C/EBPs: recipients of extracellular signals through proteome modulation

Expression and Activity of the Transcription Factor CCAAT/Enhancer-Binding Protein β (C/EBPβ) Is Regulated by Specific Pulse-Modulated Radio Frequencies in Oligodendroglial Cells

The rapid growth of wireless electronic devices has raised concerns about the harmful effects of leaked electromagnetic radiation (EMR) on human health. Even though numerous studies have been carried out to explore the biological effects of EMR, no clear conclusions have been drawn about the effect of radio frequency (RF) EMR on oligodendrocytes. To this end, we exposed oligodendroglia and three other types of brain cells to 2.4 GHz EMR for 6 or 48 h at an average input power of 1 W in either a continuous wave (CW-RF) or a pulse-modulated wave (PW-RF, 50 Hz pulse frequency, 1/3 duty cycle) pattern. RNA sequencing, RT-qPCR, and Western blot were used to examine the expression of C/EBPβ and its related genes. Multiple reaction monitoring (MRM) was used to examine the levels of expression of C/EBPβ-interacting proteins. Our results showed that PW-RF EMR significantly increased the mRNA level of C/EBPβ in oligodendroglia but not in other types of cells. In addition, the expression of three isoforms and several interacting proteins and targeted genes of C/EBPβ were markedly changed after 6-h PW-RF but not CW-RF. Our results indicated that RF EMR regulated the expression and functions of C/EBPβ in a waveform- and cell-type-dependent manner.

Structural basis for cell type specific DNA binding of C/EBPβ: The case of cell cycle inhibitor p15INK4b promoter

C/EBPβ is a key regulator of numerous cellular processes, but it can also contribute to tumorigenesis and viral diseases. It binds to specific DNA sequences (C/EBP sites) and interacts with other transcription factors to control expression of multiple eukaryotic genes in a tissue and cell-type dependent manner. A body of evidence has established that cell-type-specific regulatory information is contained in the local DNA sequence of the binding motif. In human epithelial cells, C/EBPβ is an essential cofactor for TGFβ signaling in the case of Smad2/3/4 and FoxO-dependent induction of the cell cycle inhibitor, p15INK4b. In the TGFβ-responsive region 2 of the p15INK4b promoter, the Smad binding site is flanked by a C/EBP site, CTTAA•GAAAG, which differs from the canonical, palindromic ATTGC•GCAAT motif. The X-ray crystal structure of C/EBPβ bound to the p15INK4b promoter fragment shows how GCGC-to-AAGA substitution generates changes in the intermolecular interactions in the protein-DNA interface that enhances C/EBPβ binding specificity, limits possible epigenetic regulation of the promoter, and generates a DNA element with a unique pattern of methyl groups in the major groove. Significantly, CT/GA dinucleotides located at the 5'ends of the double stranded element maintain local narrowing of the DNA minor groove width that is necessary for DNA recognition. Our results suggest that C/EBPβ would accept all forms of modified cytosine in the context of the CpT site. This contrasts with the effect on the consensus motif, where C/EBPβ binding is modestly increased by cytosine methylation, but substantially decreased by hydroxymethylation.

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.

Bone Marrow Stroma-Induced Transcriptome and Regulome Signatures of Multiple Myeloma

Multiple myeloma (MM) is a hematological cancer with inevitable drug resistance. MM cells interacting with bone marrow stromal cells (BMSCs) undergo substantial changes in the transcriptome and develop de novo multi-drug resistance. As a critical component in transcriptional regulation, how the chromatin landscape is transformed in MM cells exposed to BMSCs and contributes to the transcriptional response to BMSCs remains elusive. We profiled the transcriptome and regulome for MM cells using a transwell coculture system with BMSCs. The transcriptome and regulome of MM cells from the upper transwell resembled MM cells that coexisted with BMSCs from the lower chamber but were distinctive to monoculture. BMSC-induced genes were enriched in the JAK2/STAT3 signaling pathway, unfolded protein stress, signatures of early plasma cells, and response to proteasome inhibitors. Genes with increasing accessibility at multiple regulatory sites were preferentially induced by BMSCs; these genes were enriched in functions linked to responses to drugs and unfavorable clinic outcomes. We proposed JUNB and ATF4::CEBPβ as candidate transcription factors (TFs) that modulate the BMSC-induced transformation of the regulome linked to the transcriptional response. Together, we characterized the BMSC-induced transcriptome and regulome signatures of MM cells to facilitate research on epigenetic mechanisms of BMSC-induced multi-drug resistance in MM.

Transcriptional control of macrophage inflammatory shift during skeletal muscle regeneration

Skeletal muscle is a tissue able to fully regenerate after an acute injury. Macrophages play an essential role during skeletal muscle regeneration. Resolution of inflammation is a crucial step during the regeneration process, allowing to contain the inflammatory response to avoid damage of the healthy surrounding muscle and triggers the recovery phase during which the muscle regenerates. Resolution of inflammation is mainly mediated by macrophage phenotypic shift that is the transition from a pro-inflammatory damage associated profile towards an anti-inflammatory restorative phenotype, which is characterized by a major transcriptional rewiring. Failure of the resolution of inflammation is observed in chronic diseases such as degenerative myopathies where permanent asynchronous muscle injuries trigger contradictory inflammatory cues, leading to fibrosis and alteration of muscle function. This review will focus on the described molecular pathways that control macrophage inflammatory shift during skeletal muscle regeneration. First, we will highlight the transcriptional changes that characterize macrophage inflammatory shift during skeletal muscle regeneration. Then, we will describe how the signaling pathways and the metabolic changes associated with this shift are controlled. Finally, we will emphasize the transcription factors involved.

Omega-3 PUFAs Suppress IL-1β-Induced Hyperactivity of Immunoproteasomes in Astrocytes

The role of immunoproteasome (iP) in astroglia, the cellular component of innate immunity, has not been clarified. The results so far indicate that neuroinflammation, a prominent hallmark of Alzheimer’s disease, strongly activates the iP subunits expression. Since omega-3 PUFAs possess anti-inflammatory and pro-resolving activity in the brain, we investigated the effect of DHA and EPA on the gene expression of constitutive (β1 and β5) and inducible (iβ1/LMP2 and iβ5/LMP7) proteasome subunits and proteasomal activity in IL-1β-stimulated astrocytes. We found that both PUFAs downregulated the expression of IL-1β-induced the iP subunits, but not the constitutive proteasome subunits. The chymotrypsin-like activity was inhibited in a dose-dependent manner by DHA, and much strongly in the lower concentration by EPA. Furthermore, we established that C/EBPα and C/EBPβ transcription factors, being the cis-regulatory element of the transcription complex, frequently activated by inflammatory mediators, participate in a reduction in the iP subunits’ expression. Moreover, the expression of connexin 43 the major gap junction protein in astrocytes, negatively regulated by IL-1β was markedly increased in PUFA-treated cells. These findings indicate that omega-3 PUFAs attenuate inflammation-induced hyperactivity of iPs in astrocytes and have a beneficial effect on preservation of interastrocytic communication by gap junctions.

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 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.

