Evidence for a stem cell hierarchy in the adult human breast

Early Steps of Mammary Stem Cell Transformation by Exogenous Signals; Effects of Bisphenol Endocrine Disrupting Chemicals and Bone Morphogenetic Proteins

Estrogens are major regulators of the mammary gland development, notably during puberty, via estrogen receptor (ER) activation, leading to the proliferation and differentiation of mammary cells. In addition to estrogens, the bone morphogenetic proteins (BMPs) family is involved in breast stem cell/progenitor commitment. However, these two pathways that synergistically contribute to the biology of the normal mammary gland have also been described to initiate and/or promote breast cancer development. In addition to intrinsic events, lifestyle habits and exposure to environmental cues are key risk factors for cancer in general, and especially for breast cancer. In the latter case, bisphenol A (BPA), an estrogen-mimetic compound, is a critical pollutant both in terms of the quantities released in our environment and of its known and speculated effects on mammary gland biology. In this review, we summarize the current knowledge on the actions of BMPs and estrogens in both normal mammary gland development and breast cancer initiation, dissemination, and resistance to treatment, focusing on the dysregulations of these processes by BPA but also by other bisphenols, including BPS and BPF, initially considered as safer alternatives to BPA.

Role of the Microenvironment in Regulating Normal and Cancer Stem Cell Activity: Implications for Breast Cancer Progression and Therapy Response

The epithelial cells in an adult woman’s breast tissue are continuously replaced throughout their reproductive life during pregnancy and estrus cycles. Such extensive epithelial cell turnover is governed by the primitive mammary stem cells (MaSCs) that proliferate and differentiate into bipotential and lineage-restricted progenitors that ultimately generate the mature breast epithelial cells. These cellular processes are orchestrated by tightly-regulated paracrine signals and crosstalk between breast epithelial cells and their tissue microenvironment. However, current evidence suggests that alterations to the communication between MaSCs, epithelial progenitors and their microenvironment plays an important role in breast carcinogenesis. In this article, we review the current knowledge regarding the role of the breast tissue microenvironment in regulating the special functions of normal and cancer stem cells. Understanding the crosstalk between MaSCs and their microenvironment will provide new insights into how an altered breast tissue microenvironment could contribute to breast cancer development, progression and therapy response and the implications of this for the development of novel therapeutic strategies to target cancer stem cells.

Cancer stem cells in breast and prostate: Fact or fiction?

Since the introduction of the cancer stem cell (CSC) hypothesis, accumulating evidence shows that most cancers present stem-like niches. However, therapies aimed at targeting this niche have not been as successful as expected. New evidence regarding CSCs hierarchy, similarities with normal tissue stem cells and cell plasticity might be key in understanding their role in cancer biology and how to efficiently eliminate them. In this Chapter, we discuss what is known in breast and prostate CSCs from their initial discoveries to the current therapeutic efforts in the field. Future challenges towards better CSC identification and isolation strategies will be key to shed light into how CSCs could accurately be targeted in combination to traditional therapies to ultimately prolong patient survival.

Application of the D492 Cell Lines to Explore Breast Morphogenesis, EMT and Cancer Progression in 3D Culture

The human female breast gland is composed of branching epithelial ducts that extend from the nipple towards the terminal duct lobular units (TDLUs), which are the functional, milk-producing units of the gland and the site of origin of most breast cancers. The epithelium of ducts and TDLUs is composed of an inner layer of polarized luminal epithelial cells and an outer layer of contractile myoepithelial cells, separated from the vascular-rich stroma by a basement membrane. The luminal- and myoepithelial cells share an origin and in recent years, there has been increasing understanding of how these cell types interact and how they contribute to breast cancer. Accumulating evidence links stem/or progenitor cells in the mammary/breast gland to breast cancer. In that regard, much knowledge has been gained from studies in mice due to specific strains that have allowed for gene knock out/in studies and lineage tracing of cellular fates. However, there is a large histologic difference between the human female breast gland and the mouse mammary gland that necessitates that research needs to be done on human material where primary cultures are important due to their close relation to the tissue of origin. However, due to difficulties of long-term cultures and lack of access to material, human cell lines are of great importance to bridge the gap between studies on mouse mammary gland and human primary breast cells. In this review, we describe D492, a breast epithelial progenitor cell line that can generate both luminal- and myoepithelial cells in culture, and in 3D culture it forms branching ducts similar to TDLUs. We have applied D492 and its daughter cell lines to explore cellular and molecular mechanisms of branching morphogenesis and cellular plasticity including EMT and MET. In addition to discussing the application of D492 in studying normal morphogenesis, we will also discuss how this cell line has been used to study breast cancer progression.

Dual TGFβ/BMP Pathway Inhibition Enables Expansion and Characterization of Multiple Epithelial Cell Types of the Normal and Cancerous Breast

Functional modeling of normal breast epithelial hierarchy and stromal-epithelial cell interactions have been difficult due to inability to obtain sufficient stem-progenitor-mature epithelial and stromal cells. Recently reported epithelial reprogramming assay has partially overcome this limitation, but cross-contamination of cells from the feeder layer is a concern. The purpose of this study was to develop a feeder-layer-independent and inexpensive method to propagate multiple cell types from limited tissue resources. Cells obtained after enzymatic digestion of tissues collected at surgery or by core-needle biopsies were plated on tissue culture dishes precoated with laminin-5-rich-conditioned media from the rat bladder tumor cell line 804G and a defined growth media with inhibitors of ROCK, TGFβ, and BMP signaling. Cells were characterized by flow cytometry, mammosphere assay, 3D cultures, and xenograft studies. Cells from the healthy breasts included CD10⁺/EpCAM^- basal/myoepithelial, CD49f⁺/EpCAM⁺ luminal progenitor, CD49f^-/EpCAM⁺ mature luminal, CD73⁺/EpCAM⁺/CD90^- rare endogenous pluripotent somatic stem, CD73⁺/CD90⁺/EpCAM^-, estrogen receptor alpha-expressing ALCAM (CD166)⁺/EpCAM⁺, and ALDFLUOR⁺ stem/luminal progenitor subpopulations. Epithelial cells were luminal (KRT19⁺), basal (KRT14⁺), or dual-positive luminal/basal hybrid cells. While breast cells derived from BRCA1, BRCA2, and PALB2 mutation carriers did not display unique characteristics, cells from women with breast cancer-protective alleles showed enhanced differentiation. Cells could also be propagated from primary tumors and metastasis of breast, ovarian, and pancreatic cancer-neuroendocrine subtype. Xenograft studies confirmed tumorigenic properties of tumor-derived cells. IMPLICATIONS: Our method expands the scope of individualized studies of patient-derived cells and provides resources to model epithelial-stromal interactions under normal and pathologic conditions.

Stem cells in human breast milk

Recent studies have demonstrated that breast milk contains a population of cells displaying many of the properties typical of stem cells. This review outlines progress made in this newly emerging field of stem cell biology and provides an analysis of the available data on purification, propagation and differentiation of certain types of progenitor cells from breast milk. The possible fates of breast milk cells, including microchimerism caused by their transmission to the distant organs of the infant, are also discussed. Unique properties of breast milk-derived stem cells, such as their unusually low tumorigenic potential and their negligible ability to form teratomas, are highlighted as obvious advantages for using these cells in regenerative therapy.

MiR-203a is differentially expressed during branching morphogenesis and EMT in breast progenitor cells and is a repressor of peroxidasin

MicroRNAs regulate developmental events such as branching morphogenesis, epithelial to mesenchymal transition (EMT) and its reverse process mesenchymal to epithelial transition (MET). In this study, we performed small RNA sequencing of a breast epithelial progenitor cell line (D492), and its mesenchymal derivative (D492M) cultured in three-dimensional microenvironment. Among the most downregulated miRNAs in D492M was miR-203a, a miRNA that plays an important role in epithelial differentiation. Increased expression of miR-203a was seen in D492, concomitant with increased complexity of branching. When miR-203a was overexpressed in D492M, a partial reversion towards epithelial phenotype was seen. Gene expression analysis of D492M and D492MmiR-203a revealed peroxidasin, a collagen IV cross-linker, as the most significantly downregulated gene in D492MmiR-203a. Collectively, we demonstrate that miR-203a expression temporally correlates with branching morphogenesis and is suppressed in D492M. Overexpression of miR-203a in D492M induces a partial MET and reduces the expression of peroxidasin. Furthermore, we demonstrate that miR-203a is a novel repressor of peroxidasin. MiR-203-peroxidasin axis may be an important regulator in branching morphogenesis, EMT/MET and basement membrane remodeling.

