Stromal effects on mammary gland development and breast cancer

From signatures to models: understanding cancer using microarrays

Genomics has the potential to revolutionize the diagnosis and management of cancer by offering an unprecedented comprehensive view of the molecular underpinnings of pathology. Computational analysis is essential to transform the masses of generated data into a mechanistic understanding of disease. Here we review current research aimed at uncovering the modular organization and function of transcriptional networks and responses in cancer. We first describe how methods that analyze biological processes in terms of higher-level modules can identify robust signatures of disease mechanisms. We then discuss methods that aim to identify the regulatory mechanisms underlying these modules and processes. Finally, we show how comparative analysis, combining human data with model organisms, can lead to more robust findings. We conclude by discussing the challenges of generalizing these methods from cells to tissues and the opportunities they offer to improve cancer diagnosis and management.

Mutation of Smooth Muscle Myosin Causes Epithelial Invasion and Cystic Expansion of the Zebrafish Intestine

Zebrafish meltdown (mlt) mutants develop cystic expansion of the posterior intestine as a result of stromal invasion of nontransformed epithelial cells. Positional cloning identified zebrafish smooth muscle myosin heavy chain (myh11) as the responsible gene. The mlt mutation constitutively activates the Myh11 ATPase, which disrupts smooth muscle cells surrounding the posterior intestine. Adjacent epithelial cells ectopically express metalloproteinases, integrins, and other genes implicated in human cancer cell invasion. Knockdown and pharmacological inhibition of these genes restores intestinal structure in mlt mutants despite persistent smooth muscle defects. These data identify an essential role for smooth muscle signaling in the maintenance of epithelial architecture and support gene expression analyses and other studies that identify a role for stromal genes in cancer cell invasion. Furthermore, they suggest that high-throughput screens to identify regulators of cancer cell invasion may be feasible in zebrafish.

Adipocyte-derived collagen VI affects early mammary tumor progression in vivo, demonstrating a critical interaction in the tumor/stroma microenvironment

The interactions of transformed cells with the surrounding stromal cells are of importance for tumor progression and metastasis. The relevance of adipocyte-derived factors to breast cancer cell survival and growth is well established. However, it remains unknown which specific adipocyte-derived factors are most critical in this process. Collagen VI is abundantly expressed in adipocytes. Collagen(-/-) mice in the background of the mouse mammary tumor virus/polyoma virus middle T oncogene (MMTV-PyMT) mammary cancer model demonstrate dramatically reduced rates of early hyperplasia and primary tumor growth. Collagen VI promotes its growth-stimulatory and pro-survival effects in part by signaling through the NG2/chondroitin sulfate proteoglycan receptor expressed on the surface of malignant ductal epithelial cells to sequentially activate Akt and beta-catenin and stabilize cyclin D1. Levels of the carboxyterminal domain of collagen VIalpha3, a proteolytic product of the full-length molecule, are dramatically upregulated in murine and human breast cancer lesions. The same fragment exerts potent growth-stimulatory effects on MCF-7 cells in vitro. Therefore, adipocytes play a vital role in defining the ECM environment for normal and tumor-derived ductal epithelial cells and contribute significantly to tumor growth at early stages through secretion and processing of collagen VI.

Adipocyte-derived collagen VI affects early mammary tumor progression in vivo, demonstrating a critical interaction in the tumor/stroma microenvironment

The interactions of transformed cells with the surrounding stromal cells are of importance for tumor progression and metastasis. The relevance of adipocyte-derived factors to breast cancer cell survival and growth is well established. However, it remains unknown which specific adipocyte-derived factors are most critical in this process. Collagen VI is abundantly expressed in adipocytes. Collagen(-/-) mice in the background of the mouse mammary tumor virus/polyoma virus middle T oncogene (MMTV-PyMT) mammary cancer model demonstrate dramatically reduced rates of early hyperplasia and primary tumor growth. Collagen VI promotes its growth-stimulatory and pro-survival effects in part by signaling through the NG2/chondroitin sulfate proteoglycan receptor expressed on the surface of malignant ductal epithelial cells to sequentially activate Akt and beta-catenin and stabilize cyclin D1. Levels of the carboxyterminal domain of collagen VIalpha3, a proteolytic product of the full-length molecule, are dramatically upregulated in murine and human breast cancer lesions. The same fragment exerts potent growth-stimulatory effects on MCF-7 cells in vitro. Therefore, adipocytes play a vital role in defining the ECM environment for normal and tumor-derived ductal epithelial cells and contribute significantly to tumor growth at early stages through secretion and processing of collagen VI.

Method for the generation and cultivation of functional three-dimensional mammary constructs without exogenous extracellular matrix

During puberty, pregnancy, lactation and post-lactation, breast tissue undergoes extensive remodelling and the disruption of these events can lead to cancer. In vitro studies of mammary tissue and its malignant transformation regularly employ mammary epithelial cells cultivated on matrigel or floating collagen rafts. In these cultures, mammary epithelial cells assemble into three-dimensional structures resembling in vivo acini. We present a novel technique for generating functional mammary constructs without the use of matrix substitutes.

Identification of extracellular and intracellular signaling components of the mammary adipose tissue and its interstitial fluid in high risk breast cancer patients: toward dissecting the molecular circuitry of epithelial-adipocyte stromal cell interactions

It has become clear that growth and progression of breast tumor cells not only depend on their malignant potential but also on factors present in the tumor microenvironment. Of the cell types that constitute the mammary stroma, the adipocytes are perhaps the least well studied despite the fact that they represent one of the most prominent cell types surrounding the breast tumor cells. There is compelling evidence demonstrating a role for the mammary fat pad in mammary gland development, and some studies have revealed the ability of fat tissue to augment the growth and ability to metastasize of mammary carcinoma cells. Very little is known, however, about which factors adipocytes produce that may orchestrate these actions and how this may come about. In an effort to shed some light on these questions, we present here a detailed proteomic analysis, using two-dimensional gel-based technology, mass spectrometry, immunoblotting, and antibody arrays, of adipose cells and interstitial fluid of fresh fat tissue samples collected from sites topologically distant from the tumors of high risk breast cancer patients that underwent mastectomy and that were not treated prior to surgery. A total of 359 unique proteins were identified, including numerous signaling molecules, hormones, cytokines, and growth factors, involved in a variety of biological processes such as signal transduction and cell communication; energy metabolism; protein metabolism; cell growth and/or maintenance; immune response; transport; regulation of nucleobase, nucleoside, and nucleic acid metabolism; and apoptosis. Apart from providing a comprehensive overview of the mammary fat proteome and its interstitial fluid, the results offer some insight as to the role of adipocytes in the breast tumor microenvironment and provide a first glance of their molecular cellular circuitry. In addition, the results open new possibilities to the study of obesity, which has a strong association with type 2 diabetes, hypertension, and coronary heart disease.

