Mammary Epithelial Cell Model Research Articles

Copper excess induces autophagy dysfunction and mitochondrial ROS-ferroptosis progression, inhibits cellular biosynthesis of milk protein and lipid in bovine mammary epithelial cells.

Excessive copper (Cu) has the potential risk to ecosystems and organism health, with its impact on dairy cow mammary glands being not well-defined. This study used a bovine mammary epithelial cell (MAC-T) model to explore how copper excess affects cellular oxidative stress, autophagy, ferroptosis, and protein and lipid biosynthesis in milk. Results showed the increased intracellular ROS, MDA, and CAT (P < 0.05), alongside decreased T-SOD and GSH in CuSO4-treated cells (P < 0.05). Transmission electron microscopy and Ad-mCherry-GFP-LC3B assays revealed significant autophagosome accumulation in CuSO4 exposed cells (P < 0.05). Additionally, CuSO4 exposure modulated autophagy markers, evidenced by upregulation of genes such as LC3, ATG5, JNK1, and Beclin1, and downregulation of genes such as ATG4B, and p62 (P < 0.05). CuSO4 also led to notable mitochondrial changes, including size reduction, membrane rupture, and cristae loss, and reduced expression of the ferroptosis inhibitor GPX4 (P < 0.05). The expression of mTOR, HIF-1α and β-catenin signaling pathway were inhibited in differentiated MAC-T cells by CuSO4 exposure (P < 0.05), activated autophagy through activation of the AMPK-mTOR pathway which in turn affected downstream levels of genes related to milk protein and lipid. In conclusion, excessive copper induces oxidative stress in MAC-T cells, promoting autophagy through JNK-Bcl2, Beclin1-Vps34 and AMPK-mTOR pathways, leading to cell ferroptosis, as well as inhibits the cellular biosynthesis of milk protein and lipid.

Hordenine Alleviates Lipopolysaccharide-Induced Mastitis by Suppressing Inflammation and Oxidative Stress, Modulating Intestinal Microbiota, and Preserving the Blood-Milk Barrier.

Mastitis is a common mammalian disease occurring in the mammary tissue and poses a major threat to agriculture and the dairy industry. Hordenine (HOR), a phenylethylamine alkaloid naturally extracted from malt, has various pharmacological effects, but its role in mastitis is unknown. The aim of this study was to investigate the role of HOR and its underlying mechanism in a lipopolysaccharide (LPS)-induced inflammatory response model of mouse mammary epithelial cells (EpH4-Ev) and mouse mastitis model. The experimental results showed that HOR attenuated LPS-induced mammary tissue damage (from 3.75 ± 0.25 to 1.75 ± 0.25) and restored the integrity of the blood-milk barrier. Further mechanistic studies revealed that HOR inhibited LPS-induced overactivation of the TLR4-MAPK/NF-κB signaling pathway and activated the AMPK/Nrf2/HO-1 signaling pathway. Additionally, HOR altered the composition of the intestinal microbiota in mice, ultimately reducing the extent of inflammatory injury (from 3.33 ± 0.33 to 0.67 ± 0.33) and upregulating the expression of tight junction proteins (ZO-1, occludin, and claudin-3). The findings of this study provide a theoretical basis in the rational use of HOR for the prevention and treatment of mastitis and the maintenance of mammalian mammary gland health.

Smad7 palmitoylation by the S-acyltransferase zDHHC17 enhances its inhibitory effect on TGF-β/Smad signaling

Intracellular signaling by the pleiotropic cytokine transforming growth factor-β (TGF-β) is inhibited by Smad7 in a feedback control mechanism. The activity of Smad7 is tightly regulated by multiple post-translational modifications. Using resin-assisted capture and metabolic labeling methods, we show here that Smad7 is S-palmitoylated in mammary epithelial cell models that are widely studied because of their strong responses to TGF-β and their biological relevance to mammary development and tumor progression. S-palmitoylation of Smad7 is mediated by zDHHC17, a member of a family of 23 S-acyltransferase enzymes. Moreover, we identified four cysteine residues (Cys202, Cys225, Cys415, and Cys417) in Smad7 as palmitoylation acceptor sites. S-palmitoylation of Smad7 on Cys415 and Cys417 promoted the translocation of Smad7 from the nucleus to the cytoplasm, enhanced the stability of the Smad7 protein, and enforced its inhibitory effect on TGF-β-induced Smad transcriptional response. Thus, our findings reveal a new post-translational modification of Smad7, and highlight an important role of S-palmitoylation to enhance inhibition of TGF-β/Smad signaling by Smad7.

