Role of the CCAAT/enhancer binding protein-alpha transcription factor in the glucocorticoid stimulation of p21waf1/cip1 gene promoter activity in growth-arrested rat hepatoma cells

Glucocorticoid Treatment in Acute Respiratory Distress Syndrome: An Overview on Mechanistic Insights and Clinical Benefit

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS), triggered by various pathogenic factors inside and outside the lungs, leads to diffuse lung injury and can result in respiratory failure and death, which are typical clinical critical emergencies. Severe acute pancreatitis (SAP), which has a poor clinical prognosis, is one of the most common diseases that induces ARDS. When SAP causes the body to produce a storm of inflammatory factors and even causes sepsis, clinicians will face a two-way choice between anti-inflammatory and anti-infection objectives while considering the damaged intestinal barrier and respiratory failure, which undoubtedly increases the difficulty of the diagnosis and treatment of SAP-ALI/ARDS. For a long time, many studies have been devoted to applying glucocorticoids (GCs) to control the inflammatory response and prevent and treat sepsis and ALI/ARDS. However, the specific mechanism is not precise, the clinical efficacy is uneven, and the corresponding side effects are endless. This review discusses the mechanism of action, current clinical application status, effectiveness assessment, and side effects of GCs in the treatment of ALI/ARDS (especially the subtype caused by SAP).

Cellular Senescence in Adrenocortical Biology and Its Disorders

Cellular senescence is considered a physiological process along with aging and has recently been reported to be involved in the pathogenesis of many age-related disorders. Cellular senescence was first found in human fibroblasts and gradually explored in many other organs, including endocrine organs. The adrenal cortex is essential for the maintenance of blood volume, carbohydrate metabolism, reaction to stress and the development of sexual characteristics. Recently, the adrenal cortex was reported to harbor some obvious age-dependent features. For instance, the circulating levels of aldosterone and adrenal androgen gradually descend, whereas those of cortisol increase with aging. The detailed mechanisms have remained unknown, but cellular senescence was considered to play an essential role in age-related changes of the adrenal cortex. Recent studies have demonstrated that the senescent phenotype of zona glomerulosa (ZG) acts in association with reduced aldosterone production in both physiological and pathological aldosterone-producing cells, whereas senescent cortical-producing cells seemed not to have a suppressed cortisol-producing ability. In addition, accumulated lipofuscin formation, telomere shortening and cellular atrophy in zona reticularis cells during aging may account for the age-dependent decline in adrenal androgen levels. In adrenocortical disorders, including both aldosterone-producing adenoma (APA) and cortisol-producing adenoma (CPA), different cellular subtypes of tumor cells presented divergent senescent phenotypes, whereby compact cells in both APA and CPA harbored more senescent phenotypes than clear cells. Autonomous cortisol production from CPA reinforced a local cellular senescence that was more severe than that in APA. Adrenocortical carcinoma (ACC) was also reported to harbor oncogene-induced senescence, which compensatorily follows carcinogenesis and tumor progress. Adrenocortical steroids can induce not only a local senescence but also a periphery senescence in many other tissues. Therefore, herein, we systemically review the recent advances related to cellular senescence in adrenocortical biology and its associated disorders.

Regulation of metabolic homeostasis by the TGF-β superfamily receptor ALK7

ALK7 (Activin receptor-like kinase 7) is a member of the TGF-β receptor superfamily predominantly expressed by cells and tissues involved in endocrine functions, such as neurons of the hypothalamus and pituitary, pancreatic β-cells and adipocytes. Recent studies have begun to delineate the processes regulated by ALK7 in these tissues and how these become integrated with the homeostatic regulation of mammalian metabolism. The picture emerging indicates that ALK7's primary function in metabolic regulation is to limit catabolic activities and preserve energy. Aside of the hypothalamic arcuate nucleus, the function of ALK7 elsewhere in the brain, particularly in the cerebellum, where it is abundantly expressed, remains to be elucidated. Although our understanding of the basic molecular events underlying ALK7 signaling has benefited from the vast knowledge available on TGF-β receptor mechanisms, how these connect to the physiological functions regulated by ALK7 in different cell types is still incompletely understood. Findings of missense and nonsense variants in the Acvr1c gene, encoding ALK7, of some mouse strains and human subjects indicate a tolerance to ALK7 loss of function. Recent discoveries suggest that specific inhibitors of ALK7 may have therapeutic applications in obesity and metabolic syndrome without overt adverse effects.

Sirt7-p21 Signaling Pathway Mediates Glucocorticoid-Induced Inhibition of Mouse Neural Stem Cell Proliferation

Prenatal glucocorticoid (GC) overexposure impacts fetal hippocampal neural stem cells (NSCs) and increases the risk for relative cognitive and mood disorders in offspring. However, the precise underlying mechanisms remain elusive. Here, we treated mouse hippocampal NSCs with dexamethasone (DEX) in vitro and found that DEX inhibited cell proliferation and Sirt7 expression. In addition, prenatal mouse overexposure to DEX induced the suppression of Sirt7 in the hippocampus of offspring. Sirt7 knockdown significantly decreased the percentage of proliferating cells but did not further reduce the NSC proliferation rate in the presence of DEX, whereas Sirt7 overexpression rescued DEX-induced inhibition of hippocampal NSC proliferation. Moreover, DEX inhibited Sirt7 expression through the glucocorticoid receptor (GR), and p21 was found to mediate the functional effect of DEX-induced Sirt7 suppression. In conclusion, our data demonstrate for the first time the effect of DEX on the Sirt7-p21 pathway in hippocampal NSCs, identifying a new potential therapeutic target for prenatal GC overexposure-related neurodevelopmental disorders in offspring.

GR-C/EBPα-IGF1 axis mediated azithromycin-induced liver developmental toxicity in fetal mice

Azithromycin is considered an effective drug to treat the perinatal mycoplasma infection. However, there is a lack of studies on developmental toxicity of azithromycin. In this study, we observed the developmental toxicity of fetal liver induced by prenatal azithromycin exposure (PAE) in mice and explored the potential mechanism. Pregnant Kunming mice were intraperitoneally injected with azithromycin (37.5 and 150 mg/kg·d) from gestational day (GD) 9 to 18. After PAE, the bodyweight gain rates of pregnant mice and the birthweights of the offspring were decreased, and the liver morphology, development indexes and metabolic function were all altered in different degree in the PAE fetuses. Meanwhile, PAE decreased the fetal serum insulin-like growth factor 1 (IGF1) levels and liver IGF1 signal pathway expression, accompanied by glucocorticoid receptor-CCAAT enhancer-binding protein α (GR-C/EBPα) signal enhancement. Furthermore, azithromycin disturbed hepatocyte differentiation, maturation and metabolic function via upregulating GR-C/EBPα signal and reducing the expression and secretion levels of IGF1 in HepG2 cells. These changes could be reversed by GR siRNA or exogenous IGF1. These results indicated that PAE could cause fetal liver developmental toxicity in mice, and one of the main mechanisms was that azithromycin activated the GR-C/EBPα signal, inhibited the IGF1 signal pathway, and then disturbed the hepatic proliferation, apoptosis, differentiation, and glycose and lipid metabolism.

Control of brown adipose tissue adaptation to nutrient stress by the activin receptor ALK7

Adaptation to nutrient availability is crucial for survival. Upon nutritional stress, such as during prolonged fasting or cold exposure, organisms need to balance the feeding of tissues and the maintenance of body temperature. The mechanisms that regulate the adaptation of brown adipose tissue (BAT), a key organ for non-shivering thermogenesis, to variations in nutritional state are not known. Here we report that specific deletion of the activin receptor ALK7 in BAT resulted in fasting-induced hypothermia due to exaggerated catabolic activity in brown adipocytes. After overnight fasting, BAT lacking ALK7 showed increased expression of genes responsive to nutrient stress, including the upstream regulator KLF15, aminoacid catabolizing enzymes, notably proline dehydrogenase (POX), and adipose triglyceride lipase (ATGL), as well as markedly reduced lipid droplet size. In agreement with this, ligand stimulation of ALK7 suppressed POX and KLF15 expression in both mouse and human brown adipocytes. Treatment of mutant mice with the glucocorticoid receptor antagonist RU486 restored KLF15 and POX expression levels in mutant BAT, suggesting that loss of BAT ALK7 results in excessive activation of glucocorticoid signaling upon fasting. These results reveal a novel signaling pathway downstream of ALK7 which regulates the adaptation of BAT to nutrient availability by limiting nutrient stress-induced overactivation of catabolic responses in brown adipocytes.

