (FN), connective tissue growth factor (CTGF/CCN2), lysyl oxidase (LOX1), tissue transglutaminase 2 (TGM2) and urinary plasminogen activator receptor (uPAR). Whereas cell aggregation was induced by TGFbeta, and by beta1-integrin overexpression and activation, these treatments did not stimulate the contractile activity required for spheroid compaction. The positive relationship found between compact spheroid formation and invasive behavior implies a preferential survival of an invasive subpopulation of ovarian cancer cells, as cells in spheroids are more resistant to several chemotherapeutics. Preventing the formation of ovarian cancer spheroids may represent a novel strategy to improve the efficacy of existing therapeutics.

Contribution of sialidase NEU1 to suppression of metastasis of human colon cancer cells through desialylation of integrin beta4

We previously found an inverse relationship between sialidase Neu1 expression and metastatic potential of murine cancer cells. To elucidate the mechanism underlying the cellular events, the human sialidase gene NEU1 was overexpressed or silenced in colon cancer HT-29 cells. When NEU1-overexpressing cells were injected transsplenically into mice, in vivo liver metastasis was significantly reduced. NEU1 suppressed cell migration, invasion and adhesion in vitro, whereas the silencing resulted in the opposite. One of the major molecular changes by NEU1 was decreased sialylation of integrin beta4, assessed by PNA- and MAL-II-lectin blotting of immunoprecipitates with anti-integrin beta4 antibody. The desialylation was accompanied by decreased phosphorylation of the integrin followed by attenuation of focal adhesion kinase and Erk1/2 pathway. Moreover, NEU1 caused downregulation of matrix metalloproteinase-7, overexpression of which is associated with cancer metastasis. Treatment of the cells with GalNAc-alpha-O-benzyl, an inhibitor of O-glycosylation, showed increased PNA-positive integrin beta4 with its decreased phosphorylation, indicating that sialic acid removal from the integrin O-glycans results in the decreased phosphorylation. Biotinylation and immunofluorescence staining exhibited some NEU1 molecules to be at the cell surface accessible to the integrin. These results suggest that NEU1 is important in regulation of integrin beta4-mediated signaling, leading to suppression of metastasis.

Expression of membrane type 1 matrix metalloproteinase (MMP-14) in epithelial ovarian cancer: high level expression in clear cell carcinoma

OBJECTIVE

Clear cell carcinomas of the ovary constitute approximately 5% of all ovarian neoplasms and have a distinct gene expression profile relative to other ovarian carcinoma histotypes. Tumors often present as an early stage large pelvic mass with a high degree of recurrence and frequent early metastasis. Matrix metalloproteinases (MMPs) play a role in intraperitoneal metastasis through breakdown of cell-cell and cell-matrix barriers, enabling anchoring of secondary lesions and promoting proliferation in a geometrically constrained matrix environment. The objective of this study was to evaluate MMP expression in ovarian clear cell carcinoma.

METHODS

Immunohistochemistry was used to evaluate expression of membrane type 1 MMP (MMP-14), MMP-2 and MMP-9 in a panel of ovarian tumors. Western blotting and gelatin zymography were used to examine MMP-14 expression and activity in the clear cell carcinoma cell line ES2. The ability of ES2 cells to invade and proliferate within three-dimensional collagen gels was evaluated.

RESULTS

High level expression of MMP-14 and MMP-2 were observed in ovarian clear cell carcinoma relative to other histotypes (94-95% strong positive). MMP-14 was expressed and active in cultured ES2 cells. ES2 cells also exhibited MMP-dependent invasion of and proliferation within three-dimensional collagen gels.

CONCLUSIONS

The high level expression of MMP-14 together with in vitro functional analyses suggest that MMP-14 may contribute to both the proliferative capacity and the enhanced parenchymal metastasis of ovarian clear cell carcinoma.

