Breast Cancer Stem Cell Phenotype Research Articles

Exploring the interplay between triple-negative breast cancer stem cells and tumor microenvironment for effective therapeutic strategies.

Triple-negative breast cancer (TNBC)is a highly aggressive and metastatic malignancy with poor treatment outcomes. The interaction between the tumor microenvironment (TME)and breast cancer stem cells (BCSCs)plays an important role in the development of TNBC. Owing to their ability of self-renewal and multidirectional differentiation, BCSCs maintain tumor growth, drive metastatic colonization, and facilitate the development of drug resistance. TME is the main factor regulating the phenotype and metastasis of BCSCs. Immune cells, cancer-related fibroblasts (CAFs),cytokines, mesenchymal cells, endothelial cells, and extracellular matrix within the TME form a complex communication network, exert highly selective pressure on the tumor, and provide a conducive environment for the formation of BCSC niches. Tumor growth and metastasis can be controlled by targeting the TME to eliminate BCSC niches or targeting BCSCs to modify the TME. These approaches may improve the treatment outcomes and possess great application potential in clinical settings. In this review, we summarized the relationship between BCSCs and the progression and drug resistance of TNBC, especially focusing on the interaction between BCSCs and TME. In addition, we discussed therapeutic strategies that target the TME to inhibit or eliminate BCSCs, providing valuable insights into the clinical treatment of TNBC.

Cuproptosis engages in c-Myc-mediated breast cancer stemness

BackgroundIntra-tumoral heterogeneity (ITH) is a distinguished hallmark of cancer, and cancer stem cells (CSCs) contribute to this malignant characteristic. Therefore, it is of great significance to investigate and even target the regulatory factors driving intra-tumoral stemness. c-Myc is a vital oncogene frequently overexpressed or amplified in various cancer types, including breast cancer. Our previous study indicated its potential association with breast cancer stem cell (BCSC) biomarkers.MethodsIn this research, we performed immunohistochemical (IHC) staining on sixty breast cancer surgical specimens for c-Myc, CD44, CD24, CD133 and ALDH1A1. Then, we analyzed transcriptomic atlas of 1533 patients with breast cancer from public database.ResultsIHC staining indicated the positive correlation between c-Myc and BCSC phenotype. Then, we used bioinformatic analysis to interrogate transcriptomics data of 1533 breast cancer specimens and identified an intriguing link among c-Myc, cancer stemness and copper-induced cell death (also known as “cuproptosis”). We screened out cuproptosis-related characteristics that predicts poor clinical outcomes and found that the pro-tumoral cuproptosis-based features were putatively enriched in MYC-targets and showed a significantly positive correlation with cancer stemness.ConclusionIn addition to previous reports on its oncogenic roles, c-Myc showed significant correlation to stemness phenotype and copper-induced cell toxicity in breast cancer tissues. Moreover, transcriptomics data demonstrated that pro-tumoral cuproptosis biomarkers had putative positive association with cancer stemness. This research combined clinical samples with large-scale bioinformatic analysis, covered description and deduction, bridged classic oncogenic mechanisms to innovative opportunities, and inspired the development of copper-based nanomaterials in targeting highly heterogeneous tumors.

Glycosphingolipids in human embryonic stem cells and breast cancer stem cells, and potential cancer therapy strategies based on their structures and functions.

