Proteolytic exposure of a cryptic site within collagen type IV is required for angiogenesis and tumor growth in vivo

Autoantibodies to endostatin in patients with breast cancer: correlation to endostatin levels and clinical outcome

Circulating autoantibodies to self-antigens overexpressed by cancer cells are common in cancer patients. As specific proteins are expressed during neoangiogenesis, a similar phenomenon might occur with particular antigens of tumour vessels. Collagen XVIII, from which endostatin is cleaved, is highly expressed in the perivascular basement membrane of tumour-associated blood vessels and autoantibodies to endostatin have been reported in cancer patients. The present study analyses the incidence of naturally occurring autoantibodies to endostatin in the sera of breast cancer patients and their relation to endostatin serum levels and patient clinical outcome. Serum samples from 36 patients with localised breast cancer and 59 patients with a fully documented history of metastatic breast cancer were used. The immunoreactivity of serum samples was tested against purified recombinant human endostatin and endostatin levels were determined by immunoassay. We could detect anti-endostatin antibodies in the sera of 66% of the patients with localised disease and 42% of the patients with metastatic disease (P=0.03). There was no correlation between the presence of antibodies to endostatin and circulating levels of endostatin. The detection of autoantibodies to endostatin was associated with better prognosis in metastatic breast cancer patients (median survival time: 20 vs 8 months, P=0.03), as was the presence of low levels of serum endostatin (median survival time: 20 vs 9 months, P=0.007). These results show that a natural immune reaction against endostatin can occur in breast cancer patients. This could have important therapeutic implications with regard to endostatin therapy and raises the question of a possible role of this humoral reaction against endostatin in the neoplastic process.

The inhibitory effects of endostatin on endothelial cells are modulated by extracellular matrix

We investigated the ability of extracellular matrix (ECM) proteins to modulate the response of endothelial cells to both promoters and inhibitors of angiogenesis. Using human dermal microvascular endothelial cells (HDMEC), we found that cells demonstrated different adhesive properties and proliferative responses to the growth factor VEGF depending upon which ECM protein with which they were in contact, with fibronectin having the most impact on VEGF-induced HDMEC proliferation and survival. More importantly, we observed that ECM could modulate the ability of the angiogenic inhibitor endostatin to prevent endothelial cell proliferation, survival and migration. We observed that growth on vitronectin or fibronectin impaired the ability of endostatin to inhibit VEGF-induced HDMEC proliferation to the greatest extent as determined by BrdU incorporation. We found that, following growth on collagen I or collagen IV, endostatin only inhibited VEGF-induced HDMEC proliferation at the highest dose tested (2500 ng/ml). In a similar manner, we observed that growth on ECM proteins modulated the ability of endostatin to induce endothelial cell apoptosis, with growth on collagen I, fibronectin and collagen IV impairing endostatin-induced apoptosis. Interestingly, endostatin inhibited VEGF-induced HDMEC migration following culture on collagen I, collagen IV and laminin, while migration was not inhibited by endostatin following HDMEC culture on other matrices including vitronectin, fibronectin and tenascin-C. These results suggest that different matrix proteins may affect different mechanisms of endostatin inhibition of angiogenesis. Taken together, our results suggest that the ECM may have a profound impact on the ability of angiostatic molecules such as endostatin to inhibit angiogenesis and thus may have impact on the clinical efficacy of such inhibitors.

Detection of Activated, TIMP-free MMPs

MMP inhibitor-tethered resins provide a method for detection of activated MMPs in tissues. These measurements will help to elucidate in situ mechanisms of MMP activation, further our understanding of the tumor microenvironment, and facilitate development of MMP-inhibitor therapy.

Characterization of a von Hippel Lindau pathway involved in extracellular matrix remodeling, cell invasion, and angiogenesis

Inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene results in highly vascularized tumors, making the VHL tumor syndrome an ideal system to study the mechanisms of angiogenesis. VHL operates along two pathways with the first involving hypoxia-inducible factor-alpha degradation and down-regulation of its proangiogenic target genes vascular endothelial growth factor and platelet-derived growth factor-beta, and the second pathway promoting extracellular matrix (ECM) assembly. Secretion of proangiogenic factors was shown to be a primary inducer of angiogenesis. Here, we show that loss of ECM assembly correlates with tumor angiogenesis in VHL disease. Upon inactivation of the VHL-ECM assembly pathway, we observe tumors that are highly vascularized, have a disrupted ECM, and show increased matrix metalloproteinase-2 activity. Loss of the VHL pathway leading to hypoxia-inducible factor-alpha degradation results in tumors with increased vascular endothelial growth factor levels but with surprisingly low microvessel density, a tightly assembled ECM and low invasive ability. We conclude that loss of ECM integrity could promote and maintain tumor angiogenesis by providing a route for blood vessels to infiltrate tumors.

Epidermal development and wound healing in matrix metalloproteinase 13-deficient mice

Degradation of the extracellular matrix, which is an indispensable step in tissue remodelling processes such as embryonic development and wound healing of the skin, has been attributed to collagenolytic activity of members of the matrix metalloproteinase family (MMPs). Here, we employed mmp13 knockout mice to elucidate the function of MMP13 in embryonic skin development, skin homeostasis, and cutaneous wound healing. Overall epidermal architecture and dermal composition of non-injured skin were indistinguishable from wild-type mice. Despite robust expression of MMP13 in the early phase of wound healing, wild-type and mmp13 knockout animals did not differ in their efficiency of re-epithelialization, inflammatory response, granulation tissue formation, angiogenesis, and restoration of basement membrane. Yet, among other MMPs also expressed during wound healing, MMP8 was found to be enhanced in wounds of MMP13-deficient mice. In summary, skin homeostasis and also tissue remodelling processes like embryonic skin development and cutaneous wound healing are independent of MMP13 either owing to MMP13 dispensability or owing to functional substitution by other collagenolytic proteinases such as MMP8.

Temporal exposure of cryptic collagen epitopes within ischemic muscle during hindlimb reperfusion

Chronic limb-threatening ischemia is a devastating disease with limited surgical options. However, inducing controlled angiogenesis and enhancing reperfusion holds therapeutic promise. To gain a better understanding of the mechanisms that contribute to limb reperfusion, we examined the temporal biochemical and structural changes occurring within the extracellular matrix of ischemic skeletal muscle. Both the latent and active forms of MMP-2 and -9 significantly increased during the active phase of limb reperfusion. Moreover, small but significant alterations in tissue inhibitors of metalloproteinase levels also occurred during a similar time course, consistent with a net increase in extracellular matrix remodeling. This temporal increase in MMP activity coincided with enhanced exposure of the unique HU177 cryptic collagen epitope. Although the HUIV26 cryptic collagen epitope has been implicated in angiogenesis, little is known concerning such epitopes within ischemic muscle tissue. Here, we provide the first evidence that a functionally distinct cryptic collagen epitope (HU177) is temporally exposed in ischemic muscle tissue during the active phase of reperfusion. Interestingly, the exposure of the HU177 epitope was greatly diminished in MMP-9 null mice, corresponding with significantly reduced limb reperfusion. Therefore, the regulated exposure of a unique cryptic collagen epitope within ischemic muscle suggests an important role for collagen remodeling during the active phase of ischemic limb reperfusion.

