Epidermal growth factor receptor inhibition promotes desmosome assembly and strengthens intercellular adhesion in squamous cell carcinoma cells

The epidermal growth factor receptor (EGFR) has been proposed as a key modulator of cadherin-containing intercellular junctions, particularly in tumors that overexpress this tyrosine kinase. Here the EGFR tyrosine kinase inhibitor PKI166 and EGFR blocking antibody C225, both of which are used clinically to treat head and neck cancers, were used to determine the effects of EGFR inhibition on intercellular junction assembly and adhesion in oral squamous cell carcinoma cells. EGFR inhibition resulted in a transition from a fibroblastic morphology to a more epithelial phenotype in cells grown in low calcium; under these conditions cadherin-mediated cell-cell adhesion is normally reduced, and desmosomes are absent. The accumulated levels of desmoglein 2 (Dsg2) and desmocollin 2 increased 1.7-2.0-fold, and both desmosomal cadherin and plaque components were recruited to cell-cell borders. This redistribution was paralleled by an increase in Dsg2 and desmoplakin in the Triton-insoluble cell fraction, suggesting that EGFR blockade promotes desmosome assembly. Importantly, E-cadherin expression and solubility were unchanged. Furthermore, PKI166 blocked tyrosine phosphorylation of Dsg2 and plakoglobin following epidermal growth factor stimulation, whereas no change in phosphorylation was detected for E-cadherin and beta-catenin. The increase in Dsg2 protein was in part due to the inhibition of matrix metalloproteinase-dependent proteolysis of this desmosomal cadherin. These morphological and biochemical changes were accompanied by an increase in intercellular adhesion based on functional assays at all calcium concentrations tested. Our results suggest that EGFR inhibition promotes desmosome assembly in oral squamous cell carcinoma cells, resulting in increased cell-cell adhesion.

Proteases, extracellular matrix, and cancer: a workshop of the path B study section

The role of the extracellular matrix (ECM) in the tumor microenvironment is not limited to being a barrier against tumor invasion. The ECM is a reservoir of cell binding proteins and growth factors that affect tumor cell behavior. It is also substantially modified by proteases produced by tumor cells or stroma cells. As a result of the activity of these proteases, cell-cell and cell-ECM interactions are altered, new biologically active ECM molecules are generated, and the bioavailability and activity of many growth factors, growth factor receptors, and cytokines are modified. ECM-degrading proteases also play a critical role in angiogenesis, where they can act as positive as well as negative regulators of endothelial cell proliferation and vascular morphogenesis. This review article summarizes some of the most relevant findings made over the recent years that were discussed at a workshop organized by the Path B Study Section of the National Institutes of Health in October 2002.

Membrane protease proteomics: Isotope-coded affinity tag MS identification of undescribed MT1-matrix metalloproteinase substrates

By proteolytic modification of low abundant signaling proteins and membrane receptors, proteases exert potent posttranslational control over cell behavior at the postsecretion level. Hence, substrate discovery is indispensable for understanding the biological role of proteases in vivo. Indeed, matrix metalloproteinases (MMPs), long associated with extracellular matrix degradation, are increasingly recognized as important processing enzymes of bioactive molecules. MS is now the primary proteomic technique for detecting, identifying, and quantitating proteins in cells or tissues. Here we used isotopecoded affinity tag labeling and multidimensional liquid chromatography inline with tandem MS to identify MDA-MB-231 breast carcinoma cell proteins shed from the cell surface or the pericellular matrix and extracellular proteins that were degraded or processed after transfection with human membrane type 1-MMP (MT1-MMP). Potential substrates were identified as those having altered protein levels compared with the E240A inactive MT1-MMP mutant or vector transfectants. New substrates were biochemically confirmed by matrix-assisted laser desorption ionization-time-of-flight MS and Edman sequencing of cleavage fragments after incubation with recombinant soluble MT1-MMP in vitro. We report many previously uncharacterized substrates of MT1-MMP, including the neutrophil chemokine IL-8, secretory leukocyte protease inhibitor, pro-tumor necrosis factor alpha, death receptor-6, and connective tissue growth factor, indicating that MT1-MMP is an important signaling protease in addition to its traditionally ascribed roles in pericellular matrix remodeling. Moreover, the high-throughput and quantitative nature of isotope-coded affinity tag labeling combined with tandem MS sequencing is a previously undescribed degradomic screen for protease substrate discovery that should be generally adaptable to other classes of protease for exploring proteolytic function in complex and dynamic biological contexts.