Regulatory roles of dopamine D2 receptor in milk protein production and apoptosis in mammary epithelial cells

Dopamine D2 receptors (D2Rs) play crucial roles in regulating diverse physiological functions of the central nervous system and peripheral organs. D2Rs are also expressed in mammary glands. However, which cell types express D2Rs and whether they are involved in milk production remains unclear. The present findings revealed that D2Rs are expressed in the apical regions of the lateral membranes of mammary epithelial cells (MECs) in lactating mice. We also investigated the effects of the D2R agonist bromocriptine and/or antagonist domperidone on intracellular cAMP levels, milk protein production, and apoptosis in a lactation culture model of MECs that produce major milk components like lactating MECs in vivo. We found that bromocriptine decreased intracellular cAMP levels, whereas domperidone dose-dependently neutralized this effect. Bromocriptine also inhibited casein and lactoferrin production and suppressed activities of STAT5 and glucocorticoid receptors (GRs). Domperidone neutralized the inhibition of casein production as well as STAT5 and GR inactivation induced by bromocriptine. Furthermore, D2R activation by bromocriptine induced apoptosis and inactivated ERK, a signaling molecule responsible for promoting cell proliferation and survival. Domperidone attenuated ERK inactivation and apoptosis induced by bromocriptine. These findings suggest that D2Rs play regulatory roles in milk protein production and apoptosis in MECs.

Methionyl-Methionine Dipeptide Enhances Mammogenesis and Lactogenesis by Suppressing the Expression of a Novel Long Noncoding RNA MGPNCR to Inhibit eIF4B Dephosphorylation.

Previous research has demonstrated that in pregnant mice deficient in l-methionine (Met), the mixture of the dipeptide l-methionyl-l-methionine (Met-Met) with Met was more effective than Met alone in promoting mammogenesis and lactogenesis. This study aimed to investigate the role of a novel long noncoding RNA (lncRNA), named mammary gland proliferation-associated lncRNA (MGPNCR), in these processes. Transcriptomic analysis of mammary tissues from Met-deficient mice, supplemented either with a Met-Met/Met mixture or with Met alone, revealed significantly higher MGPNCR expression in the Met group compared to the mixture group, a finding recapitulated in a mammary epithelial cell model. Our findings suggested that MGPNCR hindered mammogenesis and milk protein synthesis by binding to eukaryotic initiation factor 4B (eIF4B). This interaction promoted the dephosphorylation of eIF4B at serine-422 by enhancing its association with protein phosphatase 2A (PP2A). Our study sheds light on the regulatory mechanisms of lncRNA-mediated dipeptide effects on mammary cell proliferation and milk protein synthesis. These insights underscore the potential benefits of utilizing dipeptides to improve milk protein in animals and potentially in humans.

Mechanism of anti-hyperplasia of mammary glands of Xihuang Pills blood-entering component based on UPLC-Q-TOF-MS and network pharmacology

In this study, based on network pharmacology and molecular docking method, the mechanism of anti-hyperplasia of mammary glands of Xihuang Pills blood-entering components was explored, and the efficacy and key targets of Xihuang Pills blood-entering components were experimentally verified by MCF-10A proliferation model of human mammary epithelial cells. In order to clarify the material basis and mechanism of Xihuang Pills in realizing anti-hyperplasia of mammary glands, the blood-entering components of Xihuang Pills were qualitatively analyzed by UPLC-Q-TOF-MS, and 22 blood-entering components were identified. By taking the blood-entering components as the research object, the network pharmacology prediction and molecular docking verification were carried out, and finally, three key targets were screened out, namely JAK1, SRC, and CDK1. In vitro experiments show that Xihuang Pills can inhibit the proliferation of MCF-10A cells, promote the apoptosis of MCF-10A cells, and reduce the expression of JAK1, SRC, and CDK1 targets in cells. To sum up, Xihuang Pills can promote the apoptosis of mammary epithelial cells by regulating the expression of JAK1, SRC, and CDK1 and then play an anti-hyperplasia role, which provides an experimental basis for clarifying the material basis of Xihuang Pills for anti-hyperplasia effect.

