Transgenic mice expressing a dominant-negative mutant type II transforming growth factor-beta receptor exhibit impaired mammary development and enhanced mammary tumor formation

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Cell type and stage specific transcriptional, chromatin and cell-cell communication landscapes in the mammary gland

The mammary gland (MG) is composed of three main epithelial lineages, the basal cells (BC), the estrogen receptor (ER) positive luminal cells (ER+ LC), and the ER negative LC (ER- LC). Defining the cell identity of each lineage and how it is modulated throughout the different stages of life is important to understand how these cells function and communicate throughout life. Here, we used transgenic mice specifically labelling ER+ LC combined to cell surface markers to isolate with high purity the 3 distinct cell lineages of the mammary gland and defined their expression profiles and chromatin landscapes by performing bulk RNAseq and ATACseq of these isolated populations in puberty, adulthood and mid-pregnancy. Our analysis identified conserved genes, ligands and transcription factor (TF) associated with a specific lineage throughout life as well as genes, ligands and TFs specific for a particular stage of the MG. In summary, our study identified genes and TF network associated with the identity, function and cell-cell communication of the different epithelial lineages of the MG at different stages of life.

The Mammary Gland: Basic Structure and Molecular Signaling during Development

The mammary gland is a compound, branched tubuloalveolar structure and a major characteristic of mammals. The mammary gland has evolved from epidermal apocrine glands, the skin glands as an accessory reproductive organ to support postnatal survival of offspring by producing milk as a source of nutrition. The mammary gland development begins during embryogenesis as a rudimentary structure that grows into an elementary branched ductal tree and is embedded in one end of a larger mammary fat pad at birth. At the onset of ovarian function at puberty, the rudimentary ductal system undergoes dramatic morphogenetic change with ductal elongation and branching. During pregnancy, the alveolar differentiation and tertiary branching are completed, and during lactation, the mature milk-producing glands eventually develop. The early stages of mammary development are hormonal independent, whereas during puberty and pregnancy, mammary gland development is hormonal dependent. We highlight the current understanding of molecular regulators involved during different stages of mammary gland development.

Biological Mechanisms and Therapeutic Opportunities in Mammographic Density and Breast Cancer Risk

Mammographic density is an important risk factor for breast cancer; women with extremely dense breasts have a four to six fold increased risk of breast cancer compared to women with mostly fatty breasts, when matched with age and body mass index. High mammographic density is characterised by high proportions of stroma, containing fibroblasts, collagen and immune cells that suggest a pro-tumour inflammatory microenvironment. However, the biological mechanisms that drive increased mammographic density and the associated increased risk of breast cancer are not yet understood. Inflammatory factors such as monocyte chemotactic protein 1, peroxidase enzymes, transforming growth factor beta, and tumour necrosis factor alpha have been implicated in breast development as well as breast cancer risk, and also influence functions of stromal fibroblasts. Here, the current knowledge and understanding of the underlying biological mechanisms that lead to high mammographic density and the associated increased risk of breast cancer are reviewed, with particular consideration to potential immune factors that may contribute to this process.

Immune checkpoint inhibitors: review of the existing evidence and challenges in breast cancer

Cancer initiation and progression are associated with immune system responses. Tumor cells use various tricks to scape of immune system, such as activating immune checkpoint pathways that induce immunosuppressive functions. Among the different immune checkpoint receptors, CTLA-4 and PD-1/PD-L1 are prominent therapeutic targets in different cancers. Although the US FDA has approved some immune checkpoint inhibitors for several cancers, concerning breast cancer still different clinical trials are looking for optimizing efficacy and decreasing immune-related adverse events. This review will discuss the existing body of knowledge with regard to cross-talk between immune system and tumor cells and then explore immune checkpoint-related signaling pathways in the context of breast tumors. Finally, we highlight the application of different immune checkpoint blockers in breast cancer patients.

Breast cancer stem cells: A review of their characteristics and the agents that affect them

The evolving concept that cancer stem cells (CSCs) are the driving element in cancer development, evolution and heterogeneity, has overridden the previous model of a tumor consisting of cells all with similar sequentially acquired mutations and a similar potential for renewal, invasion and metastasis. This paradigm shift has focused attention on therapeutically targeting CSCs directly as a means of eradicating the disease. In breast cancers, CSCs can be identified by cell surface markers and are characterized by their ability to self-renew and differentiate, resist chemotherapy and radiation, and initiate new tumors upon serial transplantation in xenografted mice. These functional properties of CSCs are regulated by both intracellular and extracellular factors including pluripotency-related transcription factors, intracellular signaling pathways and external stimuli. Several classes of natural products and synthesized compounds have been studied to target these regulatory elements and force CSCs to lose stemness and/or terminally differentiate and thereby achieve a therapeutic effect. However, realization of an effective treatment for breast cancers, focused on the biological effects of these agents on breast CSCs, their functions and signaling, has not yet been achieved. In this review, we delineate the intrinsic and extrinsic factors identified to date that control or promote stemness in breast CSCs and provide a comprehensive compilation of potential agents that have been studied to target breast CSCs, transcription factors and stemness-related signaling. Our aim is to stimulate further study of these agents that could become the basis for their use as stand-alone treatments or components of combination therapies effective against breast cancers.

New Entrants into Clinical Trials for Targeted Therapy of Breast Cancer: An Insight

Breast cancer is too complex with various different molecular alterations involved in its pathogenesis and progression. Over the decade, we have seen a surge in the development of drugs for bimolecular targets and for the signal transduction pathways involved in the treatment line of breast cancer. These drugs, either alone or in combination with conventional treatments like chemotherapy, hormone therapy and radiotherapy, will help oncologists to get a better insight and do the needful treatment. These novel therapies bring various challenges along with them, which include the dosage selection, patient selection, schedule of treatment and weighing of clinical benefits over side effects. In this review, we highlight the recently studied target molecules that have received indications in breast carcinoma, both in the localized and in an advanced state and about their inhibitors which are in clinical development which can give the immense potential to clinical care in the near future.

Ski mediates TGF-β1-induced fibrosarcoma cell proliferation and promotes tumor growth

Background: TGF-β1 promotes cell proliferation in only some tumors and exerts bidirectional regulatory effects on the proliferation of fibroblasts. This study intends to explore whether the mechanism is related to increased expression of Ski. Methods: Cell proliferation of the fibrosarcoma cell line L929 was assessed with an ELISA BrdU kit. The mRNA and protein expression levels of the corresponding factors were measured by RT-qPCR, immunohistochemistry or Western blotting in vitro and in vivo. Additionally, c-Ski was knocked down using RNAi. The expression of Ski in human dermatofibrosarcoma protuberans (DFSP) specimens was measured by immunohistochemistry. Results: TGF-β1 promoted the continued proliferation of L929 cells in a dose-dependent manner, with increased c-Ski expression levels. Conversely, inhibition of c-Ski significantly abrogated this unidirectional effect, significantly inhibited the decrease in p21 protein levels and did not affect the increase in p-Smad2/3 levels upon TGF-β1 treatment. Similarly, inhibition of c-Ski significantly abrogated the growth-promoting effect of TGF-β1 on xenograft tumors. Furthermore, we found that high expression of Ski in DFSP was correlated with a low degree of tumor differentiation. Conclusions: Our data reveal that high c-Ski expression is a cause of TGF-β1-promoted proliferation in fibrosarcoma tumor cells and show that inhibiting Ski expression might be effective for treating tumors with high Ski levels.

