Membrane type I matrix metalloproteinase usurps tumor growth control imposed by the three-dimensional extracellular matrix

Dynamic interactions of cortactin and membrane type 1 matrix metalloproteinase at invadopodia: defining the stages of invadopodia formation and function

Metastatic tumor cells that actively migrate and invade surrounding tissues rely on invadopodia to degrade extracellular matrix (ECM) barriers. Invadopodia are membrane protrusions that localize enzymes required for ECM degradation. Little is known about the formation, function, and regulation of invadopodia. Here, we show that invadopodia have two distinct aspects: (a) structural for organizing the cellular actin cytoskeleton to form membrane protrusions and (b) functional for using proteolytic enzyme(s) for ECM degradation. Small interfering RNA (siRNA) inhibition established that organization of invadopodia structure requires cortactin, whereas protease inhibitor studies identified membrane type 1 matrix metalloproteinase (MT1-MMP) as the key invadopodial enzyme responsible for gelatin matrix degradation in the breast carcinoma cell line MDA-MB-231. The inhibition of invadopodial structure assembly by cortactin depletion resulted in a block of matrix degradation due to failure of invadopodia formation. Either protease inhibition or MT1-MMP siRNA depletion moderately decreased the formation of invadopodial structures that were identified as actin-cortactin accumulations at the ventral cell membrane adherent to matrix. The invadopodia that were able to form upon MT1-MMP inhibition or depletion retained actin-cortactin accumulations but were unable to degrade matrix. Examination of cells at different time points as well as live-cell imaging revealed four distinct invadopodial stages: membrane cortactin aggregation at membranes adherent to matrix, MT1-MMP accumulation at the region of cortactin accumulation, matrix degradation at the invadopodia region, and subsequent cortactin dissociation from the area of continued MT1-MMP accumulation associated with foci of degraded matrix. Based on these results, we propose a stepwise model of invadopodia formation and function.

Furin regulates the intracellular activation and the uptake rate of cell surface-associated MT1-MMP

Invasion-promoting membrane type-1 matrix metalloproteinase (MT1-MMP) functions in cancer cells as an oncogene and as a mediator of proteolytic events on the cell surface. To exert its functional activity, MT1-MMP requires proteolytic removal of the prodomain sequence. There are two potential furin cleavage motifs, R(89)-R-P-R-C(93) and R(108)-R-K-R-Y(112), in the prodomain sequence of MT1-MMP. Our data suggest an important role of furin and related proprotein convertases (PCs) in mediating both the activation of MT1-MMP and the levels of functionally active MT1-MMP at the surface of cancer cells. We have determined that the peptide sequence that spans the first cleavage site is susceptible to furin and PC5/6, whereas the second sequence is susceptible to furin and also to PC5/6, PC7 and PACE4. In the structure of the MT1-MMP proenzyme, the R(89)-R-P-R-C(93) site, however, is inaccessible to PCs. Our studies also demonstrated a direct functional link between the activation and the uptake rate of the proenzyme and the enzyme of MT1-MMP. Thus, the uptake rate of the latent MT1-MMP proenzyme noticeably exceeded that of the active enzyme. We conclude that furin and related PCs are the essential components of the specialized cellular machinery that controls the levels of the functionally active, mature, MT1-MMP enzyme on the cell surface to continually support the potency of pericellular proteolysis.

Caveolin-1 deficiency (-/-) conveys premalignant alterations in mammary epithelia, with abnormal lumen formation, growth factor independence, and cell invasiveness

During breast cancer development, the luminal space of the mammary acinar unit fills with proliferating epithelial cells that exhibit growth factor-independence, cell attachment defects, and a more invasive fibroblastic phenotype. Here, we used primary cultures of mammary epithelial cells derived from genetically engineered mice to identify caveolin-1 (Cav-1) as a critical factor for maintaining the normal architecture of the mammary acinar unit. Isolated cultures of normal mammary epithelial cells retained the capacity to generate mammary acini within extracellular matrix. However, those from Cav-1 (-/-) mice exhibited defects in three-dimensional acinar architecture, including disrupted lumen formation and epidermal growth factor-independent growth due to hyperactivation of the p42/44 mitogen-activated protein kinase cascade. In addition, Cav-1-null mammary epithelial cells deprived of exogenous extracellular matrix underwent a spontaneous epithelial-mesenchymal transition, with reorganization of the actin cytoskeleton, and E-cadherin redistribution. Mechanistically, these phenotypic changes appear to be caused by increases in matrix metalloproteinase-2/9 secretion and transforming growth factor-beta/Smad-2 hyperactivation. Finally, loss of Cav-1 potentiated the ability of growth factors (hepatocyte growth factor and basic fibroblast growth factor) to induce mammary acini branching, indicative of a more invasive fibroblastic phenotype. Thus, a Cav-1 deficiency profoundly affects mammary epithelia by modulating the activation state of important signaling cascades. Primary cultures of Cav-1-deficient mammary epithelia will provide a valuable new model to study the spatial/temporal progression of mammary cell transformation.

Inhibition of enzyme activity of and cell-mediated substrate cleavage by membrane type 1 matrix metalloproteinase by newly developed mercaptosulphide inhibitors

MT1-MMP (membrane type 1 matrix metalloproteinase, or MMP-14) is a key enzyme in molecular carcinogenesis, tumour-cell growth, invasion and angiogenesis. Novel and potent MMP inhibitors with a mercaptosulphide zinc-binding functionality have been designed and synthesized, and tested against human MT1-MMP and other MMPs. Binding to the MT1-MMP active site was verified by the competitive-inhibition mechanism and stereochemical requirements. MT1-MMP preferred deep P1' substituents, such as homophenylalanine instead of phenylalanine. Novel inhibitors with a non-prime phthalimido substituent had K(i) values in the low-nanomolar range; the most potent of these inhibitors was tested and found to be stable against air-oxidation in calf serum for at least 2 days. To illustrate the molecular interactions of the inhibitor-enzyme complex, theoretical docking of the inhibitors into the active site of MT1-MMP and molecular minimization of the complex were performed. In addition to maintaining the substrate-specificity pocket (S1' site) van der Waals interactions, the P1' position side chain may be critical for the peptide-backbone hydrogen-bonding network. To test the inhibition of cell-mediated substrate cleavage, two human cancer-cell culture models were used. Two of the most potent inhibitors tested reached the target enzyme and effectively inhibited activation of proMMP-2 by endogenous MT1-MMP produced by HT1080 human fibrosarcoma cells, and blocked fibronectin degradation by prostate cancer LNCaP cells stably transfected with MT1-MMP. These results provide a model for mercaptosulphide inhibitor binding to MT1-MMP that may aid in the design of more potent and selective inhibitors for MT1-MMP.

Fibroblast-derived MT1-MMP promotes tumor progression in vitro and in vivo

Background

Identification of fibroblast derived factors in tumor progression has the potential to provide novel molecular targets for modulating tumor cell growth and metastasis. Multiple matrix metalloproteases (MMPs) are expressed by both mesenchymal and epithelial cells within head and neck squamous cell carcinomas (HNSCCs), but the relative importance of these enzymes and the cell source is the subject of controversy.

Methods

The invasive potential of HNSCC tumor cells were assessed in vitro atop type I collagen gels in coculture with wild-type (WT), MMP-2 null, MMP-9 null or MT1-MMP null fibroblasts. A floor of mouth mouse model of HNSCC was used to assess in vivo growth after co-injection of FaDu tumor cells with MMP null fibroblasts.