Prenatal ethanol exposure-induced hypothalamic an imbalance of glutamatergic/GABAergic projections and low functional expression in male offspring rats

This study was designed to demonstrate that prenatal ethanol exposure (PEE) can induce low functional expression of the hypothalamus in male offspring rats and explore the underlying mechanism. Pregnant rats were administered 4 g/kg ethanol or normal saline by oral gavage each day from gestational day (GD) 9 to GD20. Male GD20 foetuses and postnatal day 120 adult offspring rats were sacrificed under anaesthesia. Hypothalamic cells from male GD20~postnatal day (PD) 7 rats were treated with different doses of corticosterone and the glucocorticoid receptor (GR) antagonist mifepristone for 5 days. In this study, we found that PEE-induced overexposure of maternal glucocorticoids enhanced the expression of L-glutamic acid decarboxylase (GAD) 67 in the hypothalamic paraventricular nucleus (PVN) by activating the glucocorticoid metabolic activation system, further inducing the conversion of glutamate to L-gamma-aminobutyric acid (GABA) and developmental imbalance of glutamatergic/GABAergic projections to the PVN. The imbalance change was maintained until after birth, resulting in the inhibition of parvocellular neurons and low functional expression of the hypothalamus in PEE offspring rats. Our study indicated that low functional expression of the hypothalamus in male PEE offspring rats was associated with developmental programming of an imbalance of glutamatergic/GABAergic projections to the PVN.

Tissue-Specific Metabolic Regulation of FOXO-Binding Protein: FOXO Does Not Act Alone

The transcription factor forkhead box (FOXO) controls important biological responses, including proliferation, apoptosis, differentiation, metabolism, and oxidative stress resistance. The transcriptional activity of FOXO is tightly regulated in a variety of cellular processes. FOXO can convert the external stimuli of insulin, growth factors, nutrients, cytokines, and oxidative stress into cell-specific biological responses by regulating the transcriptional activity of target genes. However, how a single transcription factor regulates a large set of target genes in various tissues in response to a variety of external stimuli remains to be clarified. Evidence indicates that FOXO-binding proteins synergistically function to achieve tightly controlled processes. Here, we review the elaborate mechanism of FOXO-binding proteins, focusing on adipogenesis, glucose homeostasis, and other metabolic regulations in order to deepen our understanding and to identify a novel therapeutic target for the prevention and treatment of metabolic disorders.

Brucella abortus Infection Modulates 3T3-L1 Adipocyte Inflammatory Response and Inhibits Adipogenesis

Brucellosis is a prevalent global zoonotic infection but has far more impact in developing countries. The adipocytes are the most abundant cell type of adipose tissue and their secreted factors play an important role in several aspects of the innate and adaptive immune response. Here, we demonstrated the ability of Brucella abortus to infect and replicate in both adipocytes and its precursor cells (pre-adipocytes) derived from 3T3-L1 cell line. Additionally, infection of pre-adipocytes also inhibited adipogenesis in a mechanism independent of bacterial viability and dependent on lipidated outer membrane protein (L-Omp19). B. abortus infection was able to modulate the secretion of IL-6 and the matrix metalloproteases (MMPs) -2 and-9 in pre-adipocytes and adipocytes, and also modulated de transcription of adiponectin, leptin, and resistin in differentiated adipocytes. B. abortus-infected macrophages also modulate adipocyte differentiation involving a TNF-α dependent mechanism, thus suggesting a plausible interplay between B. abortus, adipocytes, and macrophages. In conclusion, B. abortus is able to alter adipogenesis process in adipocytes and its precursors directly after their infection, or merely their exposure to the B. abortus lipoproteins, and indirectly through soluble factors released by B. abortus-infected macrophages.

Cancer Takes a Toll on Skeletal Muscle by Releasing Heat Shock Proteins-An Emerging Mechanism of Cancer-Induced Cachexia

Cancer-associated cachexia (cancer cachexia) is a major contributor to the modality and mortality of a wide variety of solid tumors. It is estimated that cachexia inflicts approximately ~60% of all cancer patients and is the immediate cause of ~30% of all cancer-related death. However, there is no established treatment of this disorder due to the poor understanding of its underlying etiology. The key manifestations of cancer cachexia are systemic inflammation and progressive loss of skeletal muscle mass and function (muscle wasting). A number of inflammatory cytokines and members of the TGFβ superfamily that promote muscle protein degradation have been implicated as mediators of muscle wasting. However, clinical trials targeting some of the identified mediators have not yielded satisfactory results. Thus, the root cause of the muscle wasting associated with cancer cachexia remains to be identified. This review focuses on recent progress of laboratory studies in the understanding of the molecular mechanisms of cancer cachexia that centers on the role of systemic activation of Toll-like receptor 4 (TLR4) by cancer-released Hsp70 and Hsp90 in the development and progression of muscle wasting, and the downstream signaling pathways that activate muscle protein degradation through the ubiquitin-proteasome and the autophagy-lysosome pathways in response to TLR4 activation. Verification of these findings in humans could lead to etiology-based therapies of cancer cachexia by targeting multiple steps in this signaling cascade.

The CCAAT/Enhancer-Binding Protein Family: Its Roles in MDSC Expansion and Function

Immunosuppressive cells have been highlighted in research due to their roles in tumor progression and treatment failure. Myeloid-derived suppressor cells (MDSCs) are among the major immunosuppressive cell populations in the tumor microenvironment, and transcription factors (TFs) are likely involved in MDSC expansion and activation. As key regulatory TFs, members of the CCAAT/enhancer-binding protein (C/EBP) family possibly modulate many biological processes, including cell growth, differentiation, metabolism, and death. Current evidence suggests that C/EBPs maintain critical regulation of MDSCs and are involved in the differentiation and function of MDSCs within the tumor microenvironment. To better understand the MDSC-associated transcriptional network and identify new therapy targets, we herein review recent findings about the C/EBP family regarding their participation in the expansion and function of MDSCs.

A p300 and SIRT1 Regulated Acetylation Switch of C/EBPα Controls Mitochondrial Function

Cellular metabolism is a tightly controlled process in which the cell adapts fluxes through metabolic pathways in response to changes in nutrient supply. Among the transcription factors that regulate gene expression and thereby cause changes in cellular metabolism is the basic leucine-zipper (bZIP) transcription factor CCAAT/enhancer-binding protein alpha (C/EBPα). Protein lysine acetylation is a key post-translational modification (PTM) that integrates cellular metabolic cues with other physiological processes. Here, we show that C/EBPα is acetylated by the lysine acetyl transferase (KAT) p300 and deacetylated by the lysine deacetylase (KDAC) sirtuin1 (SIRT1). SIRT1 is activated in times of energy demand by high levels of nicotinamide adenine dinucleotide (NAD⁺) and controls mitochondrial biogenesis and function. A hypoacetylated mutant of C/EBPα induces the transcription of mitochondrial genes and results in increased mitochondrial respiration. Our study identifies C/EBPα as a key mediator of SIRT1-controlled adaption of energy homeostasis to changes in nutrient supply.

