Shedding of membrane type 1 matrix metalloproteinase in a human breast carcinoma cell line

The Catalytic Domain Mediates Homomultimerization of MT1-MMP and the Prodomain Interferes with MT1-MMP Oligomeric Complex Assembly

Homomultimerization of MT1-MMP (membrane type 1 matrix metalloproteinase) through the hemopexin, transmembrane, and cytoplasmic domains plays a very important role in the activation of proMMP-2 and the degradation of pericellular collagen. MT1-MMP is overexpressed in many types of cancers, and it is considered to be a key enzyme in facilitating cancer cell migration. Since the oligomerization of MT1-MMP is important for its proteolytic activity in promoting cancer invasion, we have further investigated the multimerization by using heterologously expressed MT1-MMP ectodomains in insect cells to gain additional mechanistic insight into this process. We show that the whole ectodomain of MT1-MMP can form dimers and higher-order oligomeric complexes. The enzyme is secreted in its active form and the multimeric complex assembly is mediated by the catalytic domain. Blocking the prodomain removal determines the enzyme to adopt the monomeric structure, suggesting that the prodomain prevents the MT1-MMP oligomerization process. The binding affinity of MT1-MMP to type I collagen is dependent on the oligomeric state. Thus, the monomers have the weakest affinity, while the binding strength increases proportionally with the complexity of the multimers. Collectively, our experimental results indicate that the catalytic domain of MT1-MMP is necessary and sufficient to mediate the formation of multimeric structures.

Drug Development Targeting the Ubiquitin-Proteasome System (UPS) for the Treatment of Human Cancers

Cancer cells are characterized by a higher rate of protein turnover and greater demand for protein homeostasis compared to normal cells. In this scenario, the ubiquitin-proteasome system (UPS), which is responsible for the degradation of over 80% of cellular proteins within mammalian cells, becomes vital to cancer cells, making the UPS a critical target for the discovery of novel cancer therapeutics. This review systematically categorizes all current reported small molecule inhibitors of the various essential components of the UPS, including ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), ubiquitin ligases (E3s), the 20S proteasome catalytic core particle (20S CP) and the 19S proteasome regulatory particles (19S RP), as well as their mechanism/s of action and limitations. We also discuss the immunoproteasome which is considered as a prospective therapeutic target of the next generation of proteasome inhibitors in cancer therapies.

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.

Membrane-type matrix metalloproteinases: Their functions and regulations

Membrane-type matrix metalloproteinases (MT-MMPs) form a subgroup of the matrix metalloproteinase (MMP) family, and there are 6 MT-MMPs in humans. MT-MMPs are further sub-classified into type I transmembrane-type (MT1, -MT2-, MT3- and MT5-MMPs) and glycosylphosphatidylinositol (GPI)-anchored type (MT4- and MT6-MMPs). In either case MT-MMPs are tethered to the plasma membrane, and this cell surface expression provides those enzymes with unique functionalities affecting various cellular behaviours. Among the 6 MT-MMPs, MT1-MMP is the most investigated enzyme and many of its roles and regulations have been revealed to date, but the potential roles and regulatory mechanisms of other MT-MMPs are gradually getting clearer as well. Further investigations of MT-MMPs are likely to reveal novel pathophysiological mechanisms and potential therapeutic strategies for different diseases in the future.

Detection of a latent soluble form of membrane type 1 matrix metalloprotease bound with tissue inhibitor of matrix metalloproteinases-2 in periprosthetic tissues and fluids from loose arthroplasty endoprostheses