Results

Here we report changes in tumor phenotype when FaDu HNSCCs cells are cocultured with WT, MMP-2 null, MMP-9 null or MT1-MMP null fibroblasts in vitro and in vivo. WT, MMP-2 null and MMP-9 null fibroblasts, but not MT1-MMP null fibroblasts, spontaneously invaded into type I collagen gels. WT fibroblasts stimulated FaDu tumor cell invasion in coculture. This invasive phenotype was unaffected by combination with MMP-9 null fibroblasts, reduced with MMP-2 null fibroblasts (50%) and abrogated in MT1-MMP null fibroblasts. Co-injection of FaDu tumor cells with fibroblasts in an orthotopic oral cavity SCID mouse model demonstrated a reduction of tumor volume using MMP-9 and MMP-2 null fibroblasts (48% and 49%, respectively) compared to WT fibroblasts. Consistent with in vitro studies, MT1-MMP null fibroblasts when co-injected with FaDu cells resulted in a 90% reduction in tumor volume compared to FaDu cells injected with WT fibroblasts.

Conclusion

These data suggest a role for fibroblast-derived MMP-2 and MT1-MMP in HNSCC tumor invasion in vitro and tumor growth in vivo.

Functional relevance of urinary-type plasminogen activator receptor-alpha3beta1 integrin association in proteinase regulatory pathways

Squamous cell carcinoma of the oral cavity is characterized by persistent, disorganized expression of integrin alpha3beta1 and enhanced production of urinary-type plasminogen activator (uPA) and its receptor (uPAR) relative to normal oral mucosa. Because multivalent aggregation of alpha3beta1 integrin up-regulates uPA and induces a dramatic co-clustering of uPAR, we explored the hypothesis that lateral ligation of alpha3beta1 integrin by uPAR contributes to uPA regulation in oral mucosal cells. To investigate mechanisms by which uPAR/alpha3beta1 binding enhances uPA expression, integrin-dependent signal activation was assessed. Both Src and ERK1/2 were phosphorylated in response to integrin aggregation, and blocking Src kinase activity completely abrogated ERK1/2 activation and uPA induction, whereas inhibition of epidermal growth factor receptor tyrosine kinase activity did not alter uPA expression. Proteinase up-regulation occurred at the transcriptional level and mutation of the AP1 (-1967) site in the uPA promoter blocked the uPAR/integrin-mediated transcriptional activation. Because uPAR is redistributed to clustered alpha3beta1 integrins, the requirement for uPAR/alpha3beta1 interaction in uPA regulation was assessed. Clustering of alpha3beta1 in the presence of a peptide (alpha325) that disrupts uPAR/alpha3beta1 integrin binding prevented uPA induction. Depletion of cell surface uPAR using small interfering RNA also blocked uPA induction following integrin alpha3beta1 clustering. These results were confirmed using a genetic strategy in which alpha3 null epithelial cells reconstituted with wild type alpha3 integrin, but not a mutant alpha3 unable to bind uPAR, induced uPA expression upon integrin clustering, confirming the critical role of uPAR in integrin-regulated proteinase expression. Disruption of uPAR/alpha3beta1 binding using peptide alpha325 or small interfering RNA blocked filopodia formation and matrix invasion, indicating that this interaction stimulates invasive behavior. Together these data support a model wherein matrix-induced clustering ofalpha3beta1 integrin promotes uPAR/alpha3beta1 interaction, thereby potentiating cellular signal transduction pathways culminating in activation of uPA expression and enhanced uPA-dependent invasive behavior.

MT1-matrix metalloproteinase directs arterial wall invasion and neointima formation by vascular smooth muscle cells

During pathologic vessel remodeling, vascular smooth muscle cells (VSMCs) embedded within the collagen-rich matrix of the artery wall mobilize uncharacterized proteolytic systems to infiltrate the subendothelial space and generate neointimal lesions. Although the VSMC-derived serine proteinases, plasminogen activator and plasminogen, the cysteine proteinases, cathepsins L, S, and K, and the matrix metalloproteinases MMP-2 and MMP-9 have each been linked to pathologic matrix-remodeling states in vitro and in vivo, the role that these or other proteinases play in allowing VSMCs to negotiate the three-dimensional (3-D) cross-linked extracellular matrix of the arterial wall remains undefined. Herein, we demonstrate that VSMCs proteolytically remodel and invade collagenous barriers independently of plasmin, cathepsins L, S, or K, MMP-2, or MMP-9. Instead, we identify the membrane-anchored matrix metalloproteinase, MT1-MMP, as the key pericellular collagenolysin that controls the ability of VSMCs to degrade and infiltrate 3-D barriers of interstitial collagen, including the arterial wall. Furthermore, genetic deletion of the proteinase affords mice with a protected status against neointimal hyperplasia and lumen narrowing in vivo. These studies suggest that therapeutic interventions designed to target MT1-MMP could prove beneficial in a range of human vascular disease states associated with the destructive remodeling of the vessel wall extracellular matrix.

Membrane-type 1 matrix metalloproteinase modulates focal adhesion stability and cell migration

Membrane-type 1 matrix metalloproteinase (MT1-MMP) plays an important role in extracellular matrix-induced cell migration and the activation of extracellular signal-regulated kinase (ERK). We showed here that transfection of the MT1-MMP gene into HeLa cells promoted fibronectin-induced cell migration, which was accompanied by fibronectin degradation and reduction of stable focal adhesions, which function as anchors for actin-stress fibers. MT1-MMP expression attenuated integrin clustering that was induced by adhesion of cells to fibronectin. The attenuation of integrin clustering was abrogated by MT1-MMP inhibition with a synthetic MMP inhibitor, BB94. When cultured on fibronectin, HT1080 cells, which endogenously express MT1-MMP, showed so-called motile morphology with well-organized focal adhesion formation, well-oriented actin-stress fiber formation, and the lysis of fibronectin through trails of cell migration. Inhibition of endogenous MT1-MMP by BB94 treatment or expression of the MT1-MMP carboxyl-terminal domain, which negatively regulates MT1-MMP activity, resulted in the suppression of fibronectin lysis and cell migration. BB94 treatment promoted stable focal adhesion formation concomitant with enhanced phosphorylation of tyrosine 397 of focal adhesion kinase (FAK) and reduced ERK activation. These results suggest that lysis of the extracellular matrix by MT1-MMP promotes focal adhesion turnover and subsequent ERK activation, which in turn stimulates cell migration.

Matrix metalloproteinase-induced genomic instability

Increased expression of matrix metalloproteinases (MMPs) is associated with nearly every tumor type. Although many studies have shown that MMPs can promote malignancy, recent evidence has revealed that MMPs can play a causative role also in the earliest stages of cancer development. A complex story is now emerging in which MMPs not only compromise cell-cell and cell-substratum adhesion processes that impact genomic surveillance mechanisms but also act directly on molecules at the cell surface to stimulate physiological processes that cause genetic alterations. Delineating the mechanisms involved in these processes and identifying how they are coordinated in vivo could aid identification of the crucial contribution of MMPs to tumorigenesis.

Laminin-5 (laminin-332): Unique biological activity and role in tumor growth and invasion

The development and progression of tumor cells is controlled by their interactions with neighboring host cells and a variety of microenvironmental factors including extracellular matrix (ECM) molecules, growth factors and proteinases. Cell-adhesive ECM proteins are a prerequisite for growth and migration of many types of cells. Their interactions with integrins and other cell surface receptors induce intracellular signaling that regulates the actin cytoskeleton and gene expression. The basement membrane protein laminin-5 is a notable cell adhesion molecule, which promotes cellular adhesion and migration much more efficiently than other ECM proteins. There is accumulating evidence that laminin-5 is involved in tumor growth and progression. With special reference to laminin-5, this article reviews the regulatory mechanisms of cellular adhesion and migration by ECM molecules and their significance in tumor progression.