Glycosylation Broadens the Substrate Profile of Membrane Type 1 Matrix Metalloproteinase

Membrane type 1 matrix metalloproteinase (MT1-MMP) is a collagenolytic enzyme that has been implicated in normal development and in pathological processes such as cancer metastasis. The activity of MT1-MMP is regulated extensively at the post-translational level, and the current data support the hypothesis that MT1-MMP activity is modulated by glycosylation. Enzymatic deglycosylation, site-directed mutagenesis, and lectin precipitation assays were used to demonstrate that MT1-MMP contains O-linked complex carbohydrates on the Thr(291), Thr(299), Thr(300), and/or Ser(301) residues in the proline-rich linker region. MT1-MMP glycoforms were detected in human cancer cell lines, suggesting that MT1-MMP activity may be regulated by differential glycosylation in vivo. Although the autolytic processing and interstitial collagenase activity of MT1-MMP were not impaired in glycosylation-deficient mutants, cell surface MT1-MMP-catalyzed activation of pro-matrix metalloproteinase-2 (proMMP-2) required proper glycosylation of MT1-MMP. The inability of carbohydrate-free MT1-MMP to activate proMMP-2 was not a result of defective MT1-MMP zymogen activation, aberrant protein stability, or inability of the mature enzyme to oligomerize. Rather, our data support a mechanism whereby glycosylation affects the recruitment of tissue inhibitor of metalloproteinases-2 (TIMP-2) to the cell surface, resulting in defective formation of the MT1-MMP/TIMP-2/proMMP-2 trimeric activation complex. These data provide evidence for an additional mechanism for post-translational control of MT1-MMP activity and suggest that glycosylation of MT1-MMP may regulate its substrate targeting.

Selective hydrolysis of triple-helical substrates by matrix metalloproteinase-2 and -9

The role of proteases in the tumor cell invasion process is multifaceted. Members of the matrix metalloproteinase (MMP) family have been implicated in primary and metastatic tumor growth, angiogenesis, and degradation of extracellular matrix (ECM) components. Differentiating between the up-regulation of MMP production and the presence of activated MMPs can be difficult but may well dictate which MMPs are critical to invasion. Because the hydrolysis of collagens is one of the committed steps in ECM turnover, we have investigated selective MMP action on collagenous substrates as a means to evaluate active MMPs. Two triple-helical peptide (THP) models of the MMP-9 cleavage site in type V collagen, alpha1(V)436-450 THP and alpha1(V)436-447 fTHP, were hydrolyzed by MMP-2 and MMP-9 at the Gly-Val bond, analogous to the bond cleaved by MMP-9 in the corresponding native collagen. Kinetic analyses showed k(cat)/K(m) values of 14,002 and 5,449 s(-1)m(-1) for MMP-2 and -9 hydrolysis of alpha1(V)436-447 fTHP, respectively. These values, along with individual k(cat) and K(m) values, are comparable with collagen hydrolysis by MMP-2 and -9. Neither THP was hydrolyzed by MMP-1, -3, -13, or -14. alpha1(V)436-447 fTHP and a general fluorogenic THP were used to screen for triple-helical peptidase activity in alpha(2)beta(1) integrin-stimulated melanoma cells. Binding of the alpha(2)beta(1) integrin resulted in the production of substantial triple-helical peptidase activity, the majority (>95%) of which was non-MMP-2/-9. THPs were found to provide highly selective substrates for members of the MMP family and can be used to evaluate active MMP production in cellular systems.

Loss of adhesion-regulated proteinase production is correlated with invasive activity in oral squamous cell carcinoma

BACKGROUND

Oral squamous cell carcinoma (OSCC) is the most common malignancy of the oral cavity. However, the cellular and biochemical factors that underlie locoregional and distant spread of the disease are poorly understood. Invasion of OSCC requires multiple cellular events including dissolution of cell-cell junctions, basement membrane attachment, extracellular matrix proteolysis, and migration.

METHODS

We evaluated these properties in vitro using premalignant gingival keratinocytes (ppl26) and two OSCC lines (SCC15 and SCC68). Expression of adhesion molecules integrins and cadherins, cytoplasmic intermediate filaments (IF) vimentin and keratin as well as matrix degrading proteins were evaluated. Moreover, regulation of protease production by adhesion molecules was tested.