Membrane type 1 matrix metalloproteinase (MT1-MMP) is implicated in pericellular proteolysis, and, together with tissue inhibitor of matrix metalloproteinases-2 (TIMP-2), in the activation of pro-matrix metalloproteinase-2 on the cell surface. It is expressed on the cell surface either activated or as a proenzyme. A soluble form of MT1-MMP (sMT1-MMP) has been previously identified in periprosthetic tissues and fluid of patients with loose arthroplasty endoprostheses. The aim of this study was to examine periprosthetic tissues and fluids from patients with loose arthroplasty endoprostheses, as well as tissues and fluids from patients with other disorders, for the presence of sMT1-MMP, and to investigate its activation state and possible role. With antibody against MT1-MMP, a protein with molecular mass of ~ 57 kDa was detected by western blotting in all samples tested, representing a soluble form of MT1-MMP, which cannot be ascribed to alternative splicing, as northern blotting showed only one transcript. With various biochemical methods, it was shown that this species occurs in a latent form bearing the N-terminal prodomain, and, additionally, it is bound to TIMP-2, which appeared to be bound via its C-terminal domain to a site different from the active site. Cell ELISA and immunohistochemical analysis revealed that, besides fibroblasts, all other cells, such as inflammatory, epithelial, endothelial, giant and cancer cells, express MT1-MMP on their plasma membrane as a proenzyme. Taking into account the proteolytic abilities of MT1-MMP, the latent sMT1-MMP-TIMP-2 complex could be considered as a new interstitial collagenase. However, the exact role, the production mechanism and the cell origin of this complex remain to be elucidated.

Purification of matrix metalloproteinases by column chromatography

Matrix metalloproteinases (MMPs) are zinc endopeptidases composed of 23 members in humans, which belong to a subfamily of the metzincin superfamily. They play important roles in many pathophysiological events including development, organogenesis, angiogenesis, tissue remodeling and destruction, and cancer cell proliferation and progression by degradation of extracellular matrix (ECM) and non-ECM proteins and interaction with various molecules. Here, we present standard protocols for purification of native proMMPs (proMMP-1, -2, -3, -7, -9 and -10) and recombinant MT1-MMP (MMP-14) using conventional column chromatography. Purification steps comprise the initial common step [diethylaminoethyl (DEAE)-cellulose, Green A Dyematrex gel and gelatin-Sepharose columns], the second step for removal of nontarget proMMPs by immunoaffinity columns (anti-MMP-1 and/or anti-MMP-3 IgG-Sepharose columns) and the final step for further purification (IgG-Sepharose, DEAE-cellulose, Zn2+-chelate-Sepharose and/or gel filtration columns). Purified proMMPs and MMP are functionally active and suitable for biochemical analyses. The basic protocol for the purification from culture media takes approximately 7-10 d.

Significance of matrix metalloproteinases in the pathophysiology of the ovary and uterus

Matrix metalloproteinases (MMP) are capable of degrading a variety of extracellular matrix (ECM) proteins and are also involved in the processing of a number of bioactive molecules. Our findings indicate that the functions of MMP in the ovary and uterus are organ-specific and time-dependently vary during the reproductive cycle. Prolactin induces structural luteolysis indicated by loss of luteal weight, protein and DNA within 36 h after pretreatment with ergot alkaloid. MMP activation appears crucial for the selective depletion of protein during luteal involution, which entails loss of ECM accompanied by apoptosis. During GnRHagonist-induced luteolysis, this response was also associated with marked increases in MMP-2, which degraded collagen type IV, and MT1-MMP, which in addition to activating MMP-2 also degrades collagen type I, III and V. We also found that the level of MT1-MMP and MMP-2 expression in the human CL is greater during the late luteal phase than during either the early mid luteal phases or during gestation, respectively. That dehydroepiandrosterone (DHEA) treatment caused the formation of cysts from antral follicles in the ovaries of immature rats while depressing MMP-2 collagenolytic activity and enhancing lysyl oxidase expression highlights the importance of collagen degradation in the process of ovulation and suggests that changes in the activities of these enzymes play a key role in ovarian cystogenesis in polycystic ovary syndrome patients. Furthermore, immunohistochemical analyses showed that MT1-MMP and FasL co-localize with TdT-mediated dUTP-biotin nick end-labeling (TUNEL)-positive apoptotic granulosa cells in rats treated with DHEA, that the Fas/FasL/Caspase-8 (death receptor-dependent) pathway is pivotal for follicular atresia and that increased levels of MT1-MMP likely play an important role in tissue remodeling during follicular atresia. After parturition, the uterus undergoes involution, a conspicuous feature characterized by a rapid reduction in the collagen content mediated by degradation of extracellular collagen bundles. Our findings strongly suggest that MT1-MMP, MMP-2 and MMP-9 are each time-dependently regulated and play important roles in tissue remodeling during postpartum uterine involution. (Reprod Med Biol 2006; 5: 235-243).

