Interaction of C/EBPalpha and the glucocorticoid receptor in vivo and in nontransformed human cells

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.

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.

A heretical view: rather than a solely placental protective function, placental 11β hydroxysteroid dehydrogenase 2 also provides substrate for fetal peripheral cortisol synthesis in obese pregnant ewes

Exposure to glucocorticoid levels higher than appropriate for current developmental stages induces offspring metabolic dysfunction. Overfed/obese (OB) ewes and their fetuses display elevated blood cortisol, while fetal Adrenocorticotropic hormone (ACTH) remains unchanged. We hypothesized that OB pregnancies would show increased placental 11β hydroxysteroid dehydrogenase 2 (11β-HSD2) that converts maternal cortisol to fetal cortisone as it crosses the placenta and increased 11β-HSD system components responsible for peripheral tissue cortisol production, providing a mechanism for ACTH-independent increase in circulating fetal cortisol. Control ewes ate 100% National Research Council recommendations (CON) and OB ewes ate 150% CON diet from 60 days before conception until necropsy at day 135 gestation. At necropsy, maternal jugular and umbilical venous blood, fetal liver, perirenal fat, and cotyledonary tissues were harvested. Maternal plasma cortisol and fetal cortisol and cortisone were measured. Fetal liver, perirenal fat, cotyledonary 11β-HSD1, hexose-6-phosphate dehydrogenase (H6PD), and 11β-HSD2 protein abundance were determined by Western blot. Maternal plasma cortisol, fetal plasma cortisol, and cortisone were higher in OB vs. CON (p < 0.01). 11β-HSD2 protein was greater (p < 0.05) in OB cotyledonary tissue than CON. 11β-HSD1 abundance increased (p < 0.05) in OB vs. CON fetal liver and perirenal fat. Fetal H6PD, an 11β-HSD1 cofactor, also increased (p < 0.05) in OB vs. CON perirenal fat and tended to be elevated in OB liver (p < 0.10). Our data provide evidence for increased 11β-HSD system components responsible for peripheral tissue cortisol production in fetal liver and adipose tissue, thereby providing a mechanism for an ACTH-independent increase in circulating fetal cortisol in OB fetuses.

Long acting β2-agonist's activation of cyclic AMP cannot halt ongoing mitogenic stimulation in airway smooth muscle cells

Airway smooth muscle cell (ASMC) hyperplasia causes airway wall remodelling, which is resisting to therapy. Long acting β2-agonists (LABA) relax airway muscles, but their effect on remodelling is unclear. This study compared the anti-proliferative effect of LABA in human primary ASMC, in situations where LABA were applied before, together, or after platelet derived growth factor (PDGF-BB). Cells obtained from controls (n = 5), and asthma patients (n = 5) were stimulated by PDGF-BB (10 ng/ml) before or after the application of formoterol or salmeterol. Proliferation was determined by direct cell counts over three days, cell cycle control proteins p21^(Waf1/Cip1), p27^(Kip1), signalling proteins Erk1/2 and p38 mitogen activated protein kinase (MAPK) were detected by immuno-blotting. PDGF-BB induced proliferation was significantly stronger in asthmatic ASMC versus controls. Proliferation was prevented by 30 min pre-incubation with LABA. When LABA were applied together or after PDGF-BB, their anti-proliferative effect was no longer significant. In untreated ASMC, LABA increased the expression of p21^(Waf1/Cip1) and p27^(Kip1) through cAMP, and this mechanism was abolished by the presence of PDGF-BB. The data show that the anti-proliferative effect of cAMP signalling cannot overcome the mitogenic signalling cascade once it was activated. Therefore, remodelling in asthma cannot be reduced by LABA.

Inhibition of microRNA-124-3p as a novel therapeutic strategy for the treatment of Gulf War Illness: Evaluation in a rat model

Gulf War Illness (GWI) is a chronic, multisymptom illness that continues to affect up to 30% of veterans deployed to the Persian Gulf during the 1990-1991 Gulf War. After nearly 30 years, useful treatments for GWI are lacking and underlying cellular and molecular mechanisms involved in its pathobiology remain poorly understood, although exposures to pyridostigmine bromide (PB) and pesticides are consistently identified to be among the strongest risk factors. Alleviation of the broad range of symptoms manifested in GWI, which involve the central nervous system, the neuroendocrine system, and the immune system likely requires therapies that are able to activate and inactivate a large set of orchestrated genes. Previous work in our laboratory using an established rat model of GWI identified persistent elevation of microRNA-124-3p (miR-124) levels in the hippocampus whose numerous gene targets are involved in cognition-associated pathways and neuroendocrine function. This study aimed to investigate the broad effects of miR-124 inhibition in the brain 9 months after completion of a 28-day exposure regimen of PB, DEET (N,N-diethyl-3-methylbenzamide), permethrin, and mild stress by profiling the hippocampal expression of genes known to play a critical role in synaptic plasticity, glucocorticoid signaling, and neurogenesis. We determined that intracerebroventricular infusion of a miR-124 antisense oligonucleotide (miR-124 inhibitor; 0.05-0.5 nmol/day/28 days), but not a negative control oligonucleotide, into the lateral ventricle of the brain caused increased protein expression of multiple validated miR-124 targets and increased expression of downstream target genes important for cognition and neuroendocrine signaling in the hippocampus. Off-target cardiotoxic effects were revealed in GWI rats receiving 0.1 nmol/day as indicated by the detection in plasma of 5 highly elevated protein cardiac injury markers and 6 upregulated cardiac-enriched miRNAs in plasma exosomes determined by next-generation sequencing. Results from this study suggest that in vivo inhibition of miR-124 function in the hippocampus is a promising, novel therapeutic approach to improve cognition and neuroendocrine dysfunction in GWI. Additional preclinical studies in animal models to assess feasibility and safety by developing a practical, noninvasive drug delivery system to the brain and exploring potential adverse toxicologic effects of miR-124 inhibition are warranted.

Mechanism of anti-remodelling action of treprostinil in human pulmonary arterial smooth muscle cells

Treprostinil is applied for pulmonary arterial hypertension (PAH) therapy. However, the mechanism by which the drug achieves its beneficial effects in PAH vessels is not fully understood. This study investigated the effects of treprostinil on PDGF-BB induced remodelling parameters in isolated human pulmonary arterial smooth muscle cells (PASMC) of four PAH patients. The production of TGF-β1, CTGF, collagen type-I and -IV, and of fibronectin were determined by ELISA and PCR. The role of cAMP was determined by ELISA and di-deoxyadenosine treatment. Proliferation was determined by direct cell count. Treprostinil increased cAMP levels dose and time dependently, which was not affected by PDGF-BB. Treprostinil significantly reduced PDGF-BB induced secretion of TGF-β1 and CTGF, both was counteracted when cAMP generation was blocked. Similarly, the PDGF-BB induced proliferation of PASMC was dose dependently reduced by treprostinil through signalling via cAMP—C/EBP-α p42 –p21^(WAf1/Cip1). In regards to extracellular matrix remodelling, treprostinil significantly reduced PDGF-BB—TGF-β1—CTGF induced synthesis and deposition of collagen type I and fibronectin, in a cAMP sensitive manner. In contrast, the deposition of collagen IV was not affected. The data suggest that this action of treprostinil in vessel wall remodelling may benefit patients with PAH and may reduce arterial wall remodelling.

