C/EBPalpha and C/EBPdelta activate the clara cell secretory protein gene through interaction with two adjacent C/EBP-binding sites

The emerging roles of SUMOylation in pulmonary diseases

Small ubiquitin-like modifier mediated modification (SUMOylation) is a critical post-translational modification that has a broad spectrum of biological functions, including genome replication and repair, transcriptional regulation, protein stability, and cell cycle progression. Perturbation or deregulation of a SUMOylation and deSUMOylation status has emerged as a new pathophysiological feature of lung diseases. In this review, we highlighted the link between SUMO pathway and lung diseases, especially the sumoylated substrate such as C/EBPα in bronchopulmonary dysplasia (BDP), PPARγ in pneumonia, TFII-I in asthma, HDAC2 in chronic obstructive pulmonary disease (COPD), KLF15 in hypoxic pulmonary hypertension (HPH), SMAD3 in idiopathic pulmonary fibrosis (IPF), and YTHDF2 in cancer. By exploring the impact of SUMOylation in pulmonary diseases, we intend to shed light on its potential to inspire the development of innovative diagnostic and therapeutic strategies, holding promise for improving patient outcomes and overall respiratory health.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

Grass Carp Prolactin Gene: Structural Characterization and Signal Transduction for PACAP-induced Prolactin Promoter Activity

In this study, structural analysis of grass carp prolactin (PRL) gene was performed and the signaling mechanisms for pituitary adenylate cyclase-activating peptide (PACAP) regulation of PRL promoter activity were investigated. In αT3-1 cells, PRL promoter activity could be induced by oPACAP₃₈ which was blocked by PACAP antagonist but not the VIP antagonist. The stimulatory effect of oPACAP₃₈ was mimicked by activation of AC/cAMP and voltage-sensitive Ca²⁺ channel (VSCC) signaling, or induction of Ca²⁺ entry. In parallel, PACAP-induced PRL promoter activity was negated or inhibited by suppressing cAMP production, inhibiting PKA activity, removal of extracellular Ca²⁺, VSCC blockade, calmodulin (CaM) antagonism, and inactivation of CaM kinase II. Similar sensitivity to L-type VSCC, CaM and CaM kinase II inhibition were also observed by substituting cAMP analog for oPACAP₃₈ as the stimulant for PRL promoter activity. Moreover, PACAP-induced PRL promoter activity was also blocked by inhibition of PLC signaling, attenuation of [Ca²⁺]i immobilization via IP3 receptors, and blockade of PI3K/P₇₀^S6K pathway. The PACAP-induced PRL promoter activation may involve transactivation of the transcription factor CREB. These results suggest that PACAP can stimulate PRL promoter activation by PAC1 mediated functional coupling of the Ca²⁺/CaM/CaM kinase II cascades with the AC/cAMP/PKA pathway. Apparently, other signaling pathways, including PLC/IP3 and PI3K/P₇₀^S6K cascades, may also be involved in PACAP induction of PRL gene transcription.

The role of C/EBPβ phosphorylation in modulating membrane phospholipids repairing in LPS-induced human lung/bronchial epithelial cells

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a common critical emergency with high mortality in clinical practice. The key mechanism of ALI/ARDS is that the excessive inflammatory response damages the integrity of alveolar and bronchial cell membrane and thus affects their basic function. Phospholipids are the main component of cell membranes. Phospholipase A2 (PLA2), which catalyzes the cleavage of membrane phospholipids, is the most important inflammatory mediator of ALI. However, clara cell secretory protein 1 (CCSP1), an endogenous PLA2 inhibitor can increase the self-defense of membrane phospholipids. Thus, CCSP1 up-regulation and PLA2 inhibition constitutes an effective method for ensuring the stability of membrane phospholipids and for the treatment of ALI/ARDS. In the present study, we developed an in vitro model of ALI via lipopolysaccharide (LPS) stimulation of a human bronchial epithelial cell line, BEAS-2B, and assessed the mRNA and protein levels of CCSP1 and PLA2 in the model cells. The results demonstrated LPS induction inhibited the transcription and protein expression of CCSP1, but only the protein level of membrane associated PLA2 was increased, suggesting that in the in vitro ALI model, abnormally regulated CCSP1 transcription plays a crucial role in the damage of cell membrane. To find out the reason that CCSP1 expression was decreased in the ALI model, we predicted, by means of bioinformatics, putative transcription factors which would bind to CCSP1 promoter, examined their background and expression, and found that a transcription factor, CCAAT/enhancer binding protein β (C/EBP β), was correlated with the transcription of CCSP1 in the in vitro ALI model, and its phosphorylation in the model was decreased. CHIP-PCR and luciferase reporter assay revealed that C/EBP β bound to CCSP1 promoter and facilitated its transcription. Therefore, we conclude that there is a C/EBP β/CCSP1/PLA2 pathway in the in vitro ALI model. The study of underlying mechanism show that the activity of C/EBP β depends on its phosphorylation:LPS stimulation reduced C/EBP β phosphorylation and suppressed the transcription of CCSP1 in BEAS-2B cells, which resulted in enhanced PLA2 and the consequent membrane damage. And further study shows that overexpression of CDK2(Cyclindependent kinase 2), promoted the phosphorylation of C/EBP β and inhibited PLA2 through the C/EBP β/CCSP1/PLA2 pathway, so as to attenuate membrane damage. The significance of this study lies in that artificial C/EBP β phosphorylation regulation may ease the membrane damage in ALI and improve membrane repair.

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CDK2 over-expression promotes C/EBPβ phosphorylation and improves membrane repair through C/EBPβ/CCSP/PLA2 pathway in ALI.

Airway epithelial cell differentiation during lung organogenesis requires C/EBPα and C/EBPβ

BACKGROUND

CCAAT/enhancer-binding protein (C/EBP)α is crucial for lung development and differentiation of the pulmonary epithelium. Conversely, no lung defects have been observed in C/EBPβ-deficient mice, although C/EBPβ trans-activate pulmonary genes by binding to virtually identical DNA-sequences as C/EBPα. Thus, the pulmonary phenotype of mice lacking C/EBPβ could be explained by functional replacement with C/EBPα. We investigated whether C/EBPα and C/EBPβ have overlapping functions in regulating lung epithelial differentiation during organogenesis. Epithelial differentiation was assessed in mice with a lung epithelial-specific (SFTPC-Cre-mediated) deletion of C/EBPα (Cebpa(ΔLE) ), C/EBPβ (Cebpb(ΔLE) ), or both genes (Cebpa(ΔLE) ; Cebpb(ΔLE) ).

RESULTS

Both Cebpa(ΔLE) mice and Cebpa(ΔLE) ; Cebpb(ΔLE) mice demonstrated severe pulmonary immaturity compared to wild-type littermates, while no differences in lung histology or epithelial differentiation were observed in Cebpb(ΔLE) mice. In contrast to Cebpa(ΔLE) mice, Cebpa(ΔLE) ; Cebpb(ΔLE) mice also displayed undifferentiated Clara cells with markedly impaired protein and mRNA expression of Clara cell secretory protein (SCGB1A1), compared to wild-type littermates. In addition, ectopic mucus-producing cells were observed in the conducting airways of Cebpa(ΔLE) ; Cebpb(ΔLE) mice.