Improvement of chemotherapeutic drug efficacy by endoplasmic reticulum stress

Tunicamycin (TUN), an inhibitor of protein glycosylation and therefore a potent stimulator of endoplasmic reticulum (ER) stress, has been used to improve anticancer drug efficacy, but the underlying mechanism remains obscure. In this study, we show that acute administration of TUN in mice induces the unfolded protein response and suppresses the levels of P21, a cell cycle regulator with anti-apoptotic activity. The inhibition of P21 after ER stress appears to be C/EBP homologous protein (CHOP)-dependent because in CHOP-deficient mice, TUN not only failed to suppress, but rather induced the expression of P21. Results of promoter-activity reporter assays using human cancer cells and mouse fibroblasts indicated that the regulation of P21 by CHOP operates at the level of transcription and involves direct binding of CHOP transcription factor to the P21 promoter. The results of cell viability and clonogenic assays indicate that ER-stress-related suppression of P21 expression potentiates caspase activation and sensitizes cells to doxorubicin treatment, while administration of TUN to mice increases the therapeutic efficacy of anticancer therapy for HepG2 liver and A549 lung cancers.

Regulation of P21 during diabetes-associated stress of the endoplasmic reticulum

Endoplasmic reticulum (ER) stress plays a major role in the pathogenesis of diabetes by inducing β-cell apoptosis in the islets of Langerhans. In this study, we show that the transcription factor CHOP, which is instrumental for the induction of ER-stress-associated apoptosis and the pancreatic dysfunction in diabetes, regulates the expression of P21 (WAF1), a cell cycle regulator with anti-apoptotic activity that promotes cell survival. Deficiency of P21 sensitizes pancreatic β-cells to glucotoxicity, while in mice genetic ablation of P21 accelerates experimental diet-induced diabetes, results indicative of a protective role for P21 in the development of the disease. Conversely, pharmacological stimulation of P21 expression by nutlin-3a, an inhibitor of P53-MDM2 interaction, restores pancreatic function and facilitates glucose homeostasis. These findings indicate that P21 acts as an inhibitor of ER-stress-associated tissue damage and that stimulation of P21 activity can be beneficial for the management of diabetes and probably of other conditions in which ER-stress-associated death is undesirable.

C/EBPα inhibits hepatocellular carcinoma by reducing Notch3/Hes1/p27 cascades

BACKGROUND AND AIMS

CCAAT/enhancer binding protein α is one of the key transcription factors of the hepatocyte nuclear factors family, which plays a critical role in liver cell proliferation and differentiation. However, the role of CCAAT/enhancer binding protein α in hepatocarcinogenesis remains to be defined.

METHODS

A recombinant adenovirus carrying the C/EBPα gene was constructed to determine its effect on hepatocarcinogenesis in vitro and in vivo.

RESULTS

We demonstrated that overexpression of CCAAT/enhancer binding protein α inhibited the tumourigenicity of Huh7 cells, re-established the expression of certain liver-specific genes and induced G0/G1 arrest. Overexpression of CCAAT/enhancer binding protein α significantly suppressed the proliferation of primary hepatocarcinogenesis cells and tumour associated fibroblasts in vitro. Additionally, intratumoural injection of adenovirus carrying the C/EBPα reduced the growth of subcutaneous hepatocarcinogenesis xenografts in nude mice. Systemic administration of adenovirus carrying the C/EBPα resulted in the eradication of orthotopic liver hepatocarcinogenesis nodules in nude mice. Further, up-regulation of CCAAT/enhancer binding protein α reduced the expression of Notch3, thereby suppressing Hes1 transactivation activity and leading to decreased p27 expression. Overexpression of Hes1 partially abolished the anti-proliferation effect of CCAAT/enhancer binding protein α on Huh7 cells.

CONCLUSION

These results suggested that the effect of CCAAT/enhancer binding protein α on hepatocarcinogenesis is partially through by reducing Notch3/Hes1/p27 cascades and CCAAT/enhancer binding protein α may possess a novel therapeutic potential for human hepatocarcinogenesis.

Epithelial-specific deletion of 11β-HSD2 hinders Apcmin/+ mouse tumorigenesis

Cyclooxygenase-2 (COX-2)-derived prostaglandin E2 (PGE2) promotes colorectal tumorigenesis. Glucocorticoids are endogenous and potent COX-2 inhibitors, and their local actions are downregulated by 11β-hydroxysteroid dehydrogenase type II (11β-HSD2)-mediated metabolism. Previously, it was reported that 11β-HSD2 is increased in human colonic and Apc(min/+) mouse intestinal adenomas and correlated with increased COX-2, and 11β-HSD2 inhibition suppressed the COX-2 pathway and decreased tumorigenesis. Because 11β-HSD2 is expressed in Apc(min/+) mouse intestinal adenoma stromal and epithelial cells, Apc(min/+) mice were generated with selective deletion of 11β-HSD2 in intestinal epithelial cells (Vil-Cre-HSD2(-/-) Apc(min/+)). Deletion of 11β-HSD2 in intestinal epithelia led to marked inhibition of Apc(min/+) mouse intestinal tumorigenesis. Immunostaining indicated decreased 11β-HSD2 and COX-2 expression in adenoma epithelia, whereas stromal COX-2 expression was intact in Vil-Cre-HSD2(-/-) Apc(min/+) mice. In Vil-Cre-HSD2(-/-) Apc(min/+) mouse intestinal adenomas, both p53 and p21 mRNA and protein were increased, with a concomitant decrease in pRb, indicating glucocorticoid-mediated G1-arrest. Further study revealed that REDD1 (regulated in development and DNA damage responses 1), a novel stress-induced gene that inhibits mTOR signaling, was increased, whereas the mTOR signaling pathway was inhibited. Therefore, in Vil-Cre-HSD2(-/-) Apc(min/+) mice, epithelial cell 11β-HSD2 deficiency leads to inhibition of adenoma initiation and growth by attenuation of COX-2 expression, increased cell-cycle arrest, and inhibition of mTOR signaling as a result of increased tumor intracellular active glucocorticoids.

IMPLICATIONS

Inhibition of 11β-HSD2 may represent a novel approach for colorectal cancer chemoprevention by increasing tumor glucocorticoid activity, which in turn inhibits tumor growth by multiple pathways.

11β-Hydroxysteroid Dehydrogenase Type II is a Potential Target for Prevention of Colorectal Tumorigenesis

Colorectal cancer (CRC) is a leading cause of cancer death, yet primary prevention remains the best approach to reducing overall morbidity and mortality. There is a clear molecular link between cyclooxygenase-2 (COX-2)-derived prostaglandin E₂ (PGE₂) production and CRC progression. Although selective COX-2 inhibitors as well as non-steroidal anti-inflammatory drugs (NSAIDs) reduce the number and sizes of colonic adenomas, increased cardiovascular risks of selective COX-2 inhibitors and increased gastrointestinal side-effects of NSAIDs limit their use in chemoprevention of CRC. Glucocorticoids induce apoptosis and are endogenous, potent COX-2 inhibitors. Glucocorticoids have been used for the treatment of hematologic malignancies, but not for solid tumors due to adverse side-effects such as immunosuppression and osteoporosis. In tissues, glucocorticoid actions are down-regulated by t y p e 2 1 1 β-hydroxysteroid dehydrogenase (11βHSD2), and inhibition of 11βHSD2 activity will elevate intracellular active glucocorticoid to levels that effectively suppress COX-2 expression. Both COX-2 and 11βHSD2 increase in Apc^+/min mouse intestinal adenomas and human colonic adenomas and either pharmacologic or genetic 11βHSD2 inhibition leads to decreases in COX-2-mediated PGE₂ production in tumors and prevents adenoma formation, tumor growth, and metastasis. 11βHSD2 inhibition may represent a novel approach for CRC chemoprevention by increasing tumor cell intracellular glucocorticoid activity, which in turn inhibits tumor growth by suppressing the COX-2-derived PGE₂ pathway, as well as other pathways, without potential side-effects relating to chronic application of COX-2 inhibitors, NSAIDs and glucocorticoids.

