p300 coactivates the adipogenic transcription factor CCAAT/enhancer-binding protein alpha

Lactobacillus Intestinalis Primes Epithelial Cells to Suppress Colitis-Related Th17 Response by Host-Microbe Retinoic Acid Biosynthesis

Gut microbiome is integral to the pathogenesis of ulcerative colitis. A novel probiotic Lactobacillus intestinalis (L. intestinalis) exerts a protective effect against dextran sodium sulfate-induced colitis in mice. Based on flow cytometry, colitis-associated Th17 cells are the target of L. intestinalis, which is supported by the lack of protective effects of L. intestinalis in T cell-null Rag1-/- mice or upon anti-IL-17-A antibody-treated mice. Although L. intestinalis exerts no direct effect on T cell differentiation, it decreases C/EBPA-driven gut epithelial SAA1 and SAA2 production, which in turn impairs Th17 cell differentiation. Cometabolism of L. intestinalis ALDH and host ALDH1A2 contributed to elevated biosynthesis of retinoic acid (RA), which accounts for the anti-colitis effect in RAR-α -mediated way. In a cohort of ulcerative colitis patients, it is observed that fecal abundance of L. intestinalis is negatively associated with the C/EBPA-SAA1/2-Th17 axis. Finally, L. intestinalis has a synergistic effect with mesalazine in alleviating murine colitis. In conclusion, L. intestinalis and associated metabolites, RA, have potential therapeutic effects for suppressing colonic inflammation by modulating the crosstalk between intestinal epithelia and immunity.

The healing bitterness of Gentiana lutea L., phytochemistry and biological activities: A systematic review

Over many years, natural products have been a source of healing agents and have exhibited beneficial uses for treating human diseases. The Gentiana genus is the biggest genus in the Gentianaceae, with over 400 species distributed mainly in alpine zones of temperate countries around the world. Plants in the Gentiana genus have historically been used to treat a wide range of diseases. Still, only in the last years has particular attention been paid to the biological activities of Gentiana lutea Linn., also known as yellow Gentian or bitterwort. Several in vitro/vivo investigations and human interventional trials have demonstrated the promising activity of G. lutea extracts against oxidative stress, microbial infections, inflammation, obesity, atherosclerosis, etc.. A systematic approach was performed using Pubmed and Scopus databases to update G. lutea chemistry and activity. Specifically, this systematic review synthesized the major specialized bitter metabolites and the biological activity data obtained from different cell lines, animal models, and human interventional trials. This review aims to the exaltation of G. lutea as a source of bioactive compounds that can prevent and treat several human illnesses.

Large-Scale Expansion of Porcine Adipose-Derived Stem Cells Based on Microcarriers System for Cultured Meat Production

Cultured meat is an innovative meat-production technology that does not rely on animal husbandry. As a new food component, cultured fat is of great significance to cultured meat. In this study, we isolated adipose-derived stem cells (ADSCs) and identified the purity by immunofluorescence staining of ADSC-specific surface marker proteins CD44 and CD29 and showed that most of the cells were positive for CD29 and CD44. In addition, we detected the expression of FABP4 and Plin1 to confirm that ADSCs differentiated into mature adipocytes at 10 days post-induction. Subsequently, the culture conditions of ADSCs on microcarriers (MCs) were optimized and showed that cell density of living cells reached their highest after 5 days when continuously stirring at 50 rpm. Finally, the expression of FABP4 and PPARγ was detected to confirm the adipogenic differentiation ability of ADSCs on 2D and 3D culture systems and showed that ADSCs maintained their adipogenic differentiation ability after expansion on MCs. In conclusion, this research demonstrated that reliance on MCs to expand ADSCs was a promising approach for production of cultured fat.

Adipocyte-Specific Deletion of Lamin A/C Largely Models Human Familial Partial Lipodystrophy Type 2

Mechanisms by which autosomal recessive mutations in Lmna cause familial partial lipodystrophy type 2 (FPLD2) are poorly understood. To investigate the function of lamin A/C in adipose tissue, we created mice with an adipocyte-specific loss of Lmna (Lmna ^ADKO). Although Lmna ^ADKO mice develop and maintain adipose tissues in early postnatal life, they show a striking and progressive loss of white and brown adipose tissues as they approach sexual maturity. Lmna ^ADKO mice exhibit surprisingly mild metabolic dysfunction on a chow diet, but on a high-fat diet they share many characteristics of FPLD2 including hyperglycemia, hepatic steatosis, hyperinsulinemia, and almost undetectable circulating adiponectin and leptin. Whereas Lmna ^ADKO mice have reduced regulated and constitutive bone marrow adipose tissue with a concomitant increase in cortical bone, FPLD2 patients have reduced bone mass and bone mineral density compared with controls. In cell culture models of Lmna deficiency, mesenchymal precursors undergo adipogenesis without impairment, whereas fully differentiated adipocytes have increased lipolytic responses to adrenergic stimuli. Lmna ^ADKO mice faithfully reproduce many characteristics of FPLD2 and thus provide a unique animal model to investigate mechanisms underlying Lmna-dependent loss of adipose tissues.

Pluripotent Stem Cell-Derived Hepatocytes Phenotypic Screening Reveals Small Molecules Targeting the CDK2/4-C/EBPα/DGAT2 Pathway Preventing ER-Stress Induced Lipid Accumulation

Non-alcoholic fatty liver disease (NAFLD) has a large impact on global health. At the onset of disease, NAFLD is characterized by hepatic steatosis defined by the accumulation of triglycerides stored as lipid droplets. Developing therapeutics against NAFLD and progression to non-alcoholic steatohepatitis (NASH) remains a high priority in the medical and scientific community. Drug discovery programs to identify potential therapeutic compounds have supported high throughput/high-content screening of in vitro human-relevant models of NAFLD to accelerate development of efficacious anti-steatotic medicines. Human induced pluripotent stem cell (hiPSC) technology is a powerful platform for disease modeling and therapeutic assessment for cell-based therapy and personalized medicine. In this study, we applied AstraZeneca’s chemogenomic library, hiPSC technology and multiplexed high content screening to identify compounds that significantly reduced intracellular neutral lipid content. Among 13,000 compounds screened, we identified hits that protect against hiPSC-derived hepatic endoplasmic reticulum stress-induced steatosis by a mechanism of action including inhibition of the cyclin D3-cyclin-dependent kinase 2-4 (CDK2-4)/CCAAT-enhancer-binding proteins (C/EBPα)/diacylglycerol acyltransferase 2 (DGAT2) pathway, followed by alteration of the expression of downstream genes related to NAFLD. These findings demonstrate that our phenotypic platform provides a reliable approach in drug discovery, to identify novel drugs for treatment of fatty liver disease as well as to elucidate their underlying mechanisms.

Identification of ribavirin-responsive cis-elements for GPAM suppression in the GPAM genome

Glycerol-3-phosphate acyltransferase, mitochondrial (GPAM) is a rate-limiting enzyme catalyzing triglyceride synthesis. Recently, we demonstrated that the anti-viral drug ribavirin (RBV) reduces GPAM expression by downregulating CCAAT/enhancer-binding protein α (C/EBPα). However, the precise mechanisms of GPAM suppression have remained unclear. Here, we found that RBV suppressed GPAM expression by downregulating not only C/EBPα, but also sterol regulatory element-binding protein-1c (SREBP-1c). We also found that cis-elements regulated by C/EBPα and SREBP-1c functioned as distal and proximal enhancers, respectively, to express hepatocyte- and adipocytes-specific GPAM variants. These results imply that RBV disrupts formation of the enhancer machineries on the GPAM genome by downregulating both transcription factors. Our findings may contribute to the development of treatments for fatty liver diseases caused by aberrant triglyceride synthesis.

