Differentiation and cancer in the mammary gland: shedding light on an old dichotomy

Personalized models of heterogeneous 3D epithelial tumor microenvironments: Ovarian cancer as a model

Intractable human diseases such as cancers, are context dependent, unique to both the individual patient and to the specific tumor microenvironment. However, conventional cancer treatments are often nonspecific, targeting global similarities rather than unique drivers. This limits treatment efficacy across heterogeneous patient populations and even at different tumor locations within the same patient. Ultimately, this poor efficacy can lead to adverse clinical outcomes and the development of treatment-resistant relapse. To prevent this and improve outcomes, it is necessary to be selective when choosing a patient's optimal adjuvant treatment. In this review, we posit the use of personalized, tumor-specific models (TSM) as tools to achieve this remarkable feat. First, using ovarian cancer as a model disease, we outline the heterogeneity and complexity of both the cellular and extracellular components in the tumor microenvironment. Then we examine the advantages and disadvantages of contemporary cancer models and the rationale for personalized TSM. We discuss how to generate precision 3D models through careful and detailed analysis of patient biopsies. Finally, we provide clinically relevant applications of these versatile personalized cancer models to highlight their potential impact. These models are ideal for a myriad of fundamental cancer biology and translational studies. Importantly, these approaches can be extended to other carcinomas, facilitating the discovery of new therapeutics that more effectively target the unique aspects of each individual patient's TME. STATEMENT OF SIGNIFICANCE: In this article, we have presented the case for the application of biomaterials in developing personalized models of complex diseases such as cancers. TSM could bring about breakthroughs in the promise of precision medicine. The critical components of the diverse tumor microenvironments, that lead to treatment failures, include cellular- and extracellular matrix- heterogeneity, and biophysical signals to the cells. Therefore, we have described these dynamic components of the tumor microenvironments, and have highlighted how contemporary biomaterials can be utilized to create personalized in vitro models of cancers. We have also described the application of the TSM to predict the dynamic patterns of disease progression, and predict effective therapies that can produce durable responses, limit relapses, and treat any minimal residual disease.

Housekeeping genes involved in non-malignant breast phenotypes are widely expressed in multiple cancers and provide novel biomarkers of tumor classification

Clinically relevant biomarkers are useful to determine cancer patients' prognosis and treatments. To discover new putative biomarkers, we performed in silico analysis of a 325-gene panel previously associated with breast epithelial cell biology and clinical outcomes. Sixteen public datasets of microarray samples representing 8 cancer types and a total of 3,663 patients' samples were used for the analyses. Feature selection was used to identify the best subsets of the 325 genes for each classification, and linear discriminant analysis was used to quantify the accuracy of the classifications. A subset of 102 of the 325 genes were found to be housekeeping (HK) genes, and the classifications were repeated using only the 102 HK subset. The 325-gene panel and 102 HK subset were able to distinguish colon, gastric, lung, ovarian, pancreatic, and prostate tumors and leukemia from normal adjacent tissue, and classify disease subtypes of breast and lung cancers and leukemia with 70% or higher accuracy. HK genes have been overlooked as potential biomarkers due to their relative stability. This study describes a set of HK genes as putative biomarkers applicable to multiple cancer types worth following in subsequent validation studies.

Keloid disorder: Fibroblast differentiation and gene expression profile in fibrotic skin diseases

Keloid disorder, a group of fibroproliferative skin diseases, is characterized by unremitting accumulation of the extracellular matrix (ECM) of connective tissue, primarily collagen, to develop cutaneous tumors on the predilection sites of skin. There is a strong genetic predisposition for keloid formation, and individuals of African and Asian ancestry are particularly prone. The principal cell type responsible for ECM accumulation is the myofibroblast derived from quiescent resident skin fibroblasts either through trans-differentiation or from keloid progenitor stem cells with capacity for multi-lineage differentiation and self-renewal. The biosynthetic pathways leading to ECM accumulation are activated by several cytokines, but particularly by TGF-β signalling. The mechanical properties of the cellular microenvironment also play a critical role in the cell's response to TGF-β, as demonstrated by culturing of fibroblasts derived from keloids and control skin on substrata with different degrees of stiffness. These studies also demonstrated that culturing of fibroblasts on tissue culture plastic in vitro does not reflect their biosynthetic capacity in vivo. Collectively, our current understanding of the pathogenesis of keloids suggests a complex network of interacting cellular, molecular and mechanical factors, with distinct pathways leading to myofibroblast differentiation and activation. Keloids can serve as a model system of fibrotic diseases, a group of currently intractable disorders, and deciphering of the critical pathogenetic steps leading to ECM accumulation is expected to identify targets for pharmacologic intervention, not only for keloids but also for a number of other, both genetic and acquired, fibrotic diseases.

Reshaping in vitro Models of Breast Tissue: Integration of Stromal and Parenchymal Compartments in 3D Printed Hydrogels

Breast tissue consists of an epithelial parenchyma embedded in stroma, of heterogeneous and complex composition, undergoing several morphological and functional alterations throughout females' lifespan. Improved knowledge on the crosstalk between parenchymal and stromal mammary cells should provide important insights on breast tissue dynamics, both under healthy and diseased states. Here, we describe an advanced 3D in vitro model of breast tissue, combining multiple components, namely stromal cells and their extracellular matrix (ECM), as well as parenchymal epithelial cells, in a hybrid system. To build the model, porous scaffolds were produced by extrusion 3D printing of peptide-modified alginate hydrogels, and then populated with human mammary fibroblasts. Seeded fibroblasts were able to adhere, spread and produce endogenous ECM, providing adequate coverage of the scaffold surface, without obstructing the pores. On a second stage, a peptide-modified alginate pre-gel laden with mammary gland epithelial cells was used to fill the scaffold's pores, forming a hydrogel in situ by ionic crosslinking. Throughout time, epithelial cells formed prototypical mammary acini-like structures, in close proximity with fibroblasts and their ECM. This generated a heterotypic 3D model that partially recreates both stromal and parenchymal compartments of breast tissue, promoting cell-cell and cell-matrix crosstalk. Furthermore, the hybrid system could be easily dissolved for cell recovery and subsequent analysis by standard cellular/molecular assays. In particular, we show that retrieved cell populations could be discriminated by flow cytometry using cell-type specific markers. This integrative 3D model stands out as a promising in vitro platform for studying breast stroma-parenchyma interactions, both under physiological and pathological settings.

Sleeping Beauty and the Microenvironment Enchantment: Microenvironmental Regulation of the Proliferation-Quiescence Decision in Normal Tissues and in Cancer Development

Cells from prokaryota to the more complex metazoans cease proliferating at some point in their lives and enter a reversible, proliferative-dormant state termed quiescence. The appearance of quiescence in the course of evolution was essential to the acquisition of multicellular specialization and compartmentalization and is also a central aspect of tissue function and homeostasis. But what makes a cell cease proliferating even in the presence of nutrients, growth factors, and mitogens? And what makes some cells "wake up" when they should not, as is the case in cancer? Here, we summarize and discuss evidence showing how microenvironmental cues such as those originating from metabolism, extracellular matrix (ECM) composition and arrangement, neighboring cells and tissue architecture control the cellular proliferation-quiescence decision, and how this complex regulation is corrupted in cancer.