The cytoplasmic tail dileucine motif LL572 determines the glycosylation pattern of membrane-type 1 matrix metalloproteinase

Membrane-type 1 matrix metalloproteinase (MT1-MMP; MMP-14) drives fundamental physiological and pathological processes, due to its ability to process a broad spectrum of substrates. Because subtle changes in its activity can produce profound physiological effects, MT1-MMP is tightly regulated. Currently, many aspects of this regulation remain to be elucidated. It has recently been discovered that O-linked glycosylation defines the substrate spectrum of MT1-MMP. We hypothesized that a mutual interdependency exists between MT1-MMP trafficking and glycosylation. Lectin precipitation, metabolic labeling, enzymatic deglycosylation, and site-directed mutagenesis studies demonstrate that the LL(572) motif in the cytoplasmic tail of MT1-MMP influences the composition of the complex O-linked carbohydrates attached to the hinge region of the protein. This influence appears to be independent from major effects on cell surface trafficking. MT1-MMP undergoes extensive processing after its synthesis. The origins and the molecular characters of its multiple forms are incompletely understood. Here, we develop and present a model for the sequential, post-translational processing of MT1-MMP that defines stages in the post-synthetic pathway pursued by the protein.

Progress in matrix metalloproteinase research

Matrix metalloproteinases (MMPs) are now acknowledged as key players in the regulation of both cell-cell and cell-extracellular matrix interactions. They are involved in modifying matrix structure, growth factor availability and the function of cell surface signalling systems, with consequent effects on cellular differentiation, proliferation and apoptosis. They play central roles in morphogenesis, wound healing, tissue repair and remodelling in response to injury and in the progression of diseases such as arthritis, cancer and cardiovascular disease. Because of their wide spectrum of activities and expression sites, the elucidation of their potential as drug targets in disease or as important features of the repair process will be dependent upon careful analysis of their role in different cellular locations and at different disease stages. Novel approaches to the specific regulation of individual MMPs in different contexts are also being developed.

Contrasting expression of membrane metalloproteinases, MT1-MMP and MT3-MMP, suggests distinct functions in skeletal development

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is the most ubiquitous and widely studied of the membrane-type metalloproteinases (MT-MMPs). It was thus surprising to find no published data on chicken MT1-MMP. We report here the characterization of the chicken gene. Its low sequence identity with the MT1-MMP genes of other species, high GC content, and divergent catalytic domain explains the absence of data and our difficulties in characterizing the gene. The absence of structural features in the chicken gene that have been suggested to be critical for the activation of MMP-2 by MT1-MMP; for the effect of MT1-MMP on cell migration and for the recycling of MT1-MMP suggest these features are either not essential or that MT1-MMP does not perform these functions in chickens. Comparison of the expression of chicken MT1-MMP with MT3-MMP and with MMP-2 and MMP-13 has confirmed the previously recognized co-expression of MT1-MMP with MMP-2 and MMP-13 in fibrous and vascular tissues, particularly those surrounding the developing long bones in other species. By contrast, MT3-MMP expression differs markedly from that of MT1-MMP and of both MMP-2 and MMP-13. MT3-MMP is expressed by chondrocytes of the developing articular surface. Similar expression patterns of this group of MT-MMPs and MMPs have been observed in mouse embryos and suggest distinct and specific functions for MT1-MMP and MT3-MMP in skeletal development.

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.

The second dimer interface of MT1-MMP, the transmembrane domain, is essential for ProMMP-2 activation on the cell surface

Activation of proMMP-2 and cell surface collagenolysis are important activities of membrane-type 1 matrix metalloproteinase (MT1-MMP) to promote cell migration in tissue, and these activities are regulated by homodimerization of MT1-MMP on the cell surface. In this study, we have identified the transmembrane domain as a second dimer interface of MT1-MMP in addition to the previously identified hemopexin domain. Our analyses indicate that these two modes of dimerization have different roles; transmembrane-dependent dimerization is critical for proMMP-2 activation, whereas hemopexin-dependent dimerization is important for degradation of collagen on the cell surface. Our finding provides new insight into the potential molecular arrangement of MT1-MMP contributing to its function on the cell surface.

Activation-coupled membrane-type 1 matrix metalloproteinase membrane trafficking

The transmembrane collagenase MT1-MMP (membrane-type 1 matrix metalloproteinase), also known as MMP-14, has a critical function both in normal development and in cancer progression, and is subject to extensive controls at the post-translational level which affect proteinase activity. As zymogen activation is crucial for MT1-MMP activity, an alpha1-PI (alpha1-proteinase inhibitor)-based inhibitor was designed by incorporating the MT1-MMP propeptide cleavage sequence into the alpha1-PI reactive-site loop (designated alpha1-PI(MT1)) and this was compared with wild-type alpha1-PI (alpha1-PI(WT)) and the furin inhibitory mutant alpha1-PI(PDX). Alpha1-PI(MT1) formed an SDS-stable complex with furin and inhibited proMT1-MMP activation. A consequence of the loss of MT1-MMP activity was the activation of proMMP-2 and the inhibition of MT1-MMP-mediated collagen invasion. alpha1-PI(MT1) expression also resulted in the intracellular accumulation of a glycosylated species of proMT1-MMP that was retained in the perinuclear region, leading to significantly decreased cell-surface accumulation of proMT1-MMP. These observations suggest that both the subcellular localization and the activity of MT1-MMP are regulated in a coordinated fashion, such that proMT1-MMP is retained intracellularly until activation of its zymogen, then proMT1-MMP traffics to the cell surface in order to cleave extracellular substrates.