Effects of tonic immobility and corticosterone on mitochondria metabolism in pectoralis major muscle of broiler chickens

Tonic immobility (TI), which can be divided into short (STI) or long (LTI) duration, is a trait related to fear and stress response. In a previous study, we found that in broilers that LTI phenotype and chronic corticosterone (CORT) administration caused retarded growth and lower muscle weight compared with their control counterparts. The aim of this study is to determine whether the mitochondrial DNA (mtDNA) copy number and mitochondrial oxidative phosphorylation (OXPHOS), the vital factors involved in regulating energy homeostasis, have been changed by LTI or CORT treatment. The results showed that STI broilers had higher mtDNA copy number and cytochrome c oxidase (COX) enzyme activity compared with LTI broilers. Analysis of mtDNA-encoded OXPHOS genes revealed that the mRNA expression of the COX subunit 1, 2, NADH dehydrogenase (ND) subunits 1, 3 and 6, were also increased in STI broilers compared with LTI broilers. Regarding the transcriptional regulation of mtDNA-encoded OXPHOS genes, no difference was found in the methylation of the mitochondria control region between the TI phenotypes or the CORT treatments. The PGC-1α protein level was higher in STI broilers, but the av uncoupling proteins, did not show significant difference at the protein level between TI phenotypes. These results suggest that the mitochondrial function in pectoralis major muscle of STI broilers is better than that of LTI counterparts. However, chronic CORT administration did not affect the mitochondrial metabolism, indicating the mitochondrial insensitivity to CORT treatment in pectoralis major muscle.

There goes the neighborhood: Assembly of transcriptional complexes during the regulation of metabolism and inflammation by the glucocorticoid receptor

Glucocorticoids (GCs), as ligands for the glucocorticoid receptor (GR), represent one of the most effective and frequently used classes of drugs for anti-inflammatory and immunosuppressive therapy. In addition, its role in physiological and pathophysiological processes makes the GR an important research target. The past decades have yielded a wealth of insight into the physiological and pharmacological effects of GCs. Today's era of next generation sequencing techniques is now beginning to elucidate the molecular and genomic circuits underlying GR's cell type-specific actions. This review focuses on the concepts and insights gained from recent studies in two of the most important tissues for GC action: the liver (mediating GR's metabolic effects) and macrophages (as the main target of anti-inflammatory GC therapy). We summarize results obtained from transgenic mouse models, molecular and genome-wide studies to illustrate GR's complex interactions with DNA, chromatin, co-regulators and other transcription factors. Characterizing the cell type-specific transcriptional complexes assembled around GR will pave the road for the development of new anti-inflammatory and metabolic therapies in the future.

Structural Modeling of GR Interactions with the SWI/SNF Chromatin Remodeling Complex and C/EBP

The glucocorticoid receptor (GR) is a steroid-hormone-activated transcription factor that modulates gene expression. Transcriptional regulation by the GR requires dynamic receptor binding to specific target sites located across the genome. This binding remodels the chromatin structure to allow interaction with other transcription factors. Thus, chromatin remodeling is an essential component of GR-mediated transcriptional regulation, and understanding the interactions between these molecules at the structural level provides insights into the mechanisms of how GR and chromatin remodeling cooperate to regulate gene expression. This study suggests models for the assembly of the SWI/SNF-A (SWItch/Sucrose-NonFermentable) complex and its interaction with the GR. We used the PRISM algorithm (PRotein Interactions by Structural Matching) to predict the three-dimensional complex structures of the target proteins. The structural models indicate that BAF57 and/or BAF250 mediate the interaction between the GR and the SWI/SNF-A complex, corroborating experimental data. They further suggest that a BAF60a/BAF155 and/or BAF60a/BAF170 interaction is critical for association between the core and variant subunits. Further, we model the interaction between GR and CCAAT-enhancer-binding proteins (C/EBPs), since the GR can regulate gene expression indirectly by interacting with other transcription factors like C/EBPs. We observe that GR can bind to bZip domains of the C/EBPα homodimer as both a monomer and dimer of the DNA-binding domain. In silico mutagenesis of the predicted interface residues confirm the importance of these residues in binding. In vivo analysis of the computationally suggested mutations reveals that double mutations of the leucine residues (L317D+L335D) may disrupt the interaction between GR and C/EBPα. Determination of the complex structures of the GR is of fundamental relevance to understanding its interactions and functions, since the function of a protein or a complex is dictated by its structure. In addition, it may help us estimate the effects of mutations on GR interactions and signaling.

Glucocorticoid receptor is involved in the breed-dependent transcriptional regulation of 3β-hydroxysteroid dehydrogenase in the liver of preweaning piglets

Background

Hepatic 3β-hydroxysteroid dehydrogenase (3β-HSD) plays an important role in steroid inactivation and catabolism. Serum concentrations of steroid hormones differ significantly between breeds in pigs, however the molecular mechanism regulating hepatic 3β-HSD expression in different breeds of pigs is poorly understood. In the present study, we used preweaning purebred male Large White (LW) and Erhualian (EHL) piglets as model to investigate the breed difference in the expression and regulation of 3β-HSD gene in porcine liver.

Results

The hepatic expression of 3β-HSD mRNA was significantly lower (P < 0.01) in EHL piglets compared to that in LW piglets. Significant breed differences were detected for the hepatic expression of transcription factors such as androgen receptor (AR), glucocorticoid receptor (GR), and CCAAT/enhancer binding protein β (C/EBPβ). The nucleoprotein contents of AR (P < 0.05), GR (P < 0.01) and phospho-Ser²¹¹GR (P < 0.01) were significantly higher in the liver of EHL piglets. Chromatin immunoprecipitation (ChIP) assay demonstrated significantly lower binding of GR, but not AR or C/EBPβ, to 3β-HSD gene promoter in EHL piglets (P < 0.05). GR was not detected to interact with C/EBPβ or AR in the co-immunoprecipitation analysis.

Conclusions

These results indicate that GR binding to 3β-HSD promoter is involved in the breed-dependent 3β-HSD expression in the liver of piglets.