A Sox2-Sox9 signalling axis maintains human breast luminal progenitor and breast cancer stem cells

Increased cancer stem cell content during development of resistance to tamoxifen in breast cancer is driven by multiple signals, including Sox2-dependent activation of Wnt signalling. Here, we show that Sox2 increases and estrogen reduces the expression of the transcription factor Sox9. Gain and loss of function assays indicate that Sox9 is implicated in the maintenance of human breast luminal progenitor cells. CRISPR/Cas knockout of Sox9 reduces growth of tamoxifen-resistant breast tumours in vivo. Mechanistically, Sox9 acts downstream of Sox2 to control luminal progenitor cell content and is required for expression of the cancer stem cell marker ALDH1A3 and Wnt signalling activity. Sox9 is elevated in breast cancer patients after endocrine therapy failure. This new regulatory axis highlights the relevance of SOX family transcription factors as potential therapeutic targets in breast cancer.

Heterogeneity of Mammary Stem Cells

Adult female mammals are endowed with the unique ability to produce milk for nourishing their newborn offspring. Milk is secreted on demand by the mammary gland, an organ which develops during puberty, further matures during pregnancy and lactation, but reverts to a resting state after weaning. The glandular tissue (re)generated through this series of structural and functional changes is finely sourced by resident stem cells under the control of systemic hormones and local stimuli.Over the past decades a plethora of studies have been carried out in order to identify and characterize mammary stem cells, primarily in mice and humans. Intriguingly, it is now emerging that multiple mammary stem cell pools (co)exist and are characterized by distinctive molecular markers and context-dependent functions.This chapter reviews the heterogeneity of the mammary stem cell compartment with emphasis on the key properties and molecular regulators of distinct stem cell populations in both the mouse and human glands.

Identification and Characterization of a Stem Cell-Like Population in Bovine Milk: A Potential New Source for Regenerative Medicine in Veterinary

Milk is a complex fluid required for development, nutrition and immunological protection to the newborn offspring. Interestingly, latest finding proved the presence of novel stem cell population in human milk with multilineage differentiation potential. Given that little is known about cellular milk content in other mammalian species such as bovine, the purpose of our study was to isolate and characterize a potential stem cell-like population in bovine milk. In detail, we first analyzed the phenotype of the isolated cells able to grow in plastic adherence and then their capability to differentiate into osteogenic, chondrogenic, and adipogenic lineages. Bovine milk stem cells (bMSCs) resulted plastic adherent and showed a heterogeneous population with epithelial and spindle-shaped cells. Successively, their immunophenotype indicated that bovine milk cells were positive for the typical epithelial markers E-cadherin, cytokeratin-14, cytokeratin-18, and smooth muscle actin. Notably, a subset (30%-40%), constantly observed in purified milk cells, showed the typical mesenchymal surface antigens CD90, CD73, and CD105. Furthermore, the same percentage of bMSCs expressing CD90, CD73, and CD105 presented the stemness markers SOX2 and OCT4 translocated in their nuclei. Finally, our data showed that bMSCs were able to differentiate into osteoblasts, chondroblasts, and adipocytes. In addition, the flow cytometry analysis revealed the presence of a subpopulation of events characterized by typical extracellular vesicles (EVs, size 0.1-1 μm), which did not contain nuclei and were positive for the same markers identified on the surface of bMSCs (CD73, CD90, and CD105), and thus might be considered milk cell-derived EVs. In conclusion, our data suggest that bovine milk is an easily available source of multipotent stem cells able to differentiate into multiple cell lineages. These features can open new possibilities for development biology and regenerative medicine in veterinary area to improving animal health.

Spatially correlated phenotyping reveals K5-positive luminal progenitor cells and p63-K5/14-positive stem cell-like cells in human breast epithelium

Understanding the mechanisms regulating human mammary epithelium requires knowledge of the cellular constituents of this tissue. Different and partially contradictory definitions and concepts describing the cellular hierarchy of mammary epithelium have been proposed, including our studies of keratins K5 and/or K14 as markers of progenitor cells. Furthermore, we and others have suggested that the p53 homolog p63 is a marker of human breast epithelial stem cells. In this investigation, we expand our previous studies by testing whether immunohistochemical staining with monospecific anti-keratin antibodies in combination with an antibody against the stem cell marker p63 might help refine the different morphologic phenotypes in normal breast epithelium. We used in situ multilabel staining for p63, different keratins, the myoepithelial marker smooth muscle actin (SMA), the estrogen receptor (ER), and Ki67 to dissect and quantify the cellular components of 16 normal pre- and postmenopausal human breast epithelial tissue samples at the single-cell level. Importantly, we confirm the existence of K5+ only cells and suggest that they, in contrast to the current view, are key luminal precursor cells from which K8/18+ progeny cells evolve. These cells are further modified by the expression of ER and Ki67. We have also identified a population of p63+K5+ cells that are only found in nipple ducts. Based on our findings, we propose a new concept of the cellular hierarchy of human breast epithelium, including K5 luminal lineage progenitors throughout the ductal-lobular axis and p63+K5+ progenitors confined to the nipple ducts.

Expression of Luminal Progenitor Marker CD117 in the Human Breast Gland

CD117 is a putative marker of luminal progenitor cells in the human breast. However, so far mapping the expression pattern of CD117 within the normal gland has not been reported. Here, we examined the anatomical distribution of CD117-expressing cells in lobular and ductal structures by immunohistochemistry. The presence of CD117-positive luminal cells could be divided into three distinct patterns: (1) contiguous, with coherent positive cells and rare negative cells interspaced; (2) patched, with a roughly equal frequency of positive and negative cells distributed focally; or (3) scattered, with few or no positive cells in the structure. Generally, a patched or scattered expression pattern was more frequent in lobules compared with ducts. Furthermore, an age-correlated increase in heterogeneity was observed. When comparing women below and above 21 years of age this heterogeneity was evident for both lobules and ducts. Although CD117-expression was generally segregated from luminal-lineage transcription factor GATA3-positive cells, some did co-express both markers. Finally, co-staining with Ki-67 revealed that a prominent part of cycling cells belonged to the CD117-positive population. Together these data demonstrate the presence of a CD117-expressing progenitor compartment with the capacity to replenish the luminal lineage of the breast gland.

Normal Breast-Derived Epithelial Cells with Luminal and Intrinsic Subtype-Enriched Gene Expression Document Interindividual Differences in Their Differentiation Cascade

Cell-type origin is one of the factors that determine molecular features of tumors, but resources to validate this concept are scarce because of technical difficulties in propagating major cell types of adult organs. Previous attempts to generate such resources to study breast cancer have yielded predominantly basal-type cell lines. We have created a panel of immortalized cell lines from core breast biopsies of ancestry-mapped healthy women that form ductal structures similar to normal breast in 3D cultures and expressed markers of major cell types, including the luminal-differentiated cell-enriched ERα-FOXA1-GATA3 transcription factor network. We have also created cell lines from PROCR (CD201)⁺/EpCAM^- cells that are likely the "normal" counterpart of the claudin-low subtype of breast cancers. RNA-seq and PAM50-intrinsic subtype clustering identified these cell lines as the "normal" counterparts of luminal A, basal, and normal-like subtypes and validated via immunostaining with basal-enriched KRT14 and luminal-enriched KRT19. We further characterized these cell lines by flow cytometry for distribution patterns of stem/basal, luminal-progenitor, mature/differentiated, multipotent PROCR⁺ cells, and organogenesis-enriched epithelial/mesenchymal hybrid cells using CD44/CD24, CD49f/EpCAM, CD271/EpCAM, CD201/EpCAM, and ALDEFLUOR assays and E-cadherin/vimentin double staining. These cell lines showed interindividual heterogeneity in stemness/differentiation capabilities and baseline activity of signaling molecules such as NF-κB, AKT2, pERK, and BRD4. These resources can be used to test the emerging concept that genetic variations in regulatory regions contribute to widespread differences in gene expression in "normal" conditions among the general population and can delineate the impact of cell-type origin on tumor progression.Significance: In addition to providing a valuable resource for the breast cancer research community to investigate cell-type origin of different subtypes of breast cancer, this study highlights interindividual differences in normal breast, emphasizing the need to use "normal" cells from multiple sources as controls to decipher the effects of cancer-specific genomic aberrations. Cancer Res; 78(17); 5107-23. ©2018 AACR.