Laminin signals initiate the reciprocal loop that informs breast-specific gene expression and homeostasis by activating NO, p53 and microRNAs

How mammalian tissues maintain their architecture and tissue-specificity is poorly understood. Previously, we documented both the indispensable role of the extracellular matrix (ECM) protein, laminin-111 (LN1), in the formation of normal breast acini, and the phenotypic reversion of cancer cells to acini-like structures in 3-dimensional (3D) gels with inhibitors of oncogenic pathways. Here, we asked how laminin (LN) proteins integrate the signaling pathways necessary for morphogenesis. We report a surprising reciprocal circuitry comprising positive players: laminin-5 (LN5), nitric oxide (NO), p53, HOXD10 and three microRNAs (miRNAs) — that are involved in the formation of mammary acini in 3D. Significantly, cancer cells on either 2-dimensional (2D) or 3D and non-malignant cells on 2D plastic do not produce NO and upregulate negative players: NFκB, EIF5A2, SCA1 and MMP-9 — that disrupt the network. Introducing exogenous NO, LN5 or individual miRNAs to cancer cells reintegrates these pathways and induces phenotypic reversion in 3D. These findings uncover the essential elements of breast epithelial architecture, where the balance between positive- and negative-players leads to homeostasis.

Most animal cells can secrete molecules into their surroundings to form a supportive meshwork of large proteins, called the extracellular matrix. This matrix is connected to the cell membrane through receptors that can transmit signals to the cell nucleus to change the levels of small RNA molecules called microRNAs. These, in turn, can switch genes on and off in the nucleus.

In the laboratory, cells that build breast tissue and glands can be grown in gels containing extracellular matrix proteins called laminins. Under these conditions, ‘normal’ cells form organized clusters that resemble breast glands. However, if the communication between healthy cells and the extracellular matrix is interrupted, the cells can become disorganized and start to form clumps that resemble tumors, and if injected into mice, can form tumors. Conversely, if the interaction between the extracellular matrix and the cells is restored, each single cancer cell can – despite mutations – be turned into a healthy-looking cell. These cells form a normal-looking tissue through a process called reversion. Until now, it was not known which signals help normal breast tissue to form, and how cancerous cells revert into a ‘normal’ shape.

To investigate this, Furuta et al. used a unique series of breast cells from a woman who underwent breast reduction. The cells taken from the discarded tissue had been previously grown by a different group of researchers in a specific way to ensure that both normal and eventual cancer cells were from the same individual. Furuta et al. then put these cells in the type of laminin found in extracellular matrix. The other set of cells used consisted of the same cancerous cells that had been reverted to normal-looking cells.

Analysis of the three cell sets identified 60 genes that were turned down in reverted cancer cells to a level found in healthy cells, as well as 10 microRNAs that potentially target these 60 genes. A database search suggested that three of these microRNAs, which are absent in cancer cells, are necessary for healthy breast cells to form organized structures. Using this as a starting point, Furuta et al. discovered a signaling loop that was previously unknown and that organizes breast cells into healthy looking tissue.

This showed that laminins help to produce nitric oxide, an important signaling molecule that activates several specific proteins inside the breast cells and restores the levels of the three microRNAs. These, in turn, switch off two genes that are responsible for activating an enzyme that can chop the laminins. Since the two genes are deactivated in the reverted cancer cells, the laminins remain intact and the cells can form organized structures. These findings suggest that if any of the components of the loop were missing, the cells would start to form cancerous clumps again. Reverting the cancer cells in the presence of laminins, however, could help cancer cells to form ‘normal’ structures again.

These findings shed new light on how the extracellular matrix communicates with proteins in the nucleus to influence how single cells form breast tissues. It also shows that laminins are crucial for generating signals that regulate both form and function of specific tissues. A better understanding of how healthy and cancerous tissues form and re-form may in the future help to develop new cancer treatments.

Suppression of endogenous lipogenesis induces reversion of the malignant phenotype and normalized differentiation in breast cancer

The correction of specific signaling defects can reverse the oncogenic phenotype of tumor cells by acting in a dominant manner over the cancer genome. Unfortunately, there have been very few successful attempts at identifying the primary cues that could redirect malignant tissues to a normal phenotype. Here we show that suppression of the lipogenic enzyme fatty acid synthase (FASN) leads to stable reversion of the malignant phenotype and normalizes differentiation in a model of breast cancer (BC) progression. FASN knockdown dramatically reduced tumorigenicity of BC cells and restored tissue architecture, which was reminiscent of normal ductal-like structures in the mammary gland. Loss of FASN signaling was sufficient to direct tumors to a reversed phenotype that was near normal when considering the development of polarized growth-arrested acinar-like structure similar to those formed by nonmalignant breast cells in a 3D reconstituted basement membrane in vitro. This process, in vivo, resulted in a low proliferation index, mesenchymal-epithelial transition, and shut-off of the angiogenic switch in FASN-depleted BC cells orthotopically implanted into mammary fat pads. The role of FASN as a negative regulator of correct breast tissue architecture and terminal epithelial cell differentiation was dominant over the malignant phenotype of tumor cells possessing multiple cancer-driving genetic lesions as it remained stable during the course of serial in vivo passage of orthotopic tumor-derived cells. Transient knockdown of FASN suppressed hallmark structural and cytosolic/secretive proteins (vimentin, N-cadherin, fibronectin) in a model of EMT-induced cancer stem cells (CSC). Indirect pharmacological inhibition of FASN promoted a phenotypic switch from basal- to luminal-like tumorsphere architectures with reduced intrasphere heterogeneity. The fact that sole correction of exacerbated lipogenesis can stably reprogram cancer cells back to normal-like tissue architectures might open a new avenue to chronically restrain BC progression by using FASN-based differentiation therapies.

Modeling glands with PTEN deficient cells and microscopic methods for assessing PTEN loss: endometrial cancer as a model

PTEN is an important tumor suppressor gene. Interpreting PTEN deficiency in the appropriate microscopic context of cancer may be important to understand its role in tumor development and progression. This may be particularly relevant in heterogeneous tumors. Here, we discuss the usefulness of 3D cultures in understanding the consequences of PTEN inactivation in tissue architecture. Afterwards, we discuss the role of immunohistochemistry and fluorescent in situ hybridization in assessing PTEN loss in tumors. In this review, endometrial carcinoma is used as a model.

Focal adhesion-chromatin linkage controls tumor cell resistance to radio- and chemotherapy

Cancer resistance to therapy presents an ongoing and unsolved obstacle, which has clear impact on patient's survival. In order to address this problem, novel in vitro models have been established and are currently developed that enable data generation in a more physiological context. For example, extracellular-matrix- (ECM-) based scaffolds lead to the identification of integrins and integrin-associated signaling molecules as key promoters of cancer cell resistance to radio- and chemotherapy as well as modern molecular agents. In this paper, we discuss the dynamic nature of the interplay between ECM, integrins, cytoskeleton, nuclear matrix, and chromatin organization and how this affects the response of tumor cells to various kinds of cytotoxic anticancer agents.