Intrauterine programming of the glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis mediates glomerulosclerosis in female adult offspring rats induced by prenatal ethanol exposure

Prenatal ethanol exposure (PEE) causes intrauterine growth retardation (IUGR), and the occurrence of glomerulosclerosis is closely related to IUGR. This study aimed to confirm the kidney toxic effect of PEE and explore its intrauterine programming mechanism in female offspring. The Wistar female fetuses on gestational day (GD) 20 and the adult offspring at postnatal week 24 were anesthetized and decapitated. The adult offspring kidneys in the PEE group displayed glomerular hyperplasia and glomerulosclerosis. Blood urea nitrogen (BUN) and the BUN / Serum creatinine (Scr) concentration ratio in the PEE group was increased significantly compared to the control group (P<0.01, P<0.05). Meanwhile, the renal glucocorticoid-activation system was inhibited, whereas the insulin-like growth factor 1 (IGF1) signaling pathway was activated in the female adult offspring of the PEE group. In the fetal kidney of the PEE group, pathological observation showed kidney dysplasia, and the gene expression of the glial-cell-line-derived neurotrophic factor/tyrosine kinase receptor (GDNF/c-Ret) signaling pathway was reduced compared to that of the control group. Moreover, the glucocorticoid-activation system was activated, whereas the IGF1 signaling pathway was inhibited in the fetal kidneys of the PEE group. In conclusion, PEE caused fetal kidney dysplasia and adult glomerulosclerosis in the female offspring rats, and the intrauterine programming alteration of glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis might be involved in fetal-originated glomerulosclerosis.

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.

PRISMA: Protein Interaction Screen on Peptide Matrix Reveals Interaction Footprints and Modifications- Dependent Interactome of Intrinsically Disordered C/EBPβ

CCAAT enhancer-binding protein beta (C/EBPβ) is a pioneer transcription factor that specifies cell differentiation. C/EBPβ is intrinsically unstructured, a molecular feature common to many proteins involved in signal processing and epigenetics. The structure of C/EBPβ differs depending on alternative translation initiation and multiple post-translational modifications (PTM). Mutation of distinct PTM sites in C/EBPβ alters protein interactions and cell differentiation, suggesting that a C/EBPβ PTM indexing code determines epigenetic outcomes. Herein, we systematically explored the interactome of C/EBPβ using an array technique based on spot-synthesized C/EBPβ-derived linear tiling peptides with and without PTM, combined with mass spectrometric proteomic analysis of protein interactions. We identified interaction footprints of ∼1,300 proteins in nuclear extracts, many with chromatin modifying, chromatin remodeling, and RNA processing functions. The results suggest that C/EBPβ acts as a multi-tasking molecular switchboard, integrating signal-dependent modifications and structural plasticity to orchestrate interactions with numerous protein complexes directing cell fate and function.

Glucocorticoid-activation system mediated glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis programming alteration of adrenal dysfunction induced by prenatal caffeine exposure

Glucocorticoids play a major factor in fetal maturation and fate decision after birth. We have previously demonstrated that prenatal caffeine exposure (PCE) resulted in adrenal dysplasia. However, its molecular mechanism has not been clarified. In the present study, a rat model of intrauterine growth retardation (IUGR) was established by PCE, and offspring were sacrificed. Moreover, NCI-H295 A cells were used to confirm glucocorticoid-related molecular mechanism. Results showed that PCE fetal weight decreased, and the IUGR rate increased, while serum corticosterone levels increased but insulin-like growth factor 1 (IGF1) levels decreased. Fetal adrenals exhibited an activated glucocorticoid-activation system, and the downregulated expression of IGF1 signal pathway and steroidal synthetases. For adult rats, there was no significant change in the glucocorticoid-activation system in the PCE group, the IGF1 signal pathway showed increased trend, and the expression levels of adrenal steroidal synthetases were close to normal. The data in vitro showed that the cortisol of 1200 nM can inhibit the expression of adrenocortical cell steroidal synthetases and IGF1 signal pathway when compared with the control. Meanwhile, the glucocorticoid-activation system was activated while GR inhibitor mifepristone can reverse the effect of cortisol. Furthermore, cortisol can also promote GR into the nucleus after its activation. Based on these findings, we speculated that high concentrations of glucocorticoid in utero led to GR in the nucleus through its activation and then inhibited the IGF1 signaling pathway by activating the glucocorticoid-activation system, which could further downregulate steroid synthesis.

Transcriptional regulation of the matrix protein Shematrin-2 during shell formation in pearl oyster

The molluscan shell is a fascinating biomineral consisting of a highly organized calcium carbonate composite. Biomineralization is elaborately controlled and involves several macromolecules, especially matrix proteins, but little is known about the regulatory mechanisms. The matrix protein Shematrin-2, expression of which peaks in the mantle tissues and in the shell components of the pearl oyster Pinctada fucata, has been suggested to be a key participant in biomineralization. Here, we expressed and purified Shematrin-2 from P. fucata and explored its function and transcriptional regulation. An in vitro functional assay revealed that Shematrin-2 binds the calcite, aragonite, and chitin components of the shell, decreases the rate of calcium carbonate deposition, and changes the morphology of the deposited crystal in the calcite crystallization system. Furthermore, we cloned the Shematrin-2 gene promoter, and analysis of its sequence revealed putative binding sites for the transcription factors CCAAT enhancer-binding proteins (Pf-C/EBPs) and nuclear factor-Y (NF-Y). Using transient co-transfection and reporter gene assays, we found that cloned and recombinantly expressed Pf-C/EBP-A and Pf-C/EBP-B greatly and dose-dependently up-regulate the promoter activity of the Shematrin-2 gene. Importantly, Pf-C/EBP-A and Pf-C/EBP-B knockdowns decreased Shematrin-2 gene expression and induced changes in the inner-surface structures in prismatic layers that were similar to those of antibody-based Shematrin-2 inhibition. Altogether, our data reveal that the transcription factors Pf-C/EBP-A and Pf-C/EBP-B up-regulate the expression of the matrix protein Shematrin-2 during shell formation in P. fucata, improving our understanding of the transcriptional regulation of molluscan shell development at the molecular level.

Intrauterine Programming of Glucocorticoid-Insulin-Like Growth Factor-1 Axis-Mediated Developmental Origin of Osteoporosis Susceptibility in Female Offspring Rats with Prenatal Caffeine Exposure

Epidemiologic investigations suggest that excessive intake of caffeine during pregnancy is one of the risk factors for osteoporosis in adult offspring. However, the phenomena and mechanisms have remained obscure. This study found that prenatal caffeine exposure (PCE) leads to persistent bone dysplasia in gestational day 20 and postnatal week 12 offspring rats and increases the susceptibility to osteoporosis in postnatal week 28 offspring rats. In the embryonic period, PCE increases the concentration of serum corticosterone and inhibits the expression of insulin-like growth factor-1 (IGF1) and osteogenic differentiation genes. After birth, the recovery of IGF1 expression in PCE offspring is unable to completely compensate osteogenic function, and chronic stress can lead to a further decrease in IGF1 expression. In vitro experiments found that corticosterone instead of caffeine restrains mineralized nodule formation and osteoblast differentiation by inhibiting IGF1 expression. The corticosterone inhibits H3K9 and H3K14 histone acetylation of IGF1 in osteoblasts through glucocorticoid receptor and CCAAT and enhancer binding protein α, respectively. In conclusion, glucocorticoid instead of caffeine inhibits bone IGF1 expression via glucocorticoid receptor and CCAAT and enhancer binding protein α and mediates the PCE-induced bone dysplasia and bone mass reduction in offspring fetal rats, which may contribute to osteoporosis susceptibility in adulthood.