The double edge sword of fibrosis in cancer

Cancer-associated fibrosis is a critical component of the tumor microenvironment (TME) which significantly impacts cancer behavior. However, there is significant controversy regarding fibrosis as a predominantly tumor promoting or tumor suppressing factor. Cells essential to the generation of tissue fibrosis such as fibroblasts and mesenchymal stem cells (MSCs) have dual phenotypes dependent upon their independence or association with cancer cells. Cancer-associated fibroblasts and cancer-associated MSCs have unique molecular profiles which facilitate cancer cell cross talk, influence extracellular matrix deposition, and direct the immune system to generate a protumorigenic environment. In contrast, normal tissue fibroblasts and MSCs are important in restraining cancer initiation, influencing epithelial cell differentiation, and limiting cancer cell invasion. We propose this apparent dichotomy of function is due to (1) cancer mediated stromal reprogramming; (2) tissue stromal source; (3) unique subtypes of fibrosis; and (4) the impact of fibrosis on other TME elements. First, as cancer progresses, tumor cells influence their surrounding stroma to move from a cancer restraining phenotype into a cancer supportive role. Second, cancer has specific organ tropism, thus stroma derived from preferred metastatic organs support growth while less preferred metastatic tissues do not. Third, there are subtypes of fibrosis which have unique function to support or inhibit cancer growth. Fourth, depleting fibrosis influences other TME components which drive the cancer response. Collectively, this review highlights the complexity of cancer-associated fibrosis and supports a dual function of fibrosis which evolves during the continuum of cancer growth.

Current status and future prospects of transforming growth factor-β as a potential prognostic and therapeutic target in the treatment of breast cancer

The transforming growth factor-β (TGF-β) signaling pathway is one of the important pathways involved in the cancer cell proliferation, invasion, migration, angiogenesis, apoptosis, as well as in metastasis by agitation or invasion of metastasis-related factors, including matrix metalloproteinase (MMP), epithelial-to-mesenchymal transition (EMT), tumor microenvironment (TME), cancer stem cells (CSCs), and cell adhesion molecules (CAMs). These data suggest its potential value as a therapeutic object in the treatment of malignancies including breast cancer. Several pharmacological approaches have been established to suppress TGF-β pathway; such as vaccines, small molecular inhibitors, antisense oligonucleotides, and monoclonal antibodies. Some of these are now approved by the US Food and Drug Administration for targeting the TGF-β signaling pathway. This study attempts to summarize the current data about the functions of TGF-β in cancer cells, and their probable application in the cancer therapy with a specific emphasis on recent preclinical and clinical research in the treatment of breast cancer and its prognostic value.

Therapeutic potential of pharmacological TGF-β signaling pathway inhibitors in the pathogenesis of breast cancer

The TGF-β signaling pathway plays an important role in cancer cell proliferation, growth, inflammation, angiogenesis, and metastasis. The role of TGF-β signaling in the pathogenesis of breast cancer is complex. TGF-β acts as a tumor suppressor in the early stages of disease, and as a tumor promoter in its later stages. Over-activation of the TGF-β signaling pathway and over-expression of the TGF-β receptors are frequently found in breast tumors. Suppression of TGF-β pathway using biological or pharmacological inhibitors is a potentially novel therapeutic approach for breast cancer treatment. This review summarizes the regulatory role of TGF-β signaling in the pathogenesis of breast cancer for a better understanding and hence a better management of this disease.

Genetic Modifiers of the Breast Tumor Microenvironment

Multiple nonmalignant cell types in the tumor microenvironment (TME) impact breast cancer risk, metastasis, and response to therapy, yet most heritable mechanisms that influence TME cell function and breast cancer outcomes are largely unknown. Breast cancer risk is ∼30% heritable and >170 genetic loci have been associated with breast cancer traits. However, the majority of candidate genes have poorly defined mechanistic roles in breast cancer biology. Research indicates that breast cancer risk modifiers directly impact cancer cells, yet it is equally plausible that some modifier alleles impact the nonmalignant TME. The objective of this review is to examine the list of current breast cancer candidate genes that may modify breast cancer risk and outcome through the TME.

Model of vascular desmoplastic multispecies tumor growth

We present a three-dimensional nonlinear tumor growth model composed of heterogeneous cell types in a multicomponent-multispecies system, including viable, dead, healthy host, and extra-cellular matrix (ECM) tissue species. The model includes the capability for abnormal ECM dynamics noted in tumor development, as exemplified by pancreatic ductal adenocarcinoma, including dense desmoplasia typically characterized by a significant increase of interstitial connective tissue. An elastic energy is implemented to provide elasticity to the connective tissue. Cancer-associated fibroblasts (myofibroblasts) are modeled as key contributors to this ECM remodeling. The tumor growth is driven by growth factors released by these stromal cells as well as by oxygen and glucose provided by blood vasculature which along with lymphatics are stimulated to proliferate in and around the tumor based on pro-angiogenic factors released by hypoxic tissue regions. Cellular metabolic processes are simulated, including respiration and glycolysis with lactate fermentation. The bicarbonate buffering system is included for cellular pH regulation. This model system may be of use to simulate the complex interactions between tumor and stromal cells as well as the associated ECM and vascular remodeling that typically characterize malignant cancers notorious for poor therapeutic response.

Physiologically activated mammary fibroblasts promote postpartum mammary cancer

Women diagnosed with breast cancer within 5 years of childbirth have poorer prognosis than nulliparous or pregnant women. Weaning-induced breast involution is implicated, as the collagen-rich, immunosuppressive microenvironment of the involuting mammary gland is tumor promotional in mice. To investigate the role of mammary fibroblasts, isolated mammary PDGFRα⁺ cells from nulliparous and postweaning mice were assessed for activation phenotype and protumorigenic function. Fibroblast activation during involution was evident by increased expression of fibrillar collagens, lysyl oxidase, Tgfb1, and Cxcl12 genes. The ability of mammary tumors to grow in an isogenic, orthotopic transplant model was increased when tumor cells were coinjected with involution-derived compared with nulliparous-derived mammary fibroblasts. Mammary tumors in the involution-fibroblast group had increased Ly6C⁺ monocytes at the tumor border, and decreased CD8⁺ T cell infiltration and tumor cell death. Ibuprofen treatment suppressed involution-fibroblast activation and tumor promotional capacity, concurrent with decreases in tumor Ly6C⁺ monocytes, and increases in intratumoral CD8⁺ T cell infiltration, granzyme levels, and tumor cell death. In total, our data identify a COX/prostaglandin E2 (PGE2)-dependent activated mammary fibroblast within the involuting mammary gland that displays protumorigenic, immunosuppressive activity, identifying fibroblasts as potential targets for the prevention and treatment of postpartum breast cancer.

