Use of MMTV-Wnt-1 transgenic mice for studying the genetic basis of breast cancer

Fusobacterium nucleatum carcinogenesis and drug delivery interventions

The microbiome has emerged as a significant biomarker and modulator in cancer development and treatment response. Recent research highlights the notable role of Fusobacterium nucleatum (F. nucleatum) in various tumor types, including breast, colorectal, esophageal, gastric, pancreatic, and lung cancers. Accumulating evidence suggests that the local microbial community forms an integral component of the tumor microenvironment, with bacterial communities within tumors displaying specificity to tumor types. Mechanistic investigations indicate that tumor-associated microbiota can directly influence tumor initiation, progression, and responses to chemotherapy or immunotherapy. This article presents a comprehensive review of microbial communities especially F. nucleatum in tumor tissue, exploring their roles and underlying mechanisms in tumor development, treatment, and prevention. When the tumor-associated F. nucleatum is killed, the host immune response is activated to recognize tumor cells. Bacteria epitopes restricted by the host antigens, can be identified for future anti-bacteria/tumor vaccine development.

ΔNp63 regulates MDSC survival and metabolism in triple-negative breast cancer

Triple-negative breast cancer (TNBC) contributes greatly to mortality of breast cancer, demanding new targetable options. We have shown that TNBC patients have high ΔNp63 expression in tumors. However, the function of ΔNp63 in established TNBC is yet to be explored. In current studies, targeting ΔNp63 with inducible CRISPR knockout and Histone deacetylase inhibitor Quisinostat showed that ΔNp63 is important for tumor progression and metastasis in established tumors by promoting myeloid-derived suppressor cell (MDSC) survival through tumor necrosis factor alpha. Decreasing ΔNp63 levels are associated with decreased CD4+ and FOXP3+ T-cells but increased CD8+ T-cells. RNA sequencing analysis indicates that loss of ΔNp63 alters multiple MDSC properties such as lipid metabolism, chemotaxis, migration, and neutrophil degranulation besides survival. We further demonstrated that targeting ΔNp63 sensitizes chemotherapy. Overall, we showed that ΔNp63 reprograms the MDSC-mediated immunosuppressive functions in TNBC, highlighting the benefit of targeting ΔNp63 in chemotherapy-resistant TNBC.

Pirfenidone ameliorates alcohol-induced promotion of breast cancer in mice

Purpose

Alcohol consumption increases the risk of breast cancer and promotes cancer progression. Alcohol exposure could affect both processes of the mammary carcinogenesis, namely, the cell transformation and onset of tumorigenesis as well as cancer aggressiveness including metastasis and drug resistance/recurrence. However, the cellular and molecular mechanisms underlying alcohol tumor promotion remain unclear. There are four members of the mammalian p38 mitogen-activated protein kinase (MAPK) family, namely, p38α, p38β, p38γ and p38δ. We have previously demonstrated alcohol exposure selectively activated p38γ MAPK in breast cancer cells in vitro and in vivo. Pirfenidone (PFD), an antifibrotic compound approved for the treatment of idiopathic pulmonary fibrosis, is also a pharmacological inhibitor of p38γ MAPK. This study aimed to determine whether PFD is useful to inhibit alcohol-induced promotion of breast cancer.

Methods

Female adolescent (5 weeks) MMTV-Wnt1 mice were exposed to alcohol with a liquid diet containing 6.7% ethanol. Some mice received intraperitoneal (IP) injection of PFD (100 mg/kg) every other day. After that, the effects of alcohol and PFD on mammary tumorigenesis and metastasis were examined.

Results

Alcohol promoted the progression of mammary tumors in adolescent MMTV-Wnt1 mice. Treatment of PFD blocked tumor growth and alcohol-promoted metastasis. It also significantly inhibited alcohol-induced tumorsphere formation and cancer stem cell (CSC) population.

Conclusion

PFD inhibited mammary tumor growth and alcohol-promoted metastasis. Since PFD is an FDA-approved drug, the current findings may be helpful to re-purpose its application in treating aggressive breast cancer and alcohol-promoted mammary tumor progression.

Mouse retrotransposons: sequence structure, evolutionary age, genomic distribution and function

Retrotransposons are transposable elements that are transposed via transcription and reverse transcription. Their copies have accumulated in the genome of mammals, occupying approximately 40% of mammalian genomic mass. These copies are often involved in numerous phenomena, such as chromatin spatial organization, gene expression, development and disease, and have been recognized as a driving force in evolution. Different organisms have gained specific retrotransposon subfamilies and retrotransposed copies, such as hundreds of Mus-specific subfamilies with diverse sequences and genomic locations. Despite this complexity, basic information is still necessary for present-day genomic and epigenomic studies. Herein, we describe the characteristics of each subfamily of Mus-specific retrotransposons in terms of sequence structure, phylogenetic relationships, evolutionary age, and preference for A or B compartments of chromatin.

Microbiota may affect the tumor type but not overall tumor development in two models of heritable cancer

Microbial impact on tumorigenesis of heritable cancers proximal to the gut is well documented. Whether the microbiota influences cancers arising from inborn mutations at sites distal to the gut is undetermined. Using two models of heritable cancer, we found the microbiota to be inconsequential for tumor development. However, the type of tumor that develops may be influenced by the microbiota. This work furthers our understanding of the microbial impact on tumor development.

High-Throughput Identification, Modeling, and Analysis of Cancer Driver Genes In Vivo

The vast number of genomic and molecular alterations in cancer pose a substantial challenge to uncovering the mechanisms of tumorigenesis and identifying therapeutic targets. High-throughput functional genomic methods in genetically engineered mouse models allow for rapid and systematic investigation of cancer driver genes. In this review, we discuss the basic concepts and tools for multiplexed investigation of functionally important cancer genes in vivo using autochthonous cancer models. Furthermore, we highlight emerging technical advances in the field, potential opportunities for future investigation, and outline a vision for integrating multiplexed genetic perturbations with detailed molecular analyses to advance our understanding of the genetic and molecular basis of cancer.

Global Down-regulation of Gene Expression Induced by Mouse Mammary Tumor Virus (MMTV) in Normal Mammary Epithelial Cells

Mouse mammary tumor virus (MMTV) is a betaretrovirus that causes breast cancer in mice. The mouse mammary epithelial cells are the most permissive cells for MMTV, expressing the highest levels of virus upon infection and being the ones later transformed by the virus due to repeated rounds of infection/superinfection and integration, leading eventually to mammary tumors. The aim of this study was to identify genes and molecular pathways dysregulated by MMTV expression in mammary epithelial cells. Towards this end, mRNAseq was performed on normal mouse mammary epithelial cells stably expressing MMTV, and expression of host genes was analyzed compared with cells in its absence. The identified differentially expressed genes (DEGs) were grouped on the basis of gene ontology and relevant molecular pathways. Bioinformatics analysis identified 12 hub genes, of which 4 were up-regulated (Angp2, Ccl2, Icam, and Myc) and 8 were down-regulated (Acta2, Cd34, Col1a1, Col1a2, Cxcl12, Eln, Igf1, and Itgam) upon MMTV expression. Further screening of these DEGs showed their involvement in many diseases, especially in breast cancer progression when compared with available data. Gene Set Enrichment Analysis (GSEA) identified 31 molecular pathways dysregulated upon MMTV expression, amongst which the PI3-AKT-mTOR was observed to be the central pathway down-regulated by MMTV. Many of the DEGs and 6 of the 12 hub genes identified in this study showed expression profile similar to that observed in the PyMT mouse model of breast cancer, especially during tumor progression. Interestingly, a global down-regulation of gene expression was observed, where nearly 74% of the DEGs in HC11 cells were repressed by MMTV expression, an observation similar to what was observed in the PyMT mouse model during tumor progression, from hyperplasia to adenoma to early and late carcinomas. Comparison of our results with the Wnt1 mouse model revealed further insights into how MMTV expression could lead to activation of the Wnt1 pathway independent of insertional mutagenesis. Thus, the key pathways, DEGs, and hub genes identified in this study can provide important clues to elucidate the molecular mechanisms involved in MMTV replication, escape from cellular anti-viral response, and potential to cause cell transformation. These data also validate the use of the MMTV-infected HC11 cells as an important model to study early transcriptional changes that could lead to mammary cell transformation.