RESULTS

All cell lines contained comparable levels of the epithelial cell-cell adhesion molecule, E-cadherin. Differential expression of cytoplasmic IF was evident between premalignant pp126 cells and OSCC cell lines. Expression levels of the alpha3beta1 integrin, utilized for attachment to laminin-5 and other matrix proteins, was high in SCC68 cells, moderate in SCC15 cells, and low in ppl26 cells. alpha3beta1 integrin clustering up-regulates expression of urinary-type plasminogen activator (uPA) in ppl26 cells via a mechanism involving ERK activation. Both ppl26 and SCC15 cells were responsive to alpha3beta1 clustering, resulting in enhanced uPA expression. However, basal uPA levels were high in SCC68 cells and integrin clustering did not further stimulate uPA production. ERK was constitutively activated in SCC68 cells and treatment of cells with an inhibitor of ERK activation (PD98059) reduced uPA expression. Consistent with the enhanced proteolytic potential, SCC68 cells readily penetrated Matrigel and invasion was blocked by an anticatalytic uPA antibody.

CONCLUSIONS

These data suggest that loss of adhesion-regulated proteinase production may lead to elevated pericellular proteinase activity and coincident alterations in cytoskeletal IF protein expression, thereby contributing to the invasive potential of OSCC.

Calcium regulation of matrix metalloproteinase-mediated migration in oral squamous cell carcinoma cells

Activation of matrix metalloproteinase 2 (MMP-2) has been shown to play a significant role in the behavior of cancer cells, affecting both migration and invasion. The activation process requires multimolecular complex formation involving pro-MMP-2, membrane type 1-MMP (MT1-MMP), and tissue inhibitor of metalloproteinases-2 (TIMP-2). Because calcium is an important regulator of keratinocyte function, we evaluated the effect of calcium on MMP regulation in an oral squamous cell carcinoma line (SCC25). Increasing extracellular calcium (0.09-1.2 mm) resulted in a dose-dependent increase in MT1-MMP-dependent pro-MMP-2 activation. Despite the requirement for MT1-MMP in the activation process, no changes in MT1-MMP expression, cell surface localization, or endocytosis were apparent. However, increased generation of the catalytically inactive 43-kDa MT1-MMP autolysis product and decline in the TIMP-2 levels in conditioned media were observed. The decrease in TIMP-2 levels in the conditioned media was prevented by a broad spectrum MMP inhibitor, suggesting that calcium promotes recruitment of TIMP-2 to MT1-MMP on the cell surface. Despite the decline in soluble TIMP-2, no accumulation of TIMP-2 in cell lysates was seen. Blocking TIMP-2 degradation with bafilomycin A1 significantly increased cell-associated TIMP-2 levels in the presence of high calcium. These data suggest that the decline in TIMP-2 is because of increased calcium-mediated MT1-MMP-dependent degradation of TIMP-2. In functional studies, increasing calcium enhanced MMP-dependent cellular migration on laminin-5-rich matrix using an in vitro colony dispersion assay. Taken together, these results suggest that changes in extracellular calcium can regulate post-translational MMP dynamics and thus affect the cellular behavior of oral squamous cell carcinoma.

Proteinase suppression by E-cadherin-mediated cell-cell attachment in premalignant oral keratinocytes

The expression and activity of epithelial proteinases is under stringent control to prevent aberrant hydrolysis of structural proteins and disruption of tissue architecture. E-cadherin-dependent cell-cell adhesion is also important for maintenance of epithelial structural integrity, and loss of E-cadherin expression has been correlated with enhanced invasive potential in multiple tumor models. To address the hypothesis that there is a functional link between E-cadherin and proteinase expression, we have examined the role of E-cadherin in proteinase regulation. By using a calcium switch protocol to manipulate junction assembly, our data demonstrate that initiation of de novo E-cadherin-mediated adhesive contacts suppresses expression of both relative matrix metalloproteinase-9 levels and net urinary-type plasminogen activator activity. E-cadherin-mediated cell-cell adhesion increases both phosphatidylinositol 3'-kinase (PI3-kinase)-dependent AKT phosphorylation and epidermal growth factor receptor-dependent MAPK/ERK activation. Pharmacologic inhibition of the PI3-kinase pathway, but not the epidermal growth factor receptor/MAPK pathway, prevents E-cadherin-mediated suppression of proteinases and delays junction assembly. Moreover, inhibition of junction assembly with a function-blocking anti-E-cadherin antibody stimulates proteinase-dependent Matrigel invasion. As matrix metalloproteinase-9 and urinary-type plasminogen activator potentiate the invasive activity of oral squamous cell carcinoma, these data suggest E-cadherin-mediated signaling through PI3-kinase can regulate the invasive behavior of cells by modulating proteinase secretion.

