The activity of collagenase-1 is required for keratinocyte migration on a type I collagen matrix

Matrix metalloproteinases in repair

During repair, many different matrix metalloproteinases are produced by multiple cell types residing in various compartments within the wound environment. This diversity of enzymes, coupled with discreet cellular expression, implies that different matrix metalloproteinases serve different functions, acting on a variety of substrates, during wound healing. With few exceptions, however, the actual function and spectrum of functions of matrix metalloproteinases in vivo is not known. Even with the advent of genetically defined animal models, few studies have rigorously addressed the substrates and role of matrix metalloproteinases in wound repair. Before we can understand the role of matrix metalloproteinases in ulceration and disease, we need to determine the function these enzymes serve in normal tissues and repair.

Extracellular matrix remodelling and cellular differentiation

The extracellular matrix is not merely a passive structure. In the past few years, it has emerged that the matrix is a dynamic action zone that functions to instruct cellular phenotype. Extracellular matrix proteins interact directly with cell surface receptors to initiate signal transduction pathways and to modulate those triggered by differentiation and growth factors. The extracellular matrix also controls the activity and presentation of a wide range of growth factors. Thus modulation of the extracellular matrix, by remodelling its structure and activity, has profound effects on its function and the consequent behaviour of cells residing on or within it.

Proteolysis and cell migration: creating a path?

Both serine and metalloproteinases have been implicated in the complex integrated events underlying cell migration but no definitive single mechanism has emerged. Work over the past two years linking both membrane and soluble proteinases with integrins and other adhesion proteins and with intracellular signalling systems could herald the beginnings of a potential expansion of our understanding of the role and regulation of proteolysis in cell migration.

A metalloprotease prepares the way

In the nematode Caenorhabditis elegans gonad shape and size is determined by the migration of a leader cell, which is at the tip of the growing gonad arm. A metalloprotease secreted by the leader cell has recently been found to play an essential role in this process, preparing the way ahead for the cell's migration.

Matrix metalloproteinase 2 (gelatinase A) is related to migration of keratinocytes

The role of matrix metalloproteinases (MMPs) in cell migration was studied by measuring cell growth, migration, and production of MMP-2 and -9 in oral mucosal and skin keratinocytes cultured in the presence of synthetic MMP inhibitors. MMP-2 was the major gelatinolytic MMP produced by these cells while MMP-9 was produced at a low basal level. Inhibitor effects on MMP-9 production were therefore studied in keratinocytes stimulated by tumor necrosis factor alpha (TNFalpha). Tetracycline analogues at concentrations that inhibited the production of MMP-2 but not MMP-9 were able to drastically inhibit migration of both mucosal and skin keratinocytes. Tetracycline analogues also inhibited keratinocyte growth, an effect not found for the other inhibitors tested. Heterocyclic carbonate-derived compounds (LWs) that inhibited MMP-9 but not MMP-2 production had no effect on cell migration. Batimastat, a potent MMP inhibitor, did not have any effect on MMP production or cell growth but did inhibit keratinocyte migration. Tumor growth factor beta (TGFbeta) increased keratinocyte migration as well as both cell-associated and secreted MMP-2 production in wounded cell cultures. The secreted enzyme was partially converted into an active form. In this model batimastat totally blocked TGFbeta-promoted keratinocyte migration. Immunostaining of keratinocytes advancing into the wound revealed that MMP-2 was localized in extracellular matrix contactlike structures against the endogenously produced laminin-5-rich matrix. MMP-9 was localized diffusely along the cell membranes. Using in situ hybridization we observed that in chronically inflamed human gingiva MMP-2 is expressed in epithelium extending into subepithelial connective tissue. These results suggest that MMP-2 plays a specific role in epithelial migration, possibly by detaching the advancing cells from the pericellular matrix or by activating other MMPs.

Role of matrix metalloproteinases and their inhibition in cutaneous wound healing and allergic contact hypersensitivity

Normal wounds can heal by secondary intention (epidermal migration to cover a denuded surface) or by approximation of the wound edges (e.g., suturing). In healing by secondary intention, epidermis-derived MMPs are important. Keratinocyte migration begins within 3-6 hr post injury, as basal cells detach from underlying basal lamina and encounter a dermal substratum rich in type I collagen. Cell contact with type I collagen in vitro stimulates collagenase-1 expression, which is mediated by the alpha 2 beta 1 integrin, the major keratinocyte collagen-binding receptor. Collagenase-1 activity alone is necessary and sufficient for keratinocyte migration over a collagen subsurface. Stromelysins-1 and -2 are also found in the epidermis of normal acute wounds. Stromelysin-2 co-localizes with collagenase-1 and may facilitate cell migration over non-collagenous matrices of the dermis. In contrast, stromelysin-1 is expressed by keratinocytes behind the migrating front and which remain on basal lamina, i.e., the proliferative cell population. Studies with stromelysin-1-deficient mice that suggest this MMP plays a role in keratinocyte detachment from underlying basement membrane to initiate cell migration. In chronic ulcers, MMP levels are markedly elevated, in contrast to their precise temporal and spatial expression in acute wounds. Both collagenase-1 and stromelysin-1 are found in fibroblasts underlying the nonhealing epithelium, and stromelysin-1 expression is especially prominent. Two key questions underlie the use of MMP inhibitors and wound healing: (1) will these agents impair normal reepithelialization in wounds that heal by secondary intention; and (2) can MMP inhibitors be effective therapy for chronic ulcers? The answer to neither is known. Batimastat and marimastat appear not to interfere with normal wound healing, but only in sutured surgical wounds, a situation in which MMP expression has practically no role. We also show the first example of an in vivo immune response, contact hypersensitivity, which is dependent upon MMP activity. Using gene-deficient mice, we demonstrate that stromylysin-1 (MMP-3) is required for sensitization, whereas gelatinase B (MMP-9) is required for timely resolution of the reaction to antigenic challenge.