CONCLUSIONS

Our findings demonstrate that C/EBPα and C/EBPβ play pivotal, and partly overlapping roles in determining airway epithelial differentiation, with possible implications for tissue regeneration in lung homeostasis and disease.

FOXA1 plays a role in regulating secretoglobin 1a1 expression in the absence of CCAAT/enhancer binding protein activities in lung in vivo

Secretoglobin (SCGB) 1A1, also called Clara cell secretor protein (CCSP) or Clara cell-specific 10-kDa protein (CC10), is a small molecular weight secreted protein mainly expressed in lung, with anti-inflammatory/immunomodulatory properties. Previous in vitro studies demonstrated that CCAAT/enhancer-binding proteins (C/EBPs) are the major transcription factors for the regulation of Scbg1a1 gene expression, whereas FOXA1 had a minimum effect on the transcription. To determine the in vivo role of C/EBPs in the regulation of SCGB1A1 expression, experiments were performed in which A-C/EBP, a dominant-negative form of C/EBP that interferes with DNA binding activities of all C/EBPs, was specifically expressed in lung. Surprisingly, despite the in vitro findings, expression of SCGB1A1 mRNA was not decreased in vivo in the absence of C/EBPs. This may be due to a compensatory role assumed by FOXA1 in the regulation of Scgb1a1 gene expression in lung in the absence of active C/EBPs. This disconnect between in vitro and in vivo results underscores the importance of studies using animal models to determine the role of specific transcription factors in the regulation of gene expression in intact multicellular complex organs such as lung.

JUN-CCAAT/enhancer-binding protein complexes inhibit surfactant-associated protein B promoter activity

The murine surfactant-associated protein B (Sftpb) gene promoter, spanning nucleotides -653 to +42, is composed of functionally distinct proximal and distal regions. Although both regions contain consensus/putative activator protein 1 (AP-1) sites, the distal, but not the proximal, region mediates the inhibition by jun proto-oncogene (JUN) of Sftpb promoter activity. In transient cotransfection assays, JUN inhibited the luciferase reporter activity of plasmid constructs containing Sftpb promoter fragments that lacked the distal putative AP-1 site, indicating that another regulatory motif mediates JUN-dependent inhibition. Electrophoretic mobility shift assays and in silico analyses identified a DNA target sequence (Sftpb nucleotides -339 to -316) and transcription factors that regulate Sftpb promoter activity. The identified sequence contains a CCAAT/enhancer-binding protein (C/EBP) consensus recognition element. Mutation of the site reduced Sftpb promoter activity and sensitivity to inhibition by JUN. Purified recombinant JUN, which did not recognize the -339 to -316 target sequence when added alone, supershifted the mobility of in vitro translated C/EBP-α and C/EBP-β proteins complexed with the identified cis-regulatory element. These findings support the idea that heterodimerization between JUN and C/EBP-α and/or C/EBP-β targets JUN to the Sftpb promoter, thereby mediating its inhibitory regulatory role.

DNER modulates adipogenesis of human adipose tissue-derived mesenchymal stem cells via regulation of cell proliferation

OBJECTIVES

In recent years, obesity has become a global epidemic, highlighting the necessity for basic research into mechanisms underlying growth of adipose tissue and differentiation of stem cells into adipocytes, in humans. For better understanding of cell signalling in adipogenesis, the role of DNER (delta/Notch-like EGF-related receptor) in adipogenic differentiation of human adipose tissue-derived mesenchymal stem cells (hAMSC) was investigated.

MATERIALS AND METHODS

To assess the role of DNER in hAMSC adipogenesis, hAMSCs were transfected with DNER small interfering RNA (siDNER). Real-time quantitative reverse transcriptase polymerase chain reactions to assess expression levels of adipogenesis-related genes regulated by siDNER, cell cycle and immunoblot analyses were performed.

RESULTS

First, it was determined that DNER mRNA was profoundly expressed in hAMSCs and reduced during adipogenic differentiation. Knockdown of DNER altered cell morphology, inhibited proliferation and increased frequency and efficiency of adipogenesis in hAMSC. Expression of CCAAT/enhancer-binding protein delta increased and proportion of cells in S phase decreased by knockdown of DNER, using specific siRNA. Moreover, adipocyte-specific genes including peroxisome proliferator-activated receptor gamma, fatty acid binding protein 4 and perilipin were up-regulated in siDNER compared to the siControl group during adipogenesis in hAMSC.

CONCLUSIONS

These results indicate that DNER knockdown in hAMSC accelerated onset of adipogenic differentiation by bypassing mitotic clonal expansion during the early stages of adipogenesis.

Lung-specific inactivation of CCAAT/enhancer binding protein alpha causes a pathological pattern characteristic of COPD

The link between respiratory complications in prematurely born infants and susceptibility for developing chronic obstructive pulmonary disease (COPD) is receiving increasing attention. We have previously found that CCAAT/enhancer binding protein (C/EBP) activity in airway epithelial cells of COPD patients is decreased compared to healthy smokers, suggesting a previously unknown role for C/EBPs in COPD pathogenesis. To investigate the role of the transcription factor C/EBPalpha in lung development and its potential role in COPD, mice with a lung epithelial-specific disruption of the C/EBPalpha gene (Cebpa(DeltaLE)) were generated using Cre-mediated excision, and the resulting pathology was studied during development and into adulthood. Cebpa(DeltaLE) mice exhibit impaired lung development and epithelial differentiation, as well as affected vascularity. Furthermore, Cebpa(DeltaLE) mice that survive until adulthood develop a severe pathological picture with irregular emphysema; bronchiolitis, including goblet cell hyperplasia, bronchiolar metaplasia, fibrosis and mucus plugging; and an inflammatory cell and gene expression profile similar to COPD. Cebpa(DeltaLE) mice display lung immaturity during development, and adult Cebpa(DeltaLE) mice develop a majority of the histopathological and inflammatory characteristics of COPD. Cebpa(DeltaLE) mice could thus provide new valuable insights into understanding the long-term consequences of lung immaturity and the link to susceptibility of developing COPD.

