The interaction of melanoma cells with fibroblasts and endothelial cells in three-dimensional macromolecular matrices: a model for tumour cell invasion

Migration Stimulating Factor (MSF): Its Role in the Tumour Microenvironment

Migration Stimulating Factor (MSF) is a 70 kDa truncated isoform of fibronectin (FN); its mRNA is generated from the FN gene by an unusual two-stage processing. Unlike full-length FN, MSF is not a matrix molecule but a soluble protein which displays cytokine-like activities not displayed by any other FN isoform due to steric hindrance. There are two isoforms of MSF; these are referred to as MSF+aa and MSF-aa, while the term MSF is used to include both.MSF was first identified as a motogen secreted by foetal and cancer-associated fibroblasts in tissue culture. It is also produced by sprouting (angiogenic) endothelial cells, tumour cells and activated macrophages. Keratinocytes and resting endothelial cells secrete inhibitors of MSF that have been identified as NGAL and IGFBP-7, respectively. MSF+aa and MSF-aa show distinct functionality in that only MSF+aa is inhibited by NGAL.MSF is present in 70-80% of all tumours examined, expressed by the tumour cells as well as by fibroblasts, endothelial cells and macrophages in the tumour microenvironment (TME). High MSF expression is associated with tumour progression and poor prognosis in all tumours examined, including breast carcinomas, non-small cell lung cancer (NSCLC), salivary gland tumours (SGT) and oral squamous cell carcinomas (OSCC). Epithelial and stromal MSF carry independent prognostic value. MSF is also expressed systemically in cancer patients, being detected in serum and produced by fibroblast from distal uninvolved skin. MSF-aa is the main isoform associated with cancer, whereas MSF+aa may be expressed by both normal and malignant tissues.The expression of MSF is not invariant; it may be switched on and off in a reversible manner, which requires precise interactions between soluble factors present in the TME and the extracellular matrix in contact with the cells. MSF expression in fibroblasts may be switched on by a transient exposure to several molecules, including TGFβ1 and MSF itself, indicating an auto-inductive capacity.Acting by both paracrine and autocrine mechanisms, MSF stimulates cell migration/invasion, induces angiogenesis and cell differentiation and alters the matrix and cellular composition of the TME. MSF is also a survival factor for sprouting endothelial cells. IGD tri- and tetra-peptides mimic the motogenic and angiogenic activities of MSF, with both molecules inhibiting AKT activity and requiring αvβ3 functionality. MSF is active at unprecedently low concentrations in a manner which is target cell specific. Thus, different bioactive motifs and extracellular matrix requirements apply to fibroblasts, endothelial cells and tumour cells. Unlike other motogenic and angiogenic factors, MSF does not affect cell proliferation but it stimulates tumour growth through its angiogenic effect and downstream mechanisms.The epithelial-stromal pattern of expression and range of bioactivities displayed puts MSF in the unique position of potentially promoting tumour progression from both the "seed" and the "soil" perspectives.

Collagen gel analysis of epithelial-mesenchymal transition in the embryo heart: an in vitro model system for the analysis of tissue interaction, signal transduction, and environmental effects

The cellular process of epithelial-mesenchymal cell transition (EMT) is a critical event in development that is reiterated in adult pathologies of metastasis and organ fibrosis. An initial understanding of the cellular and molecular events of this process emerged from an in vitro examination of heart valve development. Explants of the chick atrioventricular valve-forming region were placed on collagen gels and removed to show that EMT was regulated by a tissue interaction. Subsequent studies showed that specific TGFβ isoforms and receptors were required and steps of activation and invasion could be distinguished. The assay was modified for mouse hearts and has been used to explore signal transduction and gene expression in both species. The principle advantages of the system are a defined temporal window, when EMT takes place and the ability to isolate cells at various stages of the EMT process. These advantages are largely unavailable in other developmental or adult models. As the mesenchymal cells produced by EMT in the heart are involved in defects found in congenital heart disease, there is also a direct relevance of cardiac EMT to human birth defects. This relationship has been explored in relation to environmental exposures and in a number of genetic models. This review provides both an overview of the findings developed from the assay and protocols to enable the use of the assay by other laboratories. The assay provides a versatile platform to explore roles of specific gene products, drugs, and environmental agents on a critical cellular process.

