Modulation of collagen and fibronectin synthesis in fibroblasts by normal and malignant cells

Targeting the secreted RGDKGE collagen fragment reduces PD‑L1 by a proteasome‑dependent mechanism and inhibits tumor growth

Structural alterations of collagen impact signaling that helps control tumor progression and the responses to therapeutic intervention. Integrins represent a class of receptors that include members that mediate collagen signaling. However, a strategy of directly targeting integrins to control tumor growth has demonstrated limited activity in the clinical setting. New molecular understanding of integrins have revealed that these receptors can regulate both pro‑ and anti‑tumorigenic functions in a cell type‑dependent manner. Therefore, designing strategies that block pro‑tumorigenic signaling, without impeding anti‑tumorigenic functions, may lead to development of more effective therapies. In the present study, evidence was provided for a novel signaling cascade in which β3‑integrin‑mediated binding to a secreted RGDKGE‑containing collagen fragment stimulates an autocrine‑like signaling pathway that differentially governs the activity of both YAP and (protein kinase‑A) PKA, ultimately leading to alterations in the levels of immune checkpoint molecule PD‑L1 by a proteasome dependent mechanism. Selectively targeting this collagen fragment, reduced nuclear YAP levels, and enhanced PKA and proteasome activity, while also exhibiting significant antitumor activity in vivo. The present findings not only provided new mechanistic insight into a previously unknown autocrine‑like signaling pathway that may provide tumor cells with the ability to regulate PD‑L1, but our findings may also help in the development of more effective strategies to control pro‑tumorigenic β3‑integrin signaling without disrupting its tumor suppressive functions in other cellular compartments.

Trisulfide linked cholesteryl PEG conjugate attenuates intracellular ROS and collagen-1 production in a breast cancer co-culture model

The progression of cancer has been closely-linked with augmentation of cellular reactive oxygen species (ROS) levels and ROS-associated changes in the tumour microenvironment (TME), including alterations to the extracellular matrix and associated low drug uptake. Herein we report the application of a co-culture model to simulate the ROS based cell-cell interactions in the TME using fibroblasts and breast cancer cells, and describe how novel reactive polymers can be used to modulate those interactions. Under the co-culture conditions, both cell types exhibited modifications in behaviour, including significant overproduction of ROS in the cancer cells, and elevation of the collagen-1 secretion and stained actin filament intensity in the fibroblasts. To examine the potential of using reactive antioxidant polymers to intercept ROS communication and thereby manipulate the TME, we employed H2S-releasing macromolecular conjugates which have been previously demonstrated to mitigate ROS production in HEK cells. The specific conjugate used, mPEG-SSS-cholesteryl (T), significantly reduced ROS levels in co-cultured cancer cells by approximately 50%. This reduction was significantly greater than that observed with the other positive antioxidant controls. Exposure to T was also found to downregulate levels of collagen-1 in the co-cultured fibroblasts, while exhibiting less impact on cells in mono-culture. This would suggest a possible downstream effect of ROS-mitigation by T on stromal-tumour cell signalling. Since fibroblast-derived collagens modulate crucial steps in tumorigenesis, this ROS-associated effect could potentially be harnessed to slow cancer progression. The model may also be beneficial for interrogating the impact of antioxidants on naturally enhanced ROS levels, rather than relying on the application of exogenous oxidants to simulate elevated ROS levels.

Role of cells in freezing-induced cell-fluid-matrix interactions within engineered tissues

During cryopreservation, ice forms in the extracellular space resulting in freezing-induced deformation of the tissue, which can be detrimental to the extracellular matrix (ECM) microstructure. Meanwhile, cells dehydrate through an osmotically driven process as the intracellular water is transported to the extracellular space, increasing the volume of fluid for freezing. Therefore, this study examines the effects of cellular presence on tissue deformation and investigates the significance of intracellular water transport and cell-ECM interactions in freezing-induced cell-fluid-matrix interactions. Freezing-induced deformation characteristics were examined through cell image deformetry (CID) measurements of collagenous engineered tissues embedded with different concentrations of MCF7 breast cancer cells versus microspheres as their osmotically inactive counterparts. Additionally, the development of a biophysical model relates the freezing-induced expansion of the tissue due to the cellular water transport and the extracellular freezing thermodynamics for further verification. The magnitude of the freezing-induced dilatation was found to be not affected by the cellular water transport for the cell concentrations considered; however, the deformation patterns for different cell concentrations were different suggesting that cell-matrix interactions may have an effect. It was, therefore, determined that intracellular water transport during freezing was insignificant at the current experimental cell concentrations; however, it may be significant at concentrations similar to native tissue. Finally, the cell-matrix interactions provided mechanical support on the ECM to minimize the expansion regions in the tissues during freezing.

