C/EBPbeta regulates body composition, energy balance-related hormones and tumor growth

Caveolin-2 controls preadipocyte survival in the mitotic clonal expansion for adipogenesis

Here, we report that Caveolin-2 (Cav-2) is a cell cycle regulator in the mitotic clonal expansion (MCE) for adipogenesis. For the G2/M phase transition and re-entry into the G1 phase, dephosphorylated Cav-2 by protein tyrosine phosphatase 1B (PTP1B) controlled epigenetic activation of Ccnb1, Cdk1, and p21 in a lamin A/C-dependent manner, thereby ensuring the survival of preadipocytes. Cav-2, associated with lamin A/C, recruited the repressed promoters of Ccnb1 and Cdk1 for activation, and disengaged the active promoter of p21 from lamin A/C for inactivation through histone H3 modifications at the nuclear periphery. Cav-2 deficiency abrogated the histone H3 modifications and impeded the transactivation of Ccnb1, Cdk1, and p21, leading to a delay in mitotic entry, retardation of re-entry into G1 phase, and the apoptotic cell death of preadipocytes. Re-expression of Cav-2 restored the G2/M phase transition and G1 phase re-entry, preadipocyte survival, and adipogenesis in Cav-2-deficient preadipocytes. Our study uncovers a novel mechanism by which cell cycle transition and apoptotic cell death are controlled for adipocyte hyperplasia.

From quiescence to repair: C/EBPβ as a regulator of muscle stem cell function in health and disease

CCAAT/Enhancer Binding protein beta (C/EBPβ) is a transcriptional regulator involved in numerous physiological processes. Herein, we describe a role for C/EBPβ as a regulator of skeletal muscle stem cell function. In particular, C/EBPβ is expressed in muscle stem cells in healthy muscle where it inhibits myogenic differentiation. Downregulation of C/EBPβ expression at the protein and transcriptional level allows for differentiation. Persistence of C/EBPβ promotes stem cell self-renewal and C/EBPβ expression is required for mitotic quiescence in this cell population. As a critical regulator of skeletal muscle homeostasis, C/EBPβ expression is stimulated in pathological conditions such as cancer cachexia, which perturbs muscle regeneration and promotes myofiber atrophy in the context of systemic inflammation. C/EBPβ is also an important regulator of cytokine expression and immune response genes, a mechanism by which it can influence muscle stem cell function. In this viewpoint, we describe a role for C/EBPβ in muscle stem cells and propose a functional intersection between C/EBPβ and NF-kB action in the regulation of cancer cachexia.

Research Note: Fine mapping of sequence variants associated with body weight of Lueyang black-boned chicken in the CCKAR gene

Cholecystokinin A receptor (CCKAR) is a key receptor mediating satiety. Previous studies found that decreased expression of CCKAR attenuated satiety, and thus contributed to the high-growth of broiler chickens. The objective of this study is to map sequence variants associated with the growth of chickens in the CCKAR. The CCKAR and upstream 1.4 kb genomic sequences were resequenced to find out all sequence variants using 35 Lueyang black-boned chickens (LBC). Haplotypes were reconstructed using the PHASE program. Linkage disequilibrium between variants was analyzed using the Haploview software. Associations of 33 tag SNPs that captured 89% of all variants with body weight of LBC (n = 675) at 16 (BW16), 20 (BW20) weeks of age and the onset (BWOEP) of egg production were tested using linear mixed models. A total of 126 SNPs were found and formed 41 haplotypes in 35 resequenced samples. Average length of haplotype blocks is 129 bp, indicating that LBC maintains low linkage disequilibrium at the CCKAR locus. Eleven of 33 tag SNPs were significantly associated with BW16, but not with BW20 and BWOEP. These significantly associated variants were most (8/11) distributed in a 2 kb region (chr4:73206169-73208244) around the Exon3. They together with 33 captured variants potentially disrupted binding sites of 471 transcription factors. Twelve variants can disrupt appetite (FOXO1) or lipid metabolism-related TF (AR and C/EBP) motifs. This study recognized chr4:73206169-73208244 as a key region harboring functional variants affecting the growth of chickens.

Sulforaphene Suppresses Adipocyte Differentiation via Induction of Post-Translational Degradation of CCAAT/Enhancer Binding Protein Beta (C/EBPβ)

Adipocyte differentiation (adipogenesis) is a crucial process that determines the total number and size of mature adipocytes that will develop. In this study, the anti-adipogenic effect of sulforaphene (SFEN), a dietary isothiocyanate (ITC) derived from radish, is investigated both in 3T3-L1 pre-adipocytes and in human adipose tissue-derived stem cells. The results revealed that SFEN significantly inhibit adipogenic cocktail-induced adipocyte differentiation and lipid accumulation at the early stage of adipogenesis. Additionally, the effects are more potent compared to those of other ITCs derived from various cruciferous vegetables. As a related molecular mechanism of action, SFEN promotes the post-translational degradation of CCAAT/enhancer-binding protein (C/EBP) β by decreasing the stability of C/EBPβ, which is responsible for decreasing the expression of master regulatory proteins such as peroxisome proliferator-activated receptor γ and C/EBPα. Collectively, these results suggest that the intake of SFEN-enriched natural materials could be helpful as a strategy for preventing obesity.