Expression profiles of glycosphingolipids (GSLs) in human embryonic stem cell (hESC) lines and their differentiated embryoid body (EB) outgrowth cells, consisting of three germ layers, were surveyed systematically. Several globo- and lacto-series GSLs were identified in undifferentiated hESCs and during differentiation of hESCs to EB outgrowth cells, and core structure switching of these GSLs to gangliosides was observed. Such switching was attributable to altered expression of key glycosyltransferases (GTs) in GSL biosynthetic pathways, reflecting the unique stage-specific transitions and mechanisms characteristic of the differentiation process. Lineage-specific differentiation of hESCs was associated with further GSL alterations. During differentiation of undifferentiated hESCs to neural progenitor cells, core structure switching from globo- and lacto-series to primarily gangliosides (particularly GD3) was again observed. During differentiation to endodermal cells, alterations of GSL profiles were distinct from those in differentiation to EB outgrowth or neural progenitor cells, with high expression of Gb4Cer and low expression of stage-specific embryonic antigen (SSEA)-3, -4, or GD3 in endodermal cells. Again, such profile changes resulted from alterations of key GTs in GSL biosynthetic pathways. Novel glycan structures identified on hESCs and their differentiated counterparts presumably play functional roles in hESCs and related cancer or cancer stem cells, and will be useful as surface biomarkers. We also examined GSL expression profiles in breast cancer stem cells (CSCs), using a model of epithelial-mesenchymal transition (EMT)-induced human breast CSCs. We found that GD2 and GD3, together with their common upstream GTs, GD3 synthase (GD3S) and GD2/GM2 synthase, maintained stem cell phenotype in breast CSCs. Subsequent studies showed that GD3 was associated with epidermal growth factor receptor (EGFR), and activated EGFR signaling in breast CSCs and breast cancer cell lines. GD3S knockdown enhanced cytotoxicity of gefitinib (an EGFR kinase inhibitor) in resistant MDA-MB468 cells, both in vitro and in vivo. Our findings indicate that GD3S contributes to gefitinib resistance in EGFR-positive breast cancer cells, and is a potentially useful therapeutic target in drug-resistant breast cancers.

Chemotherapy-induced adenosine A2B receptor expression mediates epigenetic regulation of pluripotency factors and promotes breast cancer stemness.

Rationale: Triple-negative breast cancer (TNBC) is characterized by its unique molecular profile, aggressive nature and lack of targeted therapy. Chemotherapy induces expression of pluripotency factors and mediates an active induction of breast cancer stem cells (BCSCs) in TNBC, which potentiates the risk of tumor recurrence and metastasis and increases patient mortality. Adenosine receptor 2B (A2BR) expression and activation of its downstream signaling pathway has been implied to promote breast cancer metastasis. This study is to investigate the role of A2BR in the regulation of chemotherapy-induced BCSC enrichment.Methods: We generated shRNA-mediated A2BR knockdown subclones in TNBC cell lines and evaluated the effect on the BCSC phenotype by Aldefluor and mammosphere assays in vitro. We performed chromatin immunoprecipitation (ChIP) assay to investigate recruitment of transcription factor FOXO3 and histone modification enzymes KDM6A and p300 to the regulatory regions of pluripotency factors, as well as levels of histone modification marks H3K27ac and H3K27me3 on these regions. We employed both xenograft model and genetically engineered, autochthonous breast cancer model to evaluate the effect of A2BR on chemotherapy-induced BCSC enrichment in vivo.Results: We demonstrated that chemotherapy increased protein level of A2BR, which contributed to chemotherapy-induced pluripotency factor expression and BCSC enrichment in TNBC. A2BR mediated activation of p38 MAPK and nuclear translocation of chromatin remodeling factor SMARCD3, which interacted and recruited histone demethylase KDM6A and histone acetyltransferase p300 specifically to the pluripotency factor genes NANOG, SOX2 and KLF4. Recruitment of KDM6A and p300 decreased histone H3K27me3 and increases H3K27ac marks, and increased transcription factor FOXO3 binding to NANOG, SOX2 and KLF4 genes, leading to transcriptional activation of these genes and BCSC specification. Genetic or pharmacological inhibition of A2BR blocked chemotherapy-mediated epigenetic activation of pluripotency factor genes and BCSC enrichment in vitro and in vivo, and delayed tumor recurrence after chemotherapy was discontinued.Conclusion: Chemotherapy-induced A2BR expression mediates epigenetic activation of pluripotency factors and promotes breast cancer stemness. Targeting A2BR in combination with chemotherapy may block BCSC enrichment and improve outcome in TNBC.

HIF-1–regulated expression of calreticulin promotes breast tumorigenesis and progression through Wnt/β-catenin pathway activation

Calreticulin (CALR) is a multifunctional protein that participates in various cellular processes, which include calcium homeostasis, cell adhesion, protein folding, and cancer progression. However, the role of CALR in breast cancer (BC) is unclear. Here, we report that CALR is overexpressed in BC compared with normal tissue, and its expression is correlated with patient mortality and stemness indices. CALR expression was increased in mammosphere cultures, CD24-CD44+ cells, and aldehyde dehydrogenase-expressing cells, which are enriched for breast cancer stem cells (BCSCs). Additionally, CALR knockdown led to BCSC depletion, which impaired tumor initiation and metastasis and enhanced chemosensitivity in vivo. Chromatin immunoprecipitation and reporter assays revealed that hypoxia-inducible factor 1 (HIF-1) directly activated CALR transcription in hypoxic BC cells. CALR expression was correlated with Wnt/β-catenin pathway activation, and an activator of Wnt/β-catenin signaling abrogated the inhibitory effect of CALR knockdown on mammosphere formation. Taken together, our results demonstrate that CALR facilitates BC progression by promoting the BCSC phenotype through Wnt/β-catenin signaling in an HIF-1-dependent manner and suggest that CALR may represent a target for BC therapy.