Crossroads of integrins and cadherins in epithelia and stroma remodeling

Adhesion events mediated by cadherin and integrin adhesion receptors have fundamental roles in the maintenance of the physiological balance of epithelial tissues, and it is well established that perturbations in their normal functional activity and/or changes in their expression are associated with tumorigenesis. Over the last decades, increasing evidence of a dynamic collaborative interaction between these complexes through their shared interactions with cytoskeletal proteins and common signaling pathways has emerged not only as an important regulator of several aspects of epithelial cell behavior, but also as a coordinated adhesion module that senses and transmits signals from and to the epithelia surrounding microenvironment. The tight regulation of their crosstalk is particularly important during epithelial remodeling events that normally take place during morphogenesis and tissue repair, and when defective it leads to cell transformation and aggravated responses of the tumor microenvironment that contribute to tumorigenesis. In this review we highlight some of the interactions that regulate their crosstalk and how this could be implicated in regulating signals across epithelial tissues to sustain homeostasis.

Endothelial cells stimulate growth of normal and cancerous breast epithelial cells in 3D culture

BACKGROUND

Epithelial-stromal interaction provides regulatory signals that maintain correct histoarchitecture and homeostasis in the normal breast and facilitates tumor progression in breast cancer. However, research on the regulatory role of the endothelial component in the normal and malignant breast gland has largely been neglected. The aim of the study was to investigate the effects of endothelial cells on growth and differentiation of human breast epithelial cells in a three-dimensional (3D) co-culture assay.

METHODS

Breast luminal and myoepithelial cells and endothelial cells were isolated from reduction mammoplasties. Primary cells and established normal and malignant breast cell lines were embedded in reconstituted basement membrane in direct co-culture with endothelial cells and by separation of Transwell filters. Morphogenic and phenotypic profiles of co-cultures was evaluated by phase contrast microscopy, immunostaining and confocal microscopy.

RESULTS

In co-culture, endothelial cells stimulate proliferation of both luminal- and myoepithelial cells. Furthermore, endothelial cells induce a subpopulation of luminal epithelial cells to form large acini/ducts with a large and clear lumen. Endothelial cells also stimulate growth and cloning efficiency of normal and malignant breast epithelial cell lines. Transwell and gradient co-culture studies show that endothelial derived effects are mediated - at least partially - by soluble factors.

CONCLUSION

Breast endothelial cells - beside their role in transporting nutrients and oxygen to tissues - are vital component of the epithelial microenvironment in the breast and provide proliferative signals to the normal and malignant breast epithelium. These growth promoting effects of endothelial cells should be taken into consideration in breast cancer biology.

Perspectives on tissue interactions in development and disease

From the morphogenetic movements of the three germ layers during development to the reactive stromal microenvironment in cancer, tissue interactions are vital to maintaining healthy organ morphologic architecture and function. The stromal compartment is thought to be complicit in tumor progression and, as such, represents an opportune target for disease therapies. However, recent developments in our understanding of the diversity of the stromal compartment and the lack of appropriate models to study its relevance in human disease have limited our further understanding of the role of tissue interactions in tumor progression. The failure any model to fully recapitulate the complexities of systemic biology continue to create a higher imperative for incorporating various perspectives into a broader understanding for the ultimate goal of designing interventional therapies. Understanding this potential, this review examines the biological models used to study stromal-epithelial interactions and includes an attempt to incorporate behavioral terminology to define and mathematically model ecological relationships in stromal-epithelial interactions. In addition, the current attempt to incorporate these diverse ecological perspectives into in silico mathematical models through cross-disciplinary coordination is reviewed, which will provide a fresh perspective on defining cell group behavior and tissue ecology in disease and hopefully lead to the generation of new hypotheses to be empirically validated.

Cytodifferentiation by retinoids, a novel therapeutic option in oncology: rational combinations with other therapeutic agents

Retinoic acid (RA) and derivatives are promising antineoplastic agents endowed with both therapeutic and chemopreventive potential. Although the treatment of acute promyelocytic leukemia with all-trans retinoic acid is an outstanding example, the full potential of retinoids in oncology has not yet been explored and a more generalized use of these compounds is not yet a reality. One way to enhance the therapeutic and chemopreventive activity of RA and derivatives is to identify rational combinations between these compounds and other pharmacological agents. This is now possible given the information available on the biochemical and molecular mechanisms underlying the biological activity of retinoids. At the cellular level, the antileukemia and anticancer activity of retinoids is the result of three main actions, cytodifferentiation, growth inhibition, and apoptosis. Cytodifferentiation is a particularly attractive modality of treatment and differentiating agents promise to be less toxic and more specific than conventional chemotherapy. This is the result of the fact that cytotoxicity is not the primary aim of differentiation therapy. At the molecular level, retinoids act through the activation of nuclear retinoic acid receptor-dependent and -independent pathways. The cellular pathways and molecular networks relevant for retinoid activity are modulated by a panoply of other intracellular and extracellular pathways that may be targeted by known drugs and other experimental therapeutics. This chapter aims to summarize and critically discuss the available knowledge in the field.

A bidirectional “αvβ3 integrin-ERK1/ERK2 MAPK” connection regulates the proliferation of breast cancer cells

In addition to their role in cell migration and adhesion, integrins elicit a series of transduction events that regulate cell-cycle progression and apoptosis in a process known as "outside-in" signaling. A second mode of integrin regulation known as "inside-out" signaling, in which the activation of major cell transduction cascades can influence the activation status of some integrins, has also been described. Here, we have assessed the role of the extracellular signal-regulated kinase (ERK1)/ERK2, mitogen-activated protein kinase (MAPK), and phospoinositide 3-kinase (PI-3'K) signaling pathways in the expression and function of alpha(v)beta(3) integrin in breast cancer models. Pharmacological inhibition of MEK1 and MEK2 with U0126 drastically increased the levels of alpha(v)beta(3) in Heregulin (HRG)-overexpressing MDA-MB-231 cells (231/WT, 231/VEC) and derivatives transfected with the antisense orientation of the HRG-beta2 full length cDNA (231/ASPOOL, 231/AS31). Interestingly, this was related to a significant decrease of viability and of the S- and G2/M subcompartment of the cell cycle in MDA MB 231 cells in response to U0126. Furthermore, specific inhibition of the PI-3'K pathway with LY294002 also induced an increase of alpha(v)beta(3) levels but to a lesser extent. Moreover, pretreatment of MDA-MB-231 cells with U0126 antagonized the effects of small peptidomimetic alpha(v)beta(3) antagonists. Remarkably, inhibition of the PI-3'K/AKT pathway did not exert the same effects, thus suggesting that the "outside-in" as well as the "inside-out" alpha(v)beta(3)-mediated signaling goes primarily through the ERK1/ERK2 MAPK pathway in MDA MB 231 breast cancer cells. Collectively, these results strongly suggest the existence of a bidirectional molecular connection alpha(v)beta(3)-ERK1/ERK2 MAPK that would regulate breast cancer cells survival and proliferation.

The neurotrophic receptor TrkB in anoikis resistance and metastasis: a perspective

Resistance to anoikis ("detachment-induced apoptosis") has been suggested to be a prerequisite for cancer cells to metastasize. In a functional screen for suppressors of anoikis, we identified the neurotrophic receptor TrkB. Upon s.c. inoculation in mice, TrkB-expressing cells formed highly invasive and metastatic tumors. Here, we discuss our findings within the context of the proposed role of TrkB in human malignancies and address the question of its feasibility as a target for cancer therapy.