Quaking isoforms cooperate to promote the mesenchymal phenotype.

The RNA-binding protein Quaking (QKI) has widespread effects on mRNA regulation including alternative splicing, stability, translation, and localization of target mRNAs. Recently, QKI was found to be induced during epithelial-mesenchymal transition (EMT), where it promotes a mesenchymal alternative splicing signature that contributes to the mesenchymal phenotype. QKI is itself alternatively spliced to produce three major isoforms, QKI-5, QKI-6, and QKI-7. While QKI-5 is primarily localized to the nucleus where it controls mesenchymal splicing during EMT, the functions of the two predominantly cytoplasmic isoforms, QKI-6 and QKI-7, in this context remain uncharacterized. Here we used CRISPR-mediated depletion of QKI in a human mammary epithelial cell model of EMT and studied the effects of expressing the QKI isoforms in isolation and in combination. QKI-5 was required to induce mesenchymal morphology, while combined expression of QKI-5 with either QKI-6 or QKI-7 further enhanced mesenchymal morphology and cell migration. In addition, we found that QKI-6 and QKI-7 can partially localize to the nucleus and contribute to alternative splicing of QKI target genes. These findings indicate that the QKI isoforms function in a dynamic and cooperative manner to promote the mesenchymal phenotype.

Effects of hydrostatic compression on milk production-related signaling pathways in mouse mammary epithelial cells

Mammary epithelial cells (MECs) secrete milk into the mammary alveolar lumen during lactation. The secreted milk accumulates in the alveolar lumen until milk ejection occurs, and excess milk accumulation downregulates milk production in alveolar MECs. Intramammary hydrostatic pressure also increases in the alveolar lumen in a manner dependent on milk accumulation. In this study, we investigated whether high hydrostatic compression directly affects lactating MECs, using a commercial compression device and a lactation culture model of MECs, which have milk production ability and less permeable tight junctions. High hydrostatic compression at 100 kPa for 8 h decreased β-casein and increased claudin-4 levels concurrently with inactivation of STAT5 and glucocorticoid receptor signaling pathways. In addition, high hydrostatic compression for 1 h inactivated STAT5 and activated p38 MAPK signaling. Furthermore, repeated rises and falls of the hourly hydrostatic compression induced activation of positive (Akt, mTOR) and negative (STAT3, NF-κB) signaling pathways for milk production concurrently with stimulation of casein and lactoferrin production in MECs. These results indicate that milk production-related signaling pathways in MECs change in response to hydrostatic compression. Hydrostatic compression of the alveolar lumen may directly regulate milk production in the alveolar MECs of lactating mammary glands.

FGFR2 Controls Growth, Adhesion and Migration of Nontumorigenic Human Mammary Epithelial Cells by Regulation of Integrin β1 Degradation

The role of fibroblast growth factor receptor 2 (FGFR2), an important mediator of stromal paracrine and autocrine signals, in mammary gland morphogenesis and breast cancer has been extensively studied over the last years. However, the function of FGFR2 signalling in the initiation of mammary epithelial oncogenic transformation remains elusive. Here, FGFR2-dependent behaviour of nontumorigenic model of mammary epithelial cells was studied. In vitro analyses demonstrated that FGFR2 regulates epithelial cell communication with extracellular matrix (ECM) proteins. Silencing of FGFR2 significantly changed the phenotype of cell colonies in three-dimensional cultures, decreased integrins α2, α5 and β1 protein levels and affected integrin-driven processes, such as cell adhesion and migration. More detailed analysis revealed the FGFR2 knock-down-induced proteasomal degradation of integrin β1. Analysis of RNA-seq databases showed significantly decreased FGFR2 and ITGB1 mRNA levels in breast tumour samples, when compared to non-transformed tissues. Additionally, high risk healthy individuals were found to have disrupted correlation profiles of genes associated with FGFR2 and integrin signalling, cell adhesion/migration and ECM remodelling. Taken together, our results strongly suggest that FGFR2 loss with concomitant integrin β1 degradation is responsible for deregulation of epithelial cell-ECM interactions and this process may play an important role in the initiation of mammary gland epithelial tumorigenesis.