Collagen binding properties of the membrane type-1 matrix metalloproteinase (MT1-MMP) hemopexin C domain. The ectodomain of the 44-kDa autocatalytic product of MT1-MMP inhibits cell invasion by disrupting native type I collagen cleavage

Up-regulation of the collagenolytic membrane type-1 matrix metalloproteinase (MT1-MMP) leads to increased MMP2 (gelatinase A) activation and MT1-MMP autolysis. The autocatalytic degradation product is a cell surface 44-kDa fragment of MT1-MMP (Gly(285)-Val(582)) in which the ectodomain consists of only the linker, hemopexin C domain and the stalk segment found before the transmembrane sequence. In the collagenases, hemopexin C domain exosites bind native collagen, which is required for triple helicase activity during collagen cleavage. Here we investigated the collagen binding properties and the role of the hemopexin C domain of MT1-MMP and of the 44-kDa MT1-MMP ectodomain in collagenolysis. Recombinant proteins, MT1-LCD (Gly(285)-Cys(508)), consisting of the linker and the hemopexin C domain, and MT1-CD (Gly(315)-Cys(508)), which consists of the hemopexin C domain only, were found to bind native type I collagen but not gelatin. Functionally, MT1-LCD inhibited collagen-induced MMP2 activation in fibroblasts, suggesting that interactions between collagen and endogenous MT1-MMP directly stimulate the cellular activation of pro-MMP2. MT1-LCD, but not MT1-CD, also blocked the cleavage of native type I collagen by MT1-MMP in vitro, indicating an important role for the MT1-MMP linker region in triple helicase activity. Similarly, soluble MT1-LCD, but not MT1-CD or peptide analogs of the MT1-MMP linker, reduced the invasion of type I collagen matrices by MDA-MB-231 cells as did the expression of recombinant 44-kDa MT1-MMP on the cell surface. Together, these studies demonstrate that generation of the 44-kDa MT1-MMP autolysis product regulates collagenolytic activity and subsequent invasive potential, suggesting a novel feedback mechanism for the control of pericellular proteolysis.

Critical role of lysophospholipids in the pathophysiology, diagnosis, and management of ovarian cancer

Lysophosphatidic acid (LPA), the simplest of all phospholipids, exhibits pleiomorphic functions in multiple cell lineages. The effects of LPA appear to be mediated by binding of LPA to specific members of the endothelial differentiation gene (Edg) family of G protein-coupled receptors (GPCR). Edg 2, Edg4, and Edg7 are high affinity receptors for LPA, and Edg1 may be a low affinity receptor for LPA. PSP24 has been shown to be responsive to LPA in Xenopus oocytes, however, its role in mammalian cells is unclear. The specific biochemical events initiated by the different Edg receptors, as well as the biological outcomes of activation of the individual receptors, are only beginning to be determined. LPA levels are consistently elevated in the plasma and ascites of ovarian cancer patients, but not in most other epithelial tumors, with the exception of cervix and endometrium, suggesting that LPA may be of particular importance in the pathophysiology of ovarian cancer. In support of this concept, ovarian cancer cells constitutively and inducibly produce high levels of LPA and demonstrate markedly different responses to LPA than normal ovarian surface epithelium. Edg4 and Edg7 levels are consistently increased in malignant ovarian epithelial cells contributing to the aberrant response of ovarian cancer cells to LPA. Edg2 may represent a negative regulatory LPA receptor inducing apoptosis in ovarian cancer cells. Thus, increased levels of LPA, altered receptor expression and altered responses to LPA may contribute to the initiation, progression or outcome of ovarian cancer. Over 40% of known drugs target GPCR, making LPA receptors attractive targets for molecular therapeutics. Indeed, using the structure-function relationship of LPA in model systems, we have identified selective Edg2 anatgonists, as well as Edg4 and Edg7 agonists. These lead compounds are being assessed in preclinical model systems. Understanding the mechanisms regulating LPA production, metabolism and function could lead to improved methods for early detection and to new targets for therapy in ovarian cancer.