Mammary Epithelial Cells Treated Concurrently with TGF-α and TGF-β Exhibit Enhanced Proliferation and Death

Transforming growth factor-α (TGF-α) stimulates while TGF-β inhibits mammary epithelial cell growth, suggesting that when cells are treated concurrently with the growth factors their combined effects would result in no net growth. However, combined treatments stimulate proliferation and cellular transformation in several cell lines. The objective of this paper was to describe the effect of long-term (6 days) concurrent TGF-α and TGF-β treatment on normal mammary epithelial cell growth pattern, morphology, and gene expression. Growth curve analysis showed that TGF-α enhanced while TGF-β suppressed growth rate until Day 4, when cells entered lag phase. However, cells treated concurrently with both growth factors exhibited a dichotomous pattern of growth marked by growth and death phases (with no intermittent lag phase). These changes in growth patterns were due to a marked induction of cell death from Day 2 (16.5%) to Day 4 (89.5%), resulting in the transition from growth to death phases, even though the combined treated cultures had significantly more ( P < 0.05) cells in S phase on Day 4. TGF-β stimulated epithelial to mesenchyme transdifferentiation (EMT) in the presence of TGF-α, as characterized by increased expression of fibronectin and changes in TGF-β receptor binding. Expression patterns of genes that regulate the cell cycle showed significant interaction between treatment and days, with TGF-β overriding TGF-α–stimulated effects on gene expression. Overall, the combined treatments were marked by enhanced rates of cellular proliferation, death, and trans-differentiation, behaviors reminiscent of breast tumors, and thus this system may serve as a good model to study breast tumorigenesis.

Mammary epithelial cell phagocytosis downstream of TGF-β3 is characterized by adherens junction reorganization

After weaning, during mammary gland involution, milk-producing mammary epithelial cells undergo apoptosis. Effective clearance of these dying cells is essential, as persistent apoptotic cells have a negative impact on gland homeostasis, future lactation and cancer susceptibility. In mice, apoptotic cells are cleared by the neighboring epithelium, yet little is known about how mammary epithelial cells become phagocytic or whether this function is conserved between species. Here we use a rat model of weaning-induced involution and involuting breast tissue from women, to demonstrate apoptotic cells within luminal epithelial cells and epithelial expression of the scavenger mannose receptor, suggesting conservation of phagocytosis by epithelial cells. In the rat, epithelial transforming growth factor-β (TGF-β) signaling is increased during involution, a pathway known to promote phagocytic capability. To test whether TGF-β enhances the phagocytic ability of mammary epithelial cells, non-transformed murine mammary epithelial EpH4 cells were cultured to achieve tight junction impermeability, such as occurs during lactation. TGF-β3 treatment promoted loss of tight junction impermeability, reorganization and cleavage of the adherens junction protein E-cadherin (E-cad), and phagocytosis. Phagocytosis correlated with junction disruption, suggesting junction reorganization is necessary for phagocytosis by epithelial cells. Supporting this hypothesis, epithelial cell E-cad reorganization and cleavage were observed in rat and human involuting mammary glands. Further, in the rat, E-cad cleavage correlated with increased γ-secretase activity and β-catenin nuclear localization. In vitro, pharmacologic inhibitors of γ-secretase or β-catenin reduced the effect of TGF-β3 on phagocytosis to near baseline levels. However, β-catenin signaling through LiCl treatment did not enhance phagocytic capacity, suggesting a model in which both reorganization of cell junctions and β-catenin signaling contribute to phagocytosis downstream of TGF-β3. Our data provide insight into how mammary epithelial cells contribute to apoptotic cell clearance, and in light of the negative consequences of impaired apoptotic cell clearance during involution, may shed light on involution-associated breast pathologies.

Elevated CXCL1 expression in breast cancer stroma predicts poor prognosis and is inversely associated with expression of TGF-β signaling proteins

Background

CXCL1 is a chemotactic cytokine shown to regulate breast cancer progression and chemo-resistance. However, the prognostic significance of CXCL1 expression in breast cancer has not been fully characterized. Fibroblasts are important cellular components of the breast tumor microenvironment, and recent studies indicate that this cell type is a potential source of CXCL1 expression in breast tumors. The goal of this study was to further characterize the expression patterns of CXCL1 in breast cancer stroma, determine the prognostic significance of stromal CXCL1 expression, and identify factors affecting stromal CXCL1 expression.

Methods

Stromal CXCL1 protein expression was analyzed in 54 normal and 83 breast carcinomas by immunohistochemistry staining. RNA expression of CXCL1 in breast cancer stroma was analyzed through data mining in http://www.Oncomine.org. The relationships between CXCL1 expression and prognostic factors were analyzed by univariate analysis. Co-immunofluorescence staining for CXCL1, α-Smooth Muscle Actin (α-SMA) and Fibroblast Specific Protein 1 (FSP1) expression was performed to analyze expression of CXCL1 in fibroblasts. By candidate profiling, the TGF-β signaling pathway was identified as a regulator of CXCL1 expression in fibroblasts. Expression of TGF-β and SMAD gene products were analyzed by immunohistochemistry and data mining analysis. The relationships between stromal CXCL1 and TGF-β signaling components were analyzed by univariate analysis. Carcinoma associated fibroblasts isolated from MMTV-PyVmT mammary tumors were treated with recombinant TGF-β and analyzed for CXCL1 promoter activity by luciferase assay, and protein secretion by ELISA.

Results

Elevated CXCL1 expression in breast cancer stroma correlated with tumor grade, disease recurrence and decreased patient survival. By co-immunofluorescence staining, CXCL1 expression overlapped with expression of α-SMA and FSP1 proteins. Expression of stromal CXCL1 protein expression inversely correlated with expression of TGF-β signaling components. Treatment of fibroblasts with TGF-β suppressed CXCL1 secretion and promoter activity.

Conclusions

Increased CXCL1 expression in breast cancer stroma correlates with poor patient prognosis. Furthermore, CXCL1 expression is localized to α-SMA and FSP1 positive fibroblasts, and is negatively regulated by TGF-β signaling. These studies indicate that decreased TGF-β signaling in carcinoma associated fibroblasts enhances CXCL1 expression in fibroblasts, which could contribute to breast cancer progression.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-781) contains supplementary material, which is available to authorized users.

Integrin αvβ3 drives slug activation and stemness in the pregnant and neoplastic mammary gland

Although integrin αvβ3 is linked to cancer progression, its role in epithelial development is unclear. Here, we show that αvβ3 plays a critical role in adult mammary stem cells (MaSCs) during pregnancy. Whereas αvβ3 is a luminal progenitor marker in the virgin gland, we noted increased αvβ3 expression in MaSCs at midpregnancy. Accordingly, mice lacking αvβ3 or expressing a signaling-deficient receptor showed defective mammary gland morphogenesis during pregnancy. This was associated with decreased MaSC expansion, clonogenicity, and expression of Slug, a master regulator of MaSCs. Surprisingly, αvβ3-deficient mice displayed normal development of the virgin gland with no effect on luminal progenitors. Transforming growth factor β2 (TGF-β2) induced αvβ3 expression, enhancing Slug nuclear accumulation and MaSC clonogenicity. In human breast cancer cells, αvβ3 was necessary and sufficient for Slug activation, tumorsphere formation, and tumor initiation. Thus, pregnancy-associated MaSCs require a TGF-β2/αvβ3/Slug pathway, which may contribute to breast cancer progression and stemness.