The need for complex 3D culture models to unravel novel pathways and identify accurate biomarkers in breast cancer

The recent cataloging of the genomic aberrations in breast cancer has revealed the diversity and complexity of the disease at the genetic level. To unravel the functional consequences of specific repertoires of mutations and copy number changes on signaling pathways in breast cancer, it is crucial to develop model systems that truly recapitulate the disease. Here we discuss the three-dimensional culture models currently being used or recently developed for the study of normal mammary epithelial cells and breast cancer, including primary tumors and dormancy. We discuss the insights gained from these models in regards to cell signaling and potential therapeutic strategies, and the challenges that need to be met for the generation of heterotypic breast cancer model systems that are amenable for high-throughput approaches.

Factors implicated in the assessment of aminolevulinic acid-induced protoporphyrin IX fluorescence

BACKGROUND

Photodynamic therapy and photodiagnosis of cancer requires preferential accumulation of fluorescent photosensitizers in tumors. Clinical evidence documents feasibility of ALA-based photodiagnosis for tumor detection. However, false positive results and large variations in fluorescence intensities are also reported. Furthermore, selective accumulation of fluorescent species of photosensitizers in tumor cell lines, as compared to normal ones, when cultured in vitro, is not always observed. To understand this discrepancy we analyzed the impact of various factors on the intensity of detected PpIX fluorescence.

METHODS

Impacts of cell type, mitochondrial potential, cell-cell interactions and relocalization of PpIX among different cell types in co-cultures of different cell lines were analyzed by confocal microscopy and flow cytometry. Fluorescence spectroscopy was used to estimate absolute amounts of ALA-induced PpIX in individual cell lines. Immunofluorescence staining was applied to evaluate the ability of cell lines to produce collagen.

RESULTS

Higher ALA-induced PpIX fluorescence in cancer cell lines as compared to normal ones was not detected by all the methods used. Mitochondrial activity was heterogeneous throughout the cell monolayers and could not be clearly correlated with PpIX fluorescence. Positive collagen staining was detected in all cell lines tested.

CONCLUSIONS

Contrary to in vivo situation, ALA-induced PpIX production by cell lines in vitro may not result in higher PpIX fluorescence signals in tumor cells than in normal ones. We suggest that a combination of several properties of tumor tissue, instead of tumor cells only, is responsible for increased ALA-induced PpIX fluorescence in solid tumors.

GENERAL SIGNIFICANCE

Understanding the reasons of increased ALA-induced PpIX fluorescence in tumors is necessary for reliable ALA-based photodiagnosis, which is used in various oncological fields.

Breast tumor and stromal cell responses to TGF-β and hypoxia in matrix deposition

The components that comprise the extracellular matrix (ECM) are integral to normal tissue homeostasis as well as the development and progression of breast tumors. The secretion, construction, and remodeling of the ECM are each regulated by a complex interplay between tumor cells, fibroblasts and macrophages. Transforming growth factor-β (TGF-β) is an essential molecule in regulating the cellular production of ECM molecules and the adhesive interactions of cells with the ECM. Additionally, hypoxic cell signals, initiated by oxygen deprivation, additional metabolic factors or receptor activation, are associated with ECM formation and the progression of breast cancer. Both TGF-β and hypoxic cell signals are implicated in the functional and morphological changes of cancer-associated-fibroblasts and tumor-associated-macrophages. Moreover, the enhanced recruitment of tumor and stromal cells in response to hypoxia-induced chemokines leads to increased ECM deposition and remodeling, increased blood vessel formation, and enhanced tumor migration. Thus, elucidation of the collaborative networks between tumor and stromal cells in response to the combined signals of TGF-β and hypoxia may yield insight into treatment parameters that target both tumor and stromal cells.

Issues to be considered when studying cancer in vitro

Various cancer treatment approaches have shown promising results when tested preclinically. The results of clinical trials, however, are often disappointing. While searching for the reasons responsible for their failures, the relevance of experimental and preclinical models has to be taken into account. Possible factors that should be considered, including cell modifications during in vitro cultivation, lack of both the relevant interactions and the structural context in vitro have been summarized in the present review.