Expression of matrix metalloproteinase-1, -2 and -3 in squamous cell carcinoma and actinic keratosis

Matrix metalloproteinase (MMP) plays an important role in extracellular matrix degradation associated with cancer invasion. An expression of MMP-1 (interstitial collagenase), MMP-2 (72-kDa type IV collagenase) and MMP-3 (stromelysin-1) was investigated in squamous cell carcinoma (SCC) and its precancerous condition, actinic keratosis (AK), using in situ hybridization techniques. MMP-1 mRNA was detected in tumour cells and/or in stromal cells in all cases of SCC, four of six AKs adjacent to SCC and four of 16 AKs. MMP-2 and MMP-3 mRNAs were detected in SCC but not in AK. The expression of MMP-3 correlated to that of MMP-1 (P = 0.03) localized at the tumour mass and stroma of the invasive area, while MMP-2 mRNA was detected widely throughout the stroma independent of MMP-1 expression. Our results indicated that the expression of MMP-1, -2 and -3 showed different localization patterns, suggesting a unique role of each MMP in tumour progression. Moreover, MMP-1 expression could be an early event in the development of SCC, and AK demonstrating MMP-1 mRNA, might be in a more advanced dysplastic state, progressing to SCC.

The metalloproteinase matrilysin is a target of beta-catenin transactivation in intestinal tumors

Matrilysin is a matrix metalloproteinase expressed in the tumor cells of greater than 80% of intestinal adenomas. The majority of these intestinal tumors are associated with the accumulation of beta-catenin, a component of the cadherin adhesion complex and, through its association with the T Cell Factor (Tcf) DNA binding proteins, a regulator in the Wnt signal transduction pathway. In murine intestinal tumors, matrilysin transcripts show striking overlap with the accumulation of beta-catenin protein. The matrilysin promoter is upregulated as much as 12-fold by beta-catenin in colon tumor cell lines in a manner inversely proportional to the endogenous levels of beta-catenin/Tcf complex and is dependent upon a single optimal Tcf-4 recognition site. Coexpression of the E-cadherin cytoplasmic domain blocked this induction and reduced basal promoter activity in every colon cancer cell line tested. Inactivation of the Tcf binding site increased promoter activity and overexpression of the Tcf factor, LEF-1, significantly downregulated matrilysin promoter activity, suggesting that beta-catenin transactivates the matrilysin promoter by virtue of its ability to abrogate Tcf-mediated repression. Because genetic ablation of matrilysin decreases tumor formation in multiple intestinal neoplasia (Min) mice, we propose that regulation of matrilysin production by beta-catenin accumulation is a contributing factor to intestinal tumorigenesis.

Cell surface colligin/Hsp47 associates with tetraspanin protein CD9 in epidermoid carcinoma cell lines

Hsps expressed on the cell surface have been associated with tumor invasiveness and used as targets for molecular surveillance. The present study utilized four human oral squamous cell carcinoma cells lines, SCC-4, SCC-9, SCC-15, SCC-25, the murine epidermoid carcinoma cell line LL/2, and primary cultures of human gingival fibroblasts to assess the cell surface expression of colligin/Hsp47, a proposed marker for malignancy. Immunoprecipitation studies following protein crosslinking revealed that Hsp47 was associated with a number of membrane proteins including the tetraspanin CD9. Cytometric analyses were performed to determine the distribution of cell surface colligin/Hsp47 during the phases of the cell cycle. These studies showed that colligin/Hsp47 was not limited to any phase of the cell cycle in epidermoid carcinoma cells. Boyden chamber tumor invasion assays and colloidal gold migration assays utilizing a reconstituted basement membrane (Matrigel), collagen type I, and laminin-5 substrates revealed that cell lines expressing constitutive high levels of colligin/Hsp47 manifested the lowest invasion and migration indices. The incorporation of antibodies against Hsps into the migration and invasion assays, likewise, increased the invasion indices and the phagokinetic migration indices. These data indicate that colligin/Hsp47 is anchored to the cell membrane in a complex with CD9 where it moderates tumor cell invasion and motility possibly by acting as a serpin protein inhibitor or as a receptor for collagen.