Asthma and COPD - The C/EBP Connection

Asthma and chronic obstructive pulmonary disease (COPD) are the two most prominent chronic inflammatory lung diseases with increasing prevalence. Both diseases are associated with mild or severe remodeling of the airways. In this review, we postulate that the pathologies of asthma and COPD may result from inadequate responses and/or a deregulated balance of a group of cell differentiation regulating factors, the CCAAT/Enhancer Binding Proteins (C/EBPs). In addition, we will argue that the exposure to environmental factors, such as house dust mite and cigarette smoke, changes the response of C/EBPs and are different in diseased cells. These novel insights may lead to a better understanding of the etiology of the diseases and may provide new aspects for therapies.

The emerging role of C/EBPs in glucocorticoid signaling: lessons from the lung

Glucocorticoids (GCs) have been successfully used in the treatment of inflammatory diseases for decades. However, there is a relative GC resistance in several inflammatory lung disorders, such as chronic obstructive pulmonary disease (COPD), but still the mechanism(s) behind this unresponsiveness remains unknown. Interaction between transcription factors and the GC receptor contribute to GC effects but may also provide mechanisms explaining steroid resistance. CCAAT/enhancer-binding protein (C/EBP) transcription factors are important regulators of pulmonary gene expression and have been implicated in inflammatory lung diseases such as asthma, pulmonary fibrosis, cystic fibrosis, sarcoidosis, and COPD. In addition, several studies have indicated a role for C/EBPs in mediating GC effects. In this review, we discuss the different mechanisms of GC action as well as the function of the lung-enriched members of the C/EBP transcription factor family. We also summarize the current knowledge of the role of C/EBP transcription factors in mediating the effects of GCs, with emphasis on pulmonary effects, and their potential role in mediating GC resistance.

Optimal elevation of β-cell 11β-hydroxysteroid dehydrogenase type 1 is a compensatory mechanism that prevents high-fat diet-induced β-cell failure

Type 2 diabetes ultimately results from pancreatic β-cell failure. Abnormally elevated intracellular regeneration of glucocorticoids by the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in fat or liver may underlie pathophysiological aspects of the metabolic syndrome. Elevated 11β-HSD1 is also found in pancreatic islets of obese/diabetic rodents and is hypothesized to suppress insulin secretion and promote diabetes. To define the direct impact of elevated pancreatic β-cell 11β-HSD1 on insulin secretion, we generated β-cell-specific, 11β-HSD1-overexpressing (MIP-HSD1) mice on a strain background prone to β-cell failure. Unexpectedly, MIP-HSD1(tg/+) mice exhibited a reversal of high fat-induced β-cell failure through augmentation of the number and intrinsic function of small islets in association with induction of heat shock, protein kinase A, and extracellular signal-related kinase and p21 signaling pathways. 11β-HSD1(-/-) mice showed mild β-cell impairment that was offset by improved glucose tolerance. The benefit of higher β-cell 11β-HSD1 exhibited a threshold because homozygous MIP-HSD1(tg/tg) mice and diabetic Lep(db/db) mice with markedly elevated β-cell 11β-HSD1 levels had impaired basal β-cell function. Optimal elevation of β-cell 11β-HSD1 represents a novel biological mechanism supporting compensatory insulin hypersecretion rather than exacerbating metabolic disease. These findings have immediate significance for current therapeutic strategies for type 2 diabetes.

Restoration of C/EBPα in dedifferentiated liposarcoma induces G2/M cell cycle arrest and apoptosis

Well-differentiated liposarcoma (WDLS) and dedifferentiated liposarcoma (DDLS) represent the most common biological group of liposarcoma, and there is a pressing need to develop targeted therapies for patients with advanced disease. To identify potential therapeutic targets, we sought to identify differences in the adipogenic pathways between DDLS, WDLS, and normal adipose tissue. In a microarray analysis of DDLS (n = 84), WDLS (n = 79), and normal fat (n = 23), C/EBPα, a transcription factor involved in cell cycle regulation and differentiation, was underexpressed in DDLS when compared to both WDLS and normal fat (15.2- and 27.8-fold, respectively). In normal adipose-derived stem cells, C/EBPα expression was strongly induced when cells were cultured in differentiation media, but in three DDLS cell lines, this induction was nearly absent. We restored C/EBPα expression in one of the cell lines (DDLS8817) by transfection of an inducible C/EBPα expression vector. Inducing C/EBPα expression reduced proliferation and caused cells to accumulate in G2/M. Under differentiation conditions, the cell proliferation was reduced further, and 66% of the DDLS cells containing the inducible C/EBPα expression vector underwent apoptosis as demonstrated by annexin V staining. These cells in differentiation conditions expressed early adipocyte-specific mRNAs such as LPL and FABP4, but they failed to accumulate intracellular lipid droplets, a characteristic of mature adipocytes. These results demonstrate that loss of C/EBPα is an important factor in suppressing apoptosis and maintaining the dedifferentiated state in DDLS. Restoring C/EBPα may be a useful therapeutic approach for DDLS.

Towards candidate genes affecting body fatness at the SSC7 QTL by expression analyses

A quantitative trait locus (QTL) affecting fatness in a way opposite to expectations based on breed means was mapped to swine chromosome 7 (SSC7) using crosses between Large White (LW) and Meishan (MS) founders. Defining the molecular fatness trait more explicitly would allow deducing positional candidate genes, for which expression differences must be analysed in experimental populations. First, mRNA levels of genes representing sequential steps in adipogenesis or involved in lipid metabolism were studied in backfat of pigs having homozygous LW(QTL7)/LW(QTL7) or heterozygous LW(QTL7)/MS(QTL7) alleles and considered at two ages. mRNA level of DLK1 expressed in preadipocytes was greater in MS(QTL7)/LW(QTL7) pigs than in homozygous pigs at 28 days. Transcript abundances of CEBPA involved in differentiation, the prolipogenic FASN gene and the adipocyte-specific marker FABP4 were lower in MS(QTL7)/LW(QTL7) pigs compared with LW(QTL7)/LW(QTL7) pigs at 150 days. Because these results suggest a lag time in terminal differentiation associated with the MS allele, seven genes in the QTL interval were deduced as promising candidates for the QTL effect by bioinformatics analysis. Among them, PPARD and CDKN1A had lower expression levels in MS(QTL7)/LW(QTL7) pigs at both ages. Genotype-related differences were observed in mRNA levels of PPARD target genes involved in cell differentiation (FZD7) or fatty acid oxidation (ACADL and ACOX1) at 150 days. These results re-evaluate the potential of PPARD to explain part of variation in pig adiposity.

Anti-proliferative effect and action mechanism of dexamethasone in human medullary thyroid cancer cell line

INTRODUCTION

Dexamethasone is known to inhibit the cell proliferation of certain transformed cell lines. In this study, the effect and action mechanism of dexamethasone were examined in the human medullary thyroid cancer cell line, TT cells.

METHODS

TT cells were treated with or without dexamethasone. 5-Bromo-2'-deoxyuridine uptake assay was used to evaluate cell proliferation. Cell cycle and its regulatory proteins were assessed by flow cytometry and western blot analysis, respectively. Apoptosis was analyzed by Hoechst staining and Annexin V assay.