Directed type IV collagen self-assembly on hydroxylated PTFE

A method for the creation of a type IV collagen (CNIV) scaffold on polytetrafluoroethylene (PTFE) for endothelial cell attachment is described. This mimic for the basal lamina can be used in the seeding and retention of endothelial cells for blood contacting devices. The CNIV-PTFE production technique can be defined as three processes: (i) creation of a reactive superacidic/ionic PTFE surface with retained hydrophobic characteristics; (ii) activation of this surface via covalent attachment of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC); and (iii) conjugation of the EDC with human CNIV resulting in the covalent binding of protein to the PTFE surface. This article demonstrates exciting new results showing that a reaction of CNIV to this particular surface results in a unique matrix assembly of CNIV scaffolds similar to those found in the basal lamina. This assembly is concentration-dependant, occurring in a narrow window around 0.435 microM. Following the fabrication of the CNIV matrix assembly, porcine aortic endothelial cells (PAEC) were seeded onto this material. Results described in this article demonstrate that the PAEC subsequently aligned with the direction of shear, filled voids created by dead or detached cells, and divided during the 6 h of experimentation. Under static conditions, cells remained viable for 1 week of testing. This was not observed with PAEC attached to glass with adsorbed Vitrogen. In summary, this article describes a novel biotechnological breakthrough that enables the creation of stable endothelial cell monolayers useful for fabricating blood contacting devices.

Intracellular proteolytic activity of cathepsin B is associated with capillary-like tube formation by endothelial cells in vitro

The lysosomal cysteine protease cathepsin B is implicated in degradation of extracellular matrix (ECM), a crucial step in a variety of physiological and pathological processes, including tumor dissemination and angiogenesis. In this study, we analyzed the contribution of extracellular and intracellular cathepsin B activity on the formation of capillary-like tubular structures by human umbilical vein endothelial cells (HUVECs) grown on Matrigel matrix, using general and specific cysteine protease inhibitors. We demonstrated, by confocal assay using quenched fluorescent protein substrate DQ-collagen IV, that endothelial cells degrade ECM both intracellularly and pericellularly. Intracellular cathepsin B activity detected by degradation of Z-Arg-Arg cresyl violet substrate was co-localized with the products of DQ-collagen IV degradation in the perinuclear region and in the capillary-like tubular structures. Treatment of cells with membrane-permeable CA-074 Me effectively abolished intracellular cathepsin B activity, and resulted in reduced tube length (32.3+/-9.4% at 10 microM), total tubule area (49.6+/-12.4% at 10 microM), and the number of branch points of tubules (47.5+/-7.7% at 10 microM) in a dose-dependent manner. In contrast, CA-074 (0.1-10 microM), a membrane-impermeable cathepsin B specific inhibitor, general cysteine protease inhibitors chicken cystatin (5 microM) and E-64 (10 microM), and the metalloprotease inhibitor Minocycline (10 microM) showed no significant inhibitory effect in our angiogenesis model. These results show that, besides multiple regulatory molecules, intracellular cathepsin B also contributes to the neovascularization process and should be considered as a potential therapeutic target.

N-substituted 4-aminobenzamides (procainamide analogs): an assessment of multiple cellular effects concerning ion trapping

Procainamide and related triethylamine-substituted 4-aminobenzamides, such as metoclopramide and declopramide, exert cellular effects potentially exploitable in oncology at millimolar concentrations (DNA demethylation, nuclear factor-kappaB inhibition, apoptosis) and display anti-inflammatory properties. However, these drugs induce massive cell vacuolization at similar concentrations, a response initiated by vacuolar (V-) ATPase-dependent ion trapping into and osmotic swelling of acidic organelles. We have examined whether this overlooked response might be related to the effects on cell proliferation and viability using cultured vascular smooth muscle cells and tumor-derived cell lines (Morris 7777 hepatoma, HT-1080 fibrosarcoma). Giant vacuole formation, of confirmed trans-Golgi origin (labeled with C5-ceramide, p230, golgin-97), is a cellular response to all tested amines in the series (> or = 2.5 mM), including triethylamine. These drugs and the V-ATPase inhibitor bafilomycin A1 inhibited smooth muscle cell proliferation, suggesting that acidification of a cellular compartment is essential to cell division. The cytotoxicity was maximal with metoclopramide, and this effect was minimally influenced by bafilomycin A1; furthermore, metoclopramide (2.5 mM) induced apoptosis in tumor cells as judged by poly(ADP-ribose)polymerase (PARP) cleavage. Triethylamine and procainamide exhibit a low level of cytotoxicity variably reduced by bafilomycin co-treatment. In Morris cells, the secretion of alpha-fetoprotein is inhibited by amines, consistent with the impairment of the secretory pathway. The most highly substituted 4-aminobenzamides are significant NF-kappaB inhibitors in smooth muscle cells. Although some effects of 4-aminobenzamides are independent of V-ATPase-driven ion trapping (inhibition of NF-kappaB nuclear translocation, agent-specific cytotoxicity, PARP cleavage), other effects are dependent on this phenomenon (vacuolization, a component of the cytotoxicity, inhibition of secretion).

Targeting integrins for the control of tumour angiogenesis

The crucial role of cell extracellular matrix communication in angiogenesis is well established; thus, it is not surprising that integrins have gained considerable attention as targets for the treatment of neovascular disease. Given the diversity of ligands and complexity of integrin signalling, a new appreciation for the divergent roles of integrins in angiogenesis is emerging. It is becoming clear that integrins regulate angiogenesis in both a positive and negative manner. New studies have provided a better understanding of integrin structure as it relates to ligand binding and signalling. This new insight has opened exciting possibilities for the design of novel inhibitors for clinical applications. In this review, studies concerning the cooperative interactions between integrins and regulatory molecules and possible new strategies for controlling angiogenesis will be discussed.

