Mesenchymal traits are selected along with stem features in breast cancer cells grown as mammospheres

Promyelocytic leukemia protein regulates angiogenesis and epithelial-mesenchymal transition to limit metastasis in MDA-MB-231 breast cancer cells

Promyelocytic leukemia protein (PML) modulates diverse cell functions that contribute to both tumor suppressor and pro-oncogenic effects, depending on the cellular context. We show here that PML knockdown (KD) in MDA-MB-231, but not MCF7, breast cancer cells, prolonged stem-cell-like survival, and increased cell proliferation and migration, which is in line with gene-enrichment results from their RNA sequencing analysis. Of note, increased migration was accompanied by higher levels of the epithelial-mesenchymal transition (EMT) regulator Twist-related protein 2 (TWIST2). We showed here that PML binds to TWIST2 via its basic helix-loop-helix (bHLH) region and functionally interferes with the suppression of the epithelial target of TWIST2, CD24. In addition, PML ablation in MDA-MB-231 cells led to higher protein levels of hypoxia-inducible factor 1-alpha (HIF1a), resulting in a higher cell hypoxic response. Functionally, PML directly suppressed the induction of the HIF1a target gene vascular endothelial growth factor A (VEGFa). In line with these results, tumor xenografts of MDA-MB-231 PML-KD cells had enhanced aggressive properties, including higher microvessel density, faster local growth, and higher metastatic ability, with a preference for lung. Collectively, PML suppresses the cancer aggressive behavior by multiple mechanisms that impede both the HIF-hypoxia-angiogenic and EMT pathways.

Tumor suppressor DEAR1 regulates mammary epithelial cell fate and predicts early onset and metastasis in triple negative breast cancer

Triple negative breast cancer (TNBC) is a disease of poor prognosis, with the majority classified as the basal-like subtype associated with epithelial-mesenchymal transition and metastasis. Because basal breast cancers originate from proliferative luminal progenitor-like cells upon dysregulation of proper luminal differentiation, genes regulating luminal-basal transition are critical to elucidate novel therapeutic targets to improve TNBC outcomes. Herein we demonstrate that the tumor suppressor DEAR1/TRIM62 is a critical regulator of luminal cell fate. DEAR1 loss in human mammary epithelial cells results in significantly enhanced mammosphere formation that is accelerated in the presence of TGF-β/SMAD3 signaling. Mammospheres formed following DEAR1 loss are enriched for ALDH1A1 and CK5 expression, EpCAM^-/CD49f⁺ and CD44^high/24^low basal-like epithelial cells, indicating that DEAR1 regulates stem/progenitor cell properties and luminal-basal progenitor transition. We show that DEAR1 maintains luminal differentiation as a novel ubiquitin ligase for SNAI2/SLUG, a master regulator driving stemness and generation of basal-like progenitor populations. We also identify a significant inverse correlation between DEAR1 and SNAI2 expression in a 103 TNBC case cohort and show that low DEAR1 expression significantly correlates with young age of onset and shorter time to metastasis, suggesting DEAR1 could serve as a biomarker to stratify early onset TNBCs for targeted stem cell therapies.

Quantitative CK19 biomarker detection in breast cancer cell lines

Cytokeratin19 (CK19) was detected as the most related marker for circulating tumor cells, which was assessed in specific cell lines. MCF7, SKBR3, T47D, and MDA-MB-231, and HeLa cell line as negative control were used. CK19 expression was confirmed by using mouse monoclonal anti-human CK19 antibody. CK19 detection in MDA-MB-231 was not observed. CK19 marker expression was compared in T47D, MCF7, and SKBR3 cell lines. T47D and MCF7 belonged to the luminal subtype of breast cancer (BC) that CK19 expression regulated with an ER marker. SKBR3 belonged to the HER2 positive subtype of BC. However, MDA-MB-231 belonged to the claudin-low subtype of BC that lack of CK19 expression strongly is related to negative ER, PR, and HER2. Therefore, there are not only quantitative differences in CK19 expression, but its expression could also link to the other markers of BC that should be considered in the molecular classification of breast carcinoma. Different expression levels related to cell classification could be useful in the prognosis and treatment of cancers with epithelial origins.

A Comparative Study of Gene Expression in Menstrual Blood-Derived Stromal Cells between Endometriosis and Healthy Women

Background. Research into the pathogenesis of endometriosis would substantially promote its effective treatment and early diagnosis. Currently, accumulating evidence has shed light on the importance of endometrial stem cells within the menstrual blood which are involved in the establishment and progression of endometriotic lesions in a retrograde manner. Objectives. We aimed to identify the differences in some genes’ expression between menstrual blood-derived mesenchymal stem cells (MenSCs) isolated from endometriosis patients (E-MenSCs) and MenSCs from healthy women (NE-MenSCs). Methods. Menstrual blood samples (2-3 mL) from healthy and endometriosis women in the age range of 22–35 years were collected. Isolated MenSCs by the Ficoll-Paque density-gradient centrifugation method were characterized by flow cytometry. MenSCs were evaluated for key related endometriosis genes by real-time-PCR. Results. E-MenSCs were morphologically different from NE-MenSCs and showed, respectively, higher and lower expression of CD10 and CD9. Furthermore, E-MenSCs had higher expression of Cyclin D1 (a cell cycle-related gene) and MMP-2 and MMP-9 (migration- and invasion-related genes) genes compared with NE-MenSCs. Despite higher cell proliferation in E-MenSCs, the BAX/BCL-2 ratio was significantly lower in E-MenSCs compared to NE-MenSCs. Also, the level of inflammatory genes such as IL1β, IL6, IL8, and NF-κB and stemness genes including SOX2 and SALL4 was increased in E-MenSCs compared with NE-MenSCs. Further, VEGF, as a potent angiogenic factor, showed a significant increase in E-MenSCs rather than NE-MenSCs. However, NE-MenSCs showed increased ER-α and β-catenin when compared with E-MenSCs. Conclusion. Here, we showed that there are gene expression differences between E-MenSCs and NE-MenSCs. These findings propose that MenSCs could play key role in the pathogenesis of endometriosis and further support the menstrual blood retrograde theory of endometriosis formation. This could be of great importance in exploiting promising therapeutic targets and new biomarkers for endometriosis treatment and prognosis.