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.

New sensitive discovery histoculture model for growth-inhibition studies in prostate cancer and BPH

BACKGROUND

A new, total-immersion three-dimensional histoculture (TIH) method was developed to evaluate growth of tissue containing a mixture of benign prostate hyperplasia (BPH) and prostate cancer in vitro.

METHODS

Efficacy of inhibitors, such as genistein, was determined by measuring 3H-thymidine incorporation per microgram protein. Inhibitory effects obtained in TIH were compared to those in sponge-gel supported histoculture (SSH).

RESULTS

3H-thymidine incorporation was 2-5-fold higher in tissue cultured in TIH than in SSH. The average inhibition by genistein at a concentration of 18 JIM was 73% in TIH, vs. 31% in SSH. TIH also appeared to be more sensitive, since the lowest concentration of genistein that significantly inhibited growth of BPH mixed with prostate cancer tissue was 2.3 IJM, while in SSH the lowest concentration was 9.2 F,M. Although the within-assay coefficient of variation (CV) was similar for both TIH and SSH, the between-assay CV was better in TIH.

CONCLUSIONS

These data suggest that TIH can be used as a discovery model for screening and evaluating inhibitors of prostate tissue growth in vitro.

Expression of type VI collagen during glioblastoma cell invasion in brain tissue cultures

Human glioblastoma cells, U-87 MG, were utilized in two separate rat brain tissue culture systems. In both cases, the glioblastoma cells deeply penetrated and formed tumor masses inside the brain tissues. Immunofluorescence technique, utilizing anti-type VI collagen antibodies demonstrated strong immunoreactivity of type VI collagen in the tumor masses, invading cells, and cell groups. We suggest that type VI collagen may be involved in tumor cells infiltration and invasion of healthy rat brain tissues. Furthermore, the brain tissue culture method may provide a rapid in vitro model with which cellular and extracellular determinants of invasiveness may be studied.

Biosynthesis of type VI collagen by glioblastoma cells and possible function in cell invasion of three-dimensional matrices

The biosynthesis of type VI collagen was studied in human glioblastoma cell line, U-87 MG. The effects of ascorbic acid on type VI collagen synthesis and secretion were investigated. After ascorbic acid treatment, type VI collagen in cell layers increased from 4.48% in control to 6.63% in the ascorbic acid treated cultures, an increase of 48%. The effect of ascorbic acid on type VI collagen synthesized by glioblastoma cells was lower than that reported for osteosarcoma cells (Engvall et al., 1986). The reason for these differences is still under investigation. The function of type VI collagen in glioblastoma cells is still unknown. We utilized the collagen gel system to elucidate the possible roles of type VI collagen in glioblastoma cells in vitro. Glioblastoma cells in collagen gels showed a stellate shape with long, branched processes in all directions. The strong positive reactivity of type VI collagen detected on cell bodies and cell processes by anti-type VI collagen antibody indicated that this specific collagen was associated with cell surfaces and processes, without releasing or diffusing into the gels. Type VI collagen was directly involved in the cell process extension. When living cells were treated with anti-type VI collagen antibody, a variation of cell morphology was observed. Instead of a stellate shape with processes, cells formed clusters without or with very short processes. These data suggest that type VI collagen, synthesized and secreted by glioblastoma cells, may play a role in tumor cell adhesion and spreading, and enhance cell process extension, penetration, and invasion into collagen gels.

