Characterization of epithelial phenotypes in mortal and immortal human breast cells

An Increase in HSF1 Expression Directs Human Mammary Epithelial Cells toward a Mesenchymal Phenotype

HSF1 is a well-known heat shock protein expression regulator in response to stress. It also regulates processes important for growth, development or tumorigenesis. We studied the HSF1 influence on the phenotype of non-tumorigenic human mammary epithelial (MCF10A and MCF12A) and several triple-negative breast cancer cell lines. MCF10A and MCF12A differ in terms of HSF1 levels, morphology, growth in Matrigel, expression of epithelial (CDH1) and mesenchymal (VIM) markers (MCF10A are epithelial cells; MCF12A resemble mesenchymal cells). HSF1 down-regulation led to a reduced proliferation rate and spheroid formation in Matrigel by MCF10A cells. However, it did not affect MCF12A proliferation but led to CDH1 up-regulation and the formation of better organized spheroids. HSF1 overexpression in MCF10A resulted in reduced CDH1 and increased VIM expression and the acquisition of elongated fibroblast-like morphology. The above-mentioned results suggest that elevated levels of HSF1 may direct mammary epithelial cells toward a mesenchymal phenotype, while a lowering of HSF1 could reverse the mesenchymal phenotype to an epithelial one. Therefore, HSF1 may be involved in the remodeling of mammary gland architecture over the female lifetime. Moreover, HSF1 levels positively correlated with the invasive phenotype of triple-negative breast cancer cells, and their growth was inhibited by the HSF1 inhibitor DTHIB.

The Tumor Suppressor DAB2IP Is Regulated by Cell Contact and Contributes to YAP/TAZ Inhibition in Confluent Cells

External and internal mechanical forces modulate cell morphology, movement, proliferation and metabolism, and represent crucial inputs for tissue homeostasis. The transcriptional regulators YAP and TAZ are important effectors of mechanical signaling and are frequently activated in solid tumors, correlating with metastasis, chemoresistance, and shorter patient survival. YAP/TAZ activity is controlled by various pathways that sense cell shape, polarity, contacts, and mechanical tension. In tumors, aberrant YAP/TAZ activation may result from cancer-related alterations of such regulatory networks. The tumor suppressor DAB2IP is a Ras-GAP and scaffold protein that negatively modulates multiple oncogenic pathways and is frequently downregulated or inactivated in solid tumors. Here, we provide evidence that DAB2IP expression is sustained by cell confluency. We also find that DAB2IP depletion in confluent cells alters their morphology, reducing cell packing while increasing cell stiffness. Finally, we find that DAB2IP depletion in confluent cells favors YAP/TAZ nuclear localization and transcriptional activity, while its ectopic expression in subconfluent cells increases YAP/TAZ retention in the cytoplasm. Together, these data suggest that DAB2IP may function as a sensor of cell interactions, contributing to dampening cellular responses to oncogenic inputs in confluent cells and that DAB2IP loss-of-function would facilitate YAP/TAZ activation in intact epithelia, accelerating oncogenic transformation.

Normal breast epithelial MCF-10A cells to evaluate the safety of carbon dots

The human normal breast cell line MCF-10A is being widely used as a model in toxicity studies due to its structural similarity to the normal human mammary epithelium. Over the years, application of carbon dots (C-dots) in biomedicine has been increasing due to their photoluminescence properties, biocompatibility, biosafety and possible applications in bioimaging and as drug carriers. In this work we prepared three different C-dots from the same set of carbon and nitrogen precursors (citric acid and urea, respectively) via three distinct bottom-up synthetic routes and their safety was tested against the normal breast cell line MCF-10A. The characterization results demonstrated a similar size range and composition for all the C-dots. The MCF-10A cells were treated with different concentrations of C-dots for 24, 48 and 72 h to evaluate the cell viability over time. For the 24 h incubation, there were no significant decreases in the viability of the MCF-10A cells. For the 48 h treatment, there was a significant decrease in the viability of the cells treated with calcination-based C-dots, but without significant cellular viability changes for microwave and hydrothermal-based C-dots. For 72 h, cells treated with hydrothermal-based C-dots have the most promising viability profile. Also, compared with paclitaxel, these C-dots have a safety profile very close to that of an antineoplastic in non-tumor cells. Our results suggest that these new C-dots have potential as imaging candidates or biosensing tools as well as drug carriers, and further investigation in animal models is needed for future application in medicine.

miRNA551b-3p Activates an Oncostatin Signaling Module for the Progression of Triple-Negative Breast Cancer

Genomic amplification of 3q26.2 locus leads to the increased expression of microRNA 551b-3p (miR551b-3p) in triple-negative breast cancer (TNBC). Our results demonstrate that miR551b-3p translocates to the nucleus with the aid of importin-8 (IPO8) and activates STAT3 transcription. As a consequence, miR551b upregulates the expression of oncostatin M receptor (OSMR) and interleukin-31 receptor-α (IL-31RA) as well as their ligands OSM and IL-31 through STAT3 transcription. We defined this set of genes induced by miR551b-3p as the "oncostatin signaling module," which provides oncogenic addictions in cancer cells. Notably, OSM is highly expressed in TNBC, and the elevated expression of OSM associates with poor outcome in estrogen-receptor-negative breast cancer patients. Conversely, targeting miR551b with anti-miR551b-3p reduced the expression of the OSM signaling module and reduced tumor growth, as well as migration and invasion of breast cancer cells.

Chronic circadian disruption modulates breast cancer stemness and immune microenvironment to drive metastasis in mice

Breast cancer is the most common type of cancer worldwide and one of the major causes of cancer death in women. Epidemiological studies have established a link between night-shift work and increased cancer risk, suggesting that circadian disruption may play a role in carcinogenesis. Here, we aim to shed light on the effect of chronic jetlag (JL) on mammary tumour development. To do this, we use a mouse model of spontaneous mammary tumourigenesis and subject it to chronic circadian disruption. We observe that circadian disruption significantly increases cancer-cell dissemination and lung metastasis. It also enhances the stemness and tumour-initiating potential of tumour cells and creates an immunosuppressive shift in the tumour microenvironment. Finally, our results suggest that the use of a CXCR2 inhibitor could correct the effect of JL on cancer-cell dissemination and metastasis. Altogether, our data provide a conceptual framework to better understand and manage the effects of chronic circadian disruption on breast cancer progression.

Circadian disruption is implicated in the development of different human cancers. Here the authors show that chronic circadian disruption, through continuous jet lag, only moderately affects primary tumour growth but promotes cancer-cell dissemination and metastasis in a mouse model of spontaneous mammary tumorigenesis.

Identification of valid reference genes for circadian gene-expression studies in human mammary epithelial cells

The circadian clock controls most of the physiological processes in the body throughout days and nights' alternation. Its dysregulation has a negative impact on many aspects of human health, such as obesity, lipid disorders, diabetes, skin regeneration, hematopoiesis and cancer. To date, poor is known on the molecular mechanisms that links mammary gland homeostasis to the circadian clock but recent reports highlight the importance of loss of circadian genes for mammary gland development and during tumour progression in breast cancer. Gene expression studies are then required to clarify how the circadian clock can modulates the human mammary gland development during ontology and its behaviour in physiological and oncogenic context. For this, in addition to genome-wide studies, real-time quantitative RT-PCR (qPCR) is a powerful and pertinent technique to quantify the expression of a reduced set of genes of interest in many different samples. Relative quantification of qPCR data requires the use of reference genes for normalisation. For circadian studies, reference genes expression must not oscillate in mirror of the circadian clock and must not be affected by the synchronisation protocols required in vitro to reset the circadian clock. Inappropriate selection of reference genes can consequently affect the amplitude of gene expression oscillation and bias data interpretation. Currently, no standard reference genes have been validated regarding these criteria for human mammary epithelial cells and the purpose of this study was to fill this gap. For this, we used the RefFinder tool, which combines four different algorithms, on 9 candidate reference genes. We compared reference genes stability using three different synchronisation protocols applied on four different mammary epithelial cell lines. This allowed us to define a set of reference genes in human mammary epithelial cells whose expression remains stable despite synchronisation protocols. We observed that the synchronisation of cells by serum shock was the most suitable procedure for maintaining the amplitude of oscillation of clock genes over time and we identified RPL4, RPLP0, HSPCB and TBP as an optimal combination of reference genes for the normalisation of the oscillatory expression of clock genes in human mammary epithelial cells.

Promyelocytic leukemia zinc finger triggers ATP-binding cassette subfamily E member 1-mediated growth inhibition in breast cancer cells

The promyelocytic leukemia zinc finger (PLZF) protein is a transcription factor that is involved in a number of biological processes, including those regulating cellular growth; however, little is known regarding how it achieves its inhibitory effect in different cell and tissue types. It has previously been demonstrated that PLZF expression levels become diminished during the oncogenic transformation of certain tissue types and thus, may serve as a hallmark for tumor aggressiveness. To examine this in breast cancer, survival curves from available oncology databases were analyzed and demonstrated that PLZF expression was positively associated with increased survival in patients with breast cancer. The mRNA and protein levels of PLZF were also revealed to be associated with the tumorigenicity of four breast cancer cell lines. Since ATP-binding cassette subfamily E member 1 (ABCE1), also known as RNase L inhibitor, has been determined to be a target gene of PLZF, the present study also investigated whether the tumor suppressive effect of PLZF was associated with ABCE1 expression. PLZF was revealed to downregulate the expression of ABCE1 in vitro, which relieved the inhibitory effect of ABCE1 on the ribonuclease L enzyme. Finally, it was concluded that PLZF expression caused an ABCE1-mediated increase in cellular cytotoxicity, as demonstrated by a reduction in the proliferation rate of breast cancer cell lines. The results of the present study are important for understanding how PLZF exerts its final inhibitory actions in breast cancer cells, and potentially in other solid tumors, through the modulation of immunological pathways.