Intrauterine breast development and the mammary myoepithelial lineage

As their name implies, the myoepithelial cells found at the epithelial-mesenchymal interface of the human mammary gland disclose features suggestive of a dual epithelial-like and muscle-like differentiation, i.e. they co-express various keratins and vimentin intermediate filaments, as well as smooth muscle-related antigens. This article provides an overview of the literature on intrauterine breast development with special emphasis on the myoepithelial component of the fetal human mammary gland epithelium. It discusses original and recently published immunohistochemical data on myoepithelial precursors and reasserts the relevance of developmental, morphological fetal tissue-based studies to the understanding and the clinical management of adult diseases.

Stromal-epithelial interactions in aging and cancer: senescent fibroblasts alter epithelial cell differentiation

Cellular senescence suppresses cancer by arresting cells at risk of malignant tumorigenesis. However, senescent cells also secrete molecules that can stimulate premalignant cells to proliferate and form tumors, suggesting the senescence response is antagonistically pleiotropic. We show that premalignant mammary epithelial cells exposed to senescent human fibroblasts in mice irreversibly lose differentiated properties, become invasive and undergo full malignant transformation. Moreover, using cultured mouse or human fibroblasts and non-malignant breast epithelial cells, we show that senescent fibroblasts disrupt epithelial alveolar morphogenesis, functional differentiation and branching morphogenesis. Furthermore, we identify MMP-3 as the major factor responsible for the effects of senescent fibroblasts on branching morphogenesis. Our findings support the idea that senescent cells contribute to age-related pathology, including cancer, and describe a new property of senescent fibroblasts - the ability to alter epithelial differentiation - that might also explain the loss of tissue function and organization that is a hallmark of aging.

Expression of FGF-2 alters focal adhesion dynamics in migration-restricted

Basic fibroblast growth factor (FGF-2) expression takes place during morphogenic differentiation of mammary ducts and is lost in breast cancer. Forced re-expression of FGF-2 in breast cancer cell lines induces a more differentiated phenotype and inhibits motility by unknown mechanisms. Here we demonstrate that MDA-MB-231 cells with encumbered motility due to forced re-expression of FGF-2 have activated focal complexes as determined by immunoprecipitation/western blotting and immunofluorescence staining with antibodies to FAK, p130Cas, paxillin, vinculin and phosphotyrosine. The activation of the focal adhesion complexes results in loss of stress fibers associated with malignant transformation of mammary epithelial cells and the formation of circumferentially-distributed actin bundles associated with non-transformed mammary epithelial cells. These effects require continuous FGF-2 expression, as the effects of exogenous recombinant FGF-2 are only small and transient. FGF-2 expression results in an increase in integrin alpha 3 expression and decreases in integrin beta 1 and beta 4 expression. These changes, however, induce only a small decrease in adhesion to uncoated and fibronectin-coated tissue culture dishes suggesting that the primary cause of impaired motility is due to intrinsic signaling. These data suggest that FGF-2-inhibits motility in breast cancer cells by stabilization of focal complexes and induction of a more differentiated phenotype with disruption of stress fiber formation and a characteristic cortical actin distribution.

Physiological and pathological consequences of the interactions of the p53 tumor suppressor with the glucocorticoid, androgen, and estrogen receptors

The p53 tumor suppressor plays a key role in protection from the effects of different physiological stresses (DNA damage, hypoxia, transcriptional defects, etc.), and loss of its activity has dire consequences, such as cancer. Its activity is finely tuned through interactions with other important regulatory circuits in the cell. Recently, striking evidence has emerged for crosstalk with another class of important regulators, the steroid hormone receptors, and in particular the glucocorticoid (GR), androgen (AR), and estrogen (ER) receptors. These receptors are important in maintaining homeostasis in response to internal and external stresses (GR) and in the development, growth, and maintenance of the male and female reproductive systems (AR and ER, respectively). We review how p53 interacts closely with these receptors, to the extent that they share the same E3 ubiquitin ligase, the MDM2 oncoprotein. We discuss the different physiological contexts in which such interactions occur, and also how these interactions have been undermined in various pathological situations. We will describe future areas for research, with special emphasis on GR, and how certain common features, such as cytoplasmic anchoring of p53 by the receptors, may become targets for the development of therapeutic interventions. Given the importance of GR in inflammation, erythropoiesis, and autoimmune diseases, and the importance of AR and ER in prostate and breast cancer (respectively), the studies on p53 interactions with the steroid receptors will be an important domain in the near future.

Expression analysis and genomic characterization of human melanoma differentiation associated gene-5, mda-5: a novel type I interferon-responsive apoptosis-inducing gene

Melanoma differentiation associated gene-5 (mda-5) was identified by subtraction hybridization as a novel upregulated gene in HO-1 human melanoma cells induced to terminally differentiate by treatment with IFN-beta+MEZ. Considering its unique structure, consisting of a caspase recruitment domain (CARD) and an RNA helicase domain, it was hypothesized that mda-5 contributes to apoptosis occurring during terminal differentiation. We have currently examined the expression pattern of mda-5 in normal tissues, during induction of terminal differentiation and after treatment with type I IFNs. In addition, we have defined its genomic structure and chromosomal location. IFN-beta, a type I IFN, induces mda-5 expression in a biphasic and dose-dependent manner. Based on its temporal kinetics of induction and lack of requirement for prior protein synthesis mda-5 is an early type I IFN-responsive gene. The level of mda-5 mRNA is in low abundance in normal tissues, whereas expression is induced in a spectrum of normal and cancer cells by IFN-beta. Expression of mda-5 by means of a replication incompetent adenovirus, Ad.mda-5, induces apoptosis in HO-1 cells as confirmed by morphologic, biochemical and molecular assays. Additionally, the combination of Ad.mda-5+MEZ further augments apoptosis as observed in Ad.null or uninfected HO-1 cells induced to terminally differentiate by treatment with IFN-beta+MEZ. The mda-5 gene is located on human chromosome 2q24 and consists of 16 exons, without pseudogenes, and is conserved in the mouse genome. Present data documents that mda-5 is a novel type I IFN-inducible gene, which may contribute to apoptosis induction during terminal differentiation and during IFN treatment. The conserved genomic and protein structure of mda-5 in human and mouse will permit analysis of the evolution and developmental aspects of this gene.