Cancer fitness genes: emerging therapeutic targets for metastasis

Development of cancer therapeutics has traditionally focused on targeting driver oncogenes. Such an approach is limited by toxicity to normal tissues and treatment resistance. A class of 'cancer fitness genes' with crucial roles in metastasis have been identified. Elevated or altered activities of these genes do not directly cause cancer; instead, they relieve the stresses that tumor cells encounter and help them adapt to a changing microenvironment, thus facilitating tumor progression and metastasis. Importantly, as normal cells do not experience high levels of stress under physiological conditions, targeting cancer fitness genes is less likely to cause toxicity to noncancerous tissues. Here, we summarize the key features and function of cancer fitness genes and discuss their therapeutic potential.

Breast tumor IGF1R regulates cell adhesion and metastasis: alignment of mouse single cell and human breast cancer transcriptomics

Introduction

The acquisition of a metastatic phenotype is the critical event that determines patient survival from breast cancer. Several receptor tyrosine kinases have functions both in promoting and inhibiting metastasis in breast tumors. Although the insulin-like growth factor 1 receptor (IGF1R) has been considered a target for inhibition in breast cancer, low levels of IGF1R expression are associated with worse overall patient survival.

Methods

To determine how reduced IGF1R impacts tumor phenotype in human breast cancers, we used weighted gene co-expression network analysis (WGCNA) of Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) patient data to identify gene modules associated with low IGF1R expression. We then compared these modules to single cell gene expression analyses and phenotypes of mouse mammary tumors with reduced IGF1R signaling or expression in a tumor model of triple negative breast cancer.

Results

WGCNA from METABRIC data revealed gene modules specific to cell cycle, adhesion, and immune cell signaling that were inversely correlated with IGF1R expression in human breast cancers. Integration of human patient data with single cell sequencing data from mouse tumors revealed similar pathways necessary for promoting metastasis in basal-like mammary tumors with reduced signaling or expression of IGF1R. Functional analyses revealed the basis for the enhanced metastatic phenotype including alterations in E- and P-cadherins.

Discussion

Human breast and mouse mammary tumors with reduced IGF1R are associated with upregulation of several pathways necessary for promoting metastasis supporting the conclusion that IGF1R normally helps maintain a metastasis suppressive tumor microenvironment. We further found that reduced IGF1R signaling in tumor epithelial cells dysregulates cadherin expression resulting in reduced cell adhesion.

Escape from breast tumor dormancy: The convergence of obesity and menopause

Obesity is associated with an increased risk of, and a poor prognosis for, postmenopausal (PM) breast cancer (BC). Our goal was to determine whether diet-induced obesity (DIO) promotes 1) shorter tumor latency, 2) an escape from tumor dormancy, and 3) an acceleration of tumor growth and to elucidate the underlying mechanism(s). We have developed in vitro assays and PM breast tumor models complemented by a noninvasive imaging system to detect vascular invasion of dormant tumors and have used them to determine whether obesity promotes the escape from breast tumor dormancy and tumor growth by facilitating the switch to the vascular phenotype (SVP) in PM BC. Obese mice had significantly higher tumor frequency, higher tumor volume, and lower overall survival compared with lean mice. We demonstrate that DIO exacerbates mammary gland hyperplasia and neoplasia, reduces tumor latency, and increases tumor frequency via an earlier acquisition of the SVP. DIO establishes a local and systemic proangiogenic and inflammatory environment via the up-regulation of lipocalin-2 (LCN2), vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) that may promote the escape from tumor dormancy and tumor progression. In addition, we show that targeting neovascularization via a multitargeted receptor tyrosine kinase inhibitor, sunitinib, can delay the acquisition of the SVP, thereby prolonging tumor latency, reducing tumor frequency, and increasing tumor-free survival, suggesting that targeting neovascularization may be a potential therapeutic strategy in obesity-associated PM BC progression. This study establishes the link between obesity and PM BC and, for the first time to our knowledge, bridges the dysfunctional neovascularization of obesity with the earliest stages of tumor development.

Ecdysoneless Overexpression Drives Mammary Tumorigenesis through Upregulation of C-MYC and Glucose Metabolism

Ecdysoneless (ECD) protein is essential for embryogenesis, cell-cycle progression, and cellular stress mitigation with an emerging role in mRNA biogenesis. We have previously shown that ECD protein as well as its mRNA are overexpressed in breast cancer and ECD overexpression predicts shorter survival in patients with breast cancer. However, the genetic evidence for an oncogenic role of ECD has not been established. Here, we generated transgenic mice with mammary epithelium-targeted overexpression of an inducible human ECD transgene (ECDTg). Significantly, ECDTg mice develop mammary hyperplasia, preneoplastic lesions, and heterogeneous tumors with occasional lung metastasis. ECDTg tumors exhibit epithelial to mesenchymal transition and cancer stem cell characteristics. Organoid cultures of ECDTg tumors showed ECD dependency for in vitro oncogenic phenotype and in vivo growth when implanted in mice. RNA sequencing (RNA-seq) analysis of ECDTg tumors showed a c-MYC signature, and alterations in ECD levels regulated c-MYC mRNA and protein levels as well as glucose metabolism. ECD knockdown-induced decrease in glucose uptake was rescued by overexpression of mouse ECD as well as c-MYC. Publicly available expression data analyses showed a significant correlation of ECD and c-MYC overexpression in breast cancer, and ECD and c-MYC coexpression exhibits worse survival in patients with breast cancer. Taken together, we establish a novel role of overexpressed ECD as an oncogenesis driver in the mouse mammary gland through upregulation of c-MYC-mediated glucose metabolism.

IMPLICATIONS

We demonstrate ECD overexpression in the mammary gland of mice led to the development of a tumor progression model through upregulation of c-MYC signaling and glucose metabolism.

EBF1 promotes triple-negative breast cancer progression by surveillance of the HIF1α pathway

Early B cell factor 1 (EBF1) is a transcriptional factor with a variety of roles in cell differentiation and metabolism. However, the functional roles of EBF1 in tumorigenesis remain elusive. Here, we demonstrate that EBF1 is highly expressed in triple-negative breast cancer (TNBC). Furthermore, EBF1 has a pivotal role in the tumorigenicity and progression of TNBC. Moreover, we found that depletion of EBF1 induces extensive cell mitophagy and inhibits tumor growth. Genome-wide mapping of the EBF1 transcriptional regulatory network revealed that EBF1 drives TNBC tumorigenicity by assembling a transcriptional complex with HIF1α that fine-tunes the expression of HIF1α targets via suppression of p300 activity. EBF1 therefore holds HIF1α activity in check to avert extensive mitophagy-induced cell death. Our findings reveal a key function for EBF1 as a master regulator of mitochondria homeostasis in TNBC and indicate that targeting this pathway may offer alternative treatment strategies for this aggressive subtype of breast cancer.

Ethanol Exposure Up-Regulates PD-L1/PD-1 Immune Checkpoint Pathway and Promotes Mammary Tumor Development

Alcohol consumption in women enhances breast cancer incidence and ethanol is the main causal factor. Compromised host immunity through immunosuppression facilitates the development of many types of cancer, including breast cancer. Immune cells in breast tissues, particularly tumor-infiltrating CD8 cytotoxic T cells, play a critical role in the host anti-tumor immunity against breast tumorigenesis. These cytotoxic T cells are the major immune cells to carry out anti-tumor immunity through their cytotoxic effector function, which can be regulated by immune checkpoint pathways. The PD-1/PD-L1 pathway (the interaction between programmed death-1, PD-1, and its ligand, programmed death-ligand 1, PD-L1) is the best characterized one. However, the effects of ethanol exposure on T cell anti-tumor immunity and how that may contribute to ethanol-enhanced mammary tumorigenicity remain unknown. FVB.Cg-Tg(Wnt1)1Hev/J transgenic mice develop spontaneous mammary tumors starting around the age of 2-3 months and have been a widely-used mouse model for breast cancer research. Using this mouse model, the current study determined the effects of ethanol on the PD-L1/PD-1 pathway and how that may contribute to mammary tumorigenesis. The results indicated that ethanol exposure enhanced mammary tumor formation accompanied with an up-regulation of PD-1/PD-L1 pathway (increased PD-L1 levels in tumor tissue cells and the amount of PD-1-expressing tumor-infiltrating CD8 T cells) and inhibited T cell anti-tumor function, while inhibition of PD-1/PD-L1 restored T cell anti-tumor effector function and mitigated ethanol-enhanced tumorigenesis.