MT1-MMP shedding involves an ADAM and is independent of its localization in lipid rafts

The membrane type 1-matrix metalloproteinase (MT1-MMP) is a membrane-anchored protease that its entire ectodomain is shed from the cell surface. Here we show that in HT1080 cells MT1-MMP is shed as two soluble forms of approximately 52 and approximately 50kDa. Analyses in purified HT1080 plasma membranes show that release of these species is a two-step time-dependent process that is mediated by integral membrane metalloprotease(s). Differential sensitivity to TIMP-3 inhibition of the shedding process suggests that the second cleavage step leading to the formation of the 50-kDa soluble species is mediated by an ADAM. We also show that shedding of MT1-MMP is independent of its partition into lipid rafts because both wild type and glycosylphosphatidylinositol (GPI)-anchored MT1-MMP are shed. These studies provide new insights into the process of MT1-MMP ectodomain shedding, which may regulate pericellular proteolysis.

Altered expression of Fas/Fas ligand/caspase 8 and membrane type 1-matrix metalloproteinase in atretic follicles within dehydroepiandrosterone-induced polycystic ovaries in rats

One of the characteristics of polycystic ovary syndrome (PCOS) is the presence of cystic follicles in various stages of growth and atresia, the latter of which is known to be the result of apoptosis and tissue remodeling. To further investigate the process of follicular atresia, we compared ovarian expression and localization of Fas, Fas ligand (FasL), casapse-8 and membrane-type1 matrix metalloproteinase (MT1-MMP) in rats treated with dehydroepiandrosterone (DHEA) as a model of PCOS, and in control rats. We found that the numbers of TdT-mediated dUTP-biotin nick end-labeling (TUNEL)-positive follicles were significantly higher in ovaries from PCOS rats than in those from control rats (P < 0.05), as were ovarian levels of FasL mRNA and protein, processed caspase-8 protein and MT1-MMP mRNA. Correspondingly, we also observed an increase in the level of MTI-MMP catalytic activity and a decrease in the level of pro-caspase-8 protein. In addition, immunohistochemical analyses showed that MT1-MMP and FasL co-localize with TUNEL-positive apoptotic granulosa cells within atretic follicles of PCOS ovaries. Our results suggest that under the PCOS-like conditions induced by DHEA, the Fas/FasL/Caspase-8 (death receptor dependent) pathway is pivotal for follicular atresia, and that increased levels of MT1-MMP likely play an important role in tissue remodeling during structural luteolysis.

Cleavage at the stem region releases an active ectodomain of the membrane type 1 matrix metalloproteinase

MT1-MMP (membrane type 1 matrix metalloproteinase) is a membrane-anchored MMP that can be shed to the extracellular milieu. In the present study we report the primary structure and activity of the major soluble form of MT1-MMP. MS analysis of the purified 50-kDa soluble MT1-MMP form shows that the enzyme extends from Tyr112 to Val524, indicating that formation of this species requires a proteolytic cleavage within the stem region. In agreement, deletion of the entire stem region of MT1-MMP inhibited shedding of the 50-kDa species. A recombinant 50-kDa species (Tyr112-Val524) expressed in cells exhibited enzymatic activity against pro-MMP-2 and galectin-3, and thus this species is a competent protease. The recombinant 50-kDa soluble form also decreased the level of surface-associated TIMP-2 (tissue inhibitor of metalloproteinase 2) when administered to cells expressing wild-type membrane-anchored MT1-MMP, suggesting that ectodomain shedding of MT1-MMP can alter the MMP/TIMP balance on the cell surface. A approximately 53-kDa species of MT1-MMP was also isolated from a non-detergent extract of human breast carcinoma tissue and was found to lack the cytosolic tail, as determined with specific MT1-MMP domain antibodies. Together, these data show that MT1-MMP ectodomain shedding is a physiological process that may broaden MT1-MMP activity to the pericellular space.