Human uterine leiomyoma-derived fibroblasts stimulate uterine leiomyoma cell proliferation and collagen type I production, and activate RTKs and TGF beta receptor signaling in coculture

Background

Uterine leiomyomas (fibroids) are benign smooth muscle tumors that often contain an excessive extracellular matrix (ECM). In the present study, we investigated the interactions between human uterine leiomyoma (UtLM) cells and uterine leiomyoma-derived fibroblasts (FB), and their importance in cell growth and ECM protein production using a coculture system.

Results

We found enhanced cell proliferation, and elevated levels of ECM collagen type I and insulin-like growth factor-binding protein-3 after coculturing. There was also increased secretion of vascular endothelial growth factor, epidermal growth factor, fibroblast growth factor-2, and platelet derived growth factor A and B in the media of UtLM cells cocultured with FB. Protein arrays revealed increased phosphorylated receptor tyrosine kinases (RTKs) of the above growth factor ligands, and immunoblots showed elevated levels of the RTK downstream effector, phospho-mitogen activated protein kinase 44/42 in cocultured UtLM cells. There was also increased secretion of transforming growth factor-beta 1 and 3, and immunoprecipitated transforming growth factor-beta receptor I from cocultured UtLM cells showed elevated phosphoserine expression. The downstream effectors phospho-small mothers against decapentaplegic -2 and -3 protein (SMAD) levels were also increased in cocultured UtLM cells. However, none of the above effects were seen in normal myometrial cells cocultured with FB. The soluble factors released by tumor-derived fibroblasts and/or UtLM cells, and activation of the growth factor receptors and their pathways stimulated the proliferation of UtLM cells and enhanced the production of ECM proteins.

Conclusions

These data support the importance of interactions between fibroid tumor cells and ECM fibroblasts in vivo, and the role of growth factors, and ECM proteins in the pathogenesis of uterine fibroids.

ADAMTS-1 metalloproteinase promotes tumor development through the induction of a stromal reaction in vivo

ADAMTS-1 (a disintegrin and metalloproteinase with thrombospondin motifs), the first described member of the ADAMTS family, is differentially expressed in various tumors. However, its exact role in tumor development and progression is still unclear. The aim of this study was to investigate the effects of ADAMTS-1 transfection in a bronchial epithelial tumor cell line (BZR) and its potential to modulate tumor development. ADAMTS-1 overexpression did not affect in vitro cell properties such as (a) proliferation in two-dimensional culture, (b) proliferation in three-dimensional culture, (c) anchorage-independent growth in soft agar, (d) cell migration and invasion in modified Boyden chamber assay, (e) angiogenesis in the aortic ring assay, and (f) cell apoptosis. In contrast, ADAMTS-1 stable transfection in BZR cells accelerated the in vivo tumor growth after s.c. injection into severe combined immunodeficient mice. It also promoted a stromal reaction characterized by myofibroblast infiltration and excessive matrix deposition. These features are, however, not observed in tumors derived from cells overexpressing a catalytically inactive mutant of ADAMTS-1. Conditioned media from ADAMTS-1-overexpressing cells display a potent chemotactic activity toward fibroblasts. ADAMTS-1 overexpression in tumors was associated with increased production of matrix metalloproteinase-13, fibronectin, transforming growth factor beta (TGF-beta), and interleukin-1beta (IL-1beta). Neutralizing antibodies against TGF-beta and IL-1beta blocked the chemotactic effect of medium conditioned by ADAMTS-1-expressing cells on fibroblasts, showing the contribution of these factors in ADAMTS-1-induced stromal reaction. In conclusion, we propose a new paradigm for catalytically active ADAMTS-1 contribution to tumor development, which consists of the recruitment of fibroblasts involved in tumor growth and tumor-associated stroma remodeling.

Hic-5/ARA55: a prostate stroma-specific AR coactivator

Growth factors and cytokines mediate communication between the epithelial and stromal compartments of the prostate. In prostate cancer (PCa), changes in the spatial arrangements of the two compartments (i.e. basement membrane invasion), DNA mutations, or cellular dedifferentiation (i.e. myofibroblasts) leads to significant changes in gene expression within both compartments. This results in altered cytokine and/or growth factor signaling in PCa. Recently, a stromal-specific androgen receptor (AR) coactivator, Hic-5/ARA55, has been identified that may play a role in regulating expression of the growth factor and/or cytokine expression in the prostate. Specifically, Hic-5/ARA55 expression influences androgen-induced keratinocyte growth factor (KGF) expression in WPMY-1 prostate stromal cells. Because Hic-5/ARA55's expression is also altered in PCa, it may play a role in the differential cellular signaling events that occur during tumor progression.