Keratinocyte collagenase-1 expression requires an epidermal growth factor receptor autocrine mechanism

In response to cutaneous injury, expression of collagenase-1 is induced in keratinocytes via alpha2beta1 contact with native type I collagen, and enzyme activity is essential for cell migration over this substratum. However, the cellular mechanism(s) mediating integrin signaling remain poorly understood. We demonstrate here that treatment of keratinocytes cultured on type I collagen with epidermal growth factor receptor (EGFR) blocking antibodies or a specific receptor antagonist inhibited cell migration across type I collagen and the matrix-directed stimulation of collagenase-1 production. Additionally, stimulation of collagenase-1 expression by hepatocyte growth factor, transforming growth factor-beta1, and interferon-gamma was blocked by EGFR inhibitors, suggesting a required EGFR autocrine signaling step for enzyme expression. Collagenase-1 mRNA was not detectable in keratinocytes isolated immediately from normal skin, but increased progressively following 2 h of contact with collagen. In contrast, EGFR mRNA was expressed at high steady-state levels in keratinocytes isolated immediately from intact skin but was absent following 2 h cell contact with collagen, suggesting down-regulation following receptor activation. Indeed, tyrosine phosphorylation of the EGFR was evident as early as 10 min following cell contact with collagen. Treatment of keratinocytes cultured on collagen with EGFR antagonist or heparin-binding (HB)-EGF neutralizing antibodies dramatically inhibited the sustained expression (6-24 h) of collagenase-1 mRNA, whereas initial induction by collagen alone (2 h) was unaffected. Finally, expression of collagenase-1 in ex vivo wounded skin and re-epithelialization of partial thickness porcine burn wounds was blocked following treatment with EGFR inhibitors. These results demonstrate that keratinocyte contact with type I collagen is sufficient to induce collagenase-1 expression, whereas sustained enzyme production requires autocrine EGFR activation by HB-EGF as an obligatory intermediate step, thereby maintaining collagenase-1-dependent migration during the re-epithelialization of epidermal wounds.

Bone resorption induced by parathyroid hormone is strikingly diminished in collagenase-resistant mutant mice

Parathyroid hormone (PTH) stimulates bone resorption by acting directly on osteoblasts/stromal cells and then indirectly to increase differentiation and function of osteoclasts. PTH acting on osteoblasts/stromal cells increases collagenase gene transcription and synthesis. To assess the role of collagenase in the bone resorptive actions of PTH, we used mice homozygous (r/r) for a targeted mutation (r) in Col1a1 that are resistant to collagenase cleavage of type I collagen. Human PTH(1-34) was injected subcutaneously over the hemicalvariae in wild-type (+/+) or r/r mice four times daily for three days. Osteoclast numbers, the size of the bone marrow spaces and periosteal proliferation were increased in calvariae from PTH-treated +/+ mice, whereas in r/r mice, PTH-induced bone resorption responses were minimal. The r/r mice were not resistant to other skeletal effects of PTH because abundant interstitial collagenase mRNA was detected in the calvarial periosteum of PTH-treated, but not vehicle-treated, r/r and +/+ mice. Calcemic responses, 0.5-10 hours after intraperitoneal injection of PTH, were blunted in r/r mice versus +/+ mice. Thus, collagenase cleavage of type I collagen is necessary for PTH induction of osteoclastic bone resorption.

alpha1 and alpha2 integrins mediate invasive activity of mouse mammary carcinoma cells through regulation of stromelysin-1 expression

Tumor cell invasion relies on cell migration and extracellular matrix proteolysis. We investigated the contribution of different integrins to the invasive activity of mouse mammary carcinoma cells. Antibodies against integrin subunits alpha6 and beta1, but not against alpha1 and alpha2, inhibited cell locomotion on a reconstituted basement membrane in two-dimensional cell migration assays, whereas antibodies against beta1, but not against alpha6 or alpha2, interfered with cell adhesion to basement membrane constituents. Blocking antibodies against alpha1 integrins impaired only cell adhesion to type IV collagen. Antibodies against alpha1, alpha2, alpha6, and beta1, but not alpha5, integrin subunits reduced invasion of a reconstituted basement membrane. Integrins alpha1 and alpha2, which contributed only marginally to motility and adhesion, regulated proteinase production. Antibodies against alpha1 and alpha2, but not alpha6 and beta1, integrin subunits inhibited both transcription and protein expression of the matrix metalloproteinase stromelysin-1. Inhibition of tumor cell invasion by antibodies against alpha1 and alpha2 was reversed by addition of recombinant stromelysin-1. In contrast, stromelysin-1 could not rescue invasion inhibited by anti-alpha6 antibodies. Our data indicate that alpha1 and alpha2 integrins confer invasive behavior by regulating stromelysin-1 expression, whereas alpha6 integrins regulate cell motility. These results provide new insights into the specific functions of integrins during tumor cell invasion.

