Normal Breast Stem Cells Research Articles

Computational modeling of early-stage breast cancer progression using TPFA method: A numerical investigation

In this paper, a finite volume (TPFA) method is employed to simulate a degenerate breast cancer model that captures the progressive mutations from a normal breast stem cell to a tumor cell. The model incorporates a degenerate parabolic equation to represent the interaction between solid tumor growth and its environment, which involves the release of degradative enzymes governed by a partial differential equation. The discrete maximum principle is verified to be satisfied by the proposed finite volume scheme, and the convergence of the existing discrete solutions to a weak solution is proven. Additionally, the development of breast cancer is demonstrated through a numerical experiment.

Comparison of mammosphere formation from stem-like cells of normal breast, malignant primary breast tumors, and MCF-7 cell line

BackgroundMammosphere formation assay has become a versatile tool to quantify the activity of putative breast cancer stem cells in non-adherent in vitro cultures. However, optimizing the suspension culture system is crucial to establish mammosphere cultures from primary breast tumors.MethodsThis study aimed at determining the self-renewal and sphere-forming potential of breast cancer stem-like cells derived from human primary invasive ductal carcinoma and normal breast tissue samples, and MCF-7 breast cancer cell line using an optimal suspension culture system. Mammosphere-forming efficiency of the mammospheres generated from the tissue samples and cell line were compared. We evaluated the expression of CD44+/CD24−/low and CD49f+/EpCAM−/low phenotypes in the stem-like cells by flow cytometry. CK-18, CK-19, α-SMA, and EpCAM marker expression was assessed using immunohistochemical staining.ResultsBreast epithelial cells isolated from the three samples formed two-dimensional spheroids in suspension cultures. Interestingly, mammospheres formed from patient-derived primary breast tumors were enriched in breast cancer stem-like cells with the phenotype CD44+/CD24−/low and exhibited a relatively more number of large spheres when compared to the normal breast stem cells. MCF-7-derived SCs were more aggressive and resulted in the formation of a significantly higher number of spheroids. The expression of CK-18/CK-19 and α-SMA/EpCAM proteins was confirmed in breast cancer tissues.ConclusionsThus, the use of primary tumor specimens and breast cancer cell lines as suitable models for elucidating the breast cancer stem cell activity was validated using mammosphere culture system.

LCOR mediates interferon-independent tumor immunogenicity and responsiveness to immune-checkpoint blockade in triple-negative breast cancer.

Ligand-dependent corepressor (LCOR) mediates normal and malignant breast stem cell differentiation. Cancer stem cells (CSCs) generate phenotypic heterogeneity and drive therapy resistance, yet their role in immunotherapy is poorly understood. Here we show that immune-checkpoint blockade (ICB) therapy selects for LCORlow CSCs with reduced antigen processing/presentation machinery (APM) driving immune escape and ICB resistance in triple-negative breast cancer (TNBC). We unveil an unexpected function of LCOR as a master transcriptional activator of APM genes binding to IFN-stimulated response elements (ISREs) in an IFN signaling-independent manner. Through genetic modification of LCOR expression, we demonstrate its central role in modulation of tumor immunogenicity and ICB responsiveness. In TNBC, LCOR associates with ICB clinical response. Importantly, extracellular vesicle (EV) Lcor-messenger RNA therapy in combination with anti-PD-L1 overcame resistance and eradicated breast cancer metastasis in preclinical models. Collectively, these data support LCOR as a promising target for enhancement of ICB efficacy in TNBC, by boosting of tumor APM independently of IFN.

Hybrid Stem Cell States: Insights Into the Relationship Between Mammary Development and Breast Cancer Using Single-Cell Transcriptomics.