Metabolic impairment in response to early induction of C/EBPβ leads to compromised cardiac function during pathological hypertrophy

Chronic pressure overload-induced left ventricular hypertrophy in heart is preceded by a metabolic perturbation that prefers glucose over lipid as substrate for energy requirement. Here, we establish C/EBPβ (CCAAT/enhancer-binding protein β) as an early marker of the metabolic derangement that triggers the imbalance in fatty acid (FA) oxidation and glucose uptake with increased lipid accumulation in cardiomyocytes during pathological hypertrophy, leading to contractile dysfunction and endoplasmic reticulum (ER) stress. This is the first study that shows that myocardium-targeted C/EBPβ knockdown prevents the impaired cardiac function during cardiac hypertrophy led by maladaptive metabolic response with persistent hypertrophic stimuli, whereas its targeted overexpression in control increases lipid accumulation significantly compared to control hearts. A new observation from this study was the dual and opposite transcriptional regulation of the alpha and gamma isoforms of Peroxisomal proliferator activated receptors (PPARα and PPARγ) by C/EBPβ in hypertrophied cardiomyocytes. Before the functional and structural remodeling sets in the diseased myocardium, C/EBPβ aggravates lipid accumulation with the aid of the increased FA uptake involving induced PPARγ expression and decreased fatty acid oxidation (FAO) by suppressing PPARα expression. Glucose uptake into cardiomyocytes was greatly increased by C/EBPβ via PPARα suppression. The activation of mammalian target of rapamycin complex-1 (mTORC1) during increased workload in presence of glucose as the only substrate was prevented by C/EBPβ knockdown, thereby abating contractile dysfunction in cardiomyocytes. Our study thus suggests that C/EBPβ may be considered as a novel cellular marker for deranged metabolic milieu before the heart pathologically remodels itself during hypertrophy.

Molecular cloning, characterisation, and expression patterns of pigeon CCAAT/enhancer binding protein-α and -β genes

1. CCAAT/enhancer binding proteins (C/EBPs), as a family of transcription factors, consists of six functionally and structurally related proteins which share a conserved basic leucine zipper (bZIP) DNA-binding domain. The aim of this study was to clone the full-length coding sequences (CDS) of C/EBP-α and -β genes, and determine the abundance of these two genes in various tissues of white king pigeon (C. livia). 2. The complete cDNA sequences of C/EBP-α and -β genes were cloned from pigeons by using PCR combined with rapid amplification of cDNA ends (RACE). The sequences were bioinformatically analysed, and the tissue distribution determined by quantitative real-time RT-PCR (qRT-PCR). 3. The results showed that the full-length cDNA sequences of pigeon C/EBP-α and -β genes were 2,807bp and 1,778bp, respectively. The open reading frames of C/EBP-α (978 bp) and -β (987bp) encoded 325 amino acids and 328 amino acids, respectively. The pigeon C/EBP-α and C/EBP-β proteins were predicted to have a conserved basic leucine zipper (bZIP) domain, which is a common structure feature of the C/EBP family. Multiple sequence alignments indicated that pigeon C/EBP-α and -β shared more than 90% amino-acid identity with their corresponding homologues in other avian species. Phylogenetic analysis revealed that these two proteins were highly conserved across different species and evolutionary processes. QRT-PCR results indicated that the pigeon C/EBP-α and -β mRNA transcripts were expressed in all investigated organs. The mRNA expression levels of pigeon C/EBP-α in descending order, were in spleen, heart, liver, lung, kidney and muscle. The pigeon C/EBP-β gene had the most abundant expression in lung, followed by the kidney, with minimal expression detected in muscle. 4. This study investigated the full-length cDNA sequences, genetic characteristics and tissue distribution of pigeon C/EBP-α and -β genes and found that they may have functions in various tissues of pigeon. This provides a foundation for further study for regulatory mechanisms of these two genes in birds.

Aging and lineage allocation changes of bone marrow skeletal (stromal) stem cells

Aging is associated with decreased bone mass and accumulation of bone marrow adipocytes. Both bone forming osteoblastic cells and bone marrow adipocytes are derived from a stem cell population within the bone marrow stroma called bone marrow stromal (skeletal or mesenchymal) stem cells (BMSC). In the present review, we provide an overview, based on the current literature, regarding the physiological aging processes that cause changes in BMSC lineage allocation, enhancement of adipocyte and defective osteoblast differentiation, leading to gradual exhaustion of stem cell regenerative potential and defects in bone tissue homeostasis and metabolism. We discuss strategies to preserve the "youthful" state of BMSC, to reduce bone marrow age-associated adiposity, and to counteract the overall negative effects of aging on bone tissues with the aim of decreasing bone fragility and risk of fractures.