Wnt/β-catenin signaling regulates adipose tissue lipogenesis and adipocyte-specific loss is rigorously defended by neighboring stromal-vascular cells

OBJECTIVE

Canonical Wnt/β-catenin signaling is a well-studied endogenous regulator of mesenchymal cell fate determination, promoting osteoblastogenesis and inhibiting adipogenesis. However, emerging genetic evidence in humans links a number of Wnt pathway members to body fat distribution, obesity, and metabolic dysfunction, suggesting that this pathway also functions in adipocytes. Recent studies in mice have uncovered compelling evidence that the Wnt signaling pathway plays important roles in adipocyte metabolism, particularly under obesogenic conditions. However, complexities in Wnt signaling and differences in experimental models and approaches have thus far limited our understanding of its specific roles in this context.

METHODS

To investigate roles of the canonical Wnt pathway in the regulation of adipocyte metabolism, we generated adipocyte-specific β-catenin (β-cat) knockout mouse and cultured cell models. We used RNA sequencing, ChIP sequencing, and molecular approaches to assess expression of Wnt targets and lipogenic genes. We then used functional assays to evaluate effects of β-catenin deficiency on adipocyte metabolism, including lipid and carbohydrate handling. In mice maintained on normal chow and high-fat diets, we assessed the cellular and functional consequences of adipocyte-specific β-catenin deletion on adipose tissues and systemic metabolism.

RESULTS

We report that in adipocytes, the canonical Wnt/β-catenin pathway regulates de novo lipogenesis (DNL) and fatty acid monounsaturation. Further, β-catenin mediates effects of Wnt signaling on lipid metabolism in part by transcriptional regulation of Mlxipl and Srebf1. Intriguingly, adipocyte-specific loss of β-catenin is sensed and defended by CD45^-/CD31^- stromal cells to maintain tissue-wide Wnt signaling homeostasis in chow-fed mice. With long-term high-fat diet, this compensatory mechanism is overridden, revealing that β-catenin deletion promotes resistance to diet-induced obesity and adipocyte hypertrophy and subsequent protection from metabolic dysfunction.

CONCLUSIONS

Taken together, our studies demonstrate that Wnt signaling in adipocytes is required for lipogenic gene expression, de novo lipogenesis, and lipid desaturation. In addition, adipose tissues rigorously defend Wnt signaling homeostasis under standard nutritional conditions, such that stromal-vascular cells sense and compensate for adipocyte-specific loss. These findings underscore the critical importance of this pathway in adipocyte lipid metabolism and adipose tissue function.

Wntless regulates lipogenic gene expression in adipocytes and protects against diet-induced metabolic dysfunction

OBJECTIVE

Obesity is a key risk factor for many secondary chronic illnesses, including type 2 diabetes and cardiovascular disease. Canonical Wnt/β-catenin signaling is established as an important endogenous inhibitor of adipogenesis. This pathway is operative in mature adipocytes; however, its roles in this context remain unclear due to complexities of Wnt signaling and differences in experimental models. In this study, we used novel cultured cell and mouse models to investigate functional roles of Wnts secreted from adipocytes.

METHODS

We generated adipocyte-specific Wntless (Wls) knockout mice and cultured cell models to investigate molecular and metabolic consequences of disrupting Wnt secretion from mature adipocytes. To characterize Wls-deficient cultured adipocytes, we evaluated the expression of Wnt target and lipogenic genes and the downstream functional effects on carbohydrate and lipid metabolism. We also investigated the impact of adipocyte-specific Wls deletion on adipose tissues and global glucose metabolism in mice fed normal chow or high-fat diets.

RESULTS

Many aspects of the Wnt signaling apparatus are expressed and operative in mature adipocytes, including the Wnt chaperone Wntless. Deletion of Wntless in cultured adipocytes results in the inhibition of de novo lipogenesis and lipid monounsaturation, likely through repression of Srebf1 (SREBP1c) and Mlxipl (ChREBP) and impaired cleavage of immature SREBP1c into its active form. Adipocyte-specific Wls knockout mice (Wls-/-) have lipogenic gene expression in adipose tissues and isolated adipocytes similar to that of controls when fed a normal chow diet. However, closer investigation reveals that a subset of Wnts and downstream signaling targets are upregulated within stromal-vascular cells of Wls-/- mice, suggesting that adipose tissues defend loss of Wnt secretion from adipocytes. Interestingly, this compensation is lost with long-term high-fat diet challenges. Thus, after six months of a high-fat diet, Wls-/- mice are characterized by decreased adipocyte lipogenic gene expression, reduced visceral adiposity, and improved glucose homeostasis.

CONCLUSIONS

Taken together, these studies demonstrate that adipocyte-derived Wnts regulate de novo lipogenesis and lipid desaturation and coordinate the expression of lipogenic genes in adipose tissues. In addition, we report that Wnt signaling within adipose tissues is defended, such that a loss of Wnt secretion from adipocytes is sensed and compensated for by neighboring stromal-vascular cells. With chronic overnutrition, this compensatory mechanism is lost, revealing that Wls-/- mice are resistant to diet-induced obesity, adipocyte hypertrophy, and metabolic dysfunction.

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

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

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.

The depot-specific and essential roles of CBP/p300 in regulating adipose plasticity

Fat remodeling has been extensively explored through protein deacetylation, but not yet acetylation, as a viable therapeutic approach in the management of obesity and related metabolic disorders. Here, we investigated the functions of key acetyltransferases CBP/p300 in adipose remodeling and their physiological effects by generating adipose-specific deletion of CBP (Cbp-AKO), p300 (p300-AKO) and double-knockout (Cbp/p300-AKO) models. We demonstrated that Cbp-AKO exhibited marked brown remodeling of inguinal WAT (iWAT) but not epididymal WAT (eWAT) after cold exposure and that this pattern was exaggerated in diet-induced obesity (DIO). Despite this striking browning phenotype, loss of Cbp was insufficient to impact body weight or glucose tolerance. In contrast, ablation of p300 in adipose tissues had minimal effects on fat remodeling and adiposity. Surprisingly, double-knockout mice (Cbp/p300-AKO) developed severe lipodystrophy along with marked hepatic steatosis, hyperglycemia and hyperlipidemia. Furthermore, we demonstrated that pharmacological inhibition of Cbp and p300 activity suppressed adipogenesis. Collectively, these data suggest that (i) CBP, but not p300, has distinct functions in regulating fat remodeling and that this occurs in a depot-selective manner; (ii) brown remodeling occurs independently of the improvements in glucose metabolism and obesity and (iii) the combined roles of CBP and p300 are indispensable for normal adipose development.

PU.1 and epigenetic signals modulate 1,25-dihydroxyvitamin D3 and C/EBPα regulation of the human cathelicidin antimicrobial peptide gene in lung epithelial cells

LL-37, the only known human cathelicidin which is encoded by the human antimicrobial peptide (CAMP) gene, plays a critical role in protection against bacterial infection. We previously demonstrated that cathelicidin is induced by 1,25-dihydroxyvitamin D₃ (1,25(OH) ₂ D ₃ ) in human airway epithelial cells with a resultant increase in bactericidal activity. In this study we identify key factors that co-operate with 1,25(OH) ₂ D ₃ in the regulation of CAMP. Our results show for the first time that PU.1, the myeloid transcription factor (which has also been identified in lung epithelial cells), co-operates with the vitamin D receptor and CCAAT/enhancer binding protein α (CEBPα) to enhance the induction of CAMP in lung epithelial cells. Our findings also indicate that enhancement of 1,25(OH) ₂ D ₃ regulation of CAMP by histone deacetylase inhibitors involves co-operation between acetylation and chromatin remodeling through Brahma-related gene 1 (BRG1; a component of the SWItch/sucrose nonfermentable [SWI/SNF] complex). BRG1 can be an activator or repressor depending on BRG1-associated factors. Protein arginine methyltransferase 5 (PRMT5), a methlytransferase which interacts with BRG1, represses 1,25(OH) ₂ D ₃ induced CAMP in part through dimethylation of H4R3. Our findings identify key mediators involved in the regulation of the CAMP gene in lung epithelial cells and suggest new approaches for therapeutic manipulation of gene expression to increase the antibacterial capability of the airway.

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.