Glucocorticoid augments lipopolysaccharide-induced activation of the IκBζ-dependent genes encoding the anti-microbial glycoproteins lipocalin 2 and pentraxin 3

Bacterial lipopolysaccharide (LPS), one of the most potent inducers of inflammation, activates the transcription factor NF-κB to induce expression of both proinflammatory mediators and anti-microbial glycoproteins such as lipocalin 2 (Lcn2) and pentraxin 3 (PTX3) in macrophages. Glucocorticoids are known to inhibit LPS-induced expression of proinflammatory cytokines via glucocorticoid receptor (GR)-mediated transrepression of NF-κB, whereas their effect on induction of anti-microbial effectors has remained to be elucidated. Here we show that the synthetic glucocorticoid dexamethasone (Dex) strongly enhances LPS-induced transcription of Lcn2 and Ptx3, although Dex by itself fails to trigger their transcription. In macrophages deficient in IκBζ (an inducible coactivator of NF-κB), Lcn2 and Ptx3 are not activated by LPS either alone or in combination with Dex. Association of GR as well as Brg1 (a subunit of the chromatin remodelling Swi/Snf complex) with a functional glucocorticoid response element in Lcn2 requires both the costimulation with LPS and the presence of IκBζ. Although Ptx3 does not contain the element, LPS induces recruitment of Dex-liganded GR to NF-κB-binding sites in regulatory regions of Ptx3, an event that does not occur in IκBζ-deficient macrophages. Thus glucocorticoids likely regulate infection-induced inflammation by increasing anti-microbial effectors in an IκBζ-dependent manner, while repressing proinflammatory genes.

Transcriptional dynamics of a conserved gene expression network associated with craniofacial divergence in Arctic charr

Background

Understanding the molecular basis of craniofacial variation can provide insights into key developmental mechanisms of adaptive changes and their role in trophic divergence and speciation. Arctic charr (Salvelinus alpinus) is a polymorphic fish species, and, in Lake Thingvallavatn in Iceland, four sympatric morphs have evolved distinct craniofacial structures. We conducted a gene expression study on candidates from a conserved gene coexpression network, focusing on the development of craniofacial elements in embryos of two contrasting Arctic charr morphotypes (benthic and limnetic).

Results

Four Arctic charr morphs were studied: one limnetic and two benthic morphs from Lake Thingvallavatn and a limnetic reference aquaculture morph. The presence of morphological differences at developmental stages before the onset of feeding was verified by morphometric analysis. Following up on our previous findings that Mmp2 and Sparc were differentially expressed between morphotypes, we identified a network of genes with conserved coexpression across diverse vertebrate species. A comparative expression study of candidates from this network in developing heads of the four Arctic charr morphs verified the coexpression relationship of these genes and revealed distinct transcriptional dynamics strongly correlated with contrasting craniofacial morphologies (benthic versus limnetic). A literature review and Gene Ontology analysis indicated that a significant proportion of the network genes play a role in extracellular matrix organization and skeletogenesis, and motif enrichment analysis of conserved noncoding regions of network candidates predicted a handful of transcription factors, including Ap1 and Ets2, as potential regulators of the gene network. The expression of Ets2 itself was also found to associate with network gene expression. Genes linked to glucocorticoid signalling were also studied, as both Mmp2 and Sparc are responsive to this pathway. Among those, several transcriptional targets and upstream regulators showed differential expression between the contrasting morphotypes. Interestingly, although selected network genes showed overlapping expression patterns in situ and no morph differences, Timp2 expression patterns differed between morphs.

Conclusion

Our comparative study of transcriptional dynamics in divergent craniofacial morphologies of Arctic charr revealed a conserved network of coexpressed genes sharing functional roles in structural morphogenesis. We also implicate transcriptional regulators of the network as targets for future functional studies.

Electronic supplementary material

The online version of this article (doi:10.1186/2041-9139-5-40) contains supplementary material, which is available to authorized users.

Fast beneficial systemic anti-inflammatory effects of inhaled budesonide and formoterol on circulating lymphocytes in asthma

BACKGROUND AND OBJECTIVE

Inhaled glucocorticoids and long acting β2 -agonists reduce airway inflammation. It is unclear if this effect is based on the local action of the drugs or is due to a systemic effect on circulating peripheral blood lymphocytes. We assessed whether inhaled budesonide and/or formoterol modify the activity of circulating peripheral blood lymphocytes.

METHODS

Placebo controlled crossover design, including healthy (n = 10) or mild asthmatic males (n = 8). Blood was collected in the morning at 08:00 before drug inhalation, and drugs (placebo, budesonide 400 μg, formoterol 12 μg) were inhaled alone or in combination at 08:30. Four more blood samples were collected after inhalation at 09:00, 09:30, 12:30 and at 09:30 am on the following day. The activity of the glucocorticoid receptor, NFκB and IκB was determined in isolated lymphocytes. Lymphocytes were stimulated with lipopolysaccharide (LPS 10 μg/mL) for 24 h and interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF)-α, eotaxin level were determined. Lymphocyte proliferation was induced by phytohaemagglutinin (PHA 10 μg/mL) over 24 h.

RESULTS

When combined, the drugs synergistically activated the glucocorticoid receptor within 30 min but did not modify NFκB or IκB activity. Inhaled budesonide significantly reduced LPS-induced IL-1β, IL-6, IL-8 and TNF-α secretion, while inhaled formoterol had no such effect; however when combined, the inhibitory effect of budesonide was significantly increased by formoterol. PHA-induced proliferation was reduced by both drugs alone and in combination.

CONCLUSIONS

Combined budesonide and formoterol may reduce airway inflammation and immune reactivity of circulating lymphocytes through its local and systemic effects.

Nuclear receptors in inflammation control: repression by GR and beyond

Inflammation is a protective response of organisms to pathogens, irritation or injury. Primary inflammatory sensors activate an array of signaling pathways that ultimately converge upon a few transcription factors such as AP1, NFκB and STATs that in turn stimulate expression of inflammatory genes to ultimately eradicate infection and repair the damage. A disturbed balance between activation and inhibition of inflammatory pathways can set the stage for chronic inflammation which is increasingly recognized as a key pathogenic component of autoimmune, metabolic, cardiovascular and neurodegenerative disorders. Nuclear receptors (NRs) are a large family of transcription factors many of which are known for their potent anti-inflammatory actions. Activated by small lipophilic ligands, NRs interact with a wide range of transcription factors, cofactors and chromatin-modifying enzymes, assembling numerous cell- and tissue-specific DNA-protein transcriptional regulatory complexes with diverse activities. Here we discuss established and emerging roles and mechanisms by which NRs and, in particular, the glucocorticoid receptor (GR) repress genes encoding cytokines, chemokines and other pro-inflammatory mediators.