The mechanism of action of angiostatin: can you teach an old dog new tricks?

What is angiostatin? In 1994, Folkman and colleagues published a landmark paper describing anti-tumor effects in mice with a purified fragment of plasminogen they named angiostatin (1). Although many papers have been published describing activities of cryptic polypeptides derived from plasminogen fragments, this was the first report which associated plasminogen kringles 1-4 as a suppressor of metastasis development. This review will describe what is known about the mechanism of action of angiostatin from the current literature.

Tumor production of angiostatin is enhanced after exposure to TNF-alpha

Infection of tumors with an adenoviral vector expressing a chimeric gene composed of the CArG elements of the Egr-1 promoter and a cDNA encoding TNF-alpha (Ad.Egr-TNF) has previously been shown to result in the production of high intratumoral levels of TNF-alpha and thereby tumor regression. The antitumor effects of TNF-alpha were ascribed to vascular thrombosis. We and others, have reported that inhibition of tumor vessel thrombosis using anticoagulation therapy does not abrogate the antitumor effects after TNF-alpha treatment. To investigate the potential antiangiogenic effects of TNF-alpha, we studied the generation of angiostatin after intratumoral injection of Ad.Egr-TNF. We report an increase in plasma angiostatin levels both during and after treatment with Ad.Egr-TNF that parallel tumor regression. We also report that TNF-alpha enhances angiostatin production by inducing the activity of plasminogen activator and the release of MMP-9 by tumor cells. These studies support a model in which the antiangiogenic effects of TNF-alpha on the tumor microvasculature are mediated by generation of angiostatin.

Isoform-specific differences in the size of desmosomal cadherin/catenin complexes

Via their integration of the intermediate filament cytoskeleton into the cell membrane, desmosomes facilitate the maintenance of cell shape and tissue integrity as well as intercellular communication. The transmembrane components of the desmosome, the desmogleins and desmocollins, are members of the cadherin family of cell-cell adhesion molecules. Each of these proteins exists as three distinct isoforms, which are the products of individual genes and expressed in a cell-type and differentiation-specific manner. Previous work has suggested that desmoglein 1 binds to its catenin partner, plakoglobin, in an approximately 6:1 stoichiometry. In this study, the molecular organization of complexes formed by plakoglobin and desmoglein 1, 2, or 3 are further examined through immunoprecipitation, size exclusion chromatography and sucrose density sedimentation analysis. It is shown that the complex formed between plakoglobin and desmoglein 1 has an overall molecular weight greater than that of plakoglobin/desmoglein 2 or plakoglobin/desmoglein 3; however, the stoichiometry of the plakoglobin/desmoglein 1 complex does not appear to exceed 2:1.

Functional interplay between type I collagen and cell surface matrix metalloproteinase activity

Type I collagen stimulation of pro-matrix metalloproteinase (pro-MMP)-2 activation by ovarian cancer cells involves beta(1) integrin receptor clustering; however, the specific cellular and biochemical events that accompany MMP processing are not well characterized. Collagenolysis is not required for stimulation of pro-MMP-2 activation, and denatured collagen does not elicit an MMP-2 activation response. Similarly, DOV13 cells bind to intact collagen utilizing both alpha(2)beta(1) and alpha(3)beta(1) integrins but interact poorly with collagenase-treated or thermally denatured collagen. Antibody-induced clustering of alpha(3)beta(1) strongly promotes activation of pro-MMP-2, whereas alpha(2)beta(1) integrin clustering has only marginal effects. Membrane-type 1 (MT1)-MMP is present on the DOV13 cell surface as both an active 55-kDa TIMP-2-binding species and a stable catalytically inactive 43-kDa form. Integrin clustering stimulates cell surface expression of MT1-MMP and co-localization of the proteinase to aggregated integrin complexes. Furthermore, cell surface proteolysis of the 55-kDa MT1-MMP species occurs in the absence of active MMP-2, suggesting MT1-MMP autolysis. Cellular invasion of type I collagen matrices requires collagenase activity, is blocked by tissue inhibitor of metalloproteinases-2 (TIMP-2) and collagenase-resistant collagen, is unaffected by TIMP-1, and is accompanied by pro-MMP-2 activation. Together, these data indicate that integrin stimulation of MT1-MMP activity is a rate-limiting step for type I collagen invasion and provide a mechanism by which this activity can be down-regulated following collagen clearance.