Current understanding of epigenetics mechanism as a novel target in reducing cancer stem cells resistance

At present, after extensive studies in the field of cancer, cancer stem cells (CSCs) have been proposed as a major factor in tumor initiation, progression, metastasis, and recurrence. CSCs are a subpopulation of bulk tumors, with stem cell-like properties and tumorigenic capabilities, having the abilities of self-renewal and differentiation, thereby being able to generate heterogeneous lineages of cancer cells and lead to resistance toward anti-tumor treatments. Highly resistant to conventional chemo- and radiotherapy, CSCs have heterogeneity and can migrate to different organs and metastasize. Recent studies have demonstrated that the population of CSCs and the progression of cancer are increased by the deregulation of different epigenetic pathways having effects on gene expression patterns and key pathways connected with cell proliferation and survival. Further, epigenetic modifications (DNA methylation, histone modifications, and RNA methylations) have been revealed to be key drivers in the formation and maintenance of CSCs. Hence, identifying CSCs and targeting epigenetic pathways therein can offer new insights into the treatment of cancer. In the present review, recent studies are addressed in terms of the characteristics of CSCs, the resistance thereof, and the factors influencing the development thereof, with an emphasis on different types of epigenetic changes in genes and main signaling pathways involved therein. Finally, targeted therapy for CSCs by epigenetic drugs is referred to, which is a new approach in overcoming resistance and recurrence of cancer.

p97/VCP is highly expressed in the stem-like cells of breast cancer and controls cancer stemness partly through the unfolded protein response

p97/VCP, an evolutionarily concerned ATPase, partakes in multiple cellular proteostatic processes, including the endoplasmic reticulum (ER)-associated protein degradation (ERAD). Elevated expression of p97 is common in many cancers and is often associated with poor survival. Here we report that the levels of p97 positively correlated with the histological grade, tumor size, and lymph node metastasis in breast cancers. We further examined p97 expression in the stem-like cancer cells or cancer stem cells (CSCs), a cell population that purportedly underscores cancer initiation, therapeutic resistance, and recurrence. We found that p97 was consistently at a higher level in the CD44⁺/CD24^-, ALDH⁺, or PKH26⁺ CSC populations than the respective non-CSC populations in human breast cancer tissues and cancer cell lines and p97 expression also positively correlated with that of SOX2, another CSC marker. To assess the role of p97 in breast cancers, cancer proliferation, mammosphere, and orthotopic growth were analyzed. Similarly as p97 depletion, two pharmacological inhibitors, which targets the ER-associated p97 or globally inhibits p97's ATPase activity, markedly reduced cancer growth and the CSC population. Importantly, depletion or inhibition of p97 greatly suppressed the proliferation of the ALDH⁺ CSCs and the CSC-enriched mammospheres, while exhibiting much less or insignificant inhibitory effects on the non-CSC cancer cells. Comparable phenotypes produced by blocking ERAD suggest that ER proteostasis is essential for the CSC integrity. Loss of p97 gravely activated the unfolded protein response (UPR) and modulated the expression of multiple stemness and pluripotency regulators, including C/EBPδ, c-MYC, SOX2, and SKP2, which collectively contributed to the demise of CSCs. In summary, p97 controls the breast CSC integrity through multiple targets, many of which directly affect cancer stemness and are induced by UPR activation. Our findings highlight the importance of p97 and ER proteostasis in CSC biology and anticancer therapy.

The Breast Cancer Stem Cells Traits and Drug Resistance

Drug resistance is a major challenge in breast cancer (BC) treatment at present. Accumulating studies indicate that breast cancer stem cells (BCSCs) are responsible for the BC drugs resistance, causing relapse and metastasis in BC patients. Thus, BCSCs elimination could reverse drug resistance and improve drug efficacy to benefit BC patients. Consequently, mastering the knowledge on the proliferation, resistance mechanisms, and separation of BCSCs in BC therapy is extremely helpful for BCSCs-targeted therapeutic strategies. Herein, we summarize the principal BCSCs surface markers and signaling pathways, and list the BCSCs-related drug resistance mechanisms in chemotherapy (CT), endocrine therapy (ET), and targeted therapy (TT), and display therapeutic strategies for targeting BCSCs to reverse drug resistance in BC. Even more importantly, more attention should be paid to studies on BCSC-targeted strategies to overcome the drug resistant dilemma of clinical therapies in the future.

Breast cancer organoid model allowed to reveal potentially beneficial combinations of 3,3'-diindolylmethane and chemotherapy drugs

Epigenetic alterations represent promising therapeutic targets in cancer treatment. Recently it was revealed that small molecules have the potential to act as microRNA silencers. Capacity to bind the discrete stem-looped structure of pre-miR-21 and prevent its maturation opens opportunities to utilize such compounds for the prevention of initiation, progression, and chemoresistance of cancer. Molecular simulations performed earlier identified 3,3'-diindolylmethane (DIM) as a potent microRNA-21 antagonist. However, data on DIM and microRNA-21 interplay is controversial, which may be caused by the limitations of the cell lines.

Molecular cloning and expression analysis of hybrid hazelnut (Corylus heterophylla × Corylus avellana) ChaSRK1/2 genes and their homologs from other cultivars and species

The self-incompatibility system of Corylus is a sporophytic type that is phenotypically similar to that of Brassica. While the molecular mechanism of sporophytic self-incompatibility (SSI) has been investigated extensively in Brassica (Brassicaceae), little is known about the corresponding mechanism in Corylus (Betulaceae). Here, we discuss the SSI mechanism with respect to S-locus receptor kinase (SRK) gene homologs. To obtain two SRK candidate unigenes, we compared all of the unigenes in a transcriptional protein database from our previous study with BnSRK-1 (AB270767) using BLASTX with a cutoff e-value of 10^-5. We then cloned the full-length cDNA of ChaSRK1 and ChaSRK2 genes from Ping'ou hybrid hazelnut (Corylus heterophylla × Corylus avellana) using RACE techniques. Bioinformatics approaches were used to analyze the cDNA sequences, protein sequences, and domains of the encoded proteins. The full-length ChaSRK1 cDNA was 2883 base pairs (bp) with a coding sequence (CDS) of 2,547 bp encoding 849 amino acid residues. The full-length ChaSRK2 cDNA was 2,693 bp, with a CDS of 2,433 bp encoding 811 amino acids. The ChaSRK1/2 proteins contained an S-domain (extracellular domain), a transmembrane domain, a Ser/Thr protein kinase active site (kinase domain), and DUF3660 and/or DUF3403 domains. The lengths of 18 partial SRK homologs ranged from 1347 to 1451 bp, and they contained the same structural domains as ChaSRK1 and ChaSRK2. Phylogenetic analysis revealed that all SRK homologs could be divided into two categories that were similar to the classification of SRKs in Brassica. The expression patterns of ChaSRK1 and ChaSRK2 differed: ChaSRK2 was predominantly expressed in mature stigmatic styles, while ChaSRK1 was expressed in other tissues with the highest in the root tips of Corylus. Using dual-color fluorescence in situ hybridization, ChaSRK1/2 expression was found to be localized in papillar cells. Collectively, these results revealed that SRKs from Corylus had similar characteristics to SRKs from Brassica. We therefore speculated that the SSI mechanism in Corylus might be more similar to the Brassica mechanism than to other SSI types.