Programming for increased expression of hippocampal GAD67 mediated the hypersensitivity of the hypothalamic-pituitary-adrenal axis in male offspring rats with prenatal ethanol exposure

An imbalance of excitatory and inhibitory signals in the brain has been proposed to be one of the main pathological features of various diseases related to hypothalamic-pituitary-adrenal axis (HPAA) dysfunction. Excessive glutamate release induces neuronal excitotoxicity, while glutamic acid decarboxylase (GAD) 67 promotes the transformation of excessive glutamate to γ-aminobutyric acid (GABA). Our previous studies demonstrated that prenatal ethanol exposure (PEE) causes foetal over-exposure to maternal corticosterone and hypersensitivity of the HPAA after birth, but its intrauterine programming mechanism is unknown. In this study, PEE was shown to lead to an enhanced potential excitatory ability of the hypothalamus and hypersensitivity of the HPAA, as well as mild abnormal hippocampal morphology, demethylation of the -1019 to -691-bp region in the hippocampal GAD67 promoter and upregulation of GAD67 expression accompanied by a reduction in glutamatergic neurons and increase in GABAergic neurons in PEE male offspring. Similar changes were also found in PEE male foetal rats. Furthermore, corticosterone increased the expression of the glucocorticoid receptor (GR) and GAD67 in foetal hippocampal H19-7 cells in a concentration-dependent manner, accompanied by demethylation of the GAD67 promoter, a decrease in glutamatergic neurons and increase in GABAergic neurons. The GR inhibitor, mifepristone, reversed the effects of corticosterone on H19-7 cells. These results suggested that PEE-induced excessive corticosterone can lead to upregulation of GAD67 through epigenetic modification mediated by the GR in the male foetal hippocampus, thereby weakening the negative regulation of the HPAA by the hippocampus and increasing the potential excitatory ability of the hypothalamus. These changes persisted until after birth, resulting in hypersensitivity of the HPAA. However, gender differences were observed in the hippocampal development, morphology and GAD67 expression associated with PEE. Programming for the increased expression of hippocampal GAD67 is a potential mechanism responsible for the hypersensitivity of the HPAA in PEE male rats.

Intrauterine programming mechanism for hypercholesterolemia in prenatal caffeine-exposed female adult rat offspring

Clinical and animal studies have indicated that hypercholesterolemia and its associated diseases have intrauterine developmental origins. Our previous studies showed that prenatal caffeine exposure (PCE) led to fetal overexposure to maternal glucocorticoids (GCs) and increased serum total cholesterol levels in adult rat offspring. This study further confirms the intrauterine programming of PCE-induced hypercholesterolemia in female adult rat offspring. Pregnant Wistar rats were intragastrically administered caffeine (30, 60, and 120 mg/kg/d) from gestational day (GD)9 to 20. Female rat offspring were euthanized at GD20 and postnatal wk 12; several adult rat offspring were additionally subjected to ice-water swimming stimulation to induce chronic stress prior to death. The effects of GCs on cholesterol metabolism and epigenetic regulation were verified using the L02 cell line. The results showed that PCE induced hypercholesterolemia in adult offspring, which manifested as significantly higher levels of serum total cholesterol and LDL cholesterol (LDL-C) as well as higher ratios of LDL-C/HDL cholesterol. We further found that the cholesterol levels were increased in fetal livers but were decreased in fetal blood, accompanied by increased maternal blood cholesterol levels and reduced placental cholesterol transport. Furthermore, analysis of PCE offspring in the uterus and in a postnatal basal/chronic stress state and the results of in vitro experiments showed that hepatic cholesterol metabolism underwent GC-dependent changes and was associated with cholesterol synthase via abnormalities in 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) histone acetylation. We concluded that, to compensate for intrauterine placentally derived decreases in fetal blood cholesterol levels, high intrauterine GC levels activated fetal hepatic CCAAT enhancer binding protein α signaling and down-regulated Sirtuin1 expression, which mediated the high levels of histone acetylation ( via H3K9ac and H3K14ac) and expression of HMGCR. This GC-dependent cholesterol metabolism programming effect was sustained through adulthood, leading to the occurrence of hypercholesterolemia.-Xu, D., Luo, H. W., Hu, W., Hu, S. W., Yuan, C., Wang, G. H., Zhang, L., Yu, H., Magdalou, J., Chen, L. B., Wang, H. Intrauterine programming mechanism for hypercholesterolemia in prenatal caffeine-exposed female adult rat offspring.

Loss of Stemness, EMT, and Supernumerary Tooth Formation in Cebpb-/-Runx2+/- Murine Incisors

Adult Cebpb KO mice incisors present amelogenin-positive epithelium pearls, enamel and dentin allopathic hyperplasia, fewer Sox2-positive cells in labial cervical loop epitheliums, and reduced Sox2 expression in enamel epithelial stem cells. Thus, Cebpb acts upstream of Sox2 to regulate stemness. In this study, Cebpb KO mice demonstrated cementum-like hard tissue in dental pulp, loss of polarity by ameloblasts, enamel matrix in ameloblastic layer, and increased expression of epithelial-mesenchymal transition (EMT) markers in a Cebpb knockdown mouse enamel epithelial stem cell line. Runx2 knockdown in the cell line presented a similar expression pattern. Therefore, the EMT enabled disengaged odontogenic epithelial stem cells to develop supernumerary teeth. Cebpb and Runx2 knockdown in the cell line revealed higher Biglycan and Decorin expression, and Decorin-positive staining in the periapical region, indicating their involvement in supernumerary tooth formation. Cebpb and Runx2 acted synergistically and played an important role in the formation of supernumerary teeth in adult incisors.

A feed-forward regulation of endothelin receptors by c-Jun in human non-pigmented ciliary epithelial cells and retinal ganglion cells

c-Jun, c-Jun N-terminal kinase(JNK) and endothelin B (ET_B) receptor have been shown to contribute to the pathogenesis of glaucoma. Previously, we reported that an increase of c-Jun and CCAAT/enhancer binding protein β (C/EBPβ) immunohistostaining is associated with upregulation of the ET_B receptor within the ganglion cell layer of rats with elevated intraocular pressure (IOP). In addition, both transcription factors regulate the expression of the ET_B receptor in human non-pigmented ciliary epithelial cells (HNPE). The current study addressed the mechanisms by which ET-1 produced upregulation of ET receptors in primary rat retinal ganglion cells (RGCs) and HNPE cells. Treatment of ET-1 and ET-3 increased the immunocytochemical staining of c-Jun and C/EBPβ in primary rat RGCs and co-localization of both transcription factors was observed. A marked increase in DNA binding activity of AP-1 and C/EBPβ as well as elevated protein levels of c-Jun and c-Jun-N-terminal kinase (JNK) were detected following ET-1 treatment in HNPE cells. Overexpression of ET_A or ET_B receptor promoted the upregulation of c-Jun and also elevated its promoter activity. In addition, upregulation of C/EBPβ augmented DNA binding and mRNA expression of c-Jun, and furthermore, the interaction of c-Jun and C/EBPβ was confirmed using co-immunoprecipitation. Apoptosis of HNPE cells was identified following ET-1 treatment, and overexpression of the ET_A or ET_B receptor produced enhanced apoptosis. ET-1 mediated upregulation of c-Jun and C/EBPβ and their interaction may represent a novel mechanism contributing to the regulation of endothelin receptor expression. Reciprocally, c-Jun was also found to regulate the ET receptors and C/EBPβ appeared to play a regulatory role in promoting expression of c-Jun. Taken together, the data suggests that ET-1 triggers the upregulation of c-Jun through both ET_A and ET_B receptors, and conversely c-Jun also upregulates endothelin receptor expression, thereby generating a positive feed-forward loop of endothelin receptor activation and expression. This feed-forward regulation may contribute to RGC death and astrocyte proliferation following ET-1 treatment.