Potential oncogenic action of tenascin-C in tumorigenesis

The prominent expression of tenascin-C in the stroma of most solid tumors, first observed in the mid 1980s, implicates tenascin-C in tumorigenesis. This is also supported by in vitro experiments that demonstrate the capacity of tenascin-C to stimulate tumor growth by various mechanisms including promotion of proliferation, escaping immuno-surveillance and positively influencing angiogenesis. However, tumorigenesis in tenascin-C knock-out mice is not significantly different from that observed in control animals. Perhaps this is not unexpected if one considers that tenascin-C may act as an oncogene. The potential role of tenascin-C in tumorigenesis through its oncogenic action on cellular signaling will be discussed in this review, including how tenascin-C mediated tumor cell detachment might affect genome stability.

Mutations in Apc and p53 Synergize to Promote Mammary Neoplasia

Mutations of Apc and p53 have both been implicated in human and murine mammary neoplasia. To investigate potential interactions between Apc and p53, we conditionally inactivated Apc in both the presence and the absence of functional p53. Apc deficiency on its own leads to the development of metaplasia but not neoplasia. We show here that these areas of metaplasia are characterized by elevated levels of both p53 and p21. In the additional absence of p53,there is rapid progression to neoplasia, with 44.4% of lymphoma-free mice developing a mammary tumor with earliest observed onset at pregnancy. To investigate the mechanism by which p53 deficiency accelerates neoplasia, we used the Rosa26R reporter strain as a marker of Cre-mediated recombination and show a role for p53 in the loss of Apc-deficient cells. This role seems limited to pregnancy and subsequent time points. We therefore show clear synergy between these two mutations in mammary gland neoplasia and present data to suggest that at least one mechanism for this acceleration is the p53-dependent loss of Apc-deficient cells.

Cell and tissue responses to genotoxic stress

Cancers arise as a consequence of the accumulation of multiple genetic mutations in a susceptible cell, resulting in perturbation of regulatory networks that control proliferation, survival, and cellular function. Here, the sources of cellular stress that can cause oncogenic mutations and the responses of cells to DNA damage are reviewed. The role of different repair pathways and the potential for cell- and tissue-specific reliance on individual repair mechanisms are discussed. Evidence for cell- and tissue-specific activation of p53-mediated growth arrest and apoptosis after exposure to an individual genotoxin is assessed and some of the potential mediators of these different responses are provided. These cell- and tissue-specific responses to particular forms of DNA damage are likely to be key determinants of tissue-specific tumour susceptibility, and there is good evidence for genetic variations in these responses. The role that genotoxic agents play in altering the microenvironment to produce indirect effects on tumourigenesis through altered production of free radicals and cytokines that are characteristic of inflammatory-type processes is also evaluated. Changes to the microenvironment as direct or indirect effects of genotoxic stress can be involved in both tumour initiation and progression and may even be a prerequisite for tumourigenesis. Therefore, tumour susceptibility after endogenous or exogenous genotoxic stress represents a balance between cell-intrinsic responses of target cells and changes to the microenvironment. A fuller understanding of cell- and tissue-specific responses, alterations to the microenvironment, and genetic modifiers of these responses could lead to novel prevention and therapeutic strategies for common forms of human malignancy.

Maintenance of cell type diversification in the human breast

Recent genome-wide expression analysis of breast cancer has brought new life to the classical idea of tumors as caricatures of the process of tissue renewal as envisioned by Pierce and Speers (Cancer Res 1988;48:1996-2004) more than a decade ago. The search for a cancer founder cell or different cancer founder cells is only possible if a hierarchy of differentiation has been established for the particular tissue in question. In the human breast, the luminal epithelial and myoepithelial lineages have been characterized extensively in situ by increasingly elaborate panel of markers, and methods to isolate, culture, and clone different subpopulations have improved dramatically. Comparisons have been made with the mouse mammary gland in physiological three-dimensional culture assays of morphogenesis, and the plasticity of breast epithelial cells has been challenged by immortalization and transformation. As a result of these efforts, several candidate progenitor cells have been proposed independently of each other, and some of their features have been compared. This research has all been done to better understand breast tissue homeostasis, cell-type diversification in general and breast cancer evolution in particular. The present review discusses the current approaches to address these issues and the measures taken to unravel and maintain cell type diversification for further investigation.

Targeted activation of beta-catenin signaling in basal mammary epithelial cells affects mammary development and leads to hyperplasia

Wnt/beta-catenin signaling pathway is involved in the maintenance of the progenitor cell population in the skin, intestine and other tissues, and its aberrant activation caused by stabilization of beta-catenin contributes to tumorigenesis. In the mammary gland, constitutive activation of Wnt/beta-catenin signaling in luminal secretory cells results in precocious lobuloalveolar differentiation and induces adenocarcinomas, whereas the impact of this signaling pathway on the function of the second major mammary epithelial cell lineage, the basal myoepithelial cells, has not been analyzed. We have used the keratin (K) 5 promoter to target the expression of stabilized N-terminally truncated beta-catenin to the basal cell layer of mouse mammary epithelium. The transgenic mice presented an abnormal mammary phenotype: precocious lateral bud formation, increased proliferation and premature differentiation of luminal epithelium in pregnancy, persistent proliferation in lactation and accelerated involution. Precocious development in pregnancy was accompanied by increased Myc and cyclin D1 transcript levels, and a shift in p63 variant expression towards the DeltaNp63 form. The expression of ECM-degrading proteinases and their inhibitors was altered in pregnancy and involution. Nulliparous transgenic females developed mammary hyperplasia that comprised undifferentiated basal (K5/14-positive, K8- and alpha-smooth muscle-actin-negative) cells. Multiparous mice, in addition, developed invasive basal-type carcinomas. Thus, activation of beta-catenin signaling in basal mammary epithelial cells affects the entire process of mammary gland development and induces amplification of basal-type cells that lack lineage markers, presumably, a subpopulation of mammary progenitors able to give rise to tumors.

Alterations in vascular gene expression in invasive breast carcinoma

The molecular signature that defines tumor microvasculature will likely provide clues as to how vascular-dependent tumor proliferation is regulated. Using purified endothelial cells, we generated a database of gene expression changes accompanying vascular proliferation in invasive breast cancer. In contrast to normal mammary vasculature, invasive breast cancer vasculature expresses extracellular matrix and surface proteins characteristic of proliferating and migrating endothelial cells. We define and validate the up-regulated expression of VE-cadherin and osteonectin in breast tumor vasculature. In contrast to other tumor types, invasive breast cancer vasculature induced a high expression level of specific transcription factors, including SNAIL1 and HEYL, that may drive gene expression changes necessary for breast tumor neovascularization. We demonstrate the expression of HEYL in tumor endothelial cells and additionally establish the ability of HEYL to both induce proliferation and attenuate programmed cell death of primary endothelial cells in vitro. We also establish that an additional intracellular protein and previously defined metastasis-associated gene, PRL3, appears to be expressed predominately in the vasculature of invasive breast cancers and is able to enhance the migration of endothelial cells in vitro. Together, our results provide unique insights into vascular regulation in breast tumors and suggest specific roles for genes in driving tumor angiogenesis.