High-throughput profiling of histone post-translational modifications and chromatin modifying proteins by reverse phase protein array

Epigenetic variation plays a significant role in normal development and human diseases including cancer, in part through post-translational modifications (PTMs) of histones. Identification and profiling of changes in histone PTMs, and in proteins regulating PTMs, are crucial to understanding diseases, and for discovery of epigenetic therapeutic agents. In this study, we have adapted and validated an antibody-based reverse phase protein array (RPPA) platform for profiling 20 histone PTMs and expression of 40 proteins that modify histones and other epigenomic regulators. The specificity of the RPPA assay for histone PTMs was validated with synthetic peptides corresponding to histone PTMs and by detection of histone PTM changes in response to inhibitors of histone modifier proteins in cell cultures. The useful application of the RPPA platform was demonstrated with two models: induction of pluripotent stem cells and a mouse mammary tumor progression model. Described here is a robust platform that includes a rapid microscale method for histone isolation and partially automated workflows for analysis of histone PTMs and histone modifiers that can be performed in a high-throughput manner with hundreds of samples. This RPPA platform has potential for translational applications through the discovery and validation of epigenetic states as therapeutic targets and biomarkers. SIGNIFICANCE: Our study has established an antibody-based reverse phase protein array platform for global profiling of a wide range of post-translational modifications of histones and histone modifier proteins. The high-throughput platform provides comprehensive analyses of epigenetics for biological research and disease studies and may serve as screening assay for diagnostic purpose or therapy development.

Tumor-resident intracellular microbiota promotes metastatic colonization in breast cancer

Tumor-resident intracellular microbiota is an emerging tumor component that has been documented for a variety of cancer types with unclear biological functions. Here, we explored the functional significance of these intratumor bacteria, primarily using a murine spontaneous breast-tumor model MMTV-PyMT. We found that depletion of intratumor bacteria significantly reduced lung metastasis without affecting primary tumor growth. During metastatic colonization, intratumor bacteria carried by circulating tumor cells promoted host-cell survival by enhancing resistance to fluid shear stress by reorganizing actin cytoskeleton. We further showed that intratumor administration of selected bacteria strains isolated from tumor-resident microbiota promoted metastasis in two murine tumor models with significantly different levels of metastasis potential. Our findings suggest that tumor-resident microbiota, albeit at low biomass, play an important role in promoting cancer metastasis, intervention of which might therefore be worth exploring for advancing oncology care.

Role of glypican-1 in regulating multiple cellular signaling pathways

Glypican-1 (GPC1) is one of the six glypican family members in humans. It is composed of a core protein with three heparan sulfate chains and attached to the cell membrane by a glycosyl-phosphatidylinositol anchor. GPC1 modulates various signaling pathways including fibroblast growth factors (FGF), vascular endothelial growth factor-A (VEGF-A), transforming growth factor-β (TGF-β), Wnt, Hedgehog (Hh), and bone morphogenic protein (BMP) through specific interactions with pathway ligands and receptors. The impact of these interactions on signaling pathways, activating or inhibitory, is dependent upon specific GPC1 domain interaction with pathway components, as well as cell surface context. In this review, we summarize the current understanding of the structure of GPC1, as well as its role in regulating multiple signaling pathways. We focus on the functions of GPC1 in cancer cells and how new insights into these signaling processes can inform its translational potential as a therapeutic target in cancer.

High-dimensional immunotyping of tumors grown in obese and non-obese mice

Obesity is a disease characterized by chronic low-grade systemic inflammation and has been causally linked to the development of 13 cancer types. Several studies have been undertaken to determine whether tumors evolving in obese environments adapt differential interactions with immune cells and whether this can be connected to disease outcome. Most of these studies have been limited to single-cell lines and tumor models and analysis of limited immune cell populations. Given the multicellular complexity of the immune system and its dysregulation in obesity, we applied high-dimensional suspension mass cytometry to investigate how obesity affects tumor immunity. We used a 36-marker immune-focused mass cytometry panel to interrogate the immune landscape of orthotopic syngeneic mouse models of pancreatic and breast cancer. Unanchored batch correction was implemented to enable simultaneous analysis of tumor cohorts to uncover the immunotypes of each cancer model and reveal remarkably model-specific immune regulation. In the E0771 breast cancer model, we demonstrate an important link to obesity with an increase in two T-cell-suppressive cell types and a decrease in CD8 T cells.

Advances in Rodent Models for Breast Cancer Formation, Progression, and Therapeutic Testing

Breast cancer is a highly complicated disease. Advancement in the treatment and prevention of breast cancer lies in elucidation of the mechanism of carcinogenesis and progression. Rodent models of breast cancer have developed into premier tools for investigating the mechanisms and genetic pathways in breast cancer progression and metastasis and for developing and evaluating clinical therapeutics. Every rodent model has advantages and disadvantages, and the selection of appropriate rodent models with which to investigate breast cancer is a key decision in research. Design of a suitable rodent model for a specific research purpose is based on the integration of the advantages and disadvantages of different models. Our purpose in writing this review is to elaborate on various rodent models for breast cancer formation, progression, and therapeutic testing.

Laboratory Models for Investigating Breast Cancer Therapy Resistance and Metastasis

While numerous therapies are highly efficacious in early-stage breast cancers and in particular subsets of breast cancers, therapeutic resistance and metastasis unfortunately arise in many patients. In many cases, tumors that are resistant to standard of care therapies, as well as tumors that have metastasized, are treatable but incurable with existing clinical strategies. Both therapy resistance and metastasis are multi-step processes during which tumor cells must overcome diverse environmental and selective hurdles. Mechanisms by which tumor cells achieve this are numerous and include acquisition of invasive and migratory capabilities, cell-intrinsic genetic and/or epigenetic adaptations, clonal selection, immune evasion, interactions with stromal cells, entering a state of dormancy or senescence, and maintaining self-renewal capacity. To overcome therapy resistance and metastasis in breast cancer, the ability to effectively model each of these mechanisms in the laboratory is essential. Herein we review historic and the current state-of-the-art laboratory model systems and experimental approaches used to investigate breast cancer metastasis and resistance to standard of care therapeutics. While each model system has inherent limitations, they have provided invaluable insights, many of which have translated into regimens undergoing clinical evaluation. We will discuss the limitations and advantages of a variety of model systems that have been used to investigate breast cancer metastasis and therapy resistance and outline potential strategies to improve experimental modeling to further our knowledge of these processes, which will be crucial for the continued development of effective breast cancer treatments.

Breast cancer animal models and applications

Breast cancer is the most common malignancy in women. Basic and translational breast cancer research relies heavily on experimental animal models. Ideally, such models for breast cancer should have commonality with human breast cancer in terms of tumor etiology, biological behavior, pathology, and response to therapeutics. This review introduces current progress in different breast cancer experimental animal models and analyzes their characteristics, advantages, disadvantages, and potential applications. Finally, we propose future research directions for breast cancer animal models.