IL-1β is a key inflammatory cytokine that weakens lactation-specific tight junctions of mammary epithelial cells

In lactating mammary glands, alveolar mammary epithelial cells (MECs) produce milk and form less-permeable tight junctions (TJs). However, alveolar TJs are weakened with a reduction in milk production in mammary glands due to mastitis or weaning in the presence of high levels of IL-1β, IL-6, or TNF-α. In this study, using in vitro cultured model of MECs with milk-producing ability and lactation-specific TJs, we investigated whether the aforementioned cytokines affect MEC TJs. The results showed that TNF-α, IL-1β, and IL-6 affected lactation-specific TJs in different ways. In particular, upon activation of p38 and JNK signalling, IL-1β caused rapid disruption of TJs at tricellular contact points. IL-1β treatment led to decreased CLDN3, CLDN4, and OCLN levels and a weakened TJ barrier. The adverse effects of IL-1β on TJs were mimicked by anisomycin, which is an activator of p38 and JNK signalling, and were blocked by MEC pretreatment with a p38 inhibitor but not a JNK inhibitor. The mislocalization of tricellulin at tricellular contact areas was confirmed in MECs treated with IL-1β or anisomycin. These results indicate that IL-1β is a key cytokine that adversely affects the TJs between MECs by activating p38.

Genistein Directly Represses the Phosphorylation of STAT5 in Lactating Mammary Epithelial Cells.

Genistein is a soy isoflavone and shows various physiological activities, such as affinities for estrogen receptors (ERs) and inhibitory effects on the epidermal growth factor receptor (EGFR) pathway. A previous study reported that genistein downregulates milk production ability in mammary epithelial cells (MECs) while decreasing the phosphorylation of STAT5. The ER and EGFR pathways indirectly regulate STAT5. In this study, the repressing mechanism of genistein against the phosphorylation of STAT5 was investigated using a culture model of mouse MECs with milk production ability. The results revealed that genistein did not influence the behavior of ERα and ERβ, whereas genistein immediately repressed the phosphorylation of ERK1/2. However, the decrease in phosphorylated STAT5 occurred independent of the phosphorylation of EGFR. Genistein repressed new phosphorylation of STAT5 by prolactin without influencing the phosphorylation of JAK2. In conclusion, this study indicates that genistein directly inhibits the phosphorylation of STAT5 in lactating MECs.

Establishment of inflammatory model of bovine mammary epithelial cells induced by lipoteichoic acid

The mammary gland of the cow is particularly susceptible to infections of a wide range of pathogenic bacteria, including both Gram-positive and Gram-negative bacteria. The endotoxins of these pathogenic bacteria include peptidoglycan (PGN), lipoteichoic acid (LTA) and lipopolysaccharide (LPS), and they are the pathogen-associated molecular patterns (PAMPs) to induce mastitis. Cow mastitis is a detrimental factor in dairy farming industry. Lipoteichoic acid (LTA) is the main component of Staphylococcus aureus cell wall and the key cytotoxic factor causing inflammation. The aims of our work was to establish inflammatory model of study procedures were approved by the Animal Care and Use Committee of the Sumy National Agricultural University, Sumy, Ukraine, and the Henan Institute of Science and Technology, Xinxiang, China, and performed in accordance with the animal welfare and ethics guidelines.&#x0D; The BMECs harvested from mid-lactation dairy cow milk were isolated by our laboratory. Briefly, the base medium for this cell is DMEM/F-12 (Gibco, USA, cat.12400-024). The complete growth medium included 10% fetal bovine serum (Biological Industries, Israel, cat.04-011-1A/B), DMEM/F-12, and 10 ng/mL epidermal growth factor (Sigma, USA, cat. E4127). Cells were maintained at 37℃in an incubator containing 5% CO2. When cells grew to 80% confluency, the cells were rinsed twice with PBS, and then the primary mammary epithelial cells were trypsinized with 0.25% trypsin plus 0.02% EDTA and passaged. In this study, one inflammatory bovine mammary epithelial cell (BMEC) model was established by infecting the cells with LTA. The BMEC viability induced by LTA were evaluated. The expressions of pro-inflammatory cytokines (TNF-α and IL-6) were measured by ELISA and RT- qPCR. The results showed that the treatment of BMECs with LTA at 20 ng/μL for 24 h obviously improved TNF-α and IL-6 protein and gene expression levels. The establishment of the model will play an important role in the screening of anti-inflammatory drugs and the study of the mechanism of action in the future.