Notch Signalling in Breast Development and Cancer.

The Notch signalling pathway is a highly conserved developmental signalling pathway, with vital roles in determining cell fate during embryonic development and tissue homeostasis. Aberrant Notch signalling has been implicated in many disease pathologies, including cancer. In this review, we will outline the mechanism and regulation of the Notch signalling pathway. We will also outline the role Notch signalling plays in normal mammary gland development and how Notch signalling is implicated in breast cancer tumorigenesis and progression. We will cover how Notch signalling controls several different hallmarks of cancer within epithelial cells with sections focussed on its roles in proliferation, apoptosis, invasion, and metastasis. We will provide evidence for Notch signalling in the breast cancer stem cell phenotype, which also has implications for therapy resistance and disease relapse in breast cancer patients. Finally, we will summarise the developments in therapeutic targeting of Notch signalling, and the pros and cons of this approach for the treatment of breast cancer.

Abstract 3080: ILEI regulates LIFR expression and CSC self-renewal

Abstract Our lab has previously identified a mechanism of transforming growth factor beta (TGFβ)-mediated epithelial-to-mesenchymal transition (EMT) in normal murine mammary gland (NMuMG) cells. Reduced expression of heterogenous nuclear ribonucleoprotein E1 (hnRNP E1, hereafter “E1”) in NMuMG cells induces EMT, tumorigenesis, and metastasis. Our experimental data has revealed that increased expression of interleukin-like EMT inducer (ILEI) and of leukemia inhibitory factor receptor (LIFR) proteins occurs following E1 knockdown (E1KD). ILEI and LIFR have been shown to interact by coimmunoprecipitation/radiography experiments, and there is a correlation between ILEI expression and phosphorylation of the LIFR effector STAT3. ILEI is necessary to induce EMT in NMuMG cells, and spheroid formation capacity in non-adherent serum-depleted cell culture conditions is attenuated following either ILEI or LIFR knockdown. Loss of spheroid formation following ILEI knockdown is rescued by treatment with exogenous recombinant ILEI protein (rILEI); however, spheroid formation is not rescued by rILEI following LIFR knockdown. In immunocompromised mice, orthotopic grafts of NMuMG cells with E1KD (E1KD cells) with additional knockdown of either ILEI or LIFR display a decrease in tumor initiation, growth, and metastasis relative to control cells. These data suggest that ILEI-induced spheroid formation capacity involves LIFR, and that an ILEI/LIFR signaling axis promotes breast cancer stem cell (BCSC) phenotype. Characterization of the mechanisms that allow BCSCs to persist during chemotherapeutic interventions will advance our understanding of drug resistant and dormant breast cancer. The precise mechanisms involved in ILEI-mediated EMT and ILEI/LIFR-mediated BCSC induction are unknown. Semi-quantitative PCR data demonstrates that the increase in LIFR expression in E1KD cells is regulated at the transcriptional level. Additionally, E1KD cells with CRISPR-Cas9-mediated ILEI knockout (E1KD-ILEI-KO cells) show decreased luciferase signal relative to control cells following transfection of LIFR promoter DNA sequences placed upstream of a luciferase gene. Further, E1KD-ILEI-KO cells show attenuation of spheroid formation when compared to unaltered E1KD cells. Our data allow us to conclude that ILEI participates in the regulation of LIFR gene transcription, which plays a role in ILEI-induced maintenance of spheroid formation and self-renewal. Continued investigation will allow development of studies aimed at revealing the mechanisms involved in ILEI/LIFR axis-mediated disease progression in vivo. Citation Format: William S. Streitfeld, Annamarie C. Dalton, Philip H. Howe. ILEI regulates LIFR expression and CSC self-renewal [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3080.

Impact of miRNAs expression modulation on the methylation status of breast cancer stem cell-related genes.