The emergence of melatonin in oncology: Focus on colorectal cancer

Within the last few decades, melatonin has increasingly emerged in clinical oncology as a naturally occurring bioactive molecule with substantial anticancer properties and a pharmacological profile optimal for joining the currently available pharmacopeia. In addition, extensive experimental data shows that this chronobiotic agent exerts oncostatic effects throughout all stages of tumor growth, from initial cell transformation to mitigation of malignant progression and metastasis; additionally, melatonin alleviates the side effects and improves the welfare of radio/chemotherapy-treated patients. Thus, the support of clinicians and oncologists for the use of melatonin in both the treatment and proactive prevention of cancer is gaining strength. Because of its epidemiological importance and symptomatic debut in advanced stages of difficult clinical management, colorectal cancer (CRC) is a preferential target for testing new therapies. In this regard, the development of effective forms of clinical intervention for the improvement of CRC outcome, specifically metastatic CRC, is urgent. At the same time, the need to reduce the costs of conventional anti-CRC therapy results is also imperative. In light of this status quo, the therapeutic potential of melatonin, and the direct and indirect critical processes of CRC malignancy it modulates, have aroused much interest. To illuminate the imminent future on CRC research, we focused our attention on the molecular mechanisms underlying the multiple oncostatic actions displayed by melatonin in the onset and evolution of CRC and summarized epidemiological evidence, as well as in vitro, in vivo and clinical findings that support the broadly protective potential demonstrated by melatonin.

Novel Mechanisms for IGF-I Regulation by Glucagon in Carp Hepatocytes: Up-Regulation of HNF1α and CREB Expression via Signaling Crosstalk for IGF-I Gene Transcription

Glucagon, a key hormone for glucose homeostasis, can exert functional crosstalk with somatotropic axis via modification of IGF-I expression. However, its effect on IGF-I regulation is highly variable in different studies and the mechanisms involved are largely unknown. Using grass carp as a model, the signal transduction and transcriptional mechanisms for IGF-I regulation by glucagon were examined in Cyprinid species. As a first step, the carp HNF1α, a liver-enriched transcription factor, was cloned and confirmed to be a single-copy gene expressed in the liver. In grass carp hepatocytes, glucagon treatment could elevate IGF-I, HNF1α, and CREB mRNA levels, induce CREB phosphorylation, and up-regulate HNF1α and CREB protein expression. The effects on IGF-I, HNF1α, and CREB gene expression were mediated by cAMP/PKA and PLC/IP₃/PKC pathways with differential coupling with the MAPK and PI3K/Akt cascades. During the process, protein:protein interaction between HNF1α and CREB and recruitment of RNA Pol-II to IGF-I promoter also occurred with a rise in IGF-I primary transcript level. In parallel study to examine grass carp IGF-I promoter activity expressed in αT3 cells, similar pathways for post-receptor signaling were also confirmed in glucagon-induced IGF-I promoter activation and the trans-activating effect by glucagon was mediated by the binding sites for HNF1α and CREB located in the proximal region of IGF-I promoter. Our findings, as a whole, shed light on a previously undescribed mechanism for glucagon-induced IGF-I gene expression by increasing HNF1α and CREB production via functional crosstalk of post-receptor signaling. Probably, by protein:protein interaction between the two transcription factors and subsequent transactivation via their respective cis-acting elements in the IGF-I promoter, IGF-I gene transcription can be initiated by glucagon at the hepatic level.

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.

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.

Impaired DNA demethylation of C/EBP sites causes premature aging

Here, Schäfer et al. investigated whether DNA methylation alterations are involved in aging. Using knockout mice for adapter proteins for site-specific demethylation by TET methylcytosine dioxygenases Gadd45a and Ing1, they show that enhancer methylation can affect aging and imply that C/EBP proteins play an unexpected role in this process.

Changes in DNA methylation are among the best-documented epigenetic alterations accompanying organismal aging. However, whether and how altered DNA methylation is causally involved in aging have remained elusive. GADD45α (growth arrest and DNA damage protein 45A) and ING1 (inhibitor of growth family member 1) are adapter proteins for site-specific demethylation by TET (ten-eleven translocation) methylcytosine dioxygenases. Here we show that Gadd45a/Ing1 double-knockout mice display segmental progeria and phenocopy impaired energy homeostasis and lipodystrophy characteristic of Cebp (CCAAT/enhancer-binding protein) mutants. Correspondingly, GADD45α occupies C/EBPβ/δ-dependent superenhancers and, cooperatively with ING1, promotes local DNA demethylation via long-range chromatin loops to permit C/EBPβ recruitment. The results indicate that enhancer methylation can affect aging and imply that C/EBP proteins play an unexpected role in this process. Our study suggests a causal nexus between DNA demethylation, metabolism, and organismal aging.