Mass Cytometric Analysis Reveals Viable Activated Caspase-3+ Luminal Progenitors in the Normal Adult Human Mammary Gland

The normal adult human female mammary gland is a bilayered structure consisting of an outer basal layer and two readily distinguished subsets of cells within the inner luminal layer. We now present a validated methodology for undertaking large-scale multi-parameter mass cytometric analyses of these cell types at single-cell resolution. In addition, we show how combining this approach with in vitro clonogenic assays of the proliferative and signaling responses of normal human mammary cells to epidermal growth factor (EGF) allows additional subsets with different EGF responses to be discerned. This included the identification of a subset of cells within the phenotypically defined luminal progenitor fraction that displays an elevated content of active caspase-3, including some that generate clones in vitro in response to EGF, with immunohistochemical evidence of their presence in situ in fixed preparations of normal human breast tissue.

Dependence receptor UNC5A restricts luminal to basal breast cancer plasticity and metastasis

Background

The majority of estrogen receptor-positive (ERα⁺) breast cancers respond to endocrine therapies. However, resistance to endocrine therapies is common in 30% of cases, which may be due to altered ERα signaling and/or enhanced plasticity of cancer cells leading to breast cancer subtype conversion. The mechanisms leading to enhanced plasticity of ERα-positive cancer cells are unknown.

Methods

We used short hairpin (sh)RNA and/or the CRISPR/Cas9 system to knockdown the expression of the dependence receptor UNC5A in ERα⁺ MCF7 and T-47D cell lines. RNA-seq, quantitative reverse transcription polymerase chain reaction, chromatin immunoprecipitation, and Western blotting were used to measure the effect of UNC5A knockdown on basal and estradiol (E2)-regulated gene expression. Mammosphere assay, flow cytometry, and immunofluorescence were used to determine the role of UNC5A in restricting plasticity. Xenograft models were used to measure the effect of UNC5A knockdown on tumor growth and metastasis. Tissue microarray and immunohistochemistry were utilized to determine the prognostic value of UNC5A in breast cancer. Log-rank test, one-way, and two-way analysis of variance (ANOVA) were used for statistical analyses.

Results

Knockdown of the E2-inducible UNC5A resulted in altered basal gene expression affecting plasma membrane integrity and ERα signaling, as evident from ligand-independent activity of ERα, altered turnover of phosphorylated ERα, unique E2-dependent expression of genes effecting histone demethylase activity, enhanced upregulation of E2-inducible genes such as BCL2, and E2-independent tumorigenesis accompanied by multiorgan metastases. UNC5A depletion led to the appearance of a luminal/basal hybrid phenotype supported by elevated expression of basal/stem cell-enriched ∆Np63, CD44, CD49f, epidermal growth factor receptor (EGFR), and the lymphatic vessel permeability factor NTN4, but lower expression of luminal/alveolar differentiation-associated ELF5 while maintaining functional ERα. In addition, UNC5A-depleted cells acquired bipotent luminal progenitor characteristics based on KRT14⁺/KRT19⁺ and CD49f⁺/EpCAM⁺ phenotype. Consistent with in vitro results, UNC5A expression negatively correlated with EGFR expression in breast tumors, and lower expression of UNC5A, particularly in ERα⁺/PR⁺/HER2⁻ tumors, was associated with poor outcome.

Conclusion

These studies reveal an unexpected role of the axon guidance receptor UNC5A in fine-tuning ERα and EGFR signaling and the luminal progenitor status of hormone-sensitive breast cancers. Furthermore, UNC5A knockdown cells provide an ideal model system to investigate metastasis of ERα⁺ breast cancers.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-0963-5) contains supplementary material, which is available to authorized users.

BCL11B Drives Human Mammary Stem Cell Self-Renewal In Vitro by Inhibiting Basal Differentiation

The epithelial compartment of the mammary gland contains basal and luminal cell lineages, as well as stem and progenitor cells that reside upstream in the differentiation hierarchy. Stem and progenitor cell differentiation is regulated to maintain adult tissue and mediate expansion during pregnancy and lactation. The genetic factors that regulate the transition of cells between differentiation states remain incompletely understood. Here, we present a genome-scale method to discover genes driving cell-state specification. Applying this method, we identify a transcription factor, BCL11B, which drives stem cell self-renewal in vitro, by inhibiting differentiation into the basal lineage. To validate BCL11B's functional role, we use two-dimensional colony-forming and three-dimensional tissue differentiation assays to assess the lineage differentiation potential and functional abilities of primary human mammary cells. These findings show that BCL11B regulates mammary cell differentiation and demonstrate the utility of our proposed genome-scale strategy for identifying lineage regulators in mammalian tissues.

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Novel strategy to identify lineage-specifying genes

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BCL11B drives primary human mammary stem cell self-renewal in vitro

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BCL11B inhibits basal differentiation of mammary stem cells in vitro

Establishment of a normal-derived estrogen receptor-positive cell line comparable to the prevailing human breast cancer subtype

Understanding human cancer increasingly relies on insight gained from subtype specific comparisons between malignant and non-malignant cells. The most frequent subtype in breast cancer is the luminal. By far the most frequently used model for luminal breast cancer is the iconic estrogen receptor-positive (ER^pos) MCF7 cell line. However, luminal specific comparisons have suffered from the lack of a relevant non-malignant counterpart. Our previous work has shown that transforming growth factor-β receptor (TGFβR) inhibition suffices to propagate prospectively isolated ER^pos human breast luminal cells from reduction mammoplasties (HBEC). Here we demonstrate that transduction of these cells with hTERT/shp16 renders them immortal while remaining true to the luminal lineage including expression of functional ER (iHBEC^ERpos). Under identical culture conditions a major difference between MCF7 and normal-derived cells is the dependence of the latter on TGFβR inhibition for ER expression. In a breast fibroblast co-culture model we further show that whereas MCF7 proliferate concurrently with ER expression, iHBEC^ERpos form correctly polarized acini, and segregate into proliferating and ER expressing cells. We propose that iHBEC^ERpos may serve to shed light on hitherto unappreciated differences in ER regulation and function between normal breast and breast cancer.

Dormant tumor cells expressing LOXL2 acquire a stem-like phenotype mediating their transition to proliferative growth

Recurrence of breast cancer disease years after treatment appears to arise from disseminated dormant tumor cells (DTC). The mechanisms underlying the outgrowth of DTC remain largely unknown. Here we demonstrate that dormant MCF-7 cells expressing LOXL2 acquire a cancer stem cell (CSC)-like phenotype, mediating their outgrowth in the 3D BME system that models tumor dormancy and outgrowth. Similarly, MCF-7-LOXL2 cells colonizing the lung transitioned from dormancy to metastatic outgrowth whereas MCF-7 cells remained dormant. Notably, epithelial to mesenchymal transition (EMT) of MCF-7-LOXL2 cells was required for their CSC-like properties and their transition to metastatic outgrowth. These findings were further supported by clinical data demonstrating that increase in LOXL2 mRNA levels correlates with increase in the mRNA levels of EMT and stem cells markers, and is also associated with decrease in relapse free survival of breast cancer patients. Notably, conditional hypoxia induced expression of endogenous LOXL2 in MCF-7 cells promoted EMT and the acquisition of a CSC-like phenotype, while knockdown of LOXL2 inhibited this transition. Overall, our results demonstrate that expression of LOXL2 endowed DTC with CSC-like phenotype driving their transition to metastatic outgrowth and this stem-like phenotype is dependent on EMT that can be driven by the tumor microenvironment.