Short hairpin RNA-mediated inhibition of matrix metalloproteinase-1 in MDA-231 cells: effects on matrix destruction and tumor growth

Increased matrix metalloproteinase-1 (MMP-1) expression is associated with advanced stages of breast cancer and may be a predictive marker for the development of invasive disease. In this report, we used short hairpin RNA (shRNA) molecules to investigate whether MMP-1 production in MDA-231 breast cancer cells contributed to the degradation of a collagen matrix or tumor formation in nude mice. We created two groups of MDA-231 cell lines. MDA-231 cells containing a vector producing shRNA specific for MMP-1 had a >90% decrease in MMP-1 mRNA and protein compared with cells containing an empty vector, and blocking MMP-1 expression inhibited the in vitro collagenolytic activity of MDA-231 cells. When the cells were injected into the mammary fat pad, there was no difference in the frequency of tumor formation in mice. However, the average tumor size was larger in mice injected with cells containing the empty vector (1,216 +/- 334 mm3) than in mice injected with cells expressing the MMP-1 shRNA (272 +/- 117 mm3; P = 0.027). We conclude that MMP-1 expression is essential for the ability of MDA-231 cells to invade and destroy a collagen matrix and in vivo experiments suggest an important role for MMP-1 in breast tumor growth.

SPARC expression is associated with impaired tumor growth, inhibited angiogenesis and changes in the extracellular matrix

Secreted protein, acidic and rich in cysteine (SPARC), is a multifunctional matricellular glycoprotein. In vitro, SPARC has antiangiogenic properties, including the ability to inhibit the proliferation and migration of endothelial cells stimulated by bFGF and VEGF. Previously, we demonstrated that platelet-derived SPARC also inhibits angiogenesis and impairs the growth of neuroblastoma tumors in vivo. In the present study, we produced rhSPARC in the transformed human embryonic kidney cell line 293 and show that the recombinant molecule retains its ability to inhibit angiogenesis. Although 293 cell proliferation was not affected by exogenous expression of SPARC in vitro, growth of tumors formed by SPARC-transfected 293 cells was significantly impaired compared to tumors comprised of wild-type cells or 293 cells transfected with a control vector. Consistent with its function as an angiogenesis inhibitor, significantly fewer blood vessels were seen in SPARC-transfected 293 tumors compared to controls, and these tumors contained increased numbers of apoptotic cells. Light microscopy revealed small nests of tumor cells surrounded by abundant stromal tissue in xenografts with SPARC expression, whereas control tumors were comprised largely of neoplastic cells with scant stroma. Mature, covalently cross-linked collagen was detected in SPARC-transfected 293 xenografts but not in control tumors. Our studies suggest that SPARC may regulate tumor growth by inhibiting angiogenesis, inducing tumor cell apoptosis and mediating changes in the deposition and organization of the tumor microenvironment.

Endothelial extracellular matrix: biosynthesis, remodeling, and functions during vascular morphogenesis and neovessel stabilization

The extracellular matrix (ECM) is critical for all aspects of vascular biology. In concert with supporting cells, endothelial cells (ECs) assemble a laminin-rich basement membrane matrix that provides structural and organizational stability. During the onset of angiogenesis, this basement membrane matrix is degraded by proteinases, among which membrane-type matrix metalloproteinases (MT-MMPs) are particularly significant. As angiogenesis proceeds, ECM serves essential functions in supporting key signaling events involved in regulating EC migration, invasion, proliferation, and survival. Moreover, the provisional ECM serves as a pliable scaffold wherein mechanical guidance forces are established among distal ECs, thereby providing organizational cues in the absence of cell-cell contact. Finally, through specific integrin-dependent signal transduction pathways, ECM controls the EC cytoskeleton to orchestrate the complex process of vascular morphogenesis by which proliferating ECs organize into multicellular tubes with functional lumens. Thus, the composition of ECM and therefore the regulation of ECM degradation and remodeling serves pivotally in the control of lumen and tube formation and, finally, neovessel stability and maturation.

Discoidin domain receptor 2 mediates tumor cell cycle arrest induced by fibrillar collagen

During malignant invasion tumor cells establish contact with extracellular matrix proteins, including fibrillar collagen. In addition to providing a physical barrier against invasion, fibrillar collagen also restricts cell proliferation. It has been assumed that the growth regulatory activity of fibrillar collagen is the result of an indirect restrictive effect on cell spreading and cytoskeletal organization. Here we provide evidence for a direct inhibitory effect of fibrillar collagen on proliferation of human melanoma and fibrosarcoma cells that involves activation of the tyrosine kinase discoidin domain receptor 2 and is independent of effects on cell spreading. Cells plated in the presence of fibrillar collagen were growth arrested in the G0/G1 phase of the cell cycle. However treatment with the tyrosine kinase inhibitor genistein, down-regulation of discoidin domain receptor 2, or collagen deglycosylation that prevents discoidin domain receptor 2 activation allowed cells to enter the cell cycle in the presence of fibrillar collagen without a requirement for spreading and actin organization. Our data provide evidence for a novel direct mechanism by which cell contact with fibrillar collagen restricts proliferation.

Stromagenesis: the changing face of fibroblastic microenvironments during tumor progression

During tumorigenesis, reciprocal changes in stromal fibroblasts and tumor cells induce changes to the neoplastic microenvironmental landscape. In stromagenesis, both the complex network of bi-directional stromal fibroblastic signaling pathways and the stromal extracellular matrix are modified. The presence of a 'primed' stroma during the early, reversible stage of tumorigenesis is optimal for stromal-directed therapeutic intervention. Three-dimensional (3D) cell culture systems have been developed that mimic the in vivo microenvironment. These systems provide unique experimental tools to identify early alterations in stromagenesis that are supportive of tumor progression with the ultimate goal of blocking neoplastic permissiveness and restoring normal phenotypes.

Competitive disruption of the tumor-promoting function of membrane type 1 matrix metalloproteinase/matrix metalloproteinase-14 in vivo

Membrane type 1 matrix metalloproteinase (MT1-MMP) is a potent modulator of the pericellular environment and promotes tumor cell invasion and proliferation in many types of tumor. The activation of proMMP-2 and processing of collagen I by MT1-MMP have been thought to be important for its tumor-promoting function. These activities can be inhibited by mutant forms of MT1-MMP lacking the catalytic domain. However, the effect of such dominant-negative mutants has never been evaluated in vivo. Various mutants lacking the catalytic domain (dCAT) were prepared and confirmed to inhibit MT1-MMP activity in human fibrosarcoma HT1080 cells, and tumor cells expressing these mutants were implanted s.c. into nude mice to monitor tumor formation. Only the membrane-anchored form of a dCAT construct through the transmembrane domain [dCAT(1)] showed potent antitumor activity not only in HT1080 cells but also in gastric carcinoma MKN28 and MKN45 cells expressing MT1-MMP. A soluble form of dCAT lacking the transmembrane domain did not show such activity. The expression of dCAT(1) in MKN28 or MKN45 further prevented the metastatic spread of tumor cells into the peritoneal cavity; however, dCAT(1) showed no effect against TMK-1, another gastric carcinoma cell line expressing no MT1-MMP. It is of note that the tumorigenicity of TMK-1 cells enhanced by MT1-MMP overexpression was, in turn, canceled by the additional expression of dCAT(1). Thus, MT1-MMP expressed in tumor cells seems to play a pivotal role in tumor growth in mice. The results also suggest new possibilities to abrogate the tumor-promoting function of MT1-MMP other than the conventional protease inhibitor-based approach.

Expression pattern of four membrane-type matrix metalloproteinases in the normal and diseased mouse mammary gland

Both mammary gland development and mammary carcinogenesis involve extensive remodeling of the mammary gland extracellular matrix. The expression of four membrane-type matrix metalloproteinases (MT-MMPs) with matrix remodeling potential in development and tumorigenesis was evaluated by in-situ hybridization on mouse mammary gland sections. MT1-MMP and MT3-MMP were found in the mammary stroma mainly around epithelial structures in both developing and mature mammary gland. In contrast, MT2-MMP was found exclusively in the mammary epithelium. Lactating gland expressed none of the examined MT-MMPs. Mammary gland tumors expressed MT1-MMP, MT2-MMP, and MT3-MMP while MT4-MMP was not expressed in any developmental or cancerous stage analyzed here. Our results suggest that MT1-MMP, MT2-MMP, and MT3-MMP may be involved in remodeling of both the normal and diseased mammary gland either directly or indirectly by activation of other MMPs.