The C/EBPβ LIP isoform rescues loss of C/EBPβ function in the mouse

The transcription factor C/EBPβ regulates hematopoiesis, bone, liver, fat, and skin homeostasis, and female reproduction. C/EBPβ protein expression from its single transcript occurs by alternative in-frame translation initiation at consecutive start sites to generate three isoforms, two long (LAP*, LAP) and one truncated (LIP), with the same C-terminal bZip dimerization domain. The long C/EBPβ isoforms are considered gene activators, whereas the LIP isoform reportedly acts as a dominant-negative repressor. Here, we tested the putative repressor functions of the C/EBPβ LIP isoform in mice by comparing monoallelic WT or LIP knockin mice with Cebpb knockout mice, in combination with monoallelic Cebpa mice. The C/EBPβ LIP isoform was sufficient to function in coordination with C/EBPα in murine development, adipose tissue and sebocyte differentiation, and female fertility. Thus, the C/EBPβ LIP isoform likely has more physiological functions than its currently known role as a dominant-negative inhibitor, which are more complex than anticipated.

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.

The Bone Marrow-Derived Stromal Cells: Commitment and Regulation of Adipogenesis

Bone marrow (BM) microenvironment represents an important compartment of bone that regulates bone homeostasis and the balance between bone formation and bone resorption depending on the physiological needs of the organism. Abnormalities of BM microenvironmental dynamics can lead to metabolic bone diseases. BM stromal cells (also known as skeletal or mesenchymal stem cells) [bone marrow stromal stem cell (BMSC)] are multipotent stem cells located within BM stroma and give rise to osteoblasts and adipocytes. However, cellular and molecular mechanisms of BMSC lineage commitment to adipocytic lineage and regulation of BM adipocyte formation are not fully understood. In this review, we will discuss recent findings pertaining to identification and characterization of adipocyte progenitor cells in BM and the regulation of differentiation into mature adipocytes. We have also emphasized the clinical relevance of these findings.

C/EBP-β-activated microRNA-223 promotes tumour growth through targeting RASA1 in human colorectal cancer

Background:

Evidences have shown that the RAS signalling pathway plays an important role in colorectal cancer (CRC). Moreover, RAS-GTPase-activating proteins (RASGAPs) as RAS signalling terminators are associated with tumourigenicity and tumour progression. In this study, we used bioinformatics analysis to predict and study important miRNAs that could target RAS p21 GTPase-activating protein 1 (RASA1), an important member of RASGAPs.

Methods:

The levels of RASA1 and miR-223 were analysed by real-time PCR, western blotting or in situ immunofluorescence analyses. The functional effects of miR-223 and the effects of miR-223-targeted inhibitors were examined in vivo using established assays.

Results:

Upregulation of miR-223 was detected in CRC tissues (P<0.01) and was involved in downregulation of RASA1 in CRC tissues. Furthermore, the direct inhibition of RASA1 translation by miR-223 and the activation of miR-223 by CCAAT/enhancer binding protein-β (C/EBP-β) were evaluated in CRC cells. An in vivo xenograft model of CRC suggested that the upregulation of miR-223 could promote tumour growth and that the inhibition of miR-223 might prevent solid tumour growth.

Conclusions:

These results identify that C/EBP-β-activated miR-223 contributes to tumour growth by targeting RASA1 in CRC and miR-223-targeted inhibitors may have clinical promise for CRC treatment via suppression of miR-223.

Inhibition of Stat3 activation suppresses caspase-3 and the ubiquitin-proteasome system, leading to preservation of muscle mass in cancer cachexia

Cachexia occurs in patients with advanced cancers. Despite the adverse clinical impact of cancer-induced muscle wasting, pathways causing cachexia are controversial, and clinically reliable therapies are not available. A trigger of muscle protein loss is the Jak/Stat pathway, and indeed, we found that conditioned medium from C26 colon carcinoma (C26) or Lewis lung carcinoma cells activates Stat3 (p-Stat3) in C2C12 myotubes. We identified two proteolytic pathways that are activated in muscle by p-Stat3; one is activation of caspase-3, and the other is p-Stat3 to myostatin, MAFbx/Atrogin-1, and MuRF-1 via CAAT/enhancer-binding protein δ (C/EBPδ). Using sequential deletions of the caspase-3 promoter and CHIP assays, we determined that Stat3 activation increases caspase-3 expression in C2C12 cells. Caspase-3 expression and proteolytic activity were stimulated by p-Stat3 in muscles of tumor-bearing mice. In mice with cachexia caused by Lewis lung carcinoma or C26 tumors, knock-out of p-Stat3 in muscle or with a small chemical inhibitor of p-Stat3 suppressed muscle mass losses, improved protein synthesis and degradation in muscle, and increased body weight and grip strength. Activation of p-Stat3 stimulates a pathway from C/EBPδ to myostatin and expression of MAFbx/Atrogin-1 and increases the ubiquitin-proteasome system. Indeed, C/EBPδ KO decreases the expression of MAFbx/Atrogin-1 and myostatin, while increasing muscle mass and grip strength. In conclusion, cancer stimulates p-Stat3 in muscle, activating protein loss by stimulating caspase-3, myostatin, and the ubiquitin-proteasome system. These results could lead to novel strategies for preventing cancer-induced muscle wasting.