Characterization of MCF-12A cell phenotype, response to estrogens, and growth in 3D

Background

Three-dimensional cultures of mammary epithelial cells allow for biologically-relevant studies of the development of the mammary gland in rodents and humans under normal and pathological conditions, like carcinogenesis. Under these conditions, mammotropic hormones play significant roles in tissue morphogenesis. Therefore, a system that recreates the normal, hormonally responsive epithelium would be a valuable tool to study the normal state and its transition to carcinogenesis. MCF-12A cells have been claimed to be non-tumorigenic mammary epithelial cells with reported sensitivity to estrogens. In this study, we aimed at characterizing MCF-12A cells for use in a hormone-responsive 3D culture system to determine their usefulness as a tool to identify normal and abnormal microenvironmental cues.

Methods

MCF-12A cells were single-cell cloned in order to investigate their heterogeneous makeup. The parental cells were then treated with estradiol to investigate proliferative and transcriptional responses through the estrogen receptor alpha. Finally, parental cells and epithelial-like cell-derived clones were seeded in rat-tail collagen I to profile the morphogenesis of multicellular 3D structures. The resultant structures were then analyzed using unsupervised morphometric analysis.

Results

MCF-12A cells consist of epithelial-like colonies which shed elongated, freely growing cells on the colony's edges. The cells express E-cadherin as well as mesenchymal vimentin but do not express markers associated with myoepithelial cells or fibroblasts. Treatment with estradiol does not affect either the proliferation rate or the induction of gene expression in MCF-12A cells. Parental MCF-12A cells form acini, solid spheres and elongated branching ducts when grown in rat-tail collagen type I matrix, the geometries and distribution of which are altered following the removal of fibroblast-like cells.

Conclusions

MCF-12A cells are a heterogeneous pseudo-epithelial cell line capable of forming a variety of multicellular structures in 3D culture. We found no indication that the cells display estrogen-responsive characteristics, thus refuting previous studies which reported estrogen responsiveness. We report that MCF-12A cells are not suited for use in studies in which differential behaviors of "normal" and "cancerous" estrogen-responsive cells are to be compared.

Llgl1 prevents metaplastic survival driven by epidermal growth factor dependent migration

We have previously demonstrated that Llgl1 loss results in a gain of mesenchymal phenotypes and a loss of apicobasal and planar polarity. We now demonstrate that these changes represent a fundamental shift in cellular phenotype. Llgl1 regulates the expression of multiple cell identity markers, including CD44, CD49f, and CD24, and the nuclear translocation of TAZ and Slug. Cells lacking Llgl1 form mammospheres, where survival and transplantability is dependent upon the Epidermal Growth Factor Receptor (EGFR). Additionally, Llgl1 loss allows cells to grow in soft-agar and maintain prolonged survival as orthotopic transplants in NOD-SCIDmice. Lineage tracing and wound healing experiments demonstrate that mammosphere survival is due to enhanced EGF-dependent migration. The loss of Llgl1 drives EGFR mislocalization and an EGFR mislocalization point mutation (P667A) drives these same phenotypes, including activation of AKT and TAZ nuclear translocation. Together, these data indicate that the loss of Llgl1 results in EGFR mislocalization, promoting pre-neoplastic changes.

A bis-sulphamoylated estradiol derivative induces ROS-dependent cell cycle abnormalities and subsequent apoptosis

Clinical trials have revealed that the potential anticancer agent, 2-methoxyestradiol (2ME2) has limitations due to its low bioavailability. Subsequently, 2ME2 derivatives including (8R,13S,14S,17S)-2-ethyl-13-methyl-7,8,9,11,12,13,14,15,16,17-decahydro-6H-cyclopenta[a]phenanthrane-3,17-diyl bis(sulphamate) (EMBS) have shown improved efficacies in inducing apoptosis. However, no conclusive data exist to explain the mode of action exerted by these drugs. This study investigated the mode of action used by EMBS as a representative of the sulphamoylated 2ME2 derivatives. Hydrogen peroxide and superoxide production was quantified using dichlorofluorescein diacetate and hydroethidine. Cell proliferation and mitochondrial metabolism were investigated using crystal violet and Alamar Blue. Apoptosis was assessed using Annexin V-FITC while mitochondrial integrity was assessed using Mitocapture. Autophagy was visualised using LC3B II antibodies. The effects of EMBS on H2A phosphorylation and nuclei were visualised using phospho H2A antibody and 4',6-diamidino-2-phenylindole, dihydrochloride. Data showed that EMBS exposure leads to increased reactive oxygen species (ROS) production which is correlated with loss of cell proliferation, mitochondrial membrane damage, decreased metabolic activity, G2/M arrest, endoreduplication, DNA double stranded breaks, micronuclei and apoptosis induction. Treatment of EMBS-exposed cells with the ROS scavenger, N-acetyl cysteine, abrogated ROS production, cell cycle arrest and apoptosis implying an essential role for ROS production in EMBS signaling. The inhibition of c-Jun N-terminal kinase (JNK) activity also inhibited EMBS-induced apoptosis suggesting that EMBS triggers apoptosis via the JNK pathway. Lastly, evaluation of LC3IIB protein levels indicated that autophagy is not activated in EMBS-exposed cells. Our data shows that EMBS targets a pathway that leads to increased ROS production as an early event that culminates in G2/M arrest and apoptosis by means of JNK-signaling in cancer cells. This study suggests a novel oxidative stress-dependent mode of action for sulphamoylated derivatives.

The effects of CEP-37440, an inhibitor of focal adhesion kinase, in vitro and in vivo on inflammatory breast cancer cells

BACKGROUND

Inflammatory breast cancer (IBC) is an aggressive type of advanced breast cancer with a poor prognosis. We recently found that focal adhesion kinase 1 (FAK1) is upregulated and phosphorylated (active) in IBC. In this study, we investigated the effect of CEP-37440, a dual inhibitor of FAK1 and anaplastic lymphoma kinase (ALK), using human IBC cell lines and preclinical models of IBC.

METHODS

Cell proliferation assays were performed in the presence of several concentrations of CEP-37440 using IBC and triple-negative breast cancer non-IBC cell lines. In vitro, we studied the expression of total FAK1, phospho-FAK1 (Tyr 397), total ALK and phospho-ALK (Tyr 1604). In vivo, we tested CEP-37440 using FC-IBC02, SUM149, and SUM190 IBC xenograft mouse models.

RESULTS

CEP-37440 at low concentration decreased the proliferation of the IBC cell lines FC-IBC02, SUM190, and KPL4, while not affecting the proliferation of normal breast epithelial cells. At higher concentration, CEP-37440 was also able to inhibit the proliferation of the IBC cell line MDA-IBC03 and the triple-negative non-IBC cell lines MDA-MB-231 and MDA-MB-468; the IBC cell line SUM149 showed a slight response to the drug. CEP-37440 decreased the cell proliferation of FC-IBC02, SUM190, and KPL4 by blocking the autophosphorylation kinase activity of FAK1 (Tyr 397). None of the cells evaluated expressed ALK. In vivo, after 7 weeks of CEP-37440 treatment, the SUM190, FC-IBC02, and SUM149 breast tumor xenografts were smaller in mice treated with 55 mg/kg bid CEP-37440 compared to the controls; the tumor growth inhibition (TGI) was 79.7 %, 33 %, and 23 %, respectively. None of the FC-IBC02 breast xenografts mice treated with CEP-37440 developed brain metastasis while 20 % of the mice in the control group developed brain metastasis. Expression array analyses in FC-IBC02 cells showed that CEP-37440 affects the expression of genes related to apoptosis, interferon signaling, and cytokines.

CONCLUSIONS

CEP-37440 is effective against some IBC cells that express phospho-FAK1 (Tyr 397), and its antiproliferative activity is related to its ability to decrease phospho-FAK1. Our results suggest that combinational therapies could be more effective than using CEP-37440 as a single agent.

Slug contributes to cancer progression by direct regulation of ERα signaling pathway

Hormone therapy targeting estrogen receptor α (ERα) is the most effective treatment for breast cancer. However, this treatment eventually fails as the tumor develops resistance. Although reduced expression of ER-α is a known contributing factor to endocrine resistance, the mechanism of ER-α downregulation in endocrine resistance is still not fully understood. The present study shows that Slug has an inverse relationship with ERα in breast and prostate cancer patient samples. Also the inhibition of Slug blocks mammary stem cell activity in primary mammary epithelial cells. We hypothesize that Slug may be a key transcription factor in the regulation of ERα expression. To understand the Slug-ERα signaling pathway, we employed resistant cell line MCF-TAMR (ERα relatively negative) derived from its parental MCF-7 (ERα positive) cell line and assessed changes in cell phenotype, activity and response to therapy. Conversely, we performed knockdown of Slug in the high-Slug expressing cell line MDA-MB-231 and assessed reversal of the mesenchymal phenotype. Microarray analysis showed that Slug is overexpressed in high grade breast and prostate cancer tissues. Additionally, Slug overexpression leads to drug resistance. Furthermore, we demonstrated that Slug binds directly to ERα promoter E-boxes and represses ERα expression. This resulted in decrease in epithelial-to-mesenchymal transition in cancer cells. These findings demonstrate that Slug, by regulation of ERα expression, contributes to tumor progression and could serve as an important target for cancer therapy.