Altered miRNAs play a crucial role in the emergence of the breast cancer stem cell (BCSC) phenotype. The interplay between miRNAs and methylation enzymes has been documented. One of the most aggressive breast cancer cell lines, MDA-MB-231, has expressed much more DNMT3B than DNMT3A. This study aims to evaluate the ability of miR-203 restoration and miR-150 inhibition to regulate DNMT3B and DNMT3A to modify the methylation level of BCSC-associated genes. MDA-MB-231 cells were transfected with miR-203 mimic or miR-150 inhibitor or DNMT3B siRNA, and downstream analysis was performed by flow cytometry, real-time PCR and Western blotting. DNMT3A and DNMT3B are regulated both by miR-203a-3p and miR-150-5p. Transfection with miR-203 mimic and miR-150 inhibitor significantly reduced the CD44+CD24- subpopulation and down-regulated the expression of CD44 mRNA by increasing promoter methylation levels. SiRNA knockdown of DNMT3B increased the CD44+CD24- subpopulation and the expression of CD44 and ALDH1A3 by decreasing methylation density. The inhibition of miR-150 down-regulated OCT3/4 and SOX2 expression without affecting methylation levels, while miR-203 restoration and miR-150 inhibition down-regulated NANOG expression by elevating the methylation level. A positive-feedback loop was found between miR-203 and its target DNMT3B, as restoring miR-203 suppressed DNMT3B, while knocking down DNMT3B up-regulated miR-203. The restoration of miR-203 and knockdown of DNMT3B decreased methylation levels and increased the expression of miR-141 and miR-200c. The study concluded that miR-203 and miR-150 play a role in the regulation of genes involved in BCSC methylation, including other miRNAs, by targeting DNMT3B and DNMT3A.

The Tumor Microenvironment as a Driving Force of Breast Cancer Stem Cell Plasticity.

Simple SummaryBreast cancer stem cells are a subset of transformed cells that sustain tumor growth and can metastasize to secondary organs. Since metastasis accounts for most cancer deaths, it is of paramount importance to understand the cellular and molecular mechanisms that regulate this subgroup of cells. The tumor microenvironment (TME) is the habitat in which transformed cells evolve, and it is composed by many different cell types and the extracellular matrix (ECM). A body of evidence strongly indicates that microenvironmental cues modulate stemness in breast cancer, and that the coevolution of the TME and cancer stem cells determine the fate of breast tumors. In this review, we summarize the studies providing links between the TME and the breast cancer stem cell phenotype and we discuss their specific interactions with immune cell subsets, stromal cells, and the ECM.Tumor progression involves the co-evolution of transformed cells and the milieu in which they live and expand. Breast cancer stem cells (BCSCs) are a specialized subset of cells that sustain tumor growth and drive metastatic colonization. However, the cellular hierarchy in breast tumors is rather plastic, and the capacity to transition from one cell state to another depends not only on the intrinsic properties of transformed cells, but also on the interplay with their niches. It has become evident that the tumor microenvironment (TME) is a major player in regulating the BCSC phenotype and metastasis. The complexity of the TME is reflected in its number of players and in the interactions that they establish with each other. Multiple types of immune cells, stromal cells, and the extracellular matrix (ECM) form an intricate communication network with cancer cells, exert a highly selective pressure on the tumor, and provide supportive niches for BCSC expansion. A better understanding of the mechanisms regulating these interactions is crucial to develop strategies aimed at interfering with key BCSC niche factors, which may help reducing tumor heterogeneity and impair metastasis.

BR-BCSC Signature: The Cancer Stem Cell Profile Enriched in Brain Metastases that Predicts a Worse Prognosis in Lymph Node-Positive Breast Cancer

Brain metastases remain an unmet clinical need in breast oncology, being frequently found in HER2-overexpressing and triple-negative carcinomas. These tumors were reported to be highly cancer stem-like cell-enriched, suggesting that brain metastases probably arise by the seeding of cancer cells with stem features. Accordingly, we found that brain-tropic breast cancer cells show increased stem cell activity and tumorigenic capacity in the chick embryo choriallantoic membrane when compared to the parental cell line. These observations were supported by a significant increase in their stem cell frequency and by the enrichment for the breast cancer stem cell (BCSC) phenotype CD44+CD24−/low. Based on this data, the expression of BCSC markers (CD44, CD49f, P-cadherin, EpCAM, and ALDH1) was determined and found to be significantly enriched in breast cancer brain metastases when compared to primary tumors. Therefore, a brain (BR)-BCSC signature was defined (3–5 BCSC markers), which showed to be associated with decreased brain metastases-free and overall survival. Interestingly, this signature significantly predicted a worse prognosis in lymph node-positive patients, acting as an independent prognostic factor. Thus, an enrichment of a BCSC signature was found in brain metastases, which can be used as a new prognostic factor in clinically challenging breast cancer patients.