MT1-MMP: A potent modifier of pericellular microenvironment

Cells are regulated by many different means, and there is more and more evidence emerging that changes in the microenvironment greatly affect cell function. MT1-MMP is a type I transmembrane proteinase which participates in pericellular proteolysis of extracellular matrix (ECM) macromolecules. The enzyme is cellular collagenase essential for skeletal development, cancer invasion, growth, and angiogenesis. MT1-MMP promotes cell invasion and motility by pericellular ECM degradation, shedding of CD44 and syndecan1, and by activating ERK. Thus MT1-MMP is one of the factors that influence the cellular microenvironment and thereby affect cell-signaling pathways and eventually alters cellular behavior. As a proteinase, MT1-MMP is regulated by inhibitors, but it also requires formation of a homo-oligomer complex, localization to migration front of the cells, and internalization to become a "functionally active" cell function modifier. Developing new means to inhibit "functional activity" of MT1-MMP may be a new direction to establish treatments for the diseases that MT1-MMP mediates such as cancer and rheumatoid arthritis.

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.

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

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

Induction of membrane-type-1 matrix metalloproteinase by epidermal growth factor-mediated signaling in gliomas

Increased expression of membrane-type matrix metalloproteinases (MT-MMPs) has previously been reported to correlate with increasing grade of malignancy in gliomas, a relationship shared with alterations in epidermal growth factor receptor (EGFR) signaling. To investigate the possibility of a causative role for EGFR signaling in increasing MT-MMP expression and subsequent peritumoral proteolysis, we characterized glioma cell lines for expression of MT1-MMP, MT2-MMP, MT3-MMP, and MT5-MMP by Western blotting and by quantitative real-time polymerase chain reaction analysis, and for MMP-2 activity following epidermal growth factor (EGF) stimulation. EGF stimulation of glioma cell lines resulted in a 2- to 4-fold increase in MT1-MMP mRNA levels. Although there were slight differences in MT2-, MT3-, and MT5-MMP mRNA expression following EGF stimulation, none of these demonstrated an increase similar to that of MT1-MMP expression. Treatment of high-grade glioma cell lines U251MG and IPSB-18 with EGF for 24 h resulted in a several-fold increase in MT1-MMP protein (2.5- and 5.1-fold, respectively) and in cyclin D1 (2.9-fold), as compared to untreated controls. No significant increase was detected in other MT-MMPs at the protein level. Although there was no detectable increase in proMMP-2 protein, there was an increase in MMP-2 activity. Furthermore, the MT1-MMP induction by EGF was prevented by pretreatment with the EGFR-specific tyrphostin inhibitor AG1478. Similarly, treatment with the phosphatidylinositol 3-kinase inhibitor LY294002 prevented the induction of MT1-MMP protein by EGF stimulation. These compounds additionally inhibited EGF-stimulated invasion in Matrigel Transwell assays. Our results indicate that one mechanism of EGFR-mediated invasiveness in gliomas may involve the induction of MT1-MMP.

Processing, shedding, and endocytosis of membrane type 1‐matrix metalloproteinase (MT1‐MMP)

Matrix metalloproteinases (MMPs) are multidomain zinc-dependent proteolytic enzymes that play pivotal roles in many normal and pathological processes. Some members of the MMP family are anchored to the plasma membrane via specialized domains and thus are perfectly suited for pericellular proteolysis. Membrane-anchoring also confers the membrane type-MMPs (MT-MMPs) a unique and complex array of regulatory processes that endow cells with the ability to control MT-MMP-dependent proteolytic activity independently of the levels of endogenous protease inhibitors. Emerging evidence indicates that mechanisms as diverse as autocatalytic processing, ectodomain shedding, homodimerization and internalization can all contribute to the modulation of MT-MMP activity on the cell surface. How these distinct processes interact to attain the optimal level of enzyme activity in a particular setting and the molecular signals that trigger them constitute a new paradigm in MMP regulation. This review will discuss the recent findings concerning these diverse regulatory mechanisms in the context of MT1-MMP (MMP-14).