Hematopoietic origins of fibroblasts: I. In vivo studies of fibroblasts associated with solid tumors

OBJECTIVE

Recent studies have reported that bone marrow cells can give rise to tissue fibroblasts. However, the bone marrow cell(s) that gives rise to fibroblasts has not yet been identified. In the present study, we tested the hypothesis that tissue fibroblasts are derived from hematopoietic stem cells (HSCs) in vivo.

METHODS

These studies were conducted using mice whose hematopoiesis had been reconstituted by transplantation of a clonal population of cells derived from a single enhanced green fluorescent protein (EGFP)-positive HSC in conjunction with murine tumor models.

RESULTS

When tumors propagated in the transplanted mice were evaluated for the presence of EGFP(+) HSC-derived cells, two prominent populations of EGFP(+) cells were found. The first were determined to be fibroblasts within the tumor stromal capsule, a subset of which expressed type I collagen mRNA and alpha-smooth muscle actin. The second population was a perivascular cell associated with the CD31(+) tumor blood vessels.

CONCLUSION

These in vivo findings establish an HSC origin of fibroblasts.

Differential effects of estrogen on DNA synthesis in human periodontal ligament and breast cancer cells

BACKGROUND

It is important to clarify the biological function of the female sex hormones estrogen and progesterone in periodontal ligament cells, as these hormones may affect periodontal health. We have previously shown that human periodontal ligament cells express estrogen receptor beta (ERbeta) but not ERalpha, whereas human breast cancer cells (MCF7) express both ERalpha and ERbeta. Data on progesterone receptor (PgR) expression in human periodontal ligament cells have not been reported.

OBJECTIVES

Determine PgR expression in human periodontal ligament and MCF7 cells and to investigate how estrogen affects DNA and collagen synthesis in these two cell types showing different pattern of expression for ERalpha and beta.

METHODS

Periodontal ligament cells were obtained from the periodontal ligament of premolars extracted for orthodontic reasons and MCF7 cells from the American Type Culture Collection (ATCC). PgR expression was determined by immunocytochemistry. DNA and collagen synthesis was determined by [(3)H]thymidine and L-[(3)H]proline incorporation, respectively.

RESULTS

PgR immunoreactivity was observed in nuclei of MCF7 but not periodontal ligament cells. Treatment with estrogen (17beta-estradiol, E(2)) at physiological concentrations for 24 h stimulated DNA synthesis by more than two times in MCF7 cells, whereas there was no effect on periodontal ligament cell DNA synthesis. The ER blocker ICI 182780 fully reversed the stimulatory effect of E(2). Not only short-term (24 h) but also long-term (5 days) treatment with E(2) lacked effect on DNA synthesis in periodontal ligament cells. Neither periodontal ligament cell viability nor collagen synthesis was affected by E(2) treatment. Identical results were observed in periodontal ligament cells from male and female subjects.

CONCLUSIONS

Human MCF7 but not periodontal ligament cells express PgR, suggesting that progesterone via PgR affects MCF7 but not periodontal ligament cells. Further, estrogen stimulates breast cancer MCF7 cell proliferation, whereas it has no effect on proliferation of periodontal ligament cells, probably reflecting cell type specific ER expression pattern in these two cell types.

Use of three-dimensional basement membrane cultures to model oncogene-induced changes in mammary epithelial morphogenesis

The development of breast carcinomas involves a complex set of phenotypic alterations in breast epithelial cells and the surrounding microenvironment. While traditional transformation assays provide models for investigating certain aspects of the cellular processes associated with tumor initiation and progression, they do not model alterations in tissue architecture that are critically involved in tumor development. In this review, we provide examples of how three-dimensional (3D) cell culture models can be utilized to dissect the pathways involved in the development of mammary epithelial structures and to elucidate the mechanisms responsible for oncogene-induced phenotypic alterations in epithelial behavior and architecture. Many normal mammary epithelial cell lines undergo a stereotypic morphogenetic process when grown in the presence of exogenous matrix proteins. This 3D morphogenesis culminates in the formation of well-organized, polarized spheroids, and/or tubules that are highly reminiscent of normal glandular architecture. In contrast, transformed cell lines isolated from mammary tumors exhibit significant deviations from normal epithelial behavior in 3D culture. We describe the use of 3D models as a method for both reconstructing and deconstructing the cell biological and biochemical events involved in mammary neoplasia.