Role of Cytochrome P450 (CYP)1A in Hyperoxic Lung Injury: Analysis of the Transcriptome and Proteome

Hyperoxia contributes to lung injury in experimental animals and diseases such as acute respiratory distress syndrome in humans. Cytochrome P450 (CYP)1A enzymes are protective against hyperoxic lung injury (HLI). The molecular pathways and differences in gene expression that modulate these protective effects remain largely unknown. Our objective was to characterize genotype specific differences in the transcriptome and proteome of acute hyperoxic lung injury using the omics platforms: microarray and Reverse Phase Proteomic Array. Wild type (WT), Cyp1a1−/− and Cyp1a2−/− (8–10 wk, C57BL/6J background) mice were exposed to hyperoxia (FiO₂ > 0.95) for 48 hours. Comparison of transcriptome changes in hyperoxia-exposed animals (WT versus knock-out) identified 171 genes unique to Cyp1a1−/− and 119 unique to Cyp1a2−/− mice. Gene Set Enrichment Analysis revealed pathways including apoptosis, DNA repair and early estrogen response that were differentially regulated between WT, Cyp1a1−/− and Cyp1a2−/− mice. Candidate genes from these pathways were validated at the mRNA and protein level. Quantification of oxidative DNA adducts with ³²P-postlabeling also revealed genotype specific differences. These findings provide novel insights into mechanisms behind the differences in susceptibility of Cyp1a1−/− and Cyp1a2−/− mice to HLI and suggest novel pathways that need to be investigated as possible therapeutic targets for acute lung injury.

Insights into specificity, redundancy and new cellular functions of C/EBPa and C/EBPb transcription factors through interactome network analysis

BACKGROUND

C/EBPa and C/EBPb are transcription factors with tissue specific expression regulating several important cellular processes. They work by recruiting protein complexes to a common DNA recognition motif and both are able to compensate each other's absence in many cell types, thus showing functional redundancy. They also play distinct roles in specific cellular pathways and their abnormal functioning gives raise to different human pathologies.

METHODS

To investigate the molecular basis of C/EBPa and C/EBPb specificity and redundancy we characterized their in vivo protein-protein interaction networks by Tandem Affinity Purification (TAP) and Mass Spectrometry (MS). To unravel the functional features of C/EBPa and C/EBPb proteomes we studied the statistical enrichment of binding partners related to Gene Ontology (GO) terms and KEGG pathways.

RESULTS

Our data confirmed that the C/EBPa and C/EBPb regulate biological processes like cell proliferation, apoptosis and transformation. We found that both C/EBPa and C/EBPb are involved in other cellular pathways such as RNA maturation, RNA splicing and DNA repair. Specific interactions of C/EBPa with MRE11, RUVBL1 and RUVBL2 components of DNA repair system were confirmed by co-immunoprecipitation assays.

CONCLUSIONS

Our comparative analysis of the C/EBPa and C/EBPb proteomes provides an insight for understanding both their redundant and specific roles in cells indicating their involvement in new pathways. Such novel predicted functions are relevant to normal cellular processes and disease phenotypes controlled by these transcription factors.

GENERAL SIGNIFICANCE

Functional characterization of C/EBPa and C/EBPb proteomes suggests they can regulate novel pathways and indicate potential molecular targets for therapeutic intervention.

Prenatal caffeine exposure-induced adrenal developmental abnormality in male offspring rats and its possible intrauterine programming mechanisms

Glucocorticoid (GC) is a major factor for fetal tissue maturation and fate decision after birth. We previously demonstrated that prenatal caffeine exposure (PCE) suppressed fetal adrenal steroidogenesis and resulted in adrenal dysplasia. However, whether these changes play a role until adulthood and its intrauterine programming mechanisms remain unknown. In the present study, a rat model of intrauterine growth retardation (IUGR) was established by PCE, male fetuses and adult offspring were sacrificed at postnatal day (PD) 1, PD7, PD35, PD100 and PD168, respectively. Results showed that the PCE fetal weight decreased and the IUGR rate increased, while the serum corticosterone (CORT) level increased but the insulin-like growth factor 1 (IGF1) level decreased. Fetal adrenal exhibited an enhanced GC-activation system (11β-hydroxysteroid dehydrogenases/corticoid receptors/CCAAT/enhancer binding proteins), an inhibited IGF1 pathway and steroid synthesis function. After birth, the serum CORT levels in the PCE offspring were increased in the early period followed by falling in the later stage, while the serum IGF1 level change was the opposite and was accompanied by an obvious catch-up growth. Furthermore, the adrenal GC-activation system was inhibited but the IGF1 signaling pathway was enhanced, resulting in a compensatory increase of adrenal steroidogenesis, and the expression of steroidal synthetase was consistent with that of the IGF1 signaling pathway. Based on these findings, we proposed "two-programming mechanisms" for PCE-induced adrenal abnormality: the "first programming" mechanism is a lower function of adrenal steroidogenesis, and prenatal and postnatal adrenal structural and functional abnormalities triggered by the intrauterine GC-IGF1 axis programming-mediated by the GC-activation system that acts as "the second programming" mechanism.

Role of transcription factor acetylation in the regulation of metabolic homeostasis

Post-translational modifications (PTMs) of transcription factors play a crucial role in regulating metabolic homeostasis. These modifications include phosphorylation, methylation, acetylation, ubiquitination, SUMOylation, and O-GlcNAcylation. Recent studies have shed light on the importance of lysine acetylation at nonhistone proteins including transcription factors. Acetylation of transcription factors affects subcellular distribution, DNA affinity, stability, transcriptional activity, and current investigations are aiming to further expand our understanding of the role of lysine acetylation of transcription factors. In this review, we summarize recent studies that provide new insights into the role of protein lysine-acetylation in the transcriptional regulation of metabolic homeostasis.

Altered PKR Signalling and C / EBPβ Expression is Associated with HLA-B27 Expression in Monocytic Cells

Infection caused by certain gram-negative bacteria, e.g. Salmonella, can trigger inflammatory joint disease reactive arthritis (ReA). It is suggested that the disease-triggering bacteria or bacterial components persist in patients for an abnormally long time. Development of ReA is strongly associated with tissue antigen HLA-B27. Previously, we reported an enhanced replication of Salmonella enteritidis and altered p38 MAP kinase signalling in HLA-B27-expressing monocytic cells. Here we aimed to investigate the role of HLA-B27 in regulation of double-stranded RNA-activated kinase (PKR)-related signalling in Salmonella-infected or Salmonella lipopolysaccharide (LPS)-stimulated human U937 monocytic cells, as PKR has been reported to modify p38 signalling in Salmonella-infected cells. In cells expressing HLA-B27, PKR is overexpressed and hypophosphorylated, and the expression of transcription factor CCAAT enhancer binding protein beta (C/EBPβ) is increased upon Salmonella infection and LPS stimulation. The expression of C/EBPβ is PKR-dependent in LPS-stimulated mock cells, whereas in LPS-stimulated B27 cells the majority of C/EBPβ is expressed in a PKR-independent manner. Our results show that the expression of HLA-B27 disturbs the PKR-mediated signalling pathway. Moreover, altered signalling is related to misfolding-linked Glu45 in the B pocket of the HLA-B27 heavy chain. We suggest that the expression of HLA-B27 HCs modulates the intracellular environment of monocyte/macrophages and the mechanisms that are important in eliminating intracellular S. enteritidis by altering the intracellular signalling. This phenomenon is at least partly dependent on the misfolding feature of the B27 molecule. These observations offer a novel mechanism by which HLA-B27 may modulate inflammatory response induced by ReA-triggering bacteria.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