The transmembrane domain is essential for the microtubular trafficking of membrane type-1 matrix metalloproteinase (MT1-MMP)

Membrane type-1 matrix metalloproteinase (MT1-MMP) degrades the extracellular matrix, initiates the activation pathway of soluble MMPs and regulates the functionality of cell adhesion signaling receptors, thus playing an important role in many cell functions. Intracellular transport mechanisms, currently incompletely understood, regulate the presentation of MT1-MMP at the cell surface. We have focused our efforts on identifying these mechanisms. To understand the transport of MT1-MMP across the cell, we used substitution and deletion mutants, the trafficking of which was examined using antibody uptake and Chariot delivery experiments. Our experiments have demonstrated that the microtubulin cytoskeleton and the centrosomes (the microtubulin cytoskeleton-organizing centers) are essential for the trafficking and the internalization of MT1-MMP. We determined that after reaching the plasma membrane, MT1-MMP is internalized in the Rab-4-positive recycling endosomes and the Rab-11-positive pericentrosomal recycling endosomes. The microtubular trafficking causes the protease to accumulate in the pericentrosomal region of the cell. We believe that the presence of the transmembrane domain is required for the microtubular vesicular trafficking of MT1-MMP because the soluble mutants are not presented at the cell surface and they are not delivered to the centrosomes. The observed transport mechanisms provide a vehicle for the intracellular targets and, accordingly, for an intracellular cleavage function of MT1-MMP in malignant cells, which routinely overexpress this protease.

Mechanism of metastasis by membrane type 1-matrix metalloproteinase in hepatocellular carcinoma

AIM: To investigate the precise role of membrane type 1-matrix metalloproteinase (MT1-MMP) in hepatocellular carcinoma (HCC) metastasis.

METHODS: Human HCC cells Hep3B with overexpression of MT1-MMP were established by stable transfection, and compared with control cells carrying the empty vector. Cells were examined in vivo for their differences in the metastatic ability of athymic nude mice, and analyzed in vitro for their differences in invasion ability by invasion chamber coated with Matrigel, adhesion towards collagen I and migration through culture chamber. Cell proliferation and apoptosis in adherent and suspension status were evaluated by MTT and flow cytometry analysis.

RESULTS: We found that overexpression of MT1-MMP could increase intrahepatic metastasis in nude mice with orthotopic implantation of HCC cells (incidence of 100% [MT1-MMP transfectants] vs 40% [vector control transfectants], P<0.05). MT1-MMP could also enhance cell invasion through Matrigel (107.7 vs 39.3 cells/field, P<0.001), adhesion towards matrix (0.30 vs 0.12 absorbance unit at 540 nm, P<0.001), cell migration (89.3 vs 39.0 cells/field, P<0.001), and cell proliferation (24.3 vs 40.5 h/doubling, P<0.001). We also observed that MT1-MMP supported cell survival (71.4% vs 23.9%, P<0.001) with reduced apoptosis (43.7% vs 51.0%, P<0.05) in an attachment-free environment.

CONCLUSION: MT1-MMP overexpression could enhance metastasis. In addition to its active role in matrix degradation during tumor invasion, MT1-MMP enhances tumor cell survival upon challenge of detachment, which is important during metastasis when cells enter the circulation.

Centrosomal pericentrin is a direct cleavage target of membrane type-1 matrix metalloproteinase in humans but not in mice: potential implications for tumorigenesis

Membrane type-1 matrix metalloproteinase (MT1-MMP) exhibits distinctive and important pericellular cleavage functions. Recently, we determined that MT1-MMP was trafficked to the centrosomes in the course of endocytosis. Our data suggested that the functionally important, integral, centrosomal protein, pericentrin-2, was a cleavage target of MT1-MMP in human and in canine cells and that the sequence of the cleavage sites were ALRRLLG1156 downward arrow L1157FG and ALRRLLS2068 downward arrow L2069FG, respectively. The presence of Asp-948 at the P1 position inactivated the corresponding site (ALRRLLD948-L949FGD) in murine pericentrin. To confirm that MT1-MMP itself cleaves pericentrin directly, rather than indirectly, we analyzed the cleavage of the peptides that span the MT1-MMP cleavage site. In addition, we analyzed glioma U251 cells, which co-expressed MT1-MMP with the wild type murine pericentrin and the D948G mutant. We determined that the D948G mutant that exhibited the cleavage sequence of human pericentrin was sensitive to MT1-MMP, whereas unmodified murine pericentrin was resistant to proteolysis. Taken together, our results confirm that MT1-MMP cleaves pericentrin-2 in humans but not in mice and that mouse models of cancer probably cannot be used to critically examine MT1-MMP functionality.

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.

Akt1 regulates pathological angiogenesis, vascular maturation and permeability in vivo

Akt kinases control essential cellular functions, including proliferation, apoptosis, metabolism and transcription, and have been proposed as promising targets for treatment of angiogenesis-dependent pathologies, such as cancer and ischemic injury. But their precise roles in neovascularization remain elusive. Here we show that Akt1 is the predominant isoform in vascular cells and describe the unexpected consequences of Akt1 knockout on vascular integrity and pathological angiogenesis. Angiogenic responses in three distinct in vivo models were enhanced in Akt1(-/-) mice; these enhanced responses were associated with impairment of blood vessel maturation and increased vascular permeability. Although impaired vascular maturation in Akt1(-/-) mice may be attributed to reduced activation of endothelial nitric oxide synthase (eNOS), the major phenotypic changes in vascular permeability and angiogenesis were linked to reduced expression of two endogenous vascular regulators, thrombospondins 1 (TSP-1) and 2 (TSP-2). Re-expression of TSP-1 and TSP-2 in mice transplanted with wild-type bone marrow corrected the angiogenic abnormalities in Akt1(-/-) mice. These findings establish a crucial role of an Akt-thrombospondin axis in angiogenesis.

Cellular mechanisms for low-dose ionizing radiation-induced perturbation of the breast tissue microenvironment

Radiation exposure is an important form of environmental carcinogen and has been associated with increased risk of breast cancer. Epigenetic events, especially those involving alterations in the breast stromal microenvironment, may play an important role in radiation-induced carcinogenesis but remain not well understood. We here show that human mammary stromal fibroblasts respond to protracted low-dose ionizing radiation exposures by displaying a senescence-like phenotype. Using a three-dimensional coculture system to model the interactions of different mammary cell types with their neighbors and with their environment, we provide a direct experimental proof that ionizing radiation-induced senescence-like fibroblasts significantly perturb the mammary stromal microenvironment, which is highlighted by impaired formation of pseudopodia networks due to marked cytoskeletal alterations in senescence-like fibroblasts and increased extracellular matrix degradation because of the up-regulation of multiple secreted matrix metalloproteinases. Within such a perturbed environment, mammary ductal morphogenesis is completely disrupted and epithelial cells instead grow into enlarged cystic structures, which further develop and become disorganized cell masses on inactivation of cellular death pathways. Breast carcinoma cells growing in such an environment are enabled to fully express their malignant potential as evidenced by the alpha6beta4 integrin/phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin pathway-dependent invasive growth. Our results suggest that ionizing radiation, in addition to causing gene mutations in epithelial cells, can contribute to breast carcinogenesis by perturbing the tissue microenvironment that leads to dysregulated cell-cell and cell-matrix interactions.