Cytokine control of cell motility: modulation and mediation by the extracellular matrix

Cytokines are multifunctional regulators of cell behaviour affecting such diverse activities as cell proliferation, gene expression and motility. Matrix macromolecules influence a similarly wide range of cell functions. A review of the available literature suggests that cytokines may affect cell motility by (a) directly influencing the motility apparatus, and (b) indirectly as a consequence of the altered expression of genes coding for matrix macromolecules, their respective cell surface receptors and matrix degrading enzymes and their inhibitors. Conversely, the composition and supramolecular organisation of the matrix plays a central role in defining cellular response to potentially multifunctional cytokines. Such complex and reciprocal interactions between cytokines and the matrix elicit both positive and negative reiterative feedback loops which must be taken into account when interpreting the results of migration assays in vitro and extrapolating them to in vivo processes.

Ultrastructural aspects of tumour invasion in the central nervous system

Tumour invasion in the central nervous system (CNS) was studied using a mouse melanoma cell model. Attention was concentrated on the third ventricle as this site is distant from any implantation artefact. Transmission electron microscopy (TEM) revealed the formation of tumour cell aggregates within the ventricle. Underlying ependymal cells showed loss of cilia and microvilli. Progressive thinning of the ependymal cells took place until continuity of the ependyma was lost through ependymal retraction. Tumour cells were then in direct contact with sub-ependymal neuroglial processes. Further invasion was then accomplished by penetration between neuropil processes, followed by tumour cell infiltration along the intact basement membrane of cerebral capillaries with displacement of astrocyte foot processes from the capillary basement membrane.

Cell-matrix interactions during tumor invasion

This manuscript reviews the molecular aspects of tumor cell invasion of extracellular matrix. The changes in cell:substrate and cell:cell receptors that characterize motile cells are discussed for their importance not only in mediating invasive cell behavior, but also as diagnostic markers for invasive potential. Autocrine motility and scatter factors probably have key roles in initiating migratory behavior, while specific and non-specific extracellular matrix alterations can facilitate cell locomotion. The manuscript reviews reported changes, such as induction of cell motility, matrix degrading enzymes, and invasive/metastatic potential, which can follow transfection with ras oncogenes, and details the key roles of metalloproteinases, heparanase, and plasminogen activator in matrix degradation. Enzymatic inhibitors of initial steps in extracellular matrix degradation, such as rTIMP, and synthetic blockers of adhesive steps in tumor cell invasion represent types of reagent with potential as anti-metastatic agents. Their potential usefulness may be increased if they can be incorporated into a novel, long-term, non-traditional delivery system.

Infiltration of melanoma cells into the type I collagen gel

Melanoma cells were cultured on type I collagen gel, and the infiltration of of those cells into the gel was observed. B16 murine melanoma cells initially adopted a spherical form on the gel, but they assumed a dendritic form after infiltration into the interior. The degree of infiltration increased very rapidly and was time-dependent. No correlations between the growth rate or melanogenic activity and infiltrative potential were observed. When Syrian hamster and human melanoma cell lines were cultured, the degrees of infiltration varied. This culture system using collagen gel is considered to be a useful in vitro model of tumor cell invasion.

Surface blebbing and cytoskeletal changes induced in vitro by toxin B from Clostridium difficile: an immunochemical and ultrastructural study

Clostridium difficile toxin B is a powerful cytopathic agent without enterotoxic activity which is believed to be involved in the pathogenesis of pseudomembranous colitis. Up until today, the mechanisms of toxin B cytotoxicity have not been elucidated. The results of in vitro studies performed on different cell lines by means of immunocytochemical and ultrastructural methods are reported here. Low doses (0.15 ng/ml) of toxin B cause cell rounding and arborization. Higher doses (up to 15 micrograms/ml) induce cell rounding and appearance of numerous surface protrusions with blister or bulb-like features. These "blebs" belong to the potocytotic type, the bleb matrix being devoid of cytoplasmic organelles and filled with ribosomes only. Furthermore, a peculiar role of cytoskeletal apparatus in this phenomenon has been detected. In fact, morphological rearrangement occurs in cytoskeletal elements, mainly represented by the presence, in the blebs, of tubulin and of the actin-binding proteins alpha-actinin, filamin, and calmodulin, while actin and intermediate filaments, keratin and vimentin, appear to be absent. Moreover, beta 2-microglobulin, considered as a surface protein marker, seems to undergo changes in its expression, being absent over the blebbing surface. The results of this study may support the view that C. difficile toxin B affects one or more subcellular components that regulate the structure and function of the actin cytoskeleton.