Identification of C/EBPα as a novel target of the HPV8 E6 protein regulating miR-203 in human keratinocytes

Patients suffering from Epidermodysplasia verruciformis (EV), a rare inherited skin disease, display a particular susceptibility to persistent infection with cutaneous genus beta-human papillomavirus (beta-HPV), such as HPV type 8. They have a high risk to develop non-melanoma skin cancer at sun-exposed sites. In various models evidence is emerging that cutaneous HPV E6 proteins disturb epidermal homeostasis and support carcinogenesis, however, the underlying mechanisms are not fully understood as yet. In this study we demonstrate that microRNA-203 (miR-203), a key regulator of epidermal proliferation and differentiation, is strongly down-regulated in HPV8-positive EV-lesions. We provide evidence that CCAAT/enhancer-binding protein α (C/EBPα), a differentiation-regulating transcription factor and suppressor of UV-induced skin carcinogenesis, directly binds the miR-203 gene within its hairpin region and thereby induces miR-203 transcription. Our data further demonstrate that the HPV8 E6 protein significantly suppresses this novel C/EBPα/mir-203-pathway. As a consequence, the miR-203 target ΔNp63α, a proliferation-inducing transcription factor, is up-regulated, while the differentiation factor involucrin is suppressed. HPV8 E6 specifically down-regulates C/EBPα but not C/EBPβ expression at the transcriptional level. As shown in knock-down experiments, C/EBPα is regulated by the acetyltransferase p300, a well-described target of cutaneous E6 proteins. Notably, p300 bound significantly less to the C/EBPα regulatory region in HPV8 E6 expressing keratinocytes than in control cells as demonstrated by chromatin immunoprecipitation. In situ analysis confirmed congruent suprabasal expression patterns of C/EBPα and miR-203 in non-lesional skin of EV-patients. In HPV8-positive EV-lesions both factors are potently down-regulated in vivo further supporting our in vitro data. In conclusion our study has unraveled a novel p300/C/EBPα/mir-203-dependent mechanism, by which the cutaneous HPV8 E6 protein may expand p63-positive cells in the epidermis of EV-patients and disturbs fundamental keratinocyte functions. This may drive HPV-mediated pathogenesis and may potentially also pave the way for skin carcinogenesis in EV-patients.

Cutaneous genus beta-HPV types infect skin keratinocytes. Their potential role in skin carcinogenesis, particularly in immunosuppressed patients, has become a major field of interest. Patients suffering from the rare genetic disorder Epidermodysplasia verruciformis (EV) are highly susceptible to persistent genus beta-HPV infection and have an increased risk to develop non-melanoma skin cancer at sun-exposed sites. Thus, EV serves as a valuable model disease for studying genus beta-HPV biology. Here, we demonstrate that in human HPV8-infected EV skin lesions, the ‘stemness-repressing’ microRNA-203 is strongly down-regulated. In contrast, cells expressing the miR-203-regulated ‘stemness-maintaining’ factor p63, are highly amplified. Notably, we identified the transcription factor C/EBPα, a well-known suppressor of UV-induced skin carcinogenesis, as a p300-dependent target of the HPV8-encoded E6 oncoprotein and as a critical inducer of miR-203 gene expression. Our data provide evidence for a novel p300/C/EBPα/miR-203-dependent pathway, which links HPV8 infection to the expansion of p63-positive cells in the epidermis of EV-patients. This may contribute to the beta-HPV-induced disturbance of epidermal homeostasis and pave the way for skin carcinogenesis.

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

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

The Essential Transcriptional Function of BRD4 in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is often initiated by genetic alterations of machineries that regulate chromatin and transcription, thereby blocking cell differentiation. Such mechanisms may also render leukemia cells vulnerable to perturbations of transcriptional regulators, which includes small molecules targeting the coactivator protein BRD4. Numerous studies have validated BRD4 as a therapeutic target in diverse subtypes of AML; however, the vital function of BRD4 in this disease is only beginning to be understood. Here we discuss the recent progress in elucidating the transcriptional function of BRD4 in AML cells, with an emphasis on the desirable attributes, but also the inherent limitations, of targeting general coactivator proteins as cancer therapy.

Quantitative assessment of adipocyte differentiation in cell culture

Adipocyte cell culture is an important tool for mechanistic studies of energy metabolism. Many factors affect the differentiation of adipocytes in culture. Oil red O staining can be used to assess the degree of differentiation. However, the validity of this method for quantitative analysis has not yet been established. Here we show that a protocol with arbitrarily chosen parameters does not measure in the linear range and is not suitable for quantitative analysis (R² = 0.077, p = 0.382), and develop and validate an optimized protocol for quantitative oil red O staining of cultured adipocytes. 3T3-L1 preadipocytes and adipocytes are fixed with 4% formaldehyde and stained with 0.2% oil red O solution in 40% 2-propanol for 30 minutes. Dye is eluted with 2-propanol, and absorption of the eluate is measured photometrically at 510 nm. This optimized protocol achieves excellent correlation between defined amounts of differentiated adipocytes on constant-size culture plates and photometric absorption (R² = 0.972, p = 6.585E-14). The performance of the method is independent of the culture plates used. Thus, the optimized oil red O staining protocol can be universally employed to quantitatively assess adipocyte differentiation.

Acetylation of C/EBPα inhibits its granulopoietic function

CCAAT/enhancer-binding protein alpha (C/EBPα) is an essential transcription factor for myeloid lineage commitment. Here we demonstrate that acetylation of C/EBPα at lysine residues K298 and K302, mediated at least in part by general control non-derepressible 5 (GCN5), impairs C/EBPα DNA-binding ability and modulates C/EBPα transcriptional activity. Acetylated C/EBPα is enriched in human myeloid leukaemia cell lines and acute myeloid leukaemia (AML) samples, and downregulated upon granulocyte-colony stimulating factor (G-CSF)- mediated granulocytic differentiation of 32Dcl3 cells. C/EBPα mutants that mimic acetylation failed to induce granulocytic differentiation in C/EBPα-dependent assays, in both cell lines and in primary hematopoietic cells. Our data uncover GCN5 as a negative regulator of C/EBPα and demonstrate the importance of C/EBPα acetylation in myeloid differentiation.

C/EBPα is an essential transcription factor for myeloid lineage commitment. Here, the authors show that acetylation of C/EBPα at K298 and K302, mediated at least in part by GCN5, impairs C/EBPα DNA binding ability and modulates C/EBPα transcriptional activity.

The Cytokinome Profile in Patients with Hepatocellular Carcinoma and Type 2 Diabetes

Understanding the dynamics of the complex interaction network of cytokines, defined as ‘‘cytokinome’’, can be useful to follow progression and evolution of hepatocellular carcinoma (HCC) from its early stages as well as to define therapeutic strategies. Recently we have evaluated the cytokinome profile in patients with type 2 diabetes (T2D) and/or chronic hepatitis C (CHC) infection and/or cirrhosis suggesting specific markers for the different stages of the diseases. Since T2D has been identified as one of the contributory cause of HCC, in this paper we examined the serum levels of cytokines, growth factors, chemokines, as well as of other cancer and diabetes biomarkers in a discovery cohort of patients with T2D, chronic hepatitis C (CHC) and/or CHC-related HCC comparing them with a healthy control group to define a profile of proteins able to characterize these patients, and to recognize the association between diabetes and HCC. The results have evidenced that the serum levels of some proteins are significantly and differently up-regulated in all the patients but they increased still more when HCC develops on the background of T2D. Our results were verified also using a separate validation cohort. Furthermore, significant correlations between clinical and laboratory data characterizing the various stages of this complex disease, have been found. In overall, our results highlighted that a large and simple omics approach, such as that of the cytokinome analysis, supplemented by common biochemical and clinical data, can give a complete picture able to improve the prognosis of the various stages of the disease progression. We have also demonstrated by means of interactomic analysis that our experimental results correlate positively with the general metabolic picture that is emerging in the literature for this complex multifactorial disease.