Low Intensity Ultrasound Induces Epithelial Cell Adhesion Responses.

In this study, we investigated the cellular mechanosensitive responses to a low intensity ultrasound (LIUS) stimulation (ISATA = 1 mW/cm2, pressure = 10 kPa). The dose and temporal effects at cell-substrate adhesion (CSA) at the basal level and cell-cell adhesion (CCA) at the apical level are reported in detail. A model of mouse mammary gland epithelial cells (EpH4) and the phosphorylation of mechanosensitive 130 kDa Crk-associated substrate (p130CAS) as an indicator for cellular responses were used. The intensity of phospho-p130CAS was found to be dependent on LIUS stress level, and the p130CAS was phosphorylated after 1 min stimulation at CSA. The phospho-p130CAS was also found to increase significantly at CCA upon LIUS stimulation. We confirmed that the cellular responses to ultrasound are immediate and dose dependent. Ultrasound affects not only CSA but also CCA. An E-cadherin knockout (EpH4ECad-/-) model also confirmed that phosphorylation of p130CAS at CCA is related to E-cadherins.

A P53-Independent DNA Damage Response Suppresses Oncogenic Proliferation and Genome Instability

The Mre11-Rad50-Nbs1 complex is a DNA double-strand break sensor that mediates a tumor-suppressive DNA damage response (DDR) in cells undergoing oncogenic stress, yet the mechanisms underlying this effect are poorly understood. Using a genetically inducible primary mammary epithelial cell model, we demonstrate that Mre11 suppresses proliferation and DNA damage induced by diverse oncogenic drivers through a p53-independent mechanism. Breast tumorigenesis models engineered to express a hypomorphic Mre11 allele exhibit increased levels of oncogene-induced DNA damage, R-loop accumulation, and chromosomal instability with a characteristic copy number loss phenotype. Mre11 complex dysfunction is identified in a subset of human triple-negative breast cancers and is associated with increased sensitivity to DNA-damaging therapy and inhibitors of ataxia telangiectasia and Rad3 related (ATR) and poly (ADP-ribose) polymerase (PARP). Thus, deficiencies in the Mre11-dependent DDR drive proliferation and genome instability patterns in p53-deficient breast cancers and represent an opportunity for therapeutic exploitation.

The opposing effects of interferon-beta and oncostatin-M as regulators of cancer stem cell plasticity in triple-negative breast cancer

BackgroundHighly aggressive, metastatic and therapeutically resistant triple-negative breast cancers (TNBCs) are often enriched for cancer stem cells (CSC). Cytokines within the breast tumor microenvironment (TME) influence the CSC state by regulating tumor cell differentiation programs. Two prevalent breast TME cytokines are oncostatin-M (OSM) and interferon-β (IFN-β). OSM is a member of the IL-6 family of cytokines and can drive the de-differentiation of TNBC cells to a highly aggressive CSC state. Conversely, IFN-β induces the differentiation of TNBC, resulting in the repression of CSC properties. Here, we assess how these breast TME cytokines influence CSC plasticity and clinical outcome.MethodsUsing transformed human mammary epithelial cell (HMEC) and TNBC cell models, we assessed the CSC markers and properties following exposure to OSM and/or IFN-β. CSC markers included CD24, CD44, and SNAIL; CSC properties included tumor sphere formation, migratory capacity, and tumor initiation.ResultsThere are three major findings from our study. First, exposure of purified, non-CSC to IFN-β prevents OSM-mediated CD44 and SNAIL expression and represses tumor sphere formation and migratory capacity. Second, during OSM-induced de-differentiation, OSM represses endogenous IFN-β mRNA expression and autocrine/paracrine IFN-β signaling. Restoring IFN-β signaling to OSM-driven CSC re-engages IFN-β-mediated differentiation by repressing OSM/STAT3/SMAD3-mediated SNAIL expression, tumor initiation, and growth. Finally, the therapeutic use of IFN-β to treat OSM-driven tumors significantly suppresses tumor growth.ConclusionsOur findings suggest that the levels of IFN-β and OSM in TNBC dictate the abundance of cells with a CSC phenotype. Indeed, TNBCs with elevated IFN-β signaling have repressed CSC properties and a better clinical outcome. Conversely, TNBCs with elevated OSM signaling have a worse clinical outcome. Likewise, since OSM suppresses IFN-β expression and signaling, our studies suggest that strategies to limit OSM signaling or activate IFN-β signaling will disengage the de-differentiation programs responsible for the aggressiveness of TNBCs.