Similarities between stem cells and cancer cells have implicated mammary stem cells in breast carcinogenesis. Recent evidence suggests that normal breast stem cells exist in multiple phenotypic states: epithelial, mesenchymal, and hybrid epithelial/mesenchymal (E/M). Hybrid E/M cells in particular have been implicated in breast cancer metastasis and poor prognosis. Mounting evidence also suggests that stem cell phenotypes change throughout the life course, for example, through embryonic development and pregnancy. The goal of this study was to use single cell RNA-sequencing to quantify cell state distributions of the normal mammary (NM) gland throughout developmental stages and when perturbed into a stem-like state in vitro using conditional reprogramming (CR). Using machine learning based dataset alignment, we integrate multiple mammary gland single cell RNA-seq datasets from human and mouse, along with bulk RNA-seq data from breast tumors in the Cancer Genome Atlas (TCGA), to interrogate hybrid stem cell states in the normal mammary gland and cancer. CR of human mammary cells induces an expanded stem cell state, characterized by increased expression of embryonic stem cell associated genes. Alignment to a mouse single-cell transcriptome atlas spanning mammary gland development from in utero to adulthood revealed that NM cells align to adult mouse cells and CR cells align across the pseudotime trajectory with a stem-like population aligning to the embryonic mouse cells. Three hybrid populations emerge after CR that are rare in NM: KRT18+/KRT14+ (hybrid luminal/basal), EPCAM+/VIM+ (hybrid E/M), and a quadruple positive population, expressing all four markers. Pseudotime analysis and alignment to the mouse developmental trajectory revealed that E/M hybrids are the most developmentally immature. Analyses of single cell mouse mammary RNA-seq throughout pregnancy show that during gestation, there is an enrichment of hybrid E/M cells, suggesting that these cells play an important role in mammary morphogenesis during lactation. Finally, pseudotime analysis and alignment of TCGA breast cancer expression data revealed that breast cancer subtypes express distinct developmental signatures, with basal tumors representing the most “developmentally immature” phenotype. These results highlight phenotypic plasticity of normal mammary stem cells and provide insight into the relationship between hybrid cell populations, stemness, and cancer.

Abstract 1158: Seven genes were closely associated with ALDH1 in triple negative breast cancer

Abstract Background: Aldehyde dehydrogenase1 (ALDH1) is widely accepted as a marker of normal and malignant breast stem cells. We reported that ALDH1 expression was associated with aggressive phenotypes and poor clinical outcome of breast cancer patients. However, mechanics of how ALDH1 affects cancer stem cell features is not known. Aim: To examine genes associated with ALDH1 and find novel druggable targets for the future cancer stem cell therapy. Methods: ALDH1-positive and ALDH1-negative cells were dissected by a laser capture microdissection from 5 ALDH1 positive triple negative breast cancer samples. A differential analysis of mRNA expression was performed between ALDH1 positive and negative breast cancer cells in each sample by Affymetrix GeneChip microarrays. 1) Microarray analysis suite (MAS5) and robust multi-chip average (RMA) were used as preprocessing algorithms to analyze gene expression data and to extract genes differently expressed between ALDH1 positive and negative cells. 2) The network analysis was performed with extracted genes with MAS5 by the comprehensive information platform “KeyMolnetTM”. Results: 1) 54,682 genes were extracted and 32,264 genes were selected after eliminating background noise. One hundred and four genes: 63 up-regulated and 41 down-regulated, were extracted in ALDH1-positive cells by MAS5, while only 2 up-regulated genes by RMA. H19 was a gene that was commonly extracted by both algorithms. 2) The network with 104 genes was constructed and BRD4, SMAD4, Pitx3, RARa, MUC1, HASH1 and C/EBPb were identified as genes with the closest distance to ALDH1. Conclusions: Most of extracted 7 genes have been already known to exert critical roles for maintaining stem cell features, providing a rationale of ALDH1 for the stem cell marker of breast cancer. These genes including H19 could be targets of the cancer stem cell therapy for treating incurable breast cancer. Citation Format: Takashi Ishikawa, Kazutaka Narui, Akimitsu Yamada, Kumiko Kida, Hidetaka Shima, Chiho Endo, Shoko Adachi, Sadatoshi Sugae, Yohei Miyagi, Yasushi Ichikawa, Itaru Endo. Seven genes were closely associated with ALDH1 in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1158.