Effects of High-Fructose Diet vs. Teklad Diet in the MNU-Induced Rat Mammary Cancer Model: Altered Tumorigenesis, Metabolomics and Tumor RNA Expression

Epidemiology, clinical and experimental animal studies suggest high fructose diets are detrimental to metabolic status and may contribute to tumor development. This due to increased obesity and metabolic syndrome, known risk factors for many types of cancer. We compared tumor development in N-methyl-N-nitrosourea (MNU)-treated rats fed either a high (60%)-fructose diet (HFD) or a standard diet (SD). Female Sprague-Dawley rats at 43 days of age (DOA) were fed a SD or HFD followed by administration of MNU at 50 DOA. Rats were palpated weekly and sacrificed at 190 DOA. MNU-treated rats on HFD exhibited decreased tumor latency and roughly a two-fold increase in tumor multiplicity. RNA-Seq on frozen tumors (SD vs. HFD rats) showed altered expression of approximately 10% of genes (P < 0.05). When examined by Ingenuity Pathway Analysis, multiple highly significant pathways were identified including A) mechanisms of cancer, B) Wnt pathway, C) immune response (e.g., "Th1 and Th2 activation" and "antigen presentation") and D) LXR/RXR nuclear receptor. These generalized pathways were indirectly confirmed by alterations of various interrelated disease pathways (epithelial cancers, T cell numbers and apoptosis). In a second study, serum was collected from rats on the HFD or SD pre-MNU and at the time of sacrifice. Metabolomics revealed that the HFD yielded: A) increased levels of fructose, B) increases of various monoglycerols, C) reduced levels of various diacylglycerols and oxygenated inflammatory lipids (9 and 13 HODE and 12,13 DHOME) and D) increased levels of secondary bile acids (hyodeoxycholate and 6-oxolithocholate), which may reflect microbiome changes. These metabolomic changes, which are distinct from those on a high-fat diet, may prove relevant when examining individuals who consume higher levels of fructose.

Tumor necrosis factor receptor signaling modulates carcinogenesis in a mouse model of breast cancer

Pro-inflammatory conditions have long been associated with mammary carcinogenesis and breast cancer progression. The underlying mechanisms are incompletely understood but signaling of pro-inflammatory cytokine TNFα through its receptors TNFR1 and TNFR2 is a major mediator of inflammation in both obesity and in the response of tissues to radiation, 2 known risk factors for the development of breast cancer. Here, we demonstrated the loss of one TNFR2 allele led to ductal hyperplasia in the mammary gland with increased numbers of mammary epithelial stem cell and terminal end buds. Furthermore, loss of one TNFR2 allele increased the incidence of breast cancer in MMTV-Wnt1 mice and resulted in tumors with a more aggressive phenotype and metastatic potential. The underlying mechanisms include a preferential activation of canonical NF-κB signaling pathway and autocrine production of TNFα. Analysis of the TCGA dataset indicated inferior overall survival for patients with down-regulated TNFR2 expression. These findings unravel the imbalances in TNFR signaling promote the development and progression of breast cancer, indicating that selective agonists of TNFR2 could potentially modulate the risk for breast cancer in high-risk populations.

Prune-1 drives polarization of tumor-associated macrophages (TAMs) within the lung metastatic niche in triple-negative breast cancer

M2-tumor-associated macrophages (M2-TAMs) in the tumor microenvironment represent a prognostic indicator for poor outcome in triple-negative breast cancer (TNBC).

Here we show that Prune-1 overexpression in human TNBC patients has positive correlation to lung metastasis and infiltrating M2-TAMs. Thus, we demonstrate that Prune-1 promotes lung metastasis in a genetically engineered mouse model of metastatic TNBC augmenting M2-polarization of TAMs within the tumor microenvironment. Thus, this occurs through TGF-β enhancement, IL-17F secretion, and extracellular vesicle protein content modulation.

We also find murine inactivating gene variants in human TNBC patient cohorts that are involved in activation of the innate immune response, cell adhesion, apoptotic pathways, and DNA repair. Altogether, we indicate that the overexpression of Prune-1, IL-10, COL4A1, ILR1, and PDGFB, together with inactivating mutations of PDE9A, CD244, Sirpb1b, SV140, Iqca1, and PIP5K1B genes, might represent a route of metastatic lung dissemination that need future prognostic validations.

•

Prune-1 correlates to M2-TAMs confirming lung metastatic dissemination in GEMM

•

Cytokines and EV proteins are responsible of M2-TAMs polarization processes

•

A small molecule with immunomodulatory properties ameliorates metastatic dissemination

•

Identification of gene variants within immune response and cell adhesion in TNBC

Technical Advancements for Studying Immune Regulation of Disseminated Dormant Cancer Cells

Metastases are a major cause of cancer-related death and despite the fact that they have been focus of intense research over the last two decades, effective therapies for patients with distant secondary lesions are still very limited. In addition, in some tumor types metastases can grow years after the patients have been declared clinically cured, indicating that disseminated cancer cells (DCCs) persist undetected for years, even decades in a quiescent state. Clinical and experimental data highlight the importance of the immune system in shaping the fitness and behaviour of DCCs. Here, we review mechanisms of survival, quiescence and outgrowth of DCCs with a special focus on immune-regulation and we highlight the latest cutting-edge techniques for modelling the biology of DCCs in vitro and for studying the metastatic niche in vivo. We believe that a wide dissemination of those techniques will boost scientific findings towards new therapies to defeat metastatic relapses in cancer patients.

Studying Lymphatic Metastasis in Breast Cancer: Current Models, Strategies, and Clinical Perspectives

Breast cancer is the most commonly diagnosed cancer in women and the second most common cause of cancer-related deaths in the United States. Although early detection has significantly decreased breast cancer mortality, patients diagnosed with distant metastasis still have a very poor prognosis. The most common site that breast cancer spreads to are local lymph nodes. Therefore, the presence of lymph node metastasis remains one of most important prognostic factors in breast cancer patients. Given its significant clinical implications, increased efforts have been dedicated to better understand the molecular mechanism governing lymph node metastasis in breast cancer. The identification of lymphatic-specific biomarkers, including podoplanin and LYVE-1, has propelled the field of lymphatic metastasis forward. In addition, several animal models such as cell line-derived xenografts, patient-derived xenografts, and spontaneous tumor models have been developed to recreate the process of lymphatic metastasis. Moreover, the incorporation of various -omic platforms have provided further insight into the genetic drivers facilitating lymphatic metastasis, as well as potential biomarkers and therapeutic targets. Here, we highlight various models of lymphatic metastasis, their potential pitfalls, and other tools available to study lymphatic metastasis including imaging modalities and -omic studies.

ROCK-mediated selective activation of PERK signalling causes fibroblast reprogramming and tumour progression through a CRELD2-dependent mechanism

It is well accepted that cancers co-opt the microenvironment for their growth. However, the molecular mechanisms that underlie cancer-microenvironment interactions are still poorly defined. Here, we show that Rho-associated kinase (ROCK) in the mammary tumour epithelium selectively actuates protein-kinase-R-like endoplasmic reticulum kinase (PERK), causing the recruitment and persistent education of tumour-promoting cancer-associated fibroblasts (CAFs), which are part of the cancer microenvironment. An analysis of tumours from patients and mice reveals that cysteine-rich with EGF-like domains 2 (CRELD2) is the paracrine factor that underlies PERK-mediated CAF education downstream of ROCK. We find that CRELD2 is regulated by PERK-regulated ATF4, and depleting CRELD2 suppressed tumour progression, demonstrating that the paracrine ROCK-PERK-ATF4-CRELD2 axis promotes the progression of breast cancer, with implications for cancer therapy.

In vitro Models of Breast Cancer Metastatic Dormancy

Delayed relapses at distant sites are a common clinical observation for certain types of cancers after removal of primary tumor, such as breast and prostate cancer. This evidence has been explained by postulating a long period during which disseminated cancer cells (DCCs) survive in a foreign environment without developing into overt metastasis. Because of the asymptomatic nature of this phenomenon, isolation, and analysis of disseminated dormant cancer cells from clinically disease-free patients is ethically and technically highly problematic and currently these data are largely limited to the bone marrow. That said, detecting, profiling and treating indolent metastatic lesions before the onset of relapse is the imperative. To overcome this major limitation many laboratories developed in vitro models of the metastatic niche for different organs and different types of cancers. In this review we focus specifically on in vitro models designed to study metastatic dormancy of breast cancer cells (BCCs). We provide an overview of the BCCs employed in the different organotypic systems and address the components of the metastatic microenvironment that have been shown to impact on the dormant phenotype: tissue architecture, stromal cells, biochemical environment, oxygen levels, cell density. A brief description of the organ-specific in vitro models for bone, liver, and lung is provided. Finally, we discuss the strategies employed so far for the validation of the different systems.