A serial lectin approach to the mucin-typeO-glycoproteome ofDrosophila melanogaster S2 cells

Identification of mucin-type O-glycosylated proteins with known functions in model organisms like Drosophila could provide keys to elucidate functions of the O-glycan moiety and proteomic analyses of O-glycoproteins in higher eukaryotes remain a challenge due to structural heterogeneity and a lack of efficient tools for their specific isolation. Here we report a strategy to evaluate the O-glycosylation potential of the embryonal hemocyte-like Drosophila Schneider 2 (S2) cell line by expression of recombinant glycosylation probes derived from tandem repeats of the human mucin MUC1 or of the Drosophila salivary gland protein Sgs1. We obtained evidence that mucin-type O-glycosylation in S2 cells grown under serum-free conditions is restricted to the Tn-antigen (GalNAcalpha-Ser/Thr) and the T-antigen (Galbeta1-3GalNAcalpha-Ser/Thr) and this structural homogeneity enables unique glycoproteomic strategies. We present a label-free strategy for the isolation, profiling and analysis of O-glycosylated proteins consisting of serial lectin affinity capture, 2-DE-based glycoprotein analysis by O-glycan specific mAbs and protein identification by MALDI-MS. Protein identity and O-glycosylation was confirmed by ESI-MS/MS with detection of diagnostic sugar oxonium-ion fragments. Using this strategy, we established 2-D reference maps and identified 21 secreted and intracellular mucin-type O-glycoproteins. Our results show that Drosophila S2 cells express O-glycoproteins involved in a wide range of biological functions including proteins of the extracellular matrix (Laminin gamma-chain, Peroxidasin and Glutactin), pathogen recognition proteins (Gnbp1), stress response proteins (Glycoprotein 93), secreted proteases (Matrix-metalloprotease 1 and various trypsin-like serine proteases), protease inhibitors (Serpin 27 A) and proteins of unknown function.

Identification of a novel 82 kDa proMMP-9 species associated with the surface of leukaemic cells: (auto-)catalytic activation and resistance to inhibition by TIMP-1

MMP-9 (matrix metalloproteinase 9) plays a critical role in tumour progression. Although the biochemical properties of the secreted form of proMMP-9 are well characterized, little is known about the function and activity of cell surface-associated proMMP-9. We purified a novel 82 kDa species of proMMP-9 from the plasma membrane of THP-1 leukaemic cells, which has substantial differences from the secreted 94 kDa proMMP-9. The 82 kDa form was not detected in the medium even upon stimulation with a phorbol ester. It is truncated by nine amino acid residues at its N-terminus, lacks O-linked oligosaccharides present in the 94 kDa proMMP-9, but retains N-linked carbohydrates. Incubation of 94 kDa proMMP-9 with MMP-3 generated the well-known 82 kDa active form, but the 82 kDa proMMP-9 was converted into an active species of 35 kDa, which was also produced by autocatalytic processing in the absence of activating enzymes. The activated 35 kDa MMP-9 efficiently degraded gelatins, native collagen type IV and fibronectin. The enzyme was less sensitive to TIMP-1 (tissue inhibitor of metalloproteinase 1) inhibition with IC50 values of 82 nM compared with 1 nM for the 82 kDa active MMP-9. The synthetic MMP inhibitor GM6001 blocked the activity of both enzymes, with similar IC50 values below 1 nM. The 82 kDa proMMP-9 is also produced in HL-60 and NB4 leukaemic cell lines as well as ex vivo leukaemic blast cells. It is, however, absent from neutrophils and mononuclear cells isolated from peripheral blood of healthy individuals. Thus, the 82 kDa proMMP-9 expressed on the surface of malignant cells may escape inhibition by natural TIMP-1, thereby facilitating cellular invasion in vivo.