Analysis of clonal expansions through the normal and premalignant human breast epithelium reveals the presence of luminal stem cells

It is widely accepted that the cell of origin of breast cancer is the adult mammary epithelial stem cell; however, demonstrating the presence and location of tissue stem cells in the human breast has proved difficult. Furthermore, we do not know the clonal architecture of the normal and premalignant mammary epithelium or its cellular hierarchy. Here, we use deficiency in the mitochondrial enzyme cytochrome c oxidase (CCO), typically caused by somatic mutations in the mitochondrial genome, as a means to perform lineage tracing in the human mammary epithelium. PCR sequencing of laser-capture microdissected cells in combination with immunohistochemistry for markers of lineage differentiation was performed to determine the clonal nature of the mammary epithelium. We have shown that in the normal human breast, clonal expansions (defined here by areas of CCO deficiency) are typically uncommon and of limited size, but can occur at any site within the adult mammary epithelium. The presence of a stem cell population was shown by demonstrating multi-lineage differentiation within CCO-deficient areas. Interestingly, we observed infrequent CCO deficiency that was restricted to luminal cells, suggesting that niche succession, and by inference stem cell location, is located within the luminal layer. CCO-deficient areas appeared large within areas of ductal carcinoma in situ, suggesting that the rate of clonal expansion was altered in the premalignant lesion. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Opportunities for organoids as new models of aging

The biology of aging is challenging to study, particularly in humans. As a result, model organisms are used to approximate the physiological context of aging in humans. However, the best model organisms remain expensive and time-consuming to use. More importantly, they may not reflect directly on the process of aging in people. Human cell culture provides an alternative, but many functional signs of aging occur at the level of tissues rather than cells and are therefore not readily apparent in traditional cell culture models. Organoids have the potential to effectively balance between the strengths and weaknesses of traditional models of aging. They have sufficient complexity to capture relevant signs of aging at the molecular, cellular, and tissue levels, while presenting an experimentally tractable alternative to animal studies. Organoid systems have been developed to model many human tissues and diseases. Here we provide a perspective on the potential for organoids to serve as models for aging and describe how current organoid techniques could be applied to aging research.

Obesity reversibly depletes the basal cell population and enhances mammary epithelial cell estrogen receptor alpha expression and progenitor activity

Background

Obesity is correlated with an increased risk for developing postmenopausal breast cancer. Since obesity rates continue to rise worldwide, it is important to understand how the obese microenvironment influences normal mammary tissue to increase breast cancer risk. We hypothesized that obesity increases the proportion of luminal progenitor cells, which are thought to be the cells of origin for the most common types of breast cancer, potentially leading to an increased risk for breast cancer.

Methods

To study the obese microenvironment within the mammary gland, we used a high-fat diet mouse model of obesity and human breast tissue from reduction mammoplasty surgery. We identified changes in breast epithelial cell populations using flow cytometry for cell surface markers, in vitro functional assays and expression of markers on breast tissue sections.

Results

In both obese female mice and women, mammary epithelial cell populations demonstrated significant decreases in basal/myoepithelial cells, using either flow cytometry or cell-type-specific markers (SMA and p63). Estrogen receptor alpha (ERα) expression was significantly increased in luminal cells in obese mammary tissue, compared with control mice or breast tissue from lean women. Functional assays demonstrated significantly enhanced mammary epithelial progenitor activity in obese mammary epithelial cells and elevated numbers of ERα-positive epithelial cells that were co-labeled with markers of proliferation. Weight loss in a group of obese mice reversed increases in progenitor activity and ERα expression observed in obese mammary tissue.

Conclusions

Obesity enhances ERα-positive epithelial cells, reduces the number of basal/myoepithelial cells, and increases stem/progenitor activity within normal mammary tissue in both women and female mice. These changes in epithelial cell populations induced by obesity are reversible with weight loss. Our findings support further studies to examine how obesity-induced changes in stem/progenitor cells impact breast tumor incidence and histologic tumor types.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0921-7) contains supplementary material, which is available to authorized users.

Proof of region-specific multipotent progenitors in human breast epithelia

We have devised a culture system with conditions that allow primary breast myoepithelial cells (MEPs) to be passaged in a manner that sustains either nonmyodifferentiated or myodifferentiated cell populations without permitting contaminating luminal cells to grow. We show that progenitor activity and potency of MEPs to generate luminal cells in culture and in vivo rely on maintenance of myodifferentiation. Specific isolation and propagation of topographically distinct MEPs reveal the existence of multipotent progenitors in terminal duct lobular units. These findings have important implications for our understanding of the emergence of candidate luminal precursor cells to human breast cancer.

The human breast parenchyma consists of collecting ducts and terminal duct lobular units (TDLUs). The TDLU is the site of origin of most breast cancers. The reason for such focal susceptibility to cancer remains poorly understood. Here, we take advantage of a region-specific heterogeneity in luminal progenitors to interrogate the differentiation repertoire of candidate stem cells in TDLUs. We show that stem-like activity in serial passage culture and in vivo breast morphogenesis relies on the preservation of a myoepithelial phenotype. By enrichment for region-specific progenitors, we identify bipotent and multipotent progenitors in ducts and TDLUs, respectively. We propose that focal breast cancer susceptibility, at least in part, originates from region-specific myoepithelial progenitors.

Awareness and current knowledge of breast cancer

Breast cancer remains a worldwide public health dilemma and is currently the most common tumour in the globe. Awareness of breast cancer, public attentiveness, and advancement in breast imaging has made a positive impact on recognition and screening of breast cancer. Breast cancer is life-threatening disease in females and the leading cause of mortality among women population. For the previous two decades, studies related to the breast cancer has guided to astonishing advancement in our understanding of the breast cancer, resulting in further proficient treatments. Amongst all the malignant diseases, breast cancer is considered as one of the leading cause of death in post menopausal women accounting for 23% of all cancer deaths. It is a global issue now, but still it is diagnosed in their advanced stages due to the negligence of women regarding the self inspection and clinical examination of the breast. This review addresses anatomy of the breast, risk factors, epidemiology of breast cancer, pathogenesis of breast cancer, stages of breast cancer, diagnostic investigations and treatment including chemotherapy, surgery, targeted therapies, hormone replacement therapy, radiation therapy, complementary therapies, gene therapy and stem-cell therapy etc for breast cancer.

ErbB3 drives mammary epithelial survival and differentiation during pregnancy and lactation

Background

During pregnancy, as the mammary gland prepares for synthesis and delivery of milk to newborns, a luminal mammary epithelial cell (MEC) subpopulation proliferates rapidly in response to systemic hormonal cues that activate STAT5A. While the receptor tyrosine kinase ErbB4 is required for STAT5A activation in MECs during pregnancy, it is unclear how ErbB3, a heterodimeric partner of ErbB4 and activator of phosphatidyl inositol-3 kinase (PI3K) signaling, contributes to lactogenic expansion of the mammary gland.

Methods

We assessed mRNA expression levels by expression microarray of mouse mammary glands harvested throughout pregnancy and lactation. To study the role of ErbB3 in mammary gland lactogenesis, we used transgenic mice expressing WAP-driven Cre recombinase to generate a mouse model in which conditional ErbB3 ablation occurred specifically in alveolar mammary epithelial cells (aMECs).

Results

Profiling of RNA from mouse MECs isolated throughout pregnancy revealed robust Erbb3 induction during mid-to-late pregnancy, a time point when aMECs proliferate rapidly and undergo differentiation to support milk production. Litters nursed by ErbB3^KO dams weighed significantly less when compared to litters nursed by ErbB3^WT dams. Further analysis revealed substantially reduced epithelial content, decreased aMEC proliferation, and increased aMEC cell death during late pregnancy. Consistent with the potent ability of ErbB3 to activate cell survival through the PI3K/Akt pathway, we found impaired Akt phosphorylation in ErbB3^KO samples, as well as impaired expression of STAT5A, a master regulator of lactogenesis. Constitutively active Akt rescued cell survival in ErbB3-depleted aMECs, but failed to restore STAT5A expression or activity. Interestingly, defects in growth and survival of ErbB3^KO aMECs as well as Akt phosphorylation, STAT5A activity, and expression of milk-encoding genes observed in ErbB3^KO MECs progressively improved between late pregnancy and lactation day 5. We found a compensatory upregulation of ErbB4 activity in ErbB3^KO mammary glands. Enforced ErbB4 expression alleviated the consequences of ErbB3 ablation in aMECs, while combined ablation of both ErbB3 and ErbB4 exaggerated the phenotype.