Long non-coding RNA in bladder cancer

Bladder cancer (BC) is the ninth most common malignant disease and ranks fourteenth in cancer mortality worldwide. Moreover, among cancers, the incidence and mortality of BC in males increased to the 6th and 9th place, respectively. The overall survival (OS) declines dramatically as the cancer progresses, especially when urothelial cells transition from noninvasive to invasive. It is well known that epithelial cells can acquire invasive properties and a propensity to metastasize through the epithelial-to-mesenchymal transition (EMT) process in tumourigenesis and progression. However, the potential molecular mechanisms and key pathways are still unclear. As the sequencing technology advances, long non-coding RNAs (lncRNAs) have been proven to play an important role in regulating biological processes and cellular pathways. Here, we reviewed important lncRNAs, such as H19, UCA1 and MALAT1, that participate in the malignant phenotype of BC and regulate EMT signalling networks in the invasion-metastasis cascade during BC development. We further discuss MALAT1, PCAT-1 and SPRY4-IT1, and also urine and blood exosomal H19 and PTENP as potential noninvasive biomarkers. Moreover, antisense oligonucleotides (ASOs) and a double-stranded DNA plasmid (BC-819) have been designed for use in preclinical cancer models and clinical trials in patients. Therefore, the results of investigations have gradually prompted the utility of lncRNAs.

Estrogen Induces Mammary Ductal Dysplasia via the Upregulation of Myc Expression in a DNA-Repair-Deficient Condition

Mammary ductal dysplasia is a phenotype observed in precancerous lesions and early-stage breast cancer. However, the mechanism of dysplasia formation remains elusive. Here we show, by establishing a novel dysplasia model system, that estrogen, a female hormone, has the potential to cause mammary ductal dysplasia. We injected estradiol (E2), the most active form of estrogen, daily into scid mice with a defect in non-homologous end joining repair and observed dysplasia formation with cell proliferation at day 30. The protooncogene Myc is a downstream target of estrogen signaling, and we found that its expression is augmented in mammary epithelial cells in this dysplasia model. Treatment with a Myc inhibitor reduced E2-induced dysplasia formation. Moreover, we found that isoflavones inhibited E2-induced dysplasia formation. Our dysplasia model system provides insights into the mechanistic understanding of breast tumorigenesis and the development of breast cancer prevention.

•

Excess amount of estrogen administration in scid mice induces mammary ductal dysplasia

•

E2-induced Myc expression is one of the causes of dysplasia formation

•

Progesterone and isoflavones have a potential to prevent E2-induced dysplasia

Deletion of tetraspanin CD151 alters the Wnt oncogene-induced mammary tumorigenesis: A cell type-linked function and signaling

Tetraspanin CD151 is increasingly implicated as a multifaceted mediator of cancer development and progression. Here we investigated the role of CD151 in breast cancer in the context of the Wnt oncogenic activation. Our data showed that removal of one or both of CD151 alleles in the MMTV-Wnt1 model significantly decreased the tumor-free survival of mice from 34 weeks on average to 22 weeks and 18 weeks, respectively. This effect coincided with an accelerated tumor growth and an increased number of Ki-67⁺ proliferative cells. Mechanistically, the CD151-deficient tumors were largely ER⁺, and exhibited hyperactivation of the Wnt pathway as reflected by a marked upregulation in β-catenin and Cyclin D1, and their target genes. In addition, E-cadherin displayed a cytosolic distribution and transcription factor Snail was markedly upregulated. Collectively, this data implies that CD151 suppresses the Wnt1-driven tumorigenesis, at least in part, via counteracting the epithelial-mesenchymal transition (EMT)-like program in luminal epithelial cells. Meanwhile, the proportion of tumor cells expressing CK5 or p63, the biomarkers of myoepithelial/basal cells, markedly decreased in the absence of CD151. This change was accompanied by a decreased invasiveness of tumors and their incompetence to form a long-term cell culture. Consistent with this basal cell-linked role, the CD151 downregulation impairs mammosphere formation in MCF-10A cells and the defect was rescued by re-expression of intact CD151 ORF, but not its integrin binding-defective mutant. Overall, our study suggests that CD151 is a key player in the Wnt oncogene-driven tumorigenesis and impacts breast cancer malignancy in a cell type-dependent manner.

CD36 promotes the epithelial-mesenchymal transition and metastasis in cervical cancer by interacting with TGF-β

Background

Accumulating evidence indicates that CD36 initiates metastasis and correlates with an unfavorable prognosis in cancers. However, there are few reports regarding the roles of CD36 in initiation and metastasis of cervical cancer.

Methods

Using immunohistochemistry, we analyzed 133 cervical cancer samples for CD36 protein expression levels, and then investigated the correlation between changes in its expression and clinicopathologic parameters. The effect of CD36 expression on the epithelial–mesenchymal transition (EMT) in cervical cancer cells was evaluated by Western immunoblotting analysis. In vitro invasion and in vivo metastasis assays were also used to evaluate the role of CD36 in cervical cancer metastasis.

Results

In the present study, we confirmed that CD36 was highly expressed in cervical cancer samples relative to normal cervical tissues. Moreover, overexpression of CD36 promoted invasiveness and metastasis of cervical cancer cells in vitro and in vivo, while CD36 knockdown suppressed proliferation, migration, and invasiveness. We demonstrated that TGF-β treatment attenuated E-cadherin expression and enhanced the expression levels of CD36, vimentin, slug, snail, and twist in si-SiHa, si-HeLa, and C33a–CD36 cells, suggesting that TGF-β synergized with CD36 on EMT via active CD36 expression. We also observed that the expression levels of TGF-β in si-SiHa cells and si-HeLa cells were down-regulated, whereas the expression levels of TGF-β were up-regulated in C33a–CD36 cells. These results imply that CD36 and TGF-β interact with each other to promote the EMT in cervical cancer.

Conclusions

Our findings suggest that CD36 is likely to be an effective target for guiding individualized clinical therapy of cervical cancer.

Protein C receptor is a therapeutic stem cell target in a distinct group of breast cancers

Breast cancer is a heterogeneous disease. In particular, triple-negative breast cancer (TNBC) comprises various molecular subgroups with unclear identities and currently has few targeted treatment options. Our previous study identified protein C receptor (Procr) as a surface marker on mammary stem cells (MaSCs) located in the basal layer of the normal mammary gland. Given the possible connection of TNBC with basal layer stem cells, we conducted comparative analyses of Procr in breast cancers of mouse and human origin. In mouse mammary tumors, we showed that Procr⁺ cells are enriched for cancer stem cells (CSCs) in Wnt1 basal-like tumors, but not in Brca1 basal-like tumors or PyVT luminal tumors. In human cancers, PROCR was robustly expressed in half of TNBC cases. Experiments with patient-derived xenografts (PDXs) revealed that PROCR marks CSCs in this discrete subgroup (referred to as PROCR⁺ TNBC). Interfering with the function of PROCR using an inhibitory nanobody reduced the CSC numbers, arrested tumor growth and prevented rapid tumor recurrence. Our data suggest a key role of MaSC in breast tumorigenesis. Moreover, our work indicates that PROCR can be used as a biomarker to stratify TNBC into clinically relevant subgroups and may provide a novel targeted treatment strategy for this clinically important tumor subtype.

Transcriptional regulation of normal human mammary cell heterogeneity and its perturbation in breast cancer

The mammary gland in adult women consists of biologically distinct cell types that differ in their surface phenotypes. Isolation and molecular characterization of these subpopulations of mammary cells have provided extensive insights into their different transcriptional programs and regulation. This information is now serving as a baseline for interpreting the heterogeneous features of human breast cancers. Examination of breast cancer mutational profiles further indicates that most have undergone a complex evolutionary process even before being detected. The consequent intra-tumoral as well as inter-tumoral heterogeneity of these cancers thus poses major challenges to deriving information from early and hence likely pervasive changes in potential therapeutic interest. Recently described reproducible and efficient methods for generating human breast cancers de novo in immunodeficient mice transplanted with genetically altered primary cells now offer a promising alternative to investigate initial stages of human breast cancer development. In this review, we summarize current knowledge about key transcriptional regulatory processes operative in these partially characterized subpopulations of normal human mammary cells and effects of disrupting these processes in experimentally produced human breast cancers.