Induction of collagenase-3 (MMP-13) expression in human skin fibroblasts by three-dimensional collagen is mediated by p38 mitogen-activated protein kinase

Collagenase-3 (matrix metalloproteinase-13, MMP-13) is a recently identified human MMP with an exceptionally wide substrate specificity and restricted tissue-specific expression. Here we show that MMP-13 expression is induced in normal human skin fibroblasts cultured within three-dimensional collagen gel resulting in production and proteolytic activation of MMP-13. Induction of MMP-13 mRNAs by collagen gel was potently inhibited by blocking antibodies against alpha1 and alpha2 integrin subunits and augmented by activating antibody against beta1 integrin subunit, indicating that both alpha1 beta1 and alpha2 beta1 integrins mediate the MMP-13-inducing cellular signal generated by three-dimensional collagen. Collagen-related induction of MMP-13 expression was dependent on tyrosine kinase activity, as it was abolished by treatment of fibroblasts with tyrosine kinase inhibitors genistein and herbimycin A. Contact of fibroblasts to three-dimensional collagen resulted in simultaneous activation of mitogen-activated protein kinases (MAPKs) in three distinct subgroups: extracellular signal-regulated kinase (ERK)1 and ERK2, Jun N-terminal kinase/stress-activated protein kinase, and p38. Induction of MMP-13 expression was inhibited by treatment of fibroblasts with a specific p38 inhibitor, SB 203580, whereas blocking the ERK1,2 pathway (Raf/MEK1,2/ERK1,2) by PD 98059, a selective inhibitor of MEK1,2 activation potently augmented MMP-13 expression. Furthermore, specific activation of ERK1,2 pathway by 12-O-tetradecanoylphorbol-13-acetate markedly suppressed MMP-13 expression in dermal fibroblasts in collagen gel. These results show that collagen-dependent induction of MMP-13 in dermal fibroblasts requires p38 activity, and is inhibited by activation of ERK1,2. Therefore, the balance between the activity of ERK1,2 and p38 MAPK pathways appears to be crucial in regulation of MMP-13 expression in dermal fibroblasts, suggesting that p38 MAPK may serve as a target for selective inhibition of collagen degradation, e.g. in chronic dermal ulcers.

Role of collagenase in mediating in vitro alveolar epithelial wound repair

Type II pneumocytes are essential for repair of the injured alveolar epithelium. The effect of two MMP collagenases, MMP-1 and MMP-13 on alveolar epithelial repair was studied in vitro. The A549 alveolar epithelial cell line and primary rat alveolar epithelial cell cultures were used. Cell adhesion and cell migration were measured with and without exogenous MMP-1. Wound healing of a cell monolayer of rat alveolar epithelial cell after a mechanical injury was evaluated by time lapse video analysis. Cell adhesion on type I collagen, as well as cytoskeleton stiffness, was decreased in the presence of exogenous collagenases. A similar decrease was observed when cell adhesion was tested on collagen that was first incubated with MMP-1 (versus control on intact collagen). Cell migration on type I collagen was promoted by collagenases. Wound healing of an alveolar epithelial cell monolayer was enhanced in the presence of exogenous collagenases. Our results suggest that collagenases could modulate the repair process by decreasing cell adhesion and cell stiffness, and by increasing cell migration on type I collagen. Collagen degradation could modify cell adhesion sites and collagen degradation peptides could induce alveolar type II pneumocyte migration. New insights regarding alveolar epithelial cell migration are particularly relevant to investigate early events during alveolar epithelial repair following lung injury.

Contributions of the epidermal growth factor receptor to keratinocyte motility

The epidermal growth factor (EGF) receptor plays a central role in numerous aspects of keratinocyte biology. In normal epidermis, the EGF receptor is important for autocrine growth of this renewing tissue, suppression of terminal differentiation, promotion of cell survival, and regulation of cell migration during epidermal morphogenesis and wound healing. In wounded skin, the EGF receptor is transiently up-regulated and is an important contributor to the proliferative and migratory aspects of wound reepithelialization. In keratinocytic carcinomas, aberrant expression or activation of the EGF receptor is common and has been proposed to play a role in tumor progression. Many cellular processes such as altered cell adhesion, expression of matrix degrading proteinases, and cell migration are common to keratinocytes during wound healing and in metastatic tumors. The EGF receptor is able to regulate each of these cellular functions and we propose that transient and dynamic elevation of EGF receptor during wound healing, or constitutive overexpression in tumors, provides an important contribution to the migratory and invasive potential of keratinocytes.

Cell migration strategies in 3-D extracellular matrix: differences in morphology, cell matrix interactions, and integrin function

Cell migration in extracellular matrix is a complex process of adhesion and deadhesion events combined with cellular strategies to overcome the biophysical resistance imposed by three-dimensionally interconnected matrix ligands. Using a 3-D collagen matrix migration model in combination with computer-assisted cell tracking for reconstruction of migration paths and confocal microscopy, we investigated molecular principles governing cell-matrix interactions and migration of different cell types. Highly invasive MV3 melanoma cells and fibroblasts are large and highly polarized cells migrating at low speed (0.1-0.5 microm/min) and at high directional persistence. MV3 melanoma cells utilize adhesive migration strategies as characterized by high beta1 integrin surface expression, beta1 integrin clustering at interactions with matrix fibers, and beta1 integrin-mediated adhesion for force generation and migration. In contrast, T lymphocytes and dendritic cells are highly mobile cells of lower beta1 integrin expression migrating at 10- to 40-fold higher velocities, and directionally unpredictable path profiles. This migration occurs in the absence of focal adhesions and largely independent of beta1 integrin-mediated adhesion. Whereas cell-matrix interactions of migrating tumor cells result in traction and reorientation of collagen fibers, partial matrix degradation, and pore formation, leukocytes form transient and short-lived interactions with the collagen lacking structural proteolysis and matrix remodeling. In conclusion, the 3-D extracellular matrix provides a spatially complex and biomechanically demanding substrate for cell migration, thereby differing from cell migration across planar ligands. Highly adhesive and integrin-dependent migration strategies detected in morphologically large and slowly migrating cells may result in reorganization of the extracellular matrix, whereas leukocytes favor largely integrin-independent, rapid, and flexible migration strategies lacking typical focal adhesions and structural matrix remodeling.