RESULTS

Dexamethasone significantly reduced TT cell proliferation by 60% (p < 0.01). A substantial portion of cells was arrested at the G1 phase. The expression levels of cyclin D1, cyclin-dependent kinase (CDK)4, and CDK2 were decreased. In addition, the phosphorylation of retinoblastoma protein, which is a critical checkpoint protein in the transition of G1 to S phase, was decreased. On the other hand, the expression level of p27(Kip1), which is a cyclin/CDK inhibitor, was enhanced. Hoechst staining showed many fragmented nuclei in the dexamethasone-treated cells. The proportion of early apoptotic cells was also increased in the Annexin V assay.

CONCLUSION

Dexamethasone inhibited the proliferation of TT cells through cell cycle arrest at the G1 phase and increased apoptosis.

Glucocorticoids induce long-lasting effects in neural stem cells resulting in senescence-related alterations

Alterations in intrauterine programming occurring during critical periods of development have adverse consequences for whole-organ systems or individual tissue functions in later life. In this paper, we show that rat embryonic neural stem cells (NSCs) exposed to the synthetic glucocorticoid dexamethasone (Dex) undergo heritable alterations, possibly through epigenetic mechanisms. Exposure to Dex results in decreased NSC proliferation, with no effects on survival or differentiation, and changes in the expression of genes associated with cellular senescence and mitochondrial functions. Dex upregulates cell cycle-related genes p16 and p21 in a glucocorticoid receptor(GR)-dependent manner. The senescence-associated markers high mobility group (Hmg) A1 and heterochromatin protein 1 (HP1) are also upregulated in Dex-exposed NSCs, whereas Bmi1 (polycomb ring finger oncogene) and mitochondrial genes Nd3 (NADH dehydrogenase 3) and Cytb (cytochrome b) are downregulated. The concomitant decrease in global DNA methylation and DNA methyltransferases (Dnmts) suggests the occurrence of epigenetic changes. All these features are retained in daughter NSCs (never directly exposed to Dex) and are associated with a higher susceptibility to oxidative stress, as shown by the increased occurrence of apoptotic cell death on exposure to the redox-cycling reactive oxygen species (ROS) generator 2,3-dimethoxy-1-naphthoquinone (DMNQ). Our study provides novel evidence for programming effects induced by glucocorticoids (GCs) on NSCs and supports the idea that fetal exposure to endogenous or exogenous GCs is likely to result in long-term consequences that may predispose to neurodevelopmental and/or neurodegenerative disorders.

c/EBPbeta is a major regulatory element driving transcriptional activation of the CXCL12 promoter

CXCL12 is considered a constitutively expressed chemokine with homeostatic functions. However, induction of CXCL12 expression and its potential role in several pathologic conditions have been reported, suggesting that CXCL12 gene expression can be induced by different stimuli. To elucidate the molecular mechanisms involved in the regulation of CXCL12 gene expression, we aim to define the molecular factors that operate at the transcriptional level. Basal, constitutive expression of CXCL12 was dependent on basic helix-loop-helix factors. Transcriptional up-regulation of the CXCL12 gene was induced by cellular confluence or inflammatory stimuli such as interleukin-1 and interleukin-6, in a CCAAT/enhancer binding protein beta (c/EBPbeta)-dependent manner. Chromatin immunoprecipitation assays confirmed c/EBPbeta binding to a specific response element located at -1171 of the promoter region of CXCL12. Our data show that c/EBPbeta is a major regulatory element driving transcription of the CXCL12 gene in response to cytokines and cell confluence.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Chondrocyte p21(WAF1/CIP1) expression is increased by dexamethasone but does not contribute to dexamethasone-induced growth retardation in vivo

It has been shown that cell cycle genes play an important role in the coordination of chondrocyte proliferation and differentiation. The inhibitory effects of glucocorticoids (GCs) on chondrocyte proliferation are consistent with GCs disrupting cell cycle progression and promoting cell cycle exit. Cyclin-dependent kinase inhibitors (CDKIs) force cells to exit the cell cycle and differentiate, and studies have shown that expression of the CDKI p21(CIP1/WAF1) is increased in terminally differentiated cells. In this study, p21 mRNA and protein expression was increased during chondrocyte differentiation and after exposure to dexamethasone (Dex, 10(-6 )M) in murine chondrogenic ATDC5 cells. In 4-week-old mice lacking a functional p21 gene, Dex caused a reduction in body weight compared to saline control null mice, but this was consistent with the reduction in body weight observed in Dex-treated wild-type littermates. In addition, p21 ablation had no effect on the reduction in width of the growth plate or reduced mineral apposition rate in Dex-treated mice. However, an alteration in growth rate and epiphyseal structure is evident when comparing p21(-/-) and wild-type mice. These findings suggest that p21 does not directly contribute to GC-induced growth retardation in vivo but is involved in the maintenance of the growth plate.

Dexamethasone treatment of calves latently infected with bovine herpesvirus 1 leads to activation of the bICP0 early promoter, in part by the cellular transcription factor C/EBP-alpha

Sensory neurons within trigeminal ganglia (TG) are the primary site for bovine herpesvirus 1 (BHV-1) latency. During latency, viral gene expression is restricted to the latency-related (LR) gene and the open reading frame ORF-E. We previously constructed an LR mutant virus that expresses LR RNA but not any of the known LR proteins. In contrast to calves latently infected with wild-type (wt) BHV-1 or the LR rescued virus, the LR mutant virus does not reactivate from latency following dexamethasone (DEX) treatment. In this study, we demonstrated that bICP0, but not bICP4, transcripts were consistently detected in TG of calves infected with the LR mutant or LR rescued virus following DEX treatment. Calves latently infected with the LR rescued virus but not the LR mutant virus expressed late transcripts, which correlated with shedding of infectious virus following DEX treatment. The bICP4 and bICP0 genes share a common immediate-early promoter, suggesting that this promoter was not consistently activated during DEX-induced reactivation from latency. The bICP0 gene also contains a novel early promoter that was activated by DEX in mouse neuroblastoma cells. Expression of a cellular transcription factor, C/EBP-alpha, was stimulated by DEX, and C/EBP-alpha expression was necessary for DEX induction of bICP0 early promoter activity. C/EBP-alpha directly interacted with bICP0 early promoter sequences that were necessary for trans activation by C/EBP-alpha. In summary, DEX treatment of latently infected calves induced cellular factors that stimulated bICP0 early promoter activity. Activation of bICP0 early promoter activity does not necessarily lead to late gene expression and virus shedding.

In prostate cancer C/EBPalpha promotes cell growth by the loss of interactions with CDK2, CDK4, and E2F and by activation of AKT

BACKGROUND

The CCAAT/Enhancer binding protein alpha (C/EBPalpha) is an important transcription factor for granulopoiesis and adipogenesis. While decreased expression and mutation of C/EBPalpha has been found in several types of tumors, the role of C/EBPalpha in prostate cancer has not been well characterized.

METHODS

We quantitatively analyzed the immunochemical staining of prostate cancer tissue and examined the growth properties of prostate cancer cells stably expressing C/EBPalpha by measure growth curve, cell cycle, and anchorage independent colony formation, investigated the association of C/EBPalpha with E2Fs and CDKs by co-immunoprecipitation and examined the expression of CDKs and activation of AKT by Western blot analysis.

RESULTS

The ratio of C/EBPalpha expression between cancer cells close to the pseudolumen of glands and those nearer the basal cell layer was more than threefold greater than that seen in the normal prostate epithelium. Further, this ratio increased with increased Gleason score of the prostate cancer. Forced expression of C/EBPalpha in prostate cancer cell lines accelerated cell growth, stimulated cells into the S and G2 phases of cell cycle, and enhanced anchorage-independent colony formation. Simultaneously, forced expression of C/EBPalpha increased expression of CDK2/CDK4 and nuclear PP2A, and activated AKT. In addition, C/EBPalpha was no longer found associated with E2F1/E2F4 and CDK2/CDK4. AKT and PPA2 inhibitors restored both the anti-proliferation function of C/EBPalpha and the interaction between C/EBPalpha and E2F1/E2F4.

CONCLUSION

In prostate cancer cells C/EBPalpha cannot function as a tumor suppressor.