The MMTV-Wnt1 murine model produces two phenotypically distinct subtypes of mammary tumors with unique therapeutic responses to an EGFR inhibitor

The Wnt gene family encodes an evolutionarily conserved group of proteins that regulate cell growth, differentiation and stem cell self-renewal. Aberrant Wnt signaling in human breast tumors has been proposed as a driver of tumorigenesis, especially in the basal-like tumor subtype where canonical Wnt signaling is both enriched and predictive of poor clinical outcomes. The development of effective Wnt-based therapeutics, however, has been slowed in part by a limited understanding of the context-dependent nature with which these aberrations influence breast tumorigenesis. We previously reported that MMTV-Wnt1 mice, an established model for studying Wnt signaling in breast tumors, develop two subtypes of tumors by gene expression classification: Wnt1-Early^Ex and Wnt1-Late^Ex Here, we extend this initial observation and show that Wnt1-Early^Ex tumors exhibit high expression of canonical Wnt, non-canonical Wnt, and EGFR signaling pathway signatures. Therapeutically, Wnt1-Early^Ex tumors showed a dynamic reduction in tumor volume when treated with an EGFR inhibitor. Wnt1-Early^Ex tumors had primarily Cd49f^pos/Epcam^neg FACS profiles, but it was not possible to serially transplant these tumors into wild-type FVB female mice. Conversely, Wnt1-Late^Ex tumors had a bloody gross pathology, which was highlighted by the presence of 'blood lakes' identified by H&E staining. These tumors had primarily Cd49f^pos/Epcam^pos FACS profiles, but also contained a secondary Cd49f^pos/Epcam^neg subpopulation. Wnt1-Late^Ex tumors were enriched for activating Hras1 mutations and were capable of reproducing tumors when serially transplanted into wild-type FVB female mice. This study definitively shows that the MMTV-Wnt1 mouse model produces two phenotypically distinct subtypes of mammary tumors that differ in multiple biological aspects including sensitivity to an EGFR inhibitor.

SOD1 is essential for oncogene-driven mammary tumor formation but dispensable for normal development and proliferation

We previously reported that the dismutase SOD1 is overexpressed in breast cancer. However, whether SOD1 plays an active role in tumor formation in vivo has never been demonstrated. Further, as luminal cells of normal breast epithelial cells are enriched in SOD1, whether SOD1 is essential for normal mammary gland development has never been determined. We initiated this study to investigate the role of SOD1 in mammary gland tumorigenesis as well as in normal mammary gland development. We crossed the inducible erbB2 (MMTV-iErbB2) and Wnt (MMTV-Wnt) transgenic mice to the SOD1 heterozygote or knockout mice. Our results show that SOD1 is essential for oncogene-driven proliferation, but not normal proliferation of the mammary gland associated with pregnancy or other normal proliferative tissues such as skin and intestines. We show that activation of the oncogene ErbB2 is associated with increased ROS and that high ROS sub-population of ErbB2 cancer cells show elevated SOD1. In the same cells, decrease in SOD1 is associated with an elevation in both apoptosis as well as oncogene-induced senescence. Based on these results, we suggest that SOD1 carries a housekeeping function that maintains ROS levels below a threshold that supports oncogene-dependent proliferation, while allowing escape from oncogene-induced senescence, independently of the oncogene driving tumor formation. These results identify SOD1 as an ideal target for cancer therapy as SOD1 inhibitors hold the potential to prevent the growth of cancers cells of diverse genotypes, activate multiple modes of cell death therefore making acquired resistance more difficult, while sparing normal tissues.

GPNMB augments Wnt-1 mediated breast tumor initiation and growth by enhancing PI3K/AKT/mTOR pathway signaling and β-catenin activity

Glycoprotein Nmb (GPNMB) is overexpressed in triple-negative and basal-like breast cancers and its expression is predictive of poor prognosis within this aggressive breast cancer subtype. GPNMB promotes breast cancer growth, invasion, and metastasis; however, its role in mammary tumor initiation remains unknown. To address this question, we overexpressed GPNMB in the mammary epithelium to generate MMTV/GPNMB transgenic mice and crossed these animals to the MMTV/Wnt-1 mouse model, which is known to recapitulate features of human basal breast cancers. We show that GPNMB alone does not display oncogenic properties; however, its expression dramatically accelerates tumor onset in MMTV/Wnt-1 mice. MMTV/Wnt-1 × MMTV/GPNMB bigenic mice also exhibit a significant increase in the growth rate of established primary tumors, which is attributable to increased proliferation and decreased apoptosis. To elucidate molecular mechanisms underpinning the tumor-promoting effects of GPNMB in this context, we interrogated activated pathways in tumors derived from the MMTV/Wnt-1 and MMTV/Wnt-1 × MMTV/GPNMB mice using RPPA analysis. These data revealed that MMTV/Wnt-1 × MMTV/GPNMB bigenic tumors exhibit a pro-growth signature characterized by elevated PI3K/AKT/mTOR signaling and increased β-catenin activity. Furthermore, we extended these observations to an independent Wnt-1 expressing model of aggressive breast cancer, and confirmed that GPNMB enhances canonical Wnt pathway activation, as evidenced by increased β-catenin transcriptional activity, in breast cancer cells and tumors co-expressing Wnt-1 and GPNMB. GPNMB-dependent engagement of β-catenin occurred, in part, through AKT activation. Taken together, these data ascribe a novel, pro-growth role for GPNMB in Wnt-1 expressing basal breast cancers.

Dormancy and cancer stem cells: An enigma for cancer therapeutic targeting

Dormancy occurs when cells remain viable but stop proliferating. When most of a cancer population undergoes this phenomenon, the result is called tumor dormancy, and when a single cancer cell undergoes this process, it is termed quiescence. Cancer stem cells (CSCs) share several overlapping characteristics and signaling pathways with dormant cancer cells, including therapy resistance, and an ability to metastasize and evade the immune system. Cancer cells can be broadly grouped into dormancy-competent CSCs (DCCs), cancer-repopulating cells (CRCs), dormancy-incompetent CSCs and disseminated tumor cells (DTCs). The settings in which cancer cells exploit the dormancy phase to survive and adapt are: (i) primary cancer dormancy; (ii) metastatic dormancy; (iii) therapy-induced dormancy; and (iv) immunologic dormancy. Dormancy, therapy resistance and plasticity of CSCs are fundamentally interconnected processes mediated through mechanisms involving reversible genetic alterations. Niches including metastatic, bone marrow, and perivascular are known to harbor dormant cancer cells. Mechanisms of dormancy induction are complex and multi-factorial and can involve angiogenic switching, addictive oncogene inhibition, immunoediting, anoikis, therapy, autophagy, senescence, epigenetic, and biophysical regulation. Therapy can have opposing effects on cancer cells with respect to dormancy; some therapies can induce dormancy, while others can reactivate dormant cells. There is a lack of consensus relative to the value of therapy-induced dormancy, i.e., some researchers view dormancy induction as a beneficial strategy as it can lead to metastasis inhibition, while others argue that reactivating dormant cancer cells and then eliminating them through therapy are a better approach. More focused investigations of intrinsic cell kinetics and environmental dynamics that promote and maintain cancer cells in a dormant state, and the long-term consequences of dormancy are critical for improving current therapeutic treatment outcomes.

Mouse models of breast cancer in preclinical research

Breast cancer remains the second leading cause of cancer death among woman, worldwide, despite advances in identifying novel targeted therapies and the development of treating strategies. Classification of clinical subtypes (ER+, PR+, HER2+, and TNBC (Triple-negative)) increases the complexity of breast cancers, which thus necessitates further investigation. Mouse models used in breast cancer research provide an essential approach to examine the mechanisms and genetic pathway in cancer progression and metastasis and to develop and evaluate clinical therapeutics. In this review, we summarize tumor transplantation models and genetically engineered mouse models (GEMMs) of breast cancer and their applications in the field of human breast cancer research and anti-cancer drug development. These models may help to improve the knowledge of underlying mechanisms and genetic pathways, as well as creating approaches for modeling clinical tumor subtypes, and developing innovative cancer therapy.