Phenotypic differentiation of human breast cancer cells by 1,3 cyclic propanediol phosphate

Breast cancer cells in their virulent undifferentiated state are characterized by lack of functional estrogen receptors (ER) and/or progesterone receptors (PR) as well as relatively low levels of other normal differentiation markers such as milk proteins and lipid droplets. To date, no method for in situ elevation of the state of differentiation of breast cancer cells has yet been proven effective in patients. We have recently shown that 1,3 cyclic propanediol phosphate (1,3 cPP), an analog of 1,3 cyclic glycerophosphate (1,3 cGP), can promote morphological, neuronal-like differentiation in pheochromocytoma-12 cells in vitro. In view of this observation, we tested the potential of 1,3 cPP to elevate the state of cellular differentiation of the human breast cancer cell lines MCF-7 (ER(+)) and HCC1954 (ER(-)), as characterized by the expression of steroid receptors, casein kinase, lipid droplet histology and signal-transduction gene profiles. In the range of 5-100 microM 1,3 cPP the in vitro expression of ER-alpha, PR and casein kinase increased by approximately 2-fold while the mRNA transcription increased by 2-6-fold. Moreover, following 9-12 days of incubation with 1,3 cPP, HCC1954 cells exhibited a significant increase in the production of lipid droplets as observed by Oil Red O staining. The in vivo effect of 1,3 PP on MCF-7 xenografted into nude mice was also determined. After 4 biweekly i.p. injections of 0.5 mg 1,3 cPP per mouse, tumors in the 1,3 cPP treated virtually did not grow at all while the tumors in the control group grew rapidly. Based on these findings, we propose that this novel differentiating compound has the potential to transform the malignant tumor phenotype into a near-normal phenotype, as well as to sensitize the tumor cells to anti-estrogen therapy via upgrading the status of steroid hormone receptors.

The mechanisms by which nitric oxide affects mammary epithelial growth and differentiation

Nitric oxide (NO) enhances prolactin-stimulated DNA synthesis and inhibits prolactin-induced differentiation in mouse mammary epithelium. The molecular pathways used by NO were determined by employing specific inhibitors of the transducers utilized by NO. Inhibitors of the Jun N-terminal kinase (JNK) blocked the effect of NO on DNA synthesis, although this appeared to involve a protein kinase G (PKG)-independent pathway. In contrast, inhibitors of the extracellular signal-regulated kinase (ERK) prevented NO from suppressing alpha-lactalbumin accumulation and this effect was PKG-dependent. NO can also elevate cAMP through the inhibition of phosphodiesterase 3 and cAMP mimicks the actions of NO on both DNA synthesis and differentiation. However, suppression of cAMP levels did not prevent the effects of NO. Therefore, NO uses two separate pathways to affect mammary epithelium: it stimulates growth via JNK and inhibits differentiation through ERK.

Synthesis and evaluation of new 5-fluorouracil antitumor cell differentiating derivatives

Three new antitumour drugs containing two 5-fluorouracil moieties at both ends of the structure and a two amide bond linker were synthesized. Appropriated bis-acetal were reacted with two equivalents of 5-FU to afford the desired compounds. These drugs were evaluated for their ability to induce myogenic maturation in vitro on human rhabdomyosarcoma cells in an experimental model. Compounds 5 and 6 induced morphological and phenotypical differentiation in rhabdomyosarcoma cells at 4.5 and 3.5 microM, respectively. These new cell differentiating agents could be used as an alternative to selective destruction of undifferentiated cells. A potential role of the differentiation therapy as an alternative approach to the treatment of rhabdomyosarcomas is suggested.

Get a ligand, get a life: integrins, signaling and cell survival

Programmed cell death is crucial for the development and maintenance of multicellular organisms. The decision to live, or to die, depends, at the cellular level, upon the cell's interaction with extracellular cues that trigger cell signaling pathways promoting survival or death. The extracellular matrix (ECM) influences the execution of the apoptotic program through the actions of adhesion receptors. Among these, integrins initiate a variety of downstream signaling events in response to ECM ligation. Integrins directly activate survival pathways via the PI 3-kinase and MAPK pathways and act as essential cofactors for their stimulation by growth factors. Conversely, elevated integrin expression in the absence of appropriate ligands, or in the presence of natural or synthetic antagonists, can promote apoptosis under otherwise permissive growth conditions. Integrins thus act in a crucial biosensory role, coordinating survival or death responses as a function of ECM composition. This dual function provides an elegant mechanism through which tissue-remodeling events may regulate cell death or survival in a temporal, ECM-governed manner.

Suppression of growth and increased cellular attachment after expression of DAL-1 in MCF-7 breast cancer cells

The differentially expressed in adenocarcinoma of the lung (DAL-1) gene, which shares significant homology with members of the 4.1/ezrin/radixin/moesin/neurofibromatosis 2 (ERM/NF2) protein family, has previously been shown to suppress growth in lung cancer cell lines. This gene localizes to chromosome band 18p11.3, which undergoes loss of heterozygosity (LOH) in nonsmall cell lung carcinomas and a significant proportion of ductal carcinomas in situ (DCIS) of the breast. This finding suggests that alteration of gene(s) (possibly DAL-1) within this chromosomal region may be important early in the progression of breast disease. We generated MCF-7 cell lines expressing DAL-1 constitutively or under the control of an inducible promoter and analyzed the effect of DAL-1 expression on growth. These investigations revealed that the DAL-1 protein suppresses the growth of MCF-7 cells and may do so in part through the induction of apoptosis. In addition, expression of DAL-1 increased attachment of these cells to a variety of extracellular matrices. This is the first evidence that the DAL-1 protein functions at the interface between cell adhesion and apoptosis in controlling cell growth.

Peripheral lymph node stromal cells can promote growth and tumorigenicity of breast carcinoma cells through the release of IGF-I and EGF

The regional lymph nodes draining primary breast carcinomas are generally the first site to be invaded by disseminating tumor cells. The extent of lymph node involvement remains the most reliable indicator for staging and prognosis of breast cancer. We have investigated host-tumor interactions between breast carcinoma cells and the lymph node stroma, which may control the outcome of lymph node infiltration. In a previous study, we identified integrin-mediated cell adhesion as a correlate of the metastatic potential of human and rat carcinoma cells. Our present objective was to determine whether lymphatic stromal cells can affect cancer cell growth through the elaboration of growth-modulating factors. Two lymphatic stromal cell lines, ST-A4 and ST-B12, were established from normal rat lymph node stromal cell cultures. SFM conditioned by these cells increased the proliferation of human (Hs578T and MCF-7) and rat (TMT-081) breast carcinoma cells by up to 7-fold and augmented their ability to form colonies in semisolid agar by up to 41-fold. This effect was specific as normal, diploid human breast epithelial cells (Hs578Bst), a nontumorigenic, immortalized human breast epithelial cell line (MCF-10A) and a nonmetastatic rat mammary carcinoma cell line (MT-W9B) had either no or reduced responses. RT-PCR analysis revealed that both lymph node stromal cell lines expressed mRNA transcripts for multiple growth factors, including IGF-I, EGF, HGF and PDGF-alpha, and produced detectable levels of IGF-I, EGF and PDGF-alpha, as assessed by Western blotting. Antibody-mediated depletion assays identified IGF-I and EGF as the major mitogenic factors in the CM. The identification of these cells raises the possibility that the lymph node microenvironment may contribute actively to the process of cancer cell dissemination.