Building risk-on-a-chip models to improve breast cancer risk assessment and prevention

Preventive actions for chronic diseases hold the promise of improving lives and reducing healthcare costs. For several diseases, including breast cancer, multiple risk and protective factors have been identified by epidemiologists. The impact of most of these factors has yet to be fully understood at the organism, tissue, cellular and molecular levels. Importantly, combinations of external and internal risk and protective factors involve cooperativity thus, synergizing or antagonizing disease onset. Models are needed to mechanistically decipher cancer risks under defined cellular and microenvironmental conditions. Here, we briefly review breast cancer risk models based on 3D cell culture and propose to improve risk modeling with lab-on-a-chip approaches. We suggest epithelial tissue polarity, DNA repair and epigenetic profiles as endpoints in risk assessment models and discuss the development of 'risks-on-chips' integrating biosensors of these endpoints and of general tissue homeostasis. Risks-on-chips will help identify biomarkers of risk, serve as screening platforms for cancer preventive agents, and provide a better understanding of risk mechanisms, hence resulting in novel developments in disease prevention.

Phospholipase D1 and choline kinase-α are interactive targets in breast cancer

A consistent metabolic hallmark observed in multiple cancers is the increase of cellular phosphocholine (PC) and total choline-containing compounds (tCho), which is closely related to malignant transformation, invasion, and metastasis. Enzymes in choline phospholipid metabolism present attractive targets to exploit for treatment, but require a clear understanding of the mechanisms underlying the altered choline phospholipid metabolism observed in cancer. Choline kinase-α (Chk-α) is an enzyme in the Kennedy pathway that phosphorylates free choline (Cho) to PC, and its upregulation in several cancers is a major contributor to increased PC levels. Similarly, increased expression and activity of phospholipase D1 (PLD1), which converts phosphatidylcholine (PtdCho) to phosphatidic acid (PA) and Cho, has been well documented in gastric, ovarian and breast cancer. Here we report a strong correlation between expression of Chk-α and PLD1 with breast cancer malignancy. Data from patient samples established an association between estrogen receptor (ER) status and Chk-α and PLD1 expression. In addition, these two enzymes were found to be interactive. Downregulation of Chk-α with siRNA increased PLD1 expression, and downregulation of PLD1 increased Chk-α expression. Simultaneous silencing of PLD1 and Chk-α in MDA-MB-231 cells increased apoptosis as detected by the TUNEL assay. These data provide new insights into choline phospholipid metabolism of breast cancer, and support multiple targeting of enzymes in choline phospholipid metabolism as a strategy for treatment.

ATM suppresses SATB1-induced malignant progression in breast epithelial cells

SATB1 drives metastasis when expressed in breast tumor cells by radically reprogramming gene expression. Here, we show that SATB1 also has an oncogenic activity to transform certain non-malignant breast epithelial cell lines. We studied the non-malignant MCF10A cell line, which is used widely in the literature. We obtained aliquots from two different sources (here we refer to them as MCF10A-1 and MCF10A-2), but found them to be surprisingly dissimilar in their responses to oncogenic activity of SATB1. Ectopic expression of SATB1 in MCF10A-1 induced tumor-like morphology in three-dimensional cultures, led to tumor formation in immunocompromised mice, and when injected into tail veins, led to lung metastasis. The number of metastases correlated positively with the level of SATB1 expression. In contrast, SATB1 expression in MCF10A-2 did not lead to any of these outcomes. Yet DNA copy-number analysis revealed that MCF10A-1 is indistinguishable genetically from MCF10A-2. However, gene expression profiling analysis revealed that these cell lines have significantly divergent signatures for the expression of genes involved in oncogenesis, including cell cycle regulation and signal transduction. Above all, the early DNA damage-response kinase, ATM, was greatly reduced in MCF10A-1 cells compared to MCF10A-2 cells. We found the reason for reduction to be phenotypic drift due to long-term cultivation of MCF10A. ATM knockdown in MCF10A-2 and two other non-malignant breast epithelial cell lines, 184A1 and 184B4, enabled SATB1 to induce malignant phenotypes similar to that observed for MCF10A-1. These data indicate a novel role for ATM as a suppressor of SATB1-induced malignancy in breast epithelial cells, but also raise a cautionary note that phenotypic drift could lead to dramatically different functional outcomes.

Disruption of 3D MCF-12A breast cell cultures by estrogens--an in vitro model for ER-mediated changes indicative of hormonal carcinogenesis

Introduction

Estrogens regulate the proliferation of normal and neoplastic breast epithelium. Although the intracellular mechanisms of estrogens in the breast are largely understood, little is known about how they induce changes in the structure of the mammary epithelium, which are characteristic of breast cancer. In vitro three dimensional (3D) cultures of immortalised breast epithelial cells recapitulate features of the breast epithelium in vivo, including formation of growth arrested acini with hollow lumen and basement membrane. This model can also reproduce features of malignant transformation and breast cancer, such as increased cellular proliferation and filling of the lumen. However, a system where a connection between estrogen receptor (ER) activation and disruption of acini formation can be studied to elucidate the role of estrogens is still missing.

Methods/Principal Findings

We describe an in vitro 3D model for breast glandular structure development, using breast epithelial MCF-12A cells cultured in a reconstituted basement membrane matrix. These cells are estrogen receptor (ER)α, ERβ and G-protein coupled estrogen receptor 1 (GPER) competent, allowing the investigation of the effects of estrogens on mammary gland formation and disruption. Under normal conditions, MCF-12A cells formed organised acini, with deposition of basement membrane and hollow lumen. However, treatment with 17β-estradiol, and the exogenous estrogens bisphenol A and propylparaben resulted in deformed acini and filling of the acinar lumen. When these chemicals were combined with ER and GPER inhibitors (ICI 182,780 and G-15, respectively), the deformed acini recovered normal features, such as a spheroid shape, proliferative arrest and luminal clearing, suggesting a role for the ER and GPER in the estrogenic disruption of acinar formation.

Conclusion

This new model offers the opportunity to better understand the role of the ER and GPER in the morphogenesis of breast glandular structure as well as the events implicated in breast cancer initiation and progression.

Decreased eIF3e/Int6 expression causes epithelial-to-mesenchymal transition in breast epithelial cells

eIF3e/Int6 is a component of the multi-subunit eIF3 complex, which binds directly to the 40S ribosome to facilitate ribosome recruitment to mRNA and hence protein synthesis. Reduced expression of eIF3e/Int6 has been found in up to 37% of human breast cancers, and expression of a truncated mutant version of the mouse eIF3e/Int6 protein leads to malignant transformation of normal mammary cells. These findings suggest that eIF3e/Int6 is a tumor suppressor; however, a recent study has reported that a reduction of eIF3e/Int6 expression in breast cancer cells leads to reduced translation of oncogenes, suggesting that eIF3e/Int6 may in fact have an oncogenic role in breast cancer. To gain a better understanding of the role of eIF3e/Int6 in breast cancer, we have examined the effects of decreased eIF3e/Int6 expression in an immortalized breast epithelial cell line, MCF-10A. Surprisingly, we find that decreased expression of eIF3e/Int6 causes breast epithelial cells to undergo epithelial-to-mesenchymal transition (EMT). We show that EMT induced by a decrease in eIF3e/Int6 expression imparts invasive and migratory properties to breast epithelial cells, suggesting that regulation of EMT by eIF3e/Int6 may have an important role in breast cancer metastasis. Furthermore, we show that reduced eIF3e/Int6 expression in breast epithelial cells causes a specific increase in the expression of the key EMT regulators Snail1 and Zeb2, which occurs at both the transcriptional and post-transcriptional levels. Together, our data indicate a novel role of eIF3e/Int6 in the regulation of EMT in breast epithelial cells and support a tumor suppressor role of eIF3e/Int6.

Issues to be considered when studying cancer in vitro

Various cancer treatment approaches have shown promising results when tested preclinically. The results of clinical trials, however, are often disappointing. While searching for the reasons responsible for their failures, the relevance of experimental and preclinical models has to be taken into account. Possible factors that should be considered, including cell modifications during in vitro cultivation, lack of both the relevant interactions and the structural context in vitro have been summarized in the present review.

Transcriptomic and proteomic profiling of KEAP1 disrupted and sulforaphane-treated human breast epithelial cells reveals common expression profiles

Sulforaphane (SFN), an isothiocyanate found in cruciferous vegetables, is a potent inhibitor of experimental mammary carcinogenesis and may be an effective, safe chemopreventive agent for use in humans. SFN acts in part on the Keap1/Nrf2 pathway to regulate a battery of cytoprotective genes. In this study, transcriptomic and proteomic changes in the estrogen receptor negative, non-tumorigenic human breast epithelial MCF10A cell line were analyzed following SFN treatment or KEAP1 knockdown with siRNA using microarray and stable isotopic labeling with amino acids in culture (SILAC), respectively. Changes in selected transcripts and proteins were confirmed by PCR and Western blot in MCF10A and MCF12A cells. There was strong correlation between the transcriptomic and proteomic responses in both the SFN treatment (R = 0.679, P < 0.05) and KEAP1 knockdown (R = 0.853, P < 0.05) experiments. Common pathways for SFN treatment and KEAP1 knockdown were xenobiotic metabolism and antioxidants, glutathione metabolism, carbohydrate metabolism, and NADH/NADPH regeneration. Moreover, these pathways were most prominent in both the transcriptomic and the proteomic analyses. The aldo-keto reductase family members, AKR1B10, AKR1C1, AKR1C2 and AKR1C3, as well as NQO1 and ALDH3A1, were highly upregulated at both the transcriptomic and the proteomic levels. Collectively, these studies served to identify potential biomarkers that can be used in clinical trials to investigate the initial pharmacodynamic action of SFN in the breast.