Migration of human keratinocytes in electric fields requires growth factors and extracellular calcium

Currents that leak out of wounds generate electric fields lateral to the wound. These fields induce directional locomotion of human keratinocytes in vitro and may promote wound healing in vivo. We have examined the effects of growth factors and calcium, normally present in culture medium and the wound fluid, on the directional migration of human keratinocytes in culture. In electric fields of physiologic strength (100 mV per mm), keratinocytes migrated directionally towards the cathode at a rate of about 1 microm per min. This directional migration requires several growth factors. In the absence of these growth factors, the cell migration rate decreased but directionality was maintained. Epidermal growth factor alone restored cell migration rates at concentrations as low as 0.2 ng per ml. Insulin at 5-100 microg per ml or bovine pituitary extract at 0.2%-2% vol/vol also stimulated keratinocyte motility but was not sufficient to fully restore the migration rate. Keratinocyte migration in electric fields requires extracellular calcium. Changes in calcium concentrations from 3 microM to 3.3 mM did not significantly change keratinocyte migration rate nor directionality in electric fields; however, addition of the chelator ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to migration medium reduced, and eventually abolished, keratinocyte motility. Our results show that (i) growth factors and extracellular calcium are required for electric field-induced directional migration of human keratinocytes, and (ii) keratinocytes migrate equally well in low and high calcium media.

Matrix metalloproteinases regulate neovascularization by acting as pericellular fibrinolysins

During angiogenesis, endothelial cells penetrate fibrin barriers via undefined proteolytic mechanisms. We demonstrate that the fibrinolytic plasminogen activator (PA)-plasminogen system is not required for this process, since tissues isolated from PA- or plasminogen-deficient mice successfully neovascularize fibrin gels. By contrast, neovessel formation, in vitro and in vivo, is dependent on fibrinolytic, endothelial cell-derived matrix metalloproteinases (MMP). MMPs directly regulate this process as invasion-incompetent cells penetrate fibrin barriers when transfected with the most potent fibrinolytic metalloproteinase identified in endothelium, membrane type-1 MMP (MT1-MMP). Membrane display of MT1-MMP is required, as invasion-incompetent cells expressing a fibrinolytically active, transmembrane-deleted form of MT1-MMP remain noninvasive. These observations identify a PA-independent fibrinolytic pathway wherein tethered MMPs function as pericellular fibrinolysins during the neovascularization process.

The significance of matrix metalloproteinases during early stages of tumor progression

Matrix metalloproteinases (MMPs) orchestrate tissue remodeling and play diverse roles during organ development. They are produced excessively during the course of various pathological conditions, including solid tumors. An important function of MMPs during tumor progression is to provide the proteolytic activity that is necessary both for tumor cells to invade extracellular matrix (ECM) and for neovascularization of tumor tissue by endothelial cells. Recently, independent studies in transgenic animals suggest that MMPs may, in addition, promote very early stages of tumor progression. To investigate this possibility further, we have analyzed the consequences of MMP overexpression in functionally normal and nontumorigenic mouse mammary epithelial cells in culture. Our observations demonstrate that the MMP stromelysin-1 (SL-1) triggers an epigenetic molecular program in mammary epithelial cells that results in a number of phenotypic alterations that eventually culminate in the generation of a malignant tumor-cell phenotype.

Vascular endothelial growth factor upregulates the expression of matrix metalloproteinases in vascular smooth muscle cells: role of flt-1

Vascular endothelial growth factor (VEGF) is a critical regulator of angiogenesis that stimulates proliferation, migration, and proteolytic activity of endothelial cells. Although the mitogenic activity of VEGF is endothelial cell specific, recent reports indicate VEGF is able to stimulate chemotaxis and tissue factor production in monocytes. VEGF-stimulated activity in monocytes is mediated by the VEGF receptor flt-1. The purpose of the present study was to investigate the effects of VEGF on another major cell type in the vascular wall, namely, the vascular smooth muscle cell (SMC). Using cultured cells, we showed that VEGF has a minimal mitogenic effect on SMCs, which is in accordance with published data. However, VEGF treatment significantly enhanced production of matrix metalloproteinase (MMP)-1, -3, and -9 by human SMCs. The upregulation of MMP-1 and MMP-9 was pronounced, and the stimulation for MMP-3 was less prominent. Stimulation could be demonstrated at both protein and mRNA levels, as reflected by ELISA, zymography, and Northern blot analysis. To explore the signal transduction pathway for the effect of VEGF on SMCs, we studied the expression of 2 high-affinity VEGF receptors, the kinase insert domain-containing receptor (KDR) and flt-1, in human SMCs. Both reverse transcriptase-polymerase chain reaction and immunoblotting revealed the expression of flt-1. Immunoprecipitation followed by immunoblotting illustrated phosphorylation of the flt-1 receptor after VEGF treatment. Similar methodology failed to detect expression of KDR in human SMCs. These data suggest the role of flt-1 in mediating VEGF-stimulated MMP expression of SMCs. The physiological relevance of MMP upregulation was studied by examining VEGF-stimulated SMC migration through 2 synthetic extracellular matrix barriers, Matrigel and Vitrogen. Our results indicate that VEGF treatment accelerated SMC migration through both barriers, and that this response was blocked by MMP inhibition in Matrigel, which supports a permissive role of MMP in SMC migration. These data are the first to show a direct effect of VEGF on SMCs. SMC-derived MMPs may be an additional source of proteases to digest vascular basement membrane, which is a crucial step in the initial stage of angiogenesis. The MMPs may also contribute to SMC migration in angiogenesis and atherogenesis.