Jagged1-Notch1-deployed tumor perivascular niche promotes breast cancer stem cell phenotype through Zeb1

Zinc finger E-box binding homeobox 1 (Zeb1) has been demonstrated to participate in the acquisition of the properties of cancer stem cells (CSCs). However, it is largely unknown how signals from the tumor microenvironment (TME) contribute to aberrant Zeb1 expression. Here, we show that Zeb1 depletion suppresses stemness, colonization and the phenotypic plasticity of breast cancer. Moreover, we demonstrate that, with direct cell-cell contact, TME-derived endothelial cells provide the Notch ligand Jagged1 (Jag1) to neighboring breast CSCs, leading to Notch1-dependent upregulation of Zeb1. In turn, ectopic Zeb1 in tumor cells increases VEGFA production and reciprocally induces endothelial Jag1 in a paracrine manner. Depletion of Zeb1 disrupts this positive feedback loop in the tumor perivascular niche, which eventually lessens tumor initiation and progression in vivo and in vitro. In this work, we highlight that targeting the angiocrine Jag1-Notch1-Zeb1-VEGFA loop decreases breast cancer aggressiveness and thus enhances the efficacy of antiangiogenic therapy.

The Role of Breast Cancer Stem Cell-Related Biomarkers as Prognostic Factors.

Breast cancer is one of the leading causes of cancer-related deaths in women worldwide, and its incidence is on the rise. A small fraction of cancer stem cells was identified within the tumour bulk, which are regarded as cancer-initiating cells, possess self-renewal and propagation potential, and a key driver for tumour heterogeneity and disease progression. Cancer heterogeneity reduces the overall efficacy of chemotherapy and contributes to treatment failure and relapse. The cell-surface and subcellular biomarkers related to breast cancer stem cell (BCSC) phenotypes are increasingly being recognised. These biomarkers are useful for the isolation of BCSCs and can serve as potential therapeutic targets and prognostic tools to monitor treatment responses. Recently, the role of noncoding microRNAs (miRNAs) has extensively been explored as novel biomarker molecules for breast cancer diagnosis and prognosis with high specificity and sensitivity. An in-depth understanding of the biological roles of miRNA in breast carcinogenesis provides insights into the pathways of cancer development and its utility for disease prognostication. This review gives an overview of stem cells, highlights the biomarkers expressed in BCSCs and describes their potential role as prognostic indicators.

High type I collagen density fails to increase breast cancer stem cell phenotype.

Breast cancer is a highly frequent and lethal malignancy which metastasis and relapse frequently associates with the existence of breast cancer stem cells (CSCs). CSCs are undifferentiated, aggressive and highly resistant to therapy, with traits modulated by microenvironmental cells and the extracellular matrix (ECM), a biologically complex and dynamic structure composed mainly by type I collagen (Col-I). Col-I enrichment in the tumor-associated ECM leads to microenvironment stiffness and higher tumor aggressiveness and metastatic potential. While Col-I is also known to induce tumor stemness, it is unknown if such effect is dependent of Col-I density. To answer this question, we evaluated the stemness phenotype of MDA-MB-231 and MCF-7 human breast cancer cells cultured within gels of varying Col-I densities. High Col-I density increased CD44+CD24− breast cancer stem cell (BCSC) immunophenotype but failed to potentiate Col-I fiber alignment, cell self-renewal and clonogenicity in MDA-MB-231 cells. In MCF-7 cells, high Col-I density decreased total levels of variant CD44 (CD44v). Common to both cell types, high Col-I density induced neither markers related to CSC nor those related with mechanically-induced cell response. We conclude that high Col-I density per se is not sufficient to fully develop the BCSC phenotype.