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

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

High-throughput screening of mouse gene knockouts identifies established and novel skeletal phenotypes

Screening gene function in vivo is a powerful approach to discover novel drug targets. We present high-throughput screening (HTS) data for 3 762 distinct global gene knockout (KO) mouse lines with viable adult homozygous mice generated using either gene-trap or homologous recombination technologies. Bone mass was determined from DEXA scans of male and female mice at 14 weeks of age and by microCT analyses of bones from male mice at 16 weeks of age. Wild-type (WT) cagemates/littermates were examined for each gene KO. Lethality was observed in an additional 850 KO lines. Since primary HTS are susceptible to false positive findings, additional cohorts of mice from KO lines with intriguing HTS bone data were examined. Aging, ovariectomy, histomorphometry and bone strength studies were performed and possible non-skeletal phenotypes were explored. Together, these screens identified multiple genes affecting bone mass: 23 previously reported genes (Calcr, Cebpb, Crtap, Dcstamp, Dkk1, Duoxa2, Enpp1, Fgf23, Kiss1/Kiss1r, Kl (Klotho), Lrp5, Mstn, Neo1, Npr2, Ostm1, Postn, Sfrp4, Slc30a5, Slc39a13, Sost, Sumf1, Src, Wnt10b), five novel genes extensively characterized (Cldn18, Fam20c, Lrrk1, Sgpl1, Wnt16), five novel genes with preliminary characterization (Agpat2, Rassf5, Slc10a7, Slc26a7, Slc30a10) and three novel undisclosed genes coding for potential osteoporosis drug targets.

The many faces of C/EBPδ and their relevance for inflammation and cancer

The CCAAT/enhancer binding protein delta (CEBPD, C/EBPδ) is a transcription factor that modulates many biological processes including cell differentiation, motility, growth arrest, proliferation, and cell death. The diversity of C/EBPδ's functions depends in part on the cell type and cellular context and can have opposing outcomes. For example, C/EBPδ promotes inflammatory signaling, but it can also inhibit pro-inflammatory pathways, and in a mouse model of mammary tumorigenesis, C/EBPδ reduces tumor incidence but promotes tumor metastasis. This review highlights the multifaceted nature of C/EBPδ's functions, with an emphasis on pathways that are relevant for cancer and inflammation, and illustrates how C/EBPδ emerged from the shadow of its family members as a fascinating “jack of all trades.” Our current knowledge on C/EBPδ indicates that, rather than being essential for a specific cellular process, C/EBPδ helps to interpret a variety of cues in a cell-type and context-dependent manner, to adjust cellular functions to specific situations. Therefore, insights into the roles and mechanisms of C/EBPδ signaling can lead to a better understanding of how the integration of different signaling pathways dictates normal and pathological cell functions and physiology.

C/EBPγ suppresses senescence and inflammatory gene expression by heterodimerizing with C/EBPβ

C/EBPβ is an important regulator of oncogene-induced senescence (OIS). Here, we show that C/EBPγ, a heterodimeric partner of C/EBPβ whose biological functions are not well understood, inhibits cellular senescence. Cebpg(-/-) mouse embryonic fibroblasts (MEFs) proliferated poorly, entered senescence prematurely, and expressed a proinflammatory gene signature, including elevated levels of senescence-associated secretory phenotype (SASP) genes whose induction by oncogenic stress requires C/EBPβ. The senescence-suppressing activity of C/EBPγ required its ability to heterodimerize with C/EBPβ. Covalently linked C/EBPβ homodimers (β∼β) inhibited the proliferation and tumorigenicity of Ras(V12)-transformed NIH 3T3 cells, activated SASP gene expression, and recruited the CBP coactivator in a Ras-dependent manner, whereas γ∼β heterodimers lacked these capabilities and efficiently rescued proliferation of Cebpg(-/-) MEFs. C/EBPβ depletion partially restored growth of C/EBPγ-deficient cells, indicating that the increased levels of C/EBPβ homodimers in Cebpg(-/-) MEFs inhibit proliferation. The proliferative functions of C/EBPγ are not restricted to fibroblasts, as hematopoietic progenitors from Cebpg(-/-) bone marrow also displayed impaired growth. Furthermore, high CEBPG expression correlated with poorer clinical prognoses in several human cancers, and C/EBPγ depletion decreased proliferation and induced senescence in lung tumor cells. Our findings demonstrate that C/EBPγ neutralizes the cytostatic activity of C/EBPβ through heterodimerization, which prevents senescence and suppresses basal transcription of SASP genes.

Signaling mechanism of tumor cell-induced up-regulation of E3 ubiquitin ligase UBR2