Plasticity and Potency of Mammary Stem Cell Subsets During Mammary Gland Development

It is now widely believed that mammary epithelial cell plasticity, an important physiological process during the stages of mammary gland development, is exploited by the malignant cells for their successful disease progression. Normal mammary epithelial cells are heterogeneous and organized in hierarchical fashion, in which the mammary stem cells (MaSC) lie at the apex with regenerative capacity as well as plasticity. Despite the fact that the majority of studies supported the existence of multipotent MaSCs giving rise to both basal and luminal lineages, others proposed lineage restricted unipotent MaSCs. Consistent with the notion, the latest research has suggested that although normal MaSC subsets mainly stay in a quiescent state, they differ in their reconstituting ability, spatial localization, and molecular and epigenetic signatures in response to physiological stimuli within the respective microenvironment during the stages of mammary gland development. In this review, we will focus on current research on the biology of normal mammary stem cells with an emphasis on properties of cellular plasticity, self-renewal and quiescence, as well as the role of the microenvironment in regulating these processes. This will include a discussion of normal breast stem cell heterogeneity, stem cell markers, and lineage tracing studies.

Potential protective effect of ALDH-1 stromal expression against early recurrence of operable breast cancers.

The emerging cancer stem cell (CSC) model proposes that the stem cell niche plays a major role in the risk of cancer recurrence. Enzymatic activity of aldehydes, including aldehyde dehydrogenase 1 (ALDH-1), has been used as a marker of normal and malignant breast stem cells (BSCs). However, the clinical implications of the expression of stem cell markers in the stroma have not yet been investigated. To determine the relationships of ALDH-1 expression, the currently reliable BSCs marker, with clinical characteristics and survival, we used immunohistochemical staining of tissue microarrays from 180 stroma and epithelial cancer tissues in patients diagnosed with operable early breast cancer (stage 0-III). ALDH-1 expression was observed in 93.4% of the stromal cells and in 37.2% of the epithelial cells, and the expression levels between the two cell types were significantly correlated (P=0.001). The stromal expression of ALDH-1 was not correlated with any clinical factors, whereas epithelial expression was significantly correlated with a negative estrogen-receptor status (P<0.001), high proliferation based on Ki-67 expression (P<0.001), and younger age (P=0.04). After 27.8 months of follow up, negative stromal expression of ALDH-1 was significantly correlated with shorter overall survival (positive, 56.9±3.0 months vs. negative, 30.5±3.0 months; P=0.01). Stromal ALDH-1 expression was not directly correlated with known clinical factors, but its expression may play a protective role against early recurrence. Further observation and large-scale studies are needed to validate the clinical implications of ALDH-1 in breast cancer.

Convergence of a positive nonlinear Control Volume Finite Element scheme for solving an anisotropic degenerate breast cancer development model

In this paper, a nonlinear control volume finite element (CVFE) scheme for solving an anisotropic degenerate breast cancer development model is introduced and analyzed. This model includes both ordinary differential equations and convection–diffusion–reaction equations modeling the stepwise mutations from a normal breast stem cell to a tumor cell. The diffusion term, which generally involves an anisotropic and heterogeneous diffusion tensor, is discretized on a dual mesh by means of the piecewise linear conforming finite element method and using the Godunov scheme to approximate the diffusion fluxes provided by the conforming finite element reconstruction. The other terms are discretized using a nonclassical upwind finite volume scheme on the dual mesh, where the dual volumes are constructed around the vertices of the original mesh. This technique ensures the positivity and boundedness of discrete solutions without any restriction on the diffusion tensor nor the transmissibility coefficients. The convergence of the scheme is proved, only supposing the shape regularity condition for the original mesh and using a priori estimates as well as the Kolmogorov relative compactness theorem. The proposed scheme is robust, locally conservative, efficient, and stable, which is confirmed by numerical experiments over a general mesh.

Cadmium Exposure Inhibits Branching Morphogenesis and Causes Alterations Consistent With HIF-1α Inhibition in Human Primary Breast Organoids.