Ethanol-induced in vitro invasion of breast cancer cells: the contribution of MMP-2 by fibroblasts

Ethanol is a tumor promoter and may promote metastasis of breast cancer. However, the underlying cellular/molecular mechanisms remain unknown. Overexpression and high activity of matrix metalloproteinase-2 (MMP-2) are frequently associated with metastatic breast cancers and serve as a prognostic indicator of clinical outcome. MMP-2 is predominantly expressed in stromal fibroblasts and plays a pivotal role in regulating the invasive behavior of breast tumor cells. We hypothesized that ethanol may enhance the invasion of breast tumor cells by modulating the activity of fibroblastic MMP-2. With in vitro models (HS68 and CCD1056SK human fibroblasts), we showed that ethanol at physiologically relevant concentrations (50-200 mg/dl) activated MMP-2; conversely, at a higher concentration (400 mg/dl), it inhibited the MMP-2 activity. Consistently, conditioned medium collected from ethanol (50-200 mg/dl)-exposed fibroblasts markedly enhanced the invasive potential of breast cancer cells and mammary epithelial cells overexpressing ErbB2/HER2 (BT474, SKBR-3 and HB2(ErbB2) cells) but had little effect on cells with low ErbB2 levels (BT20 and HB2 cells). In contrast, conditioned medium obtained from ethanol (400 mg/dl)-treated fibroblasts inhibited cell invasion. Selective inhibitors of MMP-2 (SB-3CT and OA-Hy) eliminated ethanol-stimulated invasion, indicating that the effect of ethanol was mediated by MMP-2. Ethanol activated conventional PKCs and JNKs in fibroblasts; inhibitors of PKC (Go6850 and Go6976) and JNKs (SP600125) significantly inhibited ethanol-mediated MMP-2 activation as well as cell invasion, indicating that PKCs and JNKs play a role in ethanol-induced MMP-2 activation and cell invasion in vitro. Thus, ethanol-promoted breast cancer cell invasion may be mediated by the modulation of fibroblastic MMP-2.

New highlights on stroma-epithelial interactions in breast cancer

Although the stroma in which carcinomas arise has been previously regarded as a bystander to the clonal expansion and acquisition of malignant characteristics of tumor cells, it is now generally acknowledged that stromal changes are required for the establishment of cancer. In the present article, we discuss three recent publications that highlight the complex role the stroma has during the development of cancer and the potential for targeting the stroma by therapeutic approaches.

Serum concentration modifies amplitude and kinetics of voltage-gated Na+ current in the Mat-LyLu cell line of rat prostate cancer

Voltage-gated Na+ channel (VGSC) expression has previously been shown to be upregulated in strongly metastatic prostate cancer cells (rat and human) and its activity shown to potentiate a variety of cellular behaviours integral to the metastatic cascade. However, the mechanism(s) responsible for the Na+ channel upregulation is not known. As a step towards evaluating the role of the extracellular biochemical environment in this regard, we have determined the effects of serum concentration on characteristics of Na+ channel expressed in the strongly metastatic Mat-LyLu rat prostate cancer cell line. Whole-cell patch-clamp recording techniques were used to study the effects of serum concentrations, above and below the normal 1%. Both the amplitude and the kinetics of the currents were analysed. The following results were obtained: (1) Adding 1% foetal calf serum to cells starved of serum for 24h increased Na+ current density; however, increasing serum concentration further (to 5%) caused a reduction. (2) Serum-free medium produced Na+ currents with slower kinetics of activation (time to peak) and inactivation (exponential decay). (3) Increased serum concentration (a) shifted steady-state inactivation to more positive potentials without affecting conductance and (b) increased tetrodotoxin sensitivity. It is concluded that serum concentration is an important determinant of the Na+ channel characteristics leading to possible transcriptional and post-translational modifications of channel expression and/or activity. Experiments are now needed to determine which constituents (protein hormones, growth factors, etc.) are responsible for these effects.

Integrin signalling during tumour progression

During progression from tumour growth to metastasis, specific integrin signals enable cancer cells to detach from neighbouring cells, re-orientate their polarity during migration, and survive and proliferate in foreign microenvironments. There is increasing evidence that certain integrins associate with receptor tyrosine kinases (RTKs) to activate signalling pathways that are necessary for tumour invasion and metastasis. The effect of these integrins might be especially important in cancer cells that have activating mutations, or amplifications, of the genes that encode these RTKs.

The molecular basis of pancreatic fibrosis: common stromal gene expression in chronic pancreatitis and pancreatic adenocarcinoma

OBJECTIVES

Tissue desmoplasia occurs in a number of disease states, but its molecular basis is poorly understood. To determine which genes are overexpressed in cells contained within the desmoplastic stroma of pancreatic adenocarcinoma and chronic pancreatitis, we undertook genetic profiling of microdissected tissue samples of pancreatic adenocarcinoma, chronic pancreatitis, normal pancreas, and pancreatic cancer cell lines. We observed that samples of both pancreatic adenocarcinoma and chronic pancreatitis showed elevated expression of many shared genes compared with the normal pancreas. We hypothesized that these common genes likely important in stromal production and/or function could be identified using a strategy that involved comparisons between pancreatic adenocarcinoma, chronic pancreatitis, normal pancreas, and pancreatic cancer cell lines.

METHODS

We performed oligonucleotide microarray analysis of 6800 different genes expressed in 10 samples of pancreatic adenocarcinoma, 5 samples of normal pancreas, 5 samples of chronic pancreatitis, and 7 pancreatic cancer cell lines. Microarray findings were validated with RT-PCR, and immunohistochemistry was used to verify protein localization to the stromal compartment of both pancreatic cancer and chronic pancreatitis.

RESULTS

We employed a deductive comparison whereby genes expressed in the normal pancreas and pancreatic cancer cell lines were selectively eliminated from those expressed in common by pancreatic adenocarcinoma and chronic pancreatitis. This strategy identified 107 genes predicted to be expressed within cells of the stromal compartment of both pancreatic adenocarcinoma and chronic pancreatitis.

CONCLUSIONS

These genes are likely important factors in epithelial-stromal signaling in pancreatic desmoplasia and may serve as diagnostic or therapeutic targets.