The N-end rule pathway contributes significantly to accelerated muscle proteolysis mediated by the ubiquitin-proteasome pathway in various catabolic conditions. UBR2 (aka E3α-II) is the only known E3 ubiquitin ligase of the N-end rule pathway that is up-regulated by cachectic stimuli including proinflammatory cytokines and tumors. However, the signaling mechanism through which UBR2 is up-regulated remains undetermined. Here we identify a signaling pathway that mediates tumor cell-induced up-regulation of UBR2. UBR2 expression in C2C12 myotubes was up-regulated by conditioned medium from Lewis lung carcinoma cells or C26 colon adenocarcinoma cells, which was blocked by a pharmacological inhibitor of p38α/β mitogen-activated protein kinase (MAPK), SB202190. Similarly, SB202190 administration (i.p.) abolished UBR2 up-regulation in the tibialis anterior of LLC tumor-bearing mice. Genetic gain and loss of function assays in C2C12 myotubes indicated that tumor-induced activation of the p38β isoform is sufficient and necessary for UBR2 up-regulation. In addition, UBR2 up-regulation required p38β-mediated phosphorylation of CCAAT/enhancer binding protein (C/EBP)-β Thr-188, which was critical to C/EBPβ binding to the UBR2 promoter. Furthermore, luciferase reporter assay revealed that the C/EBPβ binding motif in the UBR2 promoter is a functional C/EBPβ-responsive cis-element that enhances the promoter activity on activation by p38β. Finally, genetic ablation of C/EBPβ blocked UBR2 up-regulation in LLC tumor-bearing mice. These results suggest that UBR2 up-regulation in cachectic muscle is mediated by the p38β-C/EBPβ signaling pathway responsible for the bulk of tumor-induced muscle proteolysis.

Membrane-bound and exosomal metastasis-associated C4.4A promotes migration by associating with the α(6)β(4) integrin and MT1-MMP

Metastasis-associated C4.4A, which becomes upregulated during wound healing and, in some tumors, during tumor progression, is known to be frequently associated with hypoxia. With the function of C4.4A still unknown, we explored the impact of hypoxia on C4.4A expression and functional activity. Metastatic rat and human tumor lines upregulate C4.4A expression when cultured in the presence of CoCl(2). Although hypoxia-inducible factor 1α (HIF-1α) becomes upregulated concomitantly, HIF-1α did not induce C4.4A transcription. Instead, hypoxia-induced C4.4A up-regulation promoted in vivo and in vitro wound healing, where increased migration on the C4.4A ligands laminin-111 and -332 was observed after a transient period of pronounced binding. Increased migration was accompanied by C4.4A associating with α(6)β(4), MT1-MMP1, and TACE and by laminin fragmentation. Hypoxia also promoted the release of C4.4A in exosomes and TACE-mediated C4.4A shedding. The association of C4.4A with α(6)β(4) and MT1-MMP1 was maintained in exosomes and exosomal α(6)β(4)- and MT1-MMP1-associated C4.4A but not shed C4.4A sufficient for laminin degradation. Hypoxia-induced recruitment of α(6)β(4) toward raft-located C4.4A, MT1-MMP, and TACE allows for a shift from adhesion to motility, which is supported by laminin degradation. These findings provide the first explanation for the C4.4A contribution to wound healing and metastasis.

Instruction of mesenchymal cell fate by the transcription factor C/EBPβ

The transcription factor CCAAT/enhancer binding protein beta (C/EBPβ) plays a role in the differentiation of a large variety of cell types. C/EBPβ was initially described as an early inducer of adipocyte differentiation, however, recent data have shown that this is not the only mesenchymal cell lineage where C/EBPβ has an instructive function. Mouse models and tissue culture studies have now established a regulatory role of C/EBPβ in osteoblast and in chondrocyte differentiation. These three different cell lineages are derived from the same precursor, the mesenchymal stem cell (MSC). This review will focus on the emerging role of C/EBPβ and its different protein isoforms in various mesenchymal cell lineages and its function in adipocyte, chondrocyte and osteoblast differentiation. Moreover, the mesenchymal stem cell has attracted the attention of regenerative medicine in recent years, and the possible role of C/EBPβ in this respect will be discussed.

C/EBPβ mediates tumour-induced ubiquitin ligase atrogin1/MAFbx upregulation and muscle wasting

Upregulation of ubiquitin ligase atrogin1/MAFbx and muscle wasting are hallmarks of cancer cachexia; however, the underlying mechanism is undefined. Here, we describe a novel signalling pathway through which Lewis lung carcinoma (LLC) induces atrogin1/MAFbx upregulation and muscle wasting. C2C12 myotubes treated with LLC-conditioned medium (LCM) rapidly activates p38 MAPK and AKT while inactivating FoxO1/3, resulting in atrogin1/MAFbx upregulation, myosin heavy chain loss, and myotube atrophy. The p38α/β MAPK inhibitor SB202190 blocks the catabolic effects. Upon activation, p38 associates with C/EBPβ resulting in its phosphorylation and binding to a C/EBPβ-responsive cis-element in the atrogin1/MAFbx gene promoter. The promoter activity is stimulated by LCM via p38β-mediated activation of the C/EBPβ-responsive cis-element, independent of the adjacent FoxO1/3-responsive cis-elements in the promoter. In addition, p38 activation is observed in the muscle of LLC tumour-bearing mice, and SB202190 administration blocks atrogin1/MAFbx upregulation and muscle protein loss. Furthermore, C/EBPβ(-/-) mice are resistant to LLC tumour-induced atrogin1/MAFbx upregulation and muscle wasting. Therefore, activation of the p38β MAPK-C/EBPβ signalling pathway appears a key component of the pathogenesis of LLC tumour-induced cachexia.