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.

The Autophagy Machinery Contributes to E-cadherin Turnover in Breast Cancer

Autophagy is an intracellular catabolic process that is increasingly being recognized as a crucial factor in several human diseases including cancers. Mounting evidence suggests that autophagy allows tumor cells to overcome otherwise fatal stresses and to increase dissemination. Nevertheless, how autophagy controls these processes and in particular how it impinges on cell-cell adhesion is still poorly understood. Here, we investigate the role of autophagy in the turnover of the epithelial adhesion molecule E-cadherin in the context of breast cancer. We demonstrated in breast cancer cell lines that autophagy impinges on E-cadherin expression and in the configuration of adherens junctions. Besides, we showed that E-cadherin colocalizes with LC3B and SQSTM1/p62, two components of the autophagosome machinery. Pull down and immunoprecipitation analyses provided evidence that E-cadherin and SQSTM1/p62 physically interact. Moreover, the physical closeness of E-cadherin and SQSTM1/p62 was demonstrated by proximity ligation assays in breast cancer cell lines and primary tumors. Finally, we proved that the silencing of SQSTM1/p62 diminished the E-cadherin/LC3B colocalization, further supporting the role of SQSTM1/p62 in E-cadherin delivery to autophagosomes. These findings suggest that the activation of autophagy, reported in breast cancers with poor prognosis and in dormant breast cancer cells, may contribute to the control of tumor progression via downmodulation of E-cadherin protein levels.

CD133 in Breast Cancer Cells: More than a Stem Cell Marker

Initially correlated with hematopoietic precursors, the surface expression of CD133 was also found in epithelial and nonepithelial cells from adult tissues in which it has been associated with a number of biological events. CD133 is expressed in solid tumors as well, including breast cancer, in which most of the studies have been focused on its use as a surface marker for the detection of cells with stem-like properties (i.e., cancer stem cells (CSCs)). Differently with other solid tumors, very limited and in part controversial are the information about the significance of CD133 in breast cancer, the most common malignancy among women in industrialized countries. In this review, we summarize the latest findings about the implication of CD133 in breast tumors, highlighting its role in tumor cells with a triple negative phenotype in which it directly regulates the expression of proteins involved in metastasis and drug resistance. We provide updates about the prognostic role of CD133, underlining its value as an indicator of increased malignancy of both noninvasive and invasive breast tumor cells. The molecular mechanisms at the basis of the regulation of CD133 levels in breast tumors have also been reviewed, highlighting experimental strategies capable to restrain its level that could be taken into account to reduce malignancy and/or to prevent the progression of breast tumors.

Screening of acetaminophen-induced alterations in epithelial-to-mesenchymal transition-related expression of microRNAs in a model of stem-like triple-negative breast cancer cells: The possible functional impacts

Current protocols for therapy inefficiently targets triple negative breast cancer and barely eradicate cancer stem cells. Elucidation of the pleiotropic effect of clinically proven therapeutics on cancer cells shed light on novel application of old friends. The pleiotropic effect of acetaminophen (APAP) on breast cancer was previously reported. In a cell model of triple negative breast cancer with stem-like CD44^high/CD24^low phenotype, we screened the impacts of APAP (1 mM, 72 h) on the Epithelial to mesenchymal transition (EMT)-related expression of miRs. APAP significantly overexpressed hsa-miR-130a-3p, 192-5p, 214-3p, 101-3p, 30d-5p, 10a-5p, 99a-5p, 200c-3p, 143-3p, 30b-5p and let-7f-5p showed significant overexpression, but suppressed the expression of hsa-miR-7-5p, 149-3p, 215, 150-5p, 205-5p, 206, 10b-5p, 20b-5p, 145-5p, 26b-5p, 223-3p, 17-5p, 186-5p, 146a-5p and let-7c. It also altered on the expression of selected EMT-related genes, significantly upregulated the expression of KRT19, AKT2, CD24, and TIMP1; but downregulated the expression of MMP2, ALDH1, MMP9, TWIST, NOTCH1, and AKT1. Such shifts in expression profiles increased the population of the cells with CD44^high/CD24^high, and CD44^low/CD24^high phenotypes, significantly reduced the Twist protein and shifted the balance of E-cadherin and Vimentin proteins in favor of differentiation. Treated cells showed a significant reduction of in vitro migration and were significantly chemosensitized to Camptothecin. In conclusion, APAP, at a safe clinical dose, induced a set of targeted alterations in the EMT-related miRs which implicate, even in part, significant mitigation in chemoresistance and in vitro migration. Further studies should also be piloted to elucidate the most crucial miRs and to evaluate its clinical effectiveness.

A p53/miR-30a/ZEB2 axis controls triple negative breast cancer aggressiveness

Inactivation of p53 contributes significantly to the dismal prognosis of breast tumors, most notably triple-negative breast cancers (TNBCs). How the relief from p53 tumor suppressive functions results in tumor cell aggressive behavior is only partially elucidated. In an attempt to shed light on the implication of microRNAs in this context, we discovered a new signaling axis involving p53, miR-30a and ZEB2. By an in silico approach we identified miR-30a as a putative p53 target and observed that in breast tumors reduced miR-30a expression correlated with p53 inactivation, lymph node positivity and poor prognosis. We demonstrate that p53 binds the MIR30A promoter and induces the transcription of both miRNA strands 5p and 3p. Both miR-30a-5p and -3p showed the capacity of targeting ZEB2, a transcription factor involved in epithelial–mesenchymal transition (EMT), tumor cell migration and drug resistance. Intriguingly, we found that p53 does restrain ZEB2 expression via miR-30a. Finally, we provide evidence that the new p53/miR-30a/ZEB2 axis controls tumor cell invasion and distal spreading and impinges upon miR-200c expression. Overall, this study highlights the existence of a novel axis linking p53 to EMT via miR-30a, and adds support to the notion that miRNAs represent key elements of the complex network whereby p53 inactivation affects TNBC clinical behavior.