In silico analysis of angiogenesis associated gene expression identifies angiogenic stage related profiles

In vitro models have been extensively used to map gene expression in ECs but few studies have used cells from in vivo sources directly. Here, we compare different gene expression surveys on both cultured and fresh tissue derived ECs, and it emerges that gene expression profiles can be paralleled with the angiogenic stage of the cells. ECs stimulated with different growth factors in monolayer cultures exhibit gene expression profiles indicative of an active proliferative state, whereas gene expression in tube forming cells in vitro involves genes implicated in cell adhesion processes. Genes overexpressed in tumor ECs are biased towards extracellular matrix remodeling, a late event in angiogenesis. The elucidation of gene expression profiles under these different conditions will contribute to a better understanding of the molecular mechanisms during angiogenesis in both pathological and physiological circumstances and will have implications for the development of angiogenesis interfering treatment strategies.

Matrix metalloproteinases and angiogenesis

Matrix metalloproteinases (MMPs) are a family of enzymes that proteolytically degrade various components of the extracellular matrix (ECM). Angiogenesis is the process of forming new blood vessels from existing ones and requires degradation of the vascular basement membrane and remodeling of the ECM in order to allow endothelial cells to migrate and invade into the surrounding tissue. MMPs participate in this remodeling of basement membranes and ECM. However, it has become clear that MMPs contribute more to angiogenesis than just degrading ECM components. Specific MMPs have been shown to enhance angiogenesis by helping to detach pericytes from vessels undergoing angiogenesis, by releasing ECM-bound angiogenic growth factors, by exposing cryptic proangiogenic integrin binding sites in the ECM, by generating promigratory ECM component fragments, and by cleaving endothelial cell-cell adhesions. MMPs can also contribute negatively to angiogenesis through the generation of endogenous angiogenesis inhibitors by proteolytic cleavage of certain collagen chains and plasminogen and by modulating cell receptor signaling by cleaving off their ligand-binding domains. A number of inhibitors of MMPs that show antiangiogenic activity are already in early stages of clinical trials, primarily to treat cancer and cancer-associated angiogenesis. However, because of the multiple effects of MMPs on angiogenesis, careful testing of these MMP inhibitors is necessary to show that these compounds do not actually enhance angiogenesis.

Control of colorectal metastasis formation by K-Ras

Mutational activation of the K-Ras proto-oncogene is frequently observed during the very early stages of colorectal cancer (CRC) development. The mutant alleles are preserved during the progression from pre-malignant lesions to invasive carcinomas and distant metastases. Activated K-Ras may therefore not only promote tumor initiation, but also tumor progression and metastasis formation. Metastasis formation is a very complex and inefficient process: Tumor cells have to disseminate from the primary tumor, invade the local stroma to gain access to the vasculature (intravasation), survive in the hostile environment of the circulation and the distant microvascular beds, gain access to the distant parenchyma (extravasation) and survive and grow out in this new environment. In this review, we discuss the potential influence of mutant K-Ras on each of these phases. Furthermore, we have evaluated the clinical evidence that suggests a role for K-Ras in the formation of colorectal metastases.

Canstatin acts on endothelial and tumor cells via mitochondrial damage initiated through interaction with alphavbeta3 and alphavbeta5 integrins

Canstatin, the noncollagenous domain of collagen type IV alpha-chains, belongs to a series of collagen-derived angiogenic inhibitors. We have elucidated the functional receptors and intracellular signaling induced by canstatin that explain its strong antitumor efficacy in vivo. For this purpose, we generated a canstatin-human serum albumin (CanHSA) fusion protein, employing the HSA moiety as an expression tag. We show that CanHSA triggers a crucial mitochondrial apoptotic mechanism through procaspase-9 cleavage in both endothelial and tumor cells, which is mediated through cross-talk between alphavbeta3- and alphavbeta5-integrin receptors. As a point of reference, we employed the first three kringle domains of angiostatin (K1-3), fused with HSA, which, in contrast to CanHSA, act only on endothelial cells through alphavbeta3-integrin receptor-mediated activation of caspase-8 alone, without ensuing mitochondrial damage. Taken together, these results provide insights into how canstatin might exert its strong anticancer effect.

Tumor-stroma interactions

The importance of stromal cells and the factors that they express during cancer initiation and progression has been highlighted by recent literature. The cellular components of the stroma of epithelial tissues are well-recognized as having a supportive role in carcinogenesis, where the initiating mutations of a tumor originate in the epithelial cells. The use of mouse models and xenografts suggests that mutations in the stromal fibroblasts can also initiate epithelial tumors. Many of these tumors result from the alteration of paracrine growth factor pathways that act on the epithelia. However, the tissue specificity of the responses to the growth factors is a mystery not yet solved.

Cellular abnormalities of blood vessels as targets in cancer

Tumor blood vessels have multiple structural and functional abnormalities. They are unusually dynamic, and naturally undergo sprouting, proliferation, remodeling or regression. The vessels are irregularly shaped, tortuous, and lack the normal hierarchical arrangement of arterioles, capillaries and venules. Endothelial cells in tumors have abnormalities in gene expression, require growth factors for survival and have defective barrier function to plasma proteins. Pericytes on tumor vessels are also abnormal. Aberrant endothelial cells and pericytes generate defective basement membrane. Angiogenesis inhibitors can stop the growth of tumor vessels, prune existing vessels and normalize surviving vessels. Loss of endothelial cells is not necessarily accompanied by simultaneous loss of pericytes and surrounding basement membrane, which together can then provide a scaffold for regrowth of tumor vessels. Rapid vascular regrowth reflects the ongoing drive for angiogenesis and bizarre microenvironment in tumors that promote vascular abnormalities and thereby create therapeutic targets.

Breast cancer cells induce stromal fibroblasts to express MMP-9 via secretion of TNF-alpha and TGF-beta

We used 2D-cocultures employing fibroblasts of different genetic backgrounds and MCF10A-derived human breast epithelial cells of increasingly malignant potential to investigate tumor-stroma interactions in breast cancer and to identify possible signaling pathways involved. Tumor cells induced expression of matrix-metalloproteinase 9 (MMP-9) in fibroblasts in a pattern dependent on the degree of their malignancy. In-situ zymography localized the main gelatinolytic activity around stromal cells in cocultures and xenografted tumors. Use of Smad3 knockout fibroblasts, small molecule inhibitors, and neutralizing antibodies showed that MMP-9 expression was induced by tumor cell-derived TNF-alpha and TGF-beta, dependent on Smad-, Ras-, and PI3-kinase-signaling, and likewise modulated by subsequent HGF- and EGF-signaling. Together, our results indicate that MMP-9 levels in tumor fibroblasts are regulated by a complex tumor-stroma cross-talk, involving multiple ligands and cellular signaling pathways.