Vaccination inhibits TLR2 transcription via suppression of GR nuclear translocation and binding to TLR2 promoter in porcine lung infected with Mycoplasma hyopneumoniae

Toll-like receptors (TLRs) and glucocorticoid receptor (GR) act respectively as effectors of innate immune and stress responses. The crosstalk between them is critical for the maintenance of homeostasis during the immune response. Vaccination is known to boost adaptive immunity, yet it remains elusive whether vaccination may affect GR/TLR interactions following infection. Duroc×Meishan crossbred piglets were allocated to three groups. The control group (CC) received neither vaccination nor infection; the non-vaccinated infection group (NI) was artificially infected intratracheally with Mycoplasma hyopneumoniae (M. hyopneumoniae); while the vaccinated, infected group (VI) was vaccinated intramuscularly with inactivated M. hyopneumoniae one month before infection. The clinical signs and macroscopic lung lesions were significantly reduced by vaccination. However, vaccination did not affect the concentration of M. hyopneumoniae DNA in the lung. Serum cortisol was significantly decreased in both NI and VI pigs (P<0.01), but only VI pigs demonstrated significantly diminished nuclear GR content. TLRs 1-10 were all expressed in lung, among which TLR2 was the most abundant and was significantly up-regulated (P<0.05) in NI pigs, but not in VI pigs. Accordingly, GR binding to the GR response element on TLR2 promoter was significantly increased (P<0.05) in NI pigs, but not in VI pigs. These results suggest that the inhibition of GR nuclear translocation and binding to the TLR2 promoter, which results in diminished TLR2 expression, is associated with the protective effect of vaccination on M. hyopneumoniae-induced lung lesions in the pig.

p53 cooperates with Sp1 to regulate breed-dependent expression of glucocorticoid receptor in the liver of preweaning piglets

Previous studies indicate that Chinese indigenous pig breeds demonstrate distinct pattern of glucocorticoid receptor (GR) expression, which is associated with their unique growth and metabolic phenotypes. Here we sought to unravel the transcriptional mechanisms underlying the breed-specific hepatic GR expression in preweaning Chinese Erhualian (EHL) and Western Large White (LW) piglets. Total GR mRNA and the predominant GR mRNA variant 1-9/10 were expressed significantly higher in EHL compared with LW piglets (P<0.01), which was associated with more enriched histone H3 acetylation on 1-9/10 promoter (P<0.05). Nuclear content of transcription factor specificity protein 1 (Sp1) was significantly lower in EHL piglets, yet its binding to GR 1-9/10 promoter was significantly higher in EHL piglets, as revealed by chromatin immunoprecipitation assays. Although p53 binding to GR promoter 1-9/10 did not differ between breeds, expression of p53 mRNA and protein, as well as its binding to Sp1, were significantly higher in EHL piglets. Moreover, p53 activator doxorubicin significantly enhanced GR 1-9/10 promoter activity in HepG2 cells at 100 nM, which was associated with significantly higher protein content of p53 and GR. Sp1 inhibitor, mithramycin A, significantly inhibited (P<0.05) the basal activity of GR promoter 1-9/10 and completely blocked doxorubicin -induced activation of GR promoter 1-9/10. These data indicate that higher hepatic GR expression in EHL piglets attributes mainly to the enhanced transcription of GR promoter 1-9/10, which is achieved from breed-specific interaction of p53 and Sp1 on porcine GR 1-9/10 promoter.

Exploring the transcription factor activity in high-throughput gene expression data using RLQ analysis

Background

Interpretation of gene expression microarray data in the light of external information on both columns and rows (experimental variables and gene annotations) facilitates the extraction of pertinent information hidden in these complex data. Biologists classically interpret genes of interest after retrieving functional information from a subset of genes of interest. Transcription factors play an important role in orchestrating the regulation of gene expression. Their activity can be deduced by examining the presence of putative transcription factors binding sites in the gene promoter regions.

Results

In this paper we present the multivariate statistical method RLQ which aims to analyze microarray data where additional information is available on both genes and samples. As an illustrative example, we applied RLQ methodology to analyze transcription factor activity associated with the time-course effect of steroids on the growth of primary human lung fibroblasts. RLQ could successfully predict transcription factor activity, and could integrate various other sources of external information in the main frame of the analysis. The approach was validated by means of alternative statistical methods and biological validation.

Conclusions

RLQ provides an efficient way of extracting and visualizing structures present in a gene expression dataset by directly modeling the link between experimental variables and gene annotations.

Evolutionary conservation of an atypical glucocorticoid-responsive element in the human tyrosine hydroxylase gene

The human tyrosine hydroxylase (hTH) gene has a 42 bp evolutionarily conserved region designated (CR) II at -7.24 kb, which bears 93% homology to the region we earlier identified as containing the glucocorticoid response element, a 7 bp activator protein-1 (AP-1)-like motif in the rat TH gene. We cloned this hTH-CRII region upstream of minimal basal hTH promoter in luciferase (Luc) reporter vector, and tested glucocorticoid responsiveness in human cell lines. Dexamethasone (Dex) stimulated Luc activity of hTH-CRII in HeLa cells, while mifepristone, a glucocorticoid receptor (GR) antagonist, prevented Dex stimulation. Deletion of the 7 bp 5'-TGACTAA at -7243 bp completely abolished the Dex-stimulated Luc activity of hTH-CRII construct. The AP-1 agonist, tetradeconoyl-12,13-phorbol acetate (TPA), also stimulated hTH promoter activity, and Dex and TPA together further accentuated this response. Chromatin immunoprecipitation assays revealed the presence of both GR and AP-1 proteins, especially Jun family members, at this hTH promoter site. Dex did not stimulate hTH promoter activity in a catecholaminergic cell line, which had low endogenous GR levels, but did activate the response when GR was expressed exogenously. Thus, our studies have clearly identified a glucocorticoid-responsive element in a 7 bp AP-1-like motif in the promoter region at -7.24 kb of the human TH gene.

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

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

Breed-dependent transcriptional regulation of 5'-untranslated GR (NR3C1) exon 1 mRNA variants in the liver of newborn piglets

Glucocorticoids are vital for life and regulate an array of physiological functions by binding to the ubiquitously expressed glucocorticoid receptor (GR, also known as NR3C1). Previous studies demonstrate striking breed differences in plasma cortisol levels in pigs. However, investigation into the breed-dependent GR transcriptional regulation is hampered by lacking porcine GR promoter information. In this study, we sequenced 5.3 kb upstream of the translation start codon of the porcine GR gene, and identified seven alternative 5′-untranslated exons 1–4, 1–5, 1–6, 1–7, 1–8, 1–9,10 and 1–11. Among all these mRNA variants, exons 1–4 and 1–5, as well as the total GR were expressed significantly (P<0.05) higher in the liver of newborn piglets of Large White (LW) compared with Erhualian, a Chinese indigenous breed. Overall level of CpG methylation in the region flanking exons 1–4 and 1–5 did not show breed difference. However, nuclear content of Sp1, p-CREB and GR in the liver was significantly (P<0.05) higher in LW piglets, associated with enhanced binding of p-CREB, and higher level of histone H3 acetylation in 1–4 and 1–5 promoters. In contrast, GR binding to promoters of exons 1–4 and 1–5 was significantly diminished in LW piglets, implicating the presence of negative GREs. These results indicate that the difference in the hepatic expression of GR transcript variants between two breeds of pigs is determined, at least partly, by the disparity in the binding of transcription factors and the enrichment of histone H3 acetylation to the promoters.