Arylhydrocarbon receptor activation in NCI-H441 cells and C57BL/6 mice: possible mechanisms for lung dysfunction

The arylhydrocarbon receptor (AhR) is known for its ability to bind aromatic-containing compounds, which starts a molecular cascade involving the induction of cytochrome P450s and inflammatory cytokines. Our hypothesis is that many inhaled environmental toxicant components activate these inflammatory pathways via an initial binding to the AhR. To test this possibility, we treated Clara cell-derived NCI-H441 cells with the AhR agonist, 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD), and demonstrated that AhR activation increased the expression of both cytochrome P450 s and inflammatory markers. We also found increased mucin 5AC production with TCDD treatment. Similar results were observed in NCI-H441 cells treated with urban dust particles. Mucin 5AC expression was highly correlated with increased-expression cyclooxygenase-2 and IL-1beta, thus implicating these two inflammatory markers as possible conduits for AhR-mediated mucin production. We hypothesize that this increase in mucin 5AC production is a result of inflammation-induced differentiation of our epithelial cell to a mucin-producing cell. This theory is supported by morphological changes observed in the cells, as well as decreased expression of Clara cell secretory protein (CC10). In an in vivo C57BL/6 mouse model, TCDD increased expression of inflammatory cytokines, mucin 5AC, and a number of matrix metalloproteases in whole-lung samples. These changes were not seen in mice in which AhR signaling was repressed. These markers from the whole-lung samples have been correlated to onset of bronchitis, asthma, small airways disease, and fibrosis, and their increased expression further implicates AhR activation in producing the molecular environment for the development of lung injury to occur.

Dysregulation of the C/EBPalpha differentiation pathway in human cancer

While much is known about aberrant pathways affecting cell growth and apoptosis, our understanding of another critical step of neoplastic transformation, differentiation arrest, remains poor. The differentiation-inducing transcription factor CCAAT enhancer binding protein alpha (C/EBPalpha) is required for proper control of adipogenesis, glucose metabolism, granulocytic differentiation, and lung development. Studies investigating the function of this protein in hematopoietic malignancies as well as in lung and skin cancer have revealed numerous ways how tumor cells abrogate C/EBPalpha function. Genetic and global expression analysis of acute myeloid leukemia (AML) cases identifies C/EBPalpha-deficient AML as a separate entity yielding novel classification schemes. In patients with a dysfunctional C/EBPalpha pathway, targeted therapies may overcome the block in differentiation, and in combination with conventional chemotherapy, may lead to complete eradication of the malignant clone. Overall, a better understanding of the mechanisms of how C/EBPalpha dysregulation participates in the neoplastic process has opened new gateways for differentiation biology research.

CAATT/enhancer-binding proteins alpha and delta interact with NKX2-1 to synergistically activate mouse secretoglobin 3A2 gene expression

Secretoglobin (SCGB) 3A2 is a small molecular weight secreted protein predominantly expressed in lung airways. We previously demonstrated that the expression of SCGB3A2 is regulated by homeodomain transcription factor NKX2-1. Here we show that CCAAT/enhancer-binding proteins, C/EBPalpha and C/EBPdelta, regulate mouse Scgb3a2 gene transcription in vivo and in vitro by binding to specific sites located in the Scgb3a2 promoter and the activity is synergistically enhanced through cooperative interaction with NKX2-1. Six C/EBP binding sites lie within 500 bp of the Scgb3a2 gene promoter, of which two sites, located at -44 to -54 bp and -192 to -201 bp, appear to be critical for the synergistic activation of Scgb3a2 gene transcription with NKX2-1. All three transcription factors, C/EBPalpha, C/EBPdelta, and NKX2-1, are expressed in the epithelial cells of airways, particularly the bronchus, where high expression of SCGB3A2 is found. The expression of these transcription factors markedly increases toward the end of gestation, which coincides with the marked increase of SCGB3A2, suggesting the importance of C/EBPalpha and C/EBPdelta, and their synergistic interaction with NKX2-1 in mouse Scgb3a2 gene transcription and lung development.

The Cebpd (C/EBPdelta) gene is induced by luteinizing hormones in ovarian theca and interstitial cells but is not essential for mouse ovary function

The CCAAT/enhancer binding protein (CEBP) family of transcription factors includes five genes. In the ovary, both Cebpa and Cebpb are essential for granulosa cell function. In this study we have explored the role of the Cebpd gene in ovarian physiology by expression and functional studies. Here we report that Cebpd (C/EBPdelta) is expressed in the mouse ovary in a highly restricted temporal and spatial pattern. In response to luteinizing hormone (LH/hCG), CEBPD expression is transiently induced in interstitial cells and in theca cells of follicles from the primary to pre-ovulatory stage, and overlaps in part with expression of the alpha-smooth muscle actin protein. Efficient down-regulation of CEBPD was dependent on a functional Cebpb gene. Proliferating human theca cells in culture also express Cebpd. Cells from patients with polycystic ovarian syndrome (PCOS) exhibited higher Cebpd expression levels. However, deletion of Cebpd in mice had no overt effect on ovarian physiology and reproductive function. Very little is known at present about the molecular mechanisms underlying theca/interstitial cell functions. The expression pattern of CEBPD reported here identifies a novel functional unit of mouse theca cells of primary through tertiary follicles responding to LH/hCG together with a subset of interstitial cells. This acute stimulation of CEBPD expression may be exploited to further characterize the hormonal regulation and function of theca and interstitial cells.

CCAAT/enhancer binding protein-alpha is down-regulated by toll-like receptor agonists in microglial cells

The transcription factor CCAAT/enhancer binding protein-alpha (C/EBPalpha) can regulate the expression of important genes in the inflammatory response, but little is known about its role in glial activation. By using primary cortical murine glial cultures, we show that C/EBPalpha is expressed by microglial cells in vitro. Lipopolysaccharide (LPS) down-regulates C/EBPalpha mRNA at 2 hr and all C/EBPalpha protein isoforms at 4 hr. This effect is elicited by LPS concentrations >/=100 pg/ml. LPS-induced C/EBPalpha down-regulation occurs in microglial cells both in mixed glial and in microglial-enriched cultures. As seen with LPS, other toll-like receptor agonists (polyinosinic-polycytidylic acid, peptidoglycan from Staphylococcus aureus, and the oligonucleotide CpG1668) also down-regulate C/EBPalpha whereas cytokines such as interleukin-1beta, interleukin-6, macrophage-colony stimulating factor, and interferon-gamma do not. These findings suggest that C/EBPalpha down-regulation in activated microglia could play an important role in the increased expression of genes that are potentially pathogenic in a variety of neurological disorders.

Regulation of Clara cell secretory protein gene expression by the CCAAT-binding factor NF-Y

Analysis of the transcriptional regulation of the Clara cell secretory protein (CCSP) gene has resulted in the characterization of several trans-acting factors that regulate the activity of this gene. However, little is known about negative regulatory elements involved in CCSP gene transcription. Using transient transfections of luciferase reporter constructs driven by various fragments of the Neotomodon CCSP (nCCSP) promoter, we identified an inhibitory region that contains an inverted CCAAT box located -225 to -221 bp upstream of the transcriptional start site. Sequence analysis in a broad region of the nCCSP promoter (-744/+33) identified another potentially important CCAAT motif (-459/-455). Gel shift and supershift assays indicated that the transcription factor NF-Y binds to both CCAAT boxes. Mutation of the CCAAT motif prevented the in vitro binding of NF-Y and led to a significant increase of CCSP promoter activity in both pulmonary (H441) and non-pulmonary (HeLa and MCF-7) cells, suggesting that NF-Y is involved in a negative transcriptional regulation that may potentially contribute to the highly cell-specific expression of the anti-inflammatory CCSP gene.