Cellular localization and changes in expression of prolactin receptor isoforms in sheep ovary throughout the estrous cycle

The actions of prolactin (PRL) on target cells depend on the type of prolactin receptor (PRLr) predominantly expressed, particularly whether the long PRLr isoform is expressed. The aims of this study were to determine the cellular localization and the changes in expression of long and short PRLr isoforms in sheep ovary throughout the estrous cycle. Long and short PRLrs were localized mostly in the same ovarian cells. Maximum signal intensity, particularly for long PRLrs, was found in stromal cells surrounding primordial and primary follicles, and, for both PRLrs, in granulosa cells of preantral follicles and in luteal cells. Moderate signal intensity for PRLrs was found in theca cells of preantral to ovulatory follicles, and in granulosa cells of antral follicles up to the gonadotropin-dependent stage. Decreasing immunoreactivity to PRLrs was found in granulosa cells of gonadotropin-dependent to ovulatory follicles. For long PRLrs in particular, no signal was found in mural granulosa cells of gonadotropin-dependent follicles; for both isoforms, no signal was found in most granulosa cells of ovulatory follicles. In primordial to gonadotropin-dependent follicles, cellular localization of PRLr was similar on days 0, 10 and 15 of the cycle. Oocytes consistently showed positive immunostaining for PRLrs. Comparative RT-PCR analysis of long and short PRLr expression showed that the short isoform is evenly expressed throughout the estrous cycle, whereas the expression of the long form increases at the time of estrus and decreases at mid-luteal phase and at the onset of the follicular phase. Expression of long PRLrs was greater than that of short PRLrs on day 0 of cycle; expression of both isoforms was similar on day 10 and on day 15, long PRLrs expression was lower than that of short PRLrs. Our results indicate that in sheep ovary, the maximum responsiveness to PRL might occur during the preovulatory phase of the estrous cycle.

Insulin-like growth factor I controls adhesion strength mediated by alpha5beta1 integrins in motile carcinoma cells

One of the intriguing questions regarding cell motility concerns the mechanism that makes stationary cells move. Here, we provide the first physical evidence that the onset of breast cancer cell motility in response to insulin-like growth factor I (IGF-I) correlates with lowering of adhesion strength from 2.52 +/- 0.20 to 1.52 +/- 0.13 microdynes/microm2 in cells attached to fibronectin via alpha5beta1 integrin. The adhesion strength depends on the dose of IGF-I and time of IGF-I treatment. Weakening of cell-matrix adhesion is blocked significantly (p < 0.01) by the catalytically inactive IGF-I receptor (IGF-IR) and the phosphoinositide 3-kinase (PI-3 kinase) inhibitor LY-294002, but it is unaffected by mitogen-activated protein kinase kinase inhibitor UO-126 and Src kinase inhibitor PP2. Sustained blockade of Rho-associated kinase (ROCK) with Y-27632 down-regulates adhesion strength in stationary, but not in IGF-I-treated, cells. Jasplakinolide, a drug that prevents actin filament disassembly, counteracts the effect of IGF-I on integrin-mediated cell adhesion. In the absence of growth factor signaling, ROCK supports a strong adhesion via alpha5beta1 integrin, whereas activation of the IGF-IR kinase reduces cell-matrix adhesion through a PI-3K-dependent, but ROCK-independent, mechanism. We propose that disassembly of the actin filaments via PI-3 kinase pathway contributes to weakening of adhesion strength and induction of cell movement. Understanding how cell adhesion and migration are coordinated has an important application in cancer research, developmental biology, and tissue bioengineering.

Expression of transforming growth factor-beta 1 and growth in soft agar differentiate prostate carcinoma-associated fibroblasts from normal prostate fibroblasts

Carcinoma-associated fibroblasts (CAF) promote tumor progression of pre-neoplastic epithelial cells. To investigate the basis of this phenomenon, we compared the properties of fibroblasts cultured from normal human prostate (NHPF) to prostate CAF. NHPF and CAF were assayed for growth potential, cell death and proliferative capacity by measuring population doubling time, cell cycle distribution and capability to form colonies in soft agar. Resistance to genotoxic (UV radiation: 0-50 J/cm2) and chemotoxic (0-200 nM Taxol) agents were compared between CAF and NHPF by measuring cell viability and cell cycle analysis. Transforming growth factor beta1 (TGF-beta1) immunoreactivity was assessed in non-malignant and malignant prostatic tissue. No detectable differences were found when comparing CAF and NHPF with respect to population doubling time, cell cycle distribution and response to genotoxic and chemotoxic agents. The mean number of colonies in soft agar was 120.5 for CAF vs. 18.2 for NHPF (p < 0.05). Because TGF-beta1 and matrix metalloproteinase (MMP)-9 have been associated with growth of fibroblasts in soft agar and tumor promotion, we measured the expression of these factors in NHPF and CAF by ELISA. There was no difference in expression of MMP-9; however, TGF-beta1 was expressed in higher concentrations in CAF than in NHPF (p < 0.0014). Furthermore, TGF-beta1 expression was higher in the carcinoma-associated stroma of prostate cancer tissue than stroma of non-malignant prostatic tissue. Increased capability of CAF as compared to NHPF to form colonies in soft agar may be due to a higher expression of TGF-beta1 and correlates with the ability of CAF to promote malignant progression of prostate epithelial cells.

The ras/mitogen-activated protein kinase pathway inhibitor and likely tumor suppressor proteins, sprouty 1 and sprouty 2 are deregulated in breast cancer

Sprouty (Spry) proteins were found to be endogenous inhibitors of the Ras/mitogen-activated protein kinase pathway that play an important role in the remodeling of branching tissues. We investigated Spry expression levels in various cancers and found that Spry1 and Spry2 were down-regulated consistently in breast cancers. Such prevalent patterns of down-regulation may herald the later application of these isoforms as tumor markers that are breast cancer specific and more profound than currently characterized markers. Spry1 and 2 were expressed specifically in the luminal epithelial cells of breast ducts, with higher expression during stages of tissue remodeling when the epithelial ducts are forming and branching. These findings suggest that Sprys might be involved as a modeling counterbalance and surveillance against inappropriate epithelial expansion. The abrogation of endogenous Spry activity in MCF-7 cells by the overexpression of a previously characterized dominant-negative mutant of Spry, hSpry2Y55F resulted in enhanced cell proliferation in vitro. The hSpry2Y55F stably expressing cells also formed larger and greater number of colonies in the soft-agar assay. An in vivo nude mice assay showed a dramatic increase in the tumorigenic potential of hSpry2Y55F stable cells. The consistent down-regulation of Spry1 and 2 in breast cancer and the experimental evidence using a dominant-negative hSpry2Y55F indicate that Spry proteins may actively maintain tissue integrity that runs amok when their expression is decreased below normal threshold levels. This alludes to a previously unrecognized role for Sprys in cancer development.