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.

Calreticulin is a negative regulator of bronchial smooth muscle cell proliferation

Background. Calreticulin controls the C/EBPαp42/p30 at the translational level trough a cis-regulatory CNG rich loop in the CEBPA mRNA. We determined the effects of steroids and long-acting beta-agonists on the p42/p30 ratio and on calreticulin expression in primary human bronchial smooth muscle (BSM) cells. Methods. The effects of budesonide (10(-8) M) and formoterol (10(-8) M) were studied in BSM cells pre-treated with siRNA targeting calreticulin. The expression of C/EBPα and calreticulin was determined by immuno-blotting. Automated cell counts were performed to measure proliferation. Results. All tested BSM cell lines (n = 5) expressed C/EBPα and calreticulin. In the presence of 5% FBS, the p42/p30 ratio significantly decreased (n = 3, P < 0.05) and coincided with BSM cell proliferation. High levels of calreticulin were associated with a decreased p42/p30 isoform ratio. FBS induced the expression of calreticulin (n = 3, P < 0.05), which was further increased by formoterol. siRNA targeting calreticulin increased the p42/p30 ratio in non-stimulated BSM cells and significantly inhibited the proliferation of PDGF-BB-stimulated BSM cells (n = 5, P < 0.05). Neither budesonide nor formoterol restored the p42 isoform expression. Conclusions. Our data show calreticulin is a negative regulator of C/EBPα protein expression in BSM cells. Modulation of calreticulin levels may provide a novel target to reduce BSM remodeling.

Dexamethasone-induced up-regulation of the human norepinephrine transporter involves the glucocorticoid receptor and increased binding of C/EBP-β to the proximal promoter of norepinephrine transporter

Previously, we have found glucocorticoids up-regulate norepinephrine (NE) transporter (NET) expression in vitro. However, the underlying transcriptional mechanism is poorly understood. In this study, the role of glucocorticoids on the transcriptional regulation of NET was investigated. Exposure of neuroblastoma SK-N-BE(2)M17 cells to dexamethasone (Dex) significantly increased NET mRNA and protein levels in a time- and dose-dependent manner. This effect was attenuated by glucocorticoid receptor (GR) antagonist mifepristone, suggesting that up-regulation of NET by Dex was mediated by the GR. In reporter gene assays, exposure of cells to Dex resulted in dose-dependent increases of luciferase activity that were also prevented by mifepristone. Serial deletions of the NET promoter delineated Dex-responsiveness to a -301 to -148 bp region containing a CCAAT/enhancer binding protein-β (C/EBP-β) response element. Co-immunoprecipitation experiments demonstrated that Dex treatment caused the interaction of the GR with C/EBP-β. Chromatin immunoprecipitation (ChIP) assay revealed that Dex exposure resulted in binding of both GR and C/EBP-β to the NET promoter. Further experiments showed that mutation of the C/EBP-β response element abrogated C/EBP-β- and GR-mediated transactivation of NET. These findings demonstrate that Dex-induced increase in NET expression is mediated by the GR via a non-conventional transcriptional mechanism involving interaction of C/EBP-β with a C/EBP-β response element.

Selenoprotein P regulation by the glucocorticoid receptor

Maintenance of the antioxidant activity of selenoproteins is one potential mechanism of the beneficial health effects of selenium. Selenoprotein P is the primary selenium distribution protein of the body as well as the major selenium containing protein in serum. The transcriptional regulation of selenoprotein P is of interest since the extrahepatic expression of this gene has demonstrated differentiation-dependent expression in development as well as under different disease states. SEPP1 displays patterned expression in numerous tissues during development and the loss of SEPP1 expression has been observed in malignancy. In addition, factors that influence inflammatory processes like cytokines and their regulators have been implicated in selenoprotein P transcriptional control. Herein, we identify a retinoid responsive element and describe a mechanism where the glucocorticoid receptor negatively regulates expression of selenoprotein P. Luciferase reporter assays and quantitative PCR were used to measure selenoprotein P transcription in engineered HEK-293 cells. When stimulated with ecdysone analogs, selenoprotein P expression was increased with the use of a fusion transcription factor that contains the glucocorticoid receptor DNA binding domain, an ecdysone ligand-binding domain, and a strong transactivation domain as well as the retinoid X receptor. The native glucocorticoid receptor inhibited selenoprotein P transactivation, and selenoprotein P was further attenuated in the presence of dexamethasone. Our results may provide insight into a potential mechanism by which selenium is redistributed during development, differentiation or under conditions of critical illness, where glucocorticoid levels are typically increased.

DMF inhibits PDGF-BB induced airway smooth muscle cell proliferation through induction of heme-oxygenase-1

Background

Airway wall remodelling is an important pathology of asthma. Growth factor induced airway smooth muscle cell (ASMC) proliferation is thought to be the major cause of airway wall thickening in asthma. Earlier we reported that Dimethylfumarate (DMF) inhibits platelet-derived growth factor (PDGF)-BB induced mitogen and stress activated kinase (MSK)-1 and CREB activity as well as IL-6 secretion by ASMC. In addition, DMF altered intracellular glutathione levels and thereby reduced proliferation of other cell types.

Methods

We investigated the effect of DMF on PDGF-BB induced ASMC proliferation, on mitogen activated protein kinase (MAPK) activation; and on heme oxygenase (HO)-1 expression. ASMC were pre-incubated for 1 hour with DMF and/or glutathione ethylester (GSH-OEt), SB203580, hemin, cobalt-protoporphyrin (CoPP), or siRNA specific to HO-1 before stimulation with PDGF-BB (10 ng/ml).

Results

PDGF-BB induced ASMC proliferation was inhibited in a dose-dependant manner by DMF. PDGF-BB induced the phosphorylation of ERK1/2 and p38 MAPK, but not of JNK. DMF enhanced the PDGF-BB induced phosphorylation of p38 MAPK and there by up-regulated the expression of HO-1. HO-1 induction inhibited the proliferative effect of PDGF-BB. HO-1 expression was reversed by GSH-OEt, or p38 MAPK inhibition, or HO-1 siRNA, which all reversed the anti-proliferative effect of DMF.

Conclusion

Our data indicate that DMF inhibits ASMC proliferation by reducing the intracellular GSH level with subsequent activation of p38 MAPK and induction of HO-1. Thus, DMF might reduce ASMC and airway remodelling processes in asthma.