Corticosteroids induce COX-2 expression in cardiomyocytes: role of glucocorticoid receptor and C/EBP-beta

Psychological stress increases the level of glucocorticoids in the circulating system. We found that dexamethasone administration in adult mice elevates the expression of COX-2 in the myocardium. With isolated neonatal cardiomyocytes, corticosterone (CT) at physiologically relevant doses (0.01-1 microM) induces the expression of COX-2 gene. The induction first appeared at 4 h and remained for at least 24 h with 1 microM CT treatment. This response is likely cardiomyocyte cell type specific since CT did not induce COX-2 expression in cardiac fibroblasts and glucocorticoids are known to suppress the expression of COX-2 in lymphocytes and several organs. Corticosteroids, but not estrogen or progesterone, induce COX-2 expression. The glucocorticoid receptor (GR) antagonist mifepristone (MF) prevented CT from inducing COX-2 gene, suggesting a GR-dependent induction in cardiomyocytes. COX-2 gene promoter deletion and mutation studies indicate a role of CCAAT/enhancer binding protein-beta (C/EBP-beta) in CT-induced COX-2 gene expression. Chromatin immunoprecipitation assays revealed that CT caused the binding of both GR and C/EBP-beta to COX-2 promoter, while MF pretreatment blocked such binding. Coimmunoprecipitation experiments demonstrated that CT treatment induced the interaction of GR with C/EBP-beta. Small interfering RNA against C/EBP-beta prevented CT from activating COX-2 promoter or elevating COX-2 protein. Our data suggest that the interaction between GR and C/EBP-beta contributes to elevated COX-2 gene transcription by CT in cardiomyocytes.

Cyclin-dependent kinase inhibitor, p21WAF1/CIP1, is involved in adipocyte differentiation and hypertrophy, linking to obesity, and insulin resistance

Both adipocyte hyperplasia and hypertrophy are determinant factors for adipocyte differentiation during the development of obesity. p21(WAF1/CIP1), a cyclin-dependent kinase inhibitor, is induced during adipocyte differentiation; however, its precise contribution to this process is unknown. Using both in vitro and in vivo systems, we show that p21 is crucial for maintaining adipocyte hypertrophy and obesity-induced insulin resistance. The absence of p21 in 3T3-L1 fibroblasts by RNA-mediated interference knockdown or in embryonic fibroblasts from p21(-/-) mice impaired adipocyte differentiation, resulting in smaller adipocytes. Despite normal adipose tissue mass on a normal diet, p21(-/-) mice fed high energy diets had reduced adipose tissue mass and adipocyte size accompanied by a marked improvement in insulin sensitivity. Knockdown of p21 in enlarged epididymal fat of diet-induced obese mice and also in fully differentiated 3T3-L1 adipocytes caused vigorous apoptosis by activating p53. Thus, p21 is involved in both adipocyte differentiation and in protecting hypertrophied adipocytes against apoptosis. Via both of these mechanisms, p21 promotes adipose tissue expansion during high fat diet feeding, leading to increased downstream pathophysiological consequences such as insulin resistance.

p21 Waf1/Cip1 expression by curcumin in U-87MG human glioma cells: role of early growth response-1 expression

Curcumin, a natural compound, is a well-known chemopreventive agent with potent anticarcinogenic activity in a wide variety of tumor cells. Curcumin inhibits cancer cell proliferation in part by suppressing cyclin D1 and inducing expression of the cyclin-dependent kinase inhibitor p21(Waf1/Cip1). Both p53-dependent and p53-independent mechanisms regulate p21(Waf1/Cip1) expression, but the mechanism by which curcumin regulates p21(Waf1/Cip1) expression remains unknown. Here, we report that transcription of the p21(Waf1/Cip1) gene is activated by early growth response-1 (Egr-1) independently of p53 in response to curcumin treatment in U-87MG human glioblastoma cells. Egr-1 is a transcription factor that helps regulate differentiation, growth, and apoptosis in many cell types. Egr-1 expression is induced by curcumin through extracellular signal-regulated kinase (ERK) and c-Jun NH(2)-terminal kinase (JNK), but not the p38, mitogen-activated protein kinase (MAPK) pathways, which mediate the transactivation of Elk-1. Transient expression of Egr-1 enhanced curcumin-induced p21(Waf1/Cip1) promoter activity, whereas suppression of Egr-1 expression by small interfering RNA abrogated the ability of curcumin to induce p21(Waf1/Cip1) promoter activity. In addition, stable knockdown of Egr-1 expression in U-87MG cells suppressed curcumin-induced p21 expression. Our results indicate that ERK and JNK MAPK/Elk-1/Egr-1 signal cascade is required for p53-independent transcriptional activation of p21(Waf1/Cip1) in response to curcumin in U-87MG human glioblastoma cells.

Regulation of the rat glutathione S-transferase A2 gene by glucocorticoids: crosstalk through C/EBPs

Regulation of the rat glutathione S-transferase A2 (GSTA2) gene by glucocorticoids is biphasic in its concentration dependence to glucocorticoids, with concentrations of 10-100 nM repressing gene activity (GR-dependent), and concentrations above 1 microM increasing transactivation (PXR-dependent) in adult rat hepatocytes or transient transfection assays. Over-expression of either C/EBP alpha or beta negatively regulates basal and inducible expression of a 1.65 Kb GSTA2 luciferase reporter, and synergizes the response to glucocorticoids (GC). C/EBP responsive elements have been identified in the GSTA2 5'-flanking sequence, associated with the palindrominic Glucocorticoid Responsive Element (GRE), the Ah receptor response elements, and the antioxidant response element. In reporters lacking the palindromic GRE, negative regulation by GC is observed only when C/EBP alpha is co-expressed. Co-transfection of C/EBP alpha/beta induced gene expression of the GSTA2 XRE reporter, but negatively regulated the GSTA2 ARE-reporter. In contrast, the ARE from the rat NAD(P)H quinone oxidoreductase gene was induced by co-transfection of C/EBPs, but was still negatively regulated by GC. PXR-induction of the GSTA2 reporter was partially ablated by co-transfection of C/EBP alpha and enhanced by co-transfection of C/EBPbeta. We conclude that C/EBP alpha and beta are involved in GC-dependent repression of GSTA2 gene expression and ARE sequences that bind C/EBPs appears to be critical for these responses.

Anti-inflammatory functions of glucocorticoid-induced genes

There is a broad consensus that glucocorticoids (GCs) exert anti-inflammatory effects largely by inhibiting the function of nuclear factor kappaB (NFkappaB) and consequently the transcription of pro-inflammatory genes. In contrast, side effects are thought to be largely dependent on GC-induced gene expression. Biochemical and genetic evidence suggests that the positive and negative effects of GCs on transcription can be uncoupled from one another. Hence, novel GC-related drugs that mediate inhibition of NFkappaB but do not activate gene expression are predicted to retain therapeutic effects but cause fewer or less severe side effects. Here, we critically re-examine the evidence in favor of the consensus, binary model of GC action and discuss conflicting evidence, which suggests that anti-inflammatory actions of GCs depend on the induction of anti-inflammatory mediators. We propose an alternative model, in which GCs exert anti-inflammatory effects at both transcriptional and post-transcriptional levels, both by activating and inhibiting expression of target genes. The implications of such a model in the search for safer anti-inflammatory drugs are discussed.