Apoptosis and involution in the mammary gland are altered in mice lacking a novel receptor, beta1,4-Galactosyltransferase I

Receptor-mediated cell-extracellular matrix (ECM) interactions are critical regulators of cell survival, and perturbing these signaling pathways can disrupt cellular differentiation and function in a variety of tissues, including the mammary gland. One such receptor is the cell surface-associated, long isoform of beta1,4-galactosyltransferase I (GalT I). Deletion of long GalT I leads to increased mammary ductal branching morphogenesis [Dev. Biol., 244 (2002) 114]. Here, we show that this expansion in the mammary epithelial (ME) cell compartment is accomplished through decreased apoptosis during pregnancy and involution. Decreased apoptosis during involution is concomitant with delayed alveolar collapse, persistent expression of the milk protein gene alpha-lactalbumin and delayed expression of genes associated with the tissue-remodeling phase of involution. Using 3-dimensional in vitro cultures, we show that the decrease in apoptosis is dependent on laminin 1, a ligand for surface GalT I, suggesting that surface GalT I negatively influences ECM-dependent cell survival, a novel function for an ECM receptor. In the best-studied examples, ECM promotes survival through integrin receptor-mediated activation of focal adhesion kinase (FAK). Aggregation of surface GalT I also activates FAK, therefore, we asked if FAK activation was altered in ME from long GalT I null mice. Activated FAK was appropriately localized to focal adhesions in long GalT I null ME. However, FAK activation was constitutively reduced 4.5-fold in long GalT I nulls relative to wild type. Expression of the integrin beta1 subunit was not affected by loss of long GalT I. Collectively, these results suggest that surface GalT I might negatively regulate ME cell survival by linking integrin-independent FAK activation to apoptotic rather than survival signaling events.

The tension mounts: mechanics meets morphogenesis and malignancy

The tissue microenvironment regulates mammary gland development and tissue homeostasis through soluble, insoluble and cellular cues that operate within the three dimensional architecture of the gland. Disruption of these critical cues and loss of tissue architecture characterize breast tumors. The developing and lactating mammary gland are also subject to a plethora of tensional forces that shape the morphology of the gland and orchestrate its functionally differentiated state. Moreover, malignant transformation of the breast is associated with dramatic changes in gland tension that include elevated compression forces, high tensional resistance stresses and increased extracellular matrix stiffness. Chronically increased mammary gland tension may influence tumor growth, perturb tissue morphogenesis, facilitate tumor invasion, and alter tumor survival and treatment responsiveness. Because mammary tissue differentiation is compromised by high mechanical force and transformed cells exhibit altered mechanoresponsiveness, malignant transformation of the breast may be functionally linked to perturbed tensional-homeostasis. Accordingly, it will be important to define the role of tensional force in mammary gland development and tumorigenesis. Additionally, it will be critical to identify the key molecular elements regulating tensional-homeostasis of the mammary gland and thereafter to characterize their associated mechanotransduction pathways.

Colony-stimulating factor-1 blockade by antisense oligonucleotides and small interfering RNAs suppresses growth of human mammary tumor xenografts in mice

Colony-stimulating factor (CSF)-1 is the primary regulator of tissue macrophage production. CSF-1 expression is correlated with poor prognosis in breast cancer and is believed to enhance mammary tumor progression and metastasis through the recruitment and regulation of tumor-associated macrophages. Macrophages produce matrix metalloproteases (MMPs) and vascular endothelial growth factor, which are crucial for tumor invasion and angiogenesis. Given the important role of CSF-1, we hypothesized that blockade of CSF-1 or the CSF-1 receptor (the product of the c-fms proto-oncogene) would suppress macrophage infiltration and mammary tumor growth. Human MCF-7 mammary carcinoma cell xenografts in mice were treated with either mouse CSF-1 antisense oligonucleotide for 2 weeks or five intratumoral injections of either CSF-1 small interfering RNAs or c-fms small interfering RNAs. These treatments suppressed mammary tumor growth by 50%, 45%, and 40%, respectively, and selectively down-regulated target protein expression in tumor lysates. Host macrophage infiltration; host MMP-12, MMP-2, and vascular endothelial growth factor A expression; and endothelial cell proliferation within tumors of treated mice were decreased compared with tumors in control mice. In addition, mouse survival significantly increased after CSF-1 blockade. These studies demonstrate that CSF-1 and CSF-1 receptor are potential therapeutic targets for the treatment of mammary cancer.

Carcinoma and stromal enzyme activity profiles associated with breast tumor growth in vivo

Cancer research depends on the use of human cell lines for both the in vitro (culture) and in vivo (xenograft) analysis of tumor progression and treatment. However, the extent to which cultured preparations of human cancer lines display similar properties in vivo, where important host factors may influence tumor biology, remains unclear. Here, we address this question by conducting a functional proteomic analysis of the human breast cancer line MDA-MB-231 grown in culture and as orthotopic xenograft tumors in the mammary fad pad of immunodeficient mice. Using a suite of activity-based chemical probes, we identified carcinoma (human) enzyme activities that were expressed selectively in culture or in xenograft tumors. Likewise, distinct groups of stromal (mouse) enzyme activities were found that either infiltrated or were excluded from xenograft tumors, indicating a contribution by specific host components to breast cancer development. MDA-MB-231 cells isolated from tumors exhibited profound differences in their enzyme activity profiles compared with the parent cell line, including the dramatic posttranscriptional up-regulation of the serine proteases urokinase plasminogen activator and tissue plasminogen activator and down-regulation of the glycolytic enzyme phosphofructokinase. These altered enzyme activity profiles correlated with significantly greater tumor growth rates and metastases for xenograft-derived MDA-MB-231 cells upon reintroduction into mice. Collectively, these data indicate that the in vivo environment of the mouse mammary fat pad cultivates the growth of human breast cancer cells with elevated tumorigenic properties and highlight the value of activity-based protein profiling for identifying proteomic signatures that depict such changes in cancer cell biology.

Targeted disruption of beta1-integrin in a transgenic mouse model of human breast cancer reveals an essential role in mammary tumor induction

Despite evidence demonstrating the role of beta1-integrin in the regulation of cancer cell proliferation in vitro, the importance of this cell adhesion receptor during the initiation and progression of epithelial tumors in vivo remains unclear. Here we have used the Cre/LoxP1 recombination system to disrupt beta1-integrin function in the mammary epithelium of a transgenic mouse model of human breast cancer. Using this approach, we show that beta1-integrin expression is critical for the initiation of mammary tumorigenesis in vivo, and for maintaining the proliferative capacity of late-stage tumor cells. These observations provide a direct demonstration that beta1-integrin plays a critical role in both the initiation and maintenance of mammary tumor growth in vivo.