Insulin-like growth factor receptor signaling in breast tumor epithelium protects cells from endoplasmic reticulum stress and regulates the tumor microenvironment

BACKGROUND

Early analyses of human breast cancer identified high expression of the insulin-like growth factor type 1 receptor (IGF-1R) correlated with hormone receptor positive breast cancer and associated with a favorable prognosis, whereas low expression of IGF-1R correlated with triple negative breast cancer (TNBC). We previously demonstrated that the IGF-1R acts as a tumor and metastasis suppressor in the Wnt1 mouse model of TNBC. The mechanisms for how reduced IGF-1R contributes to TNBC phenotypes is unknown.

METHODS

We analyzed the METABRIC dataset to further stratify IGF-1R expression with patient survival and specific parameters of TNBC. To investigate molecular events associated with the loss of IGF-1R function in breast tumor cells, we inhibited IGF-1R in human cell lines using an IGF-1R blocking antibody and analyzed MMTV-Wnt1-mediated mouse tumors with reduced IGF-1R function through expression of a dominant-negative transgene.

RESULTS

Our analysis of the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) dataset revealed association between low IGF-1R and reduced overall patient survival. IGF-1R expression was inversely correlated with patient survival even within hormone receptor-positive breast cancers, indicating reduced overall patient survival with low IGF-1R was not due simply to low IGF-1R expression within TNBCs. Inhibiting IGF-1R in either mouse or human tumor epithelial cells increased reactive oxygen species (ROS) production and activation of the endoplasmic reticulum stress response. IGF-1R inhibition in tumor epithelial cells elevated interleukin (IL)-6 and C-C motif chemokine ligand 2 (CCL2) expression, which was reversed by ROS scavenging. Moreover, the Wnt1/dnIGF-1R primary tumors displayed a tumor-promoting immune phenotype. The increased CCL2 promoted an influx of CD11b⁺ monocytes into the primary tumor that also had increased matrix metalloproteinase (MMP)-2, MMP-3, and MMP-9 expression. Increased MMP activity in the tumor stroma was associated with enhanced matrix remodeling and collagen deposition. Further analysis of the METABRIC dataset revealed an increase in IL-6, CCL2, and MMP-9 expression in patients with low IGF-1R, consistent with our mouse tumor model and data in human breast cancer cell lines.

CONCLUSIONS

Our data support the hypothesis that reduction of IGF-1R function increases cellular stress and cytokine production to promote an aggressive tumor microenvironment through infiltration of immune cells and matrix remodeling.

Mammary Precancerous Stem and Non-Stem Cells Evolve into Cancers of Distinct Subtypes

There are distinct cell subpopulations in normal epithelial tissue, including stem cells, progenitor cells, and more differentiated cells, all of which have been extensively studied for their susceptibility to tumorigenesis. However, normal cells usually have to progress through a precancerous lesion state before becoming a full-blown tumor. Precancerous early lesions are heterogeneous, and the cell subset that is the primary source of the eventual tumor remains largely unknown. By using mouse models that are tailored to address this question, we identified a keratin 6a-expressing precancerous stem cell (PcSC) subset and a more differentiated whey acidic protein-positive (WAP+) cell subset in mammary precancerous lesions initiated by the Wnt1 oncogene. Both cell subsets rapidly progressed to cancer upon introduction of constitutively active versions of either HRAS or BRAF. However, the resulting tumors were dramatically different in protein profiles and histopathology: keratin 6a+ precancerous cells gave rise to adenocarcinoma, whereas WAP+ cells yielded metaplastic carcinoma with severe squamous differentiation and more robust activation of MEK/ERK signaling. Therefore, both stem and non-stem cells in mammary precancerous lesions can contribute to the eventual cancers, but their differentiation status determines the resulting cancer phenotype. This work identifies a previously unknown player in cancer heterogeneity and suggests that cancer prevention should target precancerous cells broadly and not be limited to PcSC. SIGNIFICANCE: This work uses a novel mouse mammary gland cancer model to show that tumors initiated from different precancerous mammary epithelial cells are distinct.

Dual role for miR-34a in the control of early progenitor proliferation and commitment in the mammary gland and in breast cancer

The role of the tumour-suppressor miR-34 family in breast physiology and in mammary stem cells (MaSCs) is largely unknown. Here, we revealed that miR-34 family, and miR-34a in particular, is implicated in mammary epithelium homoeostasis. Expression of miR-34a occurs upon luminal commitment and differentiation and serves to inhibit the expansion of the pool of MaSCs and early progenitor cells, likely in a p53-independent fashion. Mutant mice (miR34-KO) and loss-of-function approaches revealed two separate functions of miR-34a, controlling both proliferation and fate commitment in mammary progenitors by modulating several pathways involved in epithelial cell plasticity and luminal-to-basal conversion. In particular, miR-34a acts as endogenous inhibitor of the Wnt/beta-catenin signalling pathway, targeting up to nine upstream regulators at the same time, thus modulating the expansion of the MaSCs/early progenitor pool. These multiple roles of miR-34a are maintained in a model of human breast cancer, in which chronic expression of miR-34a in triple-negative mesenchymal-like cells (enriched in cancer stem cells—CSCs) could promote a luminal-like differentiation programme, restrict the CSC pool, and inhibit tumour propagation. Hence, activation of miR-34a-dependent programmes could provide a therapeutic opportunity for the subset of breast cancers, which are rich in CSCs and respond poorly to conventional therapies.

Dramatic dysbalancing of the Wnt pathway in breast cancers

Wnt signaling is important for breast development and remodeling during pregnancy and lactation. Epigenetic modifications change expression levels of components of the Wnt pathway, underlying oncogenic transformation. However, no clear Wnt component increasing expression universally across breast cancer (BC) or its most Wnt-dependent triple-negative BC (TNBC) subgroup has been identified, delaying development of targeted therapies. Here we perform network correlation analysis of expression of >100 Wnt pathway components in hundreds of healthy and cancerous breast tissues. Varying in expression levels among people, Wnt components remarkably coordinate their production; this coordination is dramatically decreased in BC. Clusters with coordinated gene expression exist within the healthy cohort, highlighting Wnt signaling subtypes. Different BC subgroups are identified, characterized by different remaining Wnt signaling signatures, providing the rational for patient stratification for personalizing the therapeutic applications. Key pairwise interactions within the Wnt pathway (some inherited and some established de novo) emerge as targets for future drug discovery against BC.

Silencing PRDM14 expression by an innovative RNAi therapy inhibits stemness, tumorigenicity, and metastasis of breast cancer

PR domain zinc finger protein 14 (PRDM14) maintains stemness in embryonic stem cells via epigenetic mechanisms. Although PRDM14 is elevated in several cancers, it is unclear if and how PRDM14 confers stem cell-like properties and epigenetic changes to cancer cells. Here, we examined the phenotypic characteristics and epigenetic and gene expression profiles of cancer cells that differentially express PRDM14, and assessed the potential of PRDM14-targeted cancer therapy. PRDM14 expression was markedly increased in many different cancer types and correlated with poor survival of breast cancer patients. PRDM14 conferred stem cell-like phenotypes to cancer cells and regulated the expression of genes involved in cancer stemness, metastasis, and chemoresistance. PRDM14 also reduced the methylation of proto-oncogene and stemness gene promoters and PRDM14-binding regions were primarily occupied by histone H3 Lys-4 trimethylation (H3K4me3), both of which are positively correlated with gene expression. Moreover, strong PRDM14 binding sites coincided with promoters containing both H3K4me3 and H3K27me3 histone marks. Using calcium phosphate hybrid micelles as an RNAi delivery system, silencing of PRDM14 expression by chimera RNAi reduced tumor size and metastasis in vivo without causing adverse effects. Conditional loss of PRDM14 function also improved survival of MMTV-Wnt-1 transgenic mice, a spontaneous model of murine breast cancer. Our findings suggest that PRDM14 inhibition may be an effective and novel therapy for cancer stem cells.