Isolation, immortalization, and characterization of a human breast epithelial cell line with stem cell properties

The epithelial compartment of the human breast comprises two distinct lineages: the luminal epithelial and the myoepithelial lineage. We have shown previously that a subset of the luminal epithelial cells could convert to myoepithelial cells in culture signifying the possible existence of a progenitor cell. We therefore set out to identify and isolate the putative precursor in the luminal epithelial compartment. Using cell surface markers and immunomagnetic sorting, we isolated two luminal epithelial cell populations from primary cultures of reduction mammoplasties. The major population coexpresses sialomucin (MUC(+)) and epithelial-specific antigen (ESA(+)) whereas the minor population has a suprabasal position and expresses epithelial specific antigen but no sialomucin (MUC(-)/ESA(+)). Two cell lines were further established by transduction of the E6/E7 genes from human papilloma virus type 16. Both cell lines maintained a luminal epithelial phenotype as evidenced by expression of the tight junction proteins, claudin-1 and occludin, and by generation of a high transepithelial electrical resistance on semipermeable filters. Whereas in clonal cultures, the MUC(+)/ESA(+) epithelial cell line was luminal epithelial restricted in its differentiation repertoire, the suprabasal-derived MUC(-)/ESA(+) epithelial cell line was able to generate itself as well as MUC(+)/ESA(+) epithelial cells and Thy-1(+)/alpha-smooth muscle actin(+) (ASMA(+)) myoepithelial cells. The MUC(-)/ESA(+) epithelial cell line further differed from the MUC(+)/ESA(+) epithelial cell line by the expression of keratin K19, a feature of a subpopulation of epithelial cells in terminal duct lobular units in vivo. Within a reconstituted basement membrane, the MUC(+)/ESA(+) epithelial cell line formed acinus-like spheres. In contrast, the MUC(-)/ESA(+) epithelial cell line formed elaborate branching structures resembling uncultured terminal duct lobular units both by morphology and marker expression. Similar structures were obtained by inoculating the extracellular matrix-embedded cells subcutaneously in nude mice. Thus, MUC(-)/ESA(+) epithelial cells within the luminal epithelial lineage may function as precursor cells of terminal duct lobular units in the human breast.

Jolkinolide B induces neuroendocrine differentiation of human prostate LNCaP cancer cell line

Euphorbia fischeriana is a Chinese herbal medicine which has been reported to possess chemotherapeutic effects, yet the underlying mechanism is unclear. In order to understand its possible anti-tumor property, we have isolated a number of chemical compounds from the roots of this plant [Phytochemistry 52 (1999) 117] and studied their in vitro effects by using human prostate LNCaP cancer cell line. Among the six compounds tested, jolkinolide B exhibited the most potent anti-proliferative activity (IC(50)=12.5 microg/mL=40 microM) and it inhibited DNA synthesis by down-regulating bromodeoxyuridine (BrdU) incorporation in LNCaP cells in a dose-dependent manner. Jolkinolide B, at concentrations up to 25 microg/mL, induced G1 arrest and neuroendocrine differentiation of LNCaP cells. Immunoblotting analysis confirmed the increased expression of neuroendocrine markers, keratin 8/18 (K8/18) and neuron specific enolase (NSE), in these cells. Apoptotic bodies and DNA fragmentation were observed by fluorescence microscopy and flow cytometry when the cells were exposed to a concentration higher than 25 microg/mL jolkinolide B. Taken all data together, jolkinolide B seems to play a role in the regulation of proliferation, differentiation, and apoptosis of LNCaP cells.

Dissection of HEF1-dependent functions in motility and transcriptional regulation

Cas-family proteins have been implicated as signaling intermediaries in diverse processes including cellular attachment, motility, growth factor response, apoptosis and oncogenic transformation. The three defined Cas-family members (p130Cas, HEF1/Cas-L and Efs/Sin) are subject to multiple forms of regulation (including cell-cycle- and cell-attachment-mediated post-translational modification and cleavage) that complicate elucidation of the function of specific Cas proteins in defined biological processes. To explore the biological role of HEF1 further, we have developed a series of cell lines in which HEF1 production is regulated by an inducible promoter. In this system, HEF1 production rapidly induces changes in cellular morphology and motility, enhancing cell speed and haptotaxis towards fibronectin in a process partially dependent on intact ERK and p38 MAPK signaling pathways. Finally, cDNA expression array analysis and subsequent studies indicate that HEF1 production increases levels of mRNA transcripts encoding proteins that are associated with motility, cell transformation and invasiveness, including several metalloproteinases, MLCK, p160ROCK and ErbB2. Upregulation of such proteins suggests mechanisms through which misregulation of HEF1 may be involved in cancer progression.

Integrin-mediated differentiation of a pancreatic carcinoma cell line is independent of FAK or MAPK activation levels

INTRODUCTION

The extracellular matrix (ECM) plays a salient role for proliferation and differentiation of epithelial cells. It was demonstrated that cell-ECM interactions mediated through integrins control gene expression and the tissue phenotype even in malignant tumors. Alterations of the ECM are a key feature of ductal adenocarcinoma of the pancreas.

AIMS

To examine the role of integrins and related signaling events for differentiation.

METHODOLOGY AND RESULTS

We established an in vitro model for ECM-induced differentiation of poorly differentiated pancreatic carcinoma cells and found that a specific pattern of ECM proteins resembling basal laminas (matrigel) induces differentiation of the PaTu-II pancreatic carcinoma cell line to a ductal phenotype. Both beta1- and beta4-integrins are required for cellular differentiation. Integrin-associated signaling events include activation of pp125 focal adhesion kinase (FAK) and mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinases (ERKs) and c-Jun NH2-terminal kinases (JNKs). However, beta1- and beta4-integrin-mediated differentiation of PaTu-II cells was independent from FAK, ERK, and JNK activation levels. Inhibition of MAPK kinases by PD98059 led to a reduction of proliferation but did not interfere with cellular differentiation of PaTu-II cells on matrigel.

CONCLUSION

The integrin-mediated differentiation of PaTu-II cells is regulated and maintained through FAK- and MAPK-independent signal transduction pathways.

Mammary gland architecture as a determining factor in the susceptibility of the human breast to cancer

The developmental pattern of the breast can be assessed by determining the composition of the breast in specific lobular structures, which are designated as lobules type 1 (Lob 1), lobules type 2 (Lob 2), and lobules type 3 (Lob 3), with Lob 1 being the less developed and Lob 3 being the most differentiated or with the highest number of ductules per lobular unit. In the present work, the patient population consisted of three groups of women who underwent surgical procedures: The first group included women who underwent reduction mammoplasty (RM) for cosmetic reasons. The second group included women who underwent prophylactic subcutaneous mastectomy after genetic counseling for either carrying the BRCA-1 gene or belonging to a pedigree with familial breast cancer (FAM), and the third group included women who underwent modified radical mastectomy (MRM) for the diagnosis of invasive carcinoma. The RM group consisted of 33 women, of whom 9 were nulliparous and 24 were parous. The FAM group consisted of 17 women, of whom 8 were nulliparous and 9 were parous. The MRM group consisted of 43 women, of whom 7 were nulliparous and 36 were parous. The analysis of the lobular composition of all of the samples from the RM group, which is considered the control group, revealed that Lob 1 represented 22%, Lob 2 represented 37%, and Lob 3 represented 38%, whereas the tissue examined from the FAM and MRM groups contained a preponderance of Lob 1 at 48% and 74%, respectively, over Lob 3, which was 10% and 3%, respectively. When the results of the analysis of breast tissue were separated according to the pregnancy history of the donor, it was found that in the control group or RM, there was a significant difference in lobular composition. Nulliparous women of the RM group showed a preponderance of Lob 1 (46%) over parous women, which contained only 17%, whereas the percentage of Lob 3 in the nulliparous group was significantly lower (7%) than the parous group (48%). In the breast tissues obtained from FAM and MRM, no significant differences in lobular composition were observed, as all of the samples contained a higher concentration of Lob 1, independent of the pregnancy history. The breast tissue of FAM and MRM of parous women had a developmental pattern that was similar to that of nulliparous women of the same group and that was less developed than the breast of parous women of the control group. An important difference between the Lob 1 of the FAM group versus the control (RM) and the MRM group was that most of these lobules had thin ductules with an increase in hyalinization of the intralobular stroma manifested in the whole-mount preparation as an alteration in the branching pattern. The data suggest that the breast tissue of women with invasive cancer, as well as those from a background of familial breast cancer, have an architectural pattern different from the control or normal tissues and that the BRCA-1 or related genes may have a functional role in the branching pattern of the breast during lobular development, mainly in the epithelial stroma interaction.