Type I Collagen Stabilization of Matrix Metalloproteinase-2

The activity of matrix metalloproteinase-2 (MMP-2) is regulated stringently on the posttranslational level. MMP-2 efficiently undergoes autolysis into inactive polypeptides in vitro, prompting the hypothesis that MMP-2 autolysis may function as an alternative mechanism for posttranslational control of MMP-2 in vivo. Moreover, MMP-2 binds to intact type I collagen fibrils; however, the functional consequences of this interaction have not been fully elucidated. To test the hypothesis that MMP-2 binding to type I collagen functions as a positive regulator of MMP-2 proteolytic potential, the effect of type I collagen on MMP-2 activity, inhibition by tissue inhibitor of metalloproteinase-2 (TIMP-2), and enzyme stability was examined. Here, we report that purified MMP-2 binds but does not cleave intact type I collagen. The presence of type I collagen affects neither enzymatic activity against a quenched fluorescent peptide substrate nor the kinetics of inhibition by TIMP-2. However, MMP-2 is stabilized from autolysis in the presence of type I collagen, but not by elastin, fibrinogen, or laminin. These data provide biochemical evidence that MMP-2 exosite interactions with type I collagen may function in the posttranslational control of MMP-2 activity by reducing the rate of autolytic inactivation.

Lysophosphatidic acid promotes matrix metalloproteinase (MMP) activation and MMP-dependent invasion in ovarian cancer cells

Ovarian cancer is an highly metastatic disease characterized by ascites formation and diffuse i.p. adhesion, invasion, and metastasis. Levels of lysophosphatidic acid (LPA) are elevated in the plasma of patients with ovarian carcinoma, including 90% of patients with stage I disease, suggesting that LPA may promote early events in ovarian carcinoma dissemination. Expression of matrix metalloproteinases (MMPs) is also up-regulated in ovarian cancer tissues and ascites, and numerous studies have provided evidence for a direct role of MMPs in i.p. invasion and metastasis. Using three-dimensional type I collagen cultures or immobilized beta1 integrin subunit-specific antibodies, we previously demonstrated that beta1 integrin clustering promotes activation of proMMP-2 and processing of membrane type 1 MMP in ovarian cancer cells (S. M. Ellerbroek et al., Cancer Res., 59: 1635-1641, 1999). In the current study, the effect of LPA on MMP expression and invasive activity was investigated. Treatment of ovarian cancer cells with pathophysiological levels of LPA increased cellular adhesion to type I collagen and beta1 integrin expression. A significant up-regulation of MMP-dependent proMMP-2 activation was observed in LPA-treated cells, leading to enhanced pericellular MMP activity. As a result of increased MMP activity, haptotactic and chemotactic motility, in vitro wound closure, and invasion of a synthetic basement membrane were enhanced. These data indicate that LPA contributes to metastatic dissemination of ovarian cancer cells via up-regulation of MMP activity and subsequent downstream changes in MMP-dependent migratory and invasive behavior.

Phosphatidylinositol 3-kinase activity in epidermal growth factor-stimulated matrix metalloproteinase-9 production and cell surface association

Activation of the epidermal growth factor (EGF) receptor regulates many processes associated with metastasis, including modulation of cell:cell and cell:substrate interactions, production of matrix-degrading proteinases, and cellular migration. We have demonstrated previously that EGF stimulates migration and matrix metalloproteinase (MMP)-9-dependent invasion of ovarian cancer cells. In this study, we compare the roles of EGF-induced phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) activities in regulation of cellular responses associated with ovarian tumor cell metastasis. Inhibition of PI3K and MAPK activity impairs EGF-stimulated cell migration, in vitro invasion, and MMP-9 production. PI3K activity is not required for growth factor disruption of cell:cell junctions, whereas inhibitors of extracellular signal-regulated kinase (ERK)1/ERK2 activation and p38 MAPK activity block EGF-dependent junction dissolution. EGF promotes pro-MMP-9 binding to the cell surface through a mechanism that is independent of extracellular enzyme concentration. Interestingly, inhibition of PI3K activity abolishes EGF-induced cell surface association of pro-MMP-9, whereas inhibitors of MAPKs only partially block the response. These data suggest that EGF receptor activation promotes a PI3K-dependent induction of a cell surface pro-MMP-9 binding component that may facilitate gelatinase-mediated cellular invasion and supports an expanded role for elevated PI3K activity in cellular responses associated with ovarian tumor metastasis. In addition, our findings support the hypothesis that divergent kinase activities regulate distinct cellular events associated with growth factor-induced invasion of ovarian cancer cells.