Conclusions

These studies demonstrate that ErbB3, like ErbB4, enhances lactogenic expansion and differentiation of the mammary gland during pregnancy, through activation of Akt and STAT5A, two targets crucial for lactation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0893-7) contains supplementary material, which is available to authorized users.

The transcriptional repressor Blimp1 is expressed in rare luminal progenitors and is essential for mammary gland development

Mammary gland morphogenesis depends on a tight balance between cell proliferation, differentiation and apoptosis, to create a defined functional hierarchy within the epithelia. The limited availability of stem cell/progenitor markers has made it challenging to decipher lineage relationships. Here, we identify a rare subset of luminal progenitors that express the zinc finger transcriptional repressor Blimp1, and demonstrate that this subset of highly clonogenic luminal progenitors is required for mammary gland development. Conditional inactivation experiments using K14-Cre and WAPi-Cre deleter strains revealed essential functions at multiple developmental stages. Thus, Blimp1 regulates proliferation, apoptosis and alveolar cell maturation during puberty and pregnancy. Loss of Blimp1 disrupts epithelial architecture and lumen formation both in vivo and in three-dimensional (3D) primary cell cultures. Collectively, these results demonstrate that Blimp1 is required to maintain a highly proliferative luminal subset necessary for mammary gland development and homeostasis.

Highlighted article: In the mouse mammary gland, Blimp1 marks a rare progenitor population, and is required for cell proliferation and polarity as well as efficient milk production.

The AKT inhibitor triciribine in combination with paclitaxel has order-specific efficacy against Zfp217-induced breast cancer chemoresistance

We previously identified the transcription factor ZNF217 (human) / Zfp217 (mouse) as an oncogene and prognostic indicator of reduced survival, increased metastasis, and reduced response to therapy in breast cancer patients. Here we investigated the role of Zfp217 in chemotherapy resistance. Preclinical animal models of Zfp217 overexpression were treated with a combination therapy of the microtubule inhibitor epothilone B, doxorubicin (Adriamycin), and cyclophosphamide (EAC). Tumors overexpressing Zfp217 increased their tumor burden compared to control tumors after treatment and accumulated a mammary gland progenitor cell population (K8⁺K14⁺). To overcome this chemoresistance after ZNF217 overexpression, we treated tumors ± Zfp217 overexpression with paclitaxel and triciribine, a nucleoside analog and AKT inhibitor that kills cells that overexpress ZNF217. Treatment order critically impacted the efficacy of the therapy. Combination treatment of triciribine followed by paclitaxel (TCN→PAC) inhibited tumor burden and increased survival in tumors that overexpressed Zfp217, whereas single agent or combination treatment in the reverse order (PAC→TCN) did not improve response. Analysis of these tumors and patient-derived tumor xenograft tumors treated with the same therapies suggested that Zfp217 overexpression in tumors contributes both to decreased microvessel density and vessel maturity, while TCN→PAC tumors overexpressing Zfp217 showed improved vessel maturity.

P-cadherin: a useful biomarker for axillary-based breast cancer decisions in the clinical practice

Axillary lymph node metastases represent the most powerful breast cancer prognostic factor, dictating disease staging and clinical therapeutic decisions. Nonetheless, breast cancer patients with positive lymph nodes still exhibit a heterogeneous behavior regarding disease progression. Stem-like subpopulations of cancer cells show high migratory and metastatic capacity, thus we hypothesize that breast cancer stem cell markers evaluation in metastasized lymph nodes could provide a more accurate prediction of patient's prognosis. Therefore, the expression profile of P-cadherin, CD44, and CD49f, which have been already associated to stem cell properties in breast cancer, has been evaluated by immunohistochemistry in a series of 135 primary tumors and matched axillary lymph node metastases from 135 breast cancer patients. Taking in consideration the expression of the stem cell markers only in axillary nodes, P-cadherin was the only biomarker significantly associated with poor disease-free and overall patient's survival. Moreover, although a concordant expression between primary tumors and matched lymph nodes has been found in the majority of the cases, a small but significant percentage displayed divergent expression (18.2-26.2%). Remarkably, although CD44 and CD49f changes between primary tumors and lymph node metastasis did not impact survival, the cases that were positive for P-cadherin in lymph node metastases being negative in the primary tumor, presented the worst disease-free and overall survival of the whole series. Accordingly, negative cases for this marker in the lymph nodes with positive expression in the matched breast carcinoma demonstrated a better prognosis, which overlapped with tumors that were negative in both sites. P-cadherin and CD49f gain of expression was mainly found in triple-negative carcinomas. Our results indicate for the first time that the evaluation of P-cadherin expression in lymph node metastases is an important predictor of disease outcome, being a putative valuable marker for axillary-based breast cancer decisions in the clinical practice.

Cell and Tissue Biology Paves a Path to Breast Cancer Prevention

We hypothesize that breast cancer susceptibility stems from interactions between difficult-to-modify cultural and dietary habits and aging processes that are modifiable. We propose a pathway to prevention that uses human organotypic systems that recapitulate hallmarks of aging in order to better understand and to modulate the biological consequences of aging in breast.

Mathematical Modeling Links Pregnancy-Associated Changes and Breast Cancer Risk

Recent debate has concentrated on the contribution of bad luck to cancer development. The tight correlation between the number of tissue-specific stem cell divisions and cancer risk of the same tissue suggests that bad luck has an important role to play in tumor development, but the full extent of this contribution remains an open question. Improved understanding of the interplay between extrinsic and intrinsic factors at the molecular level is one promising route to identifying the limits on extrinsic control of tumor initiation, which is highly relevant to cancer prevention. Here, we use a simple mathematical model to show that recent data on the variation in numbers of breast epithelial cells with progenitor features due to pregnancy are sufficient to explain the known protective effect of full-term pregnancy in early adulthood for estrogen receptor-positive (ER⁺) breast cancer later in life. Our work provides a mechanism for this previously ill-understood effect and illuminates the complex influence of extrinsic factors at the molecular level in breast cancer. These findings represent an important contribution to the ongoing research into the role of bad luck in human tumorigenesis. Cancer Res; 77(11); 2800-9. ©2017 AACR.

Proteasome expression and activity in cancer and cancer stem cells

Proteasome is a multi-protein organelle that participates in cellular proteostasis by destroying damaged or short-lived proteins in an organized manner guided by the ubiquitination signal. By being in a central place in the cellular protein complement homeostasis, proteasome is involved in virtually all cell processes including decisions on cell survival or death, cell cycle, and differentiation. These processes are important also in cancer, and thus, the proteasome is an important regulator of carcinogenesis. Cancers include a variety of cells which, according to the cancer stem cell theory, descend from a small percentage of cancer stem cells, alternatively termed tumor-initiating cells. These cells constitute the subsets that have the ability to propagate the whole variety of cancer and repopulate tumors after cytostatic therapies. Proteasome plays a role in cellular processes in cancer stem cells, but it has been found to have a decreased function in them compared to the rest of cancer cells. This article will discuss the transcriptional regulation of proteasome sub-unit proteins in cancer and in particular cancer stem cells and the relationship of the proteasome with the pluripotency that is the defining characteristic of stem cells. Therapeutic opportunities that present from the understanding of the proteasome role will also be discussed.