Gelatinase-mediated migration and invasion of cancer cells

The matrix metalloproteinases(MMP)-2 and -9, also known as the gelatinases have been long recognized as major contributors to the proteolytic degradation of extracellular matrix during tumor invasion. In the recent years, a plethora of non-matrix proteins have also been identified as gelatinase substrates thus significantly broadening our understanding of these enzymes as proteolytic executors and regulators in various physiological and pathological states including embryonic growth and development, angiogenesis and tumor progression, inflammation, infective diseases, degenerative diseases of the brain and vascular diseases. Although the effect of broad-spectrum inhibitors of MMPs in the treatment of cancer has been disappointing in clinical trials, novel mechanisms of gelatinase inhibition have been now identified. Inhibition of the association of the gelatinases with cell-surface integrins appears to offer highly specific means to target these enzymes without inhibiting their catalytic activity in multiple cell types including endothelial cells, tumor cells and leukocytes. Here, we review the multiple functions of the gelatinases in cancer, and especially their role in the tumor cell migration and invasion.

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.

Regulation of matrix biology by matrix metalloproteinases

Matrix metalloproteinases (MMPs) are endopeptidases that contribute to growth, development and wound healing as well as to pathologies such as arthritis and cancer. Until recently, it has been thought that MMPs participate in these processes simply by degrading extracellular matrix (ECM) molecules. However, it is now clear that MMP activity is much more directed and causes the release of cryptic information from the ECM. By precisely cleaving large insoluble ECM components and ECM-associated molecules, MMPs liberate bioactive fragments and growth factors and change ECM architecture, all of which influence cellular behavior. Thus, MMPs have become a focal point for understanding matrix biology.

Matrikines in the regulation of extracellular matrix degradation

The term "matrikines" was coined for designating peptides liberated by partial proteolysis of extracellular matrix macromolecules, which are able to regulate cell activities. Among these peptides, some of them may modulate proliferation, migration, protease production, or apoptosis. In this review, we summarize the activity of matrikines derived from elastin and interstitial or basement membrane collagens on the regulation of matrix metalloproteinases expression and/or activation, and on the plasminogen/plasmin system. Due to their activity, matrikines may play a significant role in physiological or pathological processes such as wound healing or tumor invasion.

Angiogenesis Inhibition by Vascular Endothelial Growth Factor Receptor-2 Blockade Reduces Stromal Matrix Metalloproteinase Expression, Normalizes Stromal Tissue, and Reverts Epithelial Tumor Phenotype in Surface Heterotransplants

Inhibition of vascular endothelial growth factor (VEGF) signaling, a key regulator of tumor angiogenesis, through blockade of VEGF receptor (VEGFR)-2 by the monoclonal antibody DC101 inhibits angiogenesis, tumor growth, and invasion. In a surface xenotransplant assay on nude mice using a high-grade malignant squamous cell carcinoma cell line (A-5RT3), we show that DC101 causes vessel regression and normalization as well as stromal maturation resulting in a reversion to a noninvasive tumor phenotype. Vessel regression is followed by down-regulation of expression of both VEGFR-2 and VEGFR-1 on endothelial cells and increased association of α-smooth muscle actin–positive cells with small vessels indicating their normalization, which was further supported by a regular ultrastructure. The phenotypic regression of an invasive carcinoma to a well-demarcated dysplastic squamous epithelium is accentuated by the establishment of a clearly structured epithelial basement membrane and the accumulation of collagen bundles in the stabilized connective tissue. This normalization of the tumor-stroma border coincided with down-regulated expression of the stromal matrix metalloproteinases 9 and 13, which supposedly resulted in attenuated turnover of extracellular matrix components permitting their structural organization. Thus, in this mouse model of a human squamous cell carcinoma cell line, blockade of VEGF signaling resulted in the reversion of the epithelial tumor phenotype through stromal normalization, further substantiating the crucial role of stromal microenvironment in regulating the tumor phenotype.

Integrins and angiogenesis

The growth of new blood vessels is a dynamic yet highly regulated process that depends on coordinated signaling by growth factor and cell adhesion receptors. As part of the molecular program regulating angiogenesis, endothelial cells acquire a proliferative and invasive phenotype but also show increased susceptibility to apoptotic stimuli. Integrins are the principle adhesion receptors used by endothelial cells to interact with their extracellular microenvironment, and integrin-mediated interactions play a critical role in regulating cell proliferation, migration, and survival. Alterations in the repertoire and?or activity of integrins, as well as the availability and structural property of their ligands, regulate the vascular cell during the growth or repair of blood vessels.

Matrix Metalloproteinase-9 in Macrophages Induces Thymic Neovascularization following Thymocyte Apoptosis

Matrix metalloproteinase-9 (MMP-9) has been implicated in the degradation of the extracellular matrix in a variety of physiological and pathological processes. We found that MMP-9 expression in thymuses of BALB/c mice that had been injected with anti-CD3 Ab to induce thymocyte apoptosis was increased both at mRNA and protein levels. Macrophages are shown to be the principal stromal cells responsible for phagocytosis of dying thymocytes, and macrophages were found to constitutively express MMP-9. The activity of plasmin, which is known as one of the activators for MMP-9, was increased in the thymuses with MMP-9 activation. Binding of Ab HUIV26, which recognizes a cryptic epitope on collagen type IV following proteolytic cleavage, was found to be reduced in MMP-9 knockout mice, suggesting that collagen type IV is a substrate of MMP-9. Although the formation of thymic neovessels was found following thymocyte apoptosis, it was diminished in anti-CD3 Ab-injected MMP-9 knockout mice. In vivo administration of Ab HUIV26 resulted in a reduction of thymic neovascularization. After clearance of apoptotic thymocytes, the number of macrophages in the thymuses was decreased, and this decrease was delayed by blocking of HUIV26 epitope. Taken together, our results suggest that MMP-9 expression in macrophages mediates degradation of collagen type IV and facilitates their migration from the thymus after clearance of apoptotic thymocytes. These studies demonstrate a potential role of macrophage MMP-9 in the remodeling of thymic extracellular matrix following thymocyte apoptosis.