Collagen type I expression in experimental anaplastic thyroid carcinoma: regulation and relevance for tumorigenicity

Fibrosis in solid malignancies plays a significant role in tumor pathophysiology. Potential mechanisms for collagen type I deposition in anaplastic thyroid carcinoma (ATC) were investigated using 6 characterized ATC cell lines. Three of these cell lines, which produced collagen type I, had, as a group, a poor tumorigenicity when inoculated in athymic mice. This group of cells generated tumors in 4 of 24 injected animals (17%). Pro-alpha 1(I) collagen mRNA-expressing carcinoma and stromal cells were interdispersed in the tumors generated by these ATC cells. By contrast, the 3 noncollagen-producing ATC cell lines were all tumorigenic with a tumor take of 60% in the whole group. In the latter tumors, pro-alpha 1(I) collagen mRNA-expressing cells were confined to the stromal compartment, well delineated from carcinoma cell islets. To study the influence of ATC cells on collagen type I synthesis by fibroblasts, we used AG 1518 diploid human fibroblasts cultured on poly-(2-hydroxyethyl methacrylate) (poly[HEMA])-coated plates. This culture condition allows the study of the effect of collagen mRNA translation in the regulation of collagen type I synthesis. Conditioned media from the 6 ATC cell lines did not influence collagen synthesis. The ATC cell line KAT-4 stimulated fibroblast synthesis of collagen type I when the two cell types were cocultured on poly[HEMA]-coated substrates. Specific inhibitors of PDGF and TGF-beta reduced the KAT 4 carcinoma cell-induced stimulation of collagen type I synthesis. Our data suggest that collagen type I production by carcinoma cells correlates negatively with tumorigenicity and that the formation of a well-defined stroma is of importance for tumor growth. Furthermore, our data suggest that tumor cells are able to stimulate collagen mRNA translation in stromal fibroblasts in direct cell-cell contact by, at least in part, transferring PDGF or TGF-beta.

Reactive stroma in prostate cancer progression

PURPOSE

The development of an altered stromal microenvironment in response to carcinoma is a common feature of many tumors. We reviewed the literature describing characteristics of reactive stroma, how reactive stroma affects cancer progression and how carcinoma regulates reactive stroma. Moreover, we present a hypothesis of reactive stroma in prostate cancer and discuss how the biology of reactive stroma may be used in novel diagnostic and therapeutic approaches.

MATERIALS AND METHODS

An extensive literature search was performed to review reports of the general features of wound repair stroma, general stromal responses to carcinoma, and stromal biology of normal and prostate cancer tissues. These studies were analyzed and a reactive stroma hypothesis in prostate cancer was developed.

RESULTS

Modifications to the stroma of breast, colon and prostate tumors parallel the generation of granulation tissue in wound repair. These changes include stromal cell phenotypic switching, extracellular matrix remodeling and angiogenesis induction. Therefore, it is predicted that a modified wound healing response induces the formation of reactive stroma in cancer to create a tumor promoting environment. Based on its role in wound repair and its over expression in prostate cancer, transforming growth factor-beta stands out as a potential regulator of reactive stroma.

CONCLUSIONS

Reactive stroma in prostate cancer and granulation tissue in wound repair show similar biological responses and processes that are predicted to promote cancer progression. Further identification of specific functional and regulatory mechanisms in prostate cancer reactive stroma may aid in the use of reactive stroma for novel diagnostic and therapeutic approaches.

Breast tumour cell-induced down-regulation of type I collagen mRNA in fibroblasts

This study investigated the modulation of type I collagen gene expression in normal fibroblasts by breast tumour cells. Northern analysis of total RNA extracted from stages I, II and III breast tumour tissue revealed that collagen mRNA levels were elevated in stage I tumours compared to the adjacent normal breast tissues, whereas they were decreased in stages II and III breast tumours. This aberrant collagen gene expression was confirmed by non-radioactive RNA:RNA in situ hybridization analysis of 30 breast carcinomas which localized the production of type I collagen mRNA to the stromal fibroblasts within the vicinity of the tumour cells. In order to determine whether the tumour cells were directly responsible for this altered collagen production by the adjacent fibroblasts, breast tumour cell lines were co-cultured with normal fibroblasts for in vitro assessment of collagen and steady-state collagen RNA levels. Co-culture of tumour cells and normal fibroblasts in the same dish resulted in down-regulation of collagen mRNA and protein. Treatment of the fibroblasts with tumour-cell conditioned medium also resulted in decreased collagen protein levels but the mRNA levels, however, remained unaltered. These results suggested that the tumour cells either secrete a labile 'factor', or express a cell surface protein requiring direct contact with the fibroblasts, resulting in down-regulation of collagen gene expression. Modulation of the ECM is a common characteristic of invading tumour cells and usually involves increased production of collagenases by the tumour cells or stromal fibroblasts. This study showed that tumour cells were also able to modulate collagen mRNA production by stromal fibroblasts, which may facilitate tumour cell invasion and metastasis.