Molecular characterization of the tumor microenvironment in breast cancer

Here we describe the comprehensive gene expression profiles of each cell type composing normal breast tissue and in situ and invasive breast carcinomas using serial analysis of gene expression. Based on these data, we determined that extensive gene expression changes occur in all cell types during cancer progression and that a significant fraction of altered genes encode secreted proteins and receptors. Despite the dramatic gene expression changes in all cell types, genetic alterations were detected only in cancer epithelial cells. The CXCL14 and CXCL12 chemokines overexpressed in tumor myoepithelial cells and myofibroblasts, respectively, bind to receptors on epithelial cells and enhance their proliferation, migration, and invasion. Thus, chemokines may play a role in breast tumorigenesis by acting as paracrine factors.

Development of the mammary gland requires DGAT1 expression in stromal and epithelial tissues

Mammary gland development is a complex process that is dependent on interactions between the developing mammary epithelium and the surrounding stromal tissues. We show that mice lacking the triglyceride synthesis enzyme acyl CoA:diacylglycerol transferase 1 (DGAT1) have impaired mammary gland development, characterized by decreased epithelial proliferation and alveolar development, and reduced expression of markers of functional differentiation. Transplantation studies demonstrate that the impaired development results from a deficiency of DGAT1 in both the stromal and epithelial tissues. Our findings are the first to link defects in stromal lipid metabolism to impaired mammary gland development.

Comparison of mammary gland involution between 129S1 and C57BL/6 inbred mouse strains: differential regulation of Bcl2a1, Trp53, Cebpb, and Cebpd expression

Genetic engineering has made the mouse an invaluable tool to address the function of individual genes in a targeted manner. Over the last decade it has become apparent that the genetic mouse strain background can significantly influence the phenotype of an engineered mouse. Therefore, it is essential to characterize the biology of the different wild-type background strains. In this study, we have compared mouse mammary gland involution in the 129S1 and C57BL/6 inbred strains and report significant differences at the molecular level with differential expression of Bcl2a1 (Bfl1), Trp53 (p53), Cebpb (C/EBP beta), and Cebpd (C/EBP delta). The C57BL/6 strain exhibits dynamic responses with induction of Trp53 and Cebpd and concomitant downregulation of Bcl2a1 during the first phase of involution. In contrast, expression of these genes does not change significantly in 129S1 mice. During the second phase, C57BL/6 glands contain more Cebpb than 129S1 glands. Nevertheless, involution proceeds morphologically with similar kinetics in both strains. The data demonstrate that the genetic response of mammary tissue varies significantly between 129S1 and C57BL/6. These results may provide a basis for the interpretation of strain-specific phenotypes in engineered mice and underline the importance of pure strains for large-scale expression studies with mutant mice.

Proteolytic imbalance is reversed after therapeutic surgery in breast cancer patients

The occurrence of metastasis severely affects prognosis and survival of breast cancer patients. In order to metastasize, breast cancer cells need to cross the basement membrane (BM) tissue boundaries. Matrix metalloproteases (MMPs) are enzymes with proteolytic activity towards extracellular matrix components (ECM) of the BM, that are blocked by physiological tissue inhibitors (TIMPs). Cancer metastasis occurs as a result of an imbalance between MMPs, in particular MMP-2 and MMP-9, and TIMPs, in particular TIMP-2 and TIMP-1. This is the first study to report that pro-MMP-9 and TIMP-1 serum concentrations are inversely correlated in breast cancer patients. In the same patients, we determined the pro-MMP-9, the TIMP-1, the pro-MMP-2 and TIMP-2 before and after surgical eradication of the breast cancer. Our results show that after surgery, when the breast cancer tissue was removed, pro-MMP-9 concentrations dramatically decreased and TIMP-1 concentrations strongly increased, with statistically significant differences, so that a new balance was established. No statistically significant differences were observed regarding pro-MMP-2 and TIMP-2. Also, no correlation was found between pro-MMP-2, pro-MMP-9, TIMP-1 and TIMP-2 and a number of clinical and pathological parameters. In conclusion, our study suggests that pro-MMP-9 and TIMP-1 could be used as markers of disease during the follow-up of breast cancer patients and possibly as prognostic markers, although more studies are needed to address this issue.

Expression patterns of esophageal cancer deregulated genes in C57BL/6J mouse embryogenesis

AIM: To investigate the expression patterns of esophageal squamous cell cancer deregulated genes in mid to late stages of C57BL/6J mouse embryogenesis, and the correlation between these genes in embryonic development and tumorigenesis of esophageal squamous cell cancer.

METHODS: Reverse northern screening was performed to examine the expression patterns of esophageal cancer deregulated genes in C57BL/6J mouse embryogenesis. To confirm the gene expression patterns, semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was carried out for 3 of the randomly picked differentially expressed genes.

RESULTS: Within these esophageal cancer deregulated genes, 4 patterns of expression were observed at 3 stages embryonic d 11.5 (E11.5), embryonic d 13.5 (E13.5) and postnatal d1 (P1). (1) Up-regulation during the E11.5 period, down- regulation during the E13.5 and P1 period (up-down-down), the 10 up-regulated genes during the E11.5 period could be classified into 6 known genes and 4 unknown genes. The known genes included differentiation related genes (S100A8), immunity related gene (IGL), translation and transcription regulation genes (RPL15, EEF1A1), cytoskeletal protein (TUBA1), cysteine protease inhibitor (cystatin B). (2) Up-regulation during the E13.5 and P1 period (down-up-up), such as the SPRR2A which was down-regulated at E11.5. (3) Down-regulation during the E11.5 and E13.5 period (down-down-up), such as RHCG and keratin 4. (4) Fluctuating expression, down initially, up at E13.5, and then down again (down-up-down). EMP1 belonged to such a gene, which was highly expressed at E13.5.

CONCLUSION: The results will be helpful for understanding the function of esophageal squamous cell carcinoma (ESCC) deregulated genes in embryonic development and tumorigenesis. S100A8 and S100A9 may play different roles in early embryonic development. IGL may be an oncofetal protein, and EMP1 relates with neurogenesis at E13.5. The genes identified pertinent to embryonic development may serve as candidate susceptibility genes for inherited esophageal cancer disorders as well as for various heritable disorders of embryonic development.

Notch signaling in mammary development and oncogenesis

With the discovery of an activated Notch oncogene as a causative agent in mouse mammary tumor virus induced breast cancer in mice, the potential role for Notch signaling in normal and pathological mammary development was revealed. Subsequently, Notch receptors have been found to regulate normal development in many organ systems. In addition, inappropriate Notch signaling has been implicated in cancer of several tissues in humans and animal model systems. Here we review important features of the Notch system, and how it may regulate development and cancer in the mammary gland. A large body of literature from studies in Drosophila and C. elegans has not only revealed molecular details of how the Notch proteins signal to control biology, but shown that Notch receptor activation helps to define how other signaling pathways are interpreted. In many ways the Notch system is used to define the context in which other pathways function to control proliferation, differentiation, cell survival, branching morphogenesis, asymmetric cell division, and angiogenesis--all processes which are critical for normal development and function of the mammary gland.