Upregulated MT1-MMP/TIMP-2 axis in the TSU-Pr1-B1/B2 model of metastatic progression in transitional cell carcinoma of the bladder

Muscle invasive transitional cell carcinoma (TCC) of the bladder is associated with a high frequency of metastasis, resulting in poor prognosis for patients presenting with this disease. Models that capture and demonstrate step-wise enhancement of elements of the human metastatic cascade on a similar genetic background are useful research tools. We have utilized the transitional cell carcinoma cell line TSU-Pr1 to develop an in vivo experimental model of bladder TCC metastasis. TSU-Pr1 cells were inoculated into the left cardiac ventricle of SCID mice and the development of bone metastases was monitored using high resolution X-ray. Tumor tissue from a single bone lesion was excised and cultured in vitro to generate the TSU-Pr1-B1 subline. This cycle was repeated with the TSU-Pr1-B1 cells to generate the successive subline TSU-Pr1-B2. DNA profiling and karyotype analysis confirmed the genetic relationship of these three cell lines. In vitro, the growth rate of these cell lines was not significantly different. However, following intracardiac inoculation TSU-Pr1, TSU-Pr1-B1 and TSU-Pr1-B2 exhibited increasing metastatic potential with a concomitant decrease in time to the onset of radiologically detectable metastatic bone lesions. Significant elevations in the levels of mRNA expression of the matrix metalloproteases (MMPs) membrane type 1-MMP (MT1-MMP), MT2-MMP and MMP-9, and their inhibitor, tissue inhibitor of metalloprotease-2 (TIMP-2), across the progressively metastatic cell lines, were detected by quantitative PCR. Given the role of MT1-MMP and TIMP-2 in MMP-2 activation, and the upregulation of MMP-9, these data suggest an important role for matrix remodeling, particularly basement membrane, in this progression. The TSU-Pr1-B1/B2 model holds promise for further identification of important molecules.

Membrane type 1 matrix metalloprotease cleaves laminin-10 and promotes prostate cancer cell migration

Disruption of the extracellular matrix by proteases is crucial for tumor invasion. Laminin-10 (Ln-10) has previously been identified as a substrate for cell migration and cell adhesion, and is present in the basal lamina (BL) of both normal prostate and prostate cancer. Here, we investigate a role for membrane type 1 matrix metalloprotease (MT1-MMP) in modifying this Ln-10-rich BL. MT1-MMP is a transmembrane member of the MMP family that has been demonstrated to be upregulated as prostate cancer progresses from normal to prostate intraepithelial neoplasia to invasive cancer, suggesting a role for MT1-MMP in the invasion of prostate cancer. We show that MT1-MMP cleaves the alpha5 chain of purified human Ln-10 from its 350-kDa form into 310-, 190-, 160-, and 45-kDa fragments. This cleavage causes a decrease in DU-145 prostate cancer cell adhesion to purified Ln-10, and an increase in transmigration of DU-145 cells through cleaved Ln-10. We also show that prostate cancer cells expressing membrane-bound MT1-MMP cleave the alpha5 chain of Ln-10. Ln alpha5-chain cleavage is also observed in human prostate cancer tissues. These findings suggest that prostate cancer cells expressing high levels of MT1-MMP have increased invasive potential through their ability to degrade and invade Ln-10 barriers.

Deregulated matriptase causes ras-independent multistage carcinogenesis and promotes ras-mediated malignant transformation

Overexpression of the type II transmembrane serine protease matriptase is a highly consistent feature of human epithelial tumors. Here we show that matriptase possesses a strong oncogenic potential when unopposed by its endogenous inhibitor, HAI-1. Modest orthotopic overexpression of matriptase in the skin of transgenic mice caused spontaneous squamous cell carcinoma and dramatically potentiated carcinogen-induced tumor formation. Matriptase-induced malignant conversion was preceded by progressive interfollicular hyperplasia, dysplasia, follicular transdifferentiation, fibrosis, and dermal inflammation. Furthermore, matriptase induced activation of the pro-tumorigenic PI3K-Akt signaling pathway. This activation was frequently accompanied by H-ras or K-ras mutations in carcinogen-induced tumors, whereas matriptase-induced spontaneous carcinoma formation occurred independently of ras activation. Increasing epidermal HAI-1 expression completely negated the oncogenic effects of matriptase. The data implicate dysregulated matriptase expression in malignant epithelial transformation.

Loss of intercellular adhesion activates a transition from low- to high-grade human squamous cell carcinoma

The relationship between loss of intercellular adhesion and the biologic properties of human squamous cell carcinoma is not well understood. We investigated how abrogation of E-cadherin-mediated adhesion influenced the behavior and phenotype of squamous cell carcinoma in 3D human tissues. Cell-cell adhesion was disrupted in early-stage epithelial tumor cells (HaCaT-II-4) through expression of a dominant-negative form of E-cadherin (H-2Kd-Ecad). Three-dimensional human tissue constructs harboring either H-2Kd-Ecad-expressing or control II-4 cells (pBabe, H-2Kd-EcadDeltaC25) were cultured at an air-liquid interface for 8 days and transplanted to nude mice; tumor phenotype was analyzed 2 days and 2 and 4 weeks later. H-2Kd-Ecad-expressing tumors demonstrated a switch to a high-grade aggressive tumor phenotype characterized by poorly differentiated tumor cells that infiltrated throughout the stroma. This high-grade carcinoma revealed elevated cell proliferation in a random pattern, loss of keratin 1 and diffuse deposition of laminin 5 gamma2 chain. When II-4 cell variants were seeded into type I collagen gels as an in vitro assay for cell migration, we found that only E-cadherin-deficient cells detached, migrated as single cells and expressed N-cadherin. Function-blocking studies demonstrated that this migration was matrix metalloproteinase-dependent, as GM-6001 and TIMP-2, but not TIMP-1, could block migration. Gene expression profiles revealed that E-cadherin-deficient II-4 cells demonstrated increased expression of proteases and cell-cell and cell-matrix proteins. These findings showed that loss of E-cadherin-mediated adhesion plays a causal role in the transition from low- to high-grade squamous cell carcinomas and that the absence of E-cadherin is an important prognostic marker in the progression of this disease.

Membrane-type 1 matrix metalloproteinase is required for normal alveolar development

Matrix metalloproteinases (MMPs) are expressed during lung development, but their role may be limited, as mice deficient in MMP-3, 7, 9, or 12 develop a normal adult lung. Because membrane-type 1 matrix metalloproteinase (MT1-MMP) is expressed in the developing lung epithelium, we examined the lung structure of MT1-MMP-deficient (-/-) mice. Branching morphogenesis was normal, but alveolar development was abnormal in the MT1-MMP-/- lungs with 40% less alveolar surface area at 1 month (P < 0.01). MT1-MMP-/- airways and alveoli had an abnormal ultrastructural appearance, but epithelial cell differentiation markers were distributed similarly in both strains. There was no evidence of excess extracellular matrix deposition or inflammation at the time points examined. In contrast, by adulthood MMP-2-/- mice had normal alveolar size and structure, indicating normal alveolar development was not dependent on the ability of MT1-MMP to activate pro-MMP-2. These data indicate that MT1-MMP is required for normal lung development.

Matrix metalloproteinases contribute to insulin insufficiency in Zucker diabetic fatty rats

To assess the molecular changes associated with pancreatic beta-cell dysfunction occurring during the onset of type 2 diabetes, we profiled pancreatic islet mRNAs from diabetic male and high-fat-fed female Zucker diabetic fatty (ZDF) rats and their nondiabetic lean counterparts on custom islet-specific oligonucleotide arrays. The most prominent changes in both the male and female models of type 2 diabetes were increases in the mRNAs encoding proteases and extracellular matrix components that are associated with tissue remodeling and fibrosis. The mRNAs for metalloproteinase (MMP)-2, -12, and -14 were sharply increased with the onset of islet dysfunction and diabetes. Zymography of islet extracts revealed a concurrent, >10-fold increase in MMP-2 protease activity in islets from 9-week-old male ZDF rats. Treatment of female ZDF rats receiving a diabetogenic diet with PD166793, a broad-spectrum MMP inhibitor, substantially prevented diabetes. The effect of this compound was due in part to marked beta-cell expansion. These studies indicate that MMPs contribute to islet fibrosis and insulin insufficiency in ZDF rats. Class-targeted protease inhibitors should be explored for their potential therapeutic utility in preservation of beta-cell mass in type 2 diabetes.