The Hippo kinases LATS1 and 2 control human breast cell fate via crosstalk with ERα

Cell fate perturbations underlie many human diseases, including breast cancer. Unfortunately, the mechanisms by which breast cell fate are regulated are largely unknown. The mammary gland epithelium consists of differentiated luminal epithelial and basal myoepithelial cells, as well as undifferentiated stem cells and more restricted progenitors. Breast cancer originates from this epithelium, but the molecular mechanisms that underlie breast epithelial hierarchy remain ill-defined. Here, we use a high-content confocal image-based short hairpin RNA screen to identify tumour suppressors that regulate breast cell fate in primary human breast epithelial cells. We show that ablation of the large tumour suppressor kinases (LATS) 1 and 2 (refs 5, 6), which are part of the Hippo pathway, promotes the luminal phenotype and increases the number of bipotent and luminal progenitors, the proposed cells-of-origin of most human breast cancers. Mechanistically, we have identified a direct interaction between Hippo and oestrogen receptor-α (ERα) signalling. In the presence of LATS, ERα was targeted for ubiquitination and Ddb1-cullin4-associated-factor 1 (DCAF1)-dependent proteasomal degradation. Absence of LATS stabilized ERα and the Hippo effectors YAP and TAZ (hereafter YAP/TAZ), which together control breast cell fate through intrinsic and paracrine mechanisms. Our findings reveal a non-canonical (that is, YAP/TAZ-independent) effect of LATS in the regulation of human breast cell fate.

Upregulation of Mrps18a in breast cancer identified by selecting phage antibody libraries on breast tissue sections

Background

One of the hallmarks of cancer is an altered energy metabolism, and here, mitochondria play a central role. Previous studies have indicated that some mitochondrial ribosomal proteins change their expression patterns upon transformation.

Method

In this study, we have used the selection of recombinant antibody libraries displayed on the surface of filamentous bacteriophage as a proteomics discovery tool for the identification of breast cancer biomarkers. A small subpopulation of breast cells expressing both cytokeratin 19 and cytokeratin 14 was targeted using a novel selection procedure.

Results

We identified the mitochondrial ribosomal protein s18a (Mrps18a) as a protein which is upregulated in breast cancer. However, Mrps18a was not homogeneously upregulated in all cancer cells, suggesting the existence of sub-populations within the tumor. The upregulation was not confined to cytokeratin 19 and cytokeratin 14 double positive cells.

Conclusion

This study illustrates how phage display can be applied towards the discovery of proteins which exhibit changes in their expression patterns. We identified the mitochondrial protein Mrps18a as being upregulated in human breast cancer cells compared to normal breast cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2987-5) contains supplementary material, which is available to authorized users.

Purification of Distinct Subsets of Epithelial Cells from Normal Human Breast Tissue

The mammary epithelium is composed of a variety of specialized cell types that function in a coordinated fashion to produce and eject milk through multiple cycles of pregnancy. The ability to identify and purify these subsets of cells in order to interrogate their growth and differentiation capacities, as well as to characterize the molecular mechanisms that regulate their behavior, is essential in identifying the processes associated with breast cancer initiation and progression. This methods chapter outlines the step-by-step methods for dissociating human breast reduction specimens to a single cell suspension of viable cells. As well, strategies for purifying four distinct subsets of epithelial cells by using fluorescence-activated cell sorting and protocols for interrogating the growth and differentiation properties of these purified cells at clonal densities in adherent culture are also described.

'Normalizing' the malignant phenotype of luminal breast cancer cells via alpha(v)beta(3)-integrin

Reestablishing tissue organization of breast cancer cells into acini was previously shown to override their malignant phenotype. In our study, we demonstrate that alpha(v)beta(3) integrin (Int-αvβ3), previously shown to play a role in cancer progression, promoted differentiation and growth arrest of organoids derived from luminal A breast cancer cells grown in their relevant three-dimensional microenvironment. These organoids differentiated into normal-like acini resembling a benign stage of breast tissue. Likewise, we demonstrate that Int-αvβ3 is selectively expressed in the epithelium of the benign stage of breast tissues, and is lost during the early stages of luminal A breast cancer progression. Notably, the organoids' reversion into normal-like acini was mediated by cancer luminal progenitor-like cells expressing both EpCAM^highCD49f^lowCD24⁺ and Int-αvβ3. Furthermore, downregulation of Notch4 expression and downstream signaling was shown to mediate Int-αvβ3-induced reversion. Intriguingly, when luminal A breast cancer cells expressing Int-αvβ3 were injected into a humanized mouse model, differentiated tumors developed when compared with that generated by control cells. Hence, our data suggest that promoting differentiation of luminal A breast cancer cells by signaling emanating from Int-αvβ3 can potentially promote ‘normalization' of their malignant phenotype and may prevent the malignant cells from progressing.

Epithelial Plasticity During Human Breast Morphogenesis and Cancer Progression

Understanding the complex events leading to formation of an epithelial-based organ such as the breast requires a detailed insight into the crosstalk between epithelial and stromal compartments. These interactions occur both through heterotypic cellular interactions and between cells and matrix components. While in vivo models may partially capture these complex interactions, there is a need for in- vitro models to study these events. In this review we discuss cell-cell interactions in breast development focusing on the stem cell niche and branching morphogenesis. Given the recent understanding that the basic developmental events underlying branching morphogenesis are closely related to pathways important to cancer progression, i.e. epithelial plasticity and epithelial to mesenchymal transition (EMT), we will also discuss aspects relevant to cancer progression. In cancer, the adoption of mesenchymal phenotype by the malignant cells allows stromal invasion and subsequent intravasation to blood- or lymphatic vessels, a route that is a prerequisite for metastasis. A number of publications have demonstrated that tumor initiating cells, sometimes referred to as cancer stem cells adapt an EMT phenotype that renders them more resistant to apoptosis and drug therapy. The mechanism behind this phenomenon is currently unknown but this may partially explain relapse in breast cancer patients. Increased understanding of branching morphogenesis in the breast gland and the regulation of EMT and its reverse process mesenchymal to epithelial transition (MET) may hold the keys for future development of methods/drugs that neutralize the invading properties of cancer cells.

Molecular mechanisms of asymmetric divisions in mammary stem cells

Stem cells have the remarkable ability to undergo proliferative symmetric divisions and self-renewing asymmetric divisions. Balancing of the two modes of division sustains tissue morphogenesis and homeostasis. Asymmetric divisions of Drosophila neuroblasts (NBs) and sensory organ precursor (SOP) cells served as prototypes to learn what we consider now principles of asymmetric mitoses. They also provide initial evidence supporting the notion that aberrant symmetric divisions of stem cells could correlate with malignancy. However, transferring the molecular knowledge of circuits underlying asymmetry from flies to mammals has proven more challenging than expected. Several experimental approaches have been used to define asymmetry in mammalian systems, based on daughter cell fate, unequal partitioning of determinants and niche contacts, or proliferative potential. In this review, we aim to provide a critical evaluation of the assays used to establish the stem cell mode of division, with a particular focus on the mammary gland system. In this context, we will discuss the genetic alterations that impinge on the modality of stem cell division and their role in breast cancer development.

Evidence of two distinct functionally specialized fibroblast lineages in breast stroma

BACKGROUND

The terminal duct lobular unit (TDLU) is the most dynamic structure in the human breast and the putative site of origin of human breast cancer. Although stromal cells contribute to a specialized microenvironment in many organs, this component remains largely understudied in the human breast. We here demonstrate the impact on epithelium of two lineages of breast stromal fibroblasts, one of which accumulates in the TDLU while the other resides outside the TDLU in the interlobular stroma.

METHODS

The two lineages are prospectively isolated by fluorescence activated cell sorting (FACS) based on different expression levels of CD105 and CD26. The characteristics of the two fibroblast lineages are assessed by immunocytochemical staining and gene expression analysis. The differentiation capacity of the two fibroblast populations is determined by exposure to specific differentiating conditions followed by analysis of adipogenic and osteogenic differentiation. To test whether the two fibroblast lineages are functionally imprinted by their site of origin, single cell sorted CD271^low/MUC1^high normal breast luminal epithelial cells are plated on fibroblast feeders for the observation of morphological development. Epithelial structure formation and polarization is shown by immunofluorescence and digitalized quantification of immunoperoxidase-stained cultures.