Embryonic stem cell secreted factors decrease invasiveness of triple-negative breast cancer cells through regulome modulation

Stem cell microenvironments decrease the invasiveness of cancer cells, and elucidating the mechanisms associated with disease regression could further the development of targeted therapies for aggressive cancer subtypes. To this end, we applied an emerging technology, TRanscriptional Activity CEll aRray (TRACER), to investigate the reprogramming of triple-negative breast cancer (TNBC) cells in conditions that promoted a less aggressive phenotype. The repressive environment was established through exposure to mouse embryonic stem cell conditioned media (mESC CM). Assessment of carcinogenic phenotypes indicated that mESC CM exposure decreased proliferation, invasion, migration, and stemness in TNBC cells. Protein expression analysis revealed that mESC CM exposure increased expression of the epithelial protein E-cadherin and decreased the mesenchymal protein MMP9. Gene expression analysis showed that mESC CM decreased epithelial to mesenchymal transition (EMT) markers fibronectin, vimentin, and Snail. Over a period of 6 d, TRACER quantified changes in activity of 11 transcription factors (TFs) associated with oncogenic progression. The EMT profile was decreased in association with the activity of 7 TFs (Smad3, NF-κΒ, MEF2, GATA, Hif1, Sp1, and RXR). Further examination of Smad3 and GATA expression and phosphorylation revealed that mESC CM exposure decreased noncanonical Smad3 phosphorylation and Smad3-mediated gene expression, increased GATA3 expression and phosphorylation, and resulted in a synergistic decrease in migration of GATA3 overexpressing MDA-MB-231 cells. Collectively, the application of TRACER to examine TF activity associated with the transition of cancer cells to a less aggressive phenotype, as directed by mESC CM, identified novel mechanistic events linking the embryonic microenvironment to both favorable changes and cellular plasticity in TNBC cell phenotypes.

Pomegranate Extract Alters Breast Cancer Stem Cell Properties in Association with Inhibition of Epithelial-to-Mesenchymal Transition

Cancer stem cells (CSCs) have become an important target population in cancer therapy and prevention due to their ability to self-renew, initiate tumors, and resist therapy. We examined whether pomegranate extract (PE) alters characteristics of breast CSCs. Ability to grow as mammospheres is a hallmark of breast CSCs. PE inhibited mammosphere formation in two different cell lines, neoplastic mammary epithelial HMLER and breast cancer Hs578T. In addition, mammosphere-derived cells from PE treatment groups showed reduced mammosphere formation for at least two serial passages. These data indicate that PE inhibits CSC's ability to self-renew. In addition, incubation of mammospheres with PE reversed them into adherent cultures, indicating promotion of CSC differentiation. Epithelial-to-mesenchymal transition (EMT) is a key program in generating CSCs and maintaining their characteristics. Thus, we examined the effect of PE on EMT. PE reduced cell migration, a major feature of the EMT phenotype. In addition, PE downregulated genes involved in EMT, including the EMT-inducing transcription factor Twist family basic helix-loop-helix transcription factor 1 (TWIST1). This suggests that PE suppresses CSC characteristics in part due to inhibition of EMT. The ability of PE to suppress CSCs can be exploited in the prevention of breast cancer.

Epithelial vimentin plays a functional role in mammary gland development

In the mammary gland, vimentin intermediate filaments are expressed in stromal cells and in basal epithelial cell populations, including gland-reconstituting mammary stem cells, with largely undefined functions. Here, we have studied how vimentin deficiency affects mouse mammary gland development. We find that, in adult vimentin knockout mice (Vim^-/- ), mammary ductal outgrowth is delayed. The adult Vim^-/- glands display dilated ducts and a reduced basal-to-luminal mouse mammary epithelial cell (MMEC) ratio indicative of altered progenitor cell activity. Accordingly, isolated Vim^-/- MMECs form fewer mammospheres and basal-like organoids in vitro than their wild-type counterparts. Importantly, reduced basal MMEC number translates into defects in Vim^-/- mammary gland regeneration in vivo Global gene expression profiling of basal MMECs reveals that lack of vimentin alters multiple pathways, including adhesion, cancer and Wnt signalling. Furthermore, vimentin contributes to stem-like cell properties in MDA-MB-231 breast cancer cells, wherein vimentin depletion reduces tumoursphere formation and attenuates expression of breast cancer stem cell-associated surface markers. Together, our findings identify vimentin as a positive regulator of stemness in the developing mouse mammary gland and in breast cancer cells.

In-depth characterization of breast cancer tumor-promoting cell transcriptome by RNA sequencing and microarrays

Numerous studies have reported the existence of tumor-promoting cells (TPC) with self-renewal potential and a relevant role in drug resistance. However, pathways and modifications involved in the maintenance of such tumor subpopulations are still only partially understood. Sequencing-based approaches offer the opportunity for a detailed study of TPC including their transcriptome modulation. Using microarrays and RNA sequencing approaches, we compared the transcriptional profiles of parental MCF7 breast cancer cells with MCF7-derived TPC (i.e. MCFS). Data were explored using different bioinformatic approaches, and major findings were experimentally validated. The different analytical pipelines (Lifescope and Cufflinks based) yielded similar although not identical results. RNA sequencing data partially overlapped microarray results and displayed a higher dynamic range, although overall the two approaches concordantly predicted pathway modifications. Several biological functions were altered in TPC, ranging from production of inflammatory cytokines (i.e., IL-8 and MCP-1) to proliferation and response to steroid hormones. More than 300 non-coding RNAs were defined as differentially expressed, and 2,471 potential splicing events were identified. A consensus signature of genes up-regulated in TPC was derived and was found to be significantly associated with insensitivity to fulvestrant in a public breast cancer patient dataset. Overall, we obtained a detailed portrait of the transcriptome of a breast cancer TPC line, highlighted the role of non-coding RNAs and differential splicing, and identified a gene signature with a potential as a context-specific biomarker in patients receiving endocrine treatment.