Abstract P6-10-22: miR363-3p mediates maintenance of breast cancer stem cells (BCSCs) and predicts resistance to neoadjuvant chemotherapy and disease recurrence

Abstract Background Increasing data support the role of BCSCs in recurrence and resistance to chemotherapy. However, detecting these cells specifically and targeting them therapeutically remain challenging. We set to identify miRNAs involved in chemoresistance of BCSCs in vitro and the results were assessed in the sera of healthy donors and breast cancer patients treated with neoadjuvant chemotherapy (NAC). Methods In vitro experiments were conducted in the MCF7 cell line grown as mammospheres (MS) in order to enrich a BCSC phenotype. After treatment with 5FU or Paclitaxel (Pac), microRNA profile of chemoresistant cells was analyzed by microarray. The results were compared to miRNAs found in immortalized non-tumorigenic MCF10A cells in order to exclude miRNAs related to normal stem cells. A signature of 6 miRNAs was identified. miR-363-3p, appearing the most relevant, was chosen for further assessment. By RT-qPCR, miR363-3p levels were 20- and 100-fold higher in ALDH+ sorted cells compared to ALDH- MCF7 and MDA-MB-231 cells, respectively. Moreover, overexpression of miR363-3p in MCF7 cells correlated with an increased number of ALDH+ cells and 1.5 more MS formed. In contrast, downregulation of miR363-3p levels induced a decrease in MS size and 2-fold reduction in number. Consistently, miR-363-3p downregulation decreased tumor growth and metastasis of MCF7 cells in an intraductal human-in-mice transplantation model. miRNA was quantified by RT-qPCR in tissue and sera collected prospectively from 40 breast cancer patients before and after NAC (anthracycline-taxane) and also from 25 healthy donors. Results Fifty percent of the patients had luminal A and B tumors (n=20), 32,5% (n=13) had triple negative breast cancer (TNBC), and 17.5% (n=7) had HER2 positive BC. Excluding one patient, who refused the surgical resection, 40% achieved pathological complete response (pCR). Six patients presented disease recurrence. In patients’ tumor before and after NAC, a higher level of miR363-3p was observed compared with benign tissue. In sera of the BC patients, miR363-3p levels were significantly higher than that of healthy donors. After NAC, the levels of miR363-3p remained high among patients who relapsed, whereas they were equivalent to the healthy donors in patients who remained in remission. No correlation between Ki-67, grade 1 or 2 and miR363-3p levels was observed. However, in grade 3 BC, low level of miR363-3p before and after NAC was correlated with pCR and remission. The level of miR363-3p correlated with remission and pCR in patients with TNBC and HER2 BC. Conclusions Assessment in the sera of patients and healthy donors confirms our previous data supporting the role of miR363-3p as predictive factor of resistance to neoadjuvant chemotherapy and disease recurrence. Further investigations are warranted to confirm the role of miR363-3p as a biomarker and potential therapeutic target. Citation Format: Stephanie Renaud, Athina Stravodimou, Maryse Fiche, Ioannis Xenarios, Scabia Valentina, Valerian Dormoy, Marie Galmiche, Cathrin Brisken, Jean-Francois Delaloye, Assia Treboux, Jean-Yves Meuwly, Nicolas Mermod, Khalil Zaman. miR363-3p mediates maintenance of breast cancer stem cells (BCSCs) and predicts resistance to neoadjuvant chemotherapy and disease recurrence [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-10-22.

Long non‑coding RNA profile revealed by microarray indicates that lncCUEDC1 serves a negative regulatory role in breast cancer stem cells.

Previous studies have demonstrated that long non‑coding RNAs (lncRNAs) are involved in breast cancer development, progression and metastasis. However, the association between lncRNAs and breast cancer stem cells(BCSCs) has been poorly explored. To address this issue, microarray analyses were performed to detect the lncRNA profile of BCSCs. In addition, bioinformatics analyses, including Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes pathway analyses, were performed to explore the functional roles of lncRNAs in BCSCs. Lastly, loss of function assays were used to explore the potential function of lncRNA CUE domain containing1 (lncCUEDC1). A total of 142differentially expressed lncRNAs were identified. Among these, 25 were downregulated and 117 were upregulated in BCSCs compared with in non‑BCSCs. In addition, the present study revealed that the lncRNAs were largely associated with stemness‑related signaling pathways. Furthermore, it was demonstrated that lncCUEDC1 negatively regulated the phenotype and biological functions of BCSCs invitro. Mechanistically, lncCUEDC1 could bind NANOG to inhibit the stemness. To the best of our knowledge, the present study was the first to established the lncRNA profile of BCSCs. These findings provided evidence for exploring the functions of lncRNAs in BCSCs and indicated that lncCUEDC1 is a prospective target in BCSCs.