The C/EBPdelta tumor suppressor is silenced by hypermethylation in acute myeloid leukemia

Aberrant DNA methylation is the most frequent molecular alteration in acute myeloid leukemia (AML). To identify methylation-silenced genes in AML, we performed microarray analyses in U937 cells exposed to the demethylating agent 5-aza-deoxy-cytidine. Overall, 274 transcripts were significantly induced. Interestingly, C/EBPdelta expression was significantly induced (more than 10-fold) by demethylation whereas expression of all other C/EBP family members remained unchanged. The C/EBPdelta promoter was strongly methylated in different leukemic cell lines and showed signs of a repressed chromatin state. Analyses of the promoter regions of the entire C/EBP family (alpha, beta, gamma, delta, epsilon, zeta) in bone marrow samples from AML patients (n = 80) and controls (n = 15) by mass spectrometry revealed that C/EBPdelta is the most commonly hypermethylated C/EBP gene in AML. Hypermethylation occurred in more than 35% of AML patients at primary diagnosis. A significant correlation (P = .016) was observed between hypermethylation of the C/EBPdelta promoter and low expression of C/EBPdelta in AML patients. C/EBPdelta promoter activity was strongly repressed by methylation in vitro, and transcriptional repression partially depended on MeCP2 activity. C/EBPdelta exhibited growth-inhibitory properties in primary progenitor cells as well as in Flt3-ITD-transformed cells. Taken together, C/EBPdelta is a novel tumor suppressor gene in AML that is silenced by promoter methylation.

Transcriptional Regulation of Human CYP2A13 Expression in the Respiratory Tract by CCAAT/Enhancer Binding Protein and Epigenetic Modulation

CYP2A13, which is highly active in the metabolic activation of tobacco-specific nitrosamines, is selectively expressed in the respiratory tract, in which it is believed to play an important role in chemical carcinogenesis. The aim of this study was to determine the basis for tissue-specific regulation of CYP2A13 gene expression. We have shown that expression of CYP2A3, the rat homolog of CYP2A13, is regulated by nuclear factor I (NFI) in a tissue-specific manner. In the present study, we found that the transcriptional regulation of human CYP2A13 gene involves CCAAT/enhancer binding protein (C/EBP) transcription factors instead of NFI. DNase I footprinting and gel-shift assays with human lung nuclear extract identified two DNA elements bound by C/EBP. Reporter gene assays using a 216-base pair CYP2A13 promoter fragment confirmed the activation of CYP2A13 by transfected C/EBP factors, and results from chromatin immunoprecipitation assays indicated that C/EBP is associated with CYP2A13 promoter in vivo in the olfactory mucosa of CYP2A13-transgenic mice. In NCI-H441 human lung cancer cells, we discovered that CYP2A13 expression can be induced by a combined treatment with 5-aza-2'-deoxycytosine, a DNA demethylation agent, and trichostatin, a histone deacetylation inhibitor. In 5-aza-2'-deoxycytosine/trichostatin-treated NCI-H441 cells, overexpression of C/EBPdelta, a lung-enriched C/EBP, led to additional increases in CYP2A13 expression, whereas C/EBPdelta knockdown by small interference RNA suppressed CYP2A13 expression, findings that confirm a role for C/EBP in CYP2A13 regulation. Our findings pave the way for further studies of the regulation of the CYP2A13 gene, particularly the gene's potential suppression by airway inflammation, and the role of epigenetic modulation in the gene's tissue-selective expression.

Ectopic expression of C/EBPalpha in the lung epithelium disrupts late lung development

The lung develops from the endoderm through a process of branching morphogenesis. This process is highly active during the pseudoglandular stage of lung development and continues into the canalicular stage, resulting in the formation of terminal sacs. CCAAT/enhancer binding proteins (C/EBPs) are transcription factors regulating central aspects of differentiation and proliferation. We report here the developmental expression of C/EBPalpha, -beta, and -delta in the lung. C/EBPalpha exhibits a dynamic expression pattern and is first detected during the late pseudoglandular stage. At this stage, expression is observed in a subset of epithelial cells in the distal parts of the branching tubules. The expression of C/EBPalpha is confined to nonproliferating cells. To examine the role of C/EBPalpha in lung development, we generated transgenic mice ectopically expressing C/EBPalpha in the lung epithelium using the human surfactant protein C promoter. Lungs from these mice were of normal size but exhibited a phenotype characterized by fewer and larger developing epithelial tubules, indicating that the branching process was affected. No effects on overall proliferation or cellular differentiation were observed. When this phenotype was compared with that of mice carrying a targeted mutation of the Cebpa gene, the Cebpa-/- mice exhibited a similar developmental phenotype. In conclusion, our results show a role for C/EBPalpha in lung development and suggest a function in the later stages of lung branching morphogenesis.

Respiratory failure due to differentiation arrest and expansion of alveolar cells following lung-specific loss of the transcription factor C/EBPalpha in mice

The leucine zipper family transcription factor CCAAT enhancer binding protein alpha (C/EBPalpha) inhibits proliferation and promotes differentiation in various cell types. In this study, we show, using a lung-specific conditional mouse model of C/EBPalpha deletion, that loss of C/EBPalpha in the respiratory epithelium leads to respiratory failure at birth due to an arrest in the type II alveolar cell differentiation program. This differentiation arrest results in the lack of type I alveolar cells and differentiated surfactant-secreting type II alveolar cells. In addition to showing a block in type II cell differentiation, the neonatal lungs display increased numbers of proliferating cells and decreased numbers of apoptotic cells, leading to epithelial expansion and loss of airspace. Consistent with the phenotype observed, genes associated with alveolar maturation, survival, and proliferation were differentially expressed. Taken together, these results identify C/EBPalpha as a master regulator of airway epithelial maturation and suggest that the loss of C/EBPalpha could also be an important event in the multistep process of lung tumorigenesis. Furthermore, this study indicates that exploring the C/EBPalpha pathway might have therapeutic benefits for patients with respiratory distress syndromes.

In vivo and in vitro analysis of factor binding sites in Jaagsiekte sheep retrovirus long terminal repeat enhancer sequences: roles of HNF-3, NF-I, and C/EBP for activity in lung epithelial cells

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma, a contagious lung cancer of sheep that arises from type II pneumocytes and Clara cells of the lung epithelium. Studies of the tropism of this virus have been hindered by the lack of an efficient system for viral replication in tissue culture. To map regulatory regions important for transcriptional activation, an in vivo footprinting method that couples dimethyl sulfate treatment and ligation-mediated PCR was performed in murine type II pneumocyte-derived MLE-15 cells infected with a chimeric Moloney murine leukemia virus driven by the JSRV enhancers (DeltaMo+JS Mo-MuLV). In vivo footprints were found in the JSRV enhancers in two regions previously shown to be important for JSRV long terminal repeat (LTR) activity: a binding site for the lung-specific transcription factor HNF-3beta and an E-box element in the distal enhancer adjacent to an NF-kappaB-like binding site. In addition, in vivo footprints were detected in two downstream motifs likely to bind C/EBP and NF-I. Mutational analysis of a JSRV LTR reporter construct (pJS21luc) revealed that the C/EBP binding site is critical for LTR activity, while the putative NF-I binding element is less important; elimination of these sites resulted in 70% and 40% drops in LTR activity, respectively. Electrophoretic mobility shift assays using nuclear extracts from MLE-15 murine Clara cell-derived mtCC1-2 cells with probes corresponding to the NF-I or C/EBP sites revealed several complexes. Antiserum directed against NF-IA, C/EBPalpha, or C/EBPbeta supershifted the corresponding protein-DNA complexes, indicating that these isoforms, which are also important for the expression of several cellular lung-specific genes, may be important for JSRV expression in lung epithelial cells.