Role of DNA methylation in miR-200c/141 cluster silencing in invasive breast cancer cells

BACKGROUND

The miR-200c/141 cluster has recently been implicated in the epithelial to mesenchymal transition (EMT) process. The expression of these two miRNAs is inversely correlated with tumorigenicity and invasiveness in several human cancers. The role of these miRNAs in cancer progression is based in part on their capacity to target the EMT activators ZEB1 and ZEB2, two transcription factors, which in turn repress expression of E-cadherin. Little is known about the regulation of the mir200c/141 cluster, whose targeting has been proposed as a promising new therapy for the most aggressive tumors.

FINDINGS

We show that the miR-200c/141 cluster is repressed by DNA methylation of a CpG island located in the promoter region of these miRNAs. Whereas in vitro methylation of the miR-200c/141 promoter led to shutdown of promoter activity, treatment with a demethylating agent caused transcriptional reactivation in breast cancer cells formerly lacking expression of miR-200c and miR-141. More importantly, we observed that DNA methylation of the identified miR-200c/141 promoter was tightly correlated with phenotype and the invasive capacity in a panel of 8 human breast cancer cell lines. In line with this, in vitro induction of EMT by ectopic expression of the EMT transcription factor Twist in human immortalized mammary epithelial cells (HMLE) was accompanied by increased DNA methylation and concomitant repression of the miR-200c/141 locus.

CONCLUSIONS

The present study demonstrates that expression of the miR-200c/141 cluster is regulated by DNA methylation, suggesting epigenetic regulation of this miRNA locus in aggressive breast cancer cell lines as well as untransformed mammary epithelial cells. This epigenetic silencing mechanism might represent a novel component of the regulatory circuit for the maintenance of EMT programs in cancer and normal cells.

Ataxia telangiectasia mutated (ATM) inhibition transforms human mammary gland epithelial cells

Carriers of mutations in the cell cycle checkpoint protein kinase ataxia telangiectasia mutated (ATM), which represent 1-2% of the general population, have an increased risk of breast cancer. However, experimental evidence that ATM deficiency contributes to human breast carcinogenesis is lacking. We report here that in MCF-10A and MCF-12A cells, which are well established normal human mammary gland epithelial cell models, partial or almost complete stable ATM silencing or pharmacological inhibition resulted in cellular transformation, genomic instability, and formation of dysplastic lesions in NOD/SCID mice. These effects did not require the activity of exogenous DNA-damaging agents and were preceded by an unsuspected and striking increase in cell proliferation also observed in primary human mammary gland epithelial cells. Increased proliferation correlated with a dramatic, transient, and proteasome-dependent reduction of p21(WAF1/CIP1) and p27(KIP1) protein levels, whereas little or no effect was observed on p21(WAF1/CIP1) or p27(KIP1) mRNAs. p21(WAF1/CIP1) silencing also increased MCF-10A cell proliferation, thus identifying p21(WAF1/CIP1) down-regulation as a mediator of the proliferative effect of ATM inhibition. Our findings provide the first experimental evidence that ATM is a human breast tumor suppressor. In addition, they mirror the sensitivity of ATM tumor suppressor function and unveil a new mechanism by which ATM might prevent human breast tumorigenesis, namely a direct inhibitory effect on the basal proliferation of normal mammary epithelial cells.

Tamoxifen induces pleiotrophic changes in mammary stroma resulting in extracellular matrix that suppresses transformed phenotypes

INTRODUCTION

The functional unit of the mammary gland has been defined as the epithelial cell plus its microenvironment, a hypothesis that predicts changes in epithelial cell function will be accompanied by concurrent changes in mammary stroma. To test this hypothesis, the question was addressed of whether mammary stroma is functionally altered by the anti-oestrogen drug tamoxifen.

METHODS

Forty female rats at 70 days of age were randomised to two groups of 20 and treated with 1.0 mg/kg tamoxifen or vehicle subcutaneously daily for 30 days, followed by a three-day wash out period. Mammary tissue was harvested and effects of tamoxifen on mammary epithelium and stroma determined.

RESULTS

As expected, tamoxifen suppressed mammary alveolar development and mammary epithelial cell proliferation. Primary mammary fibroblasts isolated from tamoxifen-treated rats displayed a three-fold decrease in motility and incorporated less fibronectin in their substratum in comparison to control fibroblasts; attributes indicative of fibroblast quiescence. Immunohistochemistry analysis of CD68, a macrophage lysosomal marker, demonstrated a reduction in macrophage infiltration in mammary glands of tamoxifen-treated rats. Proteomic analyses by mass spectrometry identified several extracellular matrix (ECM) proteins with expression levels with tamoxifen treatment that were validated by Western blot. Mammary tissue from tamoxifen-treated rats had decreased fibronectin and increased collagen 1 levels. Further, ECM proteolysis was reduced in tamoxifen-treated rats as detected by reductions in fibronectin, laminin 1, laminin 5 and collagen 1 cleavage fragments. Consistent with suppression in ECM proteolysis with tamoxifen treatment, matrix metalloproteinase-2 levels and activity were decreased. Biochemically extracted mammary ECM from tamoxifen-treated rats suppressed in vitro macrophage motility, which was rescued by the addition of proteolysed collagen or fibronectin. Mammary ECM from tamoxifen-treated rats also suppressed breast tumour cell motility, invasion and haptotaxis, reduced organoid size in 3-dimensional culture and blocked tumour promotion in an orthotopic xenograft model; effects which could be partially reversed by the addition of exogenous fibronectin.

CONCLUSIONS

These data support the hypothesis that mammary stroma responds to tamoxifen treatment in concert with the epithelium and remodels to a microenvironment inhibitory to tumour cell progression. Reduced fibronectin levels and reduced ECM turnover appear to be hallmarks of the quiescent mammary microenvironment. These data may provide insight into attributes of a mammary microenvironment that facilitate tumour dormancy.

BCAR3 regulates EGF-induced DNA synthesis in normal human breast MCF-12A cells

BCAR3 (breast cancer anti-estrogen resistance 3) is a signal transducer containing an SH2 domain, a proline/serine-rich domain and a GDP-exchange factor homologous domain, whose role in signaling pathways is currently unclear. Furthermore, BCAR3 is implicated in anti-estrogen resistance of breast cancer cells. In the present study, we investigated the functional role of BCAR3 in a mitogenic signaling pathway of EGF in non-tumorigenic human breast epithelial MCF-12A cells. Microinjection of an anti-BCAR3 antibody, siRNAs targeting BCAR3 and an SH2 domain of BCAR3 inhibited EGF-induced DNA synthesis. Direct association of BCAR3 with activated EGF receptor and Cas was observed. Lastly, microinjection of a BCAR3 expression plasmid induced DNA synthesis. These findings suggest that the BCAR3 protein, through its SH2 domain, is involved in the signaling pathways of EGF leading to cell cycle progression, and that BCAR3 itself is part of a mitogenic signaling pathway.

Hypoxia increases breast cancer cell-induced lymphatic endothelial cell migration

Because tumors are characterized by hypoxic environments, we used a novel in vitro noninvasive magnetic resonance imaging assay to examine the influence of invasive MDA-MB-231 breast cancer cells on the invasion and migration of human dermal lymphatic microvascular endothelial cells (HMVEC-dLy) under normoxic and hypoxic conditions. Nonmalignant immortalized MCF-12A human mammary epithelial cells instead of cancer cells or chambers with HMVEC-dLy alone were used as controls for comparison. HMVEC-dLy cells were labeled with a T(2) contrast agent (Feridex), and their invasion and migration through extracellular matrix under normoxic and hypoxic conditions were monitored using magnetic resonance imaging. A significant increase in the invasion and migration of HMVEC-dLy cells was detected in the presence of cancer cells, which further increased significantly under hypoxic conditions. HMVEC-dLy cells formed interconnecting strands extending toward the cancer cells under normoxic but not under hypoxic conditions. Following reoxygenation, these interconnecting strands, extending from HMVEC-dLy cells toward the cancer cells, were observed. These data demonstrate the importance of hypoxia in lymphatic endothelial cell invasion and migration through extracellular matrix in the presence of cancer cells.

DNMT3b overexpression contributes to a hypermethylator phenotype in human breast cancer cell lines

BACKGROUND

DNA hypermethylation events and other epimutations occur in many neoplasms, producing gene expression changes that contribute to neoplastic transformation, tumorigenesis, and tumor behavior. Some human cancers exhibit a hypermethylator phenotype, characterized by concurrent DNA methylation-dependent silencing of multiple genes. To determine if a hypermethylation defect occurs in breast cancer, the expression profile and promoter methylation status of methylation-sensitive genes were evaluated among breast cancer cell lines.