Enhanced melanogenesis of murine melanoma cells cultured on or in collagen gel

To elucidate the interaction between melanoma and its matrix, we cultured B16 murine melanoma cells on and in type I collagen gel and evaluated specified functions of melanoma cells; tyrosinase activity and melanin-synthesizing capacity. Proliferation of cells cultured in these environments was markedly suppressed compared with that of cells cultured conventionally on plastic. On the other hand, the tyrosinase activity of cells cultured in or on collagen gel was two to three times higher than that of cells cultured on the plastics, while their melanin production was approximately double that achieved during conventional culture of cells. In conclusion, collagen gel influenced the growth and cell-specific functions of the melanoma cell. The culture system using collagen gel as substrate may be useful for the investigation of the interaction between melanoma and its matrix.

Proliferative potential of murine melanoma cells cultured in or on collagen gel

As the first step in developing an in vitro model of melanoma cells infiltrating the dermis, B16 murine melanoma cells were cultured on and in type I collagen gels. Under these conditions, the melanoma cell adopted an elongated or dendritic form. Cell proliferation was suppressed in the culture system using the collagen gel as compared with the conventional monolayer culture on plastic. Microcinematographically, this suppression was found to be due to an extension of the cell cycle time of each individual cell. On the other hand, there were no appreciable differences in proliferation pattern between the cells cultured on type I and IV collagen film and those cultured on plastic. These results suggest that there are interactions between type I collagen in the gel form and melanoma cells, especially with respect to cell growth.

In vitro studies on the expansion of endothelial cell monolayers on components of the basement membrane

The purpose of the present study was to observe the expansion of a monolayer of endothelial cells over specific components of the basement membrane. This was performed in vitro in a monolayer expansion assay over 5 days. The control surface was uncoated glass in the form of coverslips. Test substances were coated at a concentration of 10 micrograms/ml. The highest expansion was obtained with a high molecular weight fragment mixture of collagen type IV (IV-F, consisting of 75, 120 and 140 KD fragments), followed by fibronectin. Collagens type I, III and IV tetramer gave similar results, less than fibronectin or collagen type IV-F, although all of the above basement membrane coatings promoted expansion significantly above that of the control (P less than 0.01). The poorest expansion was obtained with laminin, which was significantly less than the control. The pentapeptide GRGDS, related to the fibronectin cell binding region, gave expansion significantly below that of the intact fibronectin molecule, as did the intact collagen type IV molecule compared with type IV-F (P less than 0.025). This indicates that sequences of the fibronectin molecule other than the cell binding sequence may be involved in promoting endothelial cell expansion. In addition, the integrity of the collagen type IV molecule does not appear necessary for this effect. On the contrary, the higher movement on IV-F may represent an inherent repair mechanism in damaged endothelium. Autoradiographic studies show that endothelial cell proliferation at the expanding front is involved in the migration assay.

Organ specificity of tumor metastasis: role of preferential adhesion, invasion and growth of malignant cells at specific secondary sites

The locations of distant secondary tumors in many clinical cancers and animal tumors are nonrandom, and their distributions cannot be explained by simple anatomical or mechanical hypotheses based on the simple lodgment or trapping of tumor cell emboli in the first capillary bed encountered. Evidence from certain experimental tumor systems supports Paget's 'seed and soil' hypothesis on the nonrandom distributions of metastases, in which the unique properties of particular tumor cells ('seeds') and the different characteristics of each organ microenvironment ('soil') collectively determine the organ preference of metastasis. Experimentally, differential tumor cell adhesion to organ-derived microvessel endothelial cells and organ parenchymal cells, differential invasion of basement membranes and organ tissues, and differential responses to organ-derived growth-stimulatory and -inhibitory factors all appear to be important determinants in explaining the organ preference of metastasis. Each tumor system may achieve organ specificity because of its own unique set of multiple metastasis-associated properties and responses to host microenvironments. As neoplasms progress to more highly malignant states multisite metastases are more likely and organ-specific metastases may be masked or circumvented owing to stochastic events, tumor cell diversification, host selection processes, and increased production of tumor autocrine molecules that may modulate adhesion, invasion, growth, and other properties important in metastasis. The importance of each of these properties, however, appears to vary considerably among different metastatic tumor systems. These and other tumor cell and host properties may eventually be used to predict and explain the unique metastatic distributions of certain human malignancies.