C/EBPdelta is a crucial regulator of pro-apoptotic gene expression during mammary gland involution

The STAT3 transcription factor is an important initiator of mammary gland involution in the mouse. This work shows that the STAT3 target gene CCAAT/enhancer binding protein delta (C/EBPdelta) is a crucial mediator of pro-apoptotic gene expression events in mammary epithelial cells. In the absence of C/EBPdelta, involution is delayed, the pro-apoptotic genes encoding p53, BAK, IGFBP5 and SGP2/clusterin are not activated, while the anti-apoptotic genes coding for BFL1 and Cyclin D1 are not repressed. Consequently, p53 targets such as survivin, BRCA1, BRCA2 and BAX are not regulated appropriately and protease activation is delayed. Furthermore, expression of MMP3 and C/EBPdelta during the second phase of involution is perturbed in the absence of C/EBPdelta. In HC11 cells, C/EBPdelta alone is sufficient to induce IGFBP5 and SGP2. It also suppresses Cyclin D1 expression and cooperates with p53 to elicit apoptosis. This study places C/EBPdelta between STAT3 and several pro- and anti-apoptotic genes promoting the physiological cell death response in epithelial cells at the onset of mammary gland involution.

Glucocorticoids increase C/EBPbeta activity in the lung epithelium via phosphorylation

Glucocorticoids are widely prescribed anti-inflammatory drugs used for the treatment of many inflammatory lung disorders. However, much still remains unknown about their molecular mechanisms of action. We have previously shown that glucocorticoid-induced transcription in the lung epithelial cell line NCI-H441 is mediated via C/EBP sites in the promoters of target genes, and is likely to involve the transcription factors C/EBPbeta and C/EBPdelta. Here, we report that C/EBPbeta is the most active C/EBP-factor in both human and mouse lung epithelium and that glucocorticoids induce DNA binding of C/EBPbeta in cultured primary mouse lung epithelial cells. Mechanistic studies in H441 cells revealed that glucocorticoids, acting via the glucocorticoid receptor, increase C/EBPbeta binding starting 10 min after stimulation. The mechanism is independent of de novo protein synthesis and involves phosphorylation of C/EBPbeta at Thr(235). Together this shows that glucocorticoids increase DNA-binding activity of C/EBPbeta via post-translational mechanism(s) involving phosphorylation.

C/EBPdelta is a downstream mediator of IL-6 induced growth inhibition of prostate cancer cells

BACKGROUND

Although a number of reports have investigated the effects of IL-6 family cytokines on prostate cell growth, there is limited information available identifying IL-6 inducible downstream effector genes and their function in growth control. Previous studies have demonstrated that IL-6 treatment results in the activation of signal transducer and activator of transcription3 (STAT3) in prostate cancer cells. The goal of this study was to investigate the influence of IL-6 treatment and activation of the Jak/STAT signal transduction pathway on C/EBPdelta gene expression and growth inhibition of human prostate cancer cells.

METHODS

Expression of C/EBPdelta and STAT3 activation were assayed using Northern and Western blotting techniques. Proliferation was assessed by [(3)H] thymidine incorporation, flow cytometry, and colony formation analyses. The analysis of the transcriptional regulation of C/EBPdelta was performed using luciferase-reporter constructs.

RESULTS

In this report, we demonstrate that IL-6 treatment induces STAT3 activation (pSTAT3), pSTAT3 binds to the human C/EBPdelta gene promoter and induces its expression. We also demonstrate that C/EBPdelta over-expression is capable of suppressing prostate cancer cell growth.

CONCLUSIONS

These results demonstrate that C/EBPdelta gene expression is increased in IL-6 treated LNCaP cells. Increased C/EBPdelta gene expression plays an important role in IL-6/STAT3 mediated growth arrest of LNCaP prostate cancer cells. Ongoing studies are investigating the mechanism by which C/EBPdelta controls prostate cancer cell growth and the potential role of C/EBPdelta in the survival and chemo resistance of prostate cancer metastasis. (c) 2004 Wiley-Liss, Inc.

Hochachka's "Hypoxia Defense Strategies" and the development of the pathway for oxygen

Hochachka's "Hypoxia Defense Strategies" identify oxygen signalling, metabolic arrest, channel arrest and coordinated suppression of ATP turnover rates as key factors that determine the ability of organisms to survive exposure to chronic hypoxia. In this review, I assess the developmental role played by these phenomena in the morphogenesis of the gas exchange tissues that define the pathway for oxygen transport to cytochrome c oxidase. Key areas of regulation lie in: (I) the suppression of fetal mitochondrial oxidative function in hand with mitochondrial biogenesis (metabolic arrest), (II) the role of hypoxia-driven oxygen signalling pathways in directing the scope of non-differentiated stem cell proliferation in placenta and lung development and (III) the regulation of epithelial fluid secretion/absorption in the lung through the oxygen-dependent modulation of Na+ conductance pathways. The identification of developmental roles for Hochachka's "Hypoxia Defense Strategies" in directing the morphogenesis of gas exchange structures bears with it the implication that these strategies are fundamental to establishing the scope for aerobic metabolic performance throughout life.

Redox regulation of lung development and perinatal lung epithelial function

Throughout gestation, low oxygen tensions are a dominant feature of the fetal environment and so may be important in sustaining a normal pattern of lung morphogenesis until the moment of birth. As breathing begins, the equilibration of the lung lumen to postnatal PO2 evokes a series of physiologic and morphogenic maturation events that are partially reversible by hypoxia. In this review, we discuss the experimental evidence that fetal and perinatal oxygen tensions differently influence lung morphogenesis through oxygen- and redox-responsive signaling pathways and identify five loci at which this regulation may occur: (I) proliferation of undifferentiated lung mesenchyme as governed by hypoxia-regulated transcription factors (HIF-1alpha, C/EBPbeta); (II) transient production of reactive oxygen species (ROS) and nuclear oxidation of the perinatal lung epithelium; (III) nuclear transport and oxidation of thioredoxin in hand with the acute activation of nuclear factor- kappaB (NF-kappaB); (IV) ROS-evoked chronic rise in intracellular glutathione and thioredoxin redox buffering capacity; and (V) NF-kappaB-dependent increase in transepithelial Na+ transport and lung lumenal fluid clearance. Although not exhaustive, this analysis leads us to the conclusion that redox events that occur in the lung during gestation, parturition, and the early neonatal period may dramatically influence the expression of genes and physiological events that are crucial to the successful transition from fetal to postnatal lung maturation.