Oncogenic Ras blocks anoikis by activation of a novel effector pathway independent of phosphatidylinositol 3-kinase

Activated Ras, but not Raf, causes transformation of RIE-1 rat intestinal epithelial cells, demonstrating the importance of Raf-independent effector signaling in mediating Ras transformation. To further assess the contribution of Raf-dependent and Raf-independent function in oncogenic Ras transformation, we evaluated the mechanism by which oncogenic Ras blocks suspension-induced apoptosis, or anoikis, of RIE-1 cells. We determined that oncogenic versions of H-, K-, and N-Ras, as well as the Ras-related proteins TC21 and R-Ras, protected RIE-1 cells from anoikis. Surprisingly, our analyses of Ras effector domain mutants or constitutively activated effectors indicated that activation of Raf-1, phosphatidylinositol 3-kinase (PI3K), or RalGDS alone is not sufficient to promote Ras inhibition of anoikis. Treatment of Ras-transformed cells with the U0126 MEK inhibitor caused partial reversion to an anoikis-sensitive state, indicating that extracellular signal-regulated kinase activation contributes to inhibition of anoikis. Unexpectedly, oncogenic Ras failed to activate Akt, and treatment of Ras-transformed RIE-1 cells with the LY294002 PI3K inhibitor did not affect anoikis resistance or growth in soft agar. Thus, while important for Ras transformation of fibroblasts, PI3K may not be involved in Ras transformation of RIE-1 cells. Finally, inhibition of epidermal growth factor receptor kinase activity did not overcome Ras inhibition of anoikis, indicating that this autocrine loop essential for transformation is not involved in anoikis protection. We conclude that a PI3K- and RalGEF-independent Ras effector(s) likely cooperates with Raf to confer anoikis resistance upon RIE-1 cells, thus underscoring the complex nature by which Ras transforms cells.

A growth-constrained environment drives tumor progression invivo

We recently have shown that selective growth of transplanted normal hepatocytes can be achieved in a setting of cell cycle block of endogenous parenchymal cells. Thus, massive proliferation of donor-derived normal hepatocytes was observed in the liver of rats previously given retrorsine (RS), a naturally occurring alkaloid that blocks proliferation of resident liver cells. In the present study, the fate of nodular hepatocytes transplanted into RS-treated or normal syngeneic recipients was followed. The dipeptidyl peptidase type IV-deficient (DPPIV(-)) rat model for hepatocyte transplantation was used to distinguish donor-derived cells from recipient cells. Hepatocyte nodules were chemically induced in Fischer 344, DPPIV(+) rats; livers were then perfused and larger (>5 mm) nodules were separated from surrounding tissue. Cells isolated from either tissue were then injected into normal or RS-treated DPPIV(-) recipients. One month after transplantation, grossly visible nodules (2--3 mm) were seen in RS-treated recipients transplanted with nodular cells. They grew rapidly, occupying 80--90% of the host liver at 2 months, and progressed to hepatocellular carcinoma within 4 months. By contrast, no liver nodules developed within 6 months when nodular hepatocytes were injected into the liver of recipients not exposed to RS, although small clusters of donor-derived cells were present in these animals. Taken together, these results directly point to a fundamental role played by the host environment in modulating the growth and the progression rate of altered cells during carcinogenesis. In particular, they indicate that conditions associated with growth constraint of the host tissue can drive tumor progression in vivo.

The role of nitric oxide in the biological activity of prolactin in the mouse mammary gland

In mouse mammary epithelial cells, prolactin transiently elevates nitric oxide (NO) to a maximum of 6 nmol/mg protein at 15 min, after which levels fall rapidly. This stimulation can be achieved by as little as 100 ng prolactin/ml and can be mimicked by 100 microg sodium nitroprusside/ml. NO is both necessary and sufficient to mediate the prolactin-induced redistribution of its receptor from internal pools to the cell surface. NO can also enhance DNA synthesis stimulated by submaximal prolactin concentrations (50 ng/ml), but it is not necessary at pharmacological prolactin concentrations (1 microg/ml). In contrast, NO completely inhibits alpha-lactalbumin production. In summary, prolactin transiently elevates NO to enhance DNA synthesis and suppress premature differentiation; thereafter, NO declines, DNA synthesis ceases and differentiation proceeds. This data suggest that NO may mediate some of the effects of prolactin on growth in the mammary gland.

The mammary myoepithelial cell--Cinderella or ugly sister?

The breast myoepithelial cell is the Cinderella of mammary biology. Although its contribution to benign and some malignant pathologies is recognised, it has been largely neglected in molecular and biological studies. The reason for this has been the perception that its role in normal physiology is confined to lactation and the belief that most breast cancers arise from luminal epithelial cells. This review presents our perspective on its broader biological significance and its potential use as a model system for understanding breast carcinogenesis.

The plasticity of human breast carcinoma cells is more than epithelial to mesenchymal conversion

The human breast comprises three lineages: the luminal epithelial lineage, the myoepithelial lineage, and the mesenchymal lineage. It has been widely accepted that human breast neoplasia pertains only to the luminal epithelial lineage. In recent years, however, evidence has accumulated that neoplastic breast epithelial cells may be substantially more plastic in their differentiation repertoire than previously anticipated. Thus, along with an increasing availability of markers for the myoepithelial lineage, at least a partial differentiation towards this lineage is being revealed frequently. It has also become clear that conversions towards the mesenchymal lineage actually occur, referred to as epithelial to mesenchymal transitions. Indeed, some of the so-called myofibroblasts surrounding the tumor may have an epithelial origin rather than a mesenchymal origin. Because myoepithelial cells, epithelial to mesenchymal transition-derived cells, genuine stromal cells and myofibroblasts share common markers, we now need to define a more ambitious set of markers to distinguish these cell types in the microenvironment of the tumors. This is necessary because the different microenvironments may confer different clinical outcomes. The aim of this commentary is to describe some of the inherent complexities in defining cellular phenotypes in the microenvironment of breast cancer and to expand wherever possible on the implications for tumor suppression and progression.