Reciprocal occupancy of BCL6 and STAT5 on Growth Hormone target genes: contrasting transcriptional outcomes and promoter-specific roles of p300 and HDAC3

Expression of the Growth Hormone (GH)-stimulated gene Socs2 (Suppressor of Cytokine Signaling 2) is mediated by the transcription activator STAT5 (Signal Transducer and Activator of Transcription 5) and the transcription repressor BCL6 (B-Cell Lymphoma 6). ChIP-Sequencing identified Cish (Cytokine-Inducible SH2-containing protein) and Bcl6 as having similar patterns of reciprocal occupancy by BCL6 and STAT5 in response to GH, though GH stimulates Cish and inhibits Bcl6 expression. The co-activator p300 occupied Socs2, Cish and Bcl6 promoters, and enhanced STAT5-mediated activation of Socs2 and Cish. In contrast, on Bcl6, p300 functioned as a repressor and inhibited in conjunction with STAT5 or BCL6. The co-repressor HDAC3 (Histone deacetylase 3) inhibited the Socs2, Cish and Bcl6 promoters in the presence of STAT5. Thus transcriptional outcomes on GH-regulated genes occupied by BCL6 and STAT5 are determined in a promoter-specific fashion by co-regulatory proteins which mediate the distinction between activating and repressive transcription factors.

MicroRNAs in bovine adipogenesis: genomic context, expression and function

Background

MicroRNAs (miRNAs) are small non-coding RNAs found to regulate several biological processes including adipogenesis. Understanding adipose tissue regulation is critical for beef cattle as fat is an important determinant of beef quality and nutrient value. This study analyzed the association between genomic context characteristics of miRNAs with their expression and function in bovine adipose tissue. Twenty-four subcutaneous adipose tissue biopsies were obtained from eight British-continental crossbred steers at 3 different time points. Total RNA was extracted and miRNAs were profiled using a miRNA microarray with expression further validated by qRT-PCR.

Results

A total of 224 miRNAs were detected of which 155 were expressed in all steers (n = 8), and defined as the core miRNAs of bovine subcutaneous adipose tissue. Core adipose miRNAs varied in terms of genomic location (59.5% intergenic, 38.7% intronic, 1.2% exonic, and 0.6% mirtron), organization (55.5% non-clustered and 44.5% clustered), and conservation (49% highly conserved, 14% conserved and 37% poorly conserved). Clustered miRNAs and highly conserved miRNAs were more highly expressed (p < 0.05) and had more predicted targets than non-clustered or less conserved miRNAs (p < 0.001). A total of 34 miRNAs were coordinately expressed, being part of six identified relevant networks. Two intronic miRNAs (miR-33a and miR-1281) were confirmed to have coordinated expression with their host genes, transcriptional factor SREBF2 and EP300 (a transcriptional co-activator of transcriptional factor C/EBPα), respectively which are involved in lipid metabolism, suggesting these miRNAs may also play a role in regulation of bovine lipid metabolism/adipogenesis. Furthermore, a total of 17 bovine specific miRNAs were predicted to be involved in the regulation of energy balance in adipose tissue.

Conclusions

These findings improve our understanding on the behavior of miRNAs in the regulation of bovine adipogenesis and fat metabolism as it reveals that miRNA expression patterns and functions are associated with miRNA genomic location, organization and conservation.

Diacylglycerol kinase delta promotes lipogenesis

We have studied the relationship between diacylglycerol kinase delta (DGKδ) and lipogenesis. There is a marked increase in the expression of DGKδ during the differentiation of 3T3-L1 cells to adipocytes, as well as in the synthesis of neutral and polar lipids. When 3T3-L1 undifferentiated fibroblasts are transfected to express DGKδ, there is increased triglyceride synthesis without differentiation to adipocytes. Hence, expression of DGKδ promotes lipogenesis. Lipid synthesis is decreased in DGKδ knockout mouse embryo fibroblasts, especially for lipids with shorter acyl chains and limited unsaturation. This reduction occurs for both neutral and polar lipids. These findings suggest reduced de novo lipid synthesis. This is confirmed by measuring the incorporation of glycerol into polar and neutral lipids, which is higher in the wild type cells than in the DGKδ knockouts. In comparison, there was no change in lipid synthesis in DGKε knockout mouse embryo fibroblasts. We also demonstrate that the DGKδ knockout cells had a lower expression of acetyl-CoA carboxylase and fatty acid synthase as well as a lower degree of activation by phosphorylation of ATP citrate lyase. These three enzymes are involved in the synthesis of long chain fatty acids. Our results demonstrate that DGKδ markedly increases lipid synthesis, at least in part as a result of promoting the de novo synthesis of fatty acids.

Interleukin (IL)-32β-mediated CCAAT/enhancer-binding protein α (C/EBPα) phosphorylation by protein kinase Cδ (PKCδ) abrogates the inhibitory effect of C/EBPα on IL-10 production

We previously reported that IL-32β promotes IL-10 production in myeloid cells. However, the underlying mechanism remains elusive. In this study, we demonstrated that IL-32β abrogated the inhibitory effect of CCAAT/enhancer-binding protein α (C/EBPα) on IL-10 expression in U937 cells. We observed that the phosphorylation of C/EBPα Ser-21 was inhibited by a PKCδ-specific inhibitor, rottlerin, or IL-32β knockdown by siRNA and that IL-32β shifted to the membrane from the cytosol upon phorbol 12-myristate 13-acetate treatment. We revealed that IL-32β suppressed the binding of C/EBPα to IL-10 promoter by using ChIP assay. These data suggest that PKCδ and IL-32β may modulate the effect of C/EBPα on IL-10 expression. We next demonstrated by immunoprecipitation that IL-32β interacted with PKCδ and C/EBPα, thereby mediating C/EBPα Ser-21 phosphorylation by PKCδ. We showed that IL-32β suppressed the inhibitory effect of C/EBPα on IL-10 promoter activity. However, the IL-10 promoter activity was reduced to the basal level by rottlerin treatment. When C/EBPα serine 21 was mutated to glycine (S21G), the inhibitory effect of C/EBPα S21G on IL-10 promoter activity was not modulated by IL-32β. Taken together, our results show that IL-32β-mediated C/EBPα Ser-21 phosphorylation by PKCδ suppressed C/EBPα binding to IL-10 promoter, which promoted IL-10 production in U937 cells.

Interaction and cooperation of the CCAAT-box enhancer-binding protein β (C/EBPβ) with the homeodomain-interacting protein kinase 2 (Hipk2)

CCAAT box/enhancer-binding protein β (C/EBPβ) is a bZip transcription factor that plays crucial roles in important cellular processes such as differentiation and proliferation of specific cell types. Previously, we showed that C/EBPβ cooperates with the coactivator p300 through a novel mechanism that involves the C/EBPβ-induced phosphorylation of multiple sites in the carboxyl-terminal domain of p300 by protein kinase Hipk2. We have now examined the interaction and cooperation of C/EBPβ, p300, and Hipk2 in more detail. We show that Hipk2 and C/EBPβ are direct physical binding partners whose interaction is mediated by sequences located in the amino-terminal and central domains of Hipk2 and the amino-terminal part of C/EBPβ. In addition to phosphorylating p300 recruited to C/EBPβ, Hipk2 also phosphorylates C/EBPβ at sites that have previously been shown to plays key roles in the regulation of C/EBPβ activity. Silencing of Hipk2 expression disrupts adipocyte differentiation of 3T3-L1 cells, a physiological C/EBPβ-dependent differentiation process indicating that the cooperation of C/EBPβ and Hipk2 is functionally relevant. Finally, we demonstrate that C/EBPα, a related C/EBP family member whose amino-terminal sequences differ significantly from that of C/EBPβ, is unable to interact and cooperate with Hipk2. Instead, our data suggest that C/EBPα cooperates with the protein kinase Jnk to induce phosphorylation of p300. Overall, our data identify Hipk2 as a novel regulator of C/EBPβ and implicate different protein kinases in the cooperation of p300 with C/EBPβ and C/EBPα.