Chronic Oxidative Stress Promotes Molecular Changes Associated with Epithelial Mesenchymal Transition, NRF2, and Breast Cancer Stem Cell Phenotype.

Oxidative stress plays a role in carcinogenesis, but it also contributes to the modulation of tumor cells and microenvironment caused by chemotherapeutics. One of the consequences of oxidative stress is lipid peroxidation, which can, through reactive aldehydes such as 4-hydroxy-2-nonenal (HNE), affect cell signaling pathways. On the other hand, cancer stem cells (CSC) are now recognized as a major factor of malignancy by causing metastasis, relapse, and therapy resistance. Here, we evaluated whether oxidative stress and HNE modulation of the microenvironment can influence CSC growth, modifications of the epithelial to mesenchymal transition (EMT) markers, the antioxidant system, and the frequency of breast cancer stem cells (BCSC). Our results showed that oxidative changes in the microenvironment of BCSC and particularly chronic oxidative stress caused changes in the proliferation and growth of breast cancer cells. In addition, changes associated with EMT, increase in glutathione (GSH) and Nuclear factor erythroid 2-related factor 2 (NRF2) were observed in breast cancer cells grown on HNE pretreated collagen and under chronic oxidative stress. Our results suggest that chronic oxidative stress can be a bidirectional modulator of BCSC fate. Low levels of HNE can increase differentiation markers in BCSC, while higher levels increased GSH and NRF2 as well as certain EMT markers, thereby increasing therapy resistance.

Hypoxia-inducible factors promote breast cancer stem cell specification and maintenance in response to hypoxia or cytotoxic chemotherapy.

Clinical studies have revealed that breast cancers contain regions of intratumoral hypoxia (reduced oxygen availability), which activates hypoxia-inducible factors (HIFs). The relationship between intratumoral hypoxia, distant metastasis and cancer mortality has been well established. A major mechanism by which intratumoral hypoxia contributes to disease progression is through induction of the breast cancer stem cell (BCSC) phenotype. BCSCs are a small subpopulation of cells with the capability for self-renewal. BCSCs have been implicated in resistance to chemotherapy, disease recurrence, and metastasis. In this review, we will discuss our current understanding of the molecular mechanisms underlying HIF-dependent induction of the BCSC phenotype in response to hypoxia or chemotherapy.

Suppression of Breast Cancer Stem Cells and Tumor Growth by the RUNX1 Transcription Factor.

Breast cancer remains the most common malignant disease in women worldwide. Despite advances in detection and therapies, studies are still needed to understand the mechanisms underlying this cancer. Cancer stem cells (CSC) play an important role in tumor formation, growth, drug resistance, and recurrence. Here, it is demonstrated that the transcription factor RUNX1, well known as essential for hematopoietic differentiation, represses the breast cancer stem cell (BCSC) phenotype and suppresses tumor growth in vivo. The current studies show that BCSCs sorted from premalignant breast cancer cells exhibit decreased RUNX1 levels, whereas ectopic expression of RUNX1 suppresses tumorsphere formation and reduces the BCSC population. RUNX1 ectopic expression in breast cancer cells reduces migration, invasion, and in vivo tumor growth (57%) in mouse mammary fat pad. Mechanistically, RUNX1 functions to suppress breast cancer tumor growth through repression of CSC activity and direct inhibition of ZEB1 expression. Consistent with these cellular and biochemical results, clinical findings using patient specimens reveal that the highest RUNX1 levels occur in normal mammary epithelial cells and that low RUNX1 expression in tumors is associated with poor patient survival. IMPLICATIONS: The key finding that RUNX1 represses stemness in several breast cancer cell lines points to the importance of RUNX1 in other solid tumors where RUNX1 may regulate CSC properties.