Epigenetic silencing of miR-200c in breast cancer is associated with aggressiveness and is modulated by ZEB1

Loss of expression of miR-200 family members has been implicated in cellular plasticity, a phenomenon that accounts for epithelial-to-mesenchymal transition (EMT) and stem-like features of many carcinomas and is considered a major cause of tumor aggressiveness and drug resistance. Nevertheless, the mechanisms of miR-200 downregulation in breast cancer are still largely unknown. Here we show that miR-200c expression inversely correlates with miR-200c/miR-141 locus methylation in triple-negative breast tumors (TNBC). Importantly, low levels of miR-200c expression and high levels of miR-200c/miR-141 locus methylation associated with lymph node metastasis. Moreover, miR-200c/miR-141 locus methylation was significantly related to high expression of ZEB1 in two independent TNBC series. Silencing of ZEB1 in vitro reduced miR-200c/miR-141 DNA methylation and, concurrently, decreased histone H3K9 trimethylation. This chromatin modifications were paralleled by an increase in the expression of both miR-200c and E-cadherin. Similar effects were achieved by treatment with a demethylating agent. Our data suggest that gene methylation is an important element in the regulation of the miR-200c/ZEB1 axis and that chromatin remodeling of the miR-200c/miR-141 locus is affected by ZEB1 and, thus, contributes to ZEB1-induced cellular plasticity. © 2016 Wiley Periodicals, Inc.

Genotypes of cancer stem cells characterized by epithelial-to-mesenchymal transition and proliferation related functions

Cancer stem cells (CSCs), or cancer cells with stem cell-like properties, generally exhibit drug resistance and have highly potent cancer inducing capabilities. Genome-wide expression data collected at public repositories over the last few years provide excellent material for studies that can lead to insights concerning the molecular and functional characteristics of CSCs. Here, we conducted functional genomic studies of CSC based on fourteen PCA-screened high quality public CSC whole genome gene expression datasets and, as control, four high quality non-stem-like cancer cell and non-cancerous stem cell datasets from the Gene Expression Omnibus database. A total of 6,002 molecular signatures were taken from the Molecular Signatures Database and used to characterize the datasets, which, under two-way hierarchical clustering, formed three genotypes. Type 1, consisting of mainly glia CSCs, had significantly enhanced proliferation, and significantly suppressed epithelial-mesenchymal transition (EMT), related functions. Type 2, mainly breast CSCs, had significantly enhanced EMT, but not proliferation, related functions. Type 3, composed of ovarian, prostate, and colon CSCs, had significantly suppressed proliferation related functions and mixed expressions on EMT related functions.

High mitochondrial mass identifies a sub-population of stem-like cancer cells that are chemo-resistant

Chemo-resistance is a clinical barrier to more effective anti-cancer therapy. In this context, cancer stem-like cells (CSCs) are thought to be chemo-resistant, resulting in tumor recurrence and distant metastasis. Our hypothesis is that chemo-resistance in CSCs is driven, in part, by enhanced mitochondrial function. Here, we used breast cell lines and metastatic breast cancer patient samples to begin to dissect the role of mitochondrial metabolism in conferring the CSC phenotype. More specifically, we employed fluorescent staining with MitoTracker (MT) to metabolically fractionate these cell lines into mito-high and mito-low sub-populations, by flow-cytometry. Interestingly, cells with high mitochondrial mass (mito-high) were specifically enriched in a number of known CSC markers, such as aldehyde dehydrogenase (ALDH) activity, and they were ESA+/CD24-/low and formed mammospheres with higher efficiency. Large cell size is another independent characteristic of the stem cell phenotype; here, we observed a >2-fold increase in mitochondrial mass in large cells (>12-μm), relative to the smaller cell population (4–8-μm). Moreover, the mito-high cell population showed a 2.4-fold enrichment in tumor-initiating cell activity, based on limiting dilution assays in murine xenografts. Importantly, primary human breast CSCs isolated from patients with metastatic breast cancer or a patient derived xenograft (PDX) also showed the co-enrichment of ALDH activity and mitochondrial mass. Most significantly, our investigations demonstrated that mito-high cells were resistant to paclitaxel, resulting in little or no DNA damage, as measured using the comet assay. In summary, increased mitochondrial mass in a sub-population of breast cancer cells confers a stem-like phenotype and chemo-resistance. As such, our current findings have important clinical implications for over-coming drug resistance, by therapeutically targeting the mito-high CSC population.

Assessment of Cytokeratin-19 Gene Expression in Peripheral Blood of Breast Cancer Patients and Breast Cancer Cell Lines

Detection of cytokeratin-19 (CK19) expression as an epithelial-specific marker in circulating tumor cells (CTCs) of breast cancer patients can be important for diagnostic purposes. Comparison of CK19 expression in breast cancer cell lines can indicate that expression of this marker is different in various breast cancer cell lines based on their category. Thirty-five breast cancer patients were evaluated for detection of CK19 mRNA in their peripheral blood using CK19-specific primers and a nested reverse transcriptase polymerase chain reaction (RT-PCR) technique. CK19 expression levels were detected in MCF7, T47D, SK-BR-3, and MDA-MB-231 cell lines by semiquantitative RT-PCR and Western blot analyses. Statistical analysis of our data indicates that there is no significant difference between CK19 expression and histopathological parameters and some molecular markers, including Ki-67, HER-2, and P53, but there are statistically significant correlations between estrogen receptor (P = 0.040) and progesterone receptor (P = 0.046) with CK19 expression. CK19 expression was detected in MCF7, T47D, and SK-BR-3 cell lines but not in MDA-MB-231 cell line. More studies are needed to determine the relationship between this marker and other markers in the diagnosis and treatment of breast cancer. On the other hand, the study of different markers using breast cancer cell lines as experimental models of breast cancer could have an impact on improving the health outcomes of patients with breast cancer.