Modelling glandular epithelial cancers in three-dimensional cultures

Little is known about how the genotypic and molecular abnormalities associated with epithelial cancers actually contribute to the histological phenotypes observed in tumours in vivo. 3D epithelial culture systems are a valuable tool for modelling cancer genes and pathways in a structurally appropriate context. Here, we review the important features of epithelial structures grown in 3D basement membrane cultures, and how such models have been used to investigate the mechanisms associated with tumour initiation and progression.

Intracellular collagen degradation mediated by uPARAP/Endo180 is a major pathway of extracellular matrix turnover during malignancy

We recently reported that uPARAP/Endo180 can mediate the cellular uptake and lysosomal degradation of collagen by cultured fibroblasts. Here, we show that uPARAP/Endo180 has a key role in the degradation of collagen during mammary carcinoma progression. In the normal murine mammary gland, uPARAP/Endo180 is widely expressed in periductal fibroblast-like mesenchymal cells that line mammary epithelial cells. This pattern of uPARAP/Endo180 expression is preserved during polyomavirus middle T-induced mammary carcinogenesis, with strong uPARAP/Endo180 expression by mesenchymal cells embedded within the collagenous stroma surrounding nests of uPARAP/Endo180-negative tumor cells. Genetic ablation of uPARAP/Endo180 impaired collagen turnover that is critical to tumor expansion, as evidenced by the abrogation of cellular collagen uptake, tumor fibrosis, and blunted tumor growth. These studies identify uPARAP/Endo180 as a key mediator of collagen turnover in a pathophysiological context.

Homeobox D10 Induces Phenotypic Reversion of Breast Tumor Cells in a Three-Dimensional Culture Model

Homeobox (Hox) genes are master regulatory genes that direct organogenesis and maintain differentiated tissue function. We previously reported that HoxD10 helps to maintain a quiescent, differentiated phenotype in endothelial cells by suppressing expression of genes involved in remodeling the extracellular matrix and cell migration. Here we investigated whether HoxD10 could also promote or maintain a differentiated phenotype in epithelial cells. We observed that HoxD10 expression is progressively reduced in epithelial cells as malignancy increases in both breast and endometrial tumors. Retroviral gene transfer to restore expression of HoxD10 in the malignant breast tumor cells MDA-MB-231 significantly impaired migration, and when these cells were cultured in a three-dimensional laminin-rich basement membrane (3DlrBM) model, they formed polarized, acinar structures. This phenotypic reversion was accompanied by decreased alpha3 integrin expression and reduced proliferation. Importantly, expression of HoxD10 in the MDA-MB-231 cells inhibited their ability to form tumors in mouse xenografts. Taken together, our results suggest that HoxD10 has tumor-suppressive functions for mammary epithelial cells.

Accelerated dendritic-cell migration and T-cell priming in SPARC-deficient mice

On their path to draining lymph nodes, epidermal Langerhans cells traverse collagen-dense connective tissue before reaching lymphatic vessels. The matricellular protein SPARC (secreted protein, acidic and rich in cysteine), which is induced during inflammation and tissue repair, organizes collagen deposition in tissue stroma. We analyzed Langerhans cell and dendritic-cell migration and its impact on T-cell priming in SPARC-null (SPARC–/–) and SPARC-sufficient (SPARC+/+) mice. Although the same number of Langerhans cells populate the ear skin of SPARC–/– and SPARC+/+ mice, more Langerhans cells were found in the lymph nodes draining antigen-sensitized ears of SPARC–/– mice and significantly more Langerhans cells migrated from null-mice-derived ear skin explants. Such favored Langerhans cell migration is due to the host environment, as demonstrated by SPARC+/+&gt;SPARC–/– and reciprocal chimeras, and have a profound influence on T-cell priming. Contact-, delayed type-hypersensitivity and naive T-cell receptor-transgenic T-cell priming, together indicate that the lack of SPARC in the environment accelerates the onset of T-cell priming by hastening Langerhans cell/dendritic-cell migration.

Functions for proteinases in the ovulatory process

The ovary is a unique and dynamic organ in respect to rapid and extensive degrees of tissue development and remodeling that are periodically repeated in the female reproductive activity. Ovulation is a directed and sequential process accompanied by broad-spectrum proteolysis and culminates in the follicular rupture to release the matured oocyte. This review will focus on the potential roles of six representative proteinases that are involved in various aspects of ovulatory processes: matrix metalloproteinases (MMPs), plasminogen activator (PA)/plasmin, a disintegrin and metalloproteinase domain with thrombospondin motif (ADAMTS), cathepsin-L, pregnancy-associated plasma protein-A (PAPP-A), and bone morphogenetic protein 1/mammalian Tolloid (BMP-1/mTld). Based on the studies of expression and function, these selected proteinases provide and share diverse functions ranging from cleaving components of the extracellular matrix (ECM) to modulating non-ECM molecules, such as various growth factors and their binding proteins. Consistently, the genetic deletion of each individual gene in mice shows their functional overlap in the reproductive activity.

Expression of Membrane Type 1 Matrix Metalloproteinase Is Associated with Cervical Carcinoma Progression and Invasion

Membrane type 1 matrix metalloproteinase (MT1-MMP) is frequently expressed by cancer cells and is believed to play an important role in cancer cell invasion and metastasis. However, little is known about the role of MT1-MMP in mediating invasiveness of cervical cancer cells. In this study, we examined MT1-MMP expression in 58 primary human cervical tissue specimens, including normal cervix, low-grade squamous intraepithelial lesions (LSIL), high-grade SILs (HSIL), and invasive carcinomas. We also evaluated MT1-MMP, MMP-2, and tissue inhibitor of metalloproteinase-2 expression in several cervical cancer-derived cell lines, human papillomavirus (HPV)-immortalized keratinocytes, and keratinocytes derived from a LSIL. Using in situ hybridization techniques to study the cervical tissue specimens, we found that MT1-MMP expression increases with cervical tumor progression (Spearman correlation coefficient = 0.66; P < 0.0001, exact test). Specifically, MT1-MMP expression is very low or absent in normal cervix and LSILs, is readily detectable in HSILs, and is very strongly expressed in nearly all invasive carcinomas. Most but not all cervical cancer-derived cell lines also expressed significant levels of MT1-MMP and MMP-2. Constitutive expression of exogenous MT1-MMP in cervical carcinoma-derived cells and HPV-immortalized keratinocytes with low endogenous levels of MT1-MMP induced invasiveness in collagen I, but this effect was not observed in LSIL-derived keratinocytes. Our results show that MT1-MMP is a key enzyme mediating cervical cancer progression. However, MT1-MMP alone is not always sufficient for inducing keratinocyte invasiveness at least in the collagen I invasion assay used in this study. Further studies of gene expression in preinvasive and invasive cervical cancers should assist with identification of additional critical factors mediating cervical cancer progression.

Membrane type-matrix metalloproteinases and tumor progression

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

A Causative Role of Stromelysin-3 in Extracellular Matrix Remodeling and Epithelial Apoptosis during Intestinal Metamorphosis in Xenopus laevis

The matrix metalloproteinases are a family of proteases capable of degrading various components of the extracellular matrix. Expression studies have implicated the involvement of the matrix metalloproteinase stromelysin-3 (ST3) in tissue remodeling and pathogenesis. However, the in vivo role of ST3 has been difficult to study because of a lack of good animal models. Here we used intestinal remodeling during thyroid hormone-dependent metamorphosis of Xenopus laevis as a model to investigate in vivo the role of ST3 during postembryonic organ development in vertebrates. We generated transgenic tadpoles expressing ST3 under control of a heat shock-inducible promoter. We showed for the first time in vivo that wild type ST3 but not a catalytically inactive mutant was sufficient to induce larval epithelial cell death and fibroblast activation, events that normally occur only in the presence of thyroid hormone. We further demonstrated that these changes in cell fate are associated with altered gene expression in the intestine and remodeling of the intestinal basal lamina. These results thus suggest that ST3 regulates cell fate and tissue morphogenesis through direct or indirect ECM remodeling.