Functional significance of metastasis-inducing S100A4(Mts1) in tumor-stroma interplay

Causal implication of S100A4 in inducing metastases was convincingly shown previously. However, the mechanisms that associate S100A4 with tumor progression are not well understood. S100A4 protein, as a typical member of the S100 family, exhibits dual, intracellular and extracellular, functions. This work is focused on the extracellular function of S100A4, in particular its involvement in tumor-stroma interplay in VMR (mouse adenocarcinoma cell line) tumor cells, which exhibit stroma-dependent metastatic phenotype. We demonstrated the reciprocal influence of tumor and stroma cells where tumor cells stimulate S100A4 secretion from fibroblasts in culture. In turn, extracellular S100A4 modifies the cytoskeleton and focal adhesions and triggers several other events in tumor cells. We found stabilization of the tumor suppressor protein p53 and modulation of its function. In particular, extracellular S100A4 down-regulates the pro-apoptotic bax and the angiogenesis inhibitor thrombospondin-1 genes. For the first time, we demonstrate here that the S100A4 protein added to the extracellular space strongly stimulates proteolytic activity of VMR cells. This activity most probably is associated with matrix metalloproteinases and, in particular, with matrix metalloproteinase-13. Finally, the application of the recombinant S100A4 protein confers stroma-independent metastatic phenotype on VMR tumor cells. In conclusion, our results indicate that metastasis-inducing S100A4 protein plays a pivotal role in the tumor-stroma environment. S100A4 released either by tumor or stroma cells triggers pro-metastatic cascades in tumor cells.

Mammary epithelial-mesenchymal interaction regulates fibronectin alternative splicing via phosphatidylinositol 3-kinase

The way alternative splicing is regulated within tissues is not understood. A relevant model of this process is provided by fibronectin, an important extracellular matrix protein that plays a key role in cell adhesion and migration and contains three alternatively spliced regions known as EDI, EDII, and IIICS. We used a cell culture system to simulate mammary epithelial-stromal communication, a process that is crucial for patterning and function of the mammary gland, and studied the effects of extracellular signals on the regulation of fibronectin pre-mRNA alternative splicing. We found that soluble factors from a mammary mesenchymal cell-conditioned medium, as well as the growth factors HGF/SF (hepatocyte growth factor/scatter factor), KGF (keratinocyte growth factor), and aFGF (acidic fibroblast growth factor), stimulate EDI and IIICS but not EDII inclusion into fibronectin mRNA in the mammary epithelial cell line SCp2, favoring fibronectin isoforms associated with proliferation, migration, and tissue remodeling. We explored the signaling pathways involved in this regulation and found that the mammary mesenchymal cell-conditioned medium and HGF/SF act through a phosphatidylinositol 3-kinase-dependent cascade to alter fibronectin alternative splicing. This splicing regulation is independent from promoter structure and de novo protein synthesis but does require two exonic elements within EDI. These results shed light on how extracellular stimuli are converted into changes in splicing patterns.

The stroma as a crucial target in rat mammary gland carcinogenesis

A complex network of interactions between the stroma, the extracellular matrix and the epithelium drives mammary gland development and function. Two main assumptions in chemical carcinogenesis of the mammary gland have been that carcinogens induce neoplasia by causing mutations in the DNA of the epithelial cells and that the alterations of tissue architecture observed in neoplasms are a consequence of this primary mutational event. Here, we use a rat mammary tissue recombination model and the chemical carcinogen N-nitrosomethylurea (NMU) to determine whether the primary target of the carcinogen is the epithelium, the stroma or both tissue compartments. Mammary epithelial cells were exposed in vitro either to the carcinogen or vehicle before being transplanted into the cleared fat pads of rats exposed to carcinogen or vehicle. We observed that neoplastic transformation of these mammary epithelial cells occurred only when the stroma was exposed in vivo to NMU, regardless of whether or not the epithelial cells were exposed to the carcinogen. Mammary epithelial cells exposed in vitro to the carcinogen formed phenotypically normal ducts when injected into a non-treated stroma. Mutation in the Ha-ras-1 gene did not correlate with initiation of neoplasia. Not only was it often found in both cleared mammary fat pads of vehicle-treated animals and intact mammary glands of untreated animals, but it was also absent in some tumors. Our results suggest that the stroma is a crucial target of the carcinogen and that mutation in the Ha-ras-1 gene is neither necessary nor sufficient for tumor initiation.

Death in the third dimension: apoptosis regulation and tissue architecture

Tissue development, homeostasis and tumor pathogenesis all depend upon a complex dialogue between multiple cell types operating within a dynamic three-dimensional (3D) tissue extracellular matrix microenvironment. A major issue is whether the spatial organization of a cell within this 3D tissue microenvironment could modulate cell responsiveness to regulate cell fate decisions such as survival, and if so how. Classic developmental model systems and transgenic animals are instructive but pose special challenges for investigators conducting signaling studies and biochemical assays in tissues. As an alternative, 3D culture model systems exist in which cell-adhesion dependent tissue architecture, heterotypic cell-cell interactions and tissue differentiation can be recapitulated with good fidelity. 3D cell culture models are slowly revealing how tissue architecture can dramatically influence how a cell responds to exogenous stimuli to modify its apoptotic behavior and hence should prove instrumental for identifying novel cell death pathways.

Proteolytic processing of laminin-5 by MT1-MMP in tissues and its effects on epithelial cell morphology

The extracellular matrix macromolecule laminin-5 (Ln-5) is converted by matrix metalloproteinases (MMP) MT1-MMP and MMP-2 into a migration-promoting substrate in vitro. We now report that cleavage of Ln-5 by MT1-MMP occurs in vivo and affects epithelial tissue organization and probably Ln-5 turnover. In MT1-MMP knockout (KO) mice, the kidneys showed increased levels of total Ln-5 gamma2 subunit, but significantly reduced amounts of gamma2', an amino-terminal truncated proteolytic form of gamma2. The kidney tubular epithelia of KO animals were poorly differentiated, a phenotype reminiscent of human congenital mixed hypoplastic/dysplastic disorders. To establish a better link between Ln-5 proteolytic cleavage and epithelial morphology, MT1-MMP expression was reconstituted by transfection of MT1-MMP into a Ln-5 positive, MT1-MMP deficient epithelial cell line. MT1-MMP transfectants demonstrated increased levels of processed Ln-5 gamma2 chain and enhanced spreading on Ln-5, but not fibronectin. Recombinant MT1-MMP cleaved gamma2 constructs in vitro at a known in vivo gamma2 gamma2' processing site. These results strongly indicate that Ln-5 is a physiological substrate of MT1-MMP in vivo. Proteolytic processing of gamma2 subunit by MT1-MMP may influence Ln-5 turnover in epithelial basement membranes and affect epithelial morphogenesis.