RESULTS

Lobular fibroblasts are CD105^high/CD26^low while interlobular fibroblasts are CD105^low/CD26^high. Once isolated the two lineages remain phenotypically stable and functionally distinct in culture. Lobular fibroblasts have properties in common with bone marrow derived mesenchymal stem cells and they specifically convey growth and branching morphogenesis of epithelial progenitors.

CONCLUSIONS

Two distinct functionally specialized fibroblast lineages exist in the normal human breast, of which the lobular fibroblasts have properties in common with mesenchymal stem cells and support epithelial growth and morphogenesis. We propose that lobular fibroblasts constitute a specialized microenvironment for human breast luminal epithelial progenitors, i.e. the putative precursors of breast cancer.

Mammary Epithelial Cell Hierarchy in the Dairy Cow Throughout Lactation

The plasticity of the mammary gland relies on adult mammary stem cells (MaSCs) and their progenitors, which give rise to various populations of mammary epithelial cells (MECs). To face global challenges, an in-depth characterization of milk-producing animal mammary gland plasticity is required, to select more sustainable and robust dairy cows. The identification and characterization of MaSC and their progenitors will also provide innovative tools in veterinary/human medicine regarding mammary tissue damage (carcinogenesis, bacterial infections). This study aimed to determine the dynamics of mammary cell populations throughout a lactation cycle. Using mammary biopsies from primiparous lactating dairy cows at 30, 90, 150, and 250 days of lactation, we phenotyped cell populations by flow cytometry. To investigate cell lineages, we used specific cell-surface markers, including CD49f, CD24, EpCAM (epithelial cell adhesion molecule), and CD10. Two cell populations linked to milk production were identified: CD49f(+)/EpCAM(-) (y = 0.88x + 4.42, R(2) = 0.36, P < 0.05) and CD49f(-)/EpCAM(-) (y = -1.15x + 92.44, R(2) = 0.51, P < 0.05) cells. Combining immunostaining analysis, flow cytometry, daily milk production data, and statistical approaches, we defined a stem cell population (CD24(+)/CD49f(+)) and four progenitor cell populations that include bipotent luminal progenitors (CD24(-)/CD49f(+)), lumino-alveolar progenitors (CD24(-)/EpCAM(+)), myoepithelial progenitors (CD24(+)/CD10(-)), and lumino-ductal progenitors (CD49f(-)/EpCAM(+)). Interestingly, we found that the bipotent luminal progenitors (CD24(-)/CD49f(+)) decreased significantly (P < 0.05) during lactation. This study provides the first results of mammary cell lineage, allowing insight into mammary cell plasticity during lactation.

Comparative Multifractal Analysis of Dynamic Infrared Thermograms and X-Ray Mammograms Enlightens Changes in the Environment of Malignant Tumors

There is growing evidence that the microenvironment surrounding a tumor plays a special role in cancer development and cancer therapeutic resistance. Tumors arise from the dysregulation and alteration of both the malignant cells and their environment. By providing tumor-repressing signals, the microenvironment can impose and sustain normal tissue architecture. Once tissue homeostasis is lost, the altered microenvironment can create a niche favoring the tumorigenic transformation process. A major challenge in early breast cancer diagnosis is thus to show that these physiological and architectural alterations can be detected with currently used screening techniques. In a recent study, we used a 1D wavelet-based multi-scale method to analyze breast skin temperature temporal fluctuations collected with an IR thermography camera in patients with breast cancer. This study reveals that the multifractal complexity of temperature fluctuations superimposed on cardiogenic and vasomotor perfusion oscillations observed in healthy breasts is lost in malignant tumor foci in cancerous breasts. Here we use a 2D wavelet-based multifractal method to analyze the spatial fluctuations of breast density in the X-ray mammograms of the same panel of patients. As compared to the long-range correlations and anti-correlations in roughness fluctuations, respectively observed in dense and fatty breast areas, some significant change in the nature of breast density fluctuations with some clear loss of correlations is detected in the neighborhood of malignant tumors. This attests to some architectural disorganization that may deeply affect heat transfer and related thermomechanics in breast tissues, corroborating the change to homogeneous monofractal temperature fluctuations recorded in cancerous breasts with the IR camera. These results open new perspectives in computer-aided methods to assist in early breast cancer diagnosis.

Molecular Portrait of the Normal Human Breast Tissue and Its Influence on Breast Carcinogenesis

Normal human breast tissue consists of epithelial and nonepithelial cells with different molecular profiles and differentiation grades. This molecular heterogeneity is known to yield abnormal clones that may contribute to the development of breast carcinomas. Stem cells that are found in developing and mature breast tissue are either positive or negative for cytokeratin 19 depending on their subtype. These cells are able to generate carcinogenesis along with mature cells. However, scientific data remains controversial regarding the monoclonal or polyclonal origin of breast carcinomas. The majority of breast carcinomas originate from epithelial cells that normally express BRCA1. The consecutive loss of the BRCA1 gene leads to various abnormalities in epithelial cells. Normal breast epithelial cells also express hypoxia inducible factor (HIF) 1α and HIF-2α that are associated with a high metastatic rate and a poor prognosis for malignant lesions. The nuclear expression of estrogen receptor (ER) and progesterone receptor (PR) in normal human breast tissue is maintained in malignant tissue as well. Several controversies regarding the ability of ER and PR status to predict breast cancer outcome remain. Both ER and PR act as modulators of cell activity in normal human breast tissue. Ki-67 positivity is strongly correlated with tumor grade although its specific role in applied therapy requires further studies. Human epidermal growth factor receptor 2 (HER2) oncoprotein is less expressed in normal human breast specimens but is highly expressed in certain malignant lesions of the breast. Unlike HER2, epidermal growth factor receptor expression is similar in both normal and malignant tissues. Molecular heterogeneity is not only found in breast carcinomas but also in normal breast tissue. Therefore, the molecular mapping of normal human breast tissue might represent a key research area to fully elucidate the mechanisms of breast carcinogenesis.

Cancer Stem Cell Hierarchy in Glioblastoma Multiforme

Glioblastoma multiforme (GBM), an aggressive tumor that typically exhibits treatment failure with high mortality rates, is associated with the presence of cancer stem cells (CSCs) within the tumor. CSCs possess the ability for perpetual self-renewal and proliferation, producing downstream progenitor cells that drive tumor growth. Studies of many cancer types have identified CSCs using specific markers, but it is still unclear as to where in the stem cell hierarchy these markers fall. This is compounded further by the presence of multiple GBM and glioblastoma cancer stem cell subtypes, making investigation and establishment of a universal treatment difficult. This review examines the current knowledge on the CSC markers SALL4, OCT-4, SOX2, STAT3, NANOG, c-Myc, KLF4, CD133, CD44, nestin, and glial fibrillary acidic protein, specifically focusing on their use and validity in GBM research and how they may be utilized for investigations into GBM's cancer biology.

Selection of a breast cancer subpopulation-specific antibody using phage display on tissue sections

Breast cancer tumors are composed of heterogeneous cell populations. These populations display a high variance in morphology, growth and metastatic propensity. They respond differently to therapeutic interventions, and some may be more prone to cause recurrence. Studying individual subpopulations of breast cancer may provide crucial knowledge for the development of individualized therapy. However, this process is challenged by the availability of biomarkers able to identify subpopulations specifically. Here, we demonstrate an approach for phage display selection of recombinant antibody fragments on cryostat sections of human breast cancer tissue. This method allows for selection of recombinant antibodies binding to antigens specifically expressed in a small part of the tissue section. In this case, a CD271⁺ subpopulation of breast cancer cells was targeted, and these may be potential breast cancer stem cells. We isolated an antibody fragment LH 7, which in immunohistochemistry experiments demonstrates specific binding to breast cancer subpopulations. The selection of antibody fragments directly on small defined areas within a larger section of malignant tissue is a novel approach by which it is possible to better target cellular heterogeneity in proteomic studies. The identification of novel biomarkers is relevant for our understanding and intervention in human diseases. The selection of the breast cancer-specific antibody fragment LH 7 may reveal novel subpopulation-specific biomarkers, which has the potential to provide new insight and treatment strategies for breast cancer.