The anti-inflammatory and immunosuppressive effects of glucocorticoids, recent developments and mechanistic insights

Since the discovery of glucocorticoids in the 1940s and the recognition of their anti-inflammatory effects, they have been amongst the most widely used and effective treatments to control inflammatory and autoimmune diseases. However, their clinical efficacy is compromised by the metabolic effects of long-term treatment, which include osteoporosis, hypertension, dyslipidaemia and insulin resistance/type 2 diabetes mellitus. In recent years, a great deal of effort has been invested in identifying compounds that separate the beneficial anti-inflammatory effects from the adverse metabolic effects of glucocorticoids, with limited effect. It is clear that for these efforts to be effective, a greater understanding is required of the mechanisms by which glucocorticoids exert their anti-inflammatory and immunosuppressive actions. Recent research is shedding new light on some of these mechanisms and has produced some surprising new findings. Some of these recent developments are reviewed here.

CCAAT/enhancer binding protein β-deficiency enhances type 1 diabetic bone phenotype by increasing marrow adiposity and bone resorption

Bone loss in type 1 diabetes is accompanied by increased marrow fat, which could directly reduce osteoblast activity or result from altered bone marrow mesenchymal cell lineage selection (adipocyte vs. osteoblast). CCAAT/enhancer binding protein beta (C/EBPβ) is an important regulator of both adipocyte and osteoblast differentiation. C/EBPβ-null mice have delayed bone formation and defective lipid accumulation in brown adipose tissue. To examine the balance of C/EBPβ functions in the diabetic context, we induced type 1 diabetes in C/EBPβ-null (knockout, KO) mice. We found that C/EBPβ deficiency actually enhanced the diabetic bone phenotype. While KO mice had reduced peripheral fat mass compared with wild-type mice, they had 5-fold more marrow adipocytes than diabetic wild-type mice. The enhanced marrow adiposity may be attributed to compensation by C/EBPδ, peroxisome proliferator-activated receptor-γ2, and C/EBPα. Concurrently, we observed reduced bone density. Relative to genotype controls, trabecular bone volume fraction loss was escalated in diabetic KO mice (-48%) compared with changes in diabetic wild-type mice (-22%). Despite greater bone loss, osteoblast markers were not further suppressed in diabetic KO mice. Instead, osteoclast markers were increased in the KO diabetic mice. Thus, C/EBPβ deficiency increases diabetes-induced bone marrow (not peripheral) adipose depot mass, and promotes additional bone loss through stimulating bone resorption. C/EBPβ-deficiency also reduced bone stiffness and diabetes exacerbated this (two-way ANOVA P < 0.02). We conclude that C/EBPβ alone is not responsible for the bone vs. fat phenotype switch observed in T1 diabetes and that suppression of CEBPβ levels may further bone loss and decrease bone stiffness by increasing bone resorption.

Gene expression profiling of subcutaneous adipose tissue in morbid obesity using a focused microarray: distinct expression of cell-cycle- and differentiation-related genes

Background

Obesity results from an imbalance between food intake and energy expenditure, which leads to an excess of adipose tissue. The excess of adipose tissue and adipocyte dysfunction associated with obesity are linked to the abnormal regulation of adipogenesis. The objective of this study was to analyze the expression profile of cell-cycle- and lipid-metabolism-related genes of adipose tissue in morbid obesity.

Methods

We used a custom-made focused cDNA microarray to determine the adipose tissue mRNA expression profile. Gene expression of subcutaneous abdominal fat samples from 15 morbidly obese women was compared with subcutaneous fat samples from 10 nonobese control patients. The findings were validated in an independent population of 31 obese women and 9 obese men and in an animal model of obesity (Lep^ob/ob mice) by real-time RT-PCR.

Results

Microarray analysis revealed that transcription factors that regulate the first stages of adipocyte differentiation, such as CCAAT/enhancer binding protein beta (C/EBPβ) and JUN, were upregulated in the adipose tissues of morbidly obese patients. The expression of peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor which controls lipid metabolism and the final steps of preadipocyte conversion into mature adipocytes, was downregulated. The expression of three cyclin-dependent kinase inhibitors that regulate clonal expansion and postmitotic growth arrest during adipocyte differentiation was also altered in obese subjects: p18 and p27 were downregulated, and p21 was upregulated. Angiopoietin-like 4 (ANGPTL4), which regulates angiogenesis, lipid and glucose metabolism and it is know to increase dramatically in the early stages of adipocyte differentiation, was upregulated. The expression of C/EBPβ, p18, p21, JUN, and ANGPTL4 presented similar alterations in subcutaneous adipose tissue of Lep^ob/ob mice.

Conclusions

Our microarray gene profiling study revealed that the expression of genes involved in adipogenesis is profoundly altered in the subcutaneous adipose tissue of morbidly obese subjects. This expression pattern is consistent with an immature adipocyte phenotype that could reflect the expansion of the adipose tissue during obesity.

Cigarette smoke induces C/EBP-β-mediated activation of miR-31 in normal human respiratory epithelia and lung cancer cells

BACKGROUND

Limited information is available regarding mechanisms by which miRNAs contribute to pulmonary carcinogenesis. The present study was undertaken to examine expression and function of miRNAs induced by cigarette smoke condensate (CSC) in normal human respiratory epithelia and lung cancer cells.