Synergistically enhanced CYP2B6 inducibility between a polymorphic mutation in CYP2B6 promoter and pregnane X receptor activation

CYP2B6 is a highly inducible and polymorphic enzyme involved in the metabolism of an increasing number of clinically important drugs. Significant interindividual variability in CYP2B6 expression has been attributed to either genetic polymorphisms or chemical-mediated induction through the activation of constitutive androstane receptor and/or pregnane X receptor (PXR). It was reported that the -82T→C substitution within the CYP2B6*22 allele creates a functional CCAAT/enhancer-binding protein (C/EBP) binding site and enhances the basal expression of the CYP2B6 gene. Here, we explored whether this polymorphic mutation could affect drug-mediated induction of CYP2B6. Cell-based promoter reporter assays demonstrated that CYP2B6 luciferase activity was synergistically enhanced in the presence of both -82T→C mutation and rifampicin (RIF)-activated PXR. On the other hand, this synergism was attenuated by disrupting the C/EBP binding site or knocking down C/EBPα expression. Mechanistic studies revealed that C/EBPα plays an important role in such synergism by directly interacting with PXR; enhancing RIF-mediated recruitment of PXR to the -82T→C harboring CYP2B6 promoter; and looping the PXR-bound distal phenobarbital-responsive enhancer module toward the proximal C/EBP binding site. Furthermore, the genotype-phenotype association was evaluated in cultured human primary hepatocytes from 44 donors. Interestingly, RIF-mediated induction of CYP2B6 in four -82T/C carriers was higher compared with that in the reference -82T/T homozygotes. Together, our results demonstrate, for the first time, a synergistic interplay between a CYP2B6 polymorphism and PXR-mediated induction, which may contribute to the large individual variations and inducibility of CYP2B6 in humans.

Identification of an activator protein-1-like sequence as the glucocorticoid response element in the rat tyrosine hydroxylase gene

Glucocorticoids (GCs) generally stimulate gene transcription via consensus glucocorticoid response elements (GREs) located in the promoter region. To identify the GRE in the rat tyrosine hydroxylase (TH) gene promoter, we transiently transfected PC12 cells with a 9-kilobase (kb) TH promoter-luciferase (Luc) construct. Dexamethasone (Dex) stimulated Luc activity, which was abolished by mifepristone (RU486). Serial deletion mutations revealed a Dex-responsive 7-base pair (bp) sequence, TGACTAA, located at -5734 to -5728. Deletion of just these seven nucleotides from the 9-kb promoter completely abolished the Dex response and partially reduced the response to phorbol ester but not to forskolin. The Dex response was fully retained in a construct in which most of the 9-kb promoter was deleted, except for 100 bp around the -5.7-kb region, clearly identifying this 7-bp sequence as solely responsible for GC responsiveness. Conversely, deletion of the proximal cAMP-response element (-45/-38) or activator protein-1 (AP-1) (-207/-201) sites in the 9-kb promoter did not affect Dex and phorbol ester responses. A radiolabeled 25-bp promoter fragment bearing the 7-bp TH-GRE/AP-1 showed specific binding to PC12 nuclear proteins. Using antibodies against the glucocorticoid receptors and AP-1 family of proteins and primers for the TH-GRE/AP-1 region, we detected a specific DNA amplicon in a chromatin immunoprecipitation assay. This 7-bp TH-GRE/AP-1 sequence (TGACTAA) does not bear similarity to any known GRE but closely resembles the consensus AP-1 binding site, TGACTCA. Our studies describe for the first time a novel GRE/AP-1 site present in the TH gene promoter that is critical for glucocorticoid regulation of the TH gene.

The effect of asthma therapeutics on signalling and transcriptional regulation of airway smooth muscle function

SCOPE OF THE REVIEW

Our knowledge of the multifunctional nature of airway smooth muscle (ASM) has expanded rapidly in the last decade, but the underlying molecular mechanisms and how current therapies for obstructive airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD), affect these are still being elucidated. Our current knowledge has built on the pharmacology of human ASM contraction and relaxation established prior to that and which is reviewed in detail elsewhere in this issue. The advent of methods to isolate and culture ASM cells, especially human ASM cells, has made it possible to study how they may contribute to airway remodelling through their synthetic, proliferative, and migratory capacities. Now the underlying molecular mechanisms of ASM growth factor secretion, extracellular matrix (ECM) production, proliferation and migration, as well as contraction and relaxation, are being determined. A complex network of signalling pathways leading to gene transcription in ASM cells permits this functional plasticity in healthy and diseased airways. This review is an overview of the effects of current therapies, and some of those in development, on key signalling pathways and transcription factors involved in these ASM functions.

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.

Sex-specific association of the glucocorticoid receptor gene with extreme BMD

To study the role of the GR gene on BMD regulation in the Chinese, a sex-specific association study was performed. The results indicated that GR variation contributed to the extreme BMD variation in the Chinese.

INTRODUCTION

The glucocorticoid (GC) receptor (GR) gene is an important candidate gene for BMD regulation in GC-induced osteoporosis (GIO). However, no study has explored the genetic effects of the GR gene on BMD variation in the Chinese population.

MATERIALS AND METHODS

Our sample consisted of 800 unrelated subjects (400 women and 400 men) with extreme age-adjusted hip BMD Z-scores selected from a population composed of 1988 normal adult Chinese Han. Four single nucleotide polymorphisms (SNPs) in the GR gene were genotyped. Both single SNP and haplotype association analyses were conducted.

RESULTS

SNP rs1866388 (p(c) = 0.028) was found to be significantly associated with extreme BMD only in men. In both sexes, haplotypes involving rs1866388 and rs2918419 were found to have different frequency distributions in extremely low and high BMD groups (p(p) = 0.024, 0.001, and 0.002 in women and 0.002, 0.003, and 0.003 in men for window sizes of two, three, and four SNPs, respectively). Most shared haplotypes showed opposite effects between women and men.

CONCLUSIONS

For the first time, our study suggested the possible role of the GR gene on BMD regulation and sex specificity in the association of GR with extreme BMD in the Chinese.

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.

Opposite effect of corticosteroids and long-acting beta(2)-agonists on serum- and TGF-beta(1)-induced extracellular matrix deposition by primary human lung fibroblasts

Asthma and chronic obstructive pulmonary disease (COPD) are characterized by chronic airway inflammation and major structural lung tissue changes including increased extracellular matrix (ECM) deposition. Inhaled corticosteroids and long-acting beta(2)-agonists (LABA) are the basic treatment for both diseases, but their effect on airway remodeling remains unclear. In this study, we investigated the effect of corticosteroids and LABA, alone or in combination, on total ECM and collagen deposition, gene expression, cell proliferation, and IL-6, IL-8, and TGF-beta(1) levels by primary human lung fibroblasts. In our model, fibroblasts in 0.3% albumin represented a non-inflammatory condition and stimulation with 5% FCS and/or TGF-beta(1) mimicked an inflammatory environment with activation of tissue repair. FCS (5%) increased total ECM, collagen deposition, cell proliferation, and IL-6, IL-8, and TGF-beta(1) levels. In 0.3% albumin, corticosteroids reduced total ECM and collagen deposition, involving the glucocorticoid receptor (GR) and downregulation of collagen, heat shock protein 47 (Hsp47), and Fli1 mRNA expression. In 5% FCS, corticosteroids increased ECM deposition, involving upregulation of COL4A1 and CTGF mRNA expression. LABA reduced total ECM and collagen deposition under all conditions partly via the beta(2)-adrenergic receptor. In combination, the drugs had an additive effect in the presence or absence of TGF-beta(1) further decreasing ECM deposition in 0.3% albumin whereas counteracting each other in 5% FCS. These data suggest that the effect of corticosteroids, but not of LABA, on ECM deposition by fibroblasts is altered by serum. These findings imply that as soon as airway inflammation is resolved, long-term treatment with combined drugs may beneficially reduce pathological tissue remodeling.