cDNA sequence, 5′-flanking region, and promoter activity of the Neotomodon alstoni alstoni Clara cell secretory protein gene

To better understand the phylogenetic divergence and the species-specific characteristics of the Clara cell secretory protein (CCSP), we cloned the cDNA encoding the neotomodon CCSP (nCCSP) and analyzed its tissue-specific expression. The full-length cDNA is 451bp long and predicts an amino acid sequence of 93 residues. Northern blot analysis from different neotomodon tissues demonstrated that the mRNA of CCSP appears to be solely expressed in the lung. To study the transcriptional regulation of the CCSP gene, we cloned the 5'-flanking region of the nCCSP gene and compared its features with those previously reported for the hamster gene. The neotomodon and hamster genes share 89% sequence homology in their promoter region as well as a number of conserved cis-acting elements. However, in H441 cells the expression of a reporter gene driven by the nCCSP promoter was about 4-fold greater than its hamster counterpart. Functional analysis of progressive 5'-deletion mutants identified a region involved in the higher transcriptional activity of the neotomodon promoter.

Loss of CCAAT/enhancer binding protein delta promotes chromosomal instability

The transcription factor CCAAT/enhancer binding protein delta (Cebpd, also known as C/EBPdelta, CRP3, CELF, NF-IL6beta) is implicated in diverse cellular functions such as the acute phase response, adipocyte differentiation, learning and memory, and mammary epithelial cell growth control. Here, we report that lack of Cebpd causes genomic instability and centrosome amplifications in primary embryonic fibroblasts derived from 129S1 mice. Upon spontaneous immortalization, Cebpd-deficient fibroblasts acquire transformed features such as impaired contact inhibition and reduced serum dependence. These data identify a novel role for Cebpd in the maintenance of chromosomal stability and suggest a potential tumor suppressor function in vivo.

Thymulin evokes IL-6-C/EBPbeta regenerative repair and TNF-alpha silencing during endotoxin exposure in fetal lung explants

Chorioamnionitis is associated with increased risks of perinatal respiratory failure; however, components of the inflammatory acute-phase response are known to actively promote lung maturation. To manipulate this relationship, we examined the effect of the thymic immunomodulator thymulin on fetal lung mesenchyme-epithelial differentiation during exposure to Escherichia coli lipopolysaccharide (LPS). Gestation day 14 fetal rat lung explants were cultured for 96 h at fetal (23 mmHg) or ambient (142 mmHg) Po(2). Airway surface complexity (ASC, perimeter/ radical area(2)) was greater at fetal vs. ambient Po(2); however, exposure to 0.1-50 microg/ml LPS significantly raised ASC at 2 microg/ml in ambient Po(2) explants. LPS (50 microg/ml) depressed ASC in both conditions to untreated ambient Po(2) control values without changes in necrosis or apoptosis. To manipulate LPS-evoked TNF-alpha and IL-6 release, we exposed explants and A549 cells to combinations of 50 microg/ml LPS, 10 microM ZnCl(2), and 0.1-1,000 ng/ml thymulin at either Po(2). Thymulin+Zn(2+) suppressed and potentiated LPS-evoked TNF-alpha and IL-6 release, yielding an IC(50(TNF-alpha)) of 0.5 +/- 0.01 ng/ml and EC(50(IL-6)) of 1.4 +/- 0.3 ng/ml in A549 cells. This was accompanied by activation of the p38 MAPKMAPKAP-K2 pathway with sustained expression of TNF-alpha and IL-6 transcripts at ambient Po(2). LPS+thymulin+Zn(2+)-treated explants showed proliferation of CCAAT-enhancer binding protein-beta (C/EBPbeta) and fibroblast growth factor-9 immunoreactive mesenchyme, which was abolished by IL-6 antisense oligonucleotides. The posttranscriptional suppression of immunogenic TNF-alpha synthesis coupled with raised IL-6 and C/EBPbeta-dependent mesenchyme proliferation suggests a role for bioactive thymulin in regulating regenerative repair in the fetal lung.

Regulation of postnatal lung development and homeostasis by estrogen receptor beta

Estrogens have well-documented effects on lung development and physiology. However, the classical estrogen receptor alpha (ERalpha) is undetectable in the lung, and this has left many unanswered questions about the mechanism of estrogen action in this organ. Here we show, both in vivo and in vitro, that ERbeta is abundantly expressed and biologically active in the lung. Comparisons of lungs from wild-type mice and mice with an inactivated ERbeta gene (ERbeta(-/-)) revealed decreased numbers of alveoli in adult female ERbeta(-/-) mice and findings suggesting deficient alveolar formation as well as evidence of surfactant accumulation. Platelet-derived growth factor A (PDGF-A) and granulocyte-macrophage colony-stimulating factor (GM-CSF), key regulators of alveolar formation and surfactant homeostasis, respectively, were decreased in lungs of adult female ERbeta(-/-) mice, and direct transcriptional regulation of these genes by ERbeta was demonstrated. This suggests that estrogens act via ERbeta in the lung to modify PDGF-A and GM-CSF expression. These results provide a potential molecular mechanism for the gender differences in alveolar structure observed in the adult lung and establish ERbeta as a previously unknown regulator of postnatal lung development and homeostasis.

Lipopolysaccharide induces CYP2E1 in astrocytes through MAP kinase kinase-3 and C/EBPbeta and -delta

Cytochrome P450 2E1 (CYP2E1) is highly inducible in a subset of astrocytes in vivo following ischemic or mechanical injury and in vitro by lipopolysaccharide (LPS) or interleukin-1beta. We have studied the mechanism of induction, and found that transcriptional activation of CYP2E1 occurred within 3 h, and CYP2E1 dependent catalytic activity was induced more than 4-fold within 5 h. The induction was sensitive to several tyrosine kinase inhibitors, and was further modulated by inhibitors of p38 MAP kinase. MAP kinase kinase-3 (MKK3) was phosphorylated in response to LPS, and expression of constitutively active MKK3, but not the MAP kinase kinases MEKK1 or MKK1, activated CYP2E1. Transcriptional activation was mediated through a C/EBPbeta and -delta binding element situated at -486/-474, and appeared to involve activation of prebound factors as well as recruitment of newly synthesized C/EBPbeta and -delta. It is thus suggested that LPS induces MKK3 activation in astrocytes, which in turn stimulates a C/EBPbeta and -delta binding element to mediate transcriptional activation of CYP2E1.

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.