Attenuated transforming growth factor beta signaling promotes metastasis in a model of HER2 mammary carcinogenesis

Introduction

Transforming growth factor beta (TGFβ) plays a major role in the regulation of tumor initiation, progression, and metastasis. It is depended on the type II TGFβ receptor (TβRII) for signaling. Previously, we have shown that deletion of TβRII in mammary epithelial of MMTV-PyMT mice results in shortened tumor latency and increased lung metastases. However, active TGFβ signaling increased the number of circulating tumor cells and metastases in MMTV-Neu mice. In the current study, we describe a newly discovered connection between attenuated TGFβ signaling and human epidermal growth factor receptor 2 (HER2) signaling in mammary tumor progression.

Methods

All studies were performed on MMTV-Neu mice with and without dominant-negative TβRII (DNIIR) in mammary epithelium. Mammary tumors were analyzed by flow cytometry, immunohistochemistry, and immunofluorescence staining. The levels of secreted proteins were measured by enzyme-linked immunosorbent assay. Whole-lung mount staining was used to quantitate lung metastasis. The Cancer Genome Atlas (TCGA) datasets were used to determine the relevance of our findings to human breast cancer.

Results

Attenuated TGFβ signaling led to a delay tumor onset, but increased the number of metastases in MMTVNeu/DNIIR mice. The DNIIR tumors were characterized by increased vasculogenesis, vessel leakage, and increased expression of vascular endothelial growth factor (VEGF). During DNIIR tumor progression, both the levels of CXCL1/5 and the number of CD11b+Gr1+ cells and T cells decreased. Analysis of TCGA datasets demonstrated a significant negative correlation between TGFBR2 and VEGF genes expression. Higher VEGFA expression correlated with shorter distant metastasis-free survival only in HER2+ patients with no differences in HER2-, estrogen receptor +/- or progesterone receptor +/- breast cancer patients.

Conclusion

Our studies provide insights into a novel mechanism by which epithelial TGFβ signaling modulates the tumor microenvironment, and by which it is involved in lung metastasis in HER2+ breast cancer patients. The effects of pharmacological targeting of the TGFβ pathway in vivo during tumor progression remain controversial. The targeting of TGFβ signaling should be a viable option, but because VEGF has a protumorigenic effect on HER2+ tumors, the targeting of this protein could be considered when it is associated with attenuated TGFβ signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0425-7) contains supplementary material, which is available to authorized users.

The microRNA 424/503 cluster reduces CDC25A expression during cell cycle arrest imposed by transforming growth factor β in mammary epithelial cells

Recently, we demonstrated that the microRNA 424(322)/503 [miR-424(322)/503] cluster is transcriptionally controlled by transforming growth factor β (TGF-β) in the mammary epithelium. Induction of this microRNA cluster impacts mammary epithelium fate by regulating apoptosis and insulin-like growth factor 1 (IGF1) signaling. Here, we expanded our finding to demonstrate that miR-424(322)/503 is an integral component of the cell cycle arrest mediated by TGF-β. Mechanistically, we showed that after TGF-β exposure, increased levels of miR-424(322)/503 reduce the expression of the cell cycle regulator CDC25A. miR-424(322)/503-dependent posttranscriptional downregulation of CDC25A cooperates with previously described transcriptional repression of the CDC25A promoter and proteasome-mediated degradation to reduce the levels of CDC25A expression and to induce cell cycle arrest. We also provide evidence that the TGF-β/miR-424(322)/503 axis is part of the mechanism that regulates the proliferation of hormone receptor-positive (HR(+)) mammary epithelial cells in vivo.

Concerted loss of TGFβ-mediated proliferation control and E-cadherin disrupts epithelial homeostasis and causes oral squamous cell carcinoma

Although the etiology of squamous cell carcinomas of the oral mucosa is well understood, the cellular origin and the exact molecular mechanisms leading to their formation are not. Previously, we observed the coordinated loss of E-cadherin (CDH1) and transforming growth factor beta receptor II (TGFBR2) in esophageal squamous tumors. To investigate if the coordinated loss of Cdh1 and Tgfbr2 is sufficient to induce tumorigenesis in vivo, we developed two mouse models targeting ablation of both genes constitutively or inducibly in the oral-esophageal epithelium. We show that the loss of both Cdh1 and Tgfbr2 in both models is sufficient to induce squamous cell carcinomas with animals succumbing to the invasive disease by 18 months of age. Advanced tumors have the ability to invade regional lymph nodes and to establish distant pulmonary metastasis. The mouse tumors showed molecular characteristics of human tumors such as overexpression of Cyclin D1. We addressed the question whether TGFβ signaling may target known stem cell markers and thereby influence tumorigenesis. From our mouse and human models, we conclude that TGFβ signaling regulates key aspects of stemness and quiescence in vitro and in vivo. This provides a new explanation for the importance of TGFβ in mucosal homeostasis.

Cytokine networks that mediate epithelial cell-macrophage crosstalk in the mammary gland: implications for development and cancer

Dynamic interactions between the hormone responsive mammary gland epithelium and surrounding stromal macrophage populations are critical for normal development and function of the mammary gland. Macrophages are versatile cells capable of diverse roles in mammary gland development and maintenance of homeostasis, and their function is highly dependent on signals within the local cytokine microenvironment. The mammary epithelium secretes a number of cytokines, including colony stimulating factor 1 (CSF1), transforming growth factor beta 1 (TGFB1), and chemokine ligand 2 (CCL2) that affect the abundance, phenotype and function of macrophages. However, aberrations in these interactions have been found to increase the risk of tumour formation, and utilisation of stromal macrophage support by tumours can increase the invasive and metastatic potential of the cancer. Studies utilising genetically modified mouse models have shed light on the significance of epithelial cell-macrophage crosstalk, and the cytokines that mediate this communication, in mammary gland development and tumourigenesis. This article reviews the current status of our understanding of the roles of epithelial cell-derived cytokines in mammary gland development and cancer, with a focus on the crosstalk between epithelial cells and the local macrophage population.

Two faces of TGF-beta1 in breast cancer

Breast cancer (BC) is potentially life-threatening malignancy that still causes high mortality among women. Scientific research in this field is focused on deeper understanding of pathogenesis and progressing of BC, in order to develop relevant diagnosis and improve therapeutic treatment. Multifunctional cytokine TGF- β 1 is one of many factors that have a direct influence on BC pathophysiology. Expression of TGF- β 1, induction of canonical and noncanonical signaling pathways, and mutations in genes encoding TGF- β 1 and its receptors are correlated with oncogenic activity of this cytokine. In early stages of BC this cytokine inhibits epithelial cell cycle progression and promotes apoptosis, showing tumor suppressive effects. However, in late stages, TGF- β 1 is linked with increased tumor progression, higher cell motility, cancer invasiveness, and metastasis. It is also involved in cancer microenvironment modification and promotion of epithelial to mesenchymal transition (EMT). This review summarizes the current knowledge on the phenomenon called "TGF- β 1 paradox", showing that better understanding of TGF- β 1 functions can be a step towards development of new therapeutic approaches. According to current knowledge several drugs against TGF- β 1 have been developed and are either in nonclinical or in early stages of clinical investigation.