MMP-2 release and activation in ovarian carcinoma: the role of fibroblasts

The matrix metalloproteinase MMP-2 is up-regulated in epithelial cancers and its mRNA localizes to stromal fibroblasts. In this paper we show that co-culture of ovarian carcinoma cells with fibroblasts resulted in an enhanced release of proMMP-2 and TIMP-2 into the culture medium. Cell-cell interaction was a major factor in this response and carcinoma cells stimulated proMMP-2 release from fibroblasts but not vice versa. Collagen 1, in a dose-dependent fashion, induced activation of proMMP-2 by tumour-derived, but not normal, fibroblasts. Antibody to beta1 integrin also induced proMMP-2 activation by tumour-derived fibroblasts. The activation involved the processing of proMMP-2 by a membrane-bound metalloproteinase. We propose that, in the ovarian tumour microenvironment, interaction between tumour cells and fibroblasts may enhance fibroblast production of the proMMP-2 and TIMP-2. Collagen I, also present in the ovarian tumours, then induces these fibroblasts to activate proMMP-2 even in the presence of TIMP-2. This active MMP-2 can associate with the cell surface of tumour cells and fibroblasts and is used in the processes of tissue remodelling and invasion.

Retention of intracellular fibronectin expression in primary and metastatic thyroid carcinoma: an immunohistochemical study

We previously showed that thyroid carcinoma distinctively expresses intracellular fibronectin (FN) compared to other carcinomas. To determine the persistency of such FN accumulation in metastasis, we immunohistochemically examined the accumulation of intracellular FN in 92 cases of different carcinomas originating from the thyroid gland, lung and kidney, 44 of which showed metastasis to other organs. In all of the cases, normal epithelial cells adjacent to carcinomas did not show intracellular FN. Almost all of the cases (31/32) of thyroid carcinoma with/without metastasis to the lung and/or kidney showed intracellular FN in both the primary and metastatic lesions. Few cases (2/38) of lung carcinoma and none of the 22 cases of kidney carcinoma showed intracellular FN in the primary and metastatic lesions. In conclusion, the intracellular accumulation of FN acquired after carcinogenic transformation is not a common phenomenon in carcinomas, but rather is distinctive for thyroid carcinoma, even when it metastasizes to other organs. The immunohistochemical detection of intracellular FN may be useful for diagnosing thyroid carcinoma, even in metastatic lesions.

Positive regulation of normal and tumoral mammary epithelial cell proliferation by fibroblasts in coculture

In the mammary gland, mesenchymal-epithelial interactions are of paramount importance during normal and tumoral developments. We have studied the paracrine growth regulation of a variety of breast epithelial cells in coculture with normal or pathological breast fibroblasts. Two models of coculture were used in which the two cell types were seeded and grown, either together in microchamber slides or separated by a microporous membrane. Under these two conditions, all fibroblasts were shown to stimulate the proliferation of the hormono-responsive breast carcinoma MCF-7 cell line, suggesting that cell contacts were not indispensable for the paracrine stimulation of MCF-7 cell growth by fibroblasts. Moreover, in the Transwell coculture system, the proliferation of a variety of other breast carcinoma cells (MDA-MB231, T47D, and BT-20) was also stimulated by fibroblasts. However, the amplitude of the proliferative response seemed to be dependent on the carcinoma cell line considered. Moreover, the proliferative response of normal mammary epithelial cells to the presence of fibroblasts was shown to be significantly higher than the tumor cell response. The nature of the tissue of fibroblast origin, normal or pathological, did not influence the growth response of the epithelial cells. In this study, we thus demonstrate that fibroblasts are able to stimulate the proliferation of normal and carcinoma cells through paracrine exchange mechanisms. We also conclude that the target epithelial cell phenotype will essentially determine the extent of the proliferative response.