Hedgehog signaling in mouse mammary gland development and neoplasia

Genetic analyses of two hedgehog signal transduction network genes, Patched-1 and Gli2, has demonstrated a critical role for hedgehog signaling in mediating epithelial-stromal tissue interactions during ductal development. Disruption of either gene leads to similar, yet distinct, defects in ductal morphogenesis. Defects are mainly ductal dysplasias that closely resemble some hyperplasias of the human breast. Phenotypic analyses have been coupled with in situ hybridization, transplantation and tissue recombination analyses to formulate a model for tissue compartment-specific control of mouse mammary gland development by hedgehog signaling. In addition, the similarities among hedgehog mutation-induced ductal dysplasias and human breast pathologies suggest a role for altered hedgehog signaling in the development of mammary cancer.

Intracellular FGF-2 promotes differentiation in T-47D breast cancer cells

To test the implicated role of basic fibroblast growth factor (bFGF; FGF-2) in promoting differentiation in breast cancer, we enforced the expression of FGF-2 in T-47D breast cancer cells. Expression of FGF-2 conferred an overall less malignant phenotype to T-47D cells as revealed by their reduced proliferative response, impaired capacity for anchorage-independent growth, and invasion through Matrigel. To understand one candidate mechanism for the intracellular FGF-2-mediated anti-invasive effect, we examined the effect of FGF-2 on T-47D cell motility. Addition of recombinant FGF-2 to the growth medium markedly enhanced cell motility while constitutive expression of intracellular FGF-2 significantly inhibited the migratory potential of T-47D cells in a dominant manner. FGF-2-expressing T-47D cells also formed relatively defined branching structures in Matrigel matrices, a characteristic phenotype of differentiation in breast cancer cells. These data suggest a potential role for FGF-2 in promoting functional differentiation of breast epithelial cells.

Proliferation and differentiation in the human breast during pregnancy

Using multiple immunofluorescence labelling on human breast tissues obtained and freshly frozen at the 12th, 15th, and 18th weeks of pregnancy, we have shown that markers of mammary functional differentiation, milk proteins (beta-casein and kappa-casein), are synthesised by actively cycling (Ki67 positive) as well as non-cycling (Ki67 negative) cells. These results demonstrate that functional differentiation/maturation does not coincide with loss of proliferative potential in human mammary luminal epithelial cells. In addition, we have examined expression patterns of integrin subunits (alpha1, alpha2, alpha3, alpha6, beta1, and beta4) and extracellular matrix components (laminin, fibronectin, collagen I, and collagen IV), since they have been shown to exert influences on mammary differentiation and morphogenesis in vitro. Compared to human breast tissues obtained from non-pregnant women, a decrease in alpha2 labelling on luminal epithelial cells was observed, particularly in expanding acini that showed abundant Ki67 positivity. The expression patterns of other integrin subunits, however, did not change, indicating that the expression patterns of most integrins existing prior to pregnancy are sufficient to support the morphological and functional development associated with milk protein synthesis.

Comparative genomic hybridization analysis of myoepithelial carcinoma of the breast

Although there seems to be a common stem cell for the two epithelial cell types in the breast, the vast majority of breast cancers exhibit a luminal phenotype. Pure myoepithelial carcinomas are rare. We report our findings of genetic alterations in these tumors. We have analyzed 10 cases of pure myoepithelial cell carcinomas using laser capture microdissection and comparative genomic hybridization. The mean number of changes was 2.1 (range 0-4), compared with a mean of 8.6 (range 3.6-13.8) in unselected ductal carcinomas. Common alterations included loss at 16q (3/10 cases), 17p (3/10), 11q (2/10), and 16p (2/10), regions also commonly deleted in ductal carcinomas. The single case in which both pure myoepithelial carcinoma and invasive ductal carcinoma was present showed 2 alterations in the myoepithelial tumor (losses at 17p and 17q), whereas the invasive ductal component showed 15 alterations (5 gains and 9 losses), including loss at 17p. The sharing of 17p loss in myoepithelial and ductal carcinoma is consistent with a common stem cell model in the breast. The relatively few genetic alterations in otherwise aggressive neoplasms suggests that myoepithelial tumors may be a good model for the delineation of genes important in breast tumorigenesis.

Functional culture models to study mechanisms governing apoptosis in normal and malignant mammary epithelial cells

Mammary tissue homeostasis depends upon dynamic interactions between the epithelial cells, their microenvironment (including the basement membrane and the stroma), and the tissue architecture, which influence each other reciprocally to regulate growth, death and differentiation in the gland. To study how apoptosis is regulated in normal mammary cells, and to understand its role in breast tumor pathogenesis, we need model systems that recapitulate breast tissue architecture and microenvironment in culture. We have established culture models of primary and established nonmalignant mammary cell lines from both rodent and human, and defined procedures to study how cell and tissue architecture affect signaling by the basement membrane. We show that both a basement membrane and an organized tissue structure are required to achieve sustained mammary cell survival. These models could now be used to investigate how the basement membrane represses apoptosis in normal cells, and how breast cancers become death-resistant.

Human mammary luminal epithelial cells contain progenitors to myoepithelial cells

The origin of the epithelial and myoepithelial cells in the human breast has not been delineated. In this study we have addressed whether luminal epithelial cells and myoepithelial cells are vertically connected, i.e., whether one is the precursor for the other. We used a primary culture assay allowing preservation of basic phenotypic traits of luminal epithelial and myoepithelial cells in culture. The two cell types were then separated immunomagnetically using antibodies directed against lineage-specific cell surface antigens into at best 100% purity. The cellular identity was ascertained by cytochemistry, immunoblotting, and 2-D gel electrophoresis. Luminal epithelial cells were identified by strong expression of cytokeratins 18 and 19 while myoepithelial cells were recognized by expression of vimentin and alpha-smooth muscle actin. We used a previously devised culture medium (CDM4) that allows vigorous expansion of proliferative myoepithelial cells and also devised a medium (CDM6) that allowed sufficient expansion of differentiated luminal epithelial cells based on addition of hepatocyte growth factor/scatter factor. The two different culture media supported each lineage for at least five passages without signs of interconversion. We used parallel cultures where we switched culture media, thus testing the ability of each lineage to convert to the other. Whereas the myoepithelial lineage showed no signs of interconversion, a subset of luminal epithelial cells, gradually, but distinctly, converted to myoepithelial cells. We propose that in the mature human breast, it is the luminal epithelial cell compartment that gives rise to myoepithelial cells rather than the other way around.

Cancer invasion and tissue remodeling--cooperation of protease systems and cell types

Proteolytic degradation of the extracellular matrix plays a crucial role in both cancer invasion and non-neoplastic tissue remodeling processes. In human cancers the components of matrix degrading protease systems (uPA, uPAR, PAI-1 and MMPs) can be expressed by either the non-neoplastic stromal cells, the cancer cells or both. Studies of the prognostic impact of these components in human cancer and the effect of targeted gene inactivation on cancer metastasis in mice support the assumption that proteases promote cancer progression, independent of whether they are expressed by cancer cells or stromal cells. The pattern of expression of components of protease systems is usually very similar in different cases of the same type of cancer, while it varies between different types of cancer. There are intriguing similarities between the cellular expression pattern of components of protease systems seen in cancer invasion and in certain types of non-neoplastic tissue remodeling. We propose that cancer invasion can be viewed as tissue remodeling gone out of control. The stromal cell involvement in cancer invasion represents a new paradigm with important implications for cancer pathophysiology and cancer therapy.