Regulation of invasion of epithelial ovarian cancer by transforming growth factor-beta

OBJECTIVE

The metastatic process in epithelial ovarian cancer is thought to involve surface shedding and subsequent dissemination of ovarian cancer cells, facilitated by localized proteolysis at the interface between ovarian cancer cells and peritoneal surfaces. The factors regulating the metastatic process, however, are not well understood. Transforming growth factor-beta (TGF-beta) is a multifunctional peptide that elicits numerous cellular effects pertinent to the metastatic process. The purpose of this study was to evaluate the regulatory role of TGF-beta on metastasis in ovarian cancer.

METHOD

We evaluated the effect of TGF-beta on the metastatic characteristics (adhesion, invasion, motility, proteolysis) of five ovarian cancer cell lines (DOV-13 and OVCA 420, 429, 432, and 433), two short-term primary ovarian cancer cell cultures (OVCA 10 and OVCA 208), and five normal ovarian surface epithelial (NOSE) cell cultures (OSE 133, 185, 186, 188, and 189). The effect of TGF-beta on invasion and proteolysis was quantified using a modified Boyden chamber invasion assay, zymography, a coupled colorimetric activity assay, and an HPLC-based quantitation of synthetic substrate cleavage.

RESULTS

TGF-beta significantly increased invasion in five of seven ovarian cancer cell lines in amounts ranging from 2- to 20-fold. In contrast, TGF-beta significantly decreased invasion in two of five NOSE isolates by 50 to 80% and had no significant effect on invasion in three. TGF-beta treatment increased matrix metalloproteinase (MMP) expression in OVCA 420 and 433 and DOV-13, resulting in MMP-dependent collagen cleavage and invasive activity. Addition of the MMP inhibitor GI12947 neutralized the enhancing effect of TGF-beta on invasion. TGF-beta had no effect on ovarian cancer cell motility and only increased adhesion in DOV-13.

CONCLUSIONS

These data suggest that TGF-beta may enhance the invasiveness of ovarian cancers through induction of MMP activity.

Spatial regulation and activity modulation of plasmin by high affinity binding to the G domain of the alpha 3 subunit of laminin-5

Cells in complex tissues contact extracellular matrix that interacts with integrin receptors to influence gene expression, proliferation, apoptosis, adhesion, and motility. During development, tissue remodeling, and tumorigenesis, matrix components are modified by enzymatic digestion with subsequent effects on integrin binding and signaling. We are interested in understanding the mechanisms by which broad spectrum proteinases such as plasmin are targeted to their extracellular matrix protein substrates. We have utilized plasmin-mediated cleavage of the epithelial basement membrane glycoprotein laminin-5 as a model to evaluate molecular events that direct plasmin activity to specific structural domains. We report that plasminogen and tissue plasminogen activator (tPA) exhibit high affinity, specific binding to the G(1) subdomain of the N terminus of the laminin-5 alpha(3) subunit, with equilibrium dissociation constants of 50 nm for plasminogen and 80 nm for tPA. No high affinity binding to the G(2), G(3), and G(4) subdomains was observed. As a result of binding to the G(1) subdomain, the catalytic efficiency of tPA-catalyzed plasminogen activation is enhanced 32-fold, leading to increased matrix-associated plasmin that is positioned favorably for cleavage within the G(4) subdomain as we have reported previously (Goldfinger, L. E., Stack, M. S., and Jones, J. C. R. (1998) J. Cell Biol. 141, 255-265). Thus, physical constraints dictated by interaction of proteinase and matrix macromolecule control not only enzymatic activity but may regulate substrate targeting of proteinases.

Proteolytic modification of laminins: functional consequences

The laminin family contains a number of complex, multi-domain proteins that participate in a large variety of biologic processes. Limited proteolysis has been utilized extensively as a tool with which to determine laminin structure/function relationships. In addition, proteolytic modification of laminins may occur as a component of heterotrimer assembly and secretion, or may follow incorporation of mature laminin into the extracellular matrix. Conversely, laminin binding to cellular receptors may also influence proteinase expression. This review will highlight specific examples to demonstrate the functional interplay between laminins and proteinases in the regulation of laminin structure and function as well as in the subsequent control of proteinase expression.