Increased expression of enzymes of triglyceride synthesis is essential for the development of hepatic steatosis

Molecular mechanisms underpinning nonalcoholic fatty liver disease (NAFLD) are not well understood. The earliest step of NAFLD is hepatic steatosis, which is one of the main characteristics of aging liver. Here, we present a molecular scenario of age-related liver steatosis. We show that C/EBPα-S193D knockin mice have age-associated epigenetic changes and develop hepatic steatosis at 2 months of age. The underlying mechanism of the hepatic steatosis in old wild-type (WT) mice and in young S193D mice includes increased amounts of tripartite p300-C/EBPα/β complexes that activate promoters of five genes that drive triglyceride synthesis. Knockdown of p300 in old WT mice inhibits hepatic steatosis. Indeed, transgenic mice expressing dominant-negative p300 have fewer C/EBPα/β-p300 complexes and do not develop age-dependent hepatic steatosis. Notably, the p300-C/EBPα/β pathway is activated in the livers of patients with NAFLD. Thus, our results show that p300 and C/EBP proteins are essential participants in hepatic steatosis.

The transcription factor paired-related homeobox 1 (Prrx1) inhibits adipogenesis by activating transforming growth factor-β (TGFβ) signaling

Differentiation of adipocytes from preadipocytes contributes to adipose tissue expansion in obesity. Impaired adipogenesis may underlie the development of metabolic diseases such as insulin resistance and type 2 diabetes. Mechanistically, a well defined transcriptional network coordinates adipocyte differentiation. The family of paired-related homeobox transcription factors, which includes Prrx1a, Prrx1b, and Prrx2, is implicated with regulation of mesenchymal cell fate, including myogenesis and skeletogenesis; however, whether these proteins impact adipogenesis remains to be addressed. In this study, we identify Prrx1a and Prrx1b as negative regulators of adipogenesis. We show that Prrx1a and Prrx1b are down-regulated during adipogenesis in vitro and in vivo. Stable knockdown of Prrx1a/b enhances adipogenesis, with increased expression of peroxisome proliferator-activated receptor-γ, CCAAT/enhancer-binding protein-α and FABP4 and increased secretion of the adipokines adiponectin and chemerin. Although stable low-level expression of Prrx1a, Prrx1b, or Prrx2 does not affect 3T3-L1 adipogenesis, transient overexpression of Prrx1a or Prrx1b inhibits peroxisome proliferator-activated receptor-γ activity. Prrx1 knockdown decreases expression of Tgfb2 and Tgfb3, and inhibition of TGFβ signaling during adipogenesis mimics the effects of Prrx1 knockdown. These data support the hypothesis that endogenous Prrx1 restrains adipogenesis by regulating expression of TGFβ ligands and thereby activating TGFβ signaling. Finally, we find that expression of Prrx1a or Prrx1b in adipose tissue increases during obesity and strongly correlates with Tgfb3 expression in BL6 mice. These observations suggest that increased Prrx1 expression may promote TGFβ activity in adipose tissue and thereby contribute to aberrant adipocyte function during obesity.

Fibrinogen gene regulation

The Aα, Bβ and γ polypeptide chains of fibrinogen are encoded by a three gene cluster on human chromosome four. The fibrinogen genes (FGB-FGA-FGG) are expressed almost exclusively in hepatocytes where their output is coordinated to ensure a sufficient mRNA pool for each chain and maintain an abundant plasma fibrinogen protein level. Fibrinogen gene expression is controlled by the activity of proximal promoters which contain binding sites for hepatocyte transcription factors, including proteins which influence fibrinogen transcription in response to acute-phase inflammatory stimuli. The fibrinogen gene cluster also contains cis regulatory elements; enhancer sequences with liver activities identified by sequence conservation and functional genomics. While the transcriptional control of this gene cluster is fascinating biology, the medical impetus to understand fibrinogen gene regulation stems from the association of cardiovascular disease risk with high level circulating fibrinogen. In the general population this level varies from about 1.5 to 3.5 g/l. This variation between individuals is influenced by genotype, suggesting there are genetic variants contributing to fibrinogen levels which reside in fibrinogen regulatory loci. A complete picture of how fibrinogen genes are regulated will therefore point towards novel sources of regulatory variants. In this review we discuss regulation of the fibrinogen genes from proximal promoters and enhancers, the influence of acute-phase stimulation, post-transcriptional regulation by miRNAs and functional regulatory variants identified in genetic studies. Finally, we discuss the fibrinogen locus in light of recent advances in understanding chromosomal architecture and suggest future directions for researching the mechanisms that control fibrinogen expression.

Secreted frizzled-related protein 5 suppresses adipocyte mitochondrial metabolism through WNT inhibition

Preadipocytes secrete several WNT family proteins that act through autocrine/paracrine mechanisms to inhibit adipogenesis. The activity of WNT ligands is often decreased by secreted frizzled-related proteins (SFRPs). Sfrp5 is strongly induced during adipocyte differentiation and increases in adipocytes during obesity, presumably to counteract WNT signaling. We tested the hypothesis that obesity-induced Sfrp5 expression promotes the development of new adipocytes by inhibiting endogenous suppressors of adipogenesis. As predicted, mice that lack functional SFRP5 were resistant to diet-induced obesity. However, counter to our hypothesis, we found that adipose tissue of SFRP5-deficient mice had similar numbers of adipocytes, but a reduction in large adipocytes. Transplantation of adipose tissue from SFRP5-deficient mice into leptin receptor-deficient mice indicated that the effects of SFRP5 deficiency are tissue-autonomous. Mitochondrial gene expression was increased in adipose tissue and cultured adipocytes from SFRP5-deficient mice. In adipocytes, lack of SFRP5 stimulated oxidative capacity through increased mitochondrial activity, which was mediated in part by PGC1α and mitochondrial transcription factor A. WNT3a also increased oxygen consumption and the expression of mitochondrial genes. Thus, our findings support a model of adipogenesis in which SFRP5 inhibits WNT signaling to suppress oxidative metabolism and stimulate adipocyte growth during obesity.

C/EBPα and DEK coordinately regulate myeloid differentiation

The transcription factor C/EBPα is a critical mediator of myeloid differentiation and is often functionally impaired in acute myeloid leukemia. Recent studies have suggested that oncogenic FLT3 activity disrupts wild-type C/EBPα function via phosphorylation on serine 21 (S21). Despite the apparent role of pS21 as a negative regulator of C/EBPα transcription activity, the mechanism by which phosphorylation tips the balance between transcriptionally competent and inhibited forms remains unresolved. In the present study, we used immuno-affinity purification combined with quantitative mass spectrometry to delineate the proteins associated with C/EBPα on chromatin. We identified DEK, a protein with genetic links to leukemia, as a member of the C/EBPα complexes, and demonstrate that this association is disrupted by S21 phosphorylation. We confirmed that DEK is recruited specifically to chromatin with C/EBPα to enhance GCSFR3 promoter activation. In addition, we demonstrated that genetic depletion of DEK reduces the ability of C/EBPα to drive the expression of granulocytic target genes in vitro and disrupts G-CSF-mediated granulocytic differentiation of fresh human BM-derived CD34(+) cells. Our data suggest that C/EBPα and DEK coordinately activate myeloid gene expression and that S21 phosphorylation on wild-type C/EBPα mediates protein interactions that regulate the differentiation capacity of hematopoietic progenitors.

ATXN8 -62 G/A promoter polymorphism and risk of Taiwanese Parkinson's disease

BACKGROUND AND PURPOSE

We recently reported a novel -62 G/A polymorphism within ataxin 8 (ATXN8) gene promoter region, with -62 G displaying significantly higher luciferase activity compared with -62 A. Phenotypic variability in spinocerebellar ataxia type 8 (SCA8) has been suggested, and large SCA8 repeats were found in patients with Parkinson's disease (PD). We aimed to investigate the association of ATXN8 -62 G/A polymorphism with the risk of Taiwanese PD, and identify the trans-acting factor modulating the ATXN8 promoter activity.

METHODS

A case-control study in a cohort of 569 PD cases and 547 ethnically matched controls was conducted by polymerase chain reaction (PCR) and restriction enzyme analysis. The trans-acting factor binding to the ATXN8 promoter was examined by chromatin immunoprecipitation (ChIP)-PCR assay, cDNA co-transfection and luciferase reporter assay.