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.

Asthma: is it due to an abnormal airway smooth muscle cell?

Asthma is an airway disease highly prevalent in westernized countries and of unknown etiology. Often, asthma is associated with atopy, but not all atopic individuals have asthma. Some patients with asthma outgrow symptoms, whereas many others acquire asthma later in life. Still other patients suffer from asthma their entire life. How can we explain these different patterns? It may be that asthma should be regarded as the clinical manifestation of a group of diseases with similar pathology due to a common factor. In this Pulmonary Perspective, we propose that an aberrant phenotype of airway smooth muscle (ASM) cells could be sufficient to explain the pathology of asthma. We will argue an abnormal ASM cell is a prerequisite to the development of asthma. Our postulate is that inadequate levels of C/EBPalpha, a protein that is pivotal for the suppression of both inflammation and proliferation responses, confer on ASM cells an activated phenotype that is more susceptible to mitogenic and contractile stimuli.

Ischemia-reperfusion of rat liver modulates hepcidin in vivo expression

The recently identified acute-phase response antimicrobial peptide hepcidin has been postulated to maintain iron homeostasis by modulating iron absorption at both the intestinal and macrophage levels. Hepcidin has also been reported to be responsible for anemia associated with chronic inflammatory diseases, and in anemia in patients with hepatic adenomas. Since Kupffer cells are known to be the primary contributor to early-phase ischemia-reperfusion injury in the liver and iron is known to modulate Kupffer cell production of proinflammatory cytokine and reactive oxygen species, we investigated hepcidin in vivo expression in the well-established rat partial-liver ischemia-reperfusion model. We found that both liver ischemia alone and liver ischemia-reperfusion significantly induced serum and liver hepcidin levels. Furthermore, currently proposed mediators of in vivo hepcidin expression, such as interleukin-6, signal transducers and activators of transcription-family transducers, and CCAAT/enhancing binding protein-alpha do not appear to modulate hepcidin expression in the liver ischemia-reperfusion acute inflammatory model. In this study we report the first in vivo evidence of liver ischemia and liver ischemia-reperfusion modulation of hepcidin expression. In conclusion, in the well-characterized liver ischemia-reperfusion model of acute inflammation, mechanism(s) other than interleukin-6 signal transduction via signal transducers and activators of transcription-3 may be responsible for hepcidin induction.

Cell targeting by a generic receptor-targeted polymer nanocontainer platform

Nanotechnology promises new avenues to medical diagnosis and treatment. Of special interest are injectable nanovehicles that are programmable towards specific targets, are able to evade the immune defense, and are versatile enough to be suited as carriers of complex functionality. Biotin-functionalized (poly(2-methyloxazoline)-b-poly(dimethylsiloxane)-b-poly(2-methyloxazoline) triblock copolymers were self-assembled to form nanocontainers, and biotinylated targeting ligands were attached by using streptavidin as a coupling agent. Specifically, fluorescence-labeled nanocontainers were targeted against the scavenger receptor A1 from macrophages, an important cell in human disease. In human and transgenic cell lines and in mixed cultures, receptor-specific binding of these generic carriers was followed by vesicular uptake. Low nonspecific binding supported the "stealth" properties of the carrier while cytotoxicity was absent. This versatile carrier appears promising for diagnostic or therapeutic medical use.

Combination therapy of long-acting beta2-adrenoceptor agonists and corticosteroids for asthma

Twice-daily combination therapy of inhaled corticosteroids and long-acting beta2-adrenoceptor agonists (LABA) is now established as a most effective treatment for moderate to severe asthma and is available in a combined single inhaler. The benefits of combination therapy include better day-to-day control and a reduction in exacerbations compared with monotherapy with inhaled corticosteroids at a lower dose. Total control of asthma, defined as no daytime or night-time symptoms, no use of rescue beta2-adrenoceptor agonists (beta2-agonists), no exacerbations and a peak flow rate of >80% predicted, may be achieved with the use of combined salmeterol/fluticasone in up to 41% of patients with moderate to severe asthma, compared with only 28% of patients treated with fluticasone alone. Adjustable maintenance dosing with budesonide/formoterol may provide better control when compared with fixed-dosing combination regimens. Other therapies combining effectively with inhaled corticosteroids include slow-release theophylline and leukotriene inhibitors, montelukast and zafirlukast, but LABA are the most efficacious. Molecular interactions between corticosteroids and beta2-adrenoceptors may underlie the clinical added benefits of combination therapy. Corticosteroids may increase the number of beta2-adrenoceptors and their coupling with Gs proteins, while beta2-agonists may induce glucocorticoid receptor nuclear translocation, activate transcription factor/enhancer binding protein C/EBPalpha together with corticosteroids, or phosphorylate corticosteroid receptors. The combination of corticosteroids and LABA potentiates inhibition of interleukin-8 and eotaxin release from human airway smooth muscle cells and granulocyte-macrophage colony-stimulating factor release from epithelial cells, and also the inhibition of airway smooth muscle cell proliferation. It is important to determine whether there is a potentiating effect of combination therapy compared with corticosteroid treatment alone on airway inflammation and airway wall remodelling. Improvements in combination therapy include a once-daily preparation and possible combination of inhaled corticosteroids with newer drugs such as phosphodiesterase IV inhibitors.

The calcium channel blocker amlodipine exerts its anti¬proliferative action via p21 (Waf1/Cip1) gene activation

Proliferation of vascular smooth muscle cells (VSMC) contributes to the progression of atherosclerotic plaques. Calcium channel blockers have been shown to reduce VSMC proliferation, but the underlying molecular mechanism remains unclear. p21(Waf1/Cip1) is a potent inhibitor of cell cycle progression. Here, we demonstrate that amlodipine (10(-6) to 10(-8) M) activates de novo synthesis of p21(Waf1/Cip1) in vitro. We show that amlodipine-dependent activation of p21(Waf1/Cip1) involves the action of the glucocorticoid receptor (GR) and C/EBP-alpha. The underlying pathway apparently involves the action of mitogen-activated protein kinase or protein kinase C, but not of extracellular signal-related kinase or changes of intracellular calcium. Amlodipine-induced p21(Waf1/Cip1) promoter activity and expression were abrogated by C/EBP-alpha antisense oligonucleotide or by the GR antagonist RU486. Amlodipine-dependent inhibition of cell proliferation was partially reversed by RU486 at 10(-8) M (58%+/-29%), antisense oligonucleotides targeting C/EBP-alpha (91%+/-26%), or antisense mRNAs targeting p21(Waf1/Cip1) (96%+/-32%, n=6); scrambled antisense oligonucleotides or those directed against C/EBP-beta were ineffective. The data suggest that the anti-proliferative action of amlodipine is achieved by induction of the p21 (Waf1/Cip1) gene, which may explain beneficial covert effects of this widely used cardiovascular therapeutic drug beyond a more limited role as a vascular relaxant.