CDDO induces granulocytic differentiation of myeloid leukemic blasts through translational up-regulation of p42 CCAAT enhancer binding protein alpha

2-Cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) induces differentiation and apoptosis of tumor cells in vitro and in vivo. Here we assessed the effects of CDDO on CCAAT enhancer-binding protein alpha (CEBPA), a transcription factor critical for granulocytic differentiation. In HL60 acute myeloid leukemia (AML) cells, CDDO (0.01 to 2 muM) induces apoptosis in a dose-dependent manner. Conversely, subapoptotic doses of CDDO promote phagocytic activity and granulocytic-monocytic differentiation of HL60 cells through increased de novo synthesis of p42 CEBPA protein. CEBPA translational up-regulation is required for CDDO-induced granulocytic differentiation and depends on the integrity of the CEBPA upstream open reading frame (uORF). Moreover, CDDO increases the ratio of transcriptionally active p42 and the inactive p30 CEBPA isoform, which, in turn, leads to transcriptional activation of CEBPA-regulated genes (eg, GSCFR) and is associated with dephosphorylation of eIF2alpha and phosphorylation of eIF4E. In concordance with these results, CDDO induces a CEBPA ratio change and differentiation of primary blasts from patients with acute myeloid leukemia (AML). Because AML is characterized by arrested differentiation, our data suggest the inclusion of CDDO in the therapy of AML characterized by dysfunctional CEBPA expression.

In vivo transfection of C/EBP-alpha gene could ameliorate CCL(4)-induced hepatic fibrosis in mice

AIM

Hepatic stellate cells (HSCs) play a key role in liver fibrosis. CCAAT/enhancer-binding proteins-alpha (C/EBP-alpha) can inhibit HSCs activation in vitro, as described in our previous study. However, little is known about the in vivo effect of C/EBP-alpha gene in hepatic fibrosis.

METHODS

Male BALB/c mice were injected by hydrodynamic protocol with pIRES2-EGFP-C/EBPalpha expression vector from the first to the fourth week (early intervention) or from the ninth to the 12th week (late intervention) after CCl(4) injection, respectively. Successful transfection of vector and the expression of C/EBP-alpha were confirmed with the appearance of green fluorescence in liver cells, immunohistochemical staining and the western blot.

RESULTS

High expression of C/EBP-alpha gene in liver cells, especially in non-parenchymal cells, could reduce the content of collagens by 82.5% and 72.3% (Sirius red staining + image analysis) and the content of hydroxyproline by 56.3% and 51.6%, respectively, in the early and late intervention experiments.

CONCLUSION

It is evident that exogenous C/EBP-alpha gene has an early and late intervention role in mice liver fibrosis.

Tamoxifen-induced activation of p21Waf1/Cip1 gene transcription is mediated by Early Growth Response-1 protein through the JNK and p38 MAP kinase/Elk-1 cascades in MDA-MB-361 breast carcinoma cells

Tamoxifen (TAM) is a synthetic non-steroidal anti-estrogen compound that is widely used as an effective chemotherapeutic agent for treatment and prevention of breast cancer. Unfortunately, prolonged treatment with TAM causes TAM-responsive tumors to become TAM resistant through an as-yet-unknown mechanism. To develop novel anti-breast cancer agents that are therapeutically superior to TAM, we must first fully understand the biological effects of TAM. In this study, we found that TAM treatment of MDA-MB-361 breast cancer cells activated p21Waf1/Cip1 gene transcription independently of p53. Furthermore, TAM-induced p21Waf1/Cip1 promoter activity was enhanced by transient expression of the gene encoding Early Growth Response-1 (Egr-1) protein, a transcription factor that plays an important role in cell growth and differentiation. The TAM-induced p21Waf1/Cip1 promoter activity was blocked by the expression of small interfering RNA (siRNA) targeted to Egr-1 mRNA. In addition, induction of Egr-1 expression by TAM occurred at the transcriptional level via Ets-domain transcription factor Elk-1 through the JNK and p38 mitogen-activated protein (MAP) kinase pathways. Inhibition of the JNK and p38 MAP kinase signals inhibited Egr-1-mediated p21Waf1/Cip1 promoter activity. We conclude that TAM stimulation of p21Waf1/Cip1 gene transcription in MDA-MB-361 cells depends largely on Elk-1-mediated Egr-1 expression induced by activation of the JNK and p38 MAP kinase pathways.

Phosphatidylinositol 3-Akt-kinase-dependent phosphorylation of p21(Waf1/Cip1) as a novel mechanism of neuroprotection by glucocorticoids

The role of glucocorticoids in the regulation of apoptosis remains incongruous. Here, we demonstrate that corticosterone protects neurons from apoptosis by a mechanism involving the cyclin-dependent kinase inhibitor p21(Waf1/Cip1). In primary cortical neurons, corticosterone leads to a dose- and Akt-kinase-dependent upregulation with enhanced phosphorylation and cytoplasmic appearance of p21(Waf1/Cip1) at Thr 145. Exposure of neurons to the neurotoxin ethylcholine aziridinium (AF64A) results in activation of caspase-3 and a dramatic loss of p21(Waf1/Cip1) preceding apoptosis in neurons. These effects of AF64A are reversed by pretreatment with corticosterone. Corticosterone-mediated upregulation of p21(Waf1/Cip1) and neuroprotection are completely abolished by glucocorticoid and mineralocorticoid receptor antagonists as well as inhibitors of PI3- and Akt-kinase. Both germline and somatically induced p21(Waf1/Cip1) deficiency abrogate the neuroprotection by corticosterone, whereas overexpression of p21(Waf1/Cip1) suffices to protect neurons from apoptosis. We identify p21(Waf1/Cip1) as a novel antiapoptotic factor for postmitotic neurons and implicate p21(Waf1/Cip1) as the molecular target of neuroprotection by high-dose glucocorticoids.

Glucocorticoid up-regulates transforming growth factor-beta (TGF-beta) type II receptor and enhances TGF-beta signaling in human prostate cancer PC-3 cells

Previous studies have shown that dexamethasone (Dex) induces the expression of TGF-beta1 in androgen-independent prostate cancer both in vitro and in vivo. However, it is not clear whether Dex has a direct effect on the expression of TGF-beta receptors. In this study, using the androgen-independent human prostate cancer cell line, PC-3 cells, we demonstrated that Dex increased the expression of TGF-beta receptor type II (TbetaRII), but not TGF-beta receptor type I (TbetaRI) in a time- and dose-dependent manner. The up-regulation of TbetaRII expression by Dex was mediated by glucocorticoid receptor and occurred at the transcriptional level. Dex also enhanced TGF-beta1 signaling and increased the expression of cyclin-dependent kinase inhibitors p15(INK4B) (p15) and p27(KIP1) (p27), which are the target genes of TGF-beta1 and have been identified as inducers of cell cycle arrest at the G1 checkpoint. The antiproliferative effect of Dex was partially blocked by anti-TbetaRII antibody, indicating that elevated TbetaRII and TGF-beta1 signaling were involved in the antiproliferative effect of Dex. Because the TGF-beta1 pathway could not fully explain the antiproliferative effect of Dex, we further examined the effects of Dex on the transcriptional activity of nuclear factor-kappaB (NF-kappaB) and the expression of IL-6 and found that Dex suppressed the transcriptional activity of NF-kappaB and IL-6 mRNA expression in PC-3 cells. These results demonstrated that glucocorticoid inhibited the proliferation of PC-3 cells not only through enhancing growth-inhibitory TGF-beta1 signaling, but also through suppressing transcriptional activities of NF-kappaB.

Disease-specific expression and regulation of CCAAT/enhancer-binding proteins in asthma and chronic obstructive pulmonary disease

BACKGROUND

CCAAT/enhancer-binding proteins (C/EBPs) control cell proliferation; lack of C/EBPalpha correlates with increased proliferation of bronchial smooth muscle cells (BSMCs) of asthmatic patients.

OBJECTIVE

We sought to assess disease-specific expression of C/EBPalpha, beta, delta, and epsilon and the effects of budesonide (10(-8) mol/L) and formoterol (10(-8) mol/L).

METHODS

Expression and function of C/EBPalpha, beta, delta, and epsilon BSMCs of control subjects (n = 9), asthmatic patients (n = 12), and patients with chronic obstructive pulmonary disease (COPD; n = 10) were determined.