Metastatic dissemination of human ovarian epithelial carcinoma is promoted by alpha2beta1-integrin-mediated interaction with type I collagen

Metastatic dissemination of epithelial ovarian carcinoma is thought to be mediated via tumor cell exfoliation into the peritoneal cavity, followed by adhesion to and invasion through the mesothelium which overlies the contents of the peritoneal cavity. In this study, we have utilized short-term primary cultures to analyze the effect of specific extracellular matrix proteins on properties of human ovarian epithelial carcinoma cells which contribute to the invasive phenotype. Analysis of cell:matrix adhesive profiles indicated that ovarian carcinoma cells adhere preferentially to type I collagen. Immunoprecipitation analyses demonstrated the presence of the collagen-binding alpha2beta1 integrin in biotin-labeled ovarian carcinoma cell membranes, and cellular adhesion was inhibited by blocking antibodies directed against the alpha2 and beta1 integrin subunits. The alpha2beta1-binding peptide Asp-Gly-Glu-Ala (DGEA) was also moderately effective at blocking adhesion to collagen relative to the control peptide Ala-Gly-Glu-Ala (AGEA). Analysis of cell motility on protein-coated colloidal gold coverslips demonstrated that ovarian carcinoma cells migrate preferentially on type I collagen coated surfaces. Type I collagen promoted migration in a concentration-dependent, saturable manner, with maximal migration observed at a collagen-coating concentration of 50 microg/ml. Migration on collagen was inhibited by antibodies directed against the alpha2 and beta1 integrin subunits and by DGEA peptide, providing evidence for the role of the alpha2beta1 integrin in ovarian carcinoma cell motility. Culturing ovarian carcinoma cells on type I collagen gels led to a significant increase in conversion of the matrix metalloproteinase 2 zymogen to the 66-kD form, suggesting that adhesion to collagen also influences matrix-degrading proteinases. These data suggest that alpha2beta1-integrin-mediated interaction of ovarian carcinoma cells with type I collagen, a protein prevalent both in the mesothelial extracellular matrix and in the peritoneal cavity of ovarian carcinoma patients, may function on multiple levels to promote metastatic dissemination of ovarian carcinoma cells.

Urinary-type plasminogen activator (uPA) expression and uPA receptor localization are regulated by alpha 3beta 1 integrin in oral keratinocytes

Expression of urinary-type plasminogen activator (uPA) and its receptor (uPAR) is correlated with matrix proteolysis, cell adhesion, motility, and invasion. To evaluate the functional link between adhesion and proteolysis in gingival keratinocytes (pp126), cells were treated with immobilized integrin antibodies to induce integrin clustering. Clustering of alpha(3) and beta(1) integrin subunits, but not alpha(2), alpha(5), alpha(6), or beta(4), enhanced uPA secretion. Bead-immobilized laminin-5 and collagen I, two major alpha(3)beta(1) ligands, also induced uPA expression. Coordinate regulation of the serpin plasminogen activator inhibitor 1 was also apparent; however, a net increase in uPA activity was predominant. alpha(3)beta(1) integrin clustering induced extracellular signal-regulated kinase 1/2 phosphorylation, and both uPA induction and extracellular signal-regulated kinase activation were blocked by the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibitor PD98059. Integrin aggregation also promoted a dramatic redistribution of uPAR on the cell surface to sites of clustered alpha(3)beta(1) integrins. Co-immunoprecipitation of beta(1) integrin with uPAR provided further evidence that protein-protein interactions between uPAR and beta(1) integrin control uPAR distribution. As a functional consequence of uPA up-regulation and uPA-mediated plasminogen activation, the globular domain of the laminin-5 alpha(3) subunit, a major pp126 matrix protein, was proteolytically processed from a 190-kDa form to a 160-kDa species. Laminin-5 containing the 160-kDa alpha(3) subunit efficiently nucleates hemidesmosome formation and reduces cell motility. Together, these data suggest that multivalent aggregation of the alpha(3)beta(1) integrin regulates proteinase expression, matrix proteolysis, and subsequent cellular behavior.