Novel role for Na,K-ATPase in phosphatidylinositol 3-kinase signaling and suppression of cell motility

The Na,K-ATPase, consisting of alpha- and beta-subunits, regulates intracellular ion homeostasis. Recent studies have demonstrated that Na,K-ATPase also regulates epithelial cell tight junction structure and functions. Consistent with an important role in the regulation of epithelial cell structure, both Na,K-ATPase enzyme activity and subunit levels are altered in carcinoma. Previously, we have shown that repletion of Na,K-ATPase beta1-subunit (Na,K-beta) in highly motile Moloney sarcoma virus-transformed Madin-Darby canine kidney (MSV-MDCK) cells suppressed their motility. However, until now, the mechanism by which Na,K-beta reduces cell motility remained elusive. Here, we demonstrate that Na,K-beta localizes to lamellipodia and suppresses cell motility by a novel signaling mechanism involving a cross-talk between Na,K-ATPase alpha1-subunit (Na,K-alpha) and Na,K-beta with proteins involved in phosphatidylinositol 3-kinase (PI3-kinase) signaling pathway. We show that Na,K-alpha associates with the regulatory subunit of PI3-kinase and Na,K-beta binds to annexin II. These molecular interactions locally activate PI3-kinase at the lamellipodia and suppress cell motility in MSV-MDCK cells, independent of Na,K-ATPase ion transport activity. Thus, these results demonstrate a new role for Na,K-ATPase in regulating carcinoma cell motility.

Jararhagin, a snake venom metalloproteinase-disintegrin, stimulates epithelial cell migration in an in vitro restitution model

The snake venom metalloproteinase-disintegrin jararhagin (JG) has no chemotactic activity but stimulates the migration of neutrophils in vivo through a mechanism still unclear. In this study we investigated the effects of jararhagin on epithelial cell adhesion and migration in vitro. F-actin arrangement and the distribution of laminin, fibronectin, several integrins and phosphorylated Focal Adhesion Kinase (FAK) were studied using rhodamine-phalloidin and immunofluorescence. Maximum stimulation of migration (about 100%) was obtained with 5 microg/ml JG, with about 38% inhibition of cellular adhesion. In migratory cells the toxin stimulated the formation of filopodia, lamellipodia and stress fibers. The pericellular fibronectin matrix was lost in migrating cells, while laminin was less affected. The toxin stimulated FAK phosphorylation and the recruitment of alphav-containing integrins to focal contacts, whereas integrins containing the alpha2 subunit were reduced in these junctions. Inactivation of the toxin with 1,10 phenanthroline showed that the catalytic activity is important for the effect of jararhagin on cell migration, FAK phosphorylation and for the recruitment of alphav, but not as much for the anti-adhesive effect. In conclusion, jararhagin stimulates the migration of epithelial cells in vitro through a mechanism that involves its proteolytic activity, qualitative changes in cellular adhesion and the formation of actin-rich cellular processes.

Control of melanoma cell invasion by type IV collagen

Malignant melanoma is the leading cause of death from diseases of the skin. This review summarizes the data from the literature and our laboratory addressing the effects of type IV collagen on melanoma progression. Many different sequences from type IV collagen promote melanoma cell adhesion, migration and invasion. The triple helical conformation of the collagenous domain plays a critical role in some of these interactions. However, recent studies from our group demonstrated that a sequence from the alpha3(IV) NC1 domain inhibits melanoma cell proliferation, migration and invasion by decreasing MMP production and activation. Peptide sequences from the alpha1(IV), alpha2(IV) and alpha3(IV) chains named arresten, canstatin and tumstatin, respectively were shown to inhibit angiogenesis. Further investigations regarding the inhibitory effects of the alpha(IV) NC1 domains will have a paramount relevance for the design of efficient strategies to limit melanoma development.

MT1-MMP-dependent neovessel formation within the confines of the three-dimensional extracellular matrix

During angiogenesis, endothelial cells initiate a tissue-invasive program within an interstitial matrix comprised largely of type I collagen. Extracellular matrix–degradative enzymes, including the matrix metalloproteinases (MMPs) MMP-2 and MMP-9, are thought to play key roles in angiogenesis by binding to docking sites on the cell surface after activation by plasmin- and/or membrane-type (MT) 1-MMP–dependent processes. To identify proteinases critical to neovessel formation, an ex vivo model of angiogenesis has been established wherein tissue explants from gene-targeted mice are embedded within a three-dimensional, type I collagen matrix. Unexpectedly, neither MMP-2, MMP-9, their cognate cell-surface receptors (i.e., β₃ integrin and CD44), nor plasminogen are essential for collagenolytic activity, endothelial cell invasion, or neovessel formation. Instead, the membrane-anchored MMP, MT1-MMP, confers endothelial cells with the ability to express invasive and tubulogenic activity in a collagen-rich milieu, in vitro or in vivo, where it plays an indispensable role in driving neovessel formation.

Integrin signalling during tumour progression

During progression from tumour growth to metastasis, specific integrin signals enable cancer cells to detach from neighbouring cells, re-orientate their polarity during migration, and survive and proliferate in foreign microenvironments. There is increasing evidence that certain integrins associate with receptor tyrosine kinases (RTKs) to activate signalling pathways that are necessary for tumour invasion and metastasis. The effect of these integrins might be especially important in cancer cells that have activating mutations, or amplifications, of the genes that encode these RTKs.

Control of melanoma progression by various matrikines from basement membrane macromolecules

Many biological processes such as cell differentiation, cell migration or gene expression are tightly controlled by cell-cell interactions or by various cytokines. During tumor progression, cancer cells are in contact with extracellular matrix (ECM) macromolecules involving specific receptors such as integrins. The different stages of tumor progression, and mainly the proteolytic cascades implicated in extracellular matrix degradation and cell migration, may be controlled by the extracellular matrix macromolecules or by domains released by directed and limited proteolysis of these molecules. In this review, we summarise the biological effects of various peptides, named matrikines, derived from basement membranes (BM) components, such as laminins (LN), proteoglycans or collagens. These peptides may control tumor progression by regulating the proteolytic cascades leading to cancer cell dissemination and metastasis.

Differential modulation of human melanoma cell metalloproteinase expression by alpha2beta1 integrin and CD44 triple-helical ligands derived from type IV collagen

Tumor cell binding to components of the basement membrane is well known to trigger intracellular signaling pathways. Signaling ultimately results in the modulation of gene expression, facilitating metastasis. Type IV collagen is the major structural component of the basement membrane and is known to be a polyvalent ligand, possessing sequences bound by the alpha1beta1, alpha2beta1, and alpha3beta1 integrins, as well as cell surface proteoglycan receptors, such as CD44/chondroitin sulfate proteoglycan (CSPG). The role of alpha2beta1 integrin and CD44/CSPG receptor binding on human melanoma cell activation has been evaluated herein using triple-helical peptide ligands incorporating the alpha1(IV)382-393 and alpha1(IV)1263-1277 sequences, respectively. Gene expression and protein production of matrix metalloproteinases-1 (MMP-1), -2, -3, -13, and -14 were modulated with the alpha2beta1-specific sequence, whereas the CD44-specific sequence yielded significant stimulation of MMP-8 and lower levels of modulation of MMP-1, -2, -13, and -14. Analysis of enzyme activity confirmed different melanoma cell proteolytic potentials based on engagement of either the alpha2beta1 integrin or CD44/CSPG. These results are indicative of specific activation events that tumor cells undergo upon binding to select regions of basement membrane collagen. Based on the present study, triple-helical peptide ligands provide a general approach for monitoring the regulation of proteolysis in cellular systems.