Repression of the nuclear receptor small heterodimer partner by steatotic drugs and in advanced nonalcoholic fatty liver disease

The small heterodimer partner (SHP) (NR0B2) is an atypical nuclear receptor that lacks a DNA-binding domain. It interacts with and inhibits many transcription factors, affecting key metabolic processes, including bile acid, cholesterol, fatty acid, and drug metabolism. Our aim was to determine the influence of steatotic drugs and nonalcoholic fatty liver disease (NAFLD) on SHP expression and investigate the potential mechanisms. SHP was found to be repressed by steatotic drugs (valproate, doxycycline, tetracycline, and cyclosporin A) in cultured hepatic cells and the livers of different animal models of NAFLD: iatrogenic (tetracycline-treated rats), genetic (glycine N-methyltransferase-deficient mice), and nutritional (mice fed a methionine- and choline-deficient diet). Among the different transcription factors investigated, CCAAT-enhancer-binding protein α (C/EBPα) showed the strongest dominant-repressive effect on SHP expression in HepG2 and human hepatocytes. Reporter assays revealed that the inhibitory effect of C/EBPα and steatotic drugs colocalize between -340 and -509 base pair of the SHP promoter, and mutation of a predicted C/EBPα response element at -473 base pair abolished SHP repression by both C/EBPα and drugs. Moreover, inhibition of major stress signaling pathways demonstrated that the mitogen-activated protein kinase kinase 1/2 pathway activates, while the phosphatidylinositol 3 kinase pathway represses SHP in a C/EBP-dependent manner. We conclude that SHP is downregulated by several steatotic drugs and in advanced NAFLD. These conditions can activate signals that target C/EBPα and consequently repress SHP, thus favoring the progression and severity of NAFLD.

Acetylation of C/EBPε is a prerequisite for terminal neutrophil differentiation

C/EBPε, a member of the CCAAT/enhancer binding protein (C/EBP) family of transcription factors, is exclusively expressed in myeloid cells and regulates transition from the promyelocytic stage to the myelocytic stage of neutrophil development, being indispensable for secondary and tertiary granule formation. Knowledge concerning the functional role of C/EBPε posttranslational modifications is limited to studies concerning phosphorylation and sumoylation. In the current study, using ectopic expression and ex vivo differentiation of CD34(+) hematopoietic progenitor cells, we demonstrate that C/EBPε is acetylated, which was confirmed by mass spectrometry analysis, identifying 4 acetylated lysines in 3 distinct functional domains. Regulation of C/EBPε acetylation levels by the p300 acetyltransferase and the sirtuin 1 deacetylase controls transcriptional activity, which can at least in part be explained by modulation of DNA binding. During neutrophil development, acetylation of lysines 121 and 198 were found to be crucial for terminal neutrophil differentiation and the expression of neutrophil-specific granule proteins, including lactoferrin and collagenase. Taken together, our data illustrate a critical role for acetylation in the functional regulation of C/EBPε activity during terminal neutrophil development.

Stabilization of ATF5 by TAK1-Nemo-like kinase critically regulates the interleukin-1β-stimulated C/EBP signaling pathway

Interleukin-1β (IL-1β) is a key proinflammatory cytokine that initiates several signaling cascades, including those involving CCAAT/enhancer binding proteins (C/EBPs). The mechanism by which IL-1β propagates a signal that activates C/EBP has remained elusive. Nemo-like kinase (NLK) is a mitogen-activated protein kinase (MAPK)-like kinase associated with many pathways and phenotypes that are not yet well understood. Using a luciferase reporter screen, we found that IL-1β-induced C/EBP activation was positively regulated by NLK. Overexpression of NLK activated C/EBP and potentiated IL-1β-triggered C/EBP activation, whereas knockdown or knockout of NLK had the opposite effect. NLK interacted with activating transcription factor 5 (ATF5) and inhibited the proteasome-dependent degradation of ATF5 in a kinase-independent manner. Consistently, NLK deficiency resulted in decreased levels of ATF5. NLK cooperated with ATF5 to activate C/EBP, whereas NLK could not activate C/EBP upon knockdown of ATF5. Moreover, TAK1, a downstream effector of IL-1β that acts upstream of NLK, mimicked the ability of NLK to stabilize ATF5 and activate C/EBP. Thus, our findings reveal the TAK1-NLK pathway as a novel regulator of basal or IL-1β-triggered C/EBP activation though stabilization of ATF5.

A functional N-terminal domain in C/EBPβ-LAP* is required for interacting with SWI/SNF and to repress Ric-8B gene transcription in osteoblasts

The chromatin remodeling complex SWI/SNF and the transcription factor C/EBPβ play critical roles in osteoblastic cells as they jointly control transcription of a number of bone-related target genes. The largest C/EBPβ isoform, LAP*, possesses a short additional N-terminal domain that has been proposed to mediate the interaction of this factor with SWI/SNF in myeloid cells. Here we examine the requirement of a functional N-terminus in C/EBPβ-LAP* for binding SWI/SNF and for recruiting this complex to the Ric-8B gene to mediate transcriptional repression. We find that both C/EBPβ-LAP* and SWI/SNF simultaneously bind to the Ric-8B promoter in differentiating osteoblasts that repress Ric-8B expression. This decreased expression of Ric-8B is not accompanied by significant changes in histone acetylation at the Ric-8B gene promoter sequence. A single aminoacid change at the C/EBPβ-LAP* N-terminus (R3L) that inhibits C/EBPβ-LAP*-SWI/SNF interaction, also prevents SWI/SNF recruitment to the Ric-8B promoter as well as C/EBPβ-LAP*-dependent repression of the Ric-8B gene. Inducible expression of the C/EBPβ-LAP*R3L protein in stably transfected osteoblastic cells demonstrates that this mutant protein binds to C/EBPβ-LAP*-target promoters and competes with the endogenous C/EBPβ factor. Together our results indicate that a functional N-terminus in C/EBPβ-LAP* is required for interacting with SWI/SNF and for Ric-8B gene repression in osteoblasts.

Early adipogenesis is regulated through USP7-mediated deubiquitination of the histone acetyltransferase TIP60

Transcriptional coregulators, including the acetyltransferase Tip60, have a key role in complex cellular processes such as differentiation. Whereas post-translational modifications have emerged as an important mechanism to regulate transcriptional coregulator activity, the identification of the corresponding demodifying enzymes has remained elusive. Here we show that the expression of the Tip60 protein, which is essential for adipocyte differentiation, is regulated through polyubiquitination on multiple residues. USP7, a dominant deubiquitinating enzyme in 3T3-L1 adipocytes and mouse adipose tissue, deubiquitinates Tip60 both in intact cells and in vitro and increases Tip60 protein levels. Furthermore, inhibition of USP7 expression and activity decreases adipogenesis. Transcriptome analysis reveals several cell cycle genes to be co-regulated by both Tip60 and USP7. Knockdown of either factor results in impaired mitotic clonal expansion, an early step in adipogenesis. These results reveal deubiquitination of a transcriptional coregulator to be a key mechanism in the regulation of early adipogenesis.