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.

Membrane type-1 matrix metalloproteinase (MT1-MMP) exhibits an important intracellular cleavage function and causes chromosome instability

Elevated expression of membrane type-1 matrix metalloproteinase (MT1-MMP) is closely associated with malignancies. There is a consensus among scientists that cell surface-associated MT1-MMP is a key player in pericellular proteolytic events. Now we have identified an intracellular, hitherto unknown, function of MT1-MMP. We demonstrated that MT1-MMP is trafficked along the tubulin cytoskeleton. A fraction of cellular MT1-MMP accumulates in the centrosomal compartment. MT1-MMP targets an integral centrosomal protein, pericentrin. Pericentrin is known to be essential to the normal functioning of centrosomes and to mitotic spindle formation. Expression of MT1-MMP stimulates mitotic spindle aberrations and aneuploidy in non-malignant cells. Volumes of data indicate that chromosome instability is an early event of carcinogenesis. In agreement, the presence of MT1-MMP activity correlates with degraded pericentrin in tumor biopsies, whereas normal tissues exhibit intact pericentrin. We believe that our data show a novel proteolytic pathway to chromatin instability and elucidate the close association of MT1-MMP with malignant transformation.

Oxidative stress stimulates proliferation and invasiveness of hepatic stellate cells via a MMP2-mediated mechanism

Experimental evidence indicates that reactive oxygen species (ROS) are involved in the development of hepatic fibrosis; they induce hepatic stellate cells (HSC) proliferation and collagen synthesis. To address the role of matrix metalloproteinase (MMP)-2 in promoting HSC proliferation during hepatic injury, we investigated whether oxidative stress modulates the growth and invasiveness of HSC by influencing MMP-2 activation. Cell invasiveness and proliferation, which were studied using Boyden chambers and by counting cells under a microscope, were evaluated after treatment with a superoxide-producing system, xanthine plus xanthine oxidase (X/XO), in the presence or absence of antioxidants and MMP inhibitors. Expression and activation of MMP-2 were evaluated via gel zymography, immunoassay, and ribonuclease protection assay. The addition of X/XO induced proliferation and invasiveness of human HSC in a dose-dependent manner. The addition of antioxidants as well as MMP-2-specific inhibitors impaired these phenomena. X/XO treatment increased MMP-2 expression and secretion appreciably and significantly induced members of its activation complex, specifically membrane-type 1 MMP and tissue inhibitor metalloproteinase 2. To study the intracellular signaling pathways involved in X/XO-induced MMP-2 expression, we evaluated the effects of different kinase inhibitors. The inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidyl inositol 3-kinase (PI3K) abrogated X/XO-elicited MMP-2 upregulation and completely prevented X/XO-induced growth and invasiveness of HSC. In conclusion, our findings suggest that MMP-2 is required for the mitogenic and proinvasive effects of ROS on HSC and demonstrate that ERK1/2 and PI3K are the main signals involved in ROS-mediated MMP-2 expression.

Tissue inhibitor of metalloproteinase-2 (TIMP-2) expression during cardiac neural crest cell migration and its role in proMMP-2 activation

Matrix metalloproteinases (MMPs) are important mediators of neural crest (NC) cell migration. Here, we examine the distribution of tissue inhibitor of metalloproteinase (TIMP) -2 and TIMP-3 and test whether manipulating TIMP levels alters chicken cardiac NC cell migration. TIMP-2 mRNA is expressed at stage 11 in the neural epithelium and only in migrating cardiac NC cells. TIMP-3 mRNA is expressed only in the notochord at stage 8 and later in the outflow tract myocardium. Exogenous TIMP-2 increases NC motility in vitro at low concentrations but has no effect when concentrations are increased. In vitro, NC cells express membrane type-1 matrix metalloproteinase (MT1-MMP) and TIMP-2 and they secrete and activate proMMP-2. Antisense TIMP-2 oligonucleotides block proMMP-2 activation, decrease NC cell migration from explants, and perturb NC morphogenesis in ovo. Because TIMP-2 is required for activation of proMMP-2 by MT1-MMP, this finding suggests TIMP-2 expression by cardiac NC cells initiates proMMP-2 activation important for their migration.

Tumorigenic Heterogeneity in Cancer Stem Cells Evolved from Long-term Cultures of Telomerase-Immortalized Human Mesenchymal Stem Cells

Long-term cultures of telomerase-transduced adult human mesenchymal stem cells (hMSC) may evolve spontaneous genetic changes leading to tumorigenicity in immunodeficient mice (e.g., hMSC-TERT20). We wished to clarify whether this unusual phenotype reflected a rare but dominant subpopulation or if the stem cell origin allowed most cells to behave as cancer stem cells. Cultures of the hMSC-TERT20 strain at population doubling 440 were highly clonogenic (94%). From 110 single-cell clones expanded by 20 population doublings, 6 underwent detailed comparison. Like the parental population, each clone had approximately 1.2 days doubling time with loss of contact inhibition. All retained 1,25-(OH)(2) vitamin D(3)-induced expression of osteoblastic markers: collagen type I, alkaline phosphatase, and osteocalcin. All shared INK4a/ARF gene locus deletion and epigenetic silencing of the DBCCR1 tumor suppressor gene. Despite in vitro commonality, only four of six clones shared the growth kinetics and 100% tumorigenicity of the parental population. In contrast, one clone consistently formed latent tumors and the other established tumors with only 30% penetrance. Changing the in vitro microenvironment to mimic in vivo growth aspects revealed concordant clonal heterogeneity. Latent tumor growth correlated with extracellular matrix entrapment of multicellular spheroids and high procollagen type III expression. Poor tumorigenicity correlated with in vitro serum dependence and high p27(Kip1) expression. Aggressive tumorigenicity correlated with good viability plus capillary morphogenesis on serum starvation and high cyclin D1 expression. Thus, hMSC-TERT20 clones represent cancer stem cells with hierarchical tumorigenicity, providing new models to explore the stem cell hypothesis for cancer.

Extracellular Matrix Metalloprotease Inducer–Expressing Head and Neck Squamous Cell Carcinoma Cells Promote Fibroblast-Mediated Type I Collagen Degradation In vitro

Until recently, tumor progression has been considered a multistep process defined by tumor cell mutations and the importance of the surrounding stroma poorly understood. It is now recognized that matrix-degrading enzymes that promote tumor cell invasion are elaborated by both tumor cells and fibroblasts in vivo. To determine the relative role of tumor cell-derived proteases compared with fibroblast-derived proteases, coculture experiments were done with each cell type using an in vitro model of type I collagen degradation. Head and neck squamous cell carcinoma cells in coculture with normal dermal fibroblasts showed matrix degradation, but neither cell type alone produced this effect. Manipulating the in vitro coculture environment showed that collagenolysis in this model was a result of fibroblast-derived matrix metalloproteases (MMP). To explore the possible role of extracellular matrix metalloprotease inducer (EMMPRIN) in this interaction, transfection of EMMPRIN into a cell line with low endogenous EMMPRIN expression was done and showed a significant increase in collagenolysis. Inhibition of collagenolysis with a tissue inhibitor of metalloprotease-2 (TIMP-2) and a synthetic furin inhibitor was observed but not with TIMP-1, which suggested a possible role for membrane type-1 MMP. These results suggest that fibroblast-derived MMPs but not those from tumor cells are important for in vitro collagenolysis and that this process is promoted by tumor cell-expressed EMMPRIN.