Regulation of angiogenesis by extracellular matrix

During angiogenesis, endothelial cell growth, migration, and tube formation are regulated by pro- and anti-angiogenic factors, matrix-degrading proteases, and cell-extracellular matrix interactions. Temporal and spatial regulation of extracellular matrix remodeling events allows for local changes in net matrix deposition or degradation, which in turn contributes to control of cell growth, migration, and differentiation during different stages of angiogenesis. Remodeling of the extracellular matrix can have either pro- or anti-angiogenic effects. Extracellular matrix remodeling by proteases promotes cell migration, a critical event in the formation of new vessels. Matrix-bound growth factors released by proteases and/or by angiogenic factors promote angiogenesis by enhancing endothelial migration and growth. Extracellular matrix molecules, such as thrombospondin-1 and -2, and proteolytic fragments of matrix molecules, such as endostatin, can exert anti-angiogenic effects by inhibiting endothelial cell proliferation, migration and tube formation. In contrast, other matrix molecules promote endothelial cell growth and morphogenesis, and/or stabilize nascent blood vessels. Hence, extracellular matrix molecules and extracellular matrix remodelling events play a key role in regulating angiogenesis.

Distinct Roles for the Catalytic and Hemopexin Domains of Membrane Type 1-Matrix Metalloproteinase in Substrate Degradation and Cell Migration

Substrate degradation and cell migration are key steps in cancer metastasis. Membrane-type 1-matrix metalloproteinase (MT1-MMP) has been linked with these processes. Using the fluorescein isothiocyanate (FITC)-labeled fibronectin degradation assay combined with the phagokinetic cell migration assay, structure-function relationships of MT1-MMP were studied. Our data indicate that MT1-MMP initiates substrate degradation and enhances cell migration; cell migration occurs as a concurrent but independent event. Using recombinant DNA approaches, we demonstrated that the hemopexin-like domain and a nonenzymatic component of the catalytic domain of MT1-MMP are essential for MT1-MMP-mediated cell migration. Because the cytoplasmic domain of MT1-MMP was not required for MT1-MMP-mediated fibronectin degradation and cell migration, it is proposed that cross-talk between the hemopexin domain of MT1-MMP and adjacent cell surface molecules is responsible for outside-in signaling. Employing cDNAs encoding dominant negative mutations, we demonstrated that Rac1 participates in the MT1-MMP signal transduction pathway. These data demonstrated that each domain of MT1-MMP plays a distinct role in substrate degradation and cell migration.

Implication des métalloprotéinases matricielles (MMPs) dans la progression du mélanome cutané

Among skin cancers, melanoma is probably the most highly invasive and metastasizing, with a poor outcome. During melanoma progression, tumor cells must across the dermal-epidermal junction, and invade the dermis, its principal site of propagation. Therefore, degradation of matrix proteins constituting dermal-epidermal junction and dermis by proteolytic enzymes is an essential step of melanoma invasion. Serines proteinases and Matrix Metalloproteinases (MMPs) families are the main degrading substances involved in this process. Among MMPs, the expression of MMP-1, -2, -3, -9, -14, 15, -16 by melanoma cells was shown in vitro and in vivo, and correlated with the invasive phenotype. In addition to disrupt matrix proteins, MMPs can also cleave non matrix components such as cytokines, and growth factors. The modifications generated by the remodeling of matrix and non-matrix components can influence melanoma cells proliferation, adhesion, vascularization, survival, proteases expression, and migration. Thus, using inhibitors in order to control expression, activation and activity of MMPs could regulate cellular process which led to melanoma progression.

Modulation of prostate cancer growth in bone microenvironments

Bone remains one of the major sites, and most lethal host organs, for prostate cancer metastasis. Prostate cell spread and establishment in bone depends on multiple reciprocal modifications of bone stromal and epithelial cancer cell behaviors. This review focuses on recent advances in the characterization of cell-cell and cell-matrix interplay, effects on cell growth, adhesion and invasion, and several therapeutic possibilities for co-targeting prostate cancer cells and bone stroma. We address the topic from three main perspectives: (1) the normal and aging bone stromal environment, (2) the "reactive" bone stromal environment, and (3) the cancerous prostate epithelial cells themselves. First, normal, and especially aging, bones provide uniquely rich and "fertile soil" for roaming cancer cells. The interactions between prostate cancer cells and insoluble extracellular matrices, soluble growth factors, and/or sex steroid hormones trigger bone remodeling, through increased osteoclastogenesis and furthur matrix metalloproteinase activity. Second, after cancer cell arrival and establishment in the bone, host stromal cells respond, becoming "reactive" in a process again involving extracellular matrix remodeling, together with growth factor and steroid receptor signaling this process ultimately enhances cancer cell migration, stromal transdifferentiation, and invasion of the cancer tissues by stromal, inflammatory, and immune-responsive cells. Third, prostate cancer cells also respond to supportive bone microenvironments, where soluble and matrix-associated molecules affect cancer cell growth and gene expression, especially altering cancer cell surface receptor and integrin-mediated cell signaling. We discuss both integrin cell-matrix and gap junctional cell-cell communication between cancer cells and their microenvironments during prostate cancer progression.

Mechanism of human dermal fibroblast migration driven by type I collagen and platelet-derived growth factor-BB

Migration of human dermal fibroblasts (HDFs) is critical for skin wound healing. The mechanism remains unclear. We report here that platelet-derived growth factor-BB (PDGF-BB) is the major promotility factor in human serum for HDF motility on type I collagen. PDGF-BB recapitulates the full promotility activity of human serum and anti-PDGF neutralizing antibodies completely block it. Although collagen matrix initiates HDF migration without growth factors, PDGF-BB-stimulated migration depends upon attachment of the cells to a collagen matrix. The PDGF-BB's role is to provide directionality and further enhancement for the collagen-initiated HDF motility. To study the collagen and PDGF-BB "dual signaling" in primary HDF, we establish "gene cassettes" plus lentiviral gene delivery approach, in which groups of genes are studied individually or in combination for their roles in HDF migration. Focal adhesion kinase, p21(Rac,CDC42)-activated kinase and Akt are grouped into an upstream kinase gene cassette, and the four major mitogen-activated protein kinases (extracellular signal-regulated kinase 1/2, p38, c-Jun NH2-terminal kinase, and extracellular signal-regulated kinase 5) are grouped into a downstream kinase gene cassette. The experiments demonstrate 1) the genes' individual roles and specificities, 2) their combined effects and sufficiency, and 3) the mechanisms of their intermolecular connections in HDF migration driven by collagen and PDGF-BB.