Gelatinase B/lacZ transgenic mice, a model for mapping gelatinase B expression during developmental and injury-related tissue remodeling

Matrix metalloproteinases (MMPs) drive normal tissue remodeling and are implicated in a wide range of pathologies. Although MMP activity is controlled at multiple levels, the primary regulation of MMP activity is transcriptional. The transcriptional promoter elements required for MMP gene expression in cultured cells have been defined, but this has not been extended to the in vivo situation. In this paper, we show that the DNA sequences between -522 and +19 of the rabbit gelatinase B gene (MMP-9) (as characterized in the transgenic mouse line 3445) constitute a minimal promoter that drives appropriate developmental and injury-induced reporter gene expression in transgenic mice. We further show that the expression and activity of three transcription factors (NF-kappaB, AP-2, and Sp1) that control the activity of the gelatinase B promoter are selectively induced in the epithelium migrating to heal a wound. Although promoter activity parallels expression of the endogenous gene in cell cultures, we show by several criteria that cell cultures cannot model many aspects of promoter regulation in vivo. This study reveals that the transgenic mouse line 3445 might be a useful model for investigating the regulation of gelatinase B expression in vivo and for identifying and characterizing new drugs that can control gelatinase B gene transcription.

Matrix metalloproteinase degradation of extracellular matrix: biological consequences

Targeted mutagenesis has allowed investigators to perform controlled experiments in mammals and determine the contribution of individual proteins to physiologic and pathologic processes. Recent lessons learned from matrix metalloproteinase gene targeted mice and other in vivo observations have given new life to old concepts regarding the role of proteolytic fragments of extracellular matrix proteins in regulating a variety of critical processes in cell biology.

Matrilysin expression and function in airway epithelium

We report that matrilysin, a matrix metalloproteinase, is constitutively expressed in the epithelium of peribronchial glands and conducting airways in normal lung. Matrilysin expression was increased in airway epithelial cells and was induced in alveolar type II cells in cystic fibrosis. Other metalloproteinases (collagenase-1, stromelysin-1, and 92-kD gelatinase) were not produced by normal or injured lung epithelium. These observations suggest that matrilysin functions in injury-mediated responses of the lung. Indeed, matrilysin expression was increased in migrating airway epithelial cells in wounded human and mouse trachea. In human tissue, epithelial migration was reduced by > 80% by a hydroxamate inhibitor, and in mouse tissue, reepithelialization in trachea from matrilysin-null mice was essentially blocked. In vivo observations and cell culture studies demonstrated that matrilysin was secreted lumenally by lung epithelium, but upon activation or while migrating over wounds, some matrilysin was released basally. The constitutive production of matrilysin in conducting airways, its upregulation after injury, its induction by alveolar epithelium, and its release into both lumenal and matrix compartments suggest that this metalloproteinase serves multiple functions in intact and injured lung, one of which is to facilitate reepithelialization.

Epidermal growth factor (EGF)- and scatter factor/hepatocyte growth factor (SF/HGF)- mediated keratinocyte migration is coincident with induction of matrix metalloproteinase (MMP)-9

Receptor tyrosine kinases are key regulators of cellular function including cell growth, differentiation, migration, and morphogenesis. Disruptions of receptor tyrosine kinase signaling pathways are often associated with changes in cellular proliferative capacity and tumorigenesis. Both receptor-specific and cell type-specific factors may contribute to the ultimate cellular responses observed after receptor activation. In this regard, we find that both normal keratinocytes and their tumorigenic counterparts display differential responses to activation of receptor tyrosine kinases. Multiple ligands were mitogenic for keratinocytes, but only epidermal growth factor (EGF), transforming growth factor alpha (TGFalpha), and scatter factor/hepatocyte growth factor (SF/HGF) promoted cell motility as assessed by colony dispersion (scattering) and in vitro reepithelialization. Interestingly, growth factor specificity for motility coincided with ligand-mediated cell invasion through a reconstituted basement membrane and induction of the 92-kDa metalloproteinase (MMP-9) activity as determined by gelatin zymogram analysis. Inhibitors of MMP activity or addition of an MMP-9 neutralizing antibody resulted in the loss of growth factor-induced colony dispersion, suggesting a functional role for MMP-9 induction during this response. Coordinate regulation of MMP-9 induction and the migratory response are likely to contribute to the enhanced invasive potential observed in response to EGF and SF/HGF. Our findings suggest that alternate receptor-mediated signaling pathways leading to differences in gene expression may be involved in complex cellular responses such as colony dispersion or invasion.