An improved sequencing-based strategy to estimate locus-specific DNA methylation

Background

DNA methylation is an important epigenetic mechanism of transcriptional control that plays an essential role in several cellular functions. Aberrant DNA methylation in cancer has been frequently associated with downregulation of microRNAs and protein coding genes, such as miR-200c/miR-141 cluster and E-cadherin. Current strategies to assess DNA methylation, including bisulfite treatment-based assays, tend to be time-consuming and may be quite expensive when a precise appraisal is required. The Sanger-sequencing of the amplified bisulfite-treated DNA (BSP) might represent a practical option to measure DNA methylation at single CpG resolution. However, this strategy often produces noisy data, which affects accurate quantification. Here we propose an improved, reliable and cost-effective BSP-based protocol that allows proper DNA methylation assessment.

Methods

Our strategy, named normalized-BSP (NBSP), takes advantage of tailed C-balanced primers and a normalization procedure based on C/T ratio to overcome BSP-associated noise problems and nucleotide signal unbalance. NBSP was applied to estimate miR-200c/miR-141 locus methylation in serial dilution experiments and was compared to conventional methods. Besides, it was applied in the analysis of FFPE breast cancer samples and further validated in the context of the E-cadherin promoter.

Results

NBSP strategy outperformed conventional BSP in the estimate of the fraction of methylated cytosine in serial dilution experiments, providing data in agreement with the widely used but cumbersome cloning-based protocol. This held true for both miR-200c/miR-141 locus and E-cadherin promoter analyses. Moreover, the miR-200c/miR-141 locus methylation reflected the decrease in miRNA expression both in breast cancer cell lines and in the FFPE samples.

Conclusions

NBSP is a rapid and economical method to estimate the extent of methylation at each CpG of a given locus. Notably, NBSP works efficiently on FFPE samples, thus disclosing the perspective of its application also in the diagnostic setting.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1646-6) contains supplementary material, which is available to authorized users.

Deregulation of the EGFR/PI3K/PTEN/Akt/mTORC1 pathway in breast cancer: possibilities for therapeutic intervention

The EGFR/PI3K/PTEN/Akt/mTORC1/GSK-3 pathway plays prominent roles in malignant transformation, prevention of apoptosis, drug resistance and metastasis. The expression of this pathway is frequently altered in breast cancer due to mutations at or aberrant expression of: HER2, ERalpha, BRCA1, BRCA2, EGFR1, PIK3CA, PTEN, TP53, RB as well as other oncogenes and tumor suppressor genes. In some breast cancer cases, mutations at certain components of this pathway (e.g., PIK3CA) are associated with a better prognosis than breast cancers lacking these mutations. The expression of this pathway and upstream HER2 has been associated with breast cancer initiating cells (CICs) and in some cases resistance to treatment. The anti-diabetes drug metformin can suppress the growth of breast CICs and herceptin-resistant HER2+ cells. This review will discuss the importance of the EGFR/PI3K/PTEN/Akt/mTORC1/GSK-3 pathway primarily in breast cancer but will also include relevant examples from other cancer types. The targeting of this pathway will be discussed as well as clinical trials with novel small molecule inhibitors. The targeting of the hormone receptor, HER2 and EGFR1 in breast cancer will be reviewed in association with suppression of the EGFR/PI3K/PTEN/Akt/mTORC1/GSK-3 pathway.

A differential role for CXCR4 in the regulation of normal versus malignant breast stem cell activity

C-X-C chemokine receptor type 4 (CXCR4) is known to regulate lung, pancreatic and prostate cancer stem cells. In breast cancer, CXCR4 signalling has been reported to be a mediator of metastasis, and is linked to poor prognosis. However its role in normal and malignant breast stem cell function has not been investigated. Anoikis resistant (AR) cells were collected from immortalised (MCF10A, 226L) and malignant (MCF7, T47D, SKBR3) breast cell lines and assessed for stem cell enrichment versus unsorted cells. AR cells had significantly higher mammosphere forming efficiency (MFE) than unsorted cells. The AR normal cells demonstrated increased formation of 3D structures in Matrigel compared to unsorted cells. In vivo, SKBR3 and T47D AR cells had 7- and 130-fold enrichments for tumour formationrespectively, compared with unsorted cells. AR cells contained significantly elevated CXCR4 transcript and protein levels compared to unsorted cells. Importantly, CXCR4 mRNA was higher in stem cell-enriched CD44+/CD24- patient-derived breast cancer cells compared to non-enriched cells. CXCR4 stimulation by its ligand SDF-1 reduced MFE of the normal breast cells lines but increased the MFE in T47D and patient-derived breast cancer cells. CXCR4 inhibition by AMD3100 increased stem cell activity but reduced the self-renewal capacity of the malignant breast cell line T47D. CXCR4+ FACS sorted MCF7 cells demonstrated a significantly increased MFE compared with CXCR4- cells. This significant increase in MFE was further demonstrated in CXCR4 over-expressing MCF7 cells which also had an increase in self-renewal compared to parental cells. A greater reduction in self-renewal following CXCR4 inhibition in the CXCR4 over-expressing cells compared with parental cells was also observed. Our data establish for the first time that CXCR4 signalling has contrasting effects on normal and malignant breast stem cell activity. Here, we demonstrate that CXCR4 signalling specifically regulates breast cancer stem cell activities and may therefore be important in tumour formation at the sites of metastases.

Twist1 expression induced by sunitinib accelerates tumor cell vasculogenic mimicry by increasing the population of CD133+ cells in triple-negative breast cancer

Background

Hypoxia induced by antiangiogenic agents is linked to the generation of cancer stem cells (CSCs) and treatment failure through unknown mechanisms. The generation of endothelial cell-independent microcirculation in malignant tumors is defined as tumor cell vasculogenic mimicry (VM). In the present study, we analyzed the effects of an antiangiogenic agent on VM in triple-negative breast cancer (TNBC).

Methods

Microcirculation patterns were detected in patients with TNBC and non-TNBC. Tientsin Albino 2 (TA2) mice engrafted with mouse TNBC cells and nude mice engrafted with human breast cancer cell lines with TNBC or non-TNBC phenotypes were administered sunitinib and analyzed to determine tumor progression, survival, microcirculation, and oxygen concentration. Further, we evaluated the effects of hypoxia induced with CoCl₂ and the expression levels of the transcription factor Twist1, in the presence or absence of a Twist siRNA, on the population of CD133⁺ cells and VM in TNBC and non-TNBC cells.