Developmental cadmium exposure in vivo disrupts mammary gland differentiation, while exposure of breast cell lines to cadmium causes invasion consistent with the epithelial-mesenchymal transition (EMT). The effects of cadmium on normal human breast stem cells have not been measured. Here, we quantified the effects of cadmium exposure on reduction mammoplasty patient-derived breast stem cell proliferation and differentiation. Using the mammosphere assay and organoid formation in 3D hydrogels, we tested 2 physiologically relevant doses of cadmium, 0.25 and 2.5 µM, and tested for molecular alterations using RNA-seq. We functionally validated our RNA-seq findings with a hypoxia-inducible factor (HIF)-1α activity reporter line and pharmaceutical inhibition of HIF-1α in organoid formation assays. 2.5 µM cadmium reduced primary mammosphere formation and branching structure organoid formation rates by 33% and 87%, respectively. Despite no changes in mammosphere formation, 0.25 µM cadmium inhibited branching organoid formation in hydrogels by 73%. RNA-seq revealed cadmium downregulated genes associated with extracellular matrix formation and EMT, while upregulating genes associated with metal response including metallothioneins and zinc transporters. In the RNA-seq data, cadmium downregulated HIF-1α target genes including LOXL2, ZEB1, and VIM. Cadmium significantly inhibited HIF-1α activity in a luciferase assay, and the HIF-1α inhibitor acriflavine ablated mammosphere and organoid formation. These findings show that cadmium, at doses relevant to human exposure, inhibited human mammary stem cell proliferation and differentiation, potentially through disruption of HIF-1α activity.

The Wnt Signaling Landscape of Mammary Stem Cells and Breast Tumors.

Attention has been focused on Wnt signaling in the mouse mammary gland for several decades, firstly by the discovery of several Wnt loci among the oncogenes revealed by MMTV-based insertional mutagenesis screening of mouse mammary gland, and then by the remarkable visualization of Wnt-dependent specification of mammary placodes in embryonic skin. This review aims to summarize the impact of recent data for our understanding of the roles of Wnt signaling in these roles. The amount and identity of both familiar and novel Wnt signaling components is examined for mouse mammary epithelial cells. The hierarchical arrangement of mammary epithelial cell progenitors and stem cells inferred from the study of isolated cells is reinterpreted in an era that has demonstrated almost limitless cellular plasticity. Functional definitions of stem and progenitor activities are reevaluated with the discovery of novel stem cell activities and regulators, and we draw parallels with the arrangement of replication-competent cells in other tissues. Although Wnt signaling is highly oncogenic for mouse mammary epithelia, the data supporting Wnt signaling as a tumor driver for human breast cancer are still flimsy, and there is little support for the recruitment of normal Wnt-dependent breast stem cells as tumor precursor cells for either mouse or human. We discuss possible explanations for this paradox and questions still unanswered, including the potential impact of recent discoveries of Wnt-secreting microenvironments, oncogenic changes in the Rspo/Lgr/Ubiquitin ligase amplifier complex, as they could apply to breast tissues, and the feedback suppression of Wnt signaling that characterizes its developmental activity and may hide Wnt signatures in tumors.

Mutation Mechanisms of Human Breast Cancer.

Cancer is a class of diseases caused by the accumulation of gene mutations. All mutated genes constitute a genetic network for cancer progression. It is very helpful for tumor diagnosis and therapy if we know how many mutated genes are needed for human breast cancer. In this article, we investigate the mutation mechanisms of human breast cancer by modeling the data of surveillance, epidemiology, and end results registry. The data are age-specific incidence rates of breast cancer of females in the United States. We set up stochastic multistage models to estimate the age-specific incidence rates by using several coupled ordinary differential equations derived from the Kolmogorov backward equations. Our results suggest that 2-14 mutations in the genome of breast stem cells are required for normal breast stem cells to become a malignant cell, and 3 gene mutations are most likely to occur in the development of female breast cancer.

Modulation of SOX2 expression delineates an end-point for paclitaxel-effectiveness in breast cancer stem cells