The role of stroma in breast carcinoma growth in vivo

The malignant progression of tumors is thought to be related to the expression of oncogenes and loss of expression of tumor suppressor gene. These factors are intrinsic to the cancer cells themselves. However, carcinomas are also infiltrated by host cells (fibroblasts, endothelial cells, inflammatory cells) and surrounded by an extracellular matrix which is extensively remodeled. The extracellular matrix components and infiltrating host cells provide a microenvironment that conditions both tumor progression and the metastatic process. Transplantation of human tumors into athymic nude mice has become an important experimental approach to study the biology of human cancers. The different models developed so far are beginning to elucidate the role of matrix molecules, growth factors and enzymes as well as fibroblasts in tumor progression. These animal models are likely to provide a useful tool to evaluate new antitumor treatments.

Adherence, proliferation and collagen turnover by human fibroblasts seeded into different types of collagen sponges

We describe an in vitro model that we have used to evaluate dermal substitutes and to obtain data on cell proliferation, the rate of degradation of the dermal equivalent, contractibility and de novo synthesis of collagen. We tested three classes of collagenous materials: (1) reconstituted non-crosslinked collagen, (2) reconstituted collagen that was chemically crosslinked with either glutaraldehyde, aluminium alginate or acetate, and (3) native collagen fibres, with or without other extracellular matrix molecules (elastin hydrolysate, hyaluronic acid or fibronectin). The non-crosslinked reconstituted collagen was degraded rapidly by human fibroblasts. The chemically crosslinked materials proved to be cytotoxic. Native collagen fibres were stable. In the absence of ascorbic acid, the addition of elastin hydrolysate to this type of matrix reduced the rate of collagen degradation. Both elastin hydrolysate and fibronectin partially prevented fibroblast-mediated contraction. Hyaluronic acid was only slightly effective in reducing the collagen degradation rate and more fibroblast-mediated contraction of the material was found than for the native collagen fibres with elastin hydrolysate and fibronectin. In the presence of ascorbate, collagen synthesis was enhanced in the native collagen matrix without additions and in the material containing elastin hydrolysate, but not in the material with hyaluronic acid. These results are indicative of the suitability of tissue substitutes for in vivo application.

Role of matrix, fibroblasts and type IV collagenases in tumor progression and invasion

We have studied the role of the extracellular matrix and host cells in tumor progression and tumor invasion. Our results emphasize the importance of tumoral cell-host cell interactions during this process. Addition of human fibroblasts and/or basement membrane components to human mammary adenocarcinoma cells, when injected into athymic nude mice, results in an increase of take and growth rate of the tumors. Peritumoral extracellular matrix is remodeled through multiple mechanisms: overproduction of matrix components by fibroblasts, enhanced fibroblasts proliferation, modulation of interstitial collagenase production by fibroblasts and retraction of the matrix by tumoral cells. The degradation of basement membranes during the metastatic process is often associated with the secretion of proteolytic enzymes. The 72 kDa type IV collagenase, a metalloproteinase, can be produced by some tumoral cells. However, it appears also to be secreted by peritumoral stromal fibroblasts under the influence of tumoral cells. We have demonstrated the existence of a binding site for this enzyme on the membrane of mammary tumoral cells. These results suggest a cooperation between tumor cells and fibroblasts during basement membrane destruction.

Coordinate enhancement of gelatinase A mRNA and activity levels in human fibroblasts in response to breast-adenocarcinoma cells

Gelatinases/type-IV collagenases are metalloproteinases involved in some carcinoma invasion and metastatic processes. The exact cellular source of the 72-kDa gelatinase A is controversial. We have analyzed the expression of mRNA coding for gelatinase A in vivo by in situ hybridization on breast-cancer tissues. The mRNA for gelatinase A was present in fibroblasts. We have therefore evaluated the gelatinase-A activity in vitro, in co-cultures of different breast adenocarcinoma cell lines and human fibroblasts. In monoculture, none of the tumor cells tested produced detectable amounts of gelatinase A. The gelatinase-A activity was enhanced in cultures of fibroblasts maintained in the presence of MDA-MB 231 or SKBR3 cells, or their conditioned medium. This increased enzymatic activity was evidenced both in the culture medium and in the membrane fraction and was paralleled by enhancement of the steady-state levels of mRNA. These results are an in vitro demonstration of a regulation of fibroblasts gelatinase-A production by soluble factors secreted by breast-tumor cells.