Highlights of This Issue

The transcription factor RUNX1, represses the breast cancer stem cell (BCSC) phenotype and suppresses tumor growth in vivo. BCSCs sorted from pre-malignant breast cancer cells exhibit decreased RUNX1 levels, while ectopic expression of RUNX1 suppresses tumorsphere formation and reduces the BCSC population. Ectopic expression of RUNX1 reduces breast cancer cell migration, invasion, and in vivo tumor growth. RUNX1 suppresses tumor growth by repressing cancer stem cell activity and directly inhibiting Zeb1 expression. Clinical findings reveal the highest RUNX1 levels in normal mammary epithelial cells and low RUNX1 expression in tumors is associated with poor patient survival.NUT Carcinoma (NC) is a rare, distinctly aggressive subtype of squamous carcinoma driven by NUT-fusion oncoproteins, most commonly BRD4-NUT, and there is currently no effective therapy. The current Rapid Impact, discovers a novel NUT fusion, ZNF592-NUT, from a young patient with NC arising in pelvic bone. In the more typical context of BRD4-NUT-driven NC, it was determined that ZNF592, along with its known “Z4” complex interactors (ZNF532 and ZMYND8) associate with BRD4-NUT and are required to sustain NC, but not non-NC, growth and viability. This study establishes the oncogenic role of Z4 units in NUT carcinoma, offering potential new targeted therapeutic strategies.Ubiquitin-specific protease 6 (USP6) is the key pathogenic agent in several benign tumors, however its role in malignant entities has not been examined. Henrich and colleagues describe a role for USP6 in Ewing sarcoma (ES), a highly lethal pediatric bone cancer. While USP6 does not enhance ES transformation, it is associated with an interferon (IFN) response in both cultured ES cells and clinical specimens. Further, USP6 renders ES cells exquisitely sensitive to exogenous IFNs, with Type I IFN inducing apoptosis specifically in USP6-positive ES cells through induction of the pro-apoptotic ligand TRAIL. These findings raise the possibility of using USP6 as a biomarker for IFN treatment of ES.β-catenin suppressors tightly regulate the transcriptional activity of the activated Wnt/β-catenin pathway during both normal development and cancer. Here, a novel β-catenin transcription suppressor with a FLYWCH/Zn-finger DNA-binding domain, called “FLYWCH1” is identified. The FLYWCH1 protein directly binds to nuclear β-catenin and rearranges its transcriptional activity to selectively block the expression of specific target genes associated with colorectal cancer cell-cell adhesion and migration. This study, for the first time, characterizes and describes a possible anti-metastasis and tumor suppressive role of FLYWCH1 in the context of the Wnt/β-catenin pathway.

Identification of tRNA-derived small noncoding RNAs as potential biomarkers for prediction of recurrence in triple-negative breast cancer.

Triple‐negative breast cancer (TNBC), an intrinsic subtype of breast cancer, is characterized by aggressive pathology and shorter overall survival. Yet there is no effective therapy for these patients. Breast cancer stem cells (BCSCs) in TNBC may account for treatment failure. It is urgent to identify new therapeutic targets for TNBC. tRNA‐derived small noncoding RNAs (tDRs) represent a new class of small noncoding RNAs (sncRNA), which have been reported in some human diseases and biological processes. However, there is no detailed information about the relationship between tDRs and BCSCs. In this study, a population of CD44+/CD24−/low cells was isolated and identified by reliable BCSC surface markers. tDR expression profiles in TNBC and non‐TNBC CSCs were performed by RNA sequencing. A total of 1327 differentially expressed tDRs contained 18 upregulated and 54 downregulated in TNBC group. Furthermore, the selected tDRs were validated by quantitative reverse transcription‐polymerase chain reaction (qRT‐PCR). tDR‐000620 expression level was consistently lower in TNBC cell lines CSCs (all P < 0.05) and serum samples (t = 2.597, P = 0.013). tDR‐000620 expression was significant association with age (P = 0.018), node status (P = 0.026) and local recurrence (P = 0.019) by chi‐square test. Kaplan‐Meier method with log‐rank test for comparison of recurrence curves. The results showed that the tDR‐000620 expression (P = 0.002) and node status (P = 0.001) group were statistically significant with recurrence‐free survival. Furthermore, multivariate Cox regression demonstrated that lymphatic metastasis (HR, 3.616; 95% CI, 1.234‐10.596; P = 0.019) and low tDR‐000620 expression (HR, 0.265; 95% CI, 0.073‐0.959; P = 0.043) were two independent adverse predictive factors for recurrence‐free survival. Finally, we found that tDR‐000620 participated in some important biological processes though GO and KEGG analysis. Taken together, our study reveals the expression profiles of tDRs in TNBC and non‐TNBC CSCs. It offers helpful information to understand the tDR‐000620 expression is responsible for the aggressive phenotype of BCSCs. It may provide predictive biomarkers and therapeutic targets for TNBC recurrence.