Tumor relapse in triple negative breast cancer patients has been implicated to chemoresistant cancer stem cells (CSCs), which under favorable conditions culminate in tumor re-formation and metastasis. Hence, eradication of CSCs during systemic chemotherapy is imperative. CSCs were sorted using immuno-phenotyping and aldefluor assay. Gene expression profiling of normal breast stem cells and breast CSCs from chemo-treated patients were carried out. Silencing SOX2 was achieved by siRNA method. Mammosphere culture and wound healing assays were carried out to assess efficacy of CSCs. Microarray analysis revealed elevated expression of SOX2, ABCG2 and TWIST1, unraveling an intertwined pluripotency-chemoresistance-EMT axis. Although paclitaxel treatment led to temporary arrest of cell migration, invasiveness resumed after drug removal. The ‘twist in the tale’ was a consistently elevated expression of TWIST1, substantiating that TWIST1 can also promote stemness and chemoresistance in tumors; hence, its eradication was imperative. Silencing SOX2 increased chemo-sensitivity and diminished sphere formation, and led to TWIST1 down regulation. This study eventually established that SOX2 silencing of CSCs along with paclitaxel treatment reduced SOX2-ABCG2-TWIST1 expression, disrupted sphere forming capacity and also reduced invasiveness by retaining epithelial-like properties of the cells, thereby suggesting a more comprehensive therapy for TNBC patients in future.

Abstract 939: Single cell mRNA expression profiling reveals heterogeneity of normal and malignant breast stem cell populations

Abstract The normal breast contains epithelial populations which are hierarchically organized, a profile recapitulated in breast cancer. At the apex of these hierarchies are "stem like" cells defined by their capacity to self-renew as well as to generate more differentiated progeny. In breast cancer these "cancer stem cells" (CSCs) have been shown to be important mediators of tumor metastasis and treatment resistance. Although the phenotypes of normal rodent and human mammary stem cells have been characterized, CSC populations are operationally defined by their capacity for tumor initiation. In addition, putative breast CSC markers such as CD44+/CD24low/- and or ALDH+ have proven useful in enriching for cells capable of tumor initiation and previous studies have suggested that these markers identify alternative mesenchymal and epithelial stem cell states, respectively. However, it remains unclear whether CSCs exist in discrete states or whether these cells actually represent a continuum reflected in heterogeneity of cell populations defined by expression of these markers. To address this question we utilized single cell mRNA expression profiling of normal and malignant breast stem cells. We first generated a panel of 96 genes representing stem cell and developmental pathways and analyzed expression of these 96 genes utilizing Fluidigm’s C1 and BioMark HD technologies and TaqMan gene expression assays. We also utilized Fluidigm’s Polaris to selectively isolate single cells that were then analyzed by illumina RNA-Seq method. Utilizing these advanced technologies, we demonstrated that both normal and malignant breast stem cells characterized by CD44+/CD24low/- and or ALDH+ expression are highly heterogeneous. For example, the ALDH isoforms ALDH1A1 and ALDH1A3 were each expressed in some single cells and co-expressed in others. ALDH1A1 expressing single cells appeared to express a unique gene pattern characterized by SLIT/ROBO, PLXNA2, RHOU and HNF1a. These results suggest that at the level of mRNA expression, normal and malignant breast stem cells display a greater heterogeneity than has previously been reported. These results have important implications for breast carcinogenesis as well as for the development of therapeutic strategies designed to target CSCs in breast cancer. Citation Format: Shamileh Fouladdel, Justin Colacino, Ebrahim Azizi, Max S. Wicha. Single cell mRNA expression profiling reveals heterogeneity of normal and malignant breast stem cell populations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 939. doi:10.1158/1538-7445.AM2017-939

Reducing interferon'ce in stem cells.

Little is known regarding how the interactions of stem cells with the immune system regulate their plasticity. A study now describes a mechanism by which normal breast and cancer stem cells utilize miR-199a to downregulate the corepressor LCOR and minimize responses to type I interferon.

FGF2 and EGF Are Required for Self-Renewal and Organoid Formation of Canine Normal and Tumor Breast Stem Cells.