Collagen induced MMP-2 activation in human breast cancer

Matrix metalloproteinase-2 (MMP-2), a zymogen requiring proteolytic activation for catalytic activity, has been implicated broadly in the invasion and metastasis of many cancer model systems, including human breast cancer (HBC). MMP-2 has been immunolocalized to carcinomatous human breast, where the degree of activation of MMP-2 correlates well with tumor grade and patient prognosis. Using Matrigel assays, we have stratified HBC cell lines for invasiveness in vitro, and compared this to their potential for metastatic spread in nude mice. HBC cell lines expressing the mesenchymal marker protein vimentin were found to be highly invasive in vitro, and tended to form metastases in nude mice. We have further discovered that culture on collagen-I gels (Vitrogen; Vg) induces MMP-2-activator in highly invasive but not poorly invasive HBC cell lines. As seen for other MMP-2-activator inducing regimens, this induction requires protein synthesis and an intact MMP-2 hemopexin-like domain, appears to be mediated by a cell surface activity, and can be inhibited by metalloproteinase inhibitors. The induction is highly specific to collagen I, and is not seen with thin coatings of collagen I, collagen IV, laminin, or fibronectin, or with 3-dimensional gels of laminin, Matrigel, or gelatin. This review focuses on collagen I and MMP-2, their localization and source in HBC, and their relationship(s) to MMP-2 activation and HBC metastasis. The relevance of collagen I in activation of MMP-2 in vivo is discussed in terms of stromal cell: tumor cell interaction for collagen I deposition, MMP-2 production, and MMP-2-activation. Such cooperativity may exist in vivo for MMP-2 participation in HBC dissemination. A more complete understanding of the regulation of MMP-2-activator by type I collagen may provide new avenues for improved diagnosis and prognosis of human breast cancer.

Enhancement of tumorigenicity of human breast adenocarcinoma cells in nude mice by matrigel and fibroblasts

The failure of MCF7 cells to induce the formation of tumours after sub-cutaneous inoculation into athymic nude mice can be obviated by the simultaneous injection of an extract of basement membrane proteins (matrigel). Tumour growth is promoted and the latency period is low (2 to 4 weeks). In the absence of matrigel, the simultaneous inoculation of fibroblasts and MCF7 cells also resulted in the development of tumours, but with a longer latency period (about 2 months). The tumorigenic synergy between matrigel and fibroblasts was evidenced by co-inoculating MCF7 cells MDA-MB 231 cells with fibroblasts and matrigel. This co-inoculation decreased the delay of appearance of the tumours and/or accelerated the tumour growth, depending upon the number of fibroblasts injected. Repeated injections of fibroblasts conditioned medium, at the site of inoculum of tumour cells also enhanced tumour growth, suggesting the involvement of soluble factors secreted by fibroblasts. Histologically, tumours induced by co-inoculation of tumour cells and fibroblasts contained more stromal structures including vimentin-positive cells, fibronectin and interstitial collagens. These data suggest that human tumours may be reconstituted and grown in athymic nude mice using basement membrane components and fibroblasts as inductors.

William L. McGuire Memorial Symposium. 1,25(OH)2D3 modulation of mammary tumor cell growth in vitro and in vivo

The biological role of 1,25(OH)2D3 in controlling Ca++ homeostasis in the body has been identified and widely investigated for a long time. More recently its effect in regulating cell proliferation or differentiated activity was described in a variety of normal and malignant cells. The present study was carried out to investigate the different aspects and biological mechanisms of this activity and to determine if the use of 1,25(OH)2D3 in the treatment of breast cancer patients could be considered. It is found that 1,25(OH)2D3 reduces the proliferation of MCF-7 and BT-20 cells lines regardless of their sex steroid receptor status. This effect is related to the concentration, from 10(-12) M to 10(-8) M. Its amplitude is less in other cell lines, but it opposes the EGF-induced increase of proliferation. It is observed that the proliferation rate of MCF-7 and BT-20 cells is increased when these tumor cells are cocultured with fibroblasts derived from breast tumor biopsies and that 1,25(OH)2D3 reverses this process. Moreover, experiments on DMBA induced mammary tumors in Sprague Dawley rats found that 1,25(OH)2D3 given at non toxic doses reduces significantly the tumor proliferation. These data showed that 1,25(OH)2D3 at low doses is effective on the proliferation of BT-20 and MCF-7 cells and on the paracrine growth stimulatory effect observed in the presence of fibroblasts. They suggest that 1,25(OH)2D3 or related synthetic molecules which are less active on Ca++ metabolism could be useful in the treatment of breast cancer patients.