A novel long non-coding RNA regulates the immune response in MAC-T cells and contributes to bovine mastitis.

The long non-coding RNAs (lncRNAs) are known to transcriptionally regulate a wide spectrum of diseases. Here, we screened for potentially functional lncRNAs in a mammary epithelial cell model of bovine mastitis by RNA-Seq technology and identified a class of previously undetected mastitis-related lncRNAs. A novel lncRNA was widely expressed in a variety of bovine tissues with diverse relative abundance and had a relatively low expression in mammary tissue. Given its predicted target gene is TUBA1C, we name it lncRNA-TUB. We found a higher expression of lncRNA-TUB in mammary epithelial cells that received a proinflammatory stimulus compared to normal cells. Knockout of lncRNA-TUB by the CRISPR/Cas9 system revealed that it plays crucial roles in the morphological shape, proliferation, migration and β-casein secretion of mammary epithelial cells. In addition, lncRNA-TUB mediates Escherichia coli-induced inflammatory factor secretion and Staphylococcus aureus adhesion to epithelial cells. Our results suggest that the lncRNAs identified here function in bovine mastitis, and that lncRNA-TUB affects the basic biological characteristics and functions of bovine mammary epithelial cells in inflammatory conditions, providing valuable insights into the mechanisms of bovine mastitis.

Abstract P1-06-08: A p53-independent DNA damage response that regulates breast cancer phenotypes

Abstract Defects in the DNA damage repair system result in increased genomic instability and have recently been implicated as being drivers of tumorigenesis in both familial and sporadic breast cancers. To maintain genomic integrity, cells have a DNA damage response (DDR) mechanism that functions to repair damaged DNA efficiently and commits cells to death if damage is irreparable. Failure of this mechanism results in genomic instability and cancer predisposition. Widespread chromosomal instability is a characteristic feature of Triple-Negative Breast Cancer (TNBC), making it difficult to decipher between genes that drive cancer development from those that play a bystander role. Little is known about what gives rise to the extensive genomic instability of TNBC, and presents a major deficit in our scientific and clinical knowledge. Oncogene induced hyper-proliferation results in replication-associated double strand breaks (DSBs) that engage an Mre11-Rad50-Nbs1 complex-dependent DDR. Classically, the oncogene induced DDR is believed to suppress tumorigenesis due to downstream activation of p53. Using genetically engineered primary mammary epithelial cell models, we demonstrate p53-independent effects of the Mre11-dependent DDR in suppressing proliferation and DNA damage induced by diverse oncogenic drivers. Single cell whole genome sequencing in Her2/Neu expressing primary mammary epithelial cells reveals a landscape of stochastic copy number aberrations induced by oncogenic stress that becomes enriched for a genomic scar pattern of larger-size deletions in cells with Mre11 hypomorphism. We identify Mre11 pathway hypomorphism in a subset of basal-like breast cancers (BLBC), which confers vulnerability to specific DNA damaging agents and DDR inhibitors in murine models of p53-deficient BLBC. Thus, assessing the functional status of the Mre11-dependent DDR pathway in p53-mutant breast cancers may provide an opportunity for therapeutic exploitation. Citation Format: Fagan-Solis KD, Simpson DA, Kapustina M, Martelotto L, Reis-Filho JS, Petrini JH, Gupta GP. A p53-independent DNA damage response that regulates breast cancer phenotypes [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-06-08.

A P53-Independent DNA Damage Response Suppresses Oncogenic Proliferation and Genome Instability

SummaryThe Mre11-Rad50-Nbs1 complex is a DNA double strand break sensor that mediates a tumor suppressive DNA damage response (DDR) in cells undergoing oncogenic stress, yet the mechanisms underlying this effect are poorly understood. Using a novel genetically inducible mammary epithelial cell model, we demonstrate that Mre11 suppresses proliferation and DNA damage induced by diverse oncogenic drivers through a p53-independent mechanism. Expression of a hypomorphic mutant allele of Mre11 exacerbates oncogene-driven increases in R-loops and results in a copy number loss phenotype enriched in gene-coding regions that is revealed by whole genome sequencing of mammary hyperplasia and breast tumors. Mre11 complex dysfunction is identified in a subset of human triple-negative breast cancers, and is associated with increased sensitivity to DNA damaging therapy and inhibitors of ATR and PARP. Thus, deficiencies in the Mre11-dependent DDR drive proliferation and genome instability patterns in p53-deficient breast cancers, and represent an opportunity for therapeutic exploitation.

Hydrostatic pressure incubation affects barrier properties of mammary epithelial cell monolayers, in vitro

During lactation, accumulation of milk in mammary glands (MG) causes hydrostatic pressure (HP) and concentration of bioactive compounds. Previously, a changed expression of tight junction (TJ) proteins was observed in mice MGs by accumulation of milk, in vivo. The TJ primarily determines the integrity of the MG epithelium. The present study questioned whether HP alone can affect the TJ in a mammary epithelial cell model, in vitro. Therefore, monolayers of HC11, a mammary epithelial cell line, were mounted into modified Ussing chambers and incubated with 10 kPa bilateral HP for 4 h. Short circuit current and transepithelial resistance were recorded and compared to controls, and TJ proteins were analyzed by Western blotting and immunofluorescent staining. In our first approach HC11 cells could withstand the pressure incubation and a downregulation of occludin was observed. In a second approach, using prolactin- and dexamethasone-induced cells, a decrease of short circuit current was observed, beginning after 2 h of incubation. With the addition of 1 mM barium chloride to the bathing solution the decrease could be blocked temporarily. On molecular level an upregulation of ZO-1 could be observed in hormone-induced cells, which was downregulated after the incubation with barium chloride. In conclusion, bilateral HP incubation affects mammary epithelial monolayers, in vitro. Both, the reduction of short circuit current and the change in TJ proteins may be interpreted as physiological requirements for lactation.

Leptin induces ROS via NOX5 in healthy and neoplastic mammary epithelial cells.

NADPH oxidase (NOX) complexes (a family of seven isoforms) drive cellular ROS production in patho-logical processes such as cancer. NOX-driven ROS production is involved in cell mechanisms from signalling to oxidative stress. Leptin, an adipokine overexpressed in obese patients, has been investigated in studies on breast carcinogenesis, but its effects on oxidative stress remain largely unexplored, especially in breast cancer. The study used three human mammary epithelial cell models presenting different neoplastic status (healthy primary HMECs, neoplastic MCF-7 cells and neoplastic MDA-MB-231 cells) to determine the effects of leptin on short-term ROS production and to characterize the enzymes involved. All three cell models significantly expressed NADPH oxidase isoform5 (NOX5) in our culture conditions. All models showed induced ROS production regardless of leptin concentration (10ng/ml mimicking good health, 100ng/ml mimicking obesity). Cell treatment with either siRNA against NOX5, NOX inhibitor DPI or a calcium channel blocker (verapamil) confirmed the putative involvement of the NOX5 isoenzyme in ROS production. Moreover, cell treatments suppressed ROS production under leptin at both concentrations. Neoplastic cells appeared unable to downregulate NOX5 mRNA expression under leptin. Leptin emerged as a potential activator of ROS production in human epithelial mammary cells, where the ROS production was apparently linked to NOX5 activation. This novel finding could shed light on the potential role of obesity-associated hyperleptinemia in mammary cells via the activation of NOXenzymes.