Recent studies suggest that human tumors are generated from cancer cells with stem cell (SC) properties. Spontaneously occurring cancers in dogs contain a diversity of cells that like for human tumors suggest that certain canine tumors are also generated from cancer stem cells (CSCs). CSCs, like normal SCs, have the capacity for self-renewal as mammospheres in suspension cultures. To understand how cells with SC properties contribute to canine mammary gland tumor development and progression, comparative analysis between normal SCs and CSCs, obtained from the same individual, is essential. We have utilized the property of sphere formation to develop culture conditions for propagating stem/progenitor cells from canine normal and tumor tissue. We show that cells from dissociated mammospheres retain sphere reformation capacity for several serial passages and have the capacity to generate organoid structures ex situ. Utilizing various culture conditions for passaging SCs and CSCs, fibroblast growth factor 2 (FGF2) and epidermal growth factor (EGF) were found to positively or negatively regulate mammosphere regeneration, organoid formation, and multi-lineage differentiation potential. The response of FGF2 and EGF on SCs and CSCs was different, with increased FGF2 and EGF self-renewal promoted in SCs and repressed in CSCs. Our protocol for propagating SCs from normal and tumor canine breast tissue will provide new opportunities in comparative mammary gland stem cell analysis between species and anticancer treatment and therapies for dogs. J. Cell. Biochem. 118: 570-584, 2017. © 2016 Wiley Periodicals, Inc.

Transcriptomic profiling of curcumin-treated human breast stem cells identifies a role for stearoyl-coa desaturase in breast cancer prevention.

Curcumin is a potential agent for both the prevention and treatment of cancers. Curcumin treatment alone, or in combination with piperine, limits breast stem cell self-renewal, while remaining non-toxic to normal differentiated cells. We paired fluorescence-activated cell sorting with RNA sequencing to characterize the genome-wide changes induced specifically in normal breast stem cells following treatment with these compounds. We generated genome-wide maps of the transcriptional changes that occur in epithelial-like (ALDH+) and mesenchymal-like (ALDH-/CD44+/CD24-) normal breast stem/progenitor cells following treatment with curcumin and piperine. We show that curcumin targets both stem cell populations by down-regulating expression of breast stem cell genes including ALDH1A3, CD49f, PROM1, and TP63. We also identified novel genes and pathways targeted by curcumin, including downregulation of SCD. Transient siRNA knockdown of SCD in MCF10A cells significantly inhibited mammosphere formation and the mean proportion of CD44+/CD24- cells, suggesting that SCD is a regulator of breast stemness and a target of curcumin in breast stem cells. These findings extend previous reports of curcumin targeting stem cells, here in two phenotypically distinct stem/progenitor populations isolated from normal human breast tissue. We identified novel mechanisms by which curcumin and piperine target breast stem cell self-renewal, such as by targeting lipid metabolism, providing a mechanistic link between curcumin treatment and stem cell self-renewal. These results elucidate the mechanisms by which curcumin may act as a cancer-preventive compound and provide novel targets for cancer prevention and treatment.

Abstract A29: Detection of ultra-rare mutations during breast stem cell tumor progression by Duplex Sequencing

Abstract Most studies have mainly investigated clonal mutations due to the high background error frequencies of conventional next generation sequencing (NGS) methods. We have established a new method termed Duplex Sequencing (DS) that detects mutations with unprecedented accuracy and enables us to detect sub-clonal and rare mutations as well as clonal mutations. Using DS, we present our first genome-wide analysis of mitochondrial (mt) DNA mutations during the transformation of human normal breast stem cells to tumorigenic cells. We used a model system to dissect sequential steps in the progression of normal stem cells to tumorigenic cells. Significant differences have been found among normal stem cells, immortal cells, and tumorigenic cells. These cells differ in putative breast cancer stem cell (CSC) populations, mtDNA copy numbers, and the frequencies and types of mutations. We found that putative CSCs and mtDNA copy numbers increase as normal stem cells become tumorigenic cells. The vast majority of mutations identified in our study are stochastic (rare mutations) and the frequency of rare mutations is lower in transformed cells than in normal stem cells. This lower rare mutation load in transformed cells induces lower scores of predicted pathogenicity in transformed cells than in normal stem cells. C&amp;gt;T/G&amp;gt;A and A&amp;gt;G/T&amp;gt;C transitions are the major mutation types in normal stem cells, while only C&amp;gt;T/G&amp;gt;A are the major mutation types in transformed cells. Using DS, we detected a total of 1220 rare mutations and 678 of these variants have not been reported previously. The mtDNA mutation spectra of breast tumorigenic cells correlate with published nuclear DNA mutation signatures, which are found in the majority of tumors. We have identified mutations that can serve as potential biomarkers that indicate the different stages of breast carcinogenesis. These significant differences in mutation profiles could aid in characterizing different phenotypes between normal stem cells and transformed cells. Citation Format: Eun Hyun Ahn, Kensen Hirohata, Seung Hyuk Lee, Joon Yup Kim, Brendan F. Kohrn, Edward J. Fox, Chia-Cheng Chang, Lawrence A. Loeb. Detection of ultra-rare mutations during breast stem cell tumor progression by Duplex Sequencing. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr A29.