Multiple mechanisms for oxygen-induced regulation of the Clara cell secretory protein gene

The Clara cell secretory protein (CCSP) imparts a protective effect to the lung during oxidant injury. However, exposure to supplemental oxygen, a common therapeutic modality for lung disease, represses the expression of CCSP in the adult mouse lung. We investigated the mechanisms of hyperoxia-induced repression of the mouse CCSP promoter. Deletion experiments in vivo and in vitro indicated that the hyperoxia-responsive elements are localized to the proximal -166 bp of the CCSP promoter. Electrophoretic mobility shift and supershift analyses demonstrated increased binding of c-Jun at the activator protein-1 site, increased binding of CCAAT/enhancer binding protein (C/EBP) beta at the C/EBP sites, and decreased binding at the Nkx2.1 sites. Western analyses revealed that hyperoxia exposure induced an increase in the expression of the C/EBPbeta isoform liver-inhibiting protein (LIP) and an increase in cytoplasmic Nkx2.1. Cotransfection of LIP or c-Jun expression plasmids decreased the transcriptional activity of the proximal -166-bp CCSP promoter. These observations suggest that hyperoxia-induced repression of the CCSP gene is mediated, at least in part, at the level of transcription and that multiple mechanisms mediate this repression. Moreover, these novel observations may provide insights for generation of therapeutic interventions for the amelioration of oxidant-induced lung injury.

Organic dust activates NF-kappaB in lung epithelial cells

Exposure in swine confinement facilities induces airway inflammation in healthy subjects. The aim of the present study was to elucidate the role of nuclear factor (NF)-kappaB in the inflammatory response induced by organic dust. A human lung epithelial carcinoma cell line (A549) was transfected with reporter genes of the human IL-6 promoter or the NF-kappaB binding site fused to the luciferase reporter gene and stimulated with dust from a swine confinement building. Cytokine release in cell culture supernatants and luciferase activity was measured. The dust-induced the activities of the IL-6 promoter reporter gene and the NF-kappaB reporter gene in parallel with an increase in IL-6 and IL-8 release. The addition of pyrrolidinedithiocarbamate, a chemical NF-kappaB blocking agent, inhibited IL-6 and IL-8 secretion as well as the NF-kappaB reporter gene activity. Increasing the amount of IkappaB alpha led to inhibition of organic dust-induced IL-6 promoter and NF-kappaB reporter gene activities. Fluticasone inhibited the organic dust-induced NF-kappaB activation and IL-6 and IL-8 secretion. Finally, swine dust incubation of A549 cells resulted in a NF-kappaB DNA binding, which is composed of the NF-kappaB1 and RelA proteins. In conclusion, by interference at various levels we have shown that NF-kappaB plays a key role in the inflammatory response to organic dust.

Characterization of the human lung CYP2F1 gene and identification of a novel lung-specific binding motif

The CYP2F1 gene encodes a cytochrome P450 enzyme capable of bioactivating a number of pulmonary-selective toxicants. The expression of CYP2F1 is highly tissue-selective; the highest expression is observed in the lung with little or no hepatic expression. The objective of these studies was to elucidate the mechanisms that govern the unique tissue-specific regulation of CYP2F1. Cosmid and bacterial artificial chromosome clones were screened and sequenced to identify a gene that spanned 14 kbp containing 10 exons, including an untranslated exon 1. Primer extension analysis and 5'-rapid amplification of cDNA ends were used to identify the transcription start site. Several sequences homologous to known cis-elements were identified in the 5'-upstream region of the CYP2F1 promoter. Transient transfection studies with luciferase reporter constructs demonstrated a significant functional lung cell-specific CYP2F1 promoter region (from position -129 to +115). DNase footprinting analysis of 1.6 kbp of the upstream sequence with nuclear extracts from human lung tissues revealed one strong DNA-protein complex at -152 to -182. This nuclear protein (called lung-specific factor, LSF) was present only in lung but not liver or heart tissues. Competitive electrophoretic mobility shift assays characterized a DNA consensus site, within the LSF-binding domain, that was highly similar to two E box motifs, but no known "E box" trans-factors were identified. These studies identified a novel LSF and its consensus sequence that may control tissue-specific expression of CYP2F1.

5-lipoxygenase-activating protein gene expression. Key role of CCAAT/enhancer-binding proteins (C/EBP) in constitutive and tumor necrosis factor (TNF) alpha-induced expression in THP-1 cells

We examined expression of the 5-lipoxygenase activating protein (FLAP), which is critical for inflammatory cell leukotriene synthesis. A 3.4-kb segment of the FLAP gene 5'-untranslated region accounted for a 22-fold increase in promoter activity when transfected into the monocyte-like cell line, THP-1, and demonstrated no activity in non-inflammatory cells. Virtually all of the promoter activity was mediated by the first 134 bp upstream of the transcription start site, a region that contains CCAAT/enhancer-binding proteins (C/EBP) consensus binding sites, at -36 to -28 bp (distal) and -25 to -12 bp (proximal). DNase I footprint analyses demonstrated THP-1 nuclear extract proteins bind to the proximal site. Electrophoretic mobility shift assay analyses revealed that C/EBP alpha, delta, and epsilon bind to the proximal site and C/EBP alpha and epsilon bind to the distal site, constitutively. Transfection studies indicated that mutation of both the proximal and distal sites decreased constitutive FLAP promoter activity. Overexpression of C/EBP alpha, beta, and delta transactivated promoter activity and increased native FLAP mRNA accumulation. Mutation of both C/EBP sites essentially abolished promoter induction by C/EBP overexpression. Tumor necrosis factor (TNF) alpha induced FLAP mRNA expression, FLAP promoter activity, and C/EBP alpha, delta, and epsilon binding to the proximal and distal promoter consensus sites. Chromatin immunoprecipitation assays demonstrated that C/EBP alpha, delta, and epsilon bound to this region of the 5'-untranslated region, whereas C/EBP beta does not bind even under conditions of overexpression and stimulation. We conclude that the FLAP gene is transactivated by members of the C/EBP family of transcription factors in inflammatory cells and that these factors play an important role in FLAP gene induction by TNFalpha.

Evidence that peroxisome proliferator-activated receptor delta influences cholesterol metabolism in men

OBJECTIVE

The objective of this work was to explore the role of peroxisome proliferator-activated receptor delta (PPARD) in lipid metabolism in humans.

METHODS AND RESULTS

PPARD is a nuclear receptor involved in lipid metabolism in primates and mice. We screened the 5'-region of the human gene for polymorphisms to be used as tools in association studies. Four polymorphisms were detected: -409C/T in the promoter region, +73C/T in exon 1, +255A/G in exon 3, and +294T/C in exon 4. The frequencies of the rare alleles were 4.2%, 4.2%, 1.2% and 15.6%, respectively, in a population-based group of 543 healthy men. Only the +294T/C polymorphism showed significant association with a metabolic trait. Homozygotes for the rare C allele had a higher plasma LDL-cholesterol concentration than homozygotes for the common T allele, which was verified in an independent cohort consisting of 282 healthy men. Transfection studies showed that the rare C allele had higher transcriptional activity than the common T allele. Electrophoretic mobility shift assays demonstrated that the +294T/C polymorphism influenced binding of Sp-1. An interaction with the PPAR alpha L162V polymorphism was also detected for several lipid parameters.

CONCLUSIONS

These findings suggest that PPARD plays a role in cholesterol metabolism in humans.