RESULTS

The control group expressed C/EBPalpha, beta, delta, and epsilon, which were upregulated by serum (5%). Budesonide completely inhibited C/EBPalpha and beta expression; formoterol increased C/EBPalpha expression (2-fold). C/EBPdelta and epsilon expression were not affected by the drugs. The asthmatic group did not appropriately express C/EBPalpha. Basal levels of C/EBPbeta, delta, and epsilon were upregulated by serum (5%). Budesonide and formoterol increased C/EBPbeta levels (3.4-fold and 2.5-fold, respectively), leaving C/EBPalpha, delta, and epsilon levels unaffected. The COPD group normally expressed C/EBPalpha, beta, and epsilon, which were upregulated by serum treatment (5%). Basal levels of C/EBPdelta were downregulated by serum in 7 of 10 BSMC lines. Budesonide inhibited C/EBPalpha and beta expression, upregulated C/EBPdelta (3.2-fold), and had no effect on C/EBPepsilon. Formoterol upregulated C/EBPalpha expression (3-fold) but not the other C/EBPs. Protein analysis and electrophoretic mobility shift assay confirmed the disease-specific expression pattern of C/EBPalpha in asthmatic patients and C/EBPdelta in patients with COPD.

CONCLUSIONS

The expression and regulation of C/EBPs in BSMCs of asthmatic patients and patients with COPD seems disease specific. Budesonide and formoterol modulate C/EBP expression in a drug- and disease-specific pattern.

CLINICAL IMPLICATIONS

The data could provide a method to discriminate between asthma and COPD at an early disease stage.

In prostate cancer cells the interaction of C/EBPalpha with Ku70, Ku80, and poly(ADP-ribose) polymerase-1 increases sensitivity to DNA damage

Prostate cancer cell lines were examined for proteins that partnered with the transcription factor C/EBPalpha by use of a pull-down assay with S-tagged C/EBPalpha combined with matrix-assisted laser desorption ionization time-of-flight mass spectroscopy analysis. Ku70, Ku80, and poly(ADP-ribose) polymerase-1 (PARP-1) were identified as proteins that associated with C/EBPalpha. The physical interaction of C/EBPalpha with these partner proteins was further demonstrated by glutathione S-transferase (GST) pull-downs using purified protein expressed in Escherichia coli. The strongest binding was between C/EBPalpha and PARP-1. Immunoprecipitation of C/EBPalpha expressed in prostate cancer cells co-precipitated Ku70, Ku80, and PARP-1. Deletion analysis of C/EBPalpha indicated that the C terminus of C/EBPalpha was essential for the interaction of C/EBPalpha with Ku70, Ku80, and PARP-1. Functional analysis of the interaction between C/EBPalpha and the Ku proteins as well as PARP-1 showed that cells exhibiting these interactions had increased radiation sensitivity and decreased ability to repair double strand DNA breaks. Deficient DNA repair was dependent on the prostate cancer cell line tested, suggesting a complex process. We conclude that the association of C/EBPalpha with Ku proteins and PARP-1 raises the likelihood that C/EBPalpha-expressing prostate cancer cells may be more sensitive to DNA-damaging agents and may be important in the design of new prostate cancer therapies.

CCAAT/enhancer binding protein alpha (C/EBPalpha) and C/EBPalpha myeloid oncoproteins induce bcl-2 via interaction of their basic regions with nuclear factor-kappaB p50

The CEBPA gene is mutated in 10% of acute myeloid leukemia (AML) cases. We find that CEBPA and Bcl-2 RNA levels correlate highly in low-risk human AMLs, suggesting that inhibition of apoptosis via induction of bcl-2 by CCAAT/enhancer binding protein alpha (C/EBPalpha) or its mutant variants contributes to transformation. C/EBPalphap30, lacking a NH2-terminal transactivation domain, or C/EBPalphaLZ, carrying in-frame mutations in the leucine zipper that prevent DNA binding, induced bcl-2 in hematopoietic cell lines, and C/EBPalpha induced bcl-2 in normal murine myeloid progenitors and in the splenocytes of H2K-C/EBPalpha-Emu transgenic mice. C/EBPalpha protected Ba/F3 cells from apoptosis on interleukin-3 withdrawal but not if bcl-2 was knocked down. Remarkably, C/EBPalphaLZ oncoproteins activated the bcl-2 P2 promoter despite lack of DNA binding, and C/EBPalphap30 also activated the promoter. C/EBPalpha and the C/EBPalpha oncoproteins cooperated with nuclear factor-kappaB (NF-kappaB) p50, but not p65, to induce bcl-2 transcription. Endogenous C/EBPalpha preferentially coimmunoprecipitated with p50 versus p65 in myeloid cell extracts. Mutation of residues 297 to 302 in the C/EBPalpha basic region prevented induction of endogenous bcl-2 or the bcl-2 promoter and interaction with p50 but not p65. These findings suggest that C/EBPalpha or its mutant variants tether to a subset of NF-kappaB target genes, including Bcl-2, via p50 to facilitate gene activation and offer an explanation for preferential in-frame rather than out-of-frame mutation of the leucine zipper with sparing of the basic region in C/EBPalphaLZ oncoproteins. Targeting interaction between C/EBPalpha basic region and NF-kappaB p50 may contribute to the therapy of AML and other malignancies expressing C/EBPs.

Adipogenesis: cellular and molecular aspects

Obesity and lipoatrophy are major risks for insulin resistance, non-insulin-dependent diabetes and cardiovascular disease. In the past three decades, significant advances have been made in delineating the key transcription factors of adipogenesis, as well as extracellular effectors and intracellular signalling pathways that regulate fat cell formation. This review focuses on in vitro models of adipocyte differentiation, and on the balance between pro- and anti-adipogenic factors that drive the adipocyte differentiation process. Full understanding of the mechanisms of adipose tissue differentiation represents a major issue to develop a comprehensive strategy to prevent and treat obesity.

Involvement of C/EBP-alpha gene in in vitro activation of rat hepatic stellate cells

Hepatic stellate cells (HSCs) play key roles in hepatic fibrosis. One of the most striking alterations in activated HSCs is loss of cytoplasmic lipid droplets. However, the association of lipid storage with the activation of HSCs remains unclear. CCAAT/enhancer-binding proteins family (C/EBPs), especially C/EBP-alpha, controls differentiation of adipocytes. We suggested that C/EBP-alpha gene may be involved in HSCs activation. The present results showed that the expression levels of C/EBP-alpha and C/EBP-beta genes declined in activated HSCs. Over-expression of C/EBP-alpha gene in activated HSCs: (1) inhibited HSCs proliferation, extracellular matrix-producing, alpha-smooth muscle actin gene expression, and induced rebound of cytoplasmic lipid droplets; (2) reduced retinoic acid receptor-beta, C/EBP-delta and -beta gene expressions, but increased the active form C/EBP-beta PSer(105), and induced retinoid X receptor-alpha gene expression; and (3) did not affect the protein level of p16INK4a, p21Cip1/WAF1 or p27Kip1. In conclusions, C/EBP-alpha gene is involved in in vitro activation of rat HSCs.

Liver-enriched transcription factors in liver function and development. Part II: the C/EBPs and D site-binding protein in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation

In the first part of our review (see Pharmacol Rev 2002;54:129-158), we discussed the basic principles of gene transcription and the complex interactions within the network of hepatocyte nuclear factors, coactivators, ligands, and corepressors in targeted liver-specific gene expression. Now we summarize the role of basic region/leucine zipper protein family members and particularly the albumin D site-binding protein (DBP) and the CAAT/enhancer-binding proteins (C/EBPs) for their importance in liver-specific gene expression and their role in liver function and development. Specifically, regulatory networks and molecular interactions were examined in detail, and the experimental findings summarized in this review point to pivotal roles of DBP and C/EBPs in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation. These regulatory proteins are therefore of great importance in liver physiology, liver disease, and liver development. Furthermore, interpretation of the vast data generated by novel genomic platform technologies requires a thorough understanding of regulatory networks and particularly the hierarchies that govern transcription and translation of proteins as well as intracellular protein modifications. Thus, this review aims to stimulate discussions on directions of future research and particularly the identification of molecular targets for pharmacological intervention of liver disease.