Cell migration and MMP-9 secretion are increased by epidermal growth factor in HaCaT-ras transfected cells

Mutated RAS oncoproteins and epidermal growth factor (EGF) are thought to contribute to the proliferative, invasive and metastatic properties of transformed cells. In the present study, we investigated the role of EGF in two H-ras transfected clones and compared it to that in the parental cell line, HaCaT and primary cultured keratinocytes. Our findings show that the motility on type I collagen, measured by the migration index, was similar for both the HaCaT cell line and normal human keratinocytes, whereas it was higher for the HaCaT-ras clones. These results suggest an involvement of the ras oncogene in the stimulation of cell migration. EGF in cell pretreatment or during the migration assay also caused an increase in migration of all the cells, but preserved the difference between HaCaT and HaCaT-ras. However, no significant difference in EGF-R expression was detected between normal cultured keratinocytes, HaCaT and HaCaT-ras cell lines with or without EGF pretreatment. Moreover, when the cells were stimulated with EGF, the MMP-9 activity was greatly increased in a dose-dependent manner in all the cells, and EGF stimulation particularly highlights the increased amount of MMP-9 in HaCaT-ras cells compared to HaCaT cells. In conclusion, EGF is able to enhance motility and to up-regulate MMP-9 activity in all cells, but with a higher impact in HaCaT-ras cells without an overexpression of EGF-R. As EGF acts in synergy with the H-ras mutation, they could be implicated in the local invasion by the HaCaT-ras clones.

Collagenase-3 induction in rat lung fibroblasts requires the combined effects of tumor necrosis factor-alpha and 12-lipoxygenase metabolites: a model of macrophage-induced, fibroblast-driven extracellular matrix remodeling during inflammatory lung injury

The mechanisms responsible for the induction of matrix-degrading proteases during lung injury are ill defined. Macrophage-derived mediators are believed to play a role in regulating synthesis and turnover of extracellular matrix at sites of inflammation. We find a localized increase in the expression of the rat interstitial collagenase (MMP-13; collagenase-3) gene from fibroblastic cells directly adjacent to macrophages within silicotic rat lung granulomas. Conditioned medium from macrophages isolated from silicotic rat lungs was found to induce rat lung fibroblast interstitial collagenase gene expression. Conditioned medium from primary rat lung macrophages or J774 monocytic cells activated by particulates in vitro also induced interstitial collagenase gene expression. Tumor necrosis factor-alpha (TNF-alpha) alone did not induce interstitial collagenase expression in rat lung fibroblasts but did in rat skin fibroblasts, revealing tissue specificity in the regulation of this gene. The activity of the conditioned medium was found to be dependent on the combined effects of TNF-alpha and 12-lipoxygenase-derived arachidonic acid metabolites. The fibroblast response to this conditioned medium was dependent on de novo protein synthesis and involved the induction of nuclear activator protein-1 activity. These data reveal a novel requirement for macrophage-derived 12-lipoxygenase metabolites in lung fibroblast MMP induction and provide a mechanism for the induction of resident cell MMP gene expression during inflammatory lung processes.

Collagenase-1 complexes with alpha2-macroglobulin in the acute and chronic wound environments

The purpose of this study was to examine the appearance and activation of collagenase-1 (MMP-1) in the wound environment. We found that MMP-1 accumulates in the fluid phase of the burn wound environment within 2 d of injury and reaches maximal levels by day 4. Two forms of the enzyme were evident; one that corresponded to proMMP-1 and another that corresponded to a group of high molecular mass (approximately 200 kDa and >200 kDa doublet) MMP-1 containing complexes. ProMMP-1 and MMP-1 containing complexes also occurred in wound fluid from venous stasis ulcers, but neither was detected in mastectomy fluid or in plasma. Levels of the proteinase inhibitor alpha2-macroglobulin in burn fluid and chronic ulcer wound fluid were almost as high as in plasma, and the high molecular mass MMP-1 containing complexes in burn fluid appeared to result from binding between alpha2-macroglobulin and activated MMP-1. These observations provide direct evidence that active MMP-1 in the fluid phase of the wound environment becomes complexed to alpha2-macroglobulin.

Effects of collagenase-cleavage of type I collagen on alpha2beta1 integrin-mediated cell adhesion

In this paper we show that collagenase-3 cleavage of type I collagen has a marked effect on alpha2beta1 integrin-mediated interactions with the collagen fragments generated. Isolated alpha2beta1 integrin and alpha2 integrin A-domain were found to bind to both native collagen and native 3/4 fragment and, to a lesser degree, native 1/4 fragment. Whole integrin and integrin A-domain binding were lost after heat denaturation of the collagen fragments. At physiological temperature, cell adhesion to triple-helical 3/4 fragment via alpha2beta1 integrin was still possible; however, no alpha2beta1 integrin-mediated adhesion to the 1/4 fragment was observed. Unwinding of the collagen fragment triple helices by heating to physiological temperatures prior to adsorption to plastic tissue culture plates resulted in total abrogation of HT1080 cell attachment to either fragment. These results provide significant evidence in support of a role for matrix-metalloproteinase cleavage of the extracellular matrix in modifying cell-matrix interactions.