RESULTS

The relationship between gene expression (assessed by RT-PCR and quantitative real-time PCR), promoter methylation (assessed by methylation-specific PCR, bisulfite sequencing, and 5-aza-2'deoxycytidine treatment), and the DNA methyltransferase machinery (total DNMT activity and expression of DNMT1, DNMT3a, and DNMT3b proteins) were examined in 12 breast cancer cell lines. Unsupervised cluster analysis of the expression of 64 methylation-sensitive genes revealed two groups of cell lines that possess distinct methylation signatures: (i) hypermethylator cell lines, and (ii) low-frequency methylator cell lines. The hypermethylator cell lines are characterized by high rates of concurrent methylation of six genes (CDH1, CEACAM6, CST6, ESR1, LCN2, SCNN1A), whereas the low-frequency methylator cell lines do not methylate these genes. Hypermethylator cell lines coordinately overexpress total DNMT activity and DNMT3b protein levels compared to normal breast epithelial cells. In contrast, most low-frequency methylator cell lines possess DNMT activity and protein levels that are indistinguishable from normal. Microarray data mining identified a strong cluster of primary breast tumors that express the hypermethylation signature defined by CDH1, CEACAM6, CST6, ESR1, LCN2, and SCNN1A. This subset of breast cancers represents 18/88 (20%) tumors in the dataset analyzed, and 100% of these tumors were classified as basal-like, suggesting that the hypermethylator defect cosegregates with poor prognosis breast cancers.

CONCLUSION

These observations combine to strongly suggest that: (a) a subset of breast cancer cell lines express a hypermethylator phenotype, (b) the hypermethylation defect in these breast cancer cell lines is related to aberrant overexpression of DNMT activity, (c) overexpression of DNMT3b protein significantly contributes to the elevated DNMT activity observed in tumor cells expressing this phenotype, and (d) the six-gene hypermethylator signature characterized in breast cancer cell lines defines a distinct cluster of primary basal-like breast cancers.

Cytotoxic effects of 2-arylbenzofuran phytoestrogens on human cancer cells: modulation by adrenal and gonadal steroids

Although 2-arylbenzofuran phytoalexins are known for decades, their anticancer activity has not been studied systematically. We have previously reported on the isolation and the estrogen receptor (ER) modulation properties of three new 2-arylbenzofurans from Onobrychis ebenoides, ebenfuran I [2-(2,4-dihydroxyphenyl)-5-hydroxy-6-methoxy-benzofuran], ebenfuran II [2-(2,4-dihydroxyphenyl)-3-formyl-4-hydroxy-6-methoxy-benzofuran] and ebenfuran III [2-(2,4-dihydroxyphenyl)-3-formyl-4-hydroxy-6-methoxy-5-(3-methyl-buten-2-yl)-benzofuran]. We now show that, while I and II could stimulate the proliferation of MCF-7 cells, III was inhibitory in a proliferation-dependent manner. III inhibited the growth of all human cancer cells examined, regardless of ER or multidrug resistance status. Estradiol rendered MCF-7 cells more sensitive to III, and this coincided with the ability of the hormone at concentrations > or = 0.1 nM to bind to the ER of the cells and stimulate their proliferation in the presence of III. Cell proliferation stimulating concentrations of I and II also enhanced the effect of III on MCF-7 cells. However, dehydroepiandrosterone and dihydrotestosterone were ineffective in this respect. III-treated MCF-7 cells exhibited G1 phase arrest followed by detachment-induced cell death and/or apoptosis in the adherent fraction, pronounced induction of Bax and suppression of estradiol induction of Bcl-2. Our data indicate that the largely unexplored pool of benzofuran phytoalexins includes entities potentially suitable for chemoprevention and treatment of human cancer.

Transcriptional changes associated with breast cancer occur as normal human mammary epithelial cells overcome senescence barriers and become immortalized

BACKGROUND

Human mammary epithelial cells (HMEC) overcome two well-characterized genetic and epigenetic barriers as they progress from primary cells to fully immortalized cell lines in vitro. Finite lifespan HMEC overcome an Rb-mediated stress-associated senescence barrier (stasis), and a stringent, telomere-length dependent, barrier (agonescence or crisis, depending on p53 status). HMEC that have overcome the second senescence barrier are immortalized.

METHODS

We have characterized pre-stasis, post-selection (post-stasis, with p16 silenced), and fully immortalized HMEC by transcription profiling and RT-PCR. Four pre-stasis and seven post-selection HMEC samples, along with 10 representatives of fully immortalized breast epithelial cell lines, were profiled using Affymetrix U133A/B chips and compared using both supervised and unsupervised clustering. Datasets were validated by RT-PCR for a select set of genes. Quantitative immunofluorescence was used to assess changes in transcriptional regulators associated with the gene expression changes.

RESULTS

The most dramatic and uniform changes we observed were in a set of about 30 genes that are characterized as a "cancer proliferation cluster," which includes genes expressed during mitosis (CDC2, CDC25, MCM2, PLK1) and following DNA damage. The increased expression of these genes was particularly concordant in the fully immortalized lines. Additional changes were observed in IFN-regulated genes in some post-selection and fully immortalized cultures. Nuclear localization was observed for several transcriptional regulators associated with expression of these genes in post-selection and immortalized HMEC, including Rb, Myc, BRCA1, HDAC3 and SP1.

CONCLUSION

Gene expression profiles and cytological changes in related transcriptional regulators indicate that immortalized HMEC resemble non-invasive breast cancers, such as ductal and lobular carcinomas in situ, and are strikingly distinct from finite-lifespan HMEC, particularly with regard to genes involved in proliferation, cell cycle regulation, chromosome structure and the DNA damage response. The comparison of HMEC profiles with lines harboring oncogenic changes (e.g. overexpression of Her-2neu, loss of p53 expression) identifies genes involved in tissue remodeling as well as proinflamatory cytokines and S100 proteins. Studies on carcinogenesis using immortalized cell lines as starting points or "normal" controls need to account for the significant pre-existing genetic and epigenetic changes inherent in such lines before results can be broadly interpreted.

Mechanisms of indomethacin-induced alterations in the choline phospholipid metabolism of breast cancer cells

Human mammary epithelial cells (HMECs) exhibit an increase in phosphocholine (PC) and total choline-containing compounds, as well as a switch from high glycerophosphocholine (GPC)/low PC to low GPC/high PC, with progression to malignant phenotype. The treatment of human breast cancer cells with a nonsteroidal anti-inflammatory agent, indomethacin, reverted the high PC/low GPC pattern to a low PC/high GPC pattern indicative of a less malignant phenotype, supported by decreased invasion. Here, we have characterized mechanisms underlying indomethacin-induced alterations in choline membrane metabolism in malignant breast cancer cells and nonmalignant HMECs labeled with [1,2-13C]choline using 1H and 13C magnetic resonance spectroscopy. Microarray gene expression analysis was performed to understand the molecular mechanisms underlying these changes. In breast cancer cells, indomethacin treatment activated phospholipases that, combined with an increased choline phospholipid biosynthesis, led to increased GPC and decreased PC levels. However, in nonmalignant HMECs, activation of the anabolic pathway alone was detected following indomethacin treatment. Following indomethacin treatment in breast cancer cells, several candidate genes, such as interleukin 8, NGFB, CSF2, RHOB, EDN1, and JUNB, were differentially expressed, which may have contributed to changes in choline metabolism through secondary effects or signaling cascades leading to changes in enzyme activity.

RBE of 25 kV X-rays for the survival and induction of micronuclei in the human mammary epithelial cell line MCF-12A

The broad application of low energy X-rays below about 50 keV in radiation therapy and diagnostics and especially in mammography substantiates the precise determination of their relative biological effectiveness (RBE). A quality factor of 1 is stated for photons of all energies in the International Commission on Radiological Protection Recommendations. However, the RBE of low-energy X-rays compared to high-energy photons was found to be dependent on photon energy, cell line and endpoints studied, hence varying from less than one up to about four. In the present study, the human mammary epithelial cell line MCF-12A has been chosen due to the implementation of the results in the estimation of risk from mammography procedures. The RBE of 25 kV X-rays (W anode, 0.3 mm Al filter) relative to 200 kV X-rays (W anode, 0.5 mm Cu filter) was determined for clonogenic survival in the dose range 1-10 Gy and micronuclei (MN) induction in the range 0.5-3.5 Gy. The RBE for clonogenic survival was found to be significantly higher than 1 for surviving fractions in the range 0.005<S<0.2. The RBE decreased with increasing survival, with an RBE0.1 at 10% survival of 1.13+/-0.03. The effectiveness of soft X-rays for MN induction was found to be 1.40+/-0.07 for the fraction of binuclear cells (BNC) with MN and 1.44+/-0.17 for the number of MN per BNC. In contrast, the RBE determined from the number of MN per MN-bearing BNC was found to be 1.08+/-0.32. This indicates that the effectiveness of 25 kV X-rays results from an increase in the number of damaged cells, which, however, do not have higher number of MN per cell.

