C/EBPbeta, but not C/EBPalpha, is essential for ductal morphogenesis, lobuloalveolar proliferation, and functional differentiation in the mouse mammary gland

Ehf controls mammary alveolar lineage differentiation and is a putative suppressor of breast tumorigenesis

The transcription factor EHF is highly expressed in the lactating mammary gland, but its role in mammary development and tumorigenesis is not fully understood. Utilizing a mouse model of Ehf deletion, herein, we demonstrate that loss of Ehf impairs mammary lobuloalveolar differentiation at late pregnancy, indicated by significantly reduced levels of milk genes and milk lipids, fewer differentiated alveolar cells, and an accumulation of alveolar progenitor cells. Further, deletion of Ehf increased proliferative capacity and attenuated prolactin-induced alveolar differentiation in mammary organoids. Ehf deletion also increased tumor incidence in the MMTV-PyMT mammary tumor model and increased the proliferative capacity of mammary tumor organoids, while low EHF expression was associated with higher tumor grade and poorer outcome in luminal A and basal human breast cancers. Collectively, these findings establish EHF as a non-redundant regulator of mammary alveolar differentiation and a putative suppressor of mammary tumorigenesis.

Molecular complexity of mammary glands development: a review of lactogenic differentiation in epithelial cells

The mammary gland is a dynamic organ with various physiological processes like cellular proliferation, differentiation, and apoptosis during the pregnancy-lactation-involution cycle. It is essential to understand the molecular changes during the lactogenic differentiation of mammary epithelial cells (MECs, the milk-synthesizing cells). The MECs are organized as luminal milk-secreting cells and basal myoepithelial cells (responsible for milk ejection by contraction) that form the alveoli. The branching morphogenesis and lactogenic differentiation of the MECs prepare the gland for lactation. This process is governed by many molecular mediators including hormones, growth factors, cytokines, miRNAs, regulatory proteins, etc. Interestingly, various signalling pathways guide lactation and understanding these molecular transitions from pregnancy to lactation will help researchers design further research. Manipulation of genes responsible for milk synthesis and secretion will promote augmentation of milk yield in dairy animals. Identifying protein signatures of lactation will help develop strategies for persistent lactation and shortening the dry period in farm animals. The present review article discusses in details the physiological and molecular changes occurring during lactogenic differentiation of MECs and the associated hormones, regulatory proteins, miRNAs, and signalling pathways. An in-depth knowledge of the molecular events will aid in developing engineered cellular models for studies related to mammary gland diseases of humans and animals.

Cell-specific and shared regulatory elements control a multigene locus active in mammary and salivary glands

Regulation of high-density loci harboring genes with different cell-specificities remains a puzzle. Here we investigate a locus that evolved through gene duplication and contains eight genes and 20 candidate regulatory elements, including one super-enhancer. Casein genes (Csn1s1, Csn2, Csn1s2a, Csn1s2b, Csn3) are expressed in mammary glands, induced 10,000-fold during pregnancy and account for 50% of mRNAs during lactation, Prr27 and Fdcsp are salivary-specific and Odam has dual specificity. We probed the function of 12 candidate regulatory elements, individually and in combination, in the mouse genome. The super-enhancer is essential for the expression of Csn3, Csn1s2b, Odam and Fdcsp but largely dispensable for Csn1s1, Csn2 and Csn1s2a. Csn3 activation also requires its own local enhancer. Synergism between local enhancers and cytokine-responsive promoter elements facilitates activation of Csn2 during pregnancy. Our work identifies the regulatory complexity of a multigene locus with an ancestral super-enhancer active in mammary and salivary tissue and local enhancers and promoter elements unique to mammary tissue.

Cancer invasion and metastasis: Insights from murine pubertal mammary gland morphogenesis

Cancer invasion and metastasis accounts for the majority of cancer related mortality. A better understanding of the players that drive the aberrant invasion and migration of tumors cells will provide critical targets to inhibit metastasis. Postnatal pubertal mammary gland morphogenesis is characterized by highly proliferative, invasive, and migratory normal epithelial cells. Identifying the molecular regulators of pubertal gland development is a promising strategy since tumorigenesis and metastasis is postulated to be a consequence of aberrant reactivation of developmental stages. In this review, we summarize the pubertal morphogenesis regulators that are involved in cancer metastasis and revisit pubertal mammary gland transcriptome profiling to uncover both known and unknown metastasis genes. Our updated list of pubertal morphogenesis regulators shows that most are implicated in invasion and metastasis. This review highlights molecular linkages between development and metastasis and provides a guide for exploring novel metastatic drivers.

CEBPA-Regulated Expression of SOCS1 Suppresses Milk Protein Synthesis through mTOR and JAK2-STAT5 Signaling Pathways in Buffalo Mammary Epithelial Cells

Milk protein content is a key quality indicator of milk, and therefore elucidating its synthesis mechanism has been the focus of research in recent years. Suppressor of cytokine signaling 1 (SOCS1) is an important inhibitor of cytokine signaling pathways that can inhibit milk protein synthesis in mice. However, it remains elusive whether SOCS1 plays roles in the milk protein synthesis in the buffalo mammary gland. In this study, we found that the mRNA and protein expression levels of SOCS1 in buffalo mammary tissue during the dry-off period was significantly lower than those during lactation. Overexpression and knockdown experiments of SOCS1 showed that it influenced the expression and phosphorylation of multiple key factors in the mTOR and JAK2-STAT5 signaling pathways in buffalo mammary epithelial cells (BuMECs). Consistently, intracellular milk protein content was significantly decreased in cells with SOCS1 overexpression, while it increased significantly in the cells with SOCS1 knockdown. The CCAAT/enhancer binding protein α (CEBPA) could enhance the mRNA and protein expression of SOCS1 and its promoter activity in BuMECs, but this effect was eliminated when CEBPA and NF-κB binding sites were deleted. Therefore, CEBPA was determined to promote SOCS1 transcription via the CEBPA and NF-κB binding sites located in the SOCS1 promoter. Our data indicate that buffalo SOCS1 plays a significant role in affecting milk protein synthesis through the mTOR and JAK2-STAT5 signaling pathways, and its expression is directly regulated by CEBPA. These results improve our understanding of the regulation mechanism of buffalo milk protein synthesis.

Emerging functions of C/EBPβ in breast cancer

Breast tumorigenesis relies on complex interactions between tumor cells and their surrounding microenvironment, orchestrated by tightly regulated transcriptional networks. C/EBPβ is a key transcription factor that regulates the proliferation and differentiation of multiple cell types and modulates a variety of biological processes such as tissue homeostasis and the immune response. In addition, C/EBPβ has well-established roles in mammary gland development, is overexpressed in breast cancer, and has tumor-promoting functions. In this review, we discuss context-specific roles of C/EBPβ during breast tumorigenesis, isoform-specific gene regulation, and regulation of the tumor immune response. We present challenges in C/EBPβ biology and discuss the importance of C/EBPβ isoform-specific gene regulation in devising new therapeutic strategies.

C/EBPβ deficiency enhances the keratinocyte innate immune response to direct activators of cytosolic pattern recognition receptors

The skin is the first line of defense to cutaneous microbes and viruses, and epidermal keratinocytes play a critical role in preventing infection by viruses and pathogens through activation of the type I interferon (IFN) response. Using RNAseq analysis, here we report that the conditional deletion of C/EBPβ transcription factor in mouse epidermis (CKOβ mice) resulted in the upregulation of IFNβ and numerous keratinocyte interferon-stimulated genes (ISGs). The expression of cytosolic pattern recognition receptors (cPRRs), that recognize viral RNA and DNA, were significantly increased, and enriched in the RNAseq data set. cPRRs stimulate a type I IFN response that can trigger cell death to eliminate infected cells. To determine if the observed increases in cPRRs had functional consequences, we transfected CKOβ primary keratinocytes with the pathogen and viral mimics poly(I:C) (dsRNA) or poly(dA:dT) (synthetic B-DNA) that directly activate PRRs. Transfected CKOβ primary keratinocytes displayed an amplified type I IFN response which was accompanied by increased activation of IRF3, enhanced ISG expression, enhanced activation of caspase-8, caspase-3 and increased apoptosis. Our results identify C/EBPβ as a critical repressor of the keratinocyte type I IFN response, and demonstrates that the loss of C/EBPβ primes keratinocytes to the activation of cytosolic PRRs by pathogen RNA and DNA to induce cell death mediated by caspase-8 and caspase-3.

C/EBPβ isoform-specific regulation of migration and invasion in triple-negative breast cancer cells

The transcription factor C/EBPβ is a master regulator of mammary gland development and tissue remodelling during lactation. The CEBPB-mRNA is translated into three distinct protein isoforms named C/EBPβ-LAP1, -LAP2 and -LIP that are functionally different. The smaller isoform LIP lacks the N-terminal transactivation domains and is considered to act as an inhibitor of the transactivating LAP1/2 isoforms by competitive binding for the same DNA recognition sequences. Aberrantly high expression of LIP is associated with mammary epithelial proliferation and is found in grade III, estrogen receptor (ER) and progesterone (PR) receptor-negative human breast cancer. Here, we show that reverting the high LIP/LAP ratios in triple-negative breast cancer (TNBC) cell lines into low LIP/LAP ratios by overexpression of LAP reduces migration and matrix invasion of these TNBC cells. In addition, in untransformed MCF10A human mammary epithelial cells overexpression of LIP stimulates migration. Knockout of CEBPB in TNBC cells where LIP expression prevails, resulted in strongly reduced migration that was accompanied by a downregulation of genes involved in cell migration, extracellular matrix production and cytoskeletal remodelling, many of which are epithelial to mesenchymal transition (EMT) marker genes. Together, this study suggests that the LIP/LAP ratio is involved in regulating breast cancer cell migration and invasion. This study together with studies from others shows that understanding the functions the C/EBPβ-isoforms in breast cancer development may reveal new avenues of treatment.

Cell death-inducing DNA fragmentation factor-α-like effector C (CIDEC) regulates acetate- and β-hydroxybutyrate-induced milk fat synthesis by increasing FASN expression in mammary epithelial cells of dairy cows

Increasing acetate and β-hydroxybutyrate (BHB) supply to lactating cows will increase milk fat synthesis. However, the underlying molecular mechanism remains largely unknown. Cell death-inducing DNA fragmentation factor-α-like effector C (CIDEC) is a lipid droplet-associated protein that promotes intracellular triacylglycerol accumulation. In the present study, using gene overexpression and knockdown, we detected the contributions of CIDEC on milk fat synthesis in mammary epithelial cells of dairy cows in the presence of acetate and BHB. The results showed that knockdown of CIDEC decreased fatty acid synthase (FASN) expression and intracellular triacylglycerol content, whereas overexpression of CIDEC had the opposite effect. The transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) regulates cell growth and differentiation in the mammary gland. We demonstrated that the FASN promoter had a canonical C/EBPβ binding sequence. CEBPB overexpression upregulated FASN expression and milk fat synthesis, whereas CEBPB knockdown had the opposite effect. Moreover, knockdown of CEBPB attenuated the promoting effects of CIDEC on acetate- and BHB-induced FASN transcription. Taken together, our data showed that acetate and BHB induced FASN expression in mammary epithelial cells of dairy cows in a CIDEC-C/EBPβ-dependent manner, which provides new insights into the understanding of the molecular events involved in milk fat synthesis.

AP-2γ Is Required for Maintenance of Multipotent Mammary Stem Cells

Mammary gland ductal morphogenesis depends on the differentiation of mammary stem cells (MaSCs) into basal and luminal lineages. The AP-2γ transcription factor, encoded by Tfap2c, has a central role in mammary gland development but its effect in mammary lineages and specifically MaSCs is largely unknown. Here, we utilized an inducible, conditional knockout of Tfap2c to elucidate the role of AP-2γ in maintenance and differentiation of MaSCs. Loss of AP-2γ in the basal epithelium profoundly altered the transcriptomes and decreased the number of cells within several clusters of mammary epithelial cells, including adult MaSCs and luminal progenitors. AP-2γ regulated the expression of genes known to be required for mammary development, including Cebpb, Nfkbia, and Rspo1. As a result, AP-2γ-deficient mice exhibited repressed mammary gland ductal outgrowth and inhibition of regenerative capacity. The findings demonstrate that AP-2γ can regulate development of mammary gland structures potentially regulating maintenance and differentiation of multipotent MaSCs.

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AP-2γ-deficient mice exhibit repressed ductal outgrowth and regenerative capacity

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Loss of AP-2γ reduced cells within mammary stem and luminal progenitor clusters

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AP-2γ target genes, including Cebpb, Nfkbia, and Rspo1, regulate mammary development

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AP-2γ potentially regulates maintenance of multipotent mammary stem cells

Progesterone promotes embryo adhesion by upregulating c-Fos/c-Jun transcription factor-mediated poFUT1 expression†

The proliferation and adhesion abilities of placental trophoblasts are critical for embryo implantation and successful pregnancy. Protein O-fucosyltransferase 1 (poFUT1) and the transcription factor c-Fos/c-Jun have been found to promote trophoblastic cell invade into the endometrium. Progesterone is critical to the regulation of embryonic implantation. However, the exact role of poFUT1 in embryo proliferation and adhesion to the endometrium, and the relationship between progesterone, c-Fos/c-Jun, and poFUT1 has not been studied in detail. In the current study, we found that the serum levels of poFUT1 and progesterone significantly was decreased in miscarriage patients compared with those in normal pregnancy women, and there is a positive correlation between the changes in progesterone and poFUT1. Employing a human embryo trophoblastic cell line (JAR), we showed that progesterone facilitated the activation of c-Fos/c-Jun. Using an electrophoretic mobility shift assay and chromatin immunoprecipitation, we confirmed that the specific transcription factor c-Fos/c-Jun regulated the poFUT1 promoter, which could enhance poFUT1 transcriptional activity, thus further increasing trophoblast cell proliferation and adhesion potential. Taking these findings together, progesterone upregulates poFUT1 expression via the specific transcription factor c-Fos/c-Jun, and then increase trophoblast cell proliferation and adhesion potential. poFUT1 and progesterone may be used together as potential markers of miscarriage, and they may be diagnostic and therapeutic targets for miscarriage.

The Importance of Breast Adipose Tissue in Breast Cancer

Adipose tissue is a complex endocrine organ, with a role in obesity and cancer. Adipose tissue is generally linked to excessive body fat, and it is well known that the female breast is rich in adipose tissue. Hence, one can wonder: what is the role of adipose tissue in the breast and why is it required? Adipose tissue as an organ consists of adipocytes, an extracellular matrix (ECM) and immune cells, with a significant role in the dynamics of breast changes throughout the life span of a female breast from puberty, pregnancy, lactation and involution. In this review, we will discuss the importance of breast adipose tissue in breast development and its involvement in breast changes happening during pregnancy, lactation and involution. We will focus on understanding the biology of breast adipose tissue, with an overview on its involvement in the various steps of breast cancer development and progression. The interaction between the breast adipose tissue surrounding cancer cells and vice-versa modifies the tumor microenvironment in favor of cancer. Understanding this mutual interaction and the role of breast adipose tissue in the tumor microenvironment could potentially raise the possibility of overcoming breast adipose tissue mediated resistance to therapies and finding novel candidates to target breast cancer.

Transcription Factors in Cancer: When Alternative Splicing Determines Opposite Cell Fates

Alternative splicing (AS) is a finely regulated mechanism for transcriptome and proteome diversification in eukaryotic cells. Correct balance between AS isoforms takes part in molecular mechanisms that properly define spatiotemporal and tissue specific transcriptional programs in physiological conditions. However, several diseases are associated to or even caused by AS alterations. In particular, multiple AS changes occur in cancer cells and sustain the oncogenic transcriptional program. Transcription factors (TFs) represent a key class of proteins that control gene expression by direct binding to DNA regulatory elements. AS events can generate cancer-associated TF isoforms with altered activity, leading to sustained proliferative signaling, differentiation block and apoptosis resistance, all well-known hallmarks of cancer. In this review, we focus on how AS can produce TFs isoforms with opposite transcriptional activities or antagonistic functions that severely impact on cancer biology. This summary points the attention to the relevance of the analysis of TFs splice variants in cancer, which can allow patients stratification despite the presence of interindividual genetic heterogeneity. Recurrent TFs variants that give advantage to specific cancer types not only open the opportunity to use AS transcripts as clinical biomarkers but also guide the development of new anti-cancer strategies in personalized medicine.

C/EBPß Isoform Specific Gene Regulation: It's a Lot more Complicated than you Think!

It has been almost 30 years since C/EBPß was discovered. Seminal studies have shown that C/EBPß is a master regulator of mammary gland development and has been shown to control and influence proliferation and differentiation through varying mechanisms. The single-exon C/EBPß mRNA yields at least three different protein isoforms which have diverse, specific, context-dependent, and often non-overlapping roles throughout development and breast cancer progression. These roles are dictated by a number of complex factors including: expression levels of other C/EBP family members and their stoichiometry relative to the isoform in question, binding site affinity, post-translational modifications, co-factor expression, and even hormone levels and lactogenic status. Here we summarize the historical work up to the latest findings in the field on C/EBPß in the mammary gland and in breast cancer. With the current emphasis on improving immunotherapy in breast cancer the role of specific C/EBPß isoforms in regulating specific chemokine and cytokine expression and the immune microenvironment will be of increasing interest.

C/EBPα mediates the growth inhibitory effect of progestins on breast cancer cells

Steroid hormones are key gene regulators in breast cancer cells. While estrogens stimulate cell proliferation, progestins activate a single cell cycle followed by proliferation arrest. Here, we use biochemical and genome-wide approaches to show that progestins achieve this effect via a functional crosstalk with C/EBPα. Using ChIP-seq, we identify around 1,000 sites where C/EBPα binding precedes and helps binding of progesterone receptor (PR) in response to hormone. These regions exhibit epigenetic marks of active enhancers, and C/EBPα maintains an open chromatin conformation that facilitates loading of ligand-activated PR. Prior to hormone exposure, C/EBPα favors promoter-enhancer contacts that assure hormonal regulation of key genes involved in cell proliferation by facilitating binding of RAD21, YY1, and the Mediator complex. Knockdown of C/EBPα disrupts enhancer-promoter contacts and decreases the presence of these architectural proteins, highlighting its key role in 3D chromatin looping. Thus, C/EBPα fulfills a previously unknown function as a potential growth modulator in hormone-dependent breast cancer.

MicroRNA-191 targets CCAAT/enhanced binding protein β and functions as an oncogenic molecule in human non-small cell lung carcinoma cells

The aberrant expression of microRNAs (miRs) may be involved in tumor growth and progression in human non-small cell lung carcinoma (NSCLC). The present study aimed to investigate the potential roles of miR-191 in NSCLC. Western blotting and reverse transcription-quantitative polymerase chain reaction were performed to assess protein and/or mRNA levels. Scratch wound healing and transwell assays were performed to determine the NSCLC cell migration and invasion. A luciferase demonstrated that CCAAT/enhanced binding protein β (C/EBPβ) was a target of miR-191. Previously, miR-191 has been reported to act as an oncogenic player in multiple human cancers. C/EBPβ has been identified as a target gene of miR-191; however, the roles and underlying mechanisms of miR-191 associated with the regulation of tumor invasion in NSCLC remain unknown. In the present study, it was demonstrated that miR-191 expression levels were higher in human NSCLC tumors compared with in normal adjacent tissue and elevated miR-191 expression levels were closely associated with tumor node metastasis stage in patients with NSCLC. Furthermore, transfection with miR-191 mimic inhibited C/EBPβ expression at the mRNA and protein levels and promoted A549 cell migration and invasion. C/EBPβ was reported to be the direct target gene of miR-191 using a dual luciferase reporter assay. Finally, C/EBPβ siRNA can mimic the effects of miR-191. These findings indicated that miR-191 may function as an oncogene in NSCLC, at least partially due to its negative regulatory on C/EBPβ.

Cyclooxygenase-2 is acutely induced by CCAAT/enhancer-binding protein β to produce prostaglandin E 2 and F 2α following gonadotropin stimulation in Leydig cells

Cyclooxygenase 2 (COX-2) is an inducible rate-limiting enzyme for prostanoid production. Because COX-2 represents one of the inducible genes in mouse mesenchymal stem cells upon differentiation into Leydig cells, we investigated COX-2 expression and production of prostaglandin (PG) in Leydig cells. Although COX-2 was undetectable in mouse testis, it was transiently induced in Leydig cells by human chorionic gonadotropin (hCG) administration. Consistent with the finding that Leydig cells expressed aldo-keto reductase 1B7 (PGF synthase) and PGE synthase 2, induction of COX-2 by hCG caused a marked increase in testicular PGF _2α and PGE ₂ levels. Using mouse Leydig cell tumor-derived MA-10 cells as a model, it was indicated by reporter assays and electron mobility shift assays that transcription of the COX-2 gene was activated by CCAAT/enhancer-binding protein β (C/EBPβ) with cAMP-stimulation. C/EBPβ expression was induced by cAMP-stimulation, whereas expression of C/EBP homolog protein (CHOP) was robustly downregulated. Transfection of CHOP expression plasmid inhibited cAMP-induced COX-2 promoter activity. In addition, CHOP reduced constitutive COX-2 expression in other mouse Leydig cell tumor-derived TM3 cells. These results indicate that COX-2 is induced in Leydig cells by activation of C/EBPβ via reduction of CHOP expression upon gonadotropin-stimulation to produce PGF _2α and PGE ₂ .

C/EBPβ LIP and c-Jun synergize to regulate expression of the murine progesterone receptor

CCAAT/enhancer binding protein β (C/EBPβ) is required for murine mammary ductal morphogenesis and alveologenesis. Progesterone is critical for proliferation and alveologenesis in adult mammary glands, and there is a similar requirement for progesterone receptor isoform B (PRB) in alveologenesis. We examined C/EBPβ regulation of PR expression. All three C/EBPβ isoforms, including typically inhibitory LIP, transactivated the PR promoter. LIP, particularly, strongly synergized with c-Jun to drive PR transcription. Endogenous C/EBPβ and c-Jun stimulated a PR promoter-reporter and these two factors showed promoter occupancy on the endogenous PR gene. Additionally, LIP overexpression elevated endogenous PR protein expression. In pregnancy, both PRB and the relative abundance of LIP among C/EBPβ isoforms increase. Consistent with a role in PRB expression, in vivo C/EBPβ and PR isoform A expression showed mutually exclusive localization in mammary epithelium, while C/EBPβ and PRB largely co-localized. We suggest a critical role for C/EBPβ, particularly LIP, in PRB expression.

C/EBPβ Deletion Promotes Expansion of Poorly Functional Intestinal Regulatory T Cells

BACKGROUND AND AIMS

Inflammatory Bowel Diseases [IBDs] are chronic intestinal inflammatory conditions in part mediated by CD4+ T cells. Anti-inflammatory Foxp3+ regulatory T cells [Tregs] maintain immune homeostasis and protect against IBD development via multiple mechanisms, including cytokine secretion and cell-cell interaction. CCAAT enhancer binding protein-beta [C/EBPβ] is a stress-responsive transcription factor linked with IBD susceptibility. Whole-body C/EBPβ deficiency induces CD4+ T cell-predominant hyperproliferation, and we hypothesize that this may be due to impaired Treg function.

METHODS

We used the C/EBPβ-/- mice in the CD45RBHigh adoptive transfer model, to assess C/EBPβ-/- CD4+ T cells for their colitiogenic potential, and C/EBPβ-/- CD4+ Foxp3+ Tregs for their ability to inhibit colitis. We assessed Tregs from the C/EBPβ-/- mice for expression of Treg functional genes and proteins.

RESULTS

Naïve C/EBPβ-/- CD4+ T cells are more colitogenic in vivo. The exacerbated colitis does not appear to reflect impaired Treg development, however, as C/EBPβ-/- mice displayed more, rather than fewer intestinal CD4+Foxp3+ Tregs in vivo. Instead, this reflects impaired Treg function as seen by the reduced capacity to suppress T cell proliferation in vitro, along with decreased secretion of the anti-inflammatory cytokine IL-10. These findings were corroborated in vivo by additional adoptive co-transfer studies in which wildtype Tregs prevented colitis but C/EBPβ-/- Tregs did not.

CONCLUSION

C/EBPβ deficiency impairs Treg function and potentiates T cell-mediated colitis. A clearer understanding of the function of this transcription factor may provide a novel therapeutic strategy for IBD.

Prolactin Alters the Mammary Epithelial Hierarchy, Increasing Progenitors and Facilitating Ovarian Steroid Action

Hormones drive mammary development and function and play critical roles in breast cancer. Epidemiologic studies link prolactin (PRL) to increased risk for aggressive cancers that express estrogen receptor α (ERα). However, in contrast to ovarian steroids, PRL actions on the mammary gland outside of pregnancy are poorly understood. We employed the transgenic NRL-PRL model to examine the effects of PRL alone and with defined estrogen/progesterone exposure on stem/progenitor activity and regulatory networks that drive epithelial differentiation. PRL increased progenitors and modulated transcriptional programs, even without ovarian steroids, and with steroids further raised stem cell activity associated with elevated canonical Wnt signaling. However, despite facilitating some steroid actions, PRL opposed steroid-driven luminal maturation and increased CD61⁺ luminal cells. Our findings demonstrate that PRL can powerfully influence the epithelial hierarchy alone and temper the actions of ovarian steroids, which may underlie its role in the development of breast cancer.

A tumor suppressor role for C/EBPα in solid tumors: more than fat and blood

The transcription factor CCAAT/enhancer-binding protein alpha (C/EBPα) plays a critical role during embryogenesis and is thereafter required for homeostatic glucose metabolism, adipogenesis and myeloid development. Its ability to regulate the expression of lineage-specific genes and induce growth arrest contributes to the terminal differentiation of several cell types, including hepatocytes, adipocytes and granulocytes. CEBPA loss of-function mutations contribute to the development of ~10% of acute myeloid leukemia (AML), stablishing a tumor suppressor role for C/EBPα. Deregulation of C/EBPα expression has also been reported in a variety of additional human neoplasias, including liver, breast and lung cancer. However, functional CEBPA mutations have not been found in solid tumors, suggesting that abrogation of C/EBPα function in non-hematopoietic tissues is regulated by alternative mechanisms. Here we review the function of C/EBPα in solid tumors and focus on the molecular mechanisms underlying its tumor suppressive role.

C/EBPB-CITED4 in Exercised Heart

C/EBPB is a crucial transcription factor, participating in a variety of biological processes including cell proliferation, differentiation and development. In the cardiovascular system, C/EBPB-CITED4 signaling is known as a signaling pathway mediating exercise-induced cardiac growth. After its exact role in exercised heart firstly reported in 2010, more and more evidence confirmed that. MicroRNA (e.g. miR-222) and many molecules (e.g. Alpha-lipoic acid) can regulate this pathway and then involve in the cardiac protection effect induced by endurance exercise training. In addition, in cardiac growth during pregnancy, C/EBPB is also a required regulator. This chapter will give an introduction of the C/EBPB-CITED4 signaling and the regulatory network based on this signaling pathway in exercised heart.

Regulators of genetic risk of breast cancer identified by integrative network analysis

Genetic risk for breast cancer is conferred by a combination of multiple variants of small effect. To better understand how risk loci might combine, we examined whether risk-associated genes share regulatory mechanisms. We created a breast cancer gene regulatory network comprising transcription factors and groups of putative target genes (regulons) and asked whether specific regulons are enriched for genes associated with risk loci via expression quantitative trait loci (eQTLs). We identified 36 overlapping regulons that were enriched for risk loci and formed a distinct cluster within the network, suggesting shared biology. The risk transcription factors driving these regulons are frequently mutated in cancer and lie in two opposing subgroups, which relate to estrogen receptor (ER)(+) luminal A or luminal B and ER(-) basal-like cancers and to different luminal epithelial cell populations in the adult mammary gland. Our network approach provides a foundation for determining the regulatory circuits governing breast cancer, to identify targets for intervention, and is transferable to other disease settings.

Expression of CCAAT/Enhancer Binding Protein Beta in Muscle Satellite Cells Inhibits Myogenesis in Cancer Cachexia

Cancer cachexia is a paraneoplastic syndrome that causes profound weight loss and muscle mass atrophy and is estimated to be the cause of up to 30% of cancer deaths. Though the exact cause is unknown, patients with cancer cachexia have increased muscle protein catabolism. In healthy muscle, injury activates skeletal muscle stem cells, called satellite cells, to differentiate and promote regeneration. Here, we provide evidence that this mechanism is inhibited in cancer cachexia due to persistent expression of CCAAT/Enhancer Binding Protein beta (C/EBPβ) in muscle myoblasts. C/EBPβ is a bzip transcription factor that is expressed in muscle satellite cells and is normally downregulated upon differentiation. However, in myoblasts exposed to a cachectic milieu, C/EBPβ expression remains elevated, despite activation to differentiate, resulting in the inhibition of myogenin expression and myogenesis. In vivo, cancer cachexia results in increased number of Pax7+ cells that also express C/EBPβ and the inhibition of normal repair mechanisms. Loss of C/EBPβ expression in primary myoblasts rescues differentiation under cachectic conditions without restoring myotube size, indicating that C/EBPβ is an important inhibitor of myogenesis in cancer cachexia.

Accelerated apoptosis of peripheral blood monocytes in Cebpb-deficient mice

The CCAAT/enhancer-binding protein β (C/EBPβ) transcription factor is required for granulopoiesis under stress conditions. However, little is known about its roles in steady state hematopoiesis. Here, we analyzed the peripheral blood and bone marrow of Cebpb(-/-) mice at steady state by flow cytometry and unexpectedly found that the number of peripheral blood monocytes was severely reduced, while the number of bone marrow monocytes was maintained. The ability of Cebpb(-/-) bone marrow cells to give rise to macrophages/monocytes in vitro was comparable to that of wild-type bone marrow cells. Apoptosis of monocytes was enhanced in the peripheral blood, but not in the bone marrow of Cebpb(-/-) mice. These results indicate that C/EBPβ is required for the survival of monocytes in peripheral blood.

Hormone-sensing mammary epithelial progenitors: emerging identity and hormonal regulation

The hormone-sensing mammary epithelial cell (HS-MEC-expressing oestrogen receptor-alpha (ERα) and progesterone receptor (PGR)) is often represented as being terminally differentiated and lacking significant progenitor activity after puberty. Therefore while able to profoundly influence the proliferation and function of other MEC populations, HS-MECs are purported not to respond to sex hormone signals by engaging in significant cell proliferation during adulthood. This is a convenient and practical simplification that overshadows the sublime, and potentially critical, phenotypic plasticity found within the adult HS-MEC population. This concept is exemplified by the large proportion (~80 %) of human breast cancers expressing PGR and/or ERα, demonstrating that HS-MECs clearly proliferate in the context of breast cancer. Understanding how HS-MEC proliferation and differentiation is driven could be key to unraveling the mechanisms behind uncontrolled HS-MEC proliferation associated with ERα- and/or PGR-positive breast cancers. Herein we review evidence for the existence of a HS-MEC progenitor and the emerging plasticity of the HS-MEC population in general. This is followed by an analysis of hormones other than oestrogen and progesterone that are able to influence HS-MEC proliferation and differentiation: androgens, prolactin and transforming growth factor-beta1.

Interferons, signal transduction pathways, and the central nervous system

The interferon (IFN) family of cytokines participates in the development of innate and acquired immune defenses against various pathogens and pathogenic stimuli. Discovered originally as a proteinaceous substance secreted from virus-infected cells that afforded immunity to neighboring cells from virus infection, these cytokines are now implicated in various human pathologies, including control of tumor development, cell differentiation, and autoimmunity. It is now believed that the IFN system (IFN genes and the genes induced by them, and the factors that regulate these processes) is a generalized alarm of cellular stress, including DNA damage. IFNs exert both beneficial and deleterious effects on the central nervous system (CNS). Our knowledge of the IFN-regulated processes in the CNS is far from being clear. In this article, we reviewed the current understanding of IFN signal transduction pathways and gene products that might have potential relevance to diseases of the CNS.

CCAAT/enhancer binding protein β is dispensable for development of lung adenocarcinoma

Lung cancer is the leading cause of cancer death worldwide. Although disruption of normal proliferation and differentiation is a vital component of tumorigenesis, the mechanisms of this process in lung cancer are still unclear. A transcription factor, C/EBPβ is a critical regulator of proliferation and/or differentiation in multiple tissues. In lung, C/EBPβ is expressed in alveolar pneumocytes and bronchial epithelial cells; however, its roles on normal lung homeostasis and lung cancer development have not been well described. Here we investigated whether C/EBPβ is required for normal lung development and whether its aberrant expression and/or activity contribute to lung tumorigenesis. We showed that C/EBPβ was expressed in both human normal pneumocytes and lung adenocarcinoma cell lines. We found that overall lung architecture was maintained in Cebpb knockout mice. Neither overexpression of nuclear C/EBPβ nor suppression of CEBPB expression had significant effects on cell proliferation. C/EBPβ expression and activity remained unchanged upon EGF stimulation. Furthermore, deletion of Cebpb had no impact on lung tumor burden in a lung specific, conditional mutant EGFR lung cancer mouse model. Analyses of data from The Cancer Genome Atlas (TCGA) revealed that expression, promoter methylation, or copy number of CEBPB was not significantly altered in human lung adenocarcinoma. Taken together, our data suggest that C/EBPβ is dispensable for development of lung adenocarcinoma.

Regulation of epithelial-mesenchymal transition in breast cancer cells by cell contact and adhesion

Epithelial-mesenchymal transition (EMT) is a physiological program that is activated during cancer cell invasion and metastasis. We show here that EMT-related processes are linked to a broad and conserved program of transcriptional alterations that are influenced by cell contact and adhesion. Using cultured human breast cancer and mouse mammary epithelial cells, we find that reduced cell density, conditions under which cell contact is reduced, leads to reduced expression of genes associated with mammary epithelial cell differentiation and increased expression of genes associated with breast cancer. We further find that treatment of cells with matrix metalloproteinase-3 (MMP-3), an inducer of EMT, interrupts a defined subset of cell contact-regulated genes, including genes encoding a variety of RNA splicing proteins known to regulate the expression of Rac1b, an activated splice isoform of Rac1 known to be a key mediator of MMP-3-induced EMT in breast, lung, and pancreas. These results provide new insights into how MMPs act in cancer progression and how loss of cell-cell interactions is a key step in the earliest stages of cancer development.

Transcriptional regulation of adipocyte differentiation: a central role for CCAAT/enhancer-binding protein (C/EBP) β

A detailed understanding of the processes controlling adipogenesis is instrumental in the fight against the obesity epidemic. Adipogenesis is controlled by a transcriptional cascade composed of a large number of transcriptional factors, among which CCAAT/enhancer-binding protein (C/EBP) β plays an essential role. During 3T3-L1 adipocyte differentiation, C/EBPβ is induced early to transactivate the expression of C/EBPα and peroxisome proliferator-activated receptor γ (PPARγ), two master transcription factors for terminal adipocyte differentiation. Studies in recent years have revealed many new target genes of C/EBPβ, implicating its participation in many other processes during adipogenesis, such as mitotic clonal expansion, epigenetic regulation, unfolded protein response, and autophagy. Moreover, the function of C/EBPβ is highly regulated by post-translational modifications, which are crucial for the proper activation of the adipogenic program. Advances toward elucidation of the function and roles of the post-translational modification of C/EBPβ during adipogenesis will greatly improve our understanding of the molecular mechanisms governing adipogenesis.

C/EBPβ expression is an independent predictor of overall survival in breast cancer patients by MHCII/CD4-dependent mechanism of metastasis formation

CCAAT-enhancer binding protein β (C/EBPβ) is a transcription factor that has a critical role in mammary gland development and breast cancer progression. Loss of C/EBPβ increases metastatic dissemination of mouse mammary tumor cells. However, the mechanism by which C/EBPβ expression affects metastasis formation remains unknown. This study aims at determining the relationship between C/EBPβ and survival of breast cancer patients, and elucidating C/EBPβ's link with metastasis formation. C/EBPβ expression was evaluated in 137 cases of human breast cancer, and the correlation with overall survival was estimated by Kaplan–Meier analysis. Additionally, the mouse 4T1 tumor model was used for in vivo studies. Decreased C/EBPβ expression was found to be associated with shorter overall survival of breast cancer patients. In the murine 4T1 model, loss of C/EBPβ affects tumor growth, morphology and promotes metastatic spread to the lungs. Immunohistochemical analyses showed that C/EBPβ inhibition leads to increased major histocompatibility complex II (MHCII) expression, followed by the accumulation of CD45-, CD3- and CD4-positive (CD4+) lymphocytes in the tumors. Inflammation involvement in C/EBPβ-mediated metastasis formation was confirmed by DNA microarray and by experiments on CD4+ cell-deprived nude mice. Additionally, anti-CD3 and anti-CD4 treatments of C/EBPβ-silenced tumor-bearing mice resulted in reverting the C/EBPβ effect on tumor growth and metastasis. Altogether, C/EBPβ is a predictor of overall survival in breast cancer patients, and affects tumor growth, morphology and lung metastasis formation in murine 4T1 model. The mechanism of metastasis formation involves immunologic response depending on C/EBPβ-mediated activation of MHCII and accumulation of CD4+ lymphocytes in the tumor.

C/EBPβ's role in determining Ras-induced senescence or transformation

Introduction of activated Ras into normal cells leads to senescence, a tumor suppressive mechanism, whereas expression of this oncogene in many immortalized cell lines leads to transformation. Studying the signaling differences in cells that undergo Ras-induced senescence versus Ras transformation may shed light on potential therapeutic targets in the treatment of cancer. C/EBPβ is a transcription factor necessary for both Ras-induced senescence and Ras transformation. Three isoforms of this transcription factor exist due to alternative translation initation at three in frame ATGs. C/EBPβ1 is the isoform responsible for oncogene-induced senescence, and this isoform is degraded by the proteosome during Ras transformation. Phosphorylation of C/EBPβ1 on Thr235 by Cdk2 is necessary, but not sufficient, for degradation of C/EBPβ1. Proteasomal degradation of C/EBPβ1 may represent a mechanism to evade senescence. In contrast, C/EBPβ2 is expressed in breast cancer cells and is involved in proliferation, supporting a role for this isoform in Ras transformation. We propose here that one potential signaling difference in Ras-induced senescence versus Ras transformation is that Ras signals through different C/EBPβ isoforms (C/EBPβ1 versus C/EBPβ2) during these processes.

Transcription control of DAPK

Imbalanced cell death is a common phenomenon in many human diseases, including cancer. DAPK's essential function is in promoting apoptosis. DAPK interacts with stress-induced receptors through its death domain to initiate an apoptosis cascade. In addition, DAPK phosphorylates multiple cytosolic substrates and can mediate transfer of signaling pathways to the effector caspases. A series of studies demonstrated that, depending on stimuli, DAPK expression is regulated on both the transcriptional and posttranscriptional levels. Silencing of DAPK due to hypermethylation of its promoter was reported in many types of cancer. STAT3 and p52-NFkB transcription factors have been shown to down-regulate DAPK expression. In contrast, p53, C/EBP-β and Smad transcription factors bind to their specific response elements within the DAPK promoter and induce its transcription. Post-transcriptionally, DAPK undergoes alternative splicing, which results in the production of two functionally different isoforms. Moreover, miRNA 103 and miRNA 107 recently were shown to inhibit DAPK in colorectal cancer. Here we summarize our recent knowledge about transcriptional regulation of DAPK expression.

Cyclin D1 and C/EBPβ LAP1 operate in a common pathway to promote mammary epithelial cell differentiation

Both cyclin D1 and the transcription factor C/EBPβ are required for mammary epithelial cell differentiation; however, the pathway in which they operate is uncertain. Previous analyses of the patterns of gene expression in human tumors suggested a connection between cyclin D1 overexpression and C/EBPβ, but whether this represents a cancer-specific gain of function for cyclin D1 is unknown. C/EBPβ is an intronless gene encoding three protein isoforms--LAP1, LAP2, and LIP. Here, we provide evidence that cyclin D1 engages C/EBPβ in an isoform-specific manner. Cyclin D1 binds to LAP1, an event that activates the transcriptional function of LAP1 by relieving its autoinhibited state effected by intramolecular interactions. Reexpression of LAP1 but not LAP2 or LIP restores the ability of C/EBPβ-deficient mammary epithelial cells to differentiate and does so in a manner dependent on cyclin D1. And cyclin D1-mediated activation of LAP1 participates in mammary epithelial cell differentiation. Our findings indicate that cyclin D1 and C/EBPβ LAP1 operate in a common pathway to promote mammary epithelial cell differentiation.

Prospective signs of cleidocranial dysplasia in Cebpb deficiency

Background

Although runt-related transcription factor 2 (RUNX2) has been considered a determinant of cleidocranial dysplasia (CCD), some CCD patients were free of RUNX2 mutations. CCAAT/enhancer-binding protein beta (Cebpb) is a key factor of Runx2 expression and our previous study has reported two CCD signs including hyperdontia and elongated coronoid process of the mandible in Cebpb deficient mice. Following that, this work aimed to conduct a case-control study of thoracic, zygomatic and masticatory muscular morphology to propose an association between musculoskeletal phenotypes and deficiency of Cebpb, using a sample of Cebpb^-/-, Cebpb^+/- and Cebpb^+/+ adult mice. Somatic skeletons and skulls of mice were inspected with soft x-rays and micro-computed tomography (μCT), respectively. Zygomatic inclination was assessed using methods of coordinate geometry and trigonometric function on anatomic landmarks identified with μCT. Masseter and temporal muscles were collected and weighed. Expression of Cebpb was examined with a reverse transcriptase polymerase chain reaction (RT-PCR) technique.

Results

Cebpb^-/- mice displayed hypoplastic clavicles, a narrow thoracic cage, and a downward tilted zygomatic arch (p < 0.001). Although Cebpb^+/- mice did not show the phenotypes above (p = 0.357), a larger mass percentage of temporal muscles over masseter muscles was seen in Cebpb^+/- littermates (p = 0.012). The mRNA expression of Cebpb was detected in the clavicle, the zygoma, the temporal muscle and the masseter muscle, respectively.

Conclusions

Prospective signs of CCD were identified in mice with Cebpb deficiency. These could provide an additional aetiological factor of CCD. Succeeding investigation into interactions among Cebpb, Runx2 and musculoskeletal development is indicated.

The CCAAT/enhancer-binding protein beta-2 isoform (CEBPβ-2) upregulates galectin-7 expression in human breast cancer cells

Galectin-7 is considered a gene under the control of p53. However, elevated expression of galectin-7 has been reported in several forms of cancer harboring an inactive p53 pathway. This is especially true for breast cancer where galectin-7 expression is readily expressed in a high proportion in basal-like breast cancer tissues, conferring cancer cells with increased resistance to cell death and metastatic properties. These observations suggest that other transcription factors are capable of inducing galectin-7 expression. In the present work, we have examined the role of CCAAT/enhancer-binding protein beta (C/EBPβ) in inducing expression of galectin-7. C/EBP proteins have been shown to contribute to breast cancer by upregulating pro-metastatic genes. We paid particular attention to C/EBPβ-2 (also known as LAP2), the most transcriptionally active of the C/EBPβ isoforms. Our results showed that ectopic expression of C/EBPβ-2 in human breast cancer cells was sufficient to induce expression of galectin-7 at both the mRNA and protein levels. In silico analysis further revealed the presence of an established CEBP element in the galectin-7 promoter. Mutation of this binding site abolished the transcriptional activity of the galectin-7 promoter. Chromatin immunoprecipitation analysis confirmed that C/EBPβ-2 binds to the endogenous galectin-7 promoter. Analysis of galectin-7 protein expression in normal epithelia and in breast carcinoma by immunohistochemistry further showed the expression pattern of C/EBPβ closely micmicked that of galectin-7, most notably in mammary myoepithelial cells and basal-like breast cancer where galectin-7 is preferentially expressed. Taken together, our findings suggest that C/EBPβ is an important mediator of galectin-7 gene activation in breast cancer cells and highlight the different transcriptional mechanisms controlling galectin-7 in cancer cells.

Mammary-specific gene activation is defined by progressive recruitment of STAT5 during pregnancy and the establishment of H3K4me3 marks

Differentiation of mammary secretory epithelium during pregnancy is characterized by sequential activation of genes over several orders of magnitude. Although the transcription factor STAT5 is key to alveolar development, it is not clear to what extent it controls temporal activation of genetic programs in secretory epithelium. To uncover molecular mechanisms effecting progressive differentiation, we explored genome-wide STAT5 binding and H3K4me3 (i.e., trimethylated histone H3 at K4) marks in mammary tissues at early and midpregnancy and at parturition. STAT5 binding to genes induced during pregnancy was low in immature mammary tissue but increased with epithelial differentiation. Increased STAT5 binding was associated with the establishment of H3K4me3 marks and transcriptional activation. STAT5 binding preceded the formation of H3K4me3 marks in some mammary-specific genes. De novo STAT5 binding was also found at distal sites, indicating enhancers. Furthermore, we established an exhaustive mammary transcriptome. Through integration of RNA-seq and STAT5 and H3K4me4 ChIP-seq data, we discovered novel mammary-specific alternative promoters and genes, including noncoding RNAs. Our findings suggest that STAT5 is an early step in establishing transcription complexes on genes specifically expressed in mammary epithelium. This is the first study in an organ that links progressive chromatin occupancy of STAT5 to the acquisition of H3K4me3 marks and transcription during hormone-induced differentiation.

MUC1-C oncoprotein activates ERK→C/EBPβ signaling and induction of aldehyde dehydrogenase 1A1 in breast cancer cells

Aldehyde dehydrogenase 1A1 (ALDH1A1) activity is used as a marker of breast cancer stem cells; however, little is known about the regulation of ALDH1A1 expression. Mucin 1 (MUC1) is a heterodimeric protein that is aberrantly overexpressed in most human breast cancers. In studies of breast cancer cells stably silenced for MUC1 or overexpressing the oncogenic MUC1-C subunit, we demonstrate that MUC1-C is sufficient for induction of MEK → ERK signaling and that treatment with a MUC1-C inhibitor suppresses ERK activation. In turn, MUC1-C induces ERK-mediated phosphorylation and activation of the CCAAT/enhancer-binding protein β (C/EBPβ) transcription factor. The results further show that MUC1-C and C/EBPβ form a complex on the ALDH1A1 gene promoter and activate ALDH1A1 gene transcription. MUC1-C-induced up-regulation of ALDH1A1 expression is associated with increases in ALDH activity and is detectable in stem-like cells when expanded as mammospheres. These findings demonstrate that MUC1-C (i) activates a previously unrecognized ERK→C/EBPβ→ALDH1A1 pathway, and (ii) promotes the induction of ALDH activity in breast cancer cells.

An isoform of C/EBPβ, LIP, regulates expression of the chemokine receptor CXCR4 and modulates breast cancer cell migration

Metastasis is the primary cause of death in cancer patients. CXCR4/CXCL12 chemokine axis provides directional cues for breast cancer cells to metastasize to specific organs. Despite their potential clinical importance, how CXCR4 expression in breast cancer cells is regulated at the molecular level is not well understood. We identified an isoform of C/EBPβ, liver-enriched inhibitory protein (LIP), as a previously unrecognized transcriptional regulator of CXCR4 in breast cancer cells. LIP up-regulated the transcription of CXCR4 through direct interaction with the CXCR4 promoter. The increase in CXCR4 mRNA was paralleled by an increased cell surface expression of the CXCR4, which in turn promoted CXCR4-mediated breast cancer cell migration. A significant positive correlation between LIP and CXCR4 expression was observed in stage III and IV human breast carcinoma specimens. Neuregulin 1 (or NRG1, hereafter referred to as heregulin) increased CXCR4 expression in breast cancer cells, and this coincided with increased LIP binding on the CXCR4 promoter. These findings may have important implications for understanding the molecular basis of CXCR4-mediated breast cancer cell metastasis and could potentially allow us to develop novel strategies to reduce morbidity and mortality in patients with metastatic breast cancer.

MiR-155-mediated loss of C/EBPβ shifts the TGF-β response from growth inhibition to epithelial-mesenchymal transition, invasion and metastasis in breast cancer

During breast cancer progression, transforming growth factor-beta (TGF-β) switches from acting as a growth inhibitor to become a major promoter of epithelial-mesenchymal transition (EMT), invasion and metastasis. However, the mechanisms involved in this switch are not clear. We found that loss of CCAAT-enhancer binding protein beta (C/EBPβ), a differentiation factor for the mammary epithelium, was associated with signs of EMT in triple-negative human breast cancer, and in invasive areas of mammary tumors in MMTV-PyMT mice. Using an established model of TGF-β-induced EMT in mouse mammary gland epithelial cells, we discovered that C/EBPβ was repressed during EMT by miR-155, an oncomiR in breast cancer. Depletion of C/EBPβ potentiated the TGF-β response towards EMT, and contributed to evasion of the growth inhibitory response to TGF-β. Furthermore, loss of C/EBPβ enhanced invasion and metastatic dissemination of the mouse mammary tumor cells to the lungs after subcutaneous injection into mice. The mechanism by which loss of C/EBPβ promoted the TGF-β response towards EMT, invasion and metastasis, was traced to a previously uncharacterized role of C/EBPβ as a transcriptional activator of genes encoding the epithelial junction proteins E-cadherin and coxsackie virus and adenovirus receptor. The results identify miR-155-mediated loss of C/EBPβ as a mechanism, which promotes breast cancer progression by shifting the TGF-β response from growth inhibition to EMT, invasion and metastasis.

Regulation of human endometrial stromal proliferation and differentiation by C/EBPβ involves cyclin E-cdk2 and STAT3

During each menstrual cycle, the human uterus undergoes a unique transformation, known as decidualization, which involves endometrial stromal proliferation and differentiation. During this process, the stromal cells are transformed into decidual cells, which produce factors that prepare the uterus for potential embryo implantation. We previously identified the transcription factor CCAAT/enhancer-binding protein (C/EBP)β as a regulator of endometrial stromal proliferation and differentiation in mice. In this study, we addressed the role of C/EBPβ in human endometrial decidualization. Using small interfering RNA targeted to C/EBPβ mRNA, we demonstrated that C/EBPβ controls the proliferation of primary human endometrial stromal cells (HESCs) by regulating the expression of several key cell cycle-regulatory factors during the G(1)-S phase transition. Additionally, loss of C/EBPβ expression blocked the differentiation of HESCs in response to estrogen, progesterone, and cyclic AMP. Gene expression profiling of normal and C/EBPβ-deficient HESCs revealed that the receptor for the cytokine IL-11 and its downstream signal transducer signal transducer and activator of transcription 3 (STAT3) are targets of regulation by C/EBPβ. Chromatin immunoprecipitation analysis indicated that C/EBPβ controls the expression of STAT3 gene by directly interacting with a distinct regulatory sequence in its 5'-flanking region. Attenuation of STAT3 mRNA expression in HESCs resulted in markedly reduced differentiation of these cells, indicating an important role for STAT3 in decidualization. Gene expression profiling, using STAT3-deficient HESCs, showed an extensive overlap of pathways downstream of STAT3 and C/EBPβ during stromal cell differentiation. Collectively, these findings revealed a novel functional link between C/EBPβ and STAT3 that is a critical regulator of endometrial differentiation in women.

Phenotypes of CCAAT/enhancer-binding protein beta deficiency: hyperdontia and elongated coronoid process

OBJECTIVES

This investigation aimed to conduct a case-control study of mandibular morphology and dental anomalies to propose a relationship between mandibular/dental phenotypes and deficiency of CCAAT/enhancer-binding protein beta (CEBPB).

MATERIALS AND METHODS

Skulls of CEBPB(-/-), CEBPB(+/-) and CEBPB(+/+) mice were inspected with micro-computed tomography. Mandibular morphology was assessed with a method of Euclidean distance matrix analysis.

RESULTS

Elongation of the coronoid process was identified in CEBPB(+/-) (P ≤ 0.046) and CEBPB(-/-) 12-month-olds (P ≤ 0.028) but not in 14-day-olds (P ≥ 0.217) and 0-day-olds (P ≥ 0.189) of either genotype. Formation of supernumerary teeth in CEBPB(-/-) adult mice was demonstrated (χ(2) = 6.00, df = 1, P = 0.014).

CONCLUSIONS

CEBPB deficiency was related to elongation of the coronoid process and formation of supernumerary teeth. The mandibular and dental phenotypes of CEBPB deficiency were unseen by the 14th day after birth. Future investigations into the influence of CEBPB on mandibular and dental development are needed.

Histone demethylase Kdm4b functions as a co-factor of C/EBPβ to promote mitotic clonal expansion during differentiation of 3T3-L1 preadipocytes

CCAAT/enhancer-binding protein (C/EBP) β is required for both mitotic clonal expansion (MCE) and terminal adipocyte differentiation of 3T3-L1 preadipocytes. Although the role of C/EBPβ in terminal adipocyte differentiation is well defined, its mechanism of action during MCE is not. In this report, histone demethylase Kdm4b, as well as cell cycle genes Cdc45l (cell division cycle 45 homolog), Mcm3 (mini-chromosome maintenance complex component 3), Gins1 (GINS complex subunit 1) and Cdc25c (cell division cycle 25 homolog c), were identified as potential C/EBPβ target genes during MCE by utilizing promoter-wide chromatin immunoprecipitation (ChIP)-on-chip analysis combined with gene expression microarrays. The expression of Kdm4b is induced during MCE and its induction is dependent on C/EBPβ. ChIP, Electrophoretic Mobility Shift Assay (EMSA) and luciferase assay confirmed that the promoter of Kdm4b is bound and activated by C/EBPβ. Knockdown of Kdm4b impaired MCE. Furthermore, Kdm4b interacted with C/EBPβ and was recruited to the promoters of C/EBPβ-regulated cell cycle genes, including Cdc45l, Mcm3, Gins1, and Cdc25c, demethylated H3K9me3 and activated their transcription. These findings suggest a novel feed forward mechanism involving a DNA binding transcription factor (C/EBPβ) and a chromatin regulator (Kdm4b) in the regulation of MCE by controlling cell cycle gene expression.

Cidea is an essential transcriptional coactivator regulating mammary gland secretion of milk lipids

Adequate lipid secretion by mammary glands during lactation is essential for the survival of mammalian offspring. However, the mechanism governing this process is poorly understood. Here we show that Cidea is expressed at high levels in lactating mammary glands and its deficiency leads to premature pup death as a result of severely reduced milk lipids. Furthermore, the expression of xanthine oxidoreductase (XOR), an essential factor for milk lipid secretion, is markedly lower in Cidea-deficient mammary glands. Conversely, ectopic Cidea expression induces the expression of XOR and enhances lipid secretion in vivo. Unexpectedly, as Cidea has heretofore been thought of as a cytoplasmic protein, we detected it in the nucleus and found it to physically interact with transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) in mammary epithelial cells. We also observed that Cidea induces XOR expression by promoting the association of C/EBPβ onto, and the dissociation of HDAC1 from, the promoter of the Xdh gene encoding XOR. Finally, we found that Fsp27, another CIDE family protein, is detected in the nucleus and interacts with C/EBPβ to regulate expression of a subset of C/EBPβ downstream genes in adipocytes. Thus, Cidea acts as a previously unknown transcriptional coactivator of C/EBPβ in mammary glands to control lipid secretion and pup survival.

Smooth muscle α actin is specifically required for the maintenance of lactation

Smooth muscle α-actin (Acta2) is one of six highly conserved mammalian actin isoforms that appear to exhibit functional redundancy. Nonetheless, we have postulated a specific functional role for the smooth muscle specific isoform. Here, we show that Acta2 deficient mice have a remarkable mammary phenotype such that dams lacking Acta2 are unable to nurse their offspring effectively. The phenotype was rescued in cross fostering experiments with wild type mice, excluding a developmental defect in Acta2 null pups. The mechanism for the underlying phenotype is due to myoepithelial dysfunction postpartum resulting in precocious involution. Further, we demonstrate a specific defect in myoepithelial cell contractility in Acta2 null mammary glands, despite normal expression of cytoplasmic actins. We conclude that Acta2 specifically mediates myoepithelial cell contraction during lactation and that this actin isoform therefore exhibits functional specificity.

Negative regulation of C/EBPbeta1 by sumoylation in breast cancer cells

Sumoylation is a post-translational modification that is oftentimes deregulated in diseases such as cancer. Transcription factors are frequent targets of sumoylation and modification by SUMO can affect subcellular localization, transcriptional activity, and stability of the target protein. C/EBPbeta1 is one such transcription factor that is modified by SUMO-2/3. Non-sumoylated C/EBPbeta1, p52-C/EBPbeta1, is expressed in normal mammary epithelial cells but not breast cancer cell lines and plays a role in oncogene-induced senescence, a tumor suppressive mechanism. Although p52-C/EBPbeta1 is not observed via immunoblot in breast cancer cell lines, higher molecular weight bands are observed when breast cancer cell lines are subjected to immunoblot analysis with a C/EBPbeta1-specific antibody. We show that exogenously expressed C/EBPbeta1 is sumoylated in breast cancer cells, and that the higher molecular weight bands we observe in anti-C/EBPbeta1 immunoblots of breast cancer cell lines is sumoylated C/EBPbeta1. Phosphorylation oftentimes enhances sumoylation, and phosphorylation cascades are activated in breast cancer cells. We demonstrate that phosphorylation of C/EBPbeta1Thr235 by Erk-2 enhances sumoylation of C/EBPbeta1 in vitro. In addition, sumoylated C/EBPbeta1 is phosphorylated on Thr235 and mutation of Thr235 to alanine leads to a decrease in sumoylation of C/EBPbeta1. Finally, using a C/EBPbeta1-SUMO fusion protein we show that constitutive sumoylation of C/EBPbeta1 completely blocks its capability to induce senescence in WI38 fibroblasts expressing hTERT. Thus, sumolylation of C/EBPbeta1 in breast cancer cells may be a mechanism to circumvent oncogene-induced senescence.

LIP expression is regulated by IGF-1R signaling and participates in suppression of anoikis

Background

The transcription factor, CCAAT enhancer binding protein-β (C/EBPβ), is expressed as several distinct protein isoforms (LAP1, LAP2 and LIP) that have opposing actions in cellular proliferation and differentiation. Increases in the ratio of LIP/LAP are associated with aggressive, metastatic breast cancer; however, little is known regarding the molecular mechanisms that regulate LIP expression or the biological actions of an increase in the LIP/LAP ratio. Metastasis is highly dependent upon the suppression of anoikis and the role of C/EBPβ and LIP in this anchorage-independent, survival process is currently not known in mammary epithelial cells. IGF-1R signaling is important for the survival of breast cancer cells and crosstalk between IGF-1R and EGFR signaling pathways have been implicated in the development of more aggressive disease. We therefore evaluated in mammary epithelial cells whether IGF-1R signaling regulates the LIP/LAP ratio, analyzed the potential interplay between EGFR and IGF-1R signaling and addressed the biological significance of increased LIP expression in cellular survival and suppression of anoikis.

Results

Our data provide the first evidence that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. Although crosstalk between IGF-1R signaling and EGFR signaling is detectable in MCF10A cells, this crosstalk is not required for the IGF-1 mediated regulation of LIP expression. Rather, the critical regulator of IGF-1 induced LIP expression appears to be EGFR-independent, Akt activity. Our data also demonstrate that increases in LIP expression promote cell survival via suppression of anoikis. Likewise, knockdown of total C/EBPβ leads to increased cell death and suggest that C/EBPβ expression is important for survival and resistance to anoikis. IGF-1 treatment can partially rescue vector control cells from anoikis; however, cells with reduced C/EBPβ expression do not survive anoikis.

Conclusions

Taken together, our data demonstrate that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. C/EBPβ expression and elevations in LIP play an important role in regulating cellular survival via suppression of anoikis, in an IGF-1R mediated context or in a manner independent of IGF-1R signaling.