Two-step sandwich enzyme immunoassay using monoclonal antibodies for detection of soluble and membrane-associated human membrane type 1-matrix metalloproteinase

A two-step sandwich enzyme immunoassay (EIA) system for the detection of human membrane Type 1-matrix metalloproteinase (MT1-MMP) was established by using two monoclonal antibodies against recombinant MT1-MMP. MT1-MMP in which samples were reacted with solid-phase antibody and then detected with peroxidase-labeled second antibody. At least 1.25 ng/mL was detected by the EIA system, and linearity was obtained between 1.25 and 160 ng/mL. This EIA system is specific for MT1-MMP and did not show cross-reactivity against several other MMP's examined. Shedding of soluble MT1-MMP into the medium by some cancer cell lines was also detected by this system. However, soluble MT1-MMP in serum from normal and cancer patients was under the detection limit. Membrane-associated MT1-MMP of cancer cell lines was also detected after solubilization of the membranes with extraction buffer containing detergent. Additionally, MT1-MMP in clinical samples was examined. Elevated levels of MT1-MMP were detected in homogenate of cancer tissue compared with the levels for normal tissue and the level of MT1-MMP in tumors correlated with the rate of metastasis to the regional lymph nodes. Thus, we demonstrated that this EIA system is the first to measure MTI-MMP in clinical specimens, thus suggesting its useful for diagnosis of cancer or prediction of malignancy.

Complex pattern of membrane type 1 matrix metalloproteinase shedding. Regulation by autocatalytic cells surface inactivation of active enzyme

Membrane type 1 matrix metalloproteinase (MT1-MMP) is a type I transmembrane MMP shown to play a critical role in normal development and in malignant processes. Emerging evidence indicates that MT1-MMP is regulated by a process of ectodomain shedding. Active MT1-MMP undergoes autocatalytic processing on the cell surface, leading to the formation of an inactive 44-kDa fragment and release of the entire catalytic domain. Analysis of the released MT1-MMP forms in various cell types revealed a complex pattern of shedding involving two major fragments of 50 and 18 kDa and two minor species of 56 and 31-35 kDa. Protease inhibitor studies and a catalytically inactive MT1-MMP mutant revealed both autocatalytic (18 kDa) and non-autocatalytic (56, 50, and 31-35 kDa) shedding mechanisms. Purification and sequencing of the 18-kDa fragment indicated that it extends from Tyr(112) to Ala(255). Structural and sequencing data indicate that shedding of the 18-kDa fragment is initiated at the Gly(284)-Gly(285) site, followed by cleavage between the conserved Ala(255) and Ile(256) residues near the conserved methionine turn, a structural feature of the catalytic domain of all MMPs. Consistently, a recombinant 18-kDa fragment had no catalytic activity and did not bind TIMP-2. Thus, autocatalytic shedding evolved as a specific mechanism to terminate MT1-MMP activity on the cell surface by disrupting enzyme integrity at a vital structural site. In contrast, functional data suggest that the non-autocatalytic shedding generates soluble active MT1-MMP species capable of binding TIMP-2. These studies suggest that ectodomain shedding regulates the pericellular and extracellular activities of MT1-MMP through a delicate balance of active and inactive enzyme-soluble fragments.

The role of matrix metalloproteinase genes in glioma invasion: co-dependent and interactive proteolysis

Matrix metalloproteinases (MMPs) are cation-dependent endopeptidases which have been implicated in the malignancy of gliomas. It is thought that the MMPs play a critical role in both metastasis and angiogenesis, and that interference with proteases might therefore deter local tumor dissemination and neovascularization. However, the attempt to control tumor-associated proteolysis will rely on better definition of the normal tissue function of MMPs, an area of study still in its infancy in the central nervous system (CNS). Understanding the role of MMP-mediated proteolysis in the brain relies heavily on advances in other areas of molecular neuroscience, most notably an understanding of extracellular matrix (ECM) composition and the function of cell adhesion molecules such as integrins, which communicate knowledge of ECM composition intracellularly. Recently, protease expression and function has been shown to be strongly influenced by the functional state and signaling properties of integrins. Here we review MMP function and expression in gliomas and present examples of MMP profiling studies in glioma tissues and cell lines by RT-PCR and Western blotting. Co-expression of MMPs and certain integrins substantiates the gathering evidence of a functional intersection between the two, and inhibition studies using recombinant TIMP-1 and integrin antisera demonstrate significant inhibition of glioma invasion in vitro. Use of promising new therapeutic compounds with anti-MMP and anti-invasion effects are discussed. These data underline the importance of functional interaction of MMPs with accessory proteins such as integrins during invasion, and the need for further studies to elucidate the molecular underpinnings of this process.