Establishment, growth and in vivo differentiation of a new clonal human cell line, EM-G3, derived from breast cancer progenitors

A new clonal cell line, EM-G3, was derived from a primary lesion of human infiltrating ductal breast carcinoma. The line consisted of cuboidal cells with occasional appearance of more differentiated branched cells apparently involved in cell-to-cell communication. The EM-G3 cells, population doubling time 34 h, are dependent on the epidermal growth factor. Multicolor fluorescence in situ hybridization (mFISH) analysis demonstrated a stable diploid genome with several genetic changes. Immunocytochemical analysis of EM-G3 in vitro revealed positivity for keratins (K) K5, K14, K18, nuclear protein p63, epithelial membrane antigen (EMA) and other proteins indicative of a pattern of mammary epithelium bipotent progenitors. Detection of integrins alpha-6, beta-1, and protein CD44 by cDNA array also pointed to the character of basal/stem cells. In contrast, dominant cells in the human original tumor showed the luminal character (K18+, K19+, K5-, K14-, and p63-). However, cells with the immunocytochemical profile similar to that of cultured EM-G3 cells were found in minor clusters in the patient's tumor sections. The EM-G3 cells formed limited tumors in nu/nu mice. The cells in mouse tumors were organized in primitive ductal-like structures consisting of 1-3 large central luminal-like cells (EMA+) surrounded by peripheral myoepithelial-like cells (p63+/EMA-). The large central cells gradually disintegrated, forming a pseudolumen. Apparently, EM-G3 cells are able to partially differentiate in vivo as well as in vitro. Our results indicate that EM-G3 cells were derived from a premalignant population of common progenitors of luminal and myoepithelial cells that were immortalized in an early stage of tumorigenesis.

Altered Nuclear Receptor Corepressor Expression Attenuates Vitamin D Receptor Signaling in Breast Cancer Cells

PURPOSE

We hypothesized that deregulated corepressor actions, with associated histone deacetylation activity, epigenetically suppressed vitamin D receptor (VDR) responsiveness and drives resistance towards 1alpha,25-dihydroxyvitamin D(3).

EXPERIMENTAL DESIGN

Profiling, transcriptional, and proliferation assays were undertaken in 1alpha,25(OH)(2)D(3)-sensitive MCF-12A nonmalignant breast epithelial cells, a panel of breast cancer cell lines, and a cohort of primary breast cancer tumors (n = 21).

RESULTS

Elevated NCoR1 mRNA levels correlated with suppressed regulation of VDR target genes and the ability of cells to undergo arrest in G(1) of the cell cycle. A similar increased ratio of corepressor mRNA to VDR occurred in matched primary tumor and normal cells, noticeably in estrogen receptor alpha-negative (n = 7) tumors. 1alpha,25(OH)(2)D(3) resistance in cancer cell lines was targeted by cotreatments with either 1alpha,25(OH)(2)D(3) or a metabolically stable analogue (RO-26-2198) in combination with either trichostatin A (TSA; histone deacetylation inhibitor) or 5-aza-2'-deoxycytidine (DNA methyltransferase inhibitor). Combinations of vitamin D(3) compounds with TSA restored VDR antiproliferative signaling (target gene regulation, cell cycle arrest, and antiproliferative effects in liquid culture) to levels which were indistinguishable from MCF-12A cells.

CONCLUSIONS

Increased NCoR1 mRNA is a novel molecular lesion in breast cancer cells, which acts to suppress responsiveness of VDR target genes, resulting in 1alpha,25(OH)(2)D(3) resistance and seems to be particularly associated with estrogen receptor negativity. This lesion provides a novel molecular diagnostic and can be targeted by combinations of vitamin D(3) compounds and low doses of TSA.

Remodeling of the mammary microenvironment after lactation promotes breast tumor cell metastasis

The mammary gland microenvironment during postlactational involution shares similarities with inflammation, including high matrix metalloproteinase activity, fibrillar collagen deposition, and release of bioactive fragments of fibronectin and laminin. Because inflammation can promote tumorigenesis, we evaluated whether the tissue microenvironment of the involuting gland is also promotional. Extracellular matrix was isolated from mammary glands of nulliparous rats or rats with mammary glands undergoing weaning-induced involution. Using these matrices as substratum, nulliparous matrix was found to promote ductal organization of normal mammary epithelial MCF-12A cells in three-dimensional culture and to suppress invasion of mammary tumor MDA-MB-231 cells in transwell filter assays. Conversely, involution matrix failed to support ductal development in normal cells and promoted invasiveness in tumor cells. To evaluate the effects of these matrices on metastasis in vivo, MDA-MB-231 cells, premixed with Matrigel, nulliparous matrix, or involution matrix, were injected into mammary fat pads of nude mice. Metastases to lung, liver, and kidney were increased in the involution matrix group, and correlated with a twofold increase in tumor vascular endothelial growth factor expression and increased angiogenesis. These data suggest that the mammary gland microenvironment becomes promotional for tumor cell dissemination during involution, thus providing a plausible mechanism to explain the high rate of metastases that occur with pregnancy-associated breast cancer.

AlphaB-crystallin is a novel oncoprotein that predicts poor clinical outcome in breast cancer

Recent gene profiling studies have identified a new breast cancer subtype, the basal-like group, which expresses genes characteristic of basal epithelial cells and is associated with poor clinical outcomes. However, the genes responsible for the aggressive behavior observed in this group are largely unknown. Here we report that the small heat shock protein alpha-basic-crystallin (alphaB-crystallin) was commonly expressed in basal-like tumors and predicted poor survival in breast cancer patients independently of other prognostic markers. We also demonstrate that overexpression of alphaB-crystallin transformed immortalized human mammary epithelial cells (MECs). In 3D basement membrane culture, alphaB-crystallin overexpression induced luminal filling and other neoplastic-like changes in mammary acini, while silencing alphaB-crystallin by RNA interference inhibited these abnormalities. alphaB-Crystallin overexpression also induced EGF- and anchorage-independent growth, increased cell migration and invasion, and constitutively activated the MAPK kinase/ERK (MEK/ERK) pathway. Moreover, the transformed phenotype conferred by alphaB-crystallin was suppressed by MEK inhibitors. In addition, immortalized human MECs overexpressing alphaB-crystallin formed invasive mammary carcinomas in nude mice that recapitulated aspects of human basal-like breast tumors. Collectively, our results indicate that alphaB-crystallin is a novel oncoprotein expressed in basal-like breast carcinomas that independently predicts shorter survival. Our data also implicate the MEK/ERK pathway as a potential therapeutic target for these tumors.

RNA interference-mediated choline kinase suppression in breast cancer cells induces differentiation and reduces proliferation

Choline kinase is overexpressed in breast cancer cells and activated by oncogenes and mitogenic signals, making it a potential target for cancer therapy. Here, we have examined, for the first time, the effects of RNA interference (RNAi)-mediated down-regulation of choline kinase in nonmalignant and malignant human breast epithelial cell lines using magnetic resonance spectroscopy (MRS) as well as molecular analyses of proliferation and differentiation markers. RNAi knockdown of choline kinase reduced proliferation, as detected by proliferating cell nuclear antigen and Ki-67 expression, and promoted differentiation, as detected by cytosolic lipid droplet formation and expression of galectin-3. The functional importance of RNAi-mediated choline kinase down-regulation on choline phospholipid metabolism was confirmed by the significant reduction of phosphocholine detected by MRS. These results strongly support the targeting of choline kinase in breast cancer cells with RNAi and show the potential ability of noninvasive MRS to detect and evaluate future treatments incorporating such strategies.

Synthesis of 6'-O-lissamine-rhodamine B-glucosamine as a novel probe for fluorescence imaging of lysosomes in breast tumors

Lysosomes contain multiple proteases, which play a crucial role in breast cancer invasion and metastasis. Noninvasive labeling of lysosomes in breast cancer cells and solid breast tumor models is therefore useful to study lysosomal trafficking and its role in invasion. We have synthesized a novel compound, 6'-O-lissamine-rhodamine B-glucosamine, to fluorescently label lysosomes, and evaluated the compound in human breast cancer cells in cell culture or in orthotopic human breast cancer models. We demonstrated that this novel compound biosynthetically labeled lysosomal proteins following addition to cell culture medium or following intravenous injection into mouse models of breast cancer. Fluorescence from 6'-O-lissamine-rhodamine B-glucosamine colocalized with several well-established lysosomal markers, such as lysosome-associated proteins 1 and 2 (LAMP-1 and -2) and CD63. We also demonstrated the feasibility of performing in vivo fluorescence imaging of 6'-O-lissamine-rhodamine B-glucosamine to image lysosomes in human breast cancer models.