Interleukin-1 alpha promotes tumor growth and cachexia in MCF-7 xenograft model of breast cancer

Progression of breast cancer involves cross-talk between epithelial and stromal cells. This cross-talk is mediated by growth factors and cytokines secreted by both cancer and stromal cells. We previously reported expression of interleukin (IL)-1 alpha in a subset of breast cancers and demonstrated that IL-1 alpha is an autocrine and paracrine inducer of prometastatic genes in in vitro systems. To understand the role of IL-1 alpha in breast cancer progression in vivo, we studied the growth of MCF-7 breast cancer cells overexpressing a secreted form of IL-1 alpha (MCF-7IL-1 alpha) in nude mice. MCF-7IL-1 alpha cells formed rapidly growing estrogen-dependent tumors compared to parental cells. Interestingly, IL-1 alpha expression alone was not sufficient for metastasis in vivo although in vitro studies showed induction of several prometastatic genes and matrix metalloproteinase activity in response to cross-talk between IL-1 alpha-expressing cancer cells and fibroblasts. Animals implanted with MCF-7IL-1 alpha cells were cachetic, which correlated with increased leptin serum levels but not other known cachexia-inducing cytokines such as IL-6, tumor necrosis factor, or interferon gamma. Serum triglycerides, but not blood glucose were lower in animals with MCF-7IL-1 alpha cell-derived tumors compared to animals with control cell-derived tumors. Cachexia was associated with atrophy of epidermal and adnexal structures of skin; a similar phenotype is reported in triglyceride-deficient mice and in ob/ob mice injected with leptin. Mouse leptin-specific transcripts could be detected only in MCF-7IL-1 alpha cell-derived tumors, which suggests that IL-1 alpha increases leptin expression in stromal cells recruited into the tumor microenvironment. Despite increased serum leptin levels, animals with MCF-7IL-1 alpha cell-derived tumors were not anorexic suggesting only peripheral action of tumor-derived leptin, which principally targets lipid metabolism. Taken together, these results suggest that cancer cell-derived cytokines, such as IL-1 alpha, induce cachexia by affecting leptin-dependent metabolic pathways.

Prolactin and the prolactin receptor: new targets of an old hormone

Prolactin (PRL) is one of a family of related hormones including growth hormone (GH) and placental lactogen (PL) that are hypothesized to have arisen from a common ancestral gene about 500 million years ago. Over 300 different functions of PRL have been reported, highlighting the importance of this pituitary hormone. PRL is also synthesized by a number of extra-pituitary tissues including the mammary gland and the uterus. Most of PRL's actions are mediated by the unmodified 23 kDa peptide, however, PRL may be modified post-translation, thereby altering its biological effects. PRL exerts these effects by binding to its receptor, a member of the class I cytokine receptor super-family. This activates a number of signaling pathways resulting in the transcription of genes necessary for the tissue specific changes induced by PRL. Mouse knockout models of the major forms of the PRL receptor have confirmed the importance of PRLs role in reproduction. Further knockout models have provided insight into the importance of PRL signaling intermediates and the advent of transcript profiling has allowed the elucidation of a number of PRL target genes.

Ets2-dependent stromal regulation of mouse mammary tumors

The Ets2 transcription factor is regulated by mitogen-activated protein (MAP) kinase phosphorylation of a single threonine residue. We generated by gene targeting a single codon mutation in Ets2 substituting Ala for the critical Thr-72 phosphorylation site (Ets2A72), to investigate the importance of MAP kinase activation of Ets2 in embryo and tumor development. Ets2(A72/A72) mice are viable and develop normally. However, combining the Ets2A72 allele with a deletion mutant of Ets2 results in lethality at E11.5 and shows that Ets2A72 is a hypomorphic allele. Mammary tumors caused by transgenic polyomavirus middle T antigen, activated Neu(Erbb2), or the combination of Neu and transgenic VEGF (Neu; VEGF-25) were all restricted in Ets2(A72/A72) females. The Ets2(A72/A72) restriction on Neu; VEGF-25 tumor growth was associated with increased p21Cip1 expression. The size of tumors transplanted into fat pads of mice with Ets2 targeted alleles was correlated directly with Ets2 activity and fewer stromal cells expressing matrix metalloproteinase 9 (MMP-9). Decreased MMP-3 and MMP-9 mRNAs were confirmed in Ets2(A72/A72) macrophages. Activation of Ets2 at Thr-72 acts in the stroma, downstream of vascular endothelial growth factor production, in part through the regulation of macrophage proteases to support the progression of Neu- and polyomavirus middle-T-initiated mammary tumors.

Stem cells in normal breast development and breast cancer

The main focus of this review is the role of mammary stem cells in normal breast development and carcinogenesis. We have developed a new in vitro culture system that permits, for the first time, the propagation of mammary stem and progenitor cells in an undifferentiated state, which should facilitate the elucidation of pathways that regulate normal mammary stem-cell self-renewal and differentiation. Furthermore, we propose a model in which transformation of stem cells, or early progenitor cells, results in carcinogenesis. A key event in this process is the deregulation of normal self-renewal in these cells. Transformed mammary stem or progenitor cells undergo aberrant differentiation processes that result in generation of the phenotypic heterogeneity found in human and rodent breast cancers. This phenotypic diversity is driven by a small subset of mammary tumour stem cells. We will discuss the important implications of this mammary tumour stem-cell model.

Axis of evil: molecular mechanisms of cancer metastasis

Although the genetic basis of tumorigenesis may vary greatly between different cancer types, the cellular and molecular steps required for metastasis are similar for all cancer cells. Not surprisingly, the molecular mechanisms that propel invasive growth and metastasis are also found in embryonic development, and to a less perpetual extent, in adult tissue repair processes. It is increasingly apparent that the stromal microenvironment, in which neoplastic cells develop, profoundly influences many steps of cancer progression, including the ability of tumor cells to metastasize. In carcinomas, the influences of the microenvironment are mediated, in large part, by bidirectional interactions (adhesion, survival, proteolysis, migration, immune escape mechanisms lymph-/angiogenesis, and homing on target organs) between epithelial tumor cells and neighboring stromal cells, such as fibroblasts as well as endothelial and immune cells. In this review, we summarize recent advances in understanding the molecular mechanisms that govern this frequently lethal metastatic progression along an axis from primary tumor to regional lymph nodes to distant organ sites. Affected proteins include growth factor signaling molecules, chemokines, cell-cell adhesion molecules (cadherins, integrins) as well as extracellular proteases (matrix metalloproteinases). We then discuss promising new therapeutic approaches targeting the microenvironment. We note, however, that there is still too little knowledge of how the many events are coordinated and integrated by the cancer cell, with conspiratorial help by the stromal component of the host. Before drug development can proceed with a legitimate chance of success, significant gaps in basic knowledge need to be filled.