Regulation of membrane type-matrix metalloproteinases

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

Calmodulin inhibitors trigger the proteolytic processing of membrane type-1 matrix metalloproteinase, but not its shedding in glioblastoma cells

Most transmembrane proteins are subjected to limited proteolysis by cellular proteases, and stimulation of cleavage of membrane proteins by calmodulin (CaM) inhibitors was recently shown. The present study investigated the ability of several CaM inhibitors to induce the proteolytic cleavage of the membrane type-1 matrix metalloproteinase (MT1-MMP) from the cell surface of highly invasive U-87 glioblastoma cells. Although no shedding of a soluble MT1-MMP form was induced by CaM inhibitors in the conditioned media, we showed that these inhibitors induced MT1-MMP proteolytic processing to the 43 kDa membrane-bound inactive form that was not correlated with an increase in proMMP-2 activation but rather with an increase in tissue inhibitor of MMPs (TIMP)-2 expression levels. Moreover, this proteolytic processing was sensitive to marimastat suggesting the involvement of MMPs. Interestingly, CaM inhibitors antagonized concanavalin A- and cytochalasin D-induced proMMP-2 activation, and affected the cytoskeletal actin organization resulting in the loss of migratory potential of U-87 glioblastoma cells. Cytoplasmic tail-truncated MT1-MMP constructs expressed in COS-7 cells were also affected by CaM inhibitors suggesting that these inhibitors stimulated MT1-MMP proteolytic processing by mechanisms independent of the CaM-substrate interaction. We also propose that TIMP-2 acts as a negative regulator of MT1-MMP-dependent activities promoted by the action of CaM inhibitors in U-87 glioblastoma cells.

The role of matrix metalloproteinase genes in glioma invasion: co-dependent and interactive proteolysis

Matrix metalloproteinases (MMPs) are cation-dependent endopeptidases which have been implicated in the malignancy of gliomas. It is thought that the MMPs play a critical role in both metastasis and angiogenesis, and that interference with proteases might therefore deter local tumor dissemination and neovascularization. However, the attempt to control tumor-associated proteolysis will rely on better definition of the normal tissue function of MMPs, an area of study still in its infancy in the central nervous system (CNS). Understanding the role of MMP-mediated proteolysis in the brain relies heavily on advances in other areas of molecular neuroscience, most notably an understanding of extracellular matrix (ECM) composition and the function of cell adhesion molecules such as integrins, which communicate knowledge of ECM composition intracellularly. Recently, protease expression and function has been shown to be strongly influenced by the functional state and signaling properties of integrins. Here we review MMP function and expression in gliomas and present examples of MMP profiling studies in glioma tissues and cell lines by RT-PCR and Western blotting. Co-expression of MMPs and certain integrins substantiates the gathering evidence of a functional intersection between the two, and inhibition studies using recombinant TIMP-1 and integrin antisera demonstrate significant inhibition of glioma invasion in vitro. Use of promising new therapeutic compounds with anti-MMP and anti-invasion effects are discussed. These data underline the importance of functional interaction of MMPs with accessory proteins such as integrins during invasion, and the need for further studies to elucidate the molecular underpinnings of this process.

Expression of human membrane type 1 matrix metalloproteinase in Pichia pastoris

A soluble, C-terminal truncated form of human membrane type 1 matrix metalloproteinase (MT1-MMP) containing the hemopexin-like domain was expressed in Pichia pastoris strain KM71. High levels of secreted protein were detected. Although the c-DNA for the proenzyme (Ala(21)-Glu(523) called DeltaTM-MT1-MMP) was cloned, almost only active MT1-MMP (Tyr(112)-Glu(523)) with identical N-terminus as described for the wild-type enzyme was isolated. This active enzyme was highly purified and characterized with respect to its biochemical properties. The recombinant protein showed high stability against autolysis and proteolysis by yeast proteases, although the calculated in vivo half-life is rather low. The biochemical properties of this new MT1-MMP species were compared with the well-characterized catalytic domain (Ile(114)-Ile(318)) of MT1-MMP. The novel form of MT1-MMP exhibited a higher stability against autolysis than the isolated catalytic domain (Ile(114)-Ile(318)).