Effects of Siglec on the expression of IL-10 in the macrophage cell line RAW264

Interleukin-10 (IL-10) expression was significantly elevated upon stimulation with lipopolysaccharide (LPS) when the sialic acid-recognizing Ig-superfamily lectin Siglec-5 or -9 was overexpressed in RAW264 cells. During the course to clarify the mechanism for this activation, we found that IL-10 promoter proximal region up to -500 bp led to transactivation similar to that up to -1,500 bp. Among the transcription factors that activate the mouse IL-10 promoter so far reported, the level of C/EBPβ was increased in Siglec-9-expressing cells. Transient expression of the C/EBPβ major isoform LAP led to an increase in the expression of IL-10 in Siglec-9-expressing cells, but not in mock-transfected control RAW264 cells upon stimulation with LPS, as assessed by either a luciferase assay or the production of IL-10. Without LPS, the IL-10 promoter was activated by transiently expressed LAP in Siglec-9-expressing cells, however, the magnitude of transactivation was less than that with the LPS stimulation. The knockdown of C/EBPβ down-regulated the production of IL-10. Taken together, these results suggest that one of the reasons for the stimulation of IL-10 expression in Siglec-9-expressing cells may be an increase in intracellular C/EBPβ level.

Production of a monoclonal antibody for C/EBPβ: the subnuclear localization of C/EBPβ in mouse L929 cells

The CCAAT/enhancer-binding protein (C/EBP)β belongs to the C/EBP family of proteins that possesses a basic leucine zipper DNA-binding domain. These proteins bind DNA by dimerization and play a role in the transcriptional regulation of various cells. There are six different types of C/EBPs, and some form isoforms through the use of alternative translation initiation sites. The functional analysis of the C/EBP family is therefore difficult to achieve. Here we report on the production of specific monoclonal antibodies against mouse C/EBPβ using a rat medial iliac lymph node method. Immunoblotting using C/EBPβ monoclonal antibodies identified two types of isoforms, while immunostaining revealed a subnuclear localization for C/EBPβ. Use of this antibody should contribute to the further elucidation of the transcriptional regulatory function of C/EBPβ.

HTLV-1 bZIP factor supports proliferation of adult T cell leukemia cells through suppression of C/EBPα signaling

BACKGROUND

Human T-cell leukemia virus type 1 (HTLV-1) is an oncogenic retrovirus etiologically associated with adult T-cell leukemia (ATL). The HTLV-1 bZIP factor (HBZ), which is encoded by minus strand of provirus, is expressed in all ATL cases and supports the proliferation of ATL cells. However, the precise mechanism of growth promoting activity of HBZ is poorly understood.

RESULTS

In this study, we showed that HBZ suppressed C/EBPα signaling activation induced by either Tax or C/EBPα. As mechanisms of HBZ-mediated C/EBPα inhibition, we found that HBZ physically interacted with C/EBPα and diminished its DNA binding capacity. Luciferase and immunoprecipitation assays revealed that HBZ repressed C/EBPα activation in a Smad3-dependent manner. In addition, C/EBPα was overexpressed in HTLV-1 infected cell lines and fresh ATL cases. HBZ was able to induce C/EBPα transcription by enhancing its promoter activity. Finally, HBZ selectively modulated the expression of C/EBPα target genes, leading to the impairment of C/EBPα-mediated cell growth suppression.

CONCLUSION

HBZ, by suppressing C/EBPα signaling, supports the proliferation of HTLV-1 infected cells, which is thought to be critical for oncogenesis.

Involvement of AP-1 and C/EBPβ in upregulation of endothelin B (ETB) receptor expression in a rodent model of glaucoma

Previous studies showed that the endothelin B receptor (ET_B) expression was upregulated and played a key role in neurodegeneration in rodent models of glaucoma. However, the mechanisms underlying upregulation of ET_B receptor expression remain largely unknown. Using promoter-reporter assays, the 1258 bp upstream the human ET_B promoter region was found to be essential for constitutive expression of ET_B receptor gene in human non-pigmented ciliary epithelial cells (HNPE). The −300 to −1 bp and −1258 to −600 bp upstream promoter regions of the ET_B receptor appeared to be the key binding regions for transcription factors. In addition, the crucial AP-1 binding site located at −615 to −624 bp upstream promoter was confirmed by luciferase assays and CHIP assays which were performed following overexpression of c-Jun in HNPE cells. Overexpression of either c-Jun or C/EBPβ enhanced the ET_B receptor promoter activity, which was reflected in increased mRNA and protein levels of ET_B receptor. Furthermore, knock-down of either c-Jun or C/EBPβ in HNPE cells was significantly correlated to decreased mRNA levels of both ET_B and ET_A receptor. These observations suggest that c-Jun and C/EBPβ are important for regulated expression of the ET_B receptor in HNPE cells. In separate experiments, intraocular pressure (IOP) was elevated in one eye of Brown Norway rats while the corresponding contralateral eye served as control. Two weeks of IOP elevation produced increased expression of c-Jun and C/EBPβ in the retinal ganglion cell (RGC) layer from IOP-elevated eyes. The mRNA levels of c-Jun, ET_A and ET_B receptor were upregulated by 2.2-, 3.1- and 4.4-fold in RGC layers obtained by laser capture microdissection from retinas of eyes with elevated IOP, compared to those from contralateral eyes. Taken together, these data suggest that transcription factor AP-1 plays a key role in elevation of ET_B receptor in a rodent model of ocular hypertension.

The transcription factor CCAAT enhancer-binding protein β protects rat cerebellar granule neurons from apoptosis through its transcription-activating isoforms

CCAAT enhancer-binding protein β is a transcription factor that is involved in many brain processes, although its role in neuronal survival/death remains unclear. By using primary cultures of rat cerebellar granule neurons, we have shown here that CCAAT enhancer-binding protein β is present as all of its isoforms: the transcriptional activators liver activator proteins 1 and 2, and the transcriptional inhibitor liver inhibitory protein. We have also shown that liver activator protein 1 undergoes post-translational modifications, such as phosphorylation and sumoylation. These isoforms have different subcellular localizations, liver activator protein 2 being found in the cytosolic fraction only, liver inhibitory protein in the nucleus only, and liver activator protein 1 in both fractions. Through neuronal apoptosis induction by shifting mature cerebellar granule neurons to low-potassium medium, we have demonstrated that nuclear liver activator protein 1 expression decreases and its phosphorylation disappears, whereas liver inhibitory protein levels increase in the nuclear fraction, suggesting a pro-survival role for liver activator protein transcriptional activation and a pro-apoptotic role for liver inhibitory protein transcriptional inhibition. To confirm this, we transfected cerebellar granule neurons with plasmids expressing liver activator protein 1, liver activator protein 2, or liver inhibitory protein respectively, and observed that both liver activator proteins, which increase CCAAT-dependent transcription, but not liver inhibitory protein, counteracted apoptosis, thus demonstrating the pro-survival role of liver activator proteins. These data significantly improve our current understanding of the role of CCAAT enhancer-binding protein β in neuronal survival/apoptosis.