RESULTS

When genotype distribution was calculated by comparing the rare AA genotype with the GG + GA genotypes (recessive model), a significant difference was found (P = 0.035, 1 df). Individuals carrying AA genotype exhibited a decreased risk of developing PD (odds ratio: 0.73; 95% CI: 0.55-0.98, P = 0.035). After stratification by age, individuals over 60 years of age carrying AA genotype demonstrated a further decrease in the risk of developing PD (odds ratio: 0.64; 95% CI: 0.43-0.96, P = 0.030). ChIP-PCR and cDNA over-expression revealed that CCAAT/enhancer-binding protein alpha binds to the ATXN8 proximal promoter to upregulate ATXN8 expression in neuroblastoma SK-N-SH cells.

CONCLUSIONS

Our data suggest that ATXN8 -62 G/A polymorphism plays a role in Taiwanese PD susceptibility.

Wnt6, Wnt10a and Wnt10b inhibit adipogenesis and stimulate osteoblastogenesis through a β-catenin-dependent mechanism

Wnt10b is an established regulator of mesenchymal stem cell (MSC) fate that inhibits adipogenesis and stimulates osteoblastogenesis, thereby impacting bone mass in vivo. However, downstream mechanisms through which Wnt10b exerts these effects are poorly understood. Moreover, whether other endogenous Wnt ligands also modulate MSC fate remains to be fully addressed. In this study, we identify Wnt6 and Wnt10a as additional Wnt family members that, like Wnt10b, are downregulated during development of white adipocytes in vivo and in vitro, suggesting that Wnt6 and/or Wnt10a may also inhibit adipogenesis. To assess the relative activities of Wnt6, Wnt10a and Wnt10b to regulate mesenchymal cell fate, we used gain- and loss-of function approaches in bipotential ST2 cells and in 3T3-L1 preadipocytes. Enforced expression of Wnt10a stabilizes β-catenin, suppresses adipogenesis and stimulates osteoblastogenesis to a similar extent as Wnt10b, whereas stable expression of Wnt6 has a weaker effect on these processes than Wnt10a or Wnt10b. In contrast, knockdown of endogenous Wnt6 is associated with greater preadipocyte differentiation and impaired osteoblastogenesis than knockdown of Wnt10a or Wnt10b, suggesting that, among these Wnt ligands, Wnt6 is the most potent endogenous regulator of MSC fate. Finally, we show that knockdown of β-catenin completely prevents the inhibition of adipogenesis and stimulation of osteoblast differentiation by Wnt6, Wnt10a or Wnt10b. Potential mechanisms whereby Wnts regulate fate of MSCs downstream of β-catenin are also investigated. In conclusion, this study identifies Wnt10a and Wnt6 as additional regulators of MSC fate and demonstrates that mechanisms downstream of β-catenin are required for Wnt6, Wnt10a and Wnt10b to influence differentiation of mesenchymal precursors.

Sumoylation of CCAAT/enhancer–binding protein α promotes the biased primitive hematopoiesis of zebrafish

Hematopoiesis is evolutionarily conserved from zebrafish to mammals, and this includes both primitive and definitive waves during embryogenesis. Primitive hematopoiesis is dominated by erythropoiesis with limited myelopoiesis. Protein sumoylation, a ubiquitination-like posttranslational protein modification, is implicated in a variety of biochemical processes, most notably in transcriptional repression. We show here that the loss of 6 small ubiquitin-related modifier (SUMO) paralogs triggers a sharp up-regulation of the myeloid-specific marker mpo and down-regulation of the erythroid-specific marker gata1 in myelo-erythroid progenitor cells (MPCs) in the intermediate cell mass (ICM) during primitive hematopoiesis. Accordingly, in transgenic zebrafish lines, hyposumoylation expands myelopoiesis at the expense of erythropoiesis. A SUMO–CCAAT/enhancer–binding protein α (SUMO-C/ebpα) fusion restores the normal myelopoiesis/erythropoiesis balance, suggesting that sumoylation status of C/ebpα contributes to myelo-erythroid lineage determination. Our results therefore implicate sumoylation in early lineage determination and reveal the possible molecular mechanism underlying the puzzling biased primitive hematopoiesis in vertebrates.

Upstream open reading frames: molecular switches in (patho)physiology

Conserved upstream open reading frames (uORFs) are found within many eukaryotic transcripts and are known to regulate protein translation. Evidence from genetic and bioinformatic studies implicates disturbed uORF-mediated translational control in the etiology of human diseases. A genetic mouse model has recently provided proof-of-principle support for the physiological relevance of uORF-mediated translational control in mammals. The targeted disruption of the uORF initiation codon within the transcription factor CCAAT/enhancer binding protein β (C/EBPβ) gene resulted in deregulated C/EBPβ protein isoform expression, associated with defective liver regeneration and impaired osteoclast differentiation. The high prevalence of uORFs in the human transcriptome suggests that intensified search for mutations within 5' RNA leader regions may reveal a multitude of alterations affecting uORFs, causing pathogenic deregulation of protein expression.

Roles for miRNA-378/378* in adipocyte gene expression and lipogenesis

In this study, we explored the roles of microRNAs in adipocyte differentiation and metabolism. We first knocked down Argonaute2 (Ago2), a key enzyme in the processing of micro-RNAs (miRNAs), to investigate a potential role for miRNAs in adipocyte differentiation and/or metabolism. Although we did not observe dramatic differences in adipogenesis between Ago2 knock-down and control 3T3-L1 cells, incorporation of [(14)C]glucose or acetate into triacylglycerol, and steady-state levels of triacyglycerol were all reduced, suggesting a role for miRNAs in adipocyte metabolism. To study roles of specific miRNAs in adipocyte biology, we screened for miRNAs that are differentially expressed between preadipocytes and adipocytes for the 3T3-L1 and ST2 cell lines. Distinct subsets of miRNAs decline or increase during adipocyte conversion, whereas most miRNAs are not regulated. One locus encoding two miRNAs, 378/378*, contained within the intron of PGC-1beta is highly induced during adipogenesis. When overexpressed in ST2 mesenchymal precursor cells, miRNA378/378* increases the size of lipid droplets and incorporation of [(14)C]acetate into triacylglycerol. Although protein and mRNA expression levels of C/EBPalpha, C/EBPbeta, C/EBPdelta, and PPARgamma1 are unchanged, microarray and quantitative RT-PCR analyses indicate that a set of lipogenic genes are upregulated, perhaps due to increased expression of PPARgamma2. Knock-down of miRNA378 and/or miRNA378* decreases accumulation of triacylglycerol. Interestingly, we made the unexpected finding that miRNA378/378* specifically increases transcriptional activity of C/EBPalpha and C/EBPbeta on adipocyte gene promoters.

Mechanism of HIV-1-TAT induction of interleukin-1beta from human monocytes: Involvement of the phospholipase C/protein kinase C signaling cascade

Human immunodeficiency virus TAT plays an important role in the disregulation of cytokine production associated with the neurological disorders that follow HIV infection. IL-1beta is one of the important inflammatory cytokines secreted by immune-activated monocytes/macrophages. Previous reports have shown that extracellular TAT stimulates IL-1beta expression in monocytes/macrophages. However, little is known about the mechanisms and possible TAT-responsive elements within the IL-1beta promoter. The present study shows that TAT increases the production of IL-1beta in human monocytes; PLC-PKC pathway-dependent phosphorylation of p44/42 and JNK MAP kinases participates partially in IL-1beta induction by TAT; specific C/EBP and NF-kappaB transcription factor binding elements within the IL-1beta promoter are involved in TAT regulation of IL-1beta production. This study identifies a signaling mechanism for HIV-1-induced IL-1beta production in human monocytes that may be involved in the neuropathogenesis of HIV-associated dementia.