Results

VM was detected in 35.8 and 17.8% of patients with TNBC or with non-TNBC, respectively. The growth of tumors in TNBC and non-TNBC-bearing mice was inhibited by sunitinib. The tumors in TA2 mice engrafted with mouse TNBCs and in mice engrafted a human TNBC cell line (MDA-MB-231) regrew after terminating sunitinib administration. However, this effect was not observed in mice engrafted with a non-TNBC tumor cell line. Tumor metastases in sunitinib-treated TA2 mice was accelerated, and the survival of these mice decreased when sunitinib was withdrawn. VM was the major component of the microcirculation in sunitinib-treated mice with TNBC tumors, and the population of CD133⁺ cells increased in hypoxic areas. Hypoxia also induced MDA-MB-231 cells to express Twist1, and CD133⁺ cells present in the MDA-MB-231 cell population induced VM after reoxygenation. Moreover, hypoxia did not induce MDA-MB-231 cells transfected with an sh-Twist1 siRNA cell to form VM and generate CD133⁺ cells. Conversely, hypoxia induced MCF-7 cells transfected with Twist to form VM and generate CD133⁺ cells.

Conclusions

Sunitinib induced hypoxia in TNBCs, and Twist1 expression induced by hypoxia accelerated VM by increasing population of CD133⁺ cells. VM was responsible for the regrowth of TNBCs sunitinib administration was terminated.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-207) contains supplementary material, which is available to authorized users.

Targeting breast cancer initiating cells: advances in breast cancer research and therapy

Over the past 10 years there have been significant advances in our understanding of breast cancer and the important roles that breast cancer initiating cells (CICs) play in the development and resistance of breast cancer. Breast CICs endowed with self-renewing and tumor-initiating capacities are believed to be responsible for the relapses which often occur after various breast cancer therapies. In this review, we will summarize some of the key developments in breast CICs which will include discussion of some of the key genes implicated: estrogen receptor (ER), HER2, BRCA1, TP53, PIK3CA, RB, P16INK1 and various miRs as well some drugs which are showing promise in targeting CICs. In addition, the concept of combined therapies will be discussed. Basic and clinical research is resulting in novel approaches to improve breast cancer therapy by targeting the breast CICs.

Menstrual blood-derived stromal stem cells from women with and without endometriosis reveal different phenotypic and functional characteristics

Retrograde flow of menstrual blood cells during menstruation is considered as the dominant theory for the development of endometriosis. Moreover, current evidence suggests that endometrial-derived stem cells are key players in the pathogenesis of endometriosis. In particular, endometrial stromal stem cells have been suggested to be involved in the pathogenesis of this disease. Here, we aimed to use menstrual blood, as a novel source of endometrial stem cells, to investigate whether stromal stem cells from endometriosis (E-MenSCs) and non-endometriosis (NE-MenSCs) women differed regarding their morphology, CD marker expression pattern, proliferation, invasion and adhesion capacities and their ability to express certain immunomodulatory molecules. E-MenSCs were morphologically different from NE-MenSCs and showed higher expression of CD9, CD10 and CD29. Furthermore, E-MenSCs had higher proliferation and invasion potentials compared with NE-MenSCs. The amount of indoleamine 2,3-dioxygenase-1 (IDO1) and cyclooxygenase-2 (COX-2) in E-MenSCs co-cultured with allogenic peripheral blood mononuclear cells (PBMCs) was shown to be higher both at the gene and protein levels, and higher IDO1 activity was detected in the endometriosis group. However, NE-MenSCs revealed increased concentrations of forkhead transcription factor-3 (FOXP3) when compared with E-MenSCs. Nonetheless, interferon (IFN)-γ, Interleukin (IL)-10 and monocyte chemoattractant protein-1 (MCP-1) levels were higher in the supernatant of E-MenSCs-PBMC co-cultures. Here, we showed that there are inherent differences between E-MenSCs and NE-MenSCs. These findings propose the key role MenSCs could play in the pathogenesis of endometriosis and further support the retrograde and stem cell theories of endometriosis. Hence, considering its renewable and easily available nature, menstrual blood could be viewed as a reliable and inexpensive material for studies addressing the cellular and molecular aspects of endometriosis.

HMGA1 promotes metastatic processes in basal-like breast cancer regulating EMT and stemness

Breast cancer is a heterogeneous disease that progresses to the critical hallmark of metastasis. In the present study, we show that the High Mobility Group A1 (HMGA1) protein plays a fundamental role in this process in basal-like breast cancer subtype. HMGA1 knockdown induces the mesenchymal to epithelial transition and dramatically decreases stemness and self-renewal. Notably, HMGA1 depletion in basal-like breast cancer cell lines reduced migration and invasion in vitro and the formation of metastases in vivo. Mechanistically, HMGA1 activated stemness and key migration-associated genes which were linked to the Wnt/beta-catenin, Notch and Pin1/mutant p53 signalling pathways. Moreover, we identified a specific HMGA1 gene expression signature that was activated in a large subset of human primary breast tumours and was associated with poor prognosis. Taken together, these data provide new insights into the role of HMGA1 in the acquisition of aggressive features in breast cancer.

Differences and homologies of chromosomal alterations within and between breast cancer cell lines: a clustering analysis

Background

The MCF7 (ER+/HER2-), T47D (ER+/HER2-), BT474 (ER+/HER2+) and SKBR3 (ER-/HER2+) breast cancer cell lines are widely used in breast cancer research as paradigms of the luminal and HER2 phenotypes. Although they have been subjected to cytogenetic analysis, their chromosomal abnormalities have not been carefully characterized, and their differential cytogenetic profiles have not yet been established. In addition, techniques such as comparative genomic hybridization (CGH), microarray-based CGH and multiplex ligation-dependent probe amplification (MLPA) have described specific regions of gains, losses and amplifications of these cell lines; however, these techniques cannot detect balanced chromosomal rearrangements (e.g., translocations or inversions) or low frequency mosaicism.