Upregulation of matrix metalloproteinases (MMPs) in breast cancer xenografts: a major induction of stromal MMP-13

In human breast cancer (HBC), as with many carcinoma systems, most matrix metalloproteinases (MMPs) are largely expressed by the stromal cells, whereas the tumour cells are relatively silent in MMP expression. To determine the tissue source of the most relevant MMPs, we xenografted HBC cell lines and HBC tissues into the mammary fat pad (MFP) or bone of immunocompromised mice and measured the expression of human and mouse MMP-2, -9, -11, -13, membrane-type-1 MMP (MT1-MMP), MT2-MMP and MT3-MMP by species-specific real-time quantitative RT-PCR. Our data confirm a stromal origin for most tumour-associated MMPs and indicate marked and consistent upregulation of stromal (mouse) MMP-13 and MT1-MMP in all xenografts studied, irrespective of implantation in the MFP or bone environments. In addition, we show increased expression of both human MMP-13 and human MT1-MMP by the MDA-MB-231 tumour cells grown in the MFP compared to in vitro production. MMP protein and activity data confirm the upregulation of MMP mRNA production and indicate an increase in the activated MMP-2 species as a result of tumour implantation. These data directly demonstrate tumour induction of MMP production by stromal cells in both the MFP and bone environments. These xenografts are a valuable means for examining in vivo production of MMPs and suggest that MMP-13 and MT1-MMP will be relevant targets for inhibiting breast cancer progression.

Recombinant alpha2(IV)NC1 domain inhibits tumor cell-extracellular matrix interactions, induces cellular senescence, and inhibits tumor growth in vivo

Cellular interaction with the extracellular matrix is thought to be a critical event in controlling angiogenesis and tumor growth. In our previous studies, genetically distinct noncollagenous (NC) domains of type-IV collagen were shown to interact with integrin receptors expressed on the surface of endothelial cells. Moreover, these NC1 domains were shown to inhibit angiogenesis in vivo. Here, we provide evidence that a recombinant form of the alpha2(IV)NC1 domain of type-IV collagen could bind integrins alpha1beta1 and alphavbeta3 expressed on melanoma cells and inhibit tumor cell adhesion in a ligand-specific manner. Systemic administration of recombinant alpha2(IV)NC1 domain potently inhibited M21 melanoma tumor growth within full thickness human skin and exhibited a dose-dependent inhibition of tumor growth in nude mice. Interestingly, alpha2(IV)NC1 domain enhanced cellular senescence in tumor cells in vitro and in vivo. Taken together, these results suggest that recombinant alpha2(IV)NC1 domain is not only a potent anti-angiogenic reagent, but it also directly impacts tumor cell behavior. Thus, alpha2(IV)NC1 domain represents a potent inhibitor of tumor growth by impacting both endothelial and tumor cell compartments.

Roles of membrane-type matrix metalloproteinase-1 in tumor invasion and metastasis

Degradation of extracellular matrix (ECM) is one of the first steps in tumor invasion and metastasis. Matrix metalloproteinases (MMP) have been strongly implicated in this step. Membrane-type MMP-1 (MT1-MMP) was first identified as an activator of proMMP-2 expressed on the surface of tumor cells and later, not only ECM macromolecules but also various biologically important molecules, were shown to serve as substrates for MT1-MMP. Accumulated lines of evidence have demonstrated that MT1-MMP expression level is closely associated with invasiveness and malignancy of tumors, suggesting that MT1-MMP is one of the most critical factors for tumor invasion and metastasis. Despite enthusiasm for MMP inhibitors, phase III trials have not yet demonstrated significance in overall survival and side-effects remain an issue. An understanding of the functions of MT1-MMP could supply clues for developing novel therapeutic strategies targeting MT1-MMP.

Osteoblast responses one hour after load-induced fluid flow in a three-dimensional porous matrix

When bone is loaded, substrate strain is generated by the external force and this strain induces fluid flow that creates fluid shear stress on bone cells. Our current understanding of load-driven gene regulation of osteoblasts is based primarily on in vitro studies on planer two-dimensional tissue culture substrates. However, differences between a flat layer of cells and cells in 3-dimensional (3D) ECM are being recognized for signal transduction. Proliferation and differentiation of osteoblasts are affected by substrate geometry. Here we developed a novel 3D culture system that would mimic physiologically relevant substrate strain as well as strain-induced fluid flow in a 3D porous collagen matrix. The system allowed us to evaluate the responses of osteoblasts in a 3D stress-strain environment similar to a mechanical field to which bone is exposed. Using MC3T3-E1 osteoblasts grown in the 3D collagen matrix with and without hydroxyapatite deposition, we tested the role of strain and the strain-induced fluid flow in the expression of the load-responsive genes such as c-fos, egr1, cox2, osteopontin, and mmp1B involved in transcriptional regulation, osteogenesis, and rearrangement of ECM. Strain-induced fluid flow was visualized with a microspheres approximately 3 microm in diameter in real time, and three viscoelastic parameters were determined. The results obtained by semi-quantitative PCR, immunoblot assay, enzymatic activity assays for collagenase and gelatinase, and mechanical characterization of collagen matrices supported the dominant role of strain-induced fluid flow in expression of the selected genes one hour after the mechanical treatment.

Membrane-type-1 matrix metalloproteinase confers tumorigenicity on nonmalignant epithelial cells

Overexpression of membrane-type-1 matrix metalloproteinase (MT1-MMP) in tumor cells has previously been shown to enhance tumor growth and metastasis. To establish if MT1-MMP is also able to confer tumorigenicity on nonmalignant epithelial cells, we transfected human MT1-MMP cDNA into Madin-Darby canine kidney (MDCK) cells expressing a tetracycline-repressible transactivator. Induction of MT1-MMP in the absence of doxycycline (Dox) was associated with activation of exogenous MMP-2 as well as with formation of large cysts and increased invasiveness in collagen matrices. Transfected cells were inoculated subcutaneously into two groups of nude mice, one of which received Dox to inhibit expression of MT1-MMP. Formation of tumor xenografts was observed in 11 of 17 mice maintained without Dox, but only in two of nine mice that received Dox (P<0.05). The xenografts were composed of tubular structures interspersed within a highly cellular stroma. The epithelial cells delimiting the lumen were polarized, as indicated by the basolateral distribution of Na,K-ATPase. Despite their differentiated appearance, the tumors lacked a well-defined boundary, and epithelial tubules invaded adjacent muscular layers. These results demonstrate that conditional expression of MT1-MMP in nonmalignant MDCK epithelial cells is by itself sufficient to drive formation of invasive tumors.

Identification of membrane type-1 matrix metalloproteinase as a target of hypoxia-inducible factor-2 alpha in von Hippel-Lindau renal cell carcinoma

Metastatic renal cell carcinoma (RCC) resulting from the hereditary loss of the von Hippel-Lindau (VHL) tumor suppressor gene is the leading cause of death in VHL patients due to the deleterious effects of the metastatic tumor(s). VHL functions in the destruction of the alpha subunits of the heterodimeric transcription factor, hypoxia-inducible factor (HIF-1 alpha and HIF-2 alpha), in normoxic conditions. When VHL function is lost, HIF-alpha protein is stabilized, and target hypoxia-inducible genes are transcribed. The process of tumor invasion and metastasis involves the destruction of the extracellular matrix, which is accomplished primarily by the matrix metalloproteinase (MMP) family of enzymes. Here, we describe a connection between the loss of VHL tumor suppressor function and the upregulation of membrane type-1 MMP (MT1-MMP) gene expression and protein. Specifically, MT1-MMP is upregulated in VHL-/- RCC cells through an increase in gene transcription, which is mediated by the cooperative effects of the transcription factors, HIF-2 and Sp1. Further, we identify a functional HIF-binding site in the proximal promoter of MT1-MMP. To our knowledge, this is the first report to show direct regulation of MT1-MMP by HIF-2 and to provide a direct link between the loss of VHL tumor suppressor function and an increase in MMP gene and protein expression.