Transcription factor regulatory networks in mammary epithelial development and tumorigenesis

Tumor suppressor FRMD3 controls mammary epithelial cell fate determination via notch signaling pathway

The luminal-to-basal transition in mammary epithelial cells (MECs) is accompanied by changes in epithelial cell lineage plasticity; however, the underlying mechanism remains elusive. Here, we report that deficiency of Frmd3 inhibits mammary gland lineage development and induces stemness of MECs, subsequently leading to the occurrence of triple-negative breast cancer. Loss of Frmd3 in PyMT mice results in a luminal-to-basal transition phenotype. Single-cell RNA sequencing of MECs indicated that knockout of Frmd3 inhibits the Notch signaling pathway. Mechanistically, FERM domain-containing protein 3 (FRMD3) promotes the degradation of Disheveled-2 by disrupting its interaction with deubiquitinase USP9x. FRMD3 also interrupts the interaction of Disheveled-2 with CK1, FOXK1/2, and NICD and decreases Disheveled-2 phosphorylation and nuclear localization, thereby impairing Notch-dependent luminal epithelial lineage plasticity in MECs. A low level of FRMD3 predicts poor outcomes for breast cancer patients. Together, we demonstrated that FRMD3 is a tumor suppressor that functions as an endogenous activator of the Notch signaling pathway, facilitating the basal-to-luminal transformation in MECs.

GATA3 functions downstream of BRCA1 to promote DNA damage repair and suppress dedifferentiation in breast cancer

BACKGROUND

Inadequate DNA damage repair promotes aberrant differentiation of mammary epithelial cells. Mammary luminal cell fate is mainly determined by a few transcription factors including GATA3. We previously reported that GATA3 functions downstream of BRCA1 to suppress aberrant differentiation in breast cancer. How GATA3 impacts DNA damage repair preventing aberrant cell differentiation in breast cancer remains elusive. We previously demonstrated that loss of p18, a cell cycle inhibitor, in mice induces luminal-type mammary tumors, whereas depletion of either Brca1 or Gata3 in p18 null mice leads to basal-like breast cancers (BLBCs) with activation of epithelial-mesenchymal transition (EMT). We took advantage of these mutant mice to examine the role of Gata3 as well as the interaction of Gata3 and Brca1 in DNA damage repair in mammary tumorigenesis.

RESULTS

Depletion of Gata3, like that of Brca1, promoted DNA damage accumulation in breast cancer cells in vitro and in basal-like breast cancers in vivo. Reconstitution of Gata3 improved DNA damage repair in Brca1-deficient mammary tumorigenesis. Overexpression of GATA3 promoted homologous recombination (HR)-mediated DNA damage repair and restored HR efficiency of BRCA1-deficient cells. Depletion of Gata3 sensitized tumor cells to PARP inhibitor (PARPi), and reconstitution of Gata3 enhanced resistance of Brca1-deficient tumor cells to PARP inhibitor.

CONCLUSIONS

These results demonstrate that Gata3 functions downstream of BRCA1 to promote DNA damage repair and suppress dedifferentiation in mammary tumorigenesis and progression. Our findings suggest that PARP inhibitors are effective for the treatment of GATA3-deficient BLBCs.

Expression of type VI collagen α3 chain in canine mammary carcinomas

This study aimed to investigate the expression of type VI collagen α3 chain (COL6a3) in neoplastic cells of canine mammary gland carcinomas (CMGCs) using immunohistochemistry (IHC) and to evaluate the association between COL6a3 expression and tumor histological features, histological grades, and the differentiation status of neoplastic epithelial cells. COL6a3 expression in carcinoma cells was significantly associated with histologically low malignancy and low mitotic indices. In addition, COL6a3+ carcinoma cells were more frequently detected in simple carcinomas (tubular and tubulopapillary types) than in solid carcinomas. These findings indicate that reduced expression of COL6a3 in carcinoma cells contributes to the malignant phenotype in CMGCs. We also showed that COL6a3 expression in the carcinoma cells was more frequently detected in CK19+/CD49f + and/or CK19+/CK5+ tumors. In addition, COL6a3+/CK19+/CD49f + and COL6a3+/CK19+/CK5+ tumors consisted of CK19+/CD49f + and CK19+/CD49f- cells, and CK19+/CK5+ and CK19+/CK5- cells, respectively. Most of these tumors more frequently expressed GATA3, but not Notch1. These results indicate that COL6a3 is expressed in CMGCs containing both luminal progenitor-like and mature luminal-like cells and showing differentiation ability into mature luminal cells. It is possible that COL6 may be involved in the differentiation of luminal progenitor-like carcinoma cells into mature luminal-like carcinoma cells in CMGCs, which may suppresses the development of malignant phenotypes in CMGCs.

SIM2s directed Parkin-mediated mitophagy promotes mammary epithelial cell differentiation

The functionally differentiated mammary gland adapts to extreme levels of stress from increased demand for energy by activating specific protective mechanisms to support neonatal health. Here, we identify the breast tumor suppressor gene, single-minded 2 s (SIM2s) as a novel regulator of mitophagy, a key component of this stress response. Using tissue-specific mouse models, we found that loss of Sim2 reduced lactation performance, whereas gain (overexpression) of Sim2s enhanced and extended lactation performance and survival of mammary epithelial cells (MECs). Using an in vitro model of MEC differentiation, we observed SIM2s is required for Parkin-mediated mitophagy, which we have previously shown as necessary for functional differentiation. Mechanistically, SIM2s localizes to mitochondria to directly mediate Parkin mitochondrial loading. Together, our data suggest that SIM2s regulates the rapid recycling of mitochondria via mitophagy, enhancing the function and survival of differentiated MECs.

Effects of Hormones on Breast Development and Breast Cancer Risk in Transgender Women

Transgender women experience gender dysphoria due to a gender assignment at birth that is incongruent with their gender identity. Transgender people undergo different surgical procedures and receive sex steroids hormones to reduce psychological distress and to induce and maintain desired physical changes. These persons on feminizing hormones represent a unique population to study the hormonal effects on breast development, to evaluate the risk of breast cancer and perhaps to better understand the precise role played by different hormonal components. In MTF (male to female) patients, hormonal treatment usually consists of antiandrogens and estrogens. Exogenous hormones induce breast development with the formation of ducts and lobules and an increase in the deposition of fat. A search of the existing literature dedicated to hormone regimens for MTF patients, their impact on breast tissue (incidence and type of breast lesions) and breast cancer risk provided the available information for this review. The evaluation of breast cancer risk is currently complicated by the heterogeneity of administered treatments and a lack of long-term follow-up in the great majority of studies. Large studies with longer follow-up are required to better evaluate the breast cancer risk and to understand the precise mechanisms on breast development of each exogenous hormone.

Parabolic relationship between SMAD3 expression level and the reprogramming efficiency of goat induced mammary epithelial cells

Mammary epithelial cells are the only cells of mammary glands with lactation capacity. They are closely related to mammary development and milk yield. Our earlier studies showed that the transformation of goat fibroblasts into induced mammary epithelial cells (iMECs) was closely correlated with SMAD3 overexpression. Therefore, we further explored the role of SMAD3 on iMECs reprogramming in this study. The SMAD3 gene was overexpressed in goat ear fibroblasts using the tetracycline-induced expression method. The outcomes demonstrated that goat ear fibroblasts can be converted into iMECs by overexpressing the SMAD3 gene. In contrast, it was discovered that SMAD3 downregulation by RNA interference significantly decrease the reprogramming efficiency of iMECs. These results show that SMAD3 plays a key regulatory role in the reprogramming of iMECs. Surprisingly, we also found a parabolic relationship between SMAD3 expression level and iMECs reprogramming efficiency, and that the reprogramming efficiency was maximum when the addition of doxycycline concentration was 5 μg/ml. In light of this, our findings may offer new perspectives on the regulatory mechanism governing mammary epithelial cell fate in goats as well as a fresh approach to studying mammary development and differentiation in vitro.

The Mammary Gland: Basic Structure and Molecular Signaling during Development

The mammary gland is a compound, branched tubuloalveolar structure and a major characteristic of mammals. The mammary gland has evolved from epidermal apocrine glands, the skin glands as an accessory reproductive organ to support postnatal survival of offspring by producing milk as a source of nutrition. The mammary gland development begins during embryogenesis as a rudimentary structure that grows into an elementary branched ductal tree and is embedded in one end of a larger mammary fat pad at birth. At the onset of ovarian function at puberty, the rudimentary ductal system undergoes dramatic morphogenetic change with ductal elongation and branching. During pregnancy, the alveolar differentiation and tertiary branching are completed, and during lactation, the mature milk-producing glands eventually develop. The early stages of mammary development are hormonal independent, whereas during puberty and pregnancy, mammary gland development is hormonal dependent. We highlight the current understanding of molecular regulators involved during different stages of mammary gland development.

Loss of function of GATA3 induces basal-like mammary tumors

Purpose: GATA3 is a transcription factor essential for mammary luminal epithelial cell differentiation. Expression of GATA3 is absent or significantly reduced in basal-like breast cancers. Gata3 loss-of-function impairs cell proliferation, making it difficult to investigate the role of GATA3 deficiency in vivo. We previously demonstrated that CDK inhibitor p18^INK4c (p18) is a downstream target of GATA3 and restrains mammary epithelial cell proliferation and tumorigenesis. Whether and how loss-of-function of GATA3 results in basal-like breast cancers remains elusive.

Methods: We generated mutant mouse strains with heterozygous germline deletion of Gata3 in p18 deficient backgrounds and developed a Gata3 depleted mammary tumor model system to determine the role of Gata3 loss in controlling cell proliferation and aberrant differentiation in mammary tumor development and progression.

Results: Haploid loss of Gata3 reduced mammary epithelial cell proliferation with induction of p18, impaired luminal differentiation, and promoted basal differentiation in mammary glands. p18 deficiency induced luminal type mammary tumors and rescued the proliferative defect caused by haploid loss of Gata3. Haploid loss of Gata3 accelerated p18 deficient mammary tumor development and changed the properties of these tumors, resulting in their malignant and luminal-to-basal transformation. Expression of Gata3 negatively correlated with basal differentiation markers in MMTV-PyMT mammary tumor cells. Depletion of Gata3 in luminal tumor cells also reduced cell proliferation with induction of p18 and promoted basal differentiation. We confirmed that expression of GATA3 and basal markers are inversely correlated in human basal-like breast cancers.

Conclusions: This study provides the first genetic evidence demonstrating that loss-of-function of GATA3 directly induces basal-like breast cancer. Our finding suggests that basal-like breast cancer may also originate from luminal type cancer.

GATA3 functions downstream of BRCA1 to suppress EMT in breast cancer

Purpose: Functional loss of BRCA1 is associated with poorly differentiated and metastatic breast cancers that are enriched with cancer stem cells (CSCs). CSCs can be generated from carcinoma cells through an epithelial-mesenchymal transition (EMT) program. We and others have previously demonstrated that BRCA1 suppresses EMT and regulates the expression of multiple EMT-related transcription factors. However, the downstream mediators of BRCA1 function in EMT suppression remain elusive. Methods: Depletion of BRCA1 or GATA3 activates p18INK4C , a cell cycle inhibitor which inhibits mammary epithelial cell proliferation. We have therefore created genetically engineered mice with Brca1 or Gata3 loss in addition to deletion of p18INK4C , to rescue proliferative defects caused by deficiency of Brca1 or Gata3. By using these mutant mice along with human BRCA1 deficient as well as proficient breast cancer tissues and cells, we investigated and compared the role of Brca1 and Gata3 loss in the activation of EMT in breast cancers. Results: We discovered that BRCA1 and GATA3 expressions were positively correlated in human breast cancer. Depletion of BRCA1 stimulated methylation of GATA3 promoter thereby repressing GATA3 transcription. We developed Brca1 and Gata3 deficient mouse system. We found that Gata3 deficiency in mice induced poorly-differentiated mammary tumors with the activation of EMT and promoted tumor initiating and metastatic potential. Gata3 deficient mammary tumors phenocopied Brca1 deficient tumors in the induction of EMT under the same genetic background. Reconstitution of Gata3 in Brca1-deficient tumor cells activated mesenchymal-epithelial transition, suppressing tumor initiation and metastasis. Conclusions: Our finding, for the first time, demonstrates that GATA3 functions downstream of BRCA1 to suppress EMT in controlling mammary tumorigenesis and metastasis.

Inducible knockout of ∆Np63 alters cell polarity and metabolism during pubertal mammary gland development

The ∆Np63 isoform of the p53-family transcription factor Trp63 is a key regulator of mammary epithelial stem cells that is involved in breast cancer development. To investigate the role of ∆Np63 at different stages of normal mammary gland development, we generated a ∆Np63-inducible conditional knockout (cKO) mouse model. We demonstrate that the deletion of ∆Np63 at puberty results in depletion of mammary stem cell-enriched basal cells, reduces expression of E-cadherin and β-catenin, and leads to a closed ductal lumen. RNA-sequencing analysis reveals reduced expression of oxidative phosphorylation (OXPHOS)-associated proteins and desmosomal polarity proteins. Functional assays show reduced numbers of mitochondria in the mammary epithelial cells of ΔNp63 cKO compared to wild-type, supporting the reduced OXPHOS phenotype. These findings identify a novel role for ∆Np63 in cellular metabolism and mammary epithelial cell polarity.

Focus on the glycerophosphocholine pathway in choline phospholipid metabolism of cancer

Activated choline metabolism is a hallmark of carcinogenesis and tumor progression, which leads to elevated levels of phosphocholine and glycerophosphocholine in all types of cancer tested so far. Magnetic resonance spectroscopy applications have played a key role in detecting these elevated choline phospholipid metabolites. To date, the majority of cancer-related studies have focused on phosphocholine and the Kennedy pathway, which constitutes the biosynthesis pathway for membrane phosphatidylcholine. Fewer and more recent studies have reported on the importance of glycerophosphocholine in cancer. In this review article, we summarize the recent literature on glycerophosphocholine metabolism with respect to its cancer biology and its detection by magnetic resonance spectroscopy applications.

Deciphering the roles of lncRNAs in breast development and disease

Breast cancer is the second leading cause of cancer related deaths in women. It is therefore important to understand the mechanisms underlying breast cancer development as well as raises the need for enhanced, non-invasive strategies for novel prognostic and diagnostic methods. The emergence of long non-coding RNAs (lncRNAs) as potential key players in neoplastic disease has received considerable attention over the past few years. This relatively new class of molecular regulators has been shown from ongoing research to act as critical players for key biological processes. Deregulated expression levels of lncRNAs have been observed in a number of cancers including breast cancer. Furthermore, lncRNAs have been linked to breast cancer initiation, progression, metastases and to limit sensitivity to certain targeted therapeutics. In this review we provide an update on the lncRNAs associated with breast cancer and mammary gland development and illustrate the versatility of such lncRNAs in gene control, differentiation and development both in normal physiological conditions and in diseased states. We also highlight the therapeutic and diagnostic potential of lncRNAs in cancer.

Mammary gland stem cells and their application in breast cancer

The mammary gland is an organ comprising two primary lineages, specifically the inner luminal and the outer myoepithelial cell layers. Mammary gland stem cells (MaSCs) are highly dynamic and self-renewing, and can give rise to these mammary gland lineages. The lineages are responsible for gland generation during puberty as well as expansion during pregnancy. In recent years, researchers have focused on understanding how MaSCs are regulated during mammary gland development and transformation of breast cancer. Here, we summarize the identification of MaSCs, and how they are regulated by the signaling transduction pathways, mammary gland microenvironment, and non-coding RNAs (ncRNAs). Moreover, we debate the evidence for their serving as the origin of breast cancer, and discuss the therapeutic perspectives of targeting breast cancer stem cells (BCSCs). In conclusion, a better understanding of the key regulators of MaSCs is crucial for the clinical treatment of breast cancer.

An essential role of CBL and CBL-B ubiquitin ligases in mammary stem cell maintenance

The ubiquitin ligases CBL and CBL-B are negative regulators of tyrosine kinase signaling with established roles in the immune system. However, their physiological roles in epithelial tissues are unknown. Here, we used MMTV-Cre-mediated Cbl gene deletion on a Cbl-b null background, as well as a tamoxifen-inducible mammary stem cell (MaSC)-specific Cbl and Cbl-b double knockout (Cbl/Cbl-b DKO) using Lgr5-EGFP-IRES-CreERT2, to demonstrate a mammary epithelial cell-autonomous requirement of CBL and CBL-B in the maintenance of MaSCs. Using a newly engineered tamoxifen-inducible Cbl and Cbl-b deletion model with a dual fluorescent reporter (Cbl^flox/flox; Cbl-b^flox/flox; Rosa26-CreERT; mT/mG), we show that Cbl/Cbl-b DKO in mammary organoids leads to hyperactivation of AKT-mTOR signaling with depletion of MaSCs. Chemical inhibition of AKT or mTOR rescued MaSCs from Cbl/Cbl-b DKO-induced depletion. Our studies reveal a novel, cell-autonomous requirement of CBL and CBL-B in epithelial stem cell maintenance during organ development and remodeling through modulation of mTOR signaling.

The Hippo kinases LATS1 and 2 control human breast cell fate via crosstalk with ERα

Cell fate perturbations underlie many human diseases, including breast cancer. Unfortunately, the mechanisms by which breast cell fate are regulated are largely unknown. The mammary gland epithelium consists of differentiated luminal epithelial and basal myoepithelial cells, as well as undifferentiated stem cells and more restricted progenitors. Breast cancer originates from this epithelium, but the molecular mechanisms that underlie breast epithelial hierarchy remain ill-defined. Here, we use a high-content confocal image-based short hairpin RNA screen to identify tumour suppressors that regulate breast cell fate in primary human breast epithelial cells. We show that ablation of the large tumour suppressor kinases (LATS) 1 and 2 (refs 5, 6), which are part of the Hippo pathway, promotes the luminal phenotype and increases the number of bipotent and luminal progenitors, the proposed cells-of-origin of most human breast cancers. Mechanistically, we have identified a direct interaction between Hippo and oestrogen receptor-α (ERα) signalling. In the presence of LATS, ERα was targeted for ubiquitination and Ddb1-cullin4-associated-factor 1 (DCAF1)-dependent proteasomal degradation. Absence of LATS stabilized ERα and the Hippo effectors YAP and TAZ (hereafter YAP/TAZ), which together control breast cell fate through intrinsic and paracrine mechanisms. Our findings reveal a non-canonical (that is, YAP/TAZ-independent) effect of LATS in the regulation of human breast cell fate.

A contrasting function for miR-137 in embryonic mammogenesis and adult breast carcinogenesis

MicroRNAs are differentially expressed in breast cancer cells and have been implicated in cancer formation, tumour invasion and metastasis. We investigated the miRNA expression profiles in the developing mammary gland. MiR-137 was expressed prominently in the developing mammary gland. When the miR-137 was over-expressed in the embryo, the mammary epithelium became thickened. Moreover, genes associated with mammary gland formation such as Tbx3 and Lef1 were not expressed. This suggests that miR-137 induces gland formation and invasion. When miR-137 was over-expressed in MDA-MB-231 cells, their ability to form tumours in adult mice was significantly reduced. These data support miR-137 decides epithelial cell behavior in the human breast cancer. It also suggests that miR-137 is a potential therapeutic target for amelioration of breast cancer progression.

Molecular aspects of adipoepithelial transdifferentiation in mouse mammary gland

The circular, reversible conversion of the mammary gland during pregnancy and involution is a paradigm of physiological tissue plasticity. The two most prominent cell types in mammary gland, adipocytes and epithelial cells, interact in an orchestrated way to coordinate this process. Previously, we showed that this conversion is at least partly achieved by reciprocal transdifferentiation between mammary adipocytes and lobulo-alveolar epithelial cells. Here, we aim to shed more light on the regulators of mammary transdifferentiation. Using immunohistochemistry with cell type-specific lipid droplet-coating markers (Perilipin1 and 2), we show that cells with an intermediate adipoepithelial phenotype exist during and after pregnancy. Nuclei of cells with similar transitional structural characteristics are highly positive for Elf5, a master regulator of alveologenesis. In cultured adipocytes, we could show that transient and stable ectopic expression of Elf5 induces expression of the milk component whey acidic protein, although the general adipocyte phenotype is not affected suggesting that additional pioneering factors are necessary. Furthermore, the lack of transdifferentiation of adipocytes during pregnancy after clearing of the epithelial compartment indicates that transdifferentiation signals must emanate from the epithelial part. To explore candidate genes potentially involved in the transdifferentiation process, we devised a high-throughput gene expression study to compare cleared mammary fat pads with developing, contralateral controls at several time points during pregnancy. Incorporation of bioinformatic predictions of secretory proteins provides new insights into possible paracrine signaling pathways and downstream transdifferentiation factors. We discuss a potential role for osteopontin (secreted phosphoprotein 1 [Spp1]) signaling through integrins to induce adipoepithelial transdifferentiation.

The co-factor of LIM domains (CLIM/LDB/NLI) maintains basal mammary epithelial stem cells and promotes breast tumorigenesis

Mammary gland branching morphogenesis and ductal homeostasis relies on mammary stem cell function for the maintenance of basal and luminal cell compartments. The mechanisms of transcriptional regulation of the basal cell compartment are currently unknown. We explored these mechanisms in the basal cell compartment and identified the Co-factor of LIM domains (CLIM/LDB/NLI) as a transcriptional regulator that maintains these cells. Clims act within the basal cell compartment to promote branching morphogenesis by maintaining the number and proliferative potential of basal mammary epithelial stem cells. Clim2, in a complex with LMO4, supports mammary stem cells by directly targeting the Fgfr2 promoter in basal cells to increase its expression. Strikingly, Clims also coordinate basal-specific transcriptional programs to preserve luminal cell identity. These basal-derived cues inhibit epidermis-like differentiation of the luminal cell compartment and enhance the expression of luminal cell-specific oncogenes ErbB2 and ErbB3. Consistently, basal-expressed Clims promote the initiation and progression of breast cancer in the MMTV-PyMT tumor model, and the Clim-regulated branching morphogenesis gene network is a prognostic indicator of poor breast cancer outcome in humans.

Recent advancements in mammary gland biology demonstrate conflicting models in maintenance of basal and luminal cell compartments by either unipotent or bipotent mammary stem cells. However, the molecular mechanisms underlying control of the basal cell compartment, including stem cells, remain poorly understood. Here we explore the currently unknown transcriptional mechanisms of basal stem cell (BSC) maintenance, in addition to addressing the role of the basal cell compartment in preserving luminal cell fate and promoting development of human breast tumors of luminal origin. We discover a novel function for the Co-factor of LIM domains (Clim) transcriptional regulator in promoting mammary gland branching morphogenesis and breast tumorigenesis through maintenance of the basal stem cell population. The transcriptional networks coordinated by Clims in basal mammary epithelial cells also preserve the identity of luminal epithelial cells, demonstrating a crosstalk between these two cellular compartments. Furthermore, we correlate developmental gene expression data with human breast cancer to investigate the role of developmental pathways during the initiation and progression of breast cancer. The gene regulatory networks identified during development, including those specifically coordinated by Clims, correlate with breast cancer patient outcome, suggesting these genes play an important role in the progression of breast cancer.

JARID1B is a luminal lineage-driving oncogene in breast cancer

Recurrent mutations in histone-modifying enzymes imply key roles in tumorigenesis, yet their functional relevance is largely unknown. Here, we show that JARID1B, encoding a histone H3 lysine 4 (H3K4) demethylase, is frequently amplified and overexpressed in luminal breast tumors and a somatic mutation in a basal-like breast cancer results in the gain of unique chromatin binding and luminal expression and splicing patterns. Downregulation of JARID1B in luminal cells induces basal genes expression and growth arrest, which is rescued by TGFβ pathway inhibitors. Integrated JARID1B chromatin binding, H3K4 methylation, and expression profiles suggest a key function for JARID1B in luminal cell-specific expression programs. High luminal JARID1B activity is associated with poor outcome in patients with hormone receptor-positive breast tumors.

Prognostic features of signal transducer and activator of transcription 3 in an ER(+) breast cancer model system

The aberrantly expressed signal transducer and activator of transcription 3 (STAT3) predicts poor prognosis, primarily in estrogen receptor positive (ER(+)) breast cancers. Activated STAT3 is overexpressed in luminal A subtype cells. The mechanisms contributing to the prognosis and/or subtype relevant features of STAT3 in ER(+) breast cancers are through multiple interacting regulatory pathways, including STAT3-MYC, STAT3-ERα, and STAT3-MYC-ERα interactions, as well as the direct action of activated STAT3. These data predict malignant events, treatment responses and a novel enhancer of tamoxifen resistance. The inferred crosstalk between ERα and STAT3 in regulating their shared target gene-METAP2 is partially validated in the luminal B breast cancer cell line-MCF7. Taken together, we identify a poor prognosis relevant gene set within the STAT3 network and a robust one in a subset of patients. VEGFA, ABL1, LYN, IGF2R and STAT3 are suggested therapeutic targets for further study based upon the degree of differential expression in our model.

Stem cell research: a novel boulevard towards improved bovine mastitis management

The dairy industry is a multi-billion dollar industry catering the nutritional needs of all age groups globally through the supply of milk. Clinical mastitis has a severe impact on udder tissue and is also an animal welfare issue. Moreover, it significantly reduces animal value and milk production. Mammary tissue damage reduces the number and activity of epithelial cells and consequently contributes to decreased milk production. The high incidence, low cure rate of this highly economic and sometimes deadly disease is an alarming for dairy sector as well as policy makers. Bovine mammary epithelial cells (MECs) and their stem cells are very important in milk production and bioengineering. The adult mammary epithelium consists of two main cell types; an inner layer of luminal epithelial cells, which produce the milk during lactation, and an outer layer of myoepithelial cells resting on a basement membrane, which are responsible for pushing the milk through the ductal network to the teat cistern. Inner layer of columner/luminal cells of bovine MECs, is characterized by cytokeratin18, 19 (CK18, CK19) and outer layer such as myoepithelial cells which are characterized by CK14, α-smooth muscle actin (α-SMA) and p63. Much work has been done in mouse and human, on mammary gland stem cell research, particularly in cancer therapy, but stem cell research in bovine is still in its infancy. Such stem/progenitor cell discoveries in human and mouse mammary gland bring some hope for application in bovines. These progenitors may be therapeutically adopted to correct the structural/cytological defects in the bovine udder due to mastitis. In the present review we focused on various kinds of stem/progenitor cells which can have therapeutic utility and their possibilities to use as a potential stem cell therapy in the management of bovine post-mastitis damage in orders to restore milk production. The possibilities of bovine mammary stem cell therapy offers significant potential for regeneration of tissues that can potentially replace/repair diseased and damaged tissue through differentiation into epithelial, myoepithelial and/or cuboidal/columnar cells in the udder with minimal risk of rejection and side effects.

RUNX2 in mammary gland development and breast cancer

Runx2 is best known as an essential factor in osteoblast differentiation and bone development but, like many other transcription factors involved in development, is known to operate over a much wider tissue range. Our understanding of these other aspects of Runx2 function is still at a relatively early stage and the importance of its role in cell fate decisions and lineage maintenance in non-osseous tissues is only beginning to emerge. One such tissue is the mammary gland, where Runx2 is known to be expressed and participate in the regulation of mammary specific genes. Furthermore, differential and temporal expression of this gene is observed during mammary epithelial differentiation in vivo, strongly indicative of an important functional role. Although the precise nature of that role remains elusive, preliminary evidence hints at possible involvement in the regulation of mammary stem and/or progenitor cells. As with many genes important in regulating cell fate, RUNX2 has also been linked to metastatic cancer where in some established breast cell lines, retention of expression is associated with a more invasive phenotype. More recently, expression analysis has been extended to primary breast cancers where high levels of RUNX2 align with a specific subtype of the disease. That RUNX2 expression correlates with the so called "Triple Negative" subtype is particularly interesting given the known cross talk between Runx2 and estrogen receptor signaling pathways. This review summaries our current understanding of Runx2 in mammary gland development and cancer, and postulates a role that may link both these processes.

A novel role of microRNA146b in promoting mammary alveolar progenitor cell maintenance

In this report, we have shown that miR146b promotes the maintenance of pregnancy-derived mammary luminal alveolar progenitors. MiR146b expression was significantly higher in the mammary glands of pregnant and lactating mice than in virgin mice. Furthermore, miR146b levels were significantly higher in mouse mammary glands exposed to the sex hormones, estrogen and progesterone, compared with those of untreated control animals. Pregnancy-derived primary mouse mammary epithelial cells in which miR146b was knocked down showed a significant reduction in the number of hollow acinar organoid structures formed on three-dimensional Matrigel and in β-casein expression. This demonstrates that miR146b promotes the maintenance of pregnancy-derived mammary luminal alveolar progenitors. It has been shown that mouse mammary luminal progenitors give rise to hollow organoid structures, whereas solid organoid structures are derived from stem cells. Among several miR146b targets, miR146b knockdown resulted in preferential STAT3β overexpression. In the primary mouse mammary epithelial cells, overexpression of STAT3β isoform caused mammary epithelial cell death and a significant reduction in β-casein mRNA expression. Therefore, we conclude that during pregnancy miR146b is involved in luminal alveolar progenitor cell maintenance, at least partially, by regulating STAT3β.

In utero and lactational exposure to vinclozolin and genistein induces genomic changes in the rat mammary gland

Exposure to low doses of environmental estrogens such as bisphenol A and genistein (G) alters mammary gland development. The effects of environmental anti-androgens, such as the fungicide vinclozolin (V), on mammary gland morphogenesis are unknown. We previously reported that perinatal exposure to G, V, and the GV combination causes histological changes in the mammary gland during the peripubertal period, suggesting alterations to the peripubertal hormone response. We now investigate whether perinatal exposure to these compounds alters the gene expression profiles of the developing glands to identify the dysregulated signaling pathways and the underlying mechanisms. G, V, or GV (1 mg/kg body weight per day) was added to diet of Wistar rats, from conception to weaning; female offspring mammary glands were collected at postnatal days (PNDs) 35 and 50. Genes displaying differential expression and belonging to different functional categories were validated by quantitative PCR and immunocytochemistry. At PND35, G had little effect; the slight changes noted were in genes related to morphogenesis. The changes following exposure to V concerned the functional categories associated with development (Cldn1, Krt17, and Sprr1a), carbohydrate metabolism, and steroidogenesis. The GV mixture upregulated genes (Krt17, Pvalb, and Tnni2) involved in muscle development, indicating effects on myoepithelial cells during mammary gland morphogenesis. Importantly, at PND50, cycling females exposed to GV showed an increase in the expression of genes (Csn2, Wap, and Elf5) related to differentiation, consistent with the previously reported abnormal lobuloalveolar development previously described. Thus, perinatal exposure to GV alters the mammary gland hormone response differently at PND35 (puberty) and in animals with established cycles.

Atbf1 regulates pubertal mammary gland development likely by inhibiting the pro-proliferative function of estrogen-ER signaling

ATBF1 is a candidate tumor suppressor that interacts with estrogen receptor (ER) to inhibit the function of estrogen-ER signaling in gene regulation and cell proliferation control in human breast cancer cells. We therefore tested whether Atbf1 and its interaction with ER modulate the development of pubertal mammary gland, where estrogen is the predominant steroid hormone. In an in vitro model of cell differentiation, i.e., MCF10A cells cultured in Matrigel, ATBF1 expression was significantly increased, and knockdown of ATBF1 inhibited acinus formation. During mouse mammary gland development, Atbf1 was expressed at varying levels at different stages, with higher levels during puberty, lower during pregnancy, and the highest during lactation. Knockout of Atbf1 at the onset of puberty enhanced ductal elongation and bifurcation and promoted cell proliferation in both ducts and terminal end buds of pubertal mammary glands. Enhanced cell proliferation primarily occurred in ER-positive cells and was accompanied by increased expression of ER target genes. Furthermore, inactivation of Atbf1 reduced the expression of basal cell markers (CK5, CK14 and CD44) but not luminal cell markers. These findings indicate that Atbf1 plays a role in the development of pubertal mammary gland likely by modulating the function of estrogen-ER signaling in luminal cells and by modulating gene expression in basal cells.

Elf5 regulates mammary gland stem/progenitor cell fate by influencing notch signaling

The transcription factor E74-like factor 5 (Elf5) functions downstream of the prolactin receptor signaling pathway and plays an important role in mammary gland development. Using conditional mouse knockouts, we have previously shown that Elf5-null mammary glands exhibit a complete failure of alveologenesis during pregnancy. The Elf5-null developmental phenotype is mediated through alteration in the expression of several critical genes involved in alveologenesis, particularly those belonging to the JAK/STAT pathway. Here, we demonstrate that in addition to regulating terminal differentiation of alveolar cells, Elf5 also plays a critical role in determining cell fate and in regulating the stem/progenitor function of the mammary epithelium. Targeted deletion of Elf5 in the mammary glands leads to accumulation of cell types with dual luminal/basal properties such as coexpression of K8 and K14 and an increase in CD61(+) luminal progenitor population during pregnancy. Further interrogation suggests that the abnormal increase in K14(+) K8(+) cells may represent the CD61(+) luminal progenitors blocked in differentiation. Remarkably, Elf5 deficiency in mammary epithelium also triggers an increase of adult mammary stem activity as evidenced by the accumulation of mammary stem cell (MaSC)-enriched cell population in both pregnant and virgin mice and further confirmed by mammosphere and transplantation assays. Additional support for this phenotype comes from the enriched MaSC gene signature based on transcriptomic analysis of the Elf5-null mammary gland. Finally, our biochemical studies suggest that Elf5 loss leads to hyperactivation of the Notch signaling pathway, which might constitute in part, the underlying molecular mechanism for the altered cell lineage decisions in Elf5-null mammary epithelial cells.

FoxM1 regulates mammary luminal cell fate

Elevated expression of FoxM1 in breast cancer correlates with an undifferentiated tumor phenotype and a negative clinical outcome. However, a role for FoxM1 in regulating mammary differentiation was not known. Here, we identify another function of FoxM1, the ability to act as a transcriptional repressor, which plays an important role in regulating the differentiation of luminal epithelial progenitors. Regeneration of mammary glands with elevated levels of FoxM1 leads to aberrant ductal morphology and expansion of the luminal progenitor pool. Conversely, knockdown of FoxM1 results in a shift toward the differentiated state. FoxM1 mediates these effects by repressing the key regulator of luminal differentiation, GATA-3. Through association with DNMT3b, FoxM1 promotes methylation of the GATA-3 promoter in an Rb-dependent manner. This study identifies FoxM1 as a critical regulator of mammary differentiation with significant implications for the development of aggressive breast cancers.

Down-regulation of AP-4 inhibits proliferation, induces cell cycle arrest and promotes apoptosis in human gastric cancer cells

Background

AP-4 belongs to the basic helix-loop-helix leucine-zipper subgroup; it controls target gene expression, regulates growth, development and cell apoptosis and has been implicated in tumorigenesis. Our previous studies indicated that AP-4 was frequently overexpressed in gastric cancers and may be associated with the poor prognosis. The purpose of this study is to examine whether silencing of AP-4 can alter biological characteristics of gastric cancer cells.

Methods

Two specific siRNAs targeting AP-4 were designed, synthesized, and transfected into gastric cancer cell lines and human normal mucosa cells. AP-4 expression was measured with real-time quantitative PCR and Western blot. Cell proliferation and chemo-sensitivity were detected by CCK-8 assay. Cell cycle assay and apoptosis assay were performed by flow cytometer, and relative expression of cell cycle regulators were detected by real-time quantitative PCR and Western blot, expression of the factors involved in the apoptosis pathway were examined in mRNA and protein level.

Results

The expression of AP-4 was silenced by the siRNAs transfection and the effects of AP-4 knockdown lasted 24 to 96 hrs. The siRNA-mediated silencing of AP-4 suppressed the cellular proliferation, induced apoptosis and sensitized cancer cells to anticancer drugs. In addition, the expression level of p21, p53 and Caspase-9 were increased when AP-4 was knockdown, but the expression of cyclin D1, Bcl-2 and Bcl-x_L was inhibited. It didn't induce cell cycle arrest when AP-4 was knockdown in p53 defect gastric cancer cell line Kato-III.

Conclusions

These results illustrated that gene silencing of AP-4 can efficiently inhibited cell proliferation, triggered apoptosis and sensitized cancer cells to anticancer drugs in vitro, suggesting that AP-4 siRNAs mediated silencing has a potential value in the treatment of human gastric cancer.

Noncoding RNAs involved in mammary gland development and tumorigenesis: there's a long way to go

The mammalian genome encodes thousands of noncoding RNAs. These noncoding transcripts are broadly categorized into short noncoding RNAs, such as microRNAs (miRNAs), and long noncoding RNAs (lncRNAs) of greater than 200 nt. While the role of miRNAs in development and cancer biology has been extensively studied, much less is known about the vast majority of noncoding transcripts represented by lncRNAs. LncRNAs are emerging as key regulators of developmental processes and as such, their frequent misregulation in tumorigenesis and disease in not unexpected. The role of lncRNAs in mammary gland development and breast cancer is just beginning to be elucidated. This review will discuss the role of lncRNAs in mammalian and mammary gland development. In addition, we will review the contributions of lncRNAs to the stepwise progression of tumorigenesis, highlighting the role of lncRNAs in breast cancer.

Sustained activation of the HER1-ERK1/2-RSK signaling pathway controls myoepithelial cell fate in human mammary tissue

Human mammary glands arise from multipotent progenitor cells, which likely respond both to cell-autonomous and to extrinsic cues. However, the identity of these cues and how they might act remain unclear. We analyzed HER1 ligand effects on mammary morphogenesis using a three-dimensional organoid model generated from human breast tissue that recapitulates both qualitatively and quantitatively the normal ductal network in situ. Strikingly, different HER1 ligands generate distinct patterns of cell fate. Epidermal growth factor (EGF) causes a massive expansion of the myoepithelial lineage. Amphiregulin, in contrast, enables normal ductal development. These differences cannot be ascribed to preferential apoptosis or proliferation of differentiated cell populations, but are dependent on HER1 signal intensity. Inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) effector RSK prevents the EGF-induced myoepithelial expansion. Notably, mouse mammary organoids are much less responsive to HER1 ligands. Little is known about the myoepithelial lineage or about growth factor effects on mammary progenitor differentiation, and our studies provide an important window into human mammary development that reveals unexpected differences from the mouse model.

Transcription factor networks as targets for therapeutic intervention of cancer: the breast cancer paradigm

It has long been shown that many of the presently used anticancer drugs exert their effects partly through modulating the activity of vital transcription factors. The intricacy of transcriptional regulation still represents the main obstacle for the design of transcription factor-directed agents. Systematic mapping of tumor-specific transcriptional networks and application of new molecular tools have reinforced research interest and efforts in this venue. The case of breast cancer is discussed as a representative example.