Comparison of basement membrane matrix degradation by purified proteases and by metastatic tumor cells

We have examined the nature of biochemical degradation of an isolated basement membrane matrix (bovine lens capsule) using different methodologies. The first strategy was quantitation of the release of surface-bound 125I and a second the documentation by SDS-PAGE of the appearance of putative cleavage products and the loss of high-molecular-weight components from the matrix. Basement membrane matrix bands resolved on SDS-PAGE were identified by their protease sensitivities as well as by Western immunoblots using monoclonal antibodies developed for this study. Radioiodinated components were found predominantly at positions on the gel equivalent to 160-200 kd and 400 kd proteins. Since these labeled moieties were sensitive to bacterial collagenase digestion and stained with anticollagen type IV antibodies, they were determined to represent various configurations of collagen type IV. Several other lower-molecular-weight bands also stained with the anticollagen IV antibodies. Monoclonal antibodies reactive with laminin exhibited a complex staining pattern on the gels, which included the expected 200 and 400 kd components. We confirmed that lens capsule basement membrane contained only a single heparan sulfate glycosaminoglycan species, and tumor cell-induced glycosaminoglycan degradation within the basement membrane matrix was detected using cellulose acetate electrophoresis. Distinctive putative cleavage products were resolved on SDS-PAGE gels from matrices subjected to digestion by a variety of purified proteases as well as by metastatic tumor cells or their conditioned media. Tumor cells of different histiotypes produced different characteristic cleavage patterns, suggestive of the existence of several pathways of matrix degradation. Overall, primary tumor cells exhibited a greater degradative activity towards the basement membrane matrix than did long-term tissue culture-passaged cells. The same tumor cell line could exhibit considerably different patterns of both protein and glycosaminoglycan degradation depending on recent culture history. The relevance of these biochemical studies to the pathogenesis of malignant neoplasms is shown by: 1) the evaluation of degradative activities of B16 tumor cell populations exhibiting enhanced lung-colonizing phenotypes, and 2) the ability of a known antimetastatic moiety with antiprotease activity (Haementeria leech species salivary gland extract) to protect matrix components from degradation by tumor cell-conditioned medium.

Modulation of smooth muscle cell behaviour by platelet-derived factors and the extracellular matrix

We have studied the combined effects of platelet-derived soluble factors and three types of macromolecular substrata on the proliferation and migration of smooth muscle cells in vitro. Bovine aortic smooth muscle cells were plated onto three-dimensional gels of type I collagen or onto cell-free extracellular matrices deposited on such gels by either bovine aortic endothelial cells or smooth muscle cells. The cells were cultured in the presence of whole-blood serum (WBS) or platelet-poor plasma (PPP). Smooth muscle cell proliferation on type I collagen gels was dependent on the presence of platelet-derived factors, i.e. the cells proliferated in the presence of WBS but not in PPP. In contrast, cell proliferation on the extracellular matrices occurred at the same rate in PPP and WBS. Smooth muscle cells plated onto collagen gels rapidly migrated down into the gel matrix; the percentage of cells migrating was inversely proportional to cell density. The presence of extracellular matrices did not alter the rate of cell migration into the underlying gel matrix. Irrespective of the substratum used, smooth muscle cell migration was independent of platelet-derived or plasma factors and occurred in the absence of proliferation. These results indicate that possible chemotactic, chemokinetic, and/or mitogenic factors produced by the vascular cells and deposited within the extracellular matrix may play an important role in modulating smooth muscle cell behaviour in the vascular wall.