In search of a stem cell hierarchy in the human breast and its relevance to breast cancer evolution

By deliberate analogy with the well-established concept of hematopoiesis, the term "mammopoiesis" is occasionally used to describe the development of the different cellular lineages and functional units in the mammary gland. The use of this term signifies a strong bias towards the idea that tissue homeostasis during mammary development, pregnancy, lactation and involution is brought about by the action of somatic stem cells characterized by longevity and multipotency. The progenies hereof eventually differentiate into structurally and functionally well-defined ductal-lobular units. During the past two decades evidence of such a notion in the mouse has developed from being largely circumstantial based on non-clonal in vivo experiments to a quite elaborate characterization of individual candidate stem cells by a number of different properties. Within tumor biology this has led to a renaissance of the concept of tumors as caricatures of tissue renewal. Thus, recent molecular classification of breast cancer based on genome wide expression analysis operates with different subtypes with specific reference to the normal luminal epithelial and myoepithelial/basal lineages in the breast. Apparently some tumors are lineage restricted and others differentiate more broadly as if they have preserved some stem-like properties. This holds promise for the existence of a stem cell hierarchy, the understanding of which may prove to be instrumental in further dissecting the histogenesis of breast cancer evolution. Most attention has been devoted to the question of different cellular origins of cancer subtypes and different susceptibilities of possible stem cells to gain or loss of oncogenes and tumor suppressor genes, respectively. Invaluable progress has been made over the past two decades in culture technology not only in terms of population doubling and clonal growth, but also the availability of lineage specific markers, cell sorting, and three-dimensional functional assays for tissue specific morphogenesis. Transcriptional profiling of stem cell zones has unraveled a hitherto unknown preservation of signaling pathways for maintenance of stem cell properties across tissue boundaries and species. Somatic stem cells have therefore been narrowed down to specific anatomic locations not only in rapidly renewing tissues such as skin and skin derivatives, but also in tissues with slower turnover times, such as lung, kidney and prostate. It is therefore now possible to integrate this information in a search for similar cells within the breast. Even if cell turnover after birth is provided exclusively by dividing lineage-restricted cells, more information about the robustness of breast differentiation programs during tumor progression is still very much required. Complete knowledge of the primary cell of origin of breast cancer and the mechanisms that influence differentiation programs during tumor initiation, promotion and progression may be crucial for the development of novel non-toxic therapies that influence tumor cell behaviour. The scope of this review is to discuss reports that have begun to elucidate the topographic location, key cellular type and lineage fidelity in culture and xenograft models of candidate human breast stem cells and their differentiated progenies with particular emphasis on comparison with the differentiation programs of tumor subtypes.

Autocrine metabolism of vitamin D in normal and malignant breast tissue

PURPOSE

Vitamin D seems to exert a protective effect against common cancers, although this does not correlate with circulating levels of active 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], indicating a more localized activation of vitamin D. The aim of this study was to investigate the significance of this in breast cancer.

EXPERIMENTAL DESIGN

Quantitative reverse transcription-PCR analysis of mRNA expression was carried out for the vitamin D-activating enzyme 1alpha-hydroxylase, the catabolic enzyme 24-hydroxylase, and the vitamin D receptor in 41 tumors and paired nonneoplastic tissue as well as breast cancer cell lines. Immunohistochemistry was used to assess 1alpha-hydroxylase protein expression, and enzyme assays were used to quantify vitamin D metabolism.

RESULTS

Expression of mRNA for 1alpha-hydroxylase (27-fold; P < 5 x 10(-11)), vitamin D receptor (7-fold; P < 1.5 x 10(-8)), and 24-hydroxylase (4-fold; P < 0.02) was higher in breast tumors. 1alpha-Hydroxylase enzyme activity was also higher in tumors (44.3 +/- 11.4 versus 12.4 +/- 4.8 fmol/h/mg protein in nonneoplastic tissue; P < 0.05). However, production of inactive 1,24,25-trihydroxyvitamin D3 was also significantly higher in tumors (84.8 +/- 11.7 versus 33.6 +/- 8.5 fmol/h/mg protein; P < 0.01). Antisense inhibition of 24-hydroxylase in vitro increased antiproliferative responses to 1,25(OH)2D3.

CONCLUSION

These data indicate that the vitamin D-activating enzyme 1alpha-hydroxylase is up-regulated in breast tumors. However, dysregulated expression of 24-hydroxylase seems to abrogate the effects of local 1,25(OH)2D3 production in tumors by catalyzing catabolism to less active vitamin D metabolites. The enzymes involved in autocrine metabolism of vitamin D in breast tissue may therefore provide important targets for both the prevention and treatment of breast cancer.

CCAAT/Enhancer binding protein delta (c/EBPdelta) regulation and expression in human mammary epithelial cells: I. "Loss of function" alterations in the c/EBPdelta growth inhibitory pathway in breast cancer cell lines

"Loss of function" alterations in growth inhibitory signal transduction pathways are common in cancer cells. In this study, we show that growth arrest (GA) treatments--serum and growth factor withdrawal and growth inhibitory IL-6 family cytokines (Interleukin-6 and Oncostatin M (OSM))--increase STAT3 phosphorylation (pSTAT3), increase CCAAT enhancer binding protein delta (C/EBPdelta) gene expression and induce GA of primary, finite-lifespan human mammary epithelial cells (HMECs), and immortalized breast cell lines (MCF-10A and MCF-12A). In contrast, serum and growth factor withdrawal from human breast cancer cell lines (MCF-7, SK-BR-3, T-47D, and MDA-MB-231) for up to 48 h induced a relatively modest increase in pSTAT3 levels and C/EBPdelta gene expression and resulted in varying levels of GA. In most breast cancer cell lines, IL-6 family cytokine treatment increased pSTAT3 levels and C/EBPdelta gene expression, however, growth inhibition was cell line dependent. In addition to "loss of function" alterations in growth inhibitory pathways, breast cancer cell lines also exhibit "gain of function" alterations in growth signaling pathways. The Akt growth/ survival pathway is constitutively activated in T-47D and MCF-7 breast cancer cells. The Akt inhibitor LY 294,002 significantly enhanced T-47D growth inhibition by serum and growth factor withdrawal or IL-6 family cytokine treatment. Finally, we show that activation of the pSTAT3/C/EBPdelta growth control pathway is independent of estrogen receptor status. These results demonstrate that "loss of function" alterations in the pSTAT3/C/EBPdelta growth inhibitory signal transduction pathway are relatively common in human breast cancer cell lines. Defective activation of the pSTAT3/ C/EBPdelta growth inhibitory signal transduction pathway, in conjunction with constitutive activation of the Akt growth stimulatory pathway, may play a synergistic role in the etiology or progression of breast cancer.

Analysis of the ERK1,2 transcriptome in mammary epithelial cells

MAPK (mitogen-activated protein kinase) pathways constitute major regulators of cellular transcriptional programmes. We analysed the ERK1,2 (extracellular-signal-regulated kinase 1,2) transcriptome in a non-transformed MEC (mammary epithelial cell) line, MCF-12A, utilizing rAd MEK1EE, a recombinant adenovirus encoding constitutively active MEK1 (MAPK/ERK kinase 1). rAd MEK1EE infection induced morphological changes and DNA synthesis which were inhibited by the MEK1,2 inhibitor PD184352. Hierarchical clustering of data derived from seven time points over 24 h identified 430 and 305 co-ordinately up-regulated and down-regulated genes respectively. c-Myc binding sites were identified in the promoters of most of these up-regulated genes. A total of 46 candidate effectors of the Raf/MEK/ERK1,2 pathway in MECs were identified by comparing our dataset with previously reported Raf-1-regulated genes. These analyses led to the identification of a suite of growth factors co-ordinately induced by MEK1EE, including multiple ErbB ligands, vascular endothelial growth factor and PHRP (parathyroid hormone-related protein). PHRP is the primary mediator of humoral hypercalcaemia of malignancy, and has been implicated in metastasis to bone. We demonstrate that PHRP is secreted by MEK1EE-expressing cells. This secretion is inhibited by PD184352, but not by ErbB inhibitors. Our results suggest that, in addition to anti-proliferative properties, MEK1,2 inhibitors may be anti-angiogenic and possess therapeutic utility in the treatment of PHRP-positive tumours.

Cigarette smoke condensate-induced transformation of normal human breast epithelial cells in vitro

In the present study, we showed that a single-dose treatment of normal breast epithelial cell line, MCF10A, for 72 h with cigarette smoke condensate (CSC) resulted in a transformed phenotype. The anchorage-dependent growth of these cells was decreased due to increased cell cycle arrest in S-G2/M phase; however, the surviving cells developed resistance due to an increased Bcl-xL to Bax ratio. Levels of PCNA and gadd45 proteins--involved in DNA repair in response to genomic damage--were increased, suggesting that the cells were responding to CSC-induced genomic damage. The transformation of MCF10A cells was determined by their colony-forming efficiency in soft-agar in an anchorage-independent manner. CSC-treated MCF10A cells efficiently formed colonies in soft-agar. We then re-established cell lines from the soft-agar colonies and further examined the persistence of their transforming characteristics. The re-established cell lines, when plated after 17 passages without CSC treatment, still formed colonies in the soft-agar. An increased staining of neuropilin-1 (NRP-1) further showed a transformation characteristic of MCF10A cells treated with CSC. In summary, our results suggest that CSC is capable of transforming the MCF10A cells in vitro, supporting the role of cigarette smoking and increased risk for breast cancer.

Molecular Causes of the Aberrant Choline Phospholipid Metabolism in Breast Cancer

Proton magnetic resonance spectroscopy ((1)H MRS) consistently detects significant differences in choline phospholipid metabolites of malignant versus benign breast lesions. It is critically important to understand the molecular causes underlying these metabolic differences, because this may identify novel targets for attack in cancer cells. In this study, differences in choline membrane metabolism were characterized in breast cancer cells and normal human mammary epithelial cells (HMECs) labeled with [1,2-(13)C]choline, using (1)H and (13)C magnetic resonance spectroscopy. Metabolic fluxes between membrane and water-soluble pool of choline-containing metabolites were assessed by exposing cells to [1,2-(13)C]choline for long and short periods of time to distinguish between catabolic and anabolic pathways in choline metabolism. Gene expression analysis using microarrays was performed to understand the molecular mechanisms underlying these changes. Breast cancer cells exhibited increased phosphocholine (PC; P < 0.001), total choline-containing metabolites (P < 0.01), and significantly decreased glycerophosphocholine (P < 0.05) compared with normal HMECs. Decreased (13)C-enrichment was detected in choline (P < 0.001) and phosphocholine (P < 0.05, P < 0.001) of breast cancer cells compared with HMECs, indicating a higher metabolic flux from membrane phosphatidylcholine to choline and phosphocholine in breast cancer cells. Choline kinase and phospholipase C were significantly overexpressed, and lysophospholipase 1, phospholipase A2, and phospholipase D were significantly underexpressed, in breast cancer cells compared with HMECs. The magnetic resonance spectroscopy data indicated that elevated phosphocholine in breast cancer cells was primarily attributable to increased choline kinase activity and increased catabolism mediated by increased phospholipase C activity. These observations were consistent with the overexpression of choline kinase and phospholipase C detected in the microarray analyses.