Leptin and Adiponectin Modulate the Self-renewal of Normal Human Breast Epithelial Stem Cells.

Multiple mechanisms are likely to account for the link between obesity and increased risk of postmenopausal breast cancer. Two adipokines, leptin and adiponectin, are of particular interest due to their opposing biologic functions and associations with breast cancer risk. In the current study, we investigated the effects of leptin and adiponectin on normal breast epithelial stem cells. Levels of leptin in human adipose explant-derived conditioned media positively correlated with the size of the normal breast stem cell pool. In contrast, an inverse relationship was found for adiponectin. Moreover, a strong linear relationship was observed between the leptin/adiponectin ratio in adipose conditioned media and breast stem cell self-renewal. Consistent with these findings, exogenous leptin stimulated whereas adiponectin suppressed breast stem cell self-renewal. In addition to local in-breast effects, circulating factors, including leptin and adiponectin, may contribute to the link between obesity and breast cancer. Increased levels of leptin and reduced amounts of adiponectin were found in serum from obese compared with age-matched lean postmenopausal women. Interestingly, serum from obese women increased stem cell self-renewal by 30% compared with only 7% for lean control serum. Taken together, these data suggest a plausible explanation for the obesity-driven increase in postmenopausal breast cancer risk. Leptin and adiponectin may function as both endocrine and paracrine/juxtacrine factors to modulate the size of the normal stem cell pool. Interventions that disrupt this axis and thereby normalize breast stem cell self-renewal could reduce the risk of breast cancer.

Steroid hormones, steroid receptors, and breast cancer stem cells.

The ovarian hormones progesterone and estrogen play important roles in breast cancer etiology, proliferation, and treatment. Androgens may also contribute to breast cancer risk and progression. In recent years, significant advances have been made in defining the roles of these steroid hormones in stem cell homeostasis in the breast. Stem cells are potential origins of breast cancer and may dictate tumor phenotype. At least a portion of breast cancers are proposed to be driven by cancer stem cells (CSCs), cells that mimic the self-renewing and repopulating properties of normal stem cells, and can confer drug resistance. Progesterone has been identified as the critical hormone regulating normal murine mammary stem cell (MaSC) populations and normal human breast stem cells. Synthetic progestins increase human breast cancer risk; one theory speculates that this occurs through increased stem cells. Progesterone treatment also increases breast CSCs in established breast cancer cell lines. This is mediated in part through progesterone regulation of transcription factors, signal transduction pathways, and microRNAs. There is also emerging evidence that estrogens and androgens can regulate breast CSC numbers. The evolving concept that a breast CSC phenotype is dynamic and can be influenced by cell signaling and external cues emphasizes that steroid hormones could be crucial players in controlling CSC number and function. Here we review recent studies on steroid hormone regulation of breast CSCs, and discuss mechanisms by which this occurs.

Models of Breast Morphogenesis Based on Localization of Stem Cells in the Developing Mammary Lobule

SummaryCharacterization of normal breast stem cells is important for understanding their role in breast development and in breast cancer. However, the identity of these cells is a subject of controversy and their localization in the breast epithelium is not known. In this study, we utilized a novel approach to analyze the morphogenesis of mammary lobules, by combining one-dimensional theoretical models and computer-generated 3D fractals. Comparing predictions of these models with immunohistochemical analysis of tissue sections for candidate stem cell markers, we defined distinct areas where stem cells reside in the mammary lobule. An increased representation of stem cells was found in smaller, less developed lobules compared to larger, more mature lobules, with marked differences in the gland of nulliparous versus parous women and that of BRCA1/2 mutation carriers versus non-carriers.