Breast Tumor Heterogeneity: Source of Fitness, Hurdle for Therapy

Tumor heterogeneity impinges on prognosis, response to therapy, and metastasis. As such, heterogeneity is one of the most important and clinically relevant areas of cancer research. Breast cancer displays frequent intra- and inter-tumor heterogeneity as the result of genetic and non-genetic alterations that often enhance the vigor of cancer cells. In-depth characterization and understanding of the origin of this phenotypic and molecular diversity is paramount to improving diagnosis, the definition of prognostic and predictive biomarkers, and the design of therapeutic strategies. Here, we summarize current knowledge about sources of breast cancer heterogeneity, its consequences, and possible counter-measures. We discuss especially the impact on tumor heterogeneity of the differentiation state of the cell-of-origin, cancer cell plasticity, the microenvironment, and genetic evolution. Factors that enhance cancer cell vigor are clearly detrimental for patients.

Breast cancer stem cells programs: enter the (non)-code

Breast tumors exhibit a hierarchical cellular organization driven by several subpopulations of cancer stem cells (CSCs). These breast CSC subpopulations are able to infinitely self-renew and to differentiate, giving rise to tumor heterogeneity. Accumulating evidence show that breast CSCs resist conventional therapies and i`nitiate tumor relapse. The development of anti-CSCs therapies may therefore greatly improve patient survival. A better elucidation of molecular circuitries involved in stemness would offer new relevant targets. Noncoding RNAs, especially microRNAs and long noncoding RNAs, are regulators of cell identity and are notably found deregulated in breast CSCs. This review will focus on noncoding RNAs involved in CSCs biology during breast cancer initiation, maintenance, therapeutic resistance and metastatic progression. Potential clinical applications using noncoding RNAs as biomarkers or therapies will be discussed.

Breast cancer stem cells: current advances and clinical implications

There is substantial evidence that many cancers, including breast cancer, are driven by a population of cells that display stem cell properties. These cells, termed cancer stem cells (CSCs) or tumor initiating cells, not only drive tumor initiation and growth but also mediate tumor metastasis and therapeutic resistance. In this chapter, we summarize current advances in CSC research with a major focus on breast CSCs (BCSCs). We review the prevailing methods to isolate and characterize BCSCs and recent evidence documenting their cellular origins and phenotypic plasticity that enables them to transition between mesenchymal and epithelial-like states. We describe in vitro and clinical evidence that these cells mediate metastasis and treatment resistance in breast cancer, the development of novel strategies to isolate circulating tumor cells (CTCs) that contain CSCs and the use of patient-derived xenograft (PDX) models in preclinical breast cancer research. Lastly, we highlight several signaling pathways that regulate BCSC self-renewal and describe clinical implications of targeting these cells for breast cancer treatment. The development of strategies to effectively target BCSCs has the potential to significantly improve the outcomes for patients with breast cancer.

High content screening application for cell-type specific behaviour in heterogeneous primary breast epithelial subpopulations

Background

The complex interaction between multiple cell types and the microenvironment underlies the diverse pathways to carcinogenesis and necessitates sophisticated approaches to in vitro hypotheses testing. The combination of mixed culture format with high content immunofluorescence screening technology provides a powerful platform for observation of cell type specific behavior.

Methods

We have developed a versatile, high-throughput method for assessing cell-type specific responses. In addition to the specificity and sensitivity offered traditionally by immunofluorescent detection in flow cytometry, the ‘in-cell’ analysis method we describe provides the added benefits of higher throughput and the ability to analyse protein subcellular localisation in situ. Furthermore, elimination of the cell dissociation step allows for more immediate analysis of responses to specific extrinsic stimuli. We applied this method to investigate ionising radiation treatment response in normal breast epithelial cells, measuring growth rate, cell cycle response and double-strand DNA breaks.

Results

The ‘in-cell’ analysis approach elucidated several interesting donor and cell-type specific differences. Notably, in response to ionizing radiation we observed differential expression in luminal and basal-like cells of a member of the APOBEC enzyme family, recently identified as a critical driver of an oncogenic signature. Our findings suggest that this enzyme is active in the normal breast epithelium during DNA damage response.

Conclusions

We demonstrate the practical application of a new method for assessing cell-type specific change in mixed cultures, especially the analysis of normal primary cultures, overcoming a major technical issue of dissecting the response of multiple cell types in a heterogeneous population.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0681-9) contains supplementary material, which is available to authorized users.

Fate Mapping Mammalian Corneal Epithelia

The anterior aspect of the cornea consists of a stratified squamous epithelium, thought to be maintained by a rare population of stem cells (SCs) that reside in the limbal transition zone. Although migration of cells that replenish the corneal epithelium has been studied for over a century, the process is still poorly understood and not well characterized. Numerous techniques have been employed to examine corneal epithelial dynamics, including visualization by light microscopy, the incorporation of vital dyes and DNA labels, and transplantation of genetically marked cells that have acted as cell and lineage beacons. Modern-day lineage tracing utilizes molecular methods to determine the fate of a specific cell and its progeny over time. Classically employed in developmental biology, lineage tracing has been used more recently to track the progeny of adult SCs in a number of organs to pin-point their location and understand their movement and influence on tissue regeneration. This review highlights key discoveries that have led researchers to develop cutting-edge genetic tools to effectively and more accurately monitor turnover and displacement of cells within the mammalian corneal epithelium. Collating information on the basic biology of SCs will have clinical ramifications in furthering our knowledge of the processes that govern their role in homeostasis, wound-healing, transplantation, and how we can improve current unsatisfactory SC-based therapies for patients suffering blinding corneal disease.

A maximum-likelihood approach for building cell-type trees by lifting

BACKGROUND

In cell differentiation, a less specialized cell differentiates into a more specialized one, even though all cells in one organism have (almost) the same genome. Epigenetic factors such as histone modifications are known to play a significant role in cell differentiation. We previously introduce cell-type trees to represent the differentiation of cells into more specialized types, a representation that partakes of both ontogeny and phylogeny.

RESULTS

We propose a maximum-likelihood (ML) approach to build cell-type trees and show that this ML approach outperforms our earlier distance-based and parsimony-based approaches. We then study the reconstruction of ancestral cell types; since both ancestral and derived cell types can coexist in adult organisms, we propose a lifting algorithm to infer internal nodes. We present results on our lifting algorithm obtained both through simulations and on real datasets.

CONCLUSIONS

We show that our ML-based approach outperforms previously proposed techniques such as distance-based and parsimony-based methods. We show our lifting-based approach works well on both simulated and real data.

Phenotypic and functional characterization of two bovine mammary epithelial cell lines in 2D and 3D models

Immortalized bovine mammary epithelial cells (BME-UV1) and immortalized bovine mammary alveolar cells (MAC-T) have been extensively used as in vitro cell models to understand milk production in dairy cows. Precise knowledge about their phenotype and performance remains, however, unknown. This study aims to characterize MAC-T and BME-UV1 profiles when cultured in two-dimensional adherent, three-dimensional adherent (Matrigel), and three-dimensional no adherent [ultralow attachment (ULA)] supports. MAC-T and BME-UV1 were compared according to their proliferation capacities and to specific cell surface markers CD24, CD326 [epithelial cell adhesion molecule (EpCAM)], CD10, and integrin CD49f (α-6). Cytokeratin (CK14 and CK19), signal transducer and activator of transcription 5, and other proteins (occludin and cadherin-1) were analyzed. BME-UV1 in ULA support expressed higher CD49f marker. A different intensity of CD49 staining allowed the discrimination between the two cell lines in adherent condition. CD10, EpCAM, and CK19 expressions show that BME-UV1 cells have luminal capacity, while MAC-T has a myoepithelial profile with a high expression of CK14. BME-UV1 cells possess a closer committed progenitor profile due to their higher expression in aldehyde dehydrogenase and EpCAM. We observed that BME-UV1 cells have a better capacity to form spherical structures, mammospheres, in Matrigel than MAC-T, which was confirmed by the higher mammosphere area. In the ULA condition, BME-UV1 proliferated over the 6 days of culture. Taken together, our results clearly confirm the BME-UV1 luminal profile and MAC-T ductal/myoepithelial-like phenotype.