Ecteinascidin-743 drug resistance in sarcoma cells: transcriptional and cellular alterations

A human chondrosarcoma cell line, CS-1, was treated successively with increasing concentrations of the marine chemotherapeutic Ecteinascidin-743 (ET-743), yielding a variant cell line displaying a significant degree of resistance to the cytotoxic action of this drug. Various experiments were performed to discern molecular aberrations between the parent and resistant cell line, and also identify potential molecular markers indicative of drug resistance. Although no significant differences in the levels of membrane transporters such as P-glycoprotein or multidrug resistance protein 1 (MRP1) were detected, the cell migratory ability of the ET-743-resistant cell variant was reduced, as was its attachment capability to gelatin-coated cell culture dishes. Staining of the actin-containing cytoskeleton with fluorescent-labeled phalloidin revealed marked differences in the cytoskeleton architecture between the parent and ET-743-resistant CS-1 cell lines. Comparison of serum-free conditioned medium from both cell lines showed conspicuous differences in the levels of several proteins, including a quartet of high molecular weight proteins (> or =140 kDa). The protein sequences of two of these high molecular weight proteins, present at significantly higher concentrations in conditioned medium obtained from the parent cell line, corresponded to subunits of types I and IV collagen. Analysis of type I collagen alpha1 chain mRNA revealed a significantly lower level in the ET-743-resistant CS-1 cell line. Thus, prolonged exposure to ET-743 may cause changes in cell function through cytoskeleton rearrangement and/or modulation of collagen levels.

Metalloproteinases and plasminogen activators in vessel remodeling

Remodeling of blood vessels underlies the pathogenesis of major cardiovascular disorders, including atherosclerosis, restenosis, and hypertension. Because remodeling of arteries is highly dependent on degradation of the extracellular matrix, which enables cells to migrate and proliferate, there is intense interest in the regulation and the roles of matrix metalloproteinases (MMPs) and the plasminogen activator-plasmin (PA-P) systems in vessel remodeling. Factors that promote vessel remodeling have been shown to be important in upregulating the activities of both proteolytic systems and include chronic changes in hemodynamics, vessel injury, cytokines involved in inflammation, and elevations in reactive oxygen species. The two proteolytic systems utilize common transcription factors to activate their respective genes and are frequently coexpressed in remodeling and atherosclerotic arteries. In this review, we discuss the effects of activating the MMP and PA-P systems on processes involved in vascular remodeling, factors regulating their expression and activation, their roles in restenosis, and the development and progression of atherosclerosis, as well as the ability of currently available inhibitors to prevent unfavorable remodeling and atherosclerosis.

Aggretin, a snake venom-derived endothelial integrin alpha 2 beta 1 agonist, induces angiogenesis via expression of vascular endothelial growth factor

Aggretin, a collagen-like alpha 2 beta 1 agonist purified from Calloselasma rhodostoma venom, was shown to increase human umbilical vein endothelial cell (HUVEC) proliferation and HUVEC migration toward immobilized aggretin was also increased. These effects were blocked by A2-IIE10, an antibody raised against integrin alpha 2. Aggretin bound to HUVECs in a dose-dependent and saturable manner, which was specifically inhibited by A2-IIE10, as examined by flow cytometry. Aggretin elicited significant angiogenic effects in both in vivo and in vitro angiogenesis assays, and incubation of HUVECs with aggretin activated phosphatidylinositol 3-kinase (PI3K), Akt, and extracellular-regulated kinase 1/2 (ERK1/2); these effects were blocked by A2-IIE10 or vascular endothelial growth factor (VEGF) monoclonal antibody (mAb). The angiogenic effect induced by aggretin may be via the production of VEGF because the VEGF level was elevated and VEGF mAb pretreatment inhibited Akt/ERK1/2 activation as well as the in vivo angiogenesis induced by aggretin. The VEGF production induced by aggretin can be blocked by A2-IIE10 mAb pretreatment. In conclusion, aggretin induces endothelial cell proliferation, migration, and angiogenesis by interacting with integrin alpha 2 beta 1 leading to activation of PI3K, Akt, and ERK1/2 pathways, and the increased expression of VEGF may be responsible for its angiogenic activity.

Alpha(v)beta3 and alpha(v)beta5 integrins bind both the proximal RGD site and non-RGD motifs within noncollagenous (NC1) domain of the alpha3 chain of type IV collagen: implication for the mechanism of endothelia cell adhesion

The NC1 domains of human type IV collagen, in particular alpha3NC1, are inhibitors of angiogenesis and tumor growth (Petitclerc, E., Boutaud, A., Prestayko, A., Xu, J., Sado, Y., Ninomiya, Y., Sarras, M. P., Jr., Hudson, B. G., and Brooks, P. C. (2000) J. Biol. Chem. 275, 8051-8061). The recombinant alpha3NC1 domain contained a RGD site as part of a short collagenous sequence at the N terminus, designated herein as RGD-alpha3NC1. Others, using synthetic peptides, have concluded that this RGD site is nonfunctional in cell adhesion, and therefore, the anti-angiogenic activity is attributed exclusively to alpha(v)beta(3) integrin interactions with non-RGD motifs of the RGD-alpha3NC1 domain (Maeshima, Y., Colorado, P. C., and Kalluri, R. (2000) J. Biol. Chem. 275, 23745-23750). This nonfunctionality is surprising given that RGD is a binding site for alpha(v)beta(3) integrin in several proteins. In the present study, we used the alpha3NC1 domain with or without the RGD site, expressed in HEK 293 cells for native conformation, as an alternative approach to synthetic peptides to assess the functionality of the RGD site and non-RGD motifs. Our results demonstrate a predominant role of the RGD site for endothelial adhesion and for binding of alpha(v)beta(3) and alpha(v)beta(5) integrins. Moreover, we demonstrate that the two non-RGD peptides, previously identified as the alpha(v)beta(3) integrin-binding sites of the alpha3NC1 domain, are 10-fold less potent in competing for integrin binding than the native protein, indicating the importance of additional structural and/or conformational features of the alpha3NC1 domain for integrin binding. Therefore, the RGD site, in addition to non-RGD motifs, may contribute to the mechanisms of endothelial cell adhesion in the human vasculature and the anti-angiogenic activity of the RGD-alpha3NC1 domain.