Targeting 1alpha,25-dihydroxyvitamin D3 antiproliferative insensitivity in breast cancer cells by co-treatment with histone deacetylation inhibitors

Proliferation of the non-malignant breast epithelial cell line, MCF-12A, is sensitively and completely inhibited by 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) (ED90 = 70 nM), We used real time RT-PCR to demonstrate that the relative resistance to 1alpha,25(OH)(2)D(3) of MDA-MB-231 cells (ED50 > 100 nM) correlated with significantly reduced Vitamin D receptor (VDR) and increased NCoR1 nuclear receptor co-repressor mRNA (0.1-fold reduction in VDR and 1.7-fold increase in NCoR1 relative to MCF-12A (P < 0.05)). This molecular lesion can be targeted by co-treating cells with 1alpha,25(OH)(2)D(3) or potent analogs and the histone deacetylation inhibitor trichostatin A (TSA). For example, the co-treatment of 1,25-dihydroxy-16,23,Z-diene-26,27-hexafluoro-19-nor Vitamin D(3) (RO-26-2198) (100 nM) plus TSA results in strong additive antiproliferative effects in MDA-MB-231 cells. This may represent novel chemotherapeutic regime for hormone insensitive breast cancer.

ESX induces transformation and functional epithelial to mesenchymal transition in MCF-12A mammary epithelial cells

ESX is an epithelial-restricted member of a large family of transcription factors known as the Ets family. ESX expression has been shown to be correlated with Her2/neu proto-oncogene amplification in highly aggressive breast cancers and induced by Her2/neu in breast cell lines, but its role in tumorigenesis is unknown. Previously, we have shown that ESX enhances breast cell survival in colony-formation assays. In order to determine whether ESX can act as a transforming gene, we stably transfected MCF-12A human mammary epithelial cells with the ESX expression vector, pCGN2-HA-ESX. The MCF-12A cell line is immortalized, but nontransformed, and importantly, these cells fail to express endogenous ESX protein. We used pCGN2-HA-Ets-2 and pSVRas expression vectors as positive controls for transformation. Like HA-Ets-2 and V12-Ras, stable expression of ESX induced EGF-independent proliferation, serum-independent MAPK phosphorylation and growth in soft agar. Additionally, stable ESX expression conferred increased cell adhesion, motility and invasion in two-dimensional and transwell filter assays, and an epithelial to mesenchymal morphological transition. In three-dimensional cultures, parental and vector control (pCGN2) cells formed highly organized duct-like structures with evidence of cell polarity, ECM adhesion-dependent proliferation and cell survival, and lack of cellular invasion into surrounding matrix. Remarkably, the ESX stable cells formed solid, disorganized structures, with lack of cell polarity, loss of adhesion junctions and cytokeratin staining and loss of dependence on ECM adhesion for cell proliferation and survival. In addition, ESX cells invaded the surrounding matrix, indicative of a transformed and metastatic phenotype. Taken together, these data show that ESX expression alone confers a transformed and in vitro metastatic phenotype to otherwise normal MCF-12A cells.

Extracellular acidification alters lysosomal trafficking in human breast cancer cells

Cancer cells invade by secreting degradative enzymes, which are sequestered in lysosomal vesicles. In this study, the impact of an acidic extracellular environment on lysosome size, number, and distance from the nucleus in human mammary epithelial cells (HMECs) and breast cancer cells of different degrees of malignancy was characterized because the physiological microenvironment of tumors is frequently characterized by extracellular acidity. An acidic extracellular pH (pH(e)) resulted in a distinct shift of lysosomes from the perinuclear region to the cell periphery irrespective of the HMECs' degree of malignancy. With decreasing pH, larger lysosomal vesicles were observed more frequently in highly metastatic breast cancer cells, whereas smaller lysosomes were observed in poorly metastatic breast cancer cells and HMECs. The number of lysosomes decreased with acidic pH values. The displacement of lysosomes to the cell periphery driven by extracellular acidosis may facilitate exocytosis of these lysosomes and increase secretion of degradative enzymes. Filopodia formations, which were observed more frequently in highly metastatic breast cancer cells maintained at acidic pH(e), may also contribute to invasion.

The epithelial-specific ETS transcription factor ESX/ESE-1/Elf-3 modulates breast cancer-associated gene expression

Several members of the ETS family of transcription factors contribute to tumorigenesis in many different tissues, including breast epithelium. The ESX gene is an epithelial-specific Ets member that is particularly relevant to breast cancer. ESX is amplified in early breast cancers, it is overexpressed in human breast ductal carcinoma in situ, and there may be a positive feedback loop between the HER2/neu proto-oncogene and ESX. Despite this progress in our understanding of ESX, its ability to regulate tumor-related gene expression and to modulate breast cell survival, remain unknown. Here we show that HA-ESX stimulates the collagenase and HER2/neu promoters, but fails to activate an intact stromelysin promoter. However, HA-ESX activates, in a dose-dependent manner, a heterologous promoter containing eight copies of the Ets binding site derived from the stromelysin gene (p8Xpal-CAT). Analysis of the ability of constructs encoding nine Ets family members to activate the HER2/neu promoter revealed three patterns of gene activation: (1) no effect or repressed promoter activity (Elk-1 and NET); (2) intermediate activity (ER81, GABP, ESX, and HA-Ets-2); and, (3) maximal activity (Ets-1, VP-16-Ets-1, and EHF). Based on these observations, we also determined whether ESX is capable of conferring a survival phenotype upon immortalized, but nontransformed and ESX negative MCF-12A human breast cells. Using a colony formation assay, we found that HA-ESX and HA-Ets-2, mediated MCF-12A cell survival rates that approached those generated by oncogenic V12 Ras, whereas empty vector resulted in negligible colony formation. By contrast, in immortalized and transformed T47D breast cancer cells, which express both HER2/neu and ESX, we found that antisense and dominant-negative HA-ESX inhibited T47D colony formation, whereas control vector allowed formation of many colonies. These results are significant because they show that HA-ESX is able to differentially activate several malignancy-associated gene promoters, and that ESX expression is required for cellular survival of nontransformed MCF-12A and transformed T47D human mammary cells.

Differential gene expression in human prostate cancer cells adapted to growth in bone in Beige mice

OBJECTIVE

A metastasis model was used to identify genes potentially related to the growth of human prostate cancer in the bone. Injection of the human prostate cancer line PC3 into the femurs of Beige mice induced tumors that ruptured the femurs in 4 to 6 weeks.

MATERIALS AND METHODS

The subline PC3a was cultured in vitro from one of these PC3 bone tumors. PC3a cells were reinjected into femurs, and the subline PC3b was then cultured from a resulting PC3a tumor. Likewise, PC3c was derived from a PC3b bone tumor. The PC3 tumors were osteolytic, invasive and metastatic.

RESULTS

Analysis of gene expression in these PC3 sublines by differential-display RT-PCR identified two groups of transcripts whose steady state levels differed substantially from the original PC3 line. One group of transcripts increased with progressive adaptation to tumor formation in bone. The second group showed the reverse pattern. They progressively diminished in subsequent sublines, and were virtually absent in PC3b and PC3c. Two in this group were fibroblast growth factor receptor-2 and caveolin-1. They were strongly expressed in non-malignant prostate tissue.

CONCLUSION

These two downregulated genes, which have been reported to play a role in the development of androgen independence and malignant progression, may reflect molecular changes in growth regulation of PC3 cells during readaptation to an intra-osseal environment.

A novel method of imaging lysosomes in living human mammary epithelial cells

Cancer cells invade by secreting degradative enzymes which, under normal conditions, are sequestered in lysosomal vesicles. The ability to noninvasively label lysosomes and track lysosomal trafficking would be extremely useful to understand the mechanisms by which degradative enzymes are secreted in the presence of pathophysiological environments, such as hypoxia and acidic extracellular pH, which are frequently encountered in solid tumors. In this study, a novel method of introducing a fluorescent label into lysosomes of human mammary epithelial cells (HMECs) was evaluated. Highly glycosylated lysosomal membrane proteins were labeled with a newly synthesized compound, 5-dimethylamino-naphthalene-1-sulfonic acid 5-amino-3,4,6-trihydroxy-tetrahydro-pyran-2-ylmethyl ester (6-O-dansyl-GlcNH2). The ability to optically image lysosomes using this new probe was validated by determining the colocalization of the fluorescence from the dansyl group with immunofluorescent staining of two well-established lysosomal marker proteins, LAMP-1 and LAMP-2. The location of the dansyl group in lysosomes was also verified by using an anti-dansyl antibody in Western blots of lysosomes isolated using isopycnic density gradient centrifugation. This novel method of labeling lysosomes biosynthetically was used to image lysosomes in living HMECs perfused in a microscopy-compatible cell perfusion system.