METHODOLOGY

Micro-array and quantitative RT-PCR (qRT-PCR) techniques were used to assess miRNA and host gene expression in cultured cells, and surgical specimens. Software-guided analysis, RNA cross-link immunoprecipitation (CLIP), 3' UTR luciferase reporter assays, qRT-PCR, focused super-arrays and western blot techniques were used to identify and confirm targets of miR-31. Chromatin immunoprecipitation (ChIP) techniques were used to evaluate histone marks and transcription factors within the LOC554202 promoter. Cell count and xenograft experiments were used to assess effects of miR-31 on proliferation and tumorigenicity of lung cancer cells.

RESULTS

CSC significantly increased miR-31 expression and activated LOC554202 in normal respiratory epithelia and lung cancer cells; miR-31 and LOC554202 expression persisted following discontinuation of CSC exposure. miR-31 and LOC554202 expression levels were significantly elevated in lung cancer specimens relative to adjacent normal lung tissues. CLIP and reporter assays demonstrated direct interaction of miR-31 with Dickkopf-1 (Dkk-1) and DACT-3. Over-expression of miR-31 markedly diminished Dkk-1 and DACT3 expression levels in normal respiratory epithelia and lung cancer cells. Knock-down of miR-31 increased Dkk-1 and DACT3 levels, and abrogated CSC-mediated decreases in Dkk-1 and DACT-3 expression. Furthermore, over-expression of miR-31 diminished SFRP1, SFRP4, and WIF-1, and increased Wnt-5a expression. CSC increased H3K4Me3, H3K9/14Ac and C/EBP-β levels within the LOC554202 promoter. Knock-down of C/EBP-β abrogated CSC-mediated activation of LOC554202. Over-expression of miR-31 significantly enhanced proliferation and tumorigenicity of lung cancer cells; knock-down of miR-31 inhibited growth of these cells.

CONCLUSIONS

Cigarette smoke induces expression of miR-31 targeting several antagonists of cancer stem cell signaling in normal respiratory epithelia and lung cancer cells. miR-31 functions as an oncomir during human pulmonary carcinogenesis.

Rapamycin and the transcription factor C/EBPbeta as a switch in osteoclast differentiation: implications for lytic bone diseases

Lytic bone diseases and in particular osteoporosis are common age-related diseases characterized by enhanced bone fragility due to loss of bone density. Increasingly, osteoporosis poses a major global health-care problem due to the growth of the elderly population. Recently, it was found that the gene regulatory transcription factor CCAAT/enhancer binding protein beta (C/EBPbeta) is involved in bone metabolism. C/EBPbeta occurs as different protein isoforms of variable amino terminal length, and regulation of the C/EBPbeta isoform ratio balance was found to represent an important factor in osteoclast differentiation and bone homeostasis. Interestingly, adjustment of the C/EBPbeta isoform ratio by the process of translational control is downstream of the mammalian target of rapamycin kinase (mTOR), a sensor of the nutritional status and a target of immunosuppressive and anticancer drugs. The findings imply that modulating the process of translational control of C/EBPbeta isoform expression could represent a novel therapeutic approach in osteolytic bone diseases, including cancer and infection-induced bone loss.

Misexpression of CCAAT/enhancer binding protein beta causes osteopenia

CCAAT/enhancer binding proteins (C/EBPs) are expressed by osteoblasts and adipocytes during differentiation. C/EBP beta is critical for adipogenesis; however, its role in osteoblastogenesis is unclear, and its function in the postnatal skeleton is not known. To study C/EBP beta in osteoblasts in vivo, we created transgenic mice expressing full length C/EBP beta under the control of a 3.8 kb fragment of the human osteocalcin promoter. Two transgenic lines were established in a friend leukemia virus strain B genetic background, and compared with wild type littermate controls. Both C/EBP beta transgenic lines exhibited osteopenia, with a 30% decrease in bone volume, due to a decrease in trabecular number. The number of osteoblasts and osteoclasts per bone perimeter was not changed. Bone marrow stromal cells from C/EBP beta transgenics showed reduced mineralization, and reduced alkaline phosphatase mRNA levels. Calvarial osteoblasts from C/EBP beta transgenics displayed reduced alkaline phosphatase activity. To determine the consequences of the Cebpb deletion in vivo, the phenotype of Cebpb null mice was compared with that of wild type controls of identical genetic composition. Cebpb null mice exhibited reduced weight, body fat, and bone mineral density, and decreased bone volume, due to a decrease in trabecular number. The number of osteoblasts and osteoclasts per bone perimeter was not changed. C/EBP beta downregulation by RNA interference in calvarial osteoblasts had no effect on osteoblast differentiation/function. The phenotype of the Cebpb inactivation may be secondary to systemic indirect effects, and to direct effects of C/EBP beta in osteoblasts. In conclusion, C/EBP beta plays a role in mesenchymal cell differentiation and its misexpression in vivo causes osteopenia.