Protein-DNA Array-based Identification of Transcription Factor Activities Regulated by Interaction with the Glucocorticoid Receptor

The glucocorticoid receptor (GR) regulates gene expression by binding specific sequence elements within the promoters of target genes or by cross-talk with other transcription factors (TFs). For some TFs, interaction with the GR results in alteration of DNA binding and transcriptional regulation. We used a protein-DNA array, a system that facilitates simultaneous profiling of the activities of multiple transcription factors, to systematically examine the potential cross-talk of GRalpha with 149 TFs. Using this array, we identified several TFs, including IRF, E47, and COUP-TF, whose DNA binding activities were modulated by GRalpha. We then confirmed these results with in vitro electrophoretic mobility shift assays and in vivo reporter assays. In this study, IRF and E47 were identified as participants in GRalpha cross-talk for the first time. This new finding expands our understanding of the functional role of GRalpha in the context of gene expression regulation.

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.

Chlamydia pneumoniae activates epithelial cell proliferation via NF-kappaB and the glucocorticoid receptor

Chlamydia pneumoniae is an obligate intracellular eubacterium and a common cause of acute and chronic respiratory tract infections. This study was designed to show the effect of C. pneumoniae on transcription factor activation in epithelial cells. The activation of transcription factors by C. pneumoniae was determined in human epithelial cell lines (HL and Calu3) by electrophoretic DNA mobility shift assay, Western blotting, and luciferase reporter gene assay. The activation of transcription factors was further confirmed by immunostaining of C. pneumoniae-infected HL cells and mock-infected controls. The effect of transcription factors on C. pneumoniae-induced host cell proliferation was assessed by [(3)H]thymidine incorporation and direct cell counting in the presence and absence of antisense oligonucleotides targeting transcription factors or the glucocorticoid receptor (GR) antagonist RU486. The activation of the GR, CCAAT-enhancer binding protein (C/EBP), and NF-kappaB was induced within 1 to 6 h by C. pneumoniae. While the interleukin-6 promoter was not activated by C. pneumoniae, the GR-driven p21((Waf1/Cip1)) promoter was increased 2.5- to 3-fold over controls 24 h after infection. C. pneumoniae dose-dependently increased the DNA synthesis of the host cells 2.5- to 2.9-fold, which was partly inhibited either by RU486 or by NF-kappaB antisense oligonucleotides. Furthermore, we provide evidence that heat-inactivated C. pneumoniae does not cause a significant increase in cell proliferation. Our results demonstrate that C. pneumoniae activates C/EBP-beta, NF-kappaB, and the GR in infected cells. However, only NF-kappaB and the GR were involved in C. pneumoniae-induced proliferation of epithelial cells.

C/EBP transcription factors in the lung epithelium

During recent years, the biological roles of CCAAT/enhancer binding proteins (C/EBPs) in the lung have started to be uncovered. C/EBPs form a family within the basic region-leucine zipper class of transcription factors. In the lung epithelium C/EBPalpha, -beta, and -delta are expressed. Lung-specific target genes for these transcription factors include the surfactant proteins A and D, the Clara cell secretory protein, and the P450 enzyme CYP2B1. As more information is gathered, a picture is emerging in which C/EBPalpha has a role in regulating proliferation as well as differentiation-dependent gene expression, whereas C/EBPbeta and -delta, in addition to a partly overlapping role in regulating expression of differentiation markers, also seem to be involved in responses to injury and hormones.

Asthma and the CCAAT-enhancer binding proteins: a holistic view on airway inflammation and remodeling

Asthma is an airway disease with increasing prevalence characterized by intermittent reversible airway obstruction, airway inflammation, and airway wall remodeling. The disease is generally triggered by inhalation of allergens, but nonallergic asthma triggers are quite common. The pathogenesis of asthma is well documented, and a great deal of research has been carried out to elucidate the underlying mechanisms. A multitude of articles have focused on cells alleged to be involved in the pathogenesis, including circulating cells from the immunologic compartment (ie, eosinophils and T lymphocytes) and resident cells, such as fibroblasts, airway smooth muscle cells, and, more recently, the airway epithelium. Despite the enormous amount of research, it is still unclear what exactly causes asthma. A general feature of most studies is an enhanced activation status of asthmatic cells, suggesting a general defect with respect to regulation of cellular responses. Here we discuss the ubiquitous transcription factor family of CCAAT-enhancer binding proteins (C/EBPs) and its involvement in inflammation and proliferation. We propose that an imbalance of C/EBP isoform expression might lead to an enhanced activity of asthmatic cells and provide an overall hypothesis that both airway inflammation and remodeling can be conceived as the result of an imbalance of C/EBP isoform expression.

Interaction between glucocorticoids and beta2 agonists on bronchial airway smooth muscle cells through synchronised cellular signalling

BACKGROUND

Increased airway smooth muscle bulk is a pathological feature of asthma. Asthma is well controlled by the combined inhalation of glucocorticoids and beta2-adrenoceptor agonists. The basic molecular mechanism of the interaction of the two drugs on proliferation of airway smooth muscle cells is yet to be identified. Our aim was to elucidate how glucocorticoids and beta2 agonists affect the growth of human bronchial airway smooth muscle cells.

METHODS

We assessed the effect of formoterol and budesonide on the activation and function of transcription factors by immunohistochemistry, western blotting, DNA mobility shift assay, and a luciferase reporter gene assay. The effect of the drugs and the involvement of specific transcription factors on cell proliferation was ascertained by direct cell count and confirmed by thymidine incorporation.

FINDINGS

Both classes of drugs (10(-8) mol/L) activated C/EBP-alpha and the glucocorticoid receptor with different kinetic profiles, and inhibited proliferation. The combination of lower doses of drugs (10(-12) to 10(-9) mol/L) resulted in a synchronised activation of the transcription factors and an enhanced antiproliferative effect. The action of the drugs alone or in combination on transcription-factor activity and proliferation was suppressed by either depletion of C/EBP-alpha or in the presence of a glucocorticoid-receptor blocker.

INTERPRETATION

Our findings could provide one explanation for the interaction of beta2 agonists and glucocorticoids at a molecular level, and indicate that the concentration of inhaled glucocorticoids can be reduced when combined with beta2 agonists, minimising the side-effects of the drugs.