Abnormalities of basement membrane on blood vessels and endothelial sprouts in tumors

Often described as incomplete or absent, the basement membrane of blood vessels in tumors has attracted renewed attention as a source of angiogenic and anti-angiogenic molecules, site of growth factor binding, participant in angiogenesis, and potential target in cancer therapy. This study evaluated the composition, extent, and structural integrity of the basement membrane on blood vessels in three mouse tumor models: spontaneous RIP-Tag2 pancreatic islet tumors, MCa-IV mammary carcinomas, and Lewis lung carcinomas. Tumor vessels were identified by immunohistochemical staining for the endothelial cell markers CD31, endoglin (CD105), vascular endothelial growth factor receptor-2, and integrin alpha5 (CD49e). Confocal microscopic studies revealed that basement membrane identified by type IV collagen immunoreactivity covered >99.9% of the surface of blood vessels in the three tumors, just as in normal pancreatic islets. Laminin, entactin/nidogen, and fibronectin immunoreactivities were similarly ubiquitous on tumor vessels. Holes in the basement membrane, found by analyzing 1- micro m confocal optical sections, were <2.5 micro m in diameter and involved only 0.03% of the vessel surface. Despite the extensive vessel coverage, the basement membrane had conspicuous structural abnormalities, including a loose association with endothelial cells and pericytes, broad extensions away from the vessel wall, and multiple layers visible by electron microscopy. Type IV collagen-immunoreactive sleeves were also present on endothelial sprouts, supporting the idea that basement membrane is present where sprouts grow and regress. These findings indicate that basement membrane covers most tumor vessels but has profound structural abnormalities, consistent with the dynamic nature of endothelial cells and pericytes in tumors.

Generation of a Monoclonal Antibody to a Cryptic Site Common to Both Integrin β1 as Well as Gelatinase MMP9

Integrins are one class of cell surface receptors that have been implicated in the regulation of a diverse set of cellular processes, including cell adhesion, migration, and invasion as well as gene expression, differentiation, and signal transduction. Cellular invasion not only requires the adhesive properties of integrins but also the proteolytic properties of matrix-degrading enzymes, such as the metalloproteinases (MMPs). Previous studies have shown that integrin alphavbeta3 is a receptor for MMP2, localizing its proteinase activity to the cell surface, ultimately leading to site-specific extracellular matrix (ECM) degradation. Here we develop reagents to investigate the possibility of an interplay between MMP9 and integrin alpha5beta1. With the use of EV22 viral studies, the tetrapeptide sequence, LRSG, was shown to be a dimerizing sequence mediating beta1 integrin binding to EV22. The same study also showed that cellular infection could be halted with the use of LRSG-containing peptides. In a later study, in an effort to isolate inhibitors of the MMP family, LRSG sequence was identified as one capable of binding MMP9. Interestingly, MMP9 contains an LRSG sequence, raising the possibility that MMP9 binds the cell surface via beta1 integrins through the dimerizing LRSG motif. We used the LRSG-containing sequence from beta1 integrins as an antigen to generate the monoclonal antibody (MAB) FM155 in the mouse model. MAB FM155 will help identify a cryptic epitope, LRSG, and its role in matrix remodeling as well as tumor growth, cancer cell migration, and angiogenesis.

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

Cancer cells are able to proliferate at accelerated rates within the confines of a three-dimensional (3D) extracellular matrix (ECM) that is rich in type I collagen. The mechanisms used by tumor cells to circumvent endogenous antigrowth signals have yet to be clearly defined. We find that the matrix metalloproteinase, MT1-MMP, confers tumor cells with a distinct 3D growth advantage in vitro and in vivo. The replicative advantage conferred by MT1-MMP requires pericellular proteolysis of the ECM, as proliferation is fully suppressed when tumor cells are suspended in 3D gels of protease-resistant collagen. In the absence of proteolysis, tumor cells embedded in physiologically relevant ECM matrices are trapped in a compact, spherical configuration and unable to undergo changes in cell shape or cytoskeletal reorganization required for 3D growth. These observations identify MT1-MMP as a tumor-derived growth factor that regulates proliferation by controlling cell geometry within the confines of the 3D ECM.

Extracellular matrix remodelling: the role of matrix metalloproteinases

Matrix metalloproteinases (MMPs) are a growing family of metalloendopeptidases that cleave the protein components of the extracellular matrix and thereby play a central role in tissue remodelling. For many years following their discovery, MMPs were believed to function primarily as regulators of ECM composition and to facilitate cell migration simply by removing barriers such as collagen. It is becoming increasingly clear, however, that MMPs are implicated in the functional regulation of a host of non-ECM molecules that include growth factors and their receptors, cytokines and chemokines, adhesion receptors and cell surface proteoglycans, and a variety of enzymes. MMPs therefore play an important role in the control of cellular interactions with and response to their environment in conditions that promote tissue turnover, be they physiological, such as normal development, or pathological, such as inflammation and cancer. This review summarizes some of the recent discoveries that have shed new light on the role of MMPs in physiology and disease.

Proteolyzed matrix as a template for the regulation of tumor progression

Pericellular proteolysis plays a pivotal function in cell invasion, a hallmark of tumor growth and metastasis. The minidegradome constituted of two matrix metalloproteinases (MMP), i.e. MMP-2 and MT1-MMP, associated with tissue inhibitor of metalloprotease-2 (TIMP-2) and integrin (alpha(v)beta(3)) or CD(44), is mainly involved in such invasive program. It catalyzes matrix degradation but, alternatively, proteolytic exposure of matricryptic sites or matrikines liberation by those enzymes regulates either positively or negatively tumor cell migration. That applies to types I and IV collagens, elastin, laminin 5, as described here, but such phenomenon might be extended to other matrix macromolecules. The development of tumors from epithelium origin is related to aging. Senescent fibroblasts are characterized by increased expression of MMPs, (particularly collagenase-1 (MMP-1) and stromelysin-1 (MMP-3)) and deposited matrix by those aged cells was shown to favor cancer cell growth. Thus, compositional variation of matrix-surrounding tumor cells, with formation of matricryptic sites and matrikines, can be considered as one main epigenetic factor contributing to tumor progression. A matrix-directed pharmacological approach in cancer is now emerging.