CAWS administration increases the expression of interferon γ and complement factors that lead to severe vasculitis in DBA/2 mice

Background

Candida albicans water-soluble fraction (CAWS), a mannoprotein-β-glucan complex obtained from the culture supernatant of C. albicans NBRC1385, causes CAWS-mediated vasculitis (CAWS-vasculitis) in B6 and DBA/2 mice with mild and lethal symptoms, respectively. Why CAWS is lethal only in DBA/2 mice remains unknown.

Results

We performed DNA microarray analyses using mRNA obtained from peripheral blood mononuclear cells (PBMCs) of B6 and DBA/2 mice and compared their respective transcriptomes. We found that the mRNA levels of interferon-γ (Ifng) and several genes that regulate the complement system, such as C3, C4, Cfb, Cfh, and Fcna, were increased dramatically only in DBA/2 mice at 4 and 8 weeks after CAWS administration. The dramatic increase was confirmed by quantitative real-time polymerase chain reactions (qRT-PCR). Moreover, mRNA levels of immune-related genes, such as Irf1, Irf7, Irf9, Cebpb, Ccl4, Itgam, Icam1, and IL-12rb1, whose expression levels are known to be increased by Ifng, were also increased, but only in DBA/2 mice. By contrast, the mRNA level of Dectin-2, the critical receptor for the α-mannans of CAWS, was increased slightly and similarly in both B6 and DBA/2 mice after CAWS administration.

Conclusions

Taken together, our results suggest that CAWS administration induces Dectin-2 mediated CAWS-vasculitis in both B6 and DBA/2 mice and the expression of Ifng, but only in DBA/2 mice, which led to increased expression of C3, C4, Cfb, Cfh, and Fcna and an associated increase in lethality in these mice. This model may contribute to our understanding of the pathogenesis of severe human vasculitis.

C6orf89 encodes three distinct HDAC enhancers that function in the nucleolus, the golgi and the midbody

We report here that C6orf89, which encodes a protein that interacts with bombesin receptor subtype-3 and accelerates cell cycle progression and wound repair in human bronchial epithelial cells (Liu et al., 2011, PLoS ONE 6: e23072), encodes one soluble and two type II membrane proteins that function as histone deacetylases (HDAC) enhancers. Soluble 34/64sp is selectively targeted to the nucleolus and is retained in nucleolar organiser regions (NORs) in mitotic cells. Nucleolar 34/64sp is integrated into the ribosomal gene transcription machinery, colocalises and coimmunoprecipitates with the Pol I transcription factor UBF, and undergoes a dramatic relocalisation to the nucleolus upon the arrest of rDNA transcription, protein synthesis and PI3K/mTORC2 signalling. Membrane 42/116mp localises to the Golgi and the midbody, and its controlled ectopic expression provokes the disruption of the Golgi cisternae and hinders the separation of daughter cells and the completion of mitosis. The latter effect is also produced by the microinjection of an affinity-purified amfion antibody. The identification of C60rf89 as a gene that encodes three distinct proteins with the capacity to enhance the activity of histone deacetylases (HDACs) in the nucleolus, the Golgi and the midbody provides new information regarding the components of the acetylome and their capacity to interact with different functional groups in the cell.

Epigenetic regulation of polyomavirus JC

BACKGROUND

Polyomavirus JC (JCV) causes the CNS demyelinating disease progressive multifocal leukoencephalopathy (PML), which occurs almost exclusively in people with immune deficiencies, such as HIV-1/AIDS patients. JCV infection is very common and usually occurs early in life. After primary infection, virus is controlled by the immune system but, rarely when immune function is impaired, it can re-emerge and multiply in the astrocytes and oligodendrocytes in the brain and cause PML. Thus a central question in PML pathogenesis is the nature of the molecular mechanisms maintaining JCV in a latent state and then allowing reactivation.

METHODS

Since transcription can be regulated by epigenetic mechanisms including DNA methylation and histone acetylation, we investigated their role in JCV regulation by employing inhibitors of epigenetic events.

RESULTS

The histone deacetylase inhibitors trichostatin A (TSA) and sodium butyrate powerfully stimulated JCV early and late transcription while the DNA methylation inhibitor 5-azacytidine had no effect. Analysis of JCV mutants showed that this effect was mediated by the KB element of the JCV control region, which binds transcription factors NF-κB p65, NFAT4 and C/EBPβ and mediates stimulation by TNF-α. Stimulation of transcription by p65 was additive with TSA as was cotransfection with transcriptional coactivators/acetyltransferase p300 whereas depletion of endogenous p65 by RNA interference inhibited the effect of TSA. EMSA with a KB oligonucleotide showed p65 expression, TNF-α stimulation or TSA treatment each caused a gel shift that was further shifted by antibody to p65.

CONCLUSIONS

We conclude that JCV is regulated epigenetically by protein acetylation events and that these involve the NF-κB p65 binding site in the JCV control region.

Lymphoid to myeloid cell trans-differentiation is determined by C/EBPβ structure and post-translational modifications

The transcription factor C/EBPβ controls differentiation, proliferation, and functionality of many cell types, including innate immune cells. A detailed molecular understanding of how C/EBPβ directs alternative cell fates remains largely elusive. A multitude of signal-dependent post-translational modifications (PTMs) differentially affect the protean C/EBPβ functions. In this study we apply an assay that converts primary mouse B lymphoid progenitors into myeloid cells in order to answer the question how C/EBPβ regulates (trans-) differentiation and determines myeloid cell fate. We found that structural alterations and various C/EBPβ PTMs determine the outcome of trans-differentiation of lymphoid into myeloid cells, including different types of monocytes/macrophages, dendritic cells, and granulocytes. The ability of C/EBPβ to recruit chromatin remodeling complexes is required for the granulocytic trans-differentiation outcome. These novel findings reveal that PTMs and structural plasticity of C/EBPβ are adaptable modular properties that integrate and rewire epigenetic functions to direct differentiation to diverse innate immune system cells, which are crucial for the organism survival.

C/EBP maintains chromatin accessibility in liver and facilitates glucocorticoid receptor recruitment to steroid response elements

Mechanisms regulating transcription factor interaction with chromatin in intact mammalian tissues are poorly understood. Exploiting an adrenalectomized mouse model with depleted endogenous glucocorticoids, we monitor changes of the chromatin landscape in intact liver tissue following glucocorticoid injection. Upon activation of the glucocorticoid receptor (GR), proximal regions of activated and repressed genes are remodelled, and these remodelling events correlate with RNA polymerase II occupancy of regulated genes. GR is exclusively associated with accessible chromatin and 62% percent of GR-binding sites are occupied by C/EBPβ. At the majority of these sites, chromatin is preaccessible suggesting a priming function of C/EBPβ for GR recruitment. Disruption of C/EBPβ binding to chromatin results in attenuation of pre-programmed chromatin accessibility, GR recruitment and GR-induced chromatin remodelling specifically at sites co-occupied by GR and C/EBPβ. Collectively, we demonstrate a highly cooperative mechanism by which C/EBPβ regulates selective GR binding to the genome in liver tissue. We suggest that selective targeting of GR in other tissues is likely mediated by the combined action of cell-specific priming proteins and chromatin remodellers.