Nucleolar retention of a translational C/EBPalpha isoform stimulates rDNA transcription and cell size

The messenger RNA of the intronless CEBPA gene is translated into distinct protein isoforms through the usage of consecutive translation initiation sites. These translational isoforms have distinct functions in the regulation of differentiation and proliferation due to the presence of different N-terminal sequences. Here, we describe the function of an N-terminally extended protein isoform of CCAAT enhancer-binding protein α (C/EBPα) that is translated from an alternative non-AUG initiation codon. We show that a basic amino-acid motif within its N-terminus is required for nucleolar retention and for interaction with nucleophosmin (NPM). In the nucleoli, extended-C/EBPα occupies the ribosomal DNA (rDNA) promoter and associates with the Pol I-specific factors upstream-binding factor 1 (UBF-1) and SL1 to stimulate rRNA synthesis. Furthermore, during differentiation of HL-60 cells, endogenous expression of extended-C/EBPα is lost concomitantly with nucleolar C/EBPα immunostaining probably reflecting the reduced requirement for ribosome biogenesis in differentiated cells. Finally, overexpression of extended-C/EBPα induces an increase in cell size. Altogether, our results suggest that control of rRNA synthesis is a novel function of C/EBPα adding to its role as key regulator of cell growth and proliferation.

Role of epigenetics in liver-specific gene transcription, hepatocyte differentiation and stem cell reprogrammation

Controlling both growth and differentiation of stem cells and their differentiated somatic progeny is a challenge in numerous fields, from preclinical drug development to clinical therapy. Recently, new insights into the underlying molecular mechanisms have unveiled key regulatory roles of epigenetic marks driving cellular pluripotency, differentiation and self-renewal/proliferation. Indeed, the transcription of genes, governing cell-fate decisions during development and maintenance of a cell's differentiated status in adult life, critically depends on the chromatin accessibility of transcription factors to genomic regulatory and coding regions. In this review, we discuss the epigenetic control of (liver-specific) gene-transcription and the intricate interplay between chromatin modulation, including histone (de)acetylation and DNA (de)methylation, and liver-enriched transcription factors. Special attention is paid to their role in directing hepatic differentiation of primary hepatocytes and stem cells in vitro.

On the role of FOX transcription factors in adipocyte differentiation and insulin-stimulated glucose uptake

In this study, we explore the effects of several FOX and mutant FOX transcription factors on adipocyte determination, differentiation, and metabolism. In addition to Foxc2 and Foxo1, we report that Foxf2, Foxp1, and Foxa1 are other members of the Fox family that show regulated expression during adipogenesis. Although enforced expression of FOXC2 inhibits adipogenesis, Foxf2 slightly enhances the rate of differentiation. Constitutively active FOXC2-VP16 inhibits adipogenesis through multiple mechanisms. FOXC2-VP16 impairs the transient induction of C/EBPbeta during adipogenesis and induces expression of the transcriptional repressor Hey1 as well as the activator of Wnt/beta-catenin signaling, Wnt10b. The constitutive transcriptional repressor, FOXC2-Eng, enhances adipogenesis of preadipocytes and multipotent mesenchymal precursors and determines NIH-3T3 and C2C12 cells to the adipocyte lineage. Although PPARgamma ligand or C/EBPalpha are not necessary for stimulation of adipogenesis by FOXC2-Eng, at least low levels of PPARgamma protein are absolutely required. Finally, expression of FOXC2-Eng in adipocytes increases insulin-stimulated glucose uptake, further expanding the profound and pleiotropic effects of FOX transcription factors on adipocyte biology.

Gene and protein expression profiling of the fat-1 mouse brain

Polyunsaturated fatty acids (PUFAs) are essential structural components of all cell membranes and, more so, of the central nervous system. Several studies revealed that n-3 PUFAs possess anti-inflammatory actions and are useful in the treatment of dyslipidemia. These actions explain the beneficial actions of n-3 PUFAs in the management of cardiovascular diseases, inflammatory conditions, neuronal dysfunction, and cancer. But, the exact molecular targets of these beneficial actions of n-3 PUFAs are not known. Mice engineered to carry a fat-1 gene from Caenorhabditis elegans add a double bond into an unsaturated fatty acid hydrocarbon chain and convert n-6 to n-3 fatty acids. This results in an abundance of n-3 eicosapentaenoic acid and docosapentaenoic acid specifically in the brain and a reduction in n-6 fatty acids of these mice that can be used to evaluate the actions of n-3 PUFAs. Gene expression profile, RT-PCR and protein microarray studies in the hippocampus and whole brain of wild-type and fat-1 transgenic mice revealed that genes and proteins concerned with inflammation, apoptosis, neurotransmission, and neuronal growth and synapse formation are specifically modulated in fat-1 mice. These results may explain as to why n-3 PUFAs are of benefit in the prevention and treatment of diseases such as Alzheimer's disease, schizophrenia and other diseases associated with neuronal dysfunction, low-grade systemic inflammatory conditions, and bronchial asthma. Based on these data, it is evident that n-3 PUFAs act to modulate specific genes and formation of their protein products and thus, bring about their various beneficial actions.

The tumour necrosis factor-alpha-mediated suppression of the CCAAT/enhancer binding protein-alpha gene transcription in hepatocytes involves inhibition of autoregulation

Tumour necrosis factor-alpha (TNF-alpha) is a key regulator of the immune and inflammatory responses along with numerous other cellular changes during physiological and pathophysiological conditions. The cellular actions of TNF-alpha are associated with both the activation and the inhibition of gene transcription. In contrast to gene activation, the mechanisms underlying the TNF-alpha-mediated transcriptional inhibition remain largely unclear. We have investigated this aspect using the transcription factor CCAAT/enhancer binding protein-alpha (C/EBPalpha) as a model gene. TNF-alpha decreased the expression of C/EBPalpha mRNA and protein in the human hepatoma Hep3B cell line. The activity of the proximal promoter of both the human and the Xenopus C/EBPalpha genes in transfected Hep3B cells was inhibited by TNF-alpha. Transient transfection assays using various Xenopus C/EBPalpha promoter-luciferase DNA constructs showed that a C/EBP recognition sequence was essential for the TNF-alpha response. Electrophoretic mobility shift assays showed that C/EBPalpha bound to this site and co-transfection assays revealed that it was a major activator of the promoter and its transactivation potential was reduced by TNF-alpha. The potential role of nuclear factor kappaB (NF-kappaB) in the response was also investigated in the light of its pivotal role in TNF-alpha signalling. Inhibition of NF-kappaB using pharmacological agents or by transfection of a plasmid specifying for a superrepressor attenuated the TNF-alpha-inhibited C/EBPalpha promoter activity. In addition, an involvement of NF-kappaB in DNA-protein interactions at the C/EBP recognition sequence was identified.

Effects of the SANT domain of tension-induced/inhibited proteins (TIPs), novel partners of the histone acetyltransferase p300, on p300 activity and TIP-6-induced adipogenesis

We previously identified a set of transcription regulators, referred to as TIPs (tension-induced/inhibited proteins), with a role in myogenic versus adipogenic differentiation. Here we report that the TIP family comprises eight isoforms, all bearing a SANT (switching-defective protein 3, adaptor 2, nuclear receptor corepressor, and transcription factor IIIB) domain and some of them presenting S-adenosyl-l-methionine (SAM) and nuclear receptor box (NRB) motifs, all characteristic of histone-modifying enzymatic complexes. TIPs have SANT-dependent, p300-mediated histone acetyltransferase (HAT) activity. Ectopic TIP-6 (SANT(+) SAM(-) NRB(-)) but not TIP-6DeltaSANT induced de novo PPARgamma2-mediated adipogenic gene expression in NIH 3T3 cells and promoted preadipocyte differentiation into fat cells. TIP-6 was also involved in mediating hormonally/biochemically induced adipogenic differentiation of 3T3-L1 cells. Furthermore, TIP-6 was identified in adipose tissue in vivo. TIP-6 bound directly and indirectly to p300 and histone H4 (H4). Deletion of the SANT domain did not abolish TIP-6 interaction with p300 and H4 but eliminated direct TIP-6 binding to p300. Chromatin immunoprecipitation assays showed the recruitment of TIP-6, TIP-6DeltaSANT, and p300 to the PPARgamma2 promoter, but H3/H4 acetylation occurred only when p300 was directly associated with TIP-6. These studies demonstrated the importance of TIPs in the recruitment of p300 to specific promoters and in the regulation of p300 HAT activity through the involvement of the SANT domain. Furthermore, we identified TIP-6 as a new member of the adipogenic cascade.