MT1-MMP on the cell surface causes focal degradation of gelatin films

The membrane-type matrix metalloproteinases (MT-MMPs) are a subclass of the matrix metalloproteinase (MMP) family which uniquely possess a C-terminal transmembrane domain and are initiators of an activation cascade for progelatinase A (MMP-2). Recent studies have shown that they can also efficiently directly degrade a number of matrix macromolecules. We now show that cells expressing MT1-MMP on their cell surfaces cause subjacent proteolysis of a gelatin film and that this proteolysis is inhibited by TIMP-2 but not by TIMP-1. These data indicate that expression of MT1-MMP on the cell surface may lead to both progelatinase A activation and extracellular matrix degradation.

Hypoxia increases human keratinocyte motility on connective tissue

Re-epithelialization of skin wounds depends upon the migration of keratinocytes from the cut margins of the wound and is enhanced when human keratinocytes are covered with occlusive dressings that induce hypoxia. In this study, two independent migration assays were used to compare cellular motility on connective tissue components under normoxic or hypoxic conditions. Human keratinocytes apposed to collagens or fibronectin exhibited increased motility when subjected to hypoxic (0.2 or 2% oxygen) conditions compared with normoxic (9 or 20% oxygen) conditions. When compared with normoxic cells, hypoxic keratinocytes exhibited increased expression and redistribution of the lamellipodia-associated proteins (ezrin, radixin, and moesin). Furthermore, hypoxic keratinocytes demonstrated decreased secretion of laminin-5, a laminin isoform known to inhibit keratinocyte motility. Hypoxia did not alter the number of integrin receptors on the cell surface, but did induce enhanced secretion of the 92-kD type IV collagenase. These data demonstrate that hypoxia promotes human keratinocyte motility on connective tissue. Hypoxia-driven motility is associated with increased expression of lamellipodia proteins, increased expression of collagenase and decreased expression of laminin-5, the locomotion brake for keratinocytes.

Induction and repression of collagenase-1 by keratinocytes is controlled by distinct components of different extracellular matrix compartments

In all forms of cutaneous wounds, collagenase-1 (matrix metalloproteinase-1 (MMP-1)) is invariably expressed by basal keratinocytes migrating over the dermal matrix. We report that native type I collagen mediates induction of MMP-1 by primary human keratinocytes. Collagen-mediated induction of MMP-1 was rapid, being detected 2 h after plating, and was transcriptionally regulated. As demonstrated by in situ hybridization, only migrating keratinocytes expressed MMP-1, suggesting that contact with collagen is not sufficient to induce MMP-1 expression in keratinocytes; the cells must also be migrating. Upon denaturation, type I collagen lost its ability to induce MMP-1 expression but still supported cell adhesion. Other dermal or wound matrix proteins, such as type III collagen, fibrin, and fibronectin, and a mixture of basement membrane proteins did not induce MMP-1 production. In the presence of collagen, laminin-1 inhibited induction of MMP-1 but laminin-5 did not. Taken together, these observations suggest that as basal keratinocytes migrate from the basal lamina onto the dermal matrix contact with native type I collagen induces MMP-1 expression. In addition, our findings suggest that re-establishment of the basement membrane and, in particular, contact with laminin-1 provides a potent signal to down-regulate MMP-1 production as the epithelium is repaired.

Cell type-specific inhibition of keratinocyte collagenase-1 expression by basic fibroblast growth factor and keratinocyte growth factor. A common receptor pathway

Collagenase-1 is invariantly expressed by migrating basal keratinocytes in all forms of human skin wounds, and its expression is induced by contact with native type I collagen. However, net differences in enzyme production between acute and chronic wounds may be modulated by soluble factors present within the tissue environment. Basic fibroblast growth factor (bFGF, FGF-2) and keratinocyte growth factor (KGF, FGF-9), which are produced during wound healing, inhibited collagenase-1 expression by keratinocytes in a dose-dependent manner. However, KGF was >100-fold more effective than bFGF at inhibiting collagenase-1 expression, suggesting that this differential signaling is transduced via an FGF receptor that binds these ligands with different affinities. Reverse transcriptase-polymerase chain reaction analysis of human keratinocyte mRNA for fibroblast growth factor receptors (FGFRs) revealed expression of only FGFR-2 IIIb, the KGF-specific receptor, which also binds bFGF with low affinity, and FGFR-3 IIIb, which does not bind bFGF or KGF. FGFRs that bind bFGF with high affinity were not detected. Our results suggest that bFGF and KGF inhibit collagenase-1 expression through the KGF cell-surface receptor (FGFR-2 IIIb). Because bFGF induces collagenase-1 in most cell types, cell-specific expression of FGFR family members may dictate the regulation of matrix metalloproteinases in a tissue-specific manner.