High serum transforming growth factor beta 1 (TGFB1) level predicts better survival in breast cancer

The transforming growth factor beta 1 (TGFB1) is a regulatory cytokine with both tumor suppressor and tumor-promoting effects in breast cancer (BC) cell lines and tissue. Data about level of circulating TGFB1 and its prognostic significance in BC patients is conflicting. The objective of this study is to determine the clinical significance of the serum TGFB1 levels in BC patients. We enrolled 96 female patients with histopathologically diagnosed BC who did not receive chemotherapy (CT) or radiotherapy. Serum TGFB1 levels were measured by ELISA method and compared with 30 healthy controls. The mean serum TGFB1 level of BC patients was significantly higher than controls (0.08 vs. 0.04 ng/ml, p < 0.001). There was no significant difference according to known disease-related clinicopathological or laboratory parameters. Serum TGFB1 level had a significant impact on overall survival in both univariate (p = 0.01) and multivariate analysis (p = 0.013). Serum TGFB1 level is elevated in BC patients and has a favorable prognostic value. However, it has no predictive role on CT response.

TGF-β: duality of function between tumor prevention and carcinogenesis

Several mechanisms underlying tumor progression have remained elusive, particularly in relation to transforming growth factor beta (TGF-β). Although TGF-β initially inhibits epithelial growth, it appears to promote the progression of advanced tumors. Defects in normal TGF-β pathways partially explain this paradox, which can lead to a cascade of downstream events that drive multiple oncogenic pathways, manifesting as several key features of tumorigenesis (uncontrolled proliferation, loss of apoptosis, epithelial-to-mesenchymal transition, sustained angiogenesis, evasion of immune surveillance, and metastasis). Understanding the mechanisms of TGF-β dysregulation will likely reveal novel points of convergence between TGF-β and other pathways that can be specifically targeted for therapy.

The miR-424(322)/503 cluster orchestrates remodeling of the epithelium in the involuting mammary gland

The mammary gland undergoes continuous remodeling. Llobet-Navas et al. identify the microRNA cluster miR-424(322)/503 as an important regulator of epithelial involution after pregnancy. TGF-β regulates the expression of this miR cluster, which in turn targets BCL-2 and IGF1R. This work suggests a model in which activation of the TGF-β pathway after weaning induces the transcription of the miR-424(322)/503 cluster to down-regulate the expression of key genes.

The mammary gland is a very dynamic organ that undergoes continuous remodeling. The critical regulators of this process are not fully understood. Here we identify the microRNA cluster miR-424(322)/503 as an important regulator of epithelial involution after pregnancy. Through the generation of a knockout mouse model, we found that regression of the secretory acini of the mammary gland was compromised in the absence of miR-424(322)/503. Mechanistically, we show that miR-424(322)/503 orchestrates cell life and death decisions by targeting BCL-2 and IGF1R (insulin growth factor-1 receptor). Furthermore, we demonstrate that the expression of this microRNA cluster is regulated by TGF-β, a well-characterized regulator of mammary involution. Overall, our data suggest a model in which activation of the TGF-β pathway after weaning induces the transcription of miR-424(322)/503, which in turn down-regulates the expression of key genes. Here, we unveil a previously unknown, multilayered regulation of epithelial tissue remodeling coordinated by the microRNA cluster miR-424(322)/503.

Dichloroacetate modulates cytokines toward T helper 1 function via induction of the interleukin-12-interferon-γ pathway

BACKGROUND

Dichloroacetate (DCA) is one of the new, promising anticancer drugs. DCA restores normal mitochondrial function and enables cancer cells to undergo apoptosis. In addition, DCA was found to modulate certain signaling pathways involving some transcription factors. The latter encouraged us to study DCA immunomodulatory activity on cytokines and their association with increasing DCA cancer cell cytotoxicity.

METHODS AND RESULTS

Cell viability assay was used to determine the effect of different concentrations of DCA on the survival of 3-methylcholanthrene (MCA) fibrosarcoma cell line. DCA decreased the percent survival of MCA fibrosarcoma in a dose-dependent manner (P<0.01). Furthermore, this percent survival was further reduced when MCA fibrosarcoma cells were cocultured with mouse splenocytes. The latter was observed at 10 mM DCA (P<0.01), and the inhibitory concentration at 50% dropped from 23 mM to 15.6 mM DCA (P<0.05). In addition, DCA significantly enhanced interferon (IFN)-γ but not interleukin (IL)-17 production levels in unstimulated and stimulated mouse spleen cells. To investigate the mechanism of DCA on IFN-γ production, DCA cytokine modulatory effect was tested on unstimulated macrophages, T-cells, and natural killer cells. DCA significantly increased IL-12 production from macrophages but did not modulate the production of IFN-γ from either T-cells or natural killer cells. Moreover, the DCA-enhancing effect on IFN-γ production was reversed by anti-IL-12 antibody. Also, the DCA cytokine modulatory effect was tested in vivo after inducing mouse skin inflammation using phorbol 12-myristate 13-acetate (PMA). DCA restored PMA-lowered IFN-γ and IL-12 levels and normalized PMA-increased transforming growth factor-β level, but it inhibited IL-10 levels even further (P<0.05).

CONCLUSION

DCA has immunomodulatory activity, mainly via activation of the IL-12-IFN-γ pathway and is able to modulate cytokines toward T helper 1 lymphocyte function. These DCA immunomodulatory effects are promising and further investigations are required to develop protocols for its use in cancer treatment.

Role of TGF-β in breast cancer bone metastases

Breast cancer is the most prevalent cancer among females worldwide leading to approximately 350,000 deaths each year. It has long been known that cancers preferentially metastasize to particular organs, and bone metastases occur in ~70% of patients with advanced breast cancer. Breast cancer bone metastases are predominantly osteolytic and accompanied by increased fracture risk, pain, nerve compression and hypercalcemia, causing severe morbidity. In the bone matrix, transforming growth factor-β (TGF-β) is one of the most abundant growth factors, which is released in active form upon tumor-induced osteoclastic bone resorption. TGF-β, in turn, stimulates bone metastatic tumor cells to secrete factors that further drive osteolytic bone destruction adjacent to the tumor. Thus, TGF-β is a crucial factor responsible for driving the feed-forward vicious cycle of cancer growth in bone. Moreover, TGF-β activates epithelial-to-mesenchymal transition, increases tumor cell invasiveness and angiogenesis and induces immunosuppression. Blocking the TGF-β signaling pathway to interrupt this vicious cycle between breast cancer and bone offers a promising target for therapeutic intervention to decrease skeletal metastasis. This review will describe the role of TGF-β in breast cancer and bone metastasis, and pre-clinical and clinical data will be evaluated for the potential use of TGF-β inhibitors in clinical practice to treat breast cancer bone metastases.

Lack of transforming growth factor-β signaling promotes collective cancer cell invasion through tumor-stromal crosstalk

INTRODUCTION

Transforming growth factor beta (TGF-β) has a dual role during tumor progression, initially as a suppressor and then as a promoter. Epithelial TGF-β signaling regulates fibroblast recruitment and activation. Concurrently, TGF-β signaling in stromal fibroblasts suppresses tumorigenesis in adjacent epithelia, while its ablation potentiates tumor formation. Much is known about the contribution of TGF-β signaling to tumorigenesis, yet the role of TGF-β in epithelial-stromal migration during tumor progression is poorly understood. We hypothesize that TGF-β is a critical regulator of tumor-stromal interactions that promote mammary tumor cell migration and invasion.