Transcriptional regulation of CCSP by interferon-gamma in vitro and in vivo

Interferon gamma (IFN-gamma), a potent cytokine inducing a wide range of immunologic activities, is increased in the airway secondary to viral infection or during an inflammatory response. This increase in IFN-gamma concentration may alter the expression of specific airway epithelial cell genes that regulate adaptation of airway inflammatory responses. One protein induced by IFN-gamma is Clara cell secretory protein (CCSP), which may contribute to the attenuation of airway inflammation. This study was done to investigate the molecular mechanism by which IFN-gamma stimulates the expression of the CCSP gene in mouse transformed Clara cells and transgenic mice. Deletion mapping and linker-scanning mutations demonstrated that IFN-gamma-induced expression of CCSP was regulated, in part, at the level of transcription. In vitro and in vivo studies verified that the minimal IFN-gamma-responsive segment was localized to the proximal 166 bp of the 5'-flanking region. Additionally, IFN-gamma-induced expression of CCSP was mediated indirectly through an interferon regulatory factor-1-mediated increase in hepatocyte nuclear factor-3beta.

Role and regulation of activator protein-1 in toxicant-induced responses of the lung

Aberrant cell proliferation and differentiation after toxic injury to airway epithelium can lead to the development of various lung diseases including cancer. The activator protein-1 (AP-1) transcription factor, composed of mainly Jun-Jun and Jun-Fos protein dimers, acts as an environmental biosensor to various external toxic stimuli and regulates gene expression involved in various biological processes. Gene disruption studies indicate that the AP-1 family members c-jun, junB, and fra1 are essential for embryonic development, whereas junD, c-fos, and fosB are required for normal postnatal growth. However, broad or target-specific transgenic overexpression of the some of these proteins gives very distinct phenotype(s), including tumor formation. This implies that, although they are required for normal cellular processes, their abnormal activation after toxic injury can lead to the pathogenesis of the lung disease. Consistent with this view, various environmental toxicants and carcinogens differentially regulate Jun and Fos expression in cells of the lung both in vivo and in vitro. Moreover, Jun and Fos proteins distinctly bind to the promoter regions of a wide variety of genes to differentially regulate their expression in epithelial injury, repair, and differentiation. Importantly, lung tumors induced by various carcinogens display a sustained expression of certain AP-1 family members. Therefore a better understanding of the mechanisms of regulation and functional role(s), as well as identification of target genes of members of the AP-1 family in airway epithelial cells, will provide additional insight into toxicant-induced lung diseases. These studies might offer a unique opportunity to use AP-1 family members and transactivation as potential diagnostic markers or drug targets for early detection and/or prevention of various lung diseases.

Synergistic transactivation of the differentiation-dependent lung gene Clara cell secretory protein (secretoglobin 1a1) by the basic region leucine zipper factor CCAAT/enhancer-binding protein alpha and the homeodomain factor Nkx2.1/thyroid transcription factor-1

The basic region-leucine zipper transcription factor CCAAT/enhancer-binding protein alpha (C/EBPalpha) and the homeodomain transcription factor Nkx2.1/thyroid transcription factor-1 are essential for normal lung morphogenesis. Nkx2.1 is expressed from the onset of lung development, whereas C/EBPalpha expression is turned on at later stages. The expression of C/EBPalpha correlates to the appearance of lung-specific proteins with differentiation-dependent expression patterns, such as the Clara cell secretory protein (secretoglobin 1a1 (Scgb1a1), CCSP). In this study, we demonstrate synergistic transactivation by C/EBPalpha and Nkx2.1 in the regulation of the CCSP gene. We show that the synergistic activity of C/EBPalpha and Nkx2.1 originates from cis-acting elements in the proximal promoter of CCSP and that the synergism is dependent on NH(2)-terminal transactivation domains of C/EBPalpha and Nkx2.1. Our results suggest that the cooperation of C/EBPalpha and Nkx2.1 is a major determinant for the high level, lung epithelial-specific expression of CCSP during the later stages of lung development and in the adult lung.

Mesenchymal-epithelial interactions in lung development and repair: are modeling and remodeling the same process?

We propose that lung morphogenesis and repair are characterized by complex cell-cell interactions of endodermal and mesodermal origin, leading to (or returning back to) an alveolar structure that can effectively exchange gases between the circulation and the alveolar space. We provide the developmental basis for cell/molecular control of lung development and disease, what is known about growth and transcription factors in normal and abnormal lung development, and how endodermal and mesodermal cell origins interact during lung development and disease. The global mechanisms that mediate mesenchymal-epithelial interactions and the plasticity of mesenchymal cells in normal lung development and remodeling provide a functional genomic model that may bring these concepts closer together. We present a synopsis followed by a vertical integration of the developmental and injury/repair mechanisms.

CCAAT/enhancer-binding proteins: structure, function and regulation

CCAAT/enhancer binding proteins (C/EBPs) are a family of transcription factors that all contain a highly conserved, basic-leucine zipper domain at the C-terminus that is involved in dimerization and DNA binding. At least six members of the family have been isolated and characterized to date (C/EBP alpha[bond]C/EBP zeta), with further diversity produced by the generation of different sized polypeptides, predominantly by differential use of translation initiation sites, and extensive protein-protein interactions both within the family and with other transcription factors. The function of the C/EBPs has recently been investigated by a number of approaches, including studies on mice that lack specific members, and has identified pivotal roles of the family in the control of cellular proliferation and differentiation, metabolism, inflammation and numerous other responses, particularly in hepatocytes, adipocytes and haematopoietic cells. The expression of the C/EBPs is regulated at multiple levels during several physiological and pathophysiological conditions through the action of a range of factors, including hormones, mitogens, cytokines, nutrients and certain toxins. The mechanisms through which the C/EBP members are regulated during such conditions have also been the focus of several recent studies and have revealed an immense complexity with the potential existence of cell/tissue- and species-specific differences. This review deals with the structure, biological function and the regulation of the C/EBP family.

Surfactant protein D gene regulation. Interactions among the conserved CCAAT/enhancer-binding protein elements

Surfactant protein D (SP-D) plays roles in pulmonary host defense and surfactant homeostasis and is increased following acute lung injury. Given the importance of CCAAT/enhancer-binding protein (C/EBP)-binding elements in the systemic acute-phase response and lung development and the expression of C/EBP isoforms by lung epithelial cells, we hypothesized that conserved C/EBP motifs in the near-distal and proximal promoters contribute to the regulation of SP-D expression by C/EBPs. Five SP-D motifs (-432, -340, -319, -140, and -90) homologous to the C/EBP consensus sequence specifically bound to C/EBPs in gel shift assays, and four of the five sites (-432, -340, -319, and -90) efficiently competed for the binding of C/EBPalpha, C/EBPbeta, or C/EBPdelta to consensus oligomers. Cotransfection of C/EBPalpha, C/EBPbeta, or C/EBPdelta cDNA in H441 lung adenocarcinoma cells significantly increased the luciferase activity of a wild-type SP-D promoter construct containing 698 bp of upstream sequence (SS698). Transfection of C/EBP also increased the level of endogenous SP-D mRNA in H441 cells. