Interaction and functional collaboration of p300 and C/EBPbeta

Semaphorin 3E-Plexin-D1 Pathway Downstream of the Luteinizing Hormone Surge Regulates Ovulation, Granulosa Cell Luteinization, and Ovarian Angiogenesis in Mice

Ovulation is induced by the luteinizing hormone (LH) surge and accompanied by granulosa cell luteinization and ovarian angiogenesis. Semaphorin 3E (Sema3E)-Plexin-D1 pathway regulates angiogenesis in other tissues, but its role in the ovary is unknown. Evidence indicates that Sema3E-Plexin-D1 pathway plays an important role in the mouse ovary. The expression of Sema3E and its receptor, Plexin-D1, is dynamically regulated in the mouse ovary downstream of the LH surge. This regulation requires the modulation of chromatin accessibility by CCAAT/enhancer-binding proteins α and β. Intraovarian injection of recombinant Sema3E results in reduced ovulation, impaired corpus luteum formation, and aberrant ovarian angiogenesis. These in vivo physiological abnormalities are consistent with altered expression of genes regulating these processes, and with data from in vitro cultured granulosa cells and ovarian stromal tissues treated with Sema3E or neutralizing antibody of Plexin-D1. The findings pinpoint Sema3E-Plexin-D1 pathway as a potential therapeutic target for fertility and infertility management.

NAD + Sensing by PARP7 Regulates the C/EBPβ-Dependent Transcription Program in Adipose Tissue In Vivo

We have identified PARP7, an NAD + -dependent mono(ADP-ribosyl) transferase, as a key regulator of the C/EBPβ-dependent proadipogenic transcription program. Moreover, PARP7 is required for efficient adipogenesis and downstream biological functions, including involution of the lactating mammary gland. PARP7 serves as a coregulator of C/EBPβ, and depletion of PARP7 causes a dramatic reduction in C/EBPβ binding across the genome. PARP7 functions as a sensor of nuclear NAD + levels to control gene expression. At the relatively high nuclear NAD + concentrations in undifferentiated preadipocytes, PARP7 is catalytically active for auto- mono(ADP-ribosyl)ation (autoMARylation). As nuclear NAD + concentrations decline post- differentiation, autoMARylation decreases dramatically. AutoMARylation promotes instability of PARP7 through an E3 ligase-ubiquitin-proteasome pathway mediated by the ADP-ribose (ADPR)-binding ubiquitin E3 ligases DTX2 and RNF114. Genetic depletion of PARP7 in mice promotes a dramatic reduction in a wide array of lipids in the mammary gland fat pads and milk from lactating females, as well as a significant decrease in nicotinamide mononucleotide (NMN), a key nutrient in mother's milk. The latter is due to reduced expression of Nampt , the gene encoding NAMPT, the enzyme that produces NMN, which is a direct transcriptional target of PARP7 and C/EBPβ. Collectively, our results extend the biology of PARP7 to adipogenesis and perinatal health. Moreover, our results describe the molecular events that regulate these downstream biological functions.

Transcription factor PATZ1 promotes adipogenesis by controlling promoter regulatory loci of adipogenic factors

White adipose tissue (WAT) is essential for lipid storage and systemic energy homeostasis. Understanding adipocyte formation and stability is key to developing therapies for obesity and metabolic disorders. Through a high-throughput cDNA screen, we identified PATZ1, a POZ/BTB and AT-Hook Containing Zinc Finger 1 protein, as an important adipogenic transcription factor. PATZ1 is expressed in human and mouse adipocyte precursor cells (APCs) and adipocytes. In cellular models, PATZ1 promotes adipogenesis via protein-protein interactions and DNA binding. PATZ1 ablation in mouse adipocytes and APCs leads to a reduced APC pool, decreased fat mass, and hypertrophied adipocytes. ChIP-Seq and RNA-seq analyses show that PATZ1 supports adipogenesis by interacting with transcriptional machinery at the promoter regions of key early adipogenic factors. Mass-spec results show that PATZ1 associates with GTF2I, with GTF2I modulating PATZ1's function during differentiation. These findings underscore PATZ1's regulatory role in adipocyte differentiation and adiposity, offering insights into adipose tissue development.

Adenovirus small E1A directs activation of Alu transcription at YAP/TEAD- and AP-1-bound enhancers through interactions with the EP400 chromatin remodeler

Alu retrotransposons, which form the largest family of mobile DNA elements in the human genome, have recently come to attention as a potential source of regulatory novelties, most notably by participating in enhancer function. Even though Alu transcription by RNA polymerase III is subjected to tight epigenetic silencing, their expression has long been known to increase in response to various types of stress, including viral infection. Here we show that, in primary human fibroblasts, adenovirus small e1a triggered derepression of hundreds of individual Alus by promoting TFIIIB recruitment by Alu-bound TFIIIC. Epigenome profiling revealed an e1a-induced decrease of H3K27 acetylation and increase of H3K4 monomethylation at derepressed Alus, making them resemble poised enhancers. The enhancer nature of e1a-targeted Alus was confirmed by the enrichment, in their upstream regions, of the EP300/CBP acetyltransferase, EP400 chromatin remodeler and YAP1 and FOS transcription factors. The physical interaction of e1a with EP400 was critical for Alu derepression, which was abrogated upon EP400 ablation. Our data suggest that e1a targets a subset of enhancer Alus whose transcriptional activation, which requires EP400 and is mediated by the e1a-EP400 interaction, may participate in the manipulation of enhancer activity by adenoviruses.

Celastrol as an emerging anticancer agent: Current status, challenges and therapeutic strategies

Celastrol is a pentacyclic triterpenoid extracted from the traditional Chinese medicine Tripterygium wilfordii Hook F., which has multiple pharmacological activities. In particular, modern pharmacological studies have demonstrated that celastrol exhibits significant broad-spectrum anticancer activities in the treatment of a variety of cancers, including lung cancer, liver cancer, colorectal cancer, hematological malignancies, gastric cancer, prostate cancer, renal carcinoma, breast cancer, bone tumor, brain tumor, cervical cancer, and ovarian cancer. Therefore, by searching the databases of PubMed, Web of Science, ScienceDirect and CNKI, this review comprehensively summarizes the molecular mechanisms of the anticancer effects of celastrol. According to the data, the anticancer effects of celastrol can be mediated by inhibiting tumor cell proliferation, migration and invasion, inducing cell apoptosis, suppressing autophagy, hindering angiogenesis and inhibiting tumor metastasis. More importantly, PI3K/Akt/mTOR, Bcl-2/Bax-caspase 9/3, EGFR, ROS/JNK, NF-κB, STAT3, JNK/Nrf2/HO-1, VEGF, AR/miR-101, HSF1-LKB1-AMPKα-YAP, Wnt/β-catenin and CIP2A/c-MYC signaling pathways are considered as important molecular targets for the anticancer effects of celastrol. Subsequently, studies of its toxicity and pharmacokinetic properties showed that celastrol has some adverse effects, low oral bioavailability and a narrow therapeutic window. In addition, the current challenges of celastrol and the corresponding therapeutic strategies are also discussed, thus providing a theoretical basis for the development and application of celastrol in the clinic.

C/EBPβ cooperates with MYB to maintain the oncogenic program of AML cells

Studies on the role of transcription factor MYB in acute myeloid leukemia (AML) have identified MYB as a key regulator of a transcriptional program for self-renewal of AML cells. Recent work summarized here has now highlighted the CCAAT-box/enhancer binding protein beta (C/EBPβ) as an essential factor and potential therapeutic target that cooperates with MYB and coactivator p300 in the maintenance of the leukemic cells.

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.

Potential Mechanisms by which Glucocorticoids Induce Breast Carcinogenesis through Nrf2 Inhibition

Breast cancer is the most common malignancy among women worldwide. Several studies indicate that, in addition to established risk factors for breast cancer, other factors such as cortisol release related to psychological stress and drug treatment with high levels of glucocorticoids may also contribute significantly to the initiation of breast cancer. There are several possible mechanisms by which glucocorticoids might promote neoplastic transformation of breast tissue. Among these, the least known and studied is the inhibition of the nuclear erythroid factor 2-related (Nrf2)-antioxidant/electrophile response element (ARE/EpRE) pathway by high levels of glucocorticoids. Specifically, Nrf2 is a potent transcriptional activator that plays a central role in the basal and inducible expression of many cytoprotective genes that effectively protect mammalian cells from various forms of stress and reduce the propensity of tissues and organisms to develop disease or malignancy including breast cancer. Consequently, a loss of Nrf2 in response to high levels of gluco-corticoids may lead to a decrease in cellular defense against oxidative stress, which plays an important role in the initiation of human mammary carcinogenesis. In the present review, we provide a comprehensive overview of the current state of knowledge of the cellular mechanisms by which both glucocorticoid pharmacotherapy and endogenous GCs (cortisol in humans and corticosterone in rodents) may contribute to breast cancer development through inhibition of the Nrf2-ARE/EpRE pathway and the protective role of melatonin against glucocorticoid-induced apoptosis in the immune system.

Transcriptional coactivator PGC-1α contributes to decidualization by forming a histone-modifying complex with C/EBPβ and p300

We previously reported that CCAAT/enhancer-binding protein beta (C/EBPβ) is the pioneer factor inducing transcription enhancer mark H3K27 acetylation (H3K27ac) in the promoter and enhancer regions of genes encoding insulin-like growth factor–binding protein-1 (IGFBP-1) and prolactin (PRL) and that this contributes to decidualization of human endometrial stromal cells (ESCs). Peroxisome proliferator–activated receptor gamma coactivator 1-alpha (PGC-1α; PPARGC1A) is a transcriptional coactivator known to regulate H3K27ac. However, although PGC-1α is expressed in ESCs, the potential role of PGC-1α in mediating decidualization is unclear. Here, we investigated the involvement of PGC-1α in the regulation of decidualization. We incubated ESCs with cAMP to induce decidualization and knocked down PPARGC1A to inhibit cAMP-induced expression of IGFBP-1 and PRL. We found cAMP increased the recruitment of PGC-1α and p300 to C/EBPβ-binding sites in the promoter and enhancer regions of IGFBP-1 and PRL, corresponding with increases in H3K27ac. Moreover, PGC-1α knockdown inhibited these increases, suggesting PGC-1α forms a histone-modifying complex with C/EBPβ and p300 at these regions. To further investigate the regulation of PGC-1α, we focused on C/EBPβ upstream of PGC-1α. We found cAMP increased C/EBPβ recruitment to the novel enhancer regions of PPARGC1A. Deletion of these enhancers decreased PGC-1α expression, indicating that C/EBPβ upregulates PGC-1α expression by binding to novel enhancer regions. In conclusion, PGC-1α is upregulated by C/EBPβ recruitment to novel enhancers and contributes to decidualization by forming a histone-modifying complex with C/EBPβ and p300, thereby inducing epigenomic changes in the promoters and enhancers of IGFBP-1 and PRL.

Src-Family Protein Kinase Inhibitors Suppress MYB Activity in a p300-Dependent Manner

Recent studies have disclosed transcription factor MYB as a potential drug target for malignancies that are dependent on deregulated MYB function, including acute myeloid leukemia (AML) and adenoid cystic carcinoma (ACC). Although transcription factors are often regarded as undruggable, successful targeting of MYB by low-molecular-weight compounds has recently been demonstrated. In an attempt to repurpose known drugs as novel MYB-inhibitory agents, we have screened libraries of approved drugs and drug-like compounds for molecules with MYB-inhibitory potential. Here, we present initial evidence for the MYB-inhibitory activity of the protein kinase inhibitors bosutinib, PD180970 and PD161570, that we identified in a recent screen. We show that these compounds interfere with the activity of the MYB transactivation domain, apparently by disturbing the ability of MYB to cooperate with the coactivator p300. We show that treatment of the AML cell line HL60 with these compounds triggers the up-regulation of the myeloid differentiation marker CD11b and induces cell death. Importantly, we show that these effects are significantly dampened by forced expression of an activated version of MYB, confirming that the ability to suppress MYB function is a relevant activity of these compounds. Overall, our work identifies several protein kinase inhibitors as novel MYB-inhibitory agents and suggests that the inhibition of MYB function may play a role in their pharmacological impact on leukemic cells.

Natural Products with Antitumor Potential Targeting the MYB-C/EBPβ-p300 Transcription Module

The transcription factor MYB is expressed predominantly in hematopoietic progenitor cells, where it plays an essential role in the development of most lineages of the hematopoietic system. In the myeloid lineage, MYB is known to cooperate with members of the CCAAT box/enhancer binding protein (C/EBP) family of transcription factors. MYB and C/EBPs interact with the co-activator p300 or its paralog CREB-binding protein (CBP), to form a transcriptional module involved in myeloid-specific gene expression. Recent work has demonstrated that MYB is involved in the development of human leukemia, especially in acute T-cell leukemia (T-ALL) and acute myeloid leukemia (AML). Chemical entities that inhibit the transcriptional activity of the MYB-C/EBPβ-p300 transcription module may therefore be of use as potential anti-tumour drugs. In searching for small molecule inhibitors, studies from our group over the last 10 years have identified natural products belonging to different structural classes, including various sesquiterpene lactones, a steroid lactone, quinone methide triterpenes and naphthoquinones that interfere with the activity of this transcriptional module in different ways. This review gives a comprehensive overview on the various classes of inhibitors and the inhibitory mechanisms by which they affect the MYB-C/EBPβ-p300 transcriptional module as a potential anti-tumor target. We also focus on the current knowledge on structure-activity relationships underlying these biological effects and on the potential of these compounds for further development.

C/EBPβ sustains the oncogenic program of AML cells by cooperating with MYB and co-activator p300 in a transcriptional module

Transcription factor MYB is a key regulator of gene expression in hematopoietic cells and has emerged as a novel drug target for acute myeloid leukemia (AML). Studies aiming to identify potential MYB inhibitors have shown that the natural compound helenalin acetate (HA) inhibits viability and induces cell death and differentiation of AML cells by disrupting the MYB-induced gene expression program. Interestingly, CCAAT-box/enhancer binding protein beta (C/EBPβ), a transcription factor known to cooperate with MYB and the co-activator p300 in myeloid cells, rather than MYB itself, was identified as the primary target of HA. This supports a model in which MYB, C/EBPβ and p300 form the core of a transcriptional module that is essential for the maintenance of proliferative potential of AML cells, highlighting a novel role of C/EBPβ as a pro-leukemogenic factor.

Characterization of the MYB-inhibitory potential of the Pan-HDAC inhibitor LAQ824

A large body of work has shown that MYB acts as a master transcription regulator in hematopoietic cells and has pinpointed MYB as a potential drug target for acute myeloid leukemia (AML). Here, we have examined the MYB-inhibitory potential of the HDAC inhibitor LAQ824, which was identified in a screen for novel MYB inhibitors. We show that nanomolar concentrations of LAQ824 and the related HDAC inhibitors vorinostat and panobinostat interfere with MYB function in two ways, by inducing its degradation and inhibiting its activity. Reporter assays show that the inhibition of MYB activity by LAQ824 involves the MYB transactivation domain and the cooperation of MYB with co-activator p300, a key MYB interaction partner and driver of MYB activity. In AML cells, LAQ824-induced degradation of MYB is accompanied by expression of myeloid differentiation markers and apoptotic and necrotic cell death. The ability of LAQ824 to inhibit MYB activity is supported by the observation that down-regulation of direct MYB target genes MYC and GFI1 occurs without apparent decrease of MYB expression already after 2 h of treatment with LAQ824. Furthermore, ectopic expression of an activated version of MYB In HL60 cells counteracts the induction of myeloid differentiation by LAQ824. Overall, our data identify LAQ824 and related HDAC inhibitors as potent MYB-inhibitory agents that exert dual effects on MYB expression and activity in AML cells.

Bcr-TMP, a Novel Nanomolar-Active Compound That Exhibits Both MYB- and Microtubule-Inhibitory Activity

Simple Summary

Recent work has identified the transcription regulator MYB as an interesting therapeutic target for the treatment of certain leukemias and other cancers that are dependent on deregulated MYB activity, such as acute myeloid leukemia (AML) and adenoid cystic carcinoma (ACC). Here we report the identification and characterization of 2-amino-4-(3,4,5-trimethoxyphenyl)-4H-naphtho[1,2-b]pyran-3-carbonitrile (Bcr-TMP), a novel highly active MYB inhibitory compound. We show that nanomolar concentrations of Bcr-TMP are sufficient to down-regulate the expression of MYB target genes and induce both cell-death and differentiation in AML cell lines. Importantly, Bcr-TMP also and exerts stronger anti-proliferative effects on MYB-addicted primary AML cells and patient-derived ACC cells than on their non-oncogenic counterparts. Preliminary work shows that Bcr-TMP acts through p300, a protein interacting with MYB and stimulating its activity. Interestingly, Bcr-TMP has an additional activity as an anti-microtubule agent. Overall, Bcr-TMP is an interesting compound that warrants further research to understand its mechanism of action and its therapeutic potential for MYB-dependent malignancies.

Abstract

Studies of the role of MYB in human malignancies have highlighted MYB as a potential drug target for acute myeloid leukemia (AML) and adenoid cystic carcinoma (ACC). Here, we present the initial characterization of 2-amino-4-(3,4,5-trimethoxyphenyl)-4H-naphtho[1,2-b]pyran-3-carbonitrile (Bcr-TMP), a nanomolar-active MYB-inhibitory compound identified in a screen for novel MYB inhibitors. Bcr-TMP affects MYB function in a dual manner by inducing its degradation and suppressing its transactivation potential by disrupting its cooperation with co-activator p300. Bcr-TMP also interferes with the p300-dependent stimulation of C/EBPβ, a transcription factor co-operating with MYB in myeloid cells, indicating that Bcr-TMP is a p300-inhibitor. Bcr-TMP reduces the viability of AML cell lines at nanomolar concentrations and induces cell-death and expression of myeloid differentiation markers. It also down-regulates the expression of MYB target genes and exerts stronger anti-proliferative effects on MYB-addicted primary murine AML cells and patient-derived ACC cells than on their non-oncogenic counterparts. Surprisingly, we observed that Bcr-TMP also has microtubule-disrupting activity, pointing to a possible link between MYB-activity and microtubule stability. Overall, Bcr-TMP is a highly potent multifunctional MYB-inhibitory agent that warrants further investigation of its therapeutic potential and mechanism(s) of action.

The Role of the CREB Protein Family Members and the Related Transcription Factors in Radioresistance Mechanisms

In the framework of space flight, the risk of radiation carcinogenesis is considered a "red" risk due to the high likelihood of occurrence as well as the high potential impact on the quality of life in terms of disease-free survival after space missions. The cyclic AMP response element-binding protein (CREB) is overexpressed both in haematological malignancies and solid tumours and its expression and function are modulated following irradiation. The CREB protein is a transcription factor and member of the CREB/activating transcription factor (ATF) family. As such, it has an essential role in a wide range of cell processes, including cell survival, proliferation, and differentiation. Among the CREB-related nuclear transcription factors, NF-κB and p53 have a relevant role in cell response to ionising radiation. Their expression and function can decide the fate of the cell by choosing between death or survival. The aim of this review was to define the role of the CREB/ATF family members and the related transcription factors in the response to ionising radiation of human haematological malignancies and solid tumours.

The essential glucose transporter GLUT1 is epigenetically upregulated by C/EBPβ and WT1 during decidualization of the endometrium

Human endometrial stromal cells (ESCs) differentiate into decidual cells by the action of progesterone, which is essential for implantation and maintenance of pregnancy. We previously reported that glucose uptake by human ESCs increases during decidualization and that glucose is indispensable for decidualization. Although glucose transporter 1 (GLUT1) is upregulated during decidualization, it remains unclear whether it is involved in glucose uptake. Here, we attempted to determine the role of GLUT1 during decidualization as well as the factors underlying its upregulation. ESCs were incubated with cAMP to induce decidualization. Knockdown of GLUT1 suppressed cAMP-increased glucose uptake and the expressions of specific markers of decidualization, IGF-binding protein-1 (IGFBP-1), and prolactin (PRL). To investigate the regulation of GLUT1 expression, we focused on CCAAT enhancer-binding protein β (C/EBPβ) and Wilms' tumor 1 (WT1) as the upstream transcription factors regulating GLUT1 expression. Knockdown of either C/EBPβ or WT1 suppressed cAMP-increased GLUT1 expression and glucose uptake. cAMP treatment also increased the recruitment of C/EBPβ and WT1 to the GLUT1 promoter region. Interestingly, cAMP increased the H3K27 acetylation (H3K27ac) and p300 recruitment in the GLUT1 promoter region. Knockdown of C/EBPβ or WT1 inhibited these events, indicating that both C/EBPβ and WT1 contribute to the increase of H3K27ac by recruiting p300 to the GLUT1 promoter region during decidualization. These findings indicate that GLUT1 is involved in glucose uptake in ESCs during decidualization, thus facilitating the establishment of pregnancy.

Proteasome inhibitors suppress MYB oncogenic activity in a p300-dependent manner

Studies of the role of MYB in human malignancies have highlighted MYB as a potential drug target for acute myeloid leukemia (AML) and adenoid cystic carcinoma (ACC). Although transcription factors are often considered un-druggable, recent work has demonstrated successful targeting of MYB by low molecular weight compounds. This has fueled the notion that inhibition of MYB has potential as a therapeutic approach against MYB-driven malignancies. Here, we have used a MYB reporter cell line to screen a library of FDA-approved drugs for novel MYB inhibitors. We demonstrate that proteasome inhibitors have significant MYB-inhibitory activity, prompting us to characterize the proteasome inhibitor oprozomib in more detail. Oprozomib was shown to interfere with the ability of the co-activator p300 to stimulate MYB activity and to exert anti-proliferative effects on human AML and ACC cells. Overall, our work demonstrated suppression of oncogenic MYB activity as a novel result of proteasome inhibition.

C/EBPβ is a MYB- and p300-cooperating pro-leukemogenic factor and promising drug target in acute myeloid leukemia

Transcription factor MYB has recently emerged as a promising drug target for the treatment of acute myeloid leukemia (AML). Here, we have characterized a group of natural sesquiterpene lactones (STLs), previously shown to suppress MYB activity, for their potential to decrease AML cell proliferation. Unlike what was initially thought, these compounds inhibit MYB indirectly via its cooperation partner C/EBPβ. C/EBPβ-inhibitory STLs affect the expression of a large number of MYB-regulated genes, suggesting that the cooperation of MYB and C/EBPβ broadly shapes the transcriptional program of AML cells. We show that expression of GFI1, a direct MYB target gene, is controlled cooperatively by MYB, C/EBPβ, and co-activator p300, and is down-regulated by C/EBPβ-inhibitory STLs, exemplifying that they target the activity of composite MYB-C/EBPβ-p300 transcriptional modules. Ectopic expression of GFI1, a zinc-finger protein that is required for the maintenance of hematopoietic stem and progenitor cells, partially abrogated STL-induced myelomonocytic differentiation, implicating GFI1 as a relevant target of C/EBPβ-inhibitory STLs. Overall, our data identify C/EBPβ as a pro-leukemogenic factor in AML and suggest that targeting of C/EBPβ may have therapeutic potential against AML.

The transcription factor code: a beacon for histone methyltransferase docking

Histone methylation is required for the establishment and maintenance of gene expression patterns that determine cellular identity, and its perturbation often leads to aberrant development and disease. Recruitment of histone methyltransferases (HMTs) to gene regulatory elements (GREs) of developmental genes is important for the correct activation and silencing of these genes, but the drivers of this recruitment are largely unknown. Here we propose that lineage-instructive transcription factors (Lin-TFs) act as general recruiters of HMT complexes to cell type-specific GREs through protein-protein interactions. We also postulate that the specificity of these interactions is dictated by Lin-TF post-translational modifications (PTMs), which act as a 'transcription factor code' that can determine the directionality of cell fate decisions during differentiation and development.

C/EBPβ regulates the JAK/STAT signaling pathway in triple-negative breast cancer

C/EBPβ is a member of the CCAAT/enhancer‐binding protein (C/EBP) family, which consists of a number of b‐ZIP transcription factors. Although C/EBPβ has been implicated in the development of certain cancers, including breast cancer, it remains unknown whether dysregulation of C/EBPβ in breast cancer is subtype‐specific. Moreover, the underlying mechanisms by which C/EBPβ regulates breast cancer carcinogenesis are not fully understood. Here, we present evidence that C/EBPβ is specifically overexpressed in human TNBC samples, but not in non‐TNBC samples. C/EBPβ depletion dramatically suppressed TNBC cell growth, migration, invasion, and colony formation ability. A subsequent mechanistic study revealed that the JAK/STAT signaling pathway was upregulated in C/EBPβ_high TNBC samples compared with C/EBPβ_low TNBC samples. C/EBPβ ChIP‐seq and qPCR were performed to demonstrate that C/EBPβ directly binds to and regulates JAK/STAT signaling pathway genes in TNBC. Taken together, our data indicate the oncogenic role of C/EBPβ in human TNBC and reveal a novel mechanism by which C/EBPβ promotes TNBC carcinogenesis.

Stabilization of C/EBPβ through direct interaction with STAT3 in H-Ras transformed human mammary epithelial cells

Signal transducer and activator of transcription 3 (STAT3) plays important roles in cancer-associated inflammation by controlling expression of proinflammatory cytokines and chemokines. Recent studies suggest that C/EBPβ (CCAAT-enhancer binding protein beta) and STAT3 synergistically stimulate cancer cell proliferation and epithelial-mesenchymal transition. C/EBPβ is a leucine-zipper transcription factor that regulates expression of a variety of inflammatory cytokines or chemokines, such as IL-8, G-CSF (granulocyte colony stimulating factor), and GM-CSF (granulocyte macrophage colony stimulating factor) which induce neutrophil infiltration and differentiation. However, molecular mechanisms by which STAT3 and C/EBPβ cooperatively interact had not been fully elucidated. In this study, we found that the level of C/EBPβ protein, but not that of its mRNA transcript, was decreased in the absence of STAT3 in H-Ras transformed human mammary epithelial (H-Ras MCF10A) cells. In addition, silencing STAT3 dramatically induced ubiquitination of C/EBPβ for proteasomal degradation. Furthermore, direct interaction between STAT3 and C/EBPβ was confirmed by immunoprecipitation and proximity ligation assays. Taken together, these results suggest that STAT3 stabilizes C/EBPβ, thereby promoting cancer-associated inflammation.

Production of fever mediator PGE2 in human monocytes activated with MDP adjuvant is controlled by signaling from MAPK and p300 HAT: Key role of T cell derived factor

Fever and inflammatory responses were observed in some subjects in early clinical trials of vaccines adjuvanted with muramyl dipeptide (MDP), a NOD2 agonist. Biosynthesis of Prostaglandin E2 (PGE₂) that transmits febrile signals to the brain is controlled by an inducible enzyme, Cyclooxygenase 2 (COX-2). MDP alone was not sufficient to induce expression of COX-2 and PGE₂ production in vitro. Conditioned medium prepared from Peripheral Blood Mononuclear Cells (PBMCs)-derived CD3-bead purified human T cells (TCM) dramatically increased COX2 gene transcription, COX-2 protein expression, and PGE₂ production in MDP-treated monocytes. We explored epigenetic changes at the COX2 promoter using Chromatin Immunoprecipitation assay (ChIP). Increase in COX2 transcription correlated with increased recruitment of RNA polymerase II (Pol II) and p300 histone acetyl transferase (HAT) to the COX2 promoter in monocytes activated with MDP and TCM. The role of p300 HAT was confirmed by using C646, an inhibitor of p300, that reduced binding of acetylated H3 and H4 histones at the COX2 promoter, COX2 transcription, and PGE₂ production in monocytes. Binding of p300, Nuclear Factor Kappa B (NF-κB), and Pol II to the COX2 promoter was also sensitive to inhibitors of Mitogen-Activated Protein Kinase (MAPK) pathway and to antibodies against Macrophage-1 (Mac-1) integrin in MDP/TCM-treated monocytes. Importantly, recombinant Glycoprotein Ib alfa (GPIbα), the recently identified factor in TCM, increased binding of NF-κB, p300, and of Pol II to the COX2 promoter and COX2 transcription in MDP-treated monocytes. Our findings suggest that a second signal through Mac-1 and MAPK is triggered by a T cell derived soluble GPIbα protein leading to the assembly of the transcription machinery at the COX2 promoter and production of PGE₂ in human monocytes in response to MDP/NOD2 activation.

A functional variant in the serotonin receptor 7 gene (HTR7), rs7905446, is associated with good response to SSRIs in bipolar and unipolar depression

Predicting antidepressant response has been a clinical challenge for mood disorder. Although several genome-wide association studies have suggested a number of genetic variants to be associated with antidepressant response, the sample sizes are small and the results are difficult to replicate. Previous animal studies have shown that knockout of the serotonin receptor 7 gene (HTR7) resulted in an antidepressant-like phenotype, suggesting it was important to antidepressant action. In this report, in the first stage, we used a cost-effective pooled-sequencing strategy to sequence the entire HTR7 gene and its regulatory regions to investigate the association of common variants in HTR7 and clinical response to four selective serotonin reuptake inhibitors (SSRIs: citalopram, paroxetine, fluoxetine and sertraline) in a retrospective cohort mainly consisting of subjects with bipolar disorder (n = 359). We found 80 single-nucleotide polymorphisms (SNPs) with false discovery rate < 0.05 associated with response to paroxetine. Among the significant SNPs, rs7905446 (T/G), which is located at the promoter region, also showed nominal significance (P < 0.05) in fluoxetine group. GG/TG genotypes for rs7905446 and female gender were associated with better response to two SSRIs (paroxetine and fluoxetine). In the second stage, we replicated this association in two independent prospective samples of SSRI-treated patients with major depressive disorder: the MARS (n = 253, P = 0.0169) and GENDEP studies (n = 432, P = 0.008). The GG/TG genotypes were consistently associated with response in all three samples. Functional study of rs7905446 showed greater activity of the G allele in regulating expression of HTR7. The G allele displayed higher luciferase activity in two neuronal-related cell lines, and estrogen treatment decreased the activity of only the G allele. Electrophoretic mobility shift assay suggested that the G allele interacted with CCAAT/enhancer-binding protein beta transcription factor (TF), while the T allele did not show any interaction with any TFs. Our results provided novel pharmacogenomic evidence to support the role of HTR7 in association with antidepressant response.

Targeting monocyte-intrinsic enhancer reprogramming improves immunotherapy efficacy in hepatocellular carcinoma

OBJECTIVE

Hepatocellular carcinoma (HCC), mostly developed in fibrotic/cirrhotic liver, exhibits relatively low responsiveness to immune checkpoint blockade (ICB) therapy. As myeloid-derived suppressor cell (MDSC) is pivotal for immunosuppression, we investigated its role and regulation in the fibrotic microenvironment with an aim of developing mechanism-based combination immunotherapy.

DESIGN

Functional significance of MDSCs was evaluated by flow cytometry using two orthotopic HCC models in fibrotic liver setting via carbon tetrachloride or high-fat high-carbohydrate diet and verified by clinical specimens. Mechanistic studies were conducted in human hepatic stellate cell (HSC)-peripheral blood mononuclear cell culture systems and fibrotic-HCC patient-derived MDSCs. The efficacy of single or combined therapy with anti-programmed death-1-ligand-1 (anti-PD-L1) and a clinically trialled BET bromodomain inhibitor i-BET762 was determined.

RESULTS

Accumulation of monocytic MDSCs (M-MDSCs), but not polymorphonuclear MDSCs, in fibrotic livers significantly correlated with reduced tumour-infiltrating lymphocytes (TILs) and increased tumorigenicity in both mouse models. In human HCCs, the tumour-surrounding fibrotic livers were markedly enriched with M-MDSC, with its surrogate marker CD33 significantly associated with aggressive tumour phenotypes and poor survival rates. Mechanistically, activated HSCs induced monocyte-intrinsic p38 MAPK signalling to trigger enhancer reprogramming for M-MDSC development and immunosuppression. Treatment with p38 MAPK inhibitor abrogated HSC-M-MDSC crosstalk to prevent HCC growth. Concomitant with patient-derived M-MDSC suppression by i-BET762, combined treatment with anti-PD-L1 synergistically enhanced TILs, resulting in tumour eradication and prolonged survival in the fibrotic-HCC mouse model.

CONCLUSION

Our results signify how non-tumour-intrinsic properties in the desmoplastic microenvironment can be exploited to reinstate immunosurveillance, providing readily translatable combination strategies to empower HCC immunotherapy.

Glucose Metabolism Drives Histone Acetylation Landscape Transitions that Dictate Muscle Stem Cell Function

The impact of glucose metabolism on muscle regeneration remains unresolved. We identify glucose metabolism as a crucial driver of histone acetylation and myogenic cell fate. We use single-cell mass cytometry (CyTOF) and flow cytometry to characterize the histone acetylation and metabolic states of quiescent, activated, and differentiating muscle stem cells (MuSCs). We find glucose is dispensable for mitochondrial respiration in proliferating MuSCs, so that glucose becomes available for maintaining high histone acetylation via acetyl-CoA. Conversely, quiescent and differentiating MuSCs increase glucose utilization for respiration and have consequently reduced acetylation. Pyruvate dehydrogenase (PDH) activity serves as a rheostat for histone acetylation and must be controlled for muscle regeneration. Increased PDH activity in proliferation increases histone acetylation and chromatin accessibility at genes that must be silenced for differentiation to proceed, and thus promotes self-renewal. These results highlight metabolism as a determinant of MuSC histone acetylation, fate, and function during muscle regeneration.

p300 Mediates Muscle Wasting in Lewis Lung Carcinoma

C/EBPβ is a key mediator of cancer-induced skeletal muscle wasting. However, the signaling mechanisms that activate C/EBPβ in the cancer milieu are poorly defined. Here, we report cancer-induced muscle wasting requires the transcriptional cofactor p300, which is critical for the activation of C/EBPβ. Conditioned media from diverse types of tumor cells as well as recombinant HSP70 and HSP90 provoked rapid acetylation of C/EBPβ in myotubes, particularly at its Lys39 residue. Overexpression of C/EBPβ with mutated Lys39 impaired Lewis lung carcinoma (LLC)-induced activation of the C/EBPβ-dependent catabolic response, which included upregulation of E3 ligases UBR2 and atrogin1/MAFbx, increased LC3-II, and loss of muscle proteins both in myotubes and mouse muscle. Silencing p300 in myotubes or overexpressing a dominant negative p300 mutant lacking acetyltransferase activity in mouse muscle attenuated LLC tumor-induced muscle catabolism. Administration of pharmacologic p300 inhibitor C646, but not PCAF/GCN5 inhibitor CPTH6, spared LLC tumor-bearing mice from muscle wasting. Furthermore, mice with muscle-specific p300 knockout were resistant to LLC tumor-induced muscle wasting. These data suggest that p300 is a key mediator of LLC tumor-induced muscle wasting whose acetyltransferase activity may be targeted for therapeutic benefit in this disease. SIGNIFICANCE: These findings demonstrate that tumor-induced muscle wasting in mice is abrogated by knockout, mutation of Lys39 or Asp1399, and pharmacologic inhibition of p300.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/7/1331/F1.large.jpg.

Transforming growth factor β (TGFβ) cross-talk with the unfolded protein response is critical for hepatic stellate cell activation

Transforming growth factor β (TGFβ) potently activates hepatic stellate cells (HSCs), which promotes production and secretion of extracellular matrix (ECM) proteins and hepatic fibrogenesis. Increased ECM synthesis and secretion in response to TGFβ is associated with endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). TGFβ and UPR signaling pathways are tightly intertwined during HSC activation, but the regulatory mechanism that connects these two pathways is poorly understood. Here, we found that TGFβ treatment of immortalized HSCs (i.e. LX-2 cells) induces phosphorylation of the UPR sensor inositol-requiring enzyme 1α (IRE1α) in a SMAD2/3-procollagen I-dependent manner. We further show that IRE1α mediates HSC activation downstream of TGFβ and that its role depends on activation of a signaling cascade involving apoptosis signaling kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK). ASK1-JNK signaling promoted phosphorylation of the UPR-associated transcription factor CCAAT/enhancer binding protein β (C/EBPβ), which is crucial for TGFβ- or IRE1α-mediated LX-2 activation. Pharmacological inhibition of C/EBPβ expression with the antiviral drug adefovir dipivoxil attenuated TGFβ-mediated activation of LX-2 or primary rat HSCs in vitro and hepatic fibrogenesis in vivo Finally, we identified a critical relationship between C/EBPβ and the transcriptional regulator p300 during HSC activation. p300 knockdown disrupted TGFβ- or UPR-induced HSC activation, and pharmacological inhibition of the C/EBPβ-p300 complex decreased TGFβ-induced HSC activation. These results indicate that TGFβ-induced IRE1α signaling is critical for HSC activation through a C/EBPβ-p300-dependent mechanism and suggest C/EBPβ as a druggable target for managing fibrosis.

c-MYB and DMTF1 in Cancer

The c-Myb gene encodes a transcription factor that regulates cell proliferation, differentiation, and apoptosis through protein-protein interaction and transcriptional regulation of signaling pathways. The protein is frequently overexpressed in human leukemias, breast cancers, and other solid tumors suggesting that it is a bona fide oncogene. c-MYB is often overexpressed by translocation in human tumors with t(6;7)(q23;q34) resulting in c-MYB-TCRβ in T cell ALL, t(X;6)(p11;q23) with c-MYB-GATA1 in acute basophilic leukemia, and t(6;9)(q22-23;p23-24) with c-MYB-NF1B in adenoid cystic carcinoma. Antisense oligonucleotides to c-MYB were developed to purge bone marrow cells to eliminate tumor cells in leukemias. Recently, small molecules that inhibit c-MYB activity have been developed to disrupt its interaction with p300. The Dmp1 (cyclin D binding myb-like protein 1; Dmtf1) gene was isolated through its virtue for binding to cyclin D2. It is a transcription factor that has a Myb-like repeat for DNA binding. The Dmtf1 protein directly binds to the Arf promoter for transactivation and physically interacts with p53 to activate the p53 pathway. The gene is hemizygously deleted in 35-42% of human cancers and is associated with longer survival. The significances of aberrant expression of c-MYB and DMTF1 proteins in human cancers and their clinical significances are discussed.

Molecular evolution of elements controlling HLA-C expression: Adaptation to a role as a killer-cell immunoglobulin-like receptor ligand regulating natural killer cell function

The regulatory elements controlling the transcription of the HLA-A, HLA-B, and HLA-C genes have been extensively studied and compared. However, few studies have considered regulatory differences in the HLA genes from the perspective of their role as ligands for the killer-cell immunoglobulin-like receptor (KIR) family of HLA receptors expressed by natural killer (NK) cells. HLA-C is the most recently evolved gene, and there is considerable evidence pointing to its emergence as a specialized KIR ligand playing a major role in the missing-self recognition system of NK cells. Here I evaluate gene-specific differences in regulatory elements of the HLA genes, showing alterations that are consistent with the adaptation of HLA-C to a role in NK cell regulation.

Identification of trophoblast-specific elements in the HLA-C core promoter

There are several aspects of HLA-C gene expression that distinguish it from the HLA-A and HLA-B genes. First, HLA-C is expressed by extravillous trophoblasts, whereas HLA-A and HLA-B are not. Second, its cell-surface expression is much lower, which has been linked to changes in transcription and efficiency of peptide loading and export. Third, HLA-C possesses a NK cell-specific promoter and a complex alternative splicing system that regulates expression during NK cell development. In this study, we investigate the contribution of the HLA-C core promoter to trophoblast-specific expression. Analysis of transcription start sites showed the presence of a trophoblast-associated start site and additional upstream TATA and CCAAT-box elements in the HLA-C promoter, suggesting the presence of an overlapping trophoblast-specific promoter. A comparison of in vitro promoter activity showed that the HLA-C promoter was more active in trophoblast cell lines than either the HLA-A or HLA-B promoters. Enhanced trophoblast activity was mapped to the central enhanceosome region of the promoter, and mutational analysis identified changes in the RFX-binding region that generated a trophoblast-specific enhancer.

The distal upstream region of insulin-like growth factor-binding protein-1 enhances its expression in endometrial stromal cells during decidualization

We have previously shown that decidualization of human endometrial stromal cells (ESCs) causes a genome-wide increase in the levels of acetylation of histone-H3 Lys-27 (H3K27ac). We also reported that the distal gene regions, more than 3 kb up- or downstream of gene transcription start sites have increased H3K27ac levels. Insulin-like growth factor-binding protein-1 (IGFBP-1) is a specific decidualization marker and has increased H3K27ac levels in its distal upstream region (-4701 to -7501 bp). Here, using a luciferase reporter gene construct containing this IGFBP-1 upstream region, we tested the hypothesis that it is an IGFBP-1 enhancer. To induce decidualization, we incubated ESCs with cAMP and found that cAMP increased luciferase expression, indicating that decidualization increased the transcriptional activity from the IGFBP-1 upstream region. Furthermore, CRISPR/Cas9-mediated deletion of this region in HepG2 cells significantly reduced IGFBP-1 expression, confirming its role as an IGFBP-1 enhancer. A ChIP assay revealed that cAMP increased the recruitment of the transcriptional regulators CCAAT enhancer-binding protein β (C/EBPβ), forkhead box O1 (FOXO1), and p300 to the IGFBP-1 enhancer in ESCs. Of note, C/EBPβ knockdown inhibited the stimulatory effects of cAMP on the levels of H3K27ac, chromatin opening, and p300 recruitment at the IGFBP-1 enhancer. These results indicate that the region -4701 to -7501 bp upstream of IGFBP-1 functions as an enhancer for IGFBP-1 expression in ESCs undergoing decidualization, that C/EBPβ and FOXO1 bind to the enhancer region to up-regulate IGFBP-1 expression, and that C/EBPβ induces H3K27ac by recruiting p300 to the IGFBP-1 enhancer.

The natural anti-tumor compound Celastrol targets a Myb-C/EBPβ-p300 transcriptional module implicated in myeloid gene expression

Myb is a key regulator of hematopoietic progenitor cell proliferation and differentiation and has emerged as a potential target for the treatment of acute leukemia. Using a myeloid cell line with a stably integrated Myb-inducible reporter gene as a screening tool we have previously identified Celastrol, a natural compound with anti-tumor activity, as a potent Myb inhibitor that disrupts the interaction of Myb with the co-activator p300. We showed that Celastrol inhibits the proliferation of acute myeloid leukemia (AML) cells and prolongs the survival of mice in an in vivo model of AML, demonstrating that targeting Myb with a small-molecule inhibitor is feasible and might have potential as a therapeutic approach against AML. Recently we became aware that the reporter system used for Myb inhibitor screening also responds to inhibition of C/EBPβ, a transcription factor known to cooperate with Myb in myeloid cells. By re-investigating the inhibitory potential of Celastrol we have found that Celastrol also strongly inhibits the activity of C/EBPβ by disrupting its interaction with the Taz2 domain of p300. Together with previous studies our work reveals that Celastrol independently targets Myb and C/EBPβ by disrupting the interaction of both transcription factors with p300. Myb, C/EBPβ and p300 cooperate in myeloid-specific gene expression and, as shown recently, are associated with so-called super-enhancers in AML cells that have been implicated in the maintenance of the leukemia. We hypothesize that the ability of Celastrol to disrupt the activity of a transcriptional Myb-C/EBPβ-p300 module might explain its promising anti-leukemic activity.

Downregulation of decidual SP1 and P300 is associated with severe preeclampsia

Preeclampsia (PE) is a pregnancy-induced disorder characterized by hypertension and proteinuria after 20 weeks of gestation, affecting 5-7% of pregnancies worldwide. So far, the etiology of PE remains poorly understood. Abnormal decidualization is thought to contribute to the development of PE. SP1 belongs to the Sp/KLF superfamily and can recruit P300 to regulate the transcription of several genes. SP1 is also very important for decidualization as it enhances the expression of tissue factor. In this study, we investigated the expression of SP1 and P300 in deciduae and their relationship with PE. A total of 42 decidua samples were collected, of which 21 were from normal pregnant (NP) and 21 from severe PE. SP1 and P300 expression in deciduae and the levels of SP1 and P300 in cultured human endometrial stromal cells (hESCs) and primary hESCs during decidualization were determined. To further investigate the role of SP1 and P300 in human decidualization, RNA interference was used to silence SP1 and P300 in hESCs and primary hESCs. The following results were obtained. We found that the expressions of SP1 and P300 were reduced in decidual tissues with PE compared to those from NP. In the in vitro model of induction of decidualization, we found an increase in both SP1 and P300 levels. Silencing of SP1 and P300 resulted in abnormal decidualization and a significant reduction of decidualization markers such as insulin-like growth factor-binding protein1 and prolactin. Furthermore, the expression of vascular endothelial growth factor was also decreased upon SP1 and P300 silencing. Similar results were observed in primary hESCs. Our results suggest that SP1 and P300 play an important role during decidualization. Dysfunction of SP1 and P300 leads to impaired decidualization and might contribute to PE.

Functional Studies of CCAAT/Enhancer Binding Protein Site Located Downstream of the Transcriptional Start Site

Previous studies have identified a CCAAT/enhancer binding protein (C/EBP) site located downstream of the transcriptional start site (DS3). The role of the DS3 element with respect to HIV-1 transactivation by Tat and viral replication has not been characterized. We have demonstrated that DS3 was a functional C/EBPβ binding site and mutation of this site to the C/EBP knockout DS3-9C variant showed lower HIV-1 long terminal repeat (LTR) transactivation by C/EBPβ. However, it was able to exhibit similar or even higher transcription levels by Tat compared to the parental LTR. C/EBPβ and Tat together further enhanced the transcription level of the parental LAI-LTR and DS3-9C LTR, with higher levels in the DS3-9C LTR. HIV molecular clone viruses carrying the DS3-9C variant LTR demonstrated a decreased replication capacity and delayed rate of replication. These results suggest that DS3 plays a role in virus transcriptional initiation and provides new insight into C/EBP regulation of HIV-1.

C/EBPβ contributes to transcriptional activation of long non-coding RNA NEAT1 during APL cell differentiation

Emerging evidences have shown that long non-coding RNAs (lncRNAs) play critical roles in cancer development and cancer therapy. LncRNA Nuclear Enriched Abundant Transcript 1 (NEAT1) is indispensable during acute promyelocytic leukemia (APL) cell differentiation induced by all-trans retinoic acid (ATRA). However, the precise mechanism of NEAT1 upregulation has not been fully understood. In this study, we performed chromatin immunoprecipitation and luciferase reporter assays to demonstrate that C/EBP family transcription factor C/EBPβ bind to and transactivate the promoter of lncRNA NEAT1 through the C/EBPβ binding sites both around -54 bp and -1453 bp upstream of the transcription start site. Moreover, the expression of C/EBPβ was increased after ATRA treatment, and the binding of C/EBPβ in the NEAT1 promoter was also dramatically increased. Finally, knockdown of C/EBPβ significantly reduced the ATRA-induced upregulation of NEAT1. In conclusion, C/EBPβ directly activates the expression of NEAT1 through binding to the promoter of NEAT1. Knockdown of C/EBPβ impairs ATRA-induced transcriptional activation of NEAT1. Our data indicate that C/EBPβ contributes to ATRA-induced activation of NEAT1 during APL cell differentiation. Our results enrich our knowledge on the regulation of lncRNAs and the regulatory role of C/EBPβ in APL cell differentiation.

Withaferin A, a natural compound with anti-tumor activity, is a potent inhibitor of transcription factor C/EBPβ

Recent work has shown that deregulation of the transcription factor Myb contributes to the development of leukemia and several other human cancers, making Myb and its cooperation partners attractive targets for drug development. By employing a myeloid Myb-reporter cell line we have identified Withaferin A (WFA), a natural compound that exhibits anti-tumor activities, as an inhibitor of Myb-dependent transcription. Analysis of the inhibitory mechanism of WFA showed that WFA is a significantly more potent inhibitor of C/EBPβ, a transcription factor cooperating with Myb in myeloid cells, than of Myb itself. We show that WFA covalently modifies specific cysteine residues of C/EBPβ, resulting in the disruption of the interaction of C/EBPβ with the co-activator p300. Our work identifies C/EBPβ as a novel direct target of WFA and highlights the role of p300 as a crucial co-activator of C/EBPβ. The finding that WFA is a potent inhibitor of C/EBPβ suggests that inhibition of C/EBPβ might contribute to the biological activities of WFA.

Helenalin Acetate, a Natural Sesquiterpene Lactone with Anti-inflammatory and Anti-cancer Activity, Disrupts the Cooperation of CCAAT Box/Enhancer-binding Protein β (C/EBPβ) and Co-activator p300

Recent work has demonstrated pro-oncogenic functions of the transcription factor CCAAT box/enhancer-binding protein β (C/EBPβ) in various tumors, implicating C/EBPβ as an interesting target for the development of small-molecule inhibitors. We have previously discovered that the sesquiterpene lactone helenalin acetate, a natural compound known to inhibit NF-κB, is a potent C/EBPβ inhibitor. We have now examined the inhibitory mechanism of helenalin acetate in more detail. We demonstrate that helenalin acetate is a significantly more potent inhibitor of C/EBPβ than of NF-κB. Our work shows that helenalin acetate inhibits C/EBPβ by binding to the N-terminal part of C/EBPβ, thereby disrupting the cooperation of C/EBPβ with the co-activator p300. C/EBPβ is expressed in several isoforms from alternative translational start codons. We have previously demonstrated that helenalin acetate selectively inhibits only the full-length (liver-enriched activating protein* (LAP*)) isoform but not the slightly shorter (LAP) isoform. Consistent with this, helenalin acetate binds to the LAP* but not to the LAP isoform, explaining why its inhibitory activity is selective for LAP*. Although helenalin acetate contains reactive groups that are able to interact covalently with cysteine residues, as exemplified by its effect on NF-κB, the inhibition of C/EBPβ by helenalin acetate is not due to irreversible reaction with cysteine residues of C/EBPβ. In summary, helenalin acetate is the first highly active small-molecule C/EBPβ inhibitor that inhibits C/EBPβ by a direct binding mechanism. Its selectivity for the LAP* isoform also makes helenalin acetate an interesting tool to dissect the functions of the LAP* and LAP isoforms.

Small-Molecule Disruption of the Myb/p300 Cooperation Targets Acute Myeloid Leukemia Cells

The transcription factor c-Myb is essential for the proliferation of hematopoietic cells and has been implicated in the development of leukemia and other human cancers. Pharmacologic inhibition of Myb is therefore emerging as a potential therapeutic strategy for these diseases. By using a Myb reporter cell line, we have identified plumbagin and several naphthoquinones as potent low-molecular weight Myb inhibitors. We demonstrate that these compounds inhibit c-Myb by binding to the c-Myb transactivation domain and disrupting the cooperation of c-Myb with the coactivator p300, a major driver of Myb activity. Naphthoquinone-induced inhibition of c-Myb suppresses Myb target gene expression and induces the differentiation of the myeloid leukemia cell line HL60. We demonstrate that murine and human primary acute myeloid leukemia cells are more sensitive to naphthoquinone-induced inhibition of clonogenic proliferation than normal hematopoietic progenitor cells. Overall, our work demonstrates for the first time the potential of naphthoquinones as small-molecule Myb inhibitors that may have therapeutic potential for the treatment of leukemia and other tumors driven by deregulated Myb. Mol Cancer Ther; 15(12); 2905-15. ©2016 AACR.

BRD4 localization to lineage-specific enhancers is associated with a distinct transcription factor repertoire

Proper temporal epigenetic regulation of gene expression is essential for cell fate determination and tissue development. The Bromodomain-containing Protein-4 (BRD4) was previously shown to control the transcription of defined subsets of genes in various cell systems. In this study we examined the role of BRD4 in promoting lineage-specific gene expression and show that BRD4 is essential for osteoblast differentiation. Genome-wide analyses demonstrate that BRD4 is recruited to the transcriptional start site of differentiation-induced genes. Unexpectedly, while promoter-proximal BRD4 occupancy correlated with gene expression, genes which displayed moderate expression and promoter-proximal BRD4 occupancy were most highly regulated and sensitive to BRD4 inhibition. Therefore, we examined distal BRD4 occupancy and uncovered a specific co-localization of BRD4 with the transcription factors C/EBPb, TEAD1, FOSL2 and JUND at putative osteoblast-specific enhancers. These findings reveal the intricacies of lineage specification and provide new insight into the context-dependent functions of BRD4.

Enhancer RNA-driven looping enhances the transcription of the long noncoding RNA DHRS4-AS1, a controller of the DHRS4 gene cluster

The human DHRS4 gene cluster consists of DHRS4 and two immediately downstream homologous genes, DHRS4L2 and DHRS4L1, generated by evolutionarily gene-duplication events. We previously demonstrated that a head-to-head natural antisense transcript (NAT) of DHRS4, denoted DHRS4-AS1, regulates all three genes of the DHRS4 gene cluster. However, it is puzzling that DHRS4L2 and DHRS4L1 did not evolve their own specific NATs to regulate themselves, as it seems both have retained sequences highly homologous to DHRS4-AS1. In a search of the DHRS4-AS1 region for nearby enhancers, we identified an enhancer located 13.8 kb downstream of the DHRS4-AS1 transcriptional start site. We further showed, by using a chromosome conformation capture (3C) assay, that this enhancer is capable of physically interacting with the DHRS4-AS1 promoter through chromosomal looping. The enhancer produced an eRNA, termed AS1eRNA, that enhanced DHRS4-AS1 transcription by mediating the spatial interactions of the enhancer and DHRS4-AS1 promoter in cooperation with RNA polymerase II and p300/CBP. Moreover, the distributions of activating acetyl-H3 and H3K4me3 modifications were found to be greater at the DHRS4-AS1 promoter than at the homologous duplicated regions. We propose that AS1eRNA-driven DNA looping and activating histone modifications promote the expression of DHRS4-AS1 to economically control the DHRS4 gene cluster.

CCAAT/enhancer binding protein β (C/EBPβ) regulates the transcription of growth arrest and DNA damage-inducible protein 45 β (GADD45β) in articular chondrocytes

Osteoarthritis (OA) is a whole joint disease characterized by cartilage degradation, which causes pain and disability in older adults. Our previous work showed that growth arrest and DNA damage-inducible protein 45 β (GADD45β) is upregulated in chondrocyte clusters in OA cartilage, especially in the early stage of this disease. CCAAT/enhancer binding protein β (C/EBPβ) is expressed in the hypertrophic growth plate chondrocytes and functions in synergy with GADD45β. Here, the presence and localization of these proteins was assessed by immunohistochemistry using articular cartilage from OA patients, revealing colocalization of C/EBPβ and GADD45β in OA chondrocytes. GADD45β promoter analysis was performed to determine whether C/EBPβ directly regulates GADD45β transcription. Furthermore, we analyzed the effect of C/EBPβ on Gadd45β gene regulation in articular chondrocytes in vivo and in vitro. Immunohistochemical analysis of C/ebpβ-haploinsufficient mice (C/ebpβ(+/-)) cartilage showed that C/ebpβ haploinsufficiency led to reduced Gadd45β gene expression in these cells. In vitro, we evaluated the effects of conditional C/EBPβ overexpression driven by the cartilage oligomeric matrix protein (Comp) promoter in mComp-tTA;pTRE-Tight-BI-DsRed-mC/ebpβ transgenic mice. C/EBPβ overexpression significantly stimulated Gadd45β gene expression in articular chondrocytes. Taken together, our data demonstrate that C/EBPβ plays a central role in controlling Gadd45β gene expression in these cells.

BET Bromodomain Inhibition Suppresses the Function of Hematopoietic Transcription Factors in Acute Myeloid Leukemia

The bromodomain and extraterminal (BET) protein BRD4 is a validated drug target in leukemia, yet its regulatory function in this disease is not well understood. Here, we show that BRD4 chromatin occupancy in acute myeloid leukemia closely correlates with the hematopoietic transcription factors (TFs) PU.1, FLI1, ERG, C/EBPα, C/EBPβ, and MYB at nucleosome-depleted enhancer and promoter regions. We provide evidence that these TFs, in conjunction with the lysine acetyltransferase activity of p300/CBP, facilitate BRD4 recruitment to their occupied sites to promote transcriptional activation. Chemical inhibition of BET bromodomains was found to suppress the functional output of each hematopoietic TF, thereby interfering with essential lineage-specific transcriptional circuits in this disease. These findings reveal a chromatin-based signaling cascade comprised of hematopoietic TFs, p300/CBP, and BRD4 that supports leukemia maintenance and is suppressed by BET bromodomain inhibition.

Mapping long-range promoter contacts in human cells with high-resolution capture Hi-C

Transcriptional control in large genomes often requires looping interactions between distal DNA elements, such as enhancers and target promoters. Current chromosome conformation capture techniques do not offer sufficiently high resolution to interrogate these regulatory interactions on a genomic scale. Here we use Capture Hi-C (CHi-C), an adapted genome conformation assay, to examine the long-range interactions of almost 22,000 promoters in 2 human blood cell types. We identify over 1.6 million shared and cell type-restricted interactions spanning hundreds of kilobases between promoters and distal loci. Transcriptionally active genes contact enhancer-like elements, whereas transcriptionally inactive genes interact with previously uncharacterized elements marked by repressive features that may act as long-range silencers. Finally, we show that interacting loci are enriched for disease-associated SNPs, suggesting how distal mutations may disrupt the regulation of relevant genes. This study provides new insights and accessible tools to dissect the regulatory interactions that underlie normal and aberrant gene regulation.

Inflammation and hypoxia linked to renal injury by CCAAT/enhancer-binding protein δ

Tubulointerstitial hypoxia plays a critical role in the pathogenesis of kidney injury, and hypoxia-inducible factor (HIF)-1 is a master regulator of cellular adaptation to hypoxia. Aside from oxygen molecules, factors that modify HIF-1 expression and functional operation remain obscure. Therefore, we sought to identify novel HIF-1-regulating genes in kidney. A short-hairpin RNA library consisting of 150 hypoxia-inducible genes was derived from a microarray analysis of the rat renal artery stenosis model screened for the effect on HIF-1 response. We report that CCAAT/enhancer-binding protein δ (CEBPD), a transcription factor and inflammatory response gene, is a novel HIF-1 regulator in kidney. CEBPD was induced in the nuclei of tubular epithelial cells in both acute and chronic hypoxic kidneys. In turn, CEBPD induction augmented HIF-1α expression and its transcriptional activity. Mechanistically, CEBPD directly bound to the HIF-1α promoter and enhanced its transcription. Notably, CEBPD was rapidly induced by inflammatory cytokines, such as IL-1β in a nuclear factor-κB-dependent manner, which not only increased HIF-1α expression during hypoxia, but was also indispensable for the non-hypoxic induction of HIF-1α. Thus our study provides novel insight into HIF-1 regulation in tubular epithelial cells and offers a potential hypoxia and inflammation link relevant in both acute and chronic kidney diseases.

CCAAT/enhancer binding protein β in relation to ER stress, inflammation, and metabolic disturbances

The prevalence of the metabolic syndrome and underlying metabolic disturbances increase rapidly in developed countries. Various molecular targets are currently under investigation to unravel the molecular mechanisms that cause these disturbances. This is done in attempt to counter or prevent the negative health consequences of the metabolic disturbances. Here, we reviewed the current knowledge on the role of C/EBP-β in these metabolic disturbances. C/EBP-β deletion in mice resulted in downregulation of hepatic lipogenic genes and increased expression of β-oxidation genes in brown adipose tissue. Furthermore, C/EBP-β is important in the differentiation and maturation of adipocytes and is increased during ER stress and proinflammatory conditions. So far, studies were only conducted in animals and in cell systems. The results found that C/EBP-β is an important transcription factor within the metabolic disturbances of the metabolic system. Therefore, it is interesting to examine the potential role of C/EBP-β at molecular and physiological level in humans.

Globularity and language-readiness: generating new predictions by expanding the set of genes of interest

This study builds on the hypothesis put forth in Boeckx and Benítez-Burraco (2014), according to which the developmental changes expressed at the levels of brain morphology and neural connectivity that resulted in a more globular braincase in our species were crucial to understand the origins of our language-ready brain. Specifically, this paper explores the links between two well-known 'language-related' genes like FOXP2 and ROBO1 implicated in vocal learning and the initial set of genes of interest put forth in Boeckx and Benítez-Burraco (2014), with RUNX2 as focal point. Relying on the existing literature, we uncover potential molecular links that could be of interest to future experimental inquiries into the biological foundations of language and the testing of our initial hypothesis. Our discussion could also be relevant for clinical linguistics and for the interpretation of results from paleogenomics.

Situational awareness: regulation of the myb transcription factor in differentiation, the cell cycle and oncogenesis

This review summarizes the mechanisms that control the activity of the c-Myb transcription factor in normal cells and tumors, and discusses how c-Myb plays a role in the regulation of the cell cycle. Oncogenic versions of c-Myb contribute to the development of leukemias and solid tumors such as adenoid cystic carcinoma, breast cancer and colon cancer. The activity and specificity of the c-Myb protein seems to be controlled through changes in protein-protein interactions, so understanding how it is regulated could lead to the development of novel therapeutic strategies.