The biochemistry, signalling and disease relevance of RYK and other WNT-binding receptor tyrosine kinases

The receptor tyrosine kinases (RTKs) are a well-characterized family of growth factor receptors that have central roles in human disease and are frequently therapeutically targeted. The RYK, ROR, PTK7 and MuSK subfamilies make up an understudied subset of WNT-binding RTKs. Numerous developmental, stem cell and pathological roles of WNTs, in particular WNT5A, involve signalling via these WNT receptors. The WNT-binding RTKs have highly context-dependent signalling outputs and stimulate the β-catenin-dependent, planar cell polarity and/or WNT/Ca²⁺ pathways. RYK, ROR and PTK7 members have a pseudokinase domain in their intracellular regions. Alternative signalling mechanisms, including proteolytic cleavage and protein scaffolding functions, have been identified for these receptors. This review explores the structure, signalling, physiological and pathological roles of RYK, with particular attention paid to cancer and the possibility of therapeutically targeting RYK. The other WNT-binding RTKs are compared with RYK throughout to highlight the similarities and differences within this subset of WNT receptors.

Annexin-A1 enhances breast cancer growth and migration by promoting alternative macrophage polarization in the tumour microenvironment

Macrophages are potent immune cells with well-established roles in the response to stress, injury, infection and inflammation. The classically activated macrophages (M1) are induced by lipopolysaccharide (LPS) and express a wide range of pro-inflammatory genes. M2 macrophages are induced by T helper type 2 cytokines such as interleukin-4 (IL4) and express high levels of anti-inflammatory and tissue repair genes. The strong association between macrophages and tumour cells as well as the high incidences of leukocyte infiltration in solid tumours have contributed to the discovery that tumour-associated macrophages (TAMs) are key to tumour progression. Here, we investigated the role of Annexin A1 (ANXA1), a well characterized immunomodulatory protein on macrophage polarization and the interaction between macrophages and breast cancer cells. Our results demonstrate that ANXA1 regulates macrophage polarization and activation. ANXA1 can act dually as an endogenous signalling molecule or as a secreted mediator which acts via its receptor, FPR2, to promote macrophage polarization. Furthermore, ANXA1 deficient mice exhibit reduced tumour growth and enhanced survival in vivo, possibly due to increased M1 macrophages within the tumor microenvironment. These results provide new insights into the molecular mechanisms of macrophage polarization with therapeutic potential to suppress breast cancer growth and metastasis.

Regulation of FBXO4-mediated ICAM-1 protein stability in metastatic breast cancer

Advanced or progressive cancers share common traits such as altered transcriptional modulation, genetic modification, and abnormal post-translational regulation. These processes influence protein stability and cellular activity. Intercellular adhesion molecule-1 (ICAM-1) is involved in the malignant progression of various human cancers, including breast, liver, renal, and pancreatic cancers, but protein stability has not been deal with in metastatic breast cancer. Additionally, the relevance of the stability maintenance of ICAM-1 protein remains obscure. Here, we identified a novel interaction of E3 ligase FBXO4 that is specifically presented to ICAM-1. To understand how FBXO4 modulates ICAM-1 stability, we investigated ICAM-1-overexpressing or knockdown metastatic/non-metastatic breast cancers. ICAM-1 was found to influence tumor progression and metastasis, whereas FBXO4 regulated aggressive tumorigenic conditions. These results demonstrate that FBXO4 is a major regulator of ICAM-1 stability and that alterations in the stability of ICAM-1 can influence therapeutic outcome in metastatic cancer.

APC downregulated 1 inhibits breast cancer cell invasion by inhibiting the canonical WNT signaling pathway

Canonical WNT signaling promotes breast cancer progression. Although APC downregulated 1 (APCDD1) may inhibit canonical WNT signaling, its role in breast cancer remains to be fully understood. The present study demonstrated that APCDD1 suppressed in vitro breast cancer growth and metastasis by inhibiting canonical WNT signaling. The present study demonstrated that APCDD1 expression was negatively associated with breast cancer cell invasion, which was consistent with previous studies that indicated that APCDD1 expression was decreased in invasive ductal carcinoma compared with that in ductal carcinoma in situ. Furthermore, APCDD1 expression was negatively associated with nuclear β-catenin expression and transcription factor/lymphoid enhancer binding factor 1 transcriptional activity in the present study. Silencing APCDD1 in non-invasive breast cancer cells using lentiviral APCDD1 short hairpin RNAs enhanced migration and invasion, which may be mediated by canonical WNT signaling, whereas the overexpression of human influenza hemagglutinin-tagged APCDD1 in invasive breast cancer cells repressed these properties. Therefore, the present study suggested that APCDD1 regulated breast cancer progression by targeting canonical WNT signaling and modulating breast cancer cell invasion.

Metabolic reprogramming underlies metastatic potential in an obesity-responsive murine model of metastatic triple negative breast cancer

The vast majority of cancer-related deaths are due to metastatic disease, whereby primary tumor cells disseminate and colonize distal sites within the body. Triple negative breast cancer typically displays aberrant Wnt signaling, lacks effective targeted therapies, and compared with other breast cancer subtypes, is more likely to recur and metastasize. We developed a Wnt-driven lung metastasis model of triple negative breast cancer (metM-Wnt^lung) through serial passaging of our previously described, nonmetastatic, claudin-low M-Wnt cell line. metM-Wnt^lung cells displayed characteristics of epithelial-to-mesenchymal transition (e.g., increased invasiveness) with some re-epithealization (e.g., increased adhesion, tight colony formation, increased E-cadherin expression, and decreased Vimentin and Fibronectin expression). When orthotopically transplanted into syngeneic mice, metM-Wnt^lung cells readily formed tumors and metastasized in vivo, and tumor growth and metastasis were enhanced in obese mice compared with non-obese mice. Gene expression analysis revealed several genes and pathways altered in metM-Wnt^lung cells compared with M-Wnt cells, including multiple genes associated with epithelial-to-mesenchymal transition, energy metabolism and inflammation. Moreover, obesity caused significant transcriptomic changes, especially in metabolic pathways. Metabolic flux analyses showed greater metabolic plasticity, with heightened mitochondrial and glycolytic energetics in metM-Wnt^lung cells relative to M-Wnt cells. Similar metabolic profiles were found in a second triple negative breast cancer progression series, M6 and M6C cells. These findings suggest that metabolic reprogramming is a feature of metastatic potential in triple negative breast cancer. Thus, targeting metastases-associated metabolic perturbations may represent a novel strategy for reducing the burden of metastatic triple negative breast cancer, particularly in obese women.

Metabolic changes contribute to the metastatic potential of triple negative breast cancer (TNBC), a mouse study shows. Stephen Hursting and colleagues from the University of North Carolina at Chapel Hill, USA, established metastatic mouse TNBC cells driven by Wnt-1, a signaling protein that’s highly active in this aggressive subtype of breast cancer. In a lab dish, these cells showed signs of increased invasiveness; and when transplanted into mice, the cells readily formed tumors that metastasized to the lungs. Obese mice experienced more aggressive tumor growth and spread than normal-weight animals. Gene expression analyses revealed that TNBC cells with metastatic potential have an energetic leg-up over their non-metastatic counterparts in the face of obesity-induced metabolic changes, suggesting that targeting metabolic perturbations could help reduce the burden of metastatic TNBC, particularly for obese women.

Wnt5a Signaling in Normal and Cancer Stem Cells

Wnt5a is involved in activating several noncanonical Wnt signaling pathways, which can inhibit or activate canonical Wnt/β-catenin signaling pathway in a receptor context-dependent manner. Wnt5a signaling is critical for regulating normal developmental processes, including stem cell self-renewal, proliferation, differentiation, migration, adhesion, and polarity. Moreover, the aberrant activation or inhibition of Wnt5a signaling is emerging as an important event in cancer progression, exerting both oncogenic and tumor suppressive effects. Recent studies show the involvement of Wnt5a signaling in regulating normal and cancer stem cell self-renewal, cancer cell proliferation, migration, and invasion. In this article, we review recent findings regarding the molecular mechanisms and roles of Wnt5a signaling in stem cells in embryogenesis and in the normal or neoplastic breast or ovary, highlighting that Wnt5a may have different effects on target cells depending on the surface receptors expressed by the target cell.