Results

A range of 19 to 26 metaphases of the MCF7, T47D, BT474 and SKBR3 cell lines was studied using conventional (G-banding) and molecular cytogenetic techniques (multi-color fluorescence in situ hybridization, M-FISH). We detected previously unreported chromosomal changes and determined the content and frequency of chromosomal markers. MCF7 and T47D (ER+/HER2-) cells showed a less complex chromosomal make up, with more numerical than structural alterations, compared to BT474 and SKBR3 (HER2+) cells, which harbored the highest frequency of numerical and structural aberrations. Karyotype heterogeneity and clonality were determined by comparing all metaphases within and between the four cell lines by hierarchical clustering. The latter analysis identified five main clusters. One of these clusters was characterized by numerical chromosomal abnormalities common to all cell lines, and the other four clusters encompassed cell-specific chromosomal abnormalities. T47D and BT474 cells shared the most chromosomal abnormalities, some of which were shared with SKBR3 cells. MCF7 cells showed a chromosomal pattern that was markedly different from those of the other cell lines.

Conclusions

Our study provides a comprehensive and specific characterization of complex chromosomal aberrations of MCF7, T47D, BT474 and SKBR3 cell lines.

The chromosomal pattern of ER+/HER2- cells is less complex than that of ER+/HER2+ and ER-/HER2+ cells. These chromosomal abnormalities could influence the biologic and pharmacologic response of cells. Finally, although gene expression profiling and aCGH studies have classified these four cell lines as luminal, our results suggest that they are heterogeneous at the cytogenetic level.

Inhibition of GSK-3β activity can result in drug and hormonal resistance and alter sensitivity to targeted therapy in MCF-7 breast cancer cells

The PI3K/Akt/mTORC1 pathway plays prominent roles in malignant transformation, prevention of apoptosis, drug resistance, and metastasis. One molecule regulated by this pathway is GSK-3β. GSK-3β is phosphorylated by Akt on S9, which leads to its inactivation; however, GSK-3β also can regulate the activity of the PI3K/Akt/mTORC1 pathway by phosphorylating molecules such as PTEN, TSC2, p70S6K, and 4E-BP1. To further elucidate the roles of GSK-3β in chemotherapeutic drug and hormonal resistance of MCF-7 breast cancer cells, we transfected MCF-7 breast cancer cells with wild-type (WT), kinase-dead (KD), and constitutively activated (A9) forms of GSK-3β. MCF-7/GSK-3β(KD) cells were more resistant to doxorubicin and tamoxifen compared with either MCF-7/GSK-3β(WT) or MCF-7/GSK-3β(A9) cells. In the presence and absence of doxorubicin, the MCF-7/GSK-3β(KD) cells formed more colonies in soft agar compared with MCF-7/GSK-3β(WT) or MCF-7/GSK-3β(A9) cells. In contrast, MCF-7/GSK-3β(KD) cells displayed an elevated sensitivity to the mTORC1 blocker rapamycin compared with MCF-7/GSK-3β(WT) or MCF-7/GSK-3β(A9) cells, while no differences between the 3 cell types were observed upon treatment with a MEK inhibitor by itself. However, resistance to doxorubicin and tamoxifen were alleviated in MCF-7/GSK-3β(KD) cells upon co-treatment with an MEK inhibitor, indicating regulation of this resistance by the Raf/MEK/ERK pathway. Treatment of MCF-7 and MCF-7/GSK-3β(WT) cells with doxorubicin eliminated the detection of S9-phosphorylated GSK-3β, while total GSK-3β was still detected. In contrast, S9-phosphorylated GSK-3β was still detected in MCF-7/GSK-3β(KD) and MCF-7/GSK-3β(A9) cells, indicating that one of the effects of doxorubicin on MCF-7 cells was suppression of S9-phosphorylated GSK-3β, which could result in increased GSK-3β activity. Taken together, these results demonstrate that introduction of GSK-3β(KD) into MCF-7 breast cancer cells promotes resistance to doxorubicin and tamoxifen, but sensitizes the cells to mTORC1 blockade by rapamycin. Therefore GSK-3β is a key regulatory molecule in sensitivity of breast cancer cells to chemo-, hormonal, and targeted therapy.

Mammosphere formation in breast carcinoma cell lines depends upon expression of E-cadherin

Tumors are heterogeneous at the cellular level where the ability to maintain tumor growth resides in discrete cell populations. Floating sphere-forming assays are broadly used to test stem cell activity in tissues, tumors and cell lines. Spheroids are originated from a small population of cells with stem cell features able to grow in suspension culture and behaving as tumorigenic in mice. We tested the ability of eleven common breast cancer cell lines representing the major breast cancer subtypes to grow as mammospheres, measuring the ability to maintain cell viability upon serial non-adherent passage. Only MCF7, T47D, BT474, MDA-MB-436 and JIMT1 were successfully propagated as long-term mammosphere cultures, measured as the increase in the number of viable cells upon serial non-adherent passages. Other cell lines tested (SKBR3, MDA-MB-231, MDA-MB-468 and MDA-MB-435) formed cell clumps that can be disaggregated mechanically, but cell viability drops dramatically on their second passage. HCC1937 and HCC1569 cells formed typical mammospheres, although they could not be propagated as long-term mammosphere cultures. All the sphere forming lines but MDA-MB-436 express E-cadherin on their surface. Knock down of E-cadherin expression in MCF-7 cells abrogated its ability to grow as mammospheres, while re-expression of E-cadherin in SKBR3 cells allow them to form mammospheres. Therefore, the mammosphere assay is suitable to reveal stem like features in breast cancer cell lines that express E-cadherin.

A novel zebrafish xenotransplantation model for study of glioma stem cell invasion

Invasion and metastasis of solid tumors are the major causes of death in cancer patients. Cancer stem cells (CSCs) constitute a small fraction of tumor cell population, but play a critical role in tumor invasion and metastasis. The xenograft of tumor cells in immunodeficient mice is one of commonly used in vivo models to study the invasion and metastasis of cancer cells. However, this model is time-consuming and labor intensive. Zebrafish (Danio rerio) and their transparent embryos are emerging as a promising xenograft tumor model system for studies of tumor invasion. In this study, we established a tumor invasion model by using zebrafish embryo xenografted with human glioblastoma cell line U87 and its derived cancer stem cells (CSCs). We found that CSCs-enriched from U87 cells spreaded via the vessels within zebrafish embryos and such cells displayed an extremely high level of invasiveness which was associated with the up-regulated MMP-9 by CSCs. The invasion of glioma CSCs (GSCs) in zebrafish embryos was markedly inhibited by an MMP-9 inhibitor. Thus, our zebrafish embryo model is considered a cost-effective approach tostudies of the mechanisms underlying the invasion of CSCs and suitable for high-throughput screening of novel anti-tumor invasion/metastasis agents.