Regulation of C/EBPdelta-dependent transactivation by histone deacetylases in intestinal epithelial cells

The C/EBPdelta transcription factor is involved in the positive regulation of the intestinal epithelial cell acute phase response. C/EBPdelta regulation by histone deacetylases (HDACs) during the course of inflammation remains to be determined. Our aim was to examine the effect of HDACs on C/EBPdelta-dependent regulation of haptoglobin, an acute phase protein induced in intestinal epithelial cells in response to pro-inflammatory cytokines. HDAC1, HDAC3, and HDAC4 were expressed in intestinal epithelial cells, as determined by Western blot. GST pull-down assays showed specific HDAC1 interactions with the transcriptional activation and the b-ZIP C/EBPdelta domains, while the co-repressor mSin3A interacts with the C-terminal domain. Immunoprecipitation assays confirmed the interaction between HDAC1 and the N-terminal C/EBPdelta amino acid 36-164 domain. HDAC1 overexpression decreased C/EBPdelta transcriptional activity of the haptoglobin promoter, as assessed by transient transfection and luciferase assays. Chromatin immunoprecipitation analysis showed a displacement of HDAC1 from the haptoglobin promoter in response to inflammatory stimuli and an increased acetylation of histone H3 and H4. HDAC1 silencing by shRNA expression increased both basal and IL-1beta-induced haptoglobin mRNA levels in epithelial intestinal cells. Our results suggest that interactions between C/EBPs and HDAC1 negatively regulate C/EBPdelta-dependent haptoglobin expression in intestinal epithelial cells.

JAK2, but not Src family kinases, is required for STAT, ERK, and Akt signaling in response to growth hormone in preadipocytes and hepatoma cells

Janus kinase 2 (JAK2), a tyrosine kinase that associates with the GH receptor and is activated by GH, has been implicated as a key mediator of GH signaling. Several published reports suggest that members of the Src family of tyrosine kinases may also participate in GH signaling. We therefore investigated the extent to which JAK2 and Src family kinases mediate GH activation of signal transducers and activators of transcription (STATs) 1, 3, and 5a/b, ERKs 1 and 2, and Akt, in the highly GH-responsive cell lines 3T3-F442A preadipocytes and H4IIE hepatoma cells. GH activation of Src family kinases was not detected in either cell line. Further, blocking basal activity of Src kinases with the Src inhibitors PP1 and PP2 did not inhibit GH activation of STATs 1, 3, or 5a/b, or ERKs 1 and 2. When levels of JAK2 were depressed by short hairpin RNA in 3T3-F442A and H4IIE cells, GH-stimulated activation of STATs 1, 3, and 5a/b, ERKs 1 and 2, and Akt were significantly reduced; however, basal activity of Src family kinases was unaffected. These results were supported genetically by experiments showing that GH robustly activates JAK2, STATs 3 and 5a/b, ERKs 1 and 2, and Akt in murine embryonic fibroblasts derived from Src/Yes/ Fyn triple-knockout embryos that lack known Src kinases. These results strongly suggest that JAK2, but not Src family kinases, is critical for transducing these GH signals in 3T3-F442A and H4IIE cells.

Essential role of C/EBPalpha in G-CSF-induced transcriptional activation and chromatin modification of myeloid-specific genes

Granulocyte colony-stimulating factor (G-CSF) regulates the proliferation and differentiation of neutrophilic progenitor cells. Here, we investigated the roles of CCAAT/enhancer-binding protein (C/EBP)alpha in the G-CSF-induced transcriptional activation and chromatin modification of the CCR2 and myeloperoxidase (MPO) genes in IL-3-dependent myeloid FDN1.1 cells. Chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assays revealed that G-CSF activates C/EBPalpha to bind target promoters. ChIP mapping experiments across the CCR2 and MPO genes showed that G-CSF induces histone H3 modifications: the acetylation of Lys9, trimethylation of Lys4 and trimethylation of Lys9. The distribution profile of the trimethylated Lys9 was distinct from that of the two other modifications. All the G-CSF-induced C/EBPalpha recruitment, transcriptional activation and histone modifications were reversed by re-stimulation with IL-3, and were abolished by short hairpin RNA (shRNA)-mediated knockdown of C/EBPalpha. These results indicate that C/EBPalpha is activated by G-CSF to bind target promoters, and plays critical roles in the transcriptional activation and dynamic chromatin modification of target genes during neutrophil differentiation.

Phosphorylation of CCAAT/enhancer-binding protein alpha regulates GLUT4 expression and glucose transport in adipocytes

The transcription factor CCAAT/enhancer-binding protein alpha (C/EBPalpha) is required during adipogenesis for development of insulin-stimulated glucose uptake. Modes for regulating this function of C/EBPalpha have yet to be determined. Phosphorylation of C/EBPalpha on Ser-21 has been implicated in the regulation of granulopoiesis and hepatic gene expression. To explore the role of Ser-21 phosphorylation on C/EBPalpha function during adipogenesis, we developed constructs in which Ser-21 was mutated to alanine (S21A) to model dephosphorylation. In two cell culture models deficient in endogenous C/EBPalpha, enforced expression of S21A-C/EBPalpha resulted in normal lipid accumulation and expression of many adipogenic markers. However, S21A-C/EBPalpha had impaired ability to activate the Glut4 promoter specifically, and S21A-C/EBPalpha expression resulted in diminished GLUT4 and adiponectin expression, as well as reduced insulin-stimulated glucose uptake. No defects in insulin signaling or GLUT4 vesicle trafficking were identified with S21A-C/EBPalpha expression, and when exogenous GLUT4 expression was enforced to normalize expression in S21A-C/EBPalpha cells, insulin-responsive glucose transport was reconstituted, suggesting that the primary defect was a deficit in GLUT4 levels. Mice in which endogenous C/EBPalpha was replaced with S21A-C/EBPalpha displayed reduced GLUT4 and adiponectin protein expression in epididymal adipose tissue and increased blood glucose compared with wild-type littermates. These results suggest that phosphorylation of C/EBPalpha on Ser-21 may regulate adipocyte gene expression and whole body glucose homeostasis.

Proteomic identification of the MYST domain histone acetyltransferase TIP60 (HTATIP) as a co-activator of the myeloid transcription factor C/EBPalpha

The transcription factor C/EBPalpha (CEBPA) is a key player in granulopoiesis and leukemogenesis. We have previously reported the interaction of C/EBPalpha with other proteins (utilizing mass spectrometry) in transcriptional regulation. In the present study, we characterized the association of the MYST domain histone acetyltransferase Tat-interactive protein (TIP) 60 (HTATIP) with C/EBPalpha. We show in pull-down and co-precipitation experiments that C/EBPalpha and HTATIP interact. A chromatin immunoprecipitation (ChIP) and a confirmatory Re-ChIP assay revealed in vivo occupancy of the C/EBPalpha and GCSF-R promoter by HTATIP. Reporter gene assays showed that HTATIP is a co-activator of C/EBPalpha. The co-activator function of HTATIP is dependent on its intact histone acetyltransferase (HAT) domain and on the C/EBPalpha DNA-binding domain. The resulting balance between histone acetylation and deacetylation at the C/EBPalpha promoter might represent an important mechanism of C/EBPalpha action. We observed a lower expression of HTATIP mRNA in undifferentiated U937 cells compared to retinoic acid-induced differentiated U937 cells, and correlated expression of CEBPA and HTATIP mRNA levels were observed in leukemia samples. These findings point to a functional synergism between C/EBPalpha and HTATIP in myeloid differentiation and suggest that HTATIP might be an important player in leukemogenesis.