Glial fibrillary acidic protein and vimentin expression is regulated by glucocorticoids and neurotrophic factors in primary rat astroglial cultures

The neurotrophic factors epidermal growth factor (EGF), basic fibroblast growth factor, (bFGF), insulin-like growth factor I (IGF-I) and insulin (INS) regulate neural and astroglial cell functions. Glucocorticoids may influence the metabolism of astroglial compartment and are key hormones in neurodegenerative events. This study was designed to assess the interactions between growth factors and dexamethasone (DEX) on cytoskeletal proteins (GFAP and vimentin) expression in 25 days in vitro (DIV) astrocyte cultures. An increase in GFAP and vimentin expression was observed after 12 h pretreatment with bFGF and subsequent treatment for 60 h with DEX. GFAP immunoreactivity was decreased after 24 h progression growth factors (EGF, IGF-I and INS) addition, when compared to control 36 h DEX and bFGF-pretreated cultures for the last 12 h. Vimentin immunoreactivity was decreased after 12 h bFGF pretreatment and subsequent 60 h DEX addition in astrocyte cultures compared to 12 h bFGF-pretreated ones. Pretreatment for 36 h with DEX plus bFGF in the last 12 h and subsequent treatment for 24 h with DMEM (Dulbecco's modified Eagle medium; DMEM) + BSA (bovine serum albumine) (harvesting), or with progression growth factors (EGF, IGF-I or INS) alone or two of them together, stimulated GFAP expression, compared to untreated controls. Immunochemical analysis of the mitogen-activated protein kinase ERK2 suggests an involvement of this enzyme in the control of GFAP expression. The above findings support the view of an interactive and complex dialogue between growth factors and glucocorticoids during astroglial cell proliferation and maturation in culture. This may have implications in therapeutic approach of neurologic disorders associated with astrogliosis, including cerebrovascular disease.

Physiological and pathological consequences of the interactions of the p53 tumor suppressor with the glucocorticoid, androgen, and estrogen receptors

The p53 tumor suppressor plays a key role in protection from the effects of different physiological stresses (DNA damage, hypoxia, transcriptional defects, etc.), and loss of its activity has dire consequences, such as cancer. Its activity is finely tuned through interactions with other important regulatory circuits in the cell. Recently, striking evidence has emerged for crosstalk with another class of important regulators, the steroid hormone receptors, and in particular the glucocorticoid (GR), androgen (AR), and estrogen (ER) receptors. These receptors are important in maintaining homeostasis in response to internal and external stresses (GR) and in the development, growth, and maintenance of the male and female reproductive systems (AR and ER, respectively). We review how p53 interacts closely with these receptors, to the extent that they share the same E3 ubiquitin ligase, the MDM2 oncoprotein. We discuss the different physiological contexts in which such interactions occur, and also how these interactions have been undermined in various pathological situations. We will describe future areas for research, with special emphasis on GR, and how certain common features, such as cytoplasmic anchoring of p53 by the receptors, may become targets for the development of therapeutic interventions. Given the importance of GR in inflammation, erythropoiesis, and autoimmune diseases, and the importance of AR and ER in prostate and breast cancer (respectively), the studies on p53 interactions with the steroid receptors will be an important domain in the near future.

Dysfunctional interaction of C/EBPalpha and the glucocorticoid receptor in asthmatic bronchial smooth-muscle cells

BACKGROUND

Increased proliferation of bronchial smooth-muscle cells may lead to increased muscle mass in the airways of patients with asthma. The antiproliferative effect of glucocorticoids in bronchial smooth-muscle cells in subjects without asthma is mediated by a complex of the glucocorticoid receptor and the CCAAT/enhancer binding protein alpha (C/EBPalpha). We examined the signaling pathway controlling the inhibitory effect of glucocorticoids on cell proliferation and interleukin-6 synthesis in bronchial smooth-muscle cells of subjects with asthma and those without asthma.

METHODS

Lines of bronchial smooth-muscle cells were established from cells from 20 subjects with asthma, 8 subjects with emphysema, and 26 control subjects. Cell proliferation was determined by means of cell counts and [3H]thymidine incorporation. Signal transduction was studied by means of an electrophoretic DNA mobility-shift assay, a supershift electrophoretic-mobility assay, immunoblotting, use of C/EBPalpha antisense oligonucleotides, and use of a human C/EBPalpha expression vector. Interleukin-6 release was determined by means of an enzyme-linked immunosorbent assay.

RESULTS

Glucocorticoids activated the glucocorticoid receptor and inhibited serum-induced secretion of interleukin-6 in bronchial smooth-muscle cells from both subjects with asthma and those without asthma; however, glucocorticoids inhibited proliferation only in bronchial smooth-muscle cells from subjects without asthma. C/EBPalpha protein was detected by immunoblotting in all bronchial smooth-muscle cells from subjects without asthma but not in those with asthma, whereas the protein was expressed in lymphocytes from both groups of subjects. C/EBPalpha antisense oligonucleotides or the glucocorticoid-receptor inhibitor mifepristone reversed the antiproliferative effect of glucocorticoids in bronchial smooth-muscle cells from subjects without asthma. When bronchial smooth-muscle cells from subjects with asthma were transiently transfected with an expression vector for human C/EBPalpha, two forms of the protein were expressed, and subsequent administration of glucocorticoids inhibited cell proliferation.

CONCLUSIONS

We hypothesize that a cell-type-specific absence of C/EBPalpha is responsible for the enhanced proliferation of bronchial smooth-muscle cells derived from subjects with asthma and that it explains the failure of glucocorticoids to inhibit proliferation in vitro.

C/EBP beta isoforms LIP and LAP modulate progression of the cell cycle in the regenerating mouse liver

The CCAAT enhancer-binding protein (C/EBP) beta gene can produce several N-terminally truncated isoforms. Liver-enriched activator protein (LAP) is a transcriptional activator in many systems, whereas liver-enriched inhibitory protein (LIP) is regarded as a functional LAP antagonist. In this study, we examined the impact of these two proteins on cell cycle progression in the regenerating liver. Adenoviral overexpression of LAP, in addition to its role as a transactivator of liver-specific genes, led to a delayed S-phase entry of hepatocytes after partial hepatectomy (PH) in vivo. This delay was accompanied by decreased expression of cyclin A and E as well as proliferating cell nuclear antigen and decreased cyclin-dependent kinase 2 activity at the G1/S boundary. This observation is not explained by increased p21(CIP1/Waf1) expression or lack of phosphorylation of external LAP, but LAP overexpression triggered a decreased C/EBP-alpha/C/EBP-alpha-30 ratio and a reduced basal c-jun level in the liver. In contrast, adenoviral overexpression of LIP resulted in a stronger and earlier induction of cyclin A and E after PH, but did not change the timing and extent of cyclin-dependent kinase 2 activity or the amount of hepatocytes that entered S phase in this model. In the LIP expressing group, both C/EBP-alpha isoforms and c-jun were more strongly induced after PH. In conclusion, the LAP/LIP ratio is an important modulator of cell cycle progression during liver regeneration. In the context of previous studies, our results demonstrate that LAP, through a dose-dependent effect, withholds a dual activating and inhibiting role on hepatocyte proliferation in vivo.

Kinetic profiles of p300 occupancy in vivo predict common features of promoter structure and coactivator recruitment

Understanding the language encrypted in the gene regulatory regions of the human genome is a challenging goal for the genomic era. Although customary extrapolations from steady-state mRNA levels have been effective, deciphering these regulatory codes will require additional empirical data sets that more closely reflect the dynamic progression of molecular events responsible for inducible transcription. We describe an approach using chromatin immunoprecipitation to profile the kinetic occupancy of the transcriptional coactivator and histone acetyltransferase p300 at numerous mitogen-induced genes in activated T cells. Comparison of these profiles reveals a class of promoters that share common patterns of inducible expression, p300 recruitment, dependence on selective p300 domains, and sensitivity to histone deacetylase inhibitors. Remarkably, this class also shares an evolutionarily conserved promoter composition and structure that accurately predicts additional human genes with similar functional attributes. This "reverse genomic" approach will have broad application for the genome-wide classification of promoter structure and function.