METHODS

Fluorescently labeled murine mammary carcinoma cells, isolated from either MMTV-PyVmT transforming growth factor-beta receptor II knockout (TβRII KO) or TβRIIfl/fl control mice, were combined with mammary fibroblasts and xenografted onto the chicken embryo chorioallantoic membrane. These combinatorial xenografts were used as a model to study epithelial-stromal crosstalk. Intravital imaging of migration was monitored ex ovo, and metastasis was investigated in ovo. Epithelial RNA from in ovo tumors was isolated by laser capture microdissection and analyzed to identify gene expression changes in response to TGF-β signaling loss.

RESULTS

Intravital microscopy of xenografts revealed that mammary fibroblasts promoted two migratory phenotypes dependent on epithelial TGF-β signaling: single cell/strand migration or collective migration. At epithelial-stromal boundaries, single cell/strand migration of TβRIIfl/fl carcinoma cells was characterized by expression of α-smooth muscle actin and vimentin, while collective migration of TβRII KO carcinoma cells was identified by E-cadherin+/p120+/β-catenin+ clusters. TβRII KO tumors also exhibited a twofold greater metastasis than TβRIIfl/fl tumors, attributed to enhanced extravasation ability. In TβRII KO tumor epithelium compared with TβRIIfl/fl epithelium, Igfbp4 and Tspan13 expression was upregulated while Col1α2, Bmp7, Gng11, Vcan, Tmeff1, and Dsc2 expression was downregulated. Immunoblotting and quantitative PCR analyses on cultured cells validated these targets and correlated Tmeff1 expression with disease progression of TGF-β-insensitive mammary cancer.

CONCLUSION

Fibroblast-stimulated carcinoma cells utilize TGF-β signaling to drive single cell/strand migration but migrate collectively in the absence of TGF-β signaling. These migration patterns involve the signaling regulation of several epithelial-to-mesenchymal transition pathways. Our findings concerning TGF-β signaling in epithelial-stromal interactions are important in identifying migratory mechanisms that can be targeted as recourse for breast cancer treatment.

TGF-β of lung cancer microenvironment upregulates B7H1 and GITRL expression in dendritic cells and is associated with regulatory T cell generation

The effects of TGF-β on dendritic cells (DCs) on the tumor microenvironment are not well understood. We report, here, the establishment of an in vitro lung cancer microenvironment by co-incubation of seminaphtharhodafluor (SNARF) labeled Lewis lung cancer (LLC) cells, carboxyfluorescein succinimidyl ester (CFSE) labeled fibroblasts and 4-chloromethyl-7-hydroxycoumarin (CMHC) labeled DCs. Raw 264.7, EL4 and NCI-H446 cells were able to synthesize TGF-β which was determined by flow cyto-metry and western blotting, respectively. Furthermore, TGF-β efficiently increased regulatory T-cell (Treg) expansion and upregulated DC B7H1 and GITRL expression. TGF-β and the co-incubation of LLC cells, fibroblasts with DCs could augment the expression of B7H1 and GITRL molecules of DCs. The data presented here indicate that the B7H1 and GITRL molecules may play an important role in TGF-β-induced Treg expansion of lung cancer microenvironment.

Transcriptional and post-transcriptional regulation in TGF-β-mediated epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a crucial event in appropriate embryonic development as well as in wound healing, tissue repair and cancer progression in adult tissues. EMT endows cells with migratory and invasive properties, inhibits apoptosis and senescence, contributes to immunosuppression and induces stress resistance and stem cell properties. Many secreted polypeptide factors act in a sequential or cooperative manner to elicit EMT. Transforming growth factor (TGF)-β can initiate and maintain EMT by activating intracellular signalling pathways. Recent studies have provided new insights into molecular mechanisms by which TGF-β mediates changes in transcription of EMT regulators and EMT marker proteins, as well as changes in alternative splicing controlled by epithelial splicing regulatory proteins 1 and 2. Here, we present some of the emerging molecular mechanisms that mediate EMT upon exposure to TGF-β.

Seed, soil and secreted hormones: potential interactions of breast cancer cells with their endocrine/paracrine microenvironment and implications for treatment with bisphosphonates

The process of formation of metastasis is undoubtedly inefficient, with the majority of disseminated tumour cells perishing in their metastatic environment. Their ability to survive is determined by their intrinsic abilities, with emerging evidence of the importance of cancer stem cells possessing self propagating potential, but also the interaction with the premetastatic niche, which may either help or hinder their formation into micrometastasis, thus influencing recurrence and survival in breast cancer patients. Use of the bone targeted agents bisphosphonates in the adjuvant setting has been extensively studied in large clinical trials, and demonstrated an interesting interplay with the endocrine microenvironment, with postmenopausal women or premenopausal women receiving ovarian suppression therapy gaining a survival advantage compared to pre/perimenopausal women. The interaction between the endocrine hormones and the paracrine TGFβ growth factors may provide an explanation for the differences seen according to ovarian function in the response to bisphosphonates. In this review the evidence of interplay between ovarian endocrine hormones, TGFβ paracrine growth factors and bisphosphonates will be presented, and subsequent influence on breast cancer cells in the bone pre-metastatic niche hypothesised.

The complexities of TGF-β action during mammary and squamous cell carcinogenesis

Many advanced tumors produce excess amounts of Transforming Growth Factor-β (TGF-β), which is a potent growth inhibitor of normal epithelial cells. However, in tumors its homeostatic action on cells can be diverted along several alternative pathways. Thus, TGF-β signaling has been reported to elicit a preventative or tumor suppressive effect during the earlier stages of tumorigenesis, but later in tumor development, when carcinoma cells become refractory to TGF-β-mediated growth inhibition, response to TGF-β signaling elicits predominantly tumor progressing effects. This is not a simple switch from suppression to progression, but more like a rheostat, involving multiple complementary and antagonizing activities that slowly tip the balance from one to the other. This review will focus on the multiple activities of TGF-β in regulation of two epithelial tumor types, namely squamous cell carcinoma and breast cancer. Basic findings in current mouse models of cancer are presented, as well as a discussion of the complicating issue of outcome of altered TGFβ signaling depending on genetic variability between mouse strains. This review also discusses the role TGF-β within the tumor microenvironment particularly its ability to polarize the microenvironment towards a pro-tumorigenic milieu.

TGF-β in the Bone Microenvironment: Role in Breast Cancer Metastases

Breast cancer is the most prevalent cancer among females worldwide. It has long been known that cancers preferentially metastasize to particular organs, and bone metastases occur in ∼70% of patients with advanced breast cancer. Breast cancer bone metastases are predominantly osteolytic and accompanied by bone destruction, bone fractures, pain, and hypercalcemia, causing severe morbidity and hospitalization. In the bone matrix, transforming growth factor-β (TGF-β) is one of the most abundant growth factors, which is released in active form upon tumor-induced osteoclastic bone resorption. TGF-β, in turn, stimulates bone metastatic cells to secrete factors that further drive osteolytic destruction of the bone adjacent to the tumor, categorizing TGF-β as a crucial factor responsible for driving the feed-forward vicious cycle of cancer growth in bone. Moreover, TGF-β activates epithelial-to-mesenchymal transition, increases tumor cell invasiveness and angiogenesis and induces immunosuppression. Blocking the TGF-β signaling pathway to interrupt this vicious cycle between breast cancer and bone offers a promising target for therapeutic intervention to decrease skeletal metastasis. This review will describe the role of TGF-β in breast cancer and bone metastasis, and pre-clinical and clinical data will be evaluated for the potential use of TGF-β inhibitors in clinical practice to treat breast cancer bone metastases.

IFN-γ, IL-17 and TGF-β involvement in shaping the tumor microenvironment: The significance of modulating such cytokines in treating malignant solid tumors

Multiple innate and adaptive immune effector cells and molecules partake in the recognition and destruction of cancer cells to protect against growing tumors, a concept that is known as cancer immunosurveillance. Unfortunately, cancer cells are capable of avoiding this process by immunoselection of poorly immunogenic tumor cells variants along with subversion of the immune system and thus shaping both the tumor and its microenvironment. Cytokines represent part of the complex pattern of the immune response which can assist the development of cancer as well as to eliminate it. Simultaneously, a large number of cytokines may be involved in the complex interactions between host and tumor cells where this dynamic cross-talk, between tumors and the immune system, can either regulate tumor growth or tumor growth, invasion and metastasis take place. In this review, we are stressing on the interface between infiltrated immune cells and tumor cells with the emphasis on the bidirectional activities of specific cytokines: IFN-γ, TGF-β and IL-17 within the tumor microenvironment and their role in shaping it. In addition, the significance of modulating such cytokines in favor of anti-tumor response is discussed and merits the use of mixture of targeted modulators to overcome the network complexity of cytokines in the tumor microenvironment.

Transforming growth factor-β signaling in tumor initiation, progression and therapy in breast cancer: an update

Transforming growth factor-β (TGF-β) is a ubiquitous cytokine playing an essential role in cell proliferation, differentiation, apoptosis, adhesion and invasion, as well as in cellular microenvironment. In malignant diseases, TGF-β signaling features a growth inhibitory effect at an early stage but aggressive oncogenic activity at the advanced malignant state. Here, we update the current understanding of TGF-β signaling in cancer development and progression with a focus on breast cancer. We also review the current approaches of TGF-β signaling-targeted therapeutics for human malignancies.

The role of activin in mammary gland development and oncogenesis

TGFβ contributes to mammary gland development and has paradoxical roles in breast cancer because it has both tumor suppressor and tumor promoter activity. Another member of the TGFβ superfamily, activin, also has roles in the developing mammary gland, but these functions, and the role of activin in breast cancer, are not well characterized. TGFβ and activin share the same intracellular signaling pathways, but divergence in their signaling pathways are suggested. The purpose of this review is to compare the spatial and temporal expression of TGFβ and activin during mammary gland development, with consideration given to their functions during each developmental period. We also review the contributions of TGFβ and activin to breast cancer resistance and susceptibility. Finally, we consider the systemic contributions of activin in regulating obesity and diabetes; and the impact this regulation has on breast cancer. Elevated levels of activin in serum during pregnancy and its influence on pregnancy associated breast cancer are also considered. We conclude that evidence demonstrates that activin has tumor suppressing potential, without definitive indication of tumor promoting activity in the mammary gland, making it a good target for development of therapeutics.

Role of TGF-β and the tumor microenvironment during mammary tumorigenesis

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that functions to inhibit mammary tumorigenesis by directly inducing mammary epithelial cells (MECs) to undergo cell cycle arrest or apoptosis, and to secrete a variety of cytokines, growth factors, and extracellular matrix proteins that maintain cell and tissue homeostasis. Genetic and epigenetic events that transpire during mammary tumorigenesis typically inactivate the tumor suppressing activities of TGF-beta and ultimately confer this cytokine with tumor promoting activities, including the ability to stimulate breast cancer invasion, metastasis, angiogenesis, and evasion from the immune system. This dramatic conversion in TGF-beta function is known as the "TGF-beta paradox" and reflects a variety of dynamic alterations that occur not only within the developing mammary carcinoma, but also within the cellular and structural composition of its accompanying tumor microenvironment. Recent studies have begun to elucidate the critical importance of mammary tumor microenvironments in manifesting the TGF-beta paradox and influencing the response of developing mammary carcinomas to TGF-beta. Here we highlight recent findings demonstrating the essential function of tumor microenvironments in regulating the oncogenic activities of TGF-beta and its stimulation of metastatic progression during mammary tumorigenesis.

TGF-beta biology in mammary development and breast cancer

Transforming growth factor-β1 (TGF-β) was first implicated in mammary epithelial development by Daniel and Silberstein in 1987 and in breast cancer cells and hormone resistance by Lippman and colleagues in 1988. TGF-β is critically important for mammary morphogenesis and secretory function through specific regulation of epithelial proliferation, apoptosis, and extracellular matrix. Differential TGF-β effects on distinct cell types are compounded by regulation at multiple levels and the influence of context on cellular responses. Studies using controlled expression and conditional-deletion mouse models underscore the complexity of TGF-β biology across the cycle of mammary development and differentiation. Early loss of TGF-β growth regulation in breast cancer evolves into fundamental deregulation that mediates cell interactions and phenotypes driving invasive disease. Two outstanding issues are to understand the mechanisms of biological control in situ and the circumstances by which TGF-β regulation is subverted in neoplastic progression.

SnoN in mammalian development, function and diseases

SnoN (Ski-novel protein) was discovered as a nuclear proto-oncogene on the basis of its ability to induce transformation of chicken and quail embryonic fibroblasts. As a crucial negative regulator of transforming growth factor-β (TGF-β) signaling and also an activator of p53, it plays an important role in regulating cell proliferation, senescence, apoptosis, and differentiation. Recent studies of its expression patterns and functions in mouse models and mammalian cells have revealed important functions of SnoN in normal epithelial development and tumorigenesis. Evidence suggests that SnoN has both pro-oncogenic and anti-oncogenic functions by modulating multiple signaling pathways. These studies suggest that SnoN may have broad functions in the development and homeostasis of embryonic and postnatal tissues.

Cathepsin B is the driving force of esophageal cell invasion in a fibroblast-dependent manner

Esophageal cancer, which frequently exhibits coordinated loss of E-cadherin (Ecad) and transforming growth factor beta (TGFbeta) receptor II (TbetaRII), has a high mortality rate. In a three-dimensional organotypic culture model system, esophageal keratinocytes expressing dominant-negative mutant versions of both Ecad and TbetaRII (ECdnT) invade into the underlying matrix embedded with fibroblasts. We also find that cathepsin B induction is necessary for fibroblast-mediated invasion. Furthermore, the ECdnT cells in this physiological context activate fibroblasts through the secretion of TGFbeta1, which, in turn, is activated by cathepsin B. These results suggest that the interplay between the epithelial compartment and the surrounding microenvironment is crucial to invasion into the extracellular matrix.

Transforming growth factor-beta regulator SnoN modulates mammary gland branching morphogenesis, postlactational involution, and mammary tumorigenesis

SnoN is an important negative regulator of transforming growth factor-beta (TGF-beta) signaling that was originally identified as a transforming oncogene in chicken embryonic fibroblasts. Both pro-oncogenic and antioncogenic activities of SnoN have been reported, but its function in normal epithelial cells has not been defined. In the mouse mammary gland, SnoN is expressed at relatively low levels, but it is transiently upregulated at late gestation before being downregulated during lactation and early involution. To assess the effects of elevated levels of SnoN, we generated transgenic mice expressing a SnoN fragment under the control of the mouse mammary tumor virus promoter. In this model system, SnoN elevation increased side-branching and lobular-alveolar proliferation in virgin glands, while accelerating involution in postlactation glands. Increased proliferation stimulated by SnoN was insufficient to induce mammary tumorigenesis. In contrast, elevated levels of SnoN cooperated with polyoma middle T antigen to accelerate the formation of aggressive multifocal adenocarcinomas and to increase the formation of pulmonary metastases. Our studies define functions of SnoN in mammary epithelial cell proliferation and involution, and provide the first in vivo evidence of a pro-oncogenic role for SnoN in mammalian tumorigenesis.

Key signalling nodes in mammary gland development and cancer. Mitogen-activated protein kinase signalling in experimental models of breast cancer progression and in mammary gland development

Seven classes of mitogen-activated protein kinase (MAPK) intracellular signalling cascades exist, four of which are implicated in breast disease and function in mammary epithelial cells. These are the extracellular regulated kinase (ERK)1/2 pathway, the ERK5 pathway, the p38 pathway and the c-Jun N-terminal kinase (JNK) pathway. In some forms of human breast cancer and in many experimental models of breast cancer progression, signalling through the ERK1/2 pathway, in particular, has been implicated as being important. We review the influence of ERK1/2 activity on the organised three-dimensional association of mammary epithelial cells, and in models of breast cancer cell invasion. We assess the importance of epidermal growth factor receptor family signalling through ERK1/2 in models of breast cancer progression and the influence of ERK1/2 on its substrate, the oestrogen receptor, in this context. In parallel, we consider the importance of these MAPK-centred signalling cascades during the cycle of mammary gland development. Although less extensively studied, we highlight the instances of signalling through the p38, JNK and ERK5 pathways involved in breast cancer progression and mammary gland development.

Transforming growth factor beta (TGF-beta) and inflammation in cancer

The transforming growth factor beta (TGF-beta) has been studied with regard to the regulation of cell behavior for over three decades. A large body of research has been devoted to the regulation of epithelial cell and derivative carcinoma cell populations in vitro and in vivo. TGF-beta has been shown to inhibit epithelial cell cycle progression and promote apoptosis that together significantly contribute to the tumor suppressive role for TGF-beta during carcinoma initiation and progression. TGF-beta is also able to promote an epithelial to mesenchymal transition that has been associated with increased tumor cell motility, invasion and metastasis. However, it has now been shown that loss of carcinoma cell responsiveness to TGF-beta stimulation can also promote metastasis. Interestingly, enhanced metastasis in the absence of a carcinoma cell response to TGF-beta stimulation has been shown to involve increased chemokine production resulting in recruitment of pro-metastatic myeloid derived suppressor cell (MDSC) populations to the tumor microenvironment at the leading invasive edge. When present, MDSCs enhance angiogenesis, promote immune tolerance and provide matrix degrading enzymes that promote tumor progression and metastasis. Further, the recruitment of MDSC populations in this context likely enhances the classic role for TGF-beta in immune suppression since the MDSCs are an abundant source of TGF-beta production. Importantly, it is now clear that carcinoma-immune cell cross-talk initiated by TGF-beta signaling within the carcinoma cell is a significant determinant worth consideration when designing therapeutic strategies to manage tumor progression and metastasis.

Wnt signaling can substitute for estrogen to induce division of ERalpha-positive cells in a mouse mammary tumor model

The interaction of estrogen with the estrogen receptor (ER, principally ERalpha) induces growth of human breast tumor cells. In contrast, ERalpha-positive cells have been described as non-dividing cells in normal breast (though estrogen stimulation of ERalpha cells directs the division of neighboring cells). However, there is a small sub-population of cells in normal mammary tissue that are ERalpha-positive, that can divide, and therefore share this property with human breast tumor cells. In order to investigate their pattern of growth regulation, we measured the fraction of dividing ERalpha(+) cells during normal growth and compared that to glands stimulated by oncogenic Wnt effectors. First, we found there was no difference between the rate of division of ERalpha(+) cells and ERalpha(-) cells, whether the population was responding to estrogen or Wnt mitogens. The proportion of dividing ERalpha(+) mammary epithelial cells was increased (10x) in response to pregnancy, and similar increases were observed in response to ectopic Wnt signaling. We propose that Wnt signaling can substitute for estrogen to drive total population growth (that includes ERalpha(+) cells). Although the E-ERalpha-derived mitogenic response is situated in a minority of the luminal cells, and the Wnt-LRP5/6-derived mitogenic response is situated in a minority of basal cells, overall, the growth response of the mammary epithelial population is remarkably similar.

A functional connection between pRB and transforming growth factor beta in growth inhibition and mammary gland development

Transforming growth factor beta (TGF-beta) is a crucial mediator of breast development, and loss of TGF-beta-induced growth arrest is a hallmark of breast cancer. TGF-beta has been shown to inhibit cyclin-dependent kinase (CDK) activity, which leads to the accumulation of hypophosphorylated pRB. However, unlike other components of TGF-beta cytostatic signaling, pRB is thought to be dispensable for mammary development. Using gene-targeted mice carrying subtle missense changes in pRB (Rb1(DeltaL) and Rb1(NF)), we have discovered that pRB plays a critical role in mammary gland development. In particular, Rb1 mutant female mice have hyperplastic mammary epithelium and defects in nursing due to insensitivity to TGF-beta growth inhibition. In contrast with previous studies that highlighted the inhibition of cyclin/CDK activity by TGF-beta signaling, our experiments revealed that active transcriptional repression of E2F target genes by pRB downstream of CDKs is also a key component of TGF-beta cytostatic signaling. Taken together, our work demonstrates a unique functional connection between pRB and TGF-beta in growth control and mammary gland development.

The essential roles of TGFB1 in reproduction

Transforming growth factor beta 1 (TGFB1) is implicated as a key regulator of the development and cyclic remodelling characteristic of reproductive tissues. The physiological significance of TGFB1 in reproductive biology and fertility has been extensively examined in Tgfb1 null mutant mice. Genetic deficiency in TGFB1 causes perturbed functioning of the hypothalamic-pituitary-gonadal axis, inhibiting luteinising hormone (LH) synthesis and leading to downstream effects on testosterone production in males and estrous cycle abnormalities in females. Oocyte developmental incompetence, accompanied by early embryo arrest as well as altered pubertal mammary gland morphogenesis are observed. In addition to LH and testosterone deficiency, male Tgfb1 null mice demonstrate complete inability to mate with females, associated with failure to initiate and/or sustain successful penile intromission or ejaculation. These studies demonstrate the profound significance of TGFB1 in male and female reproductive physiology, and provide a foundation for exploring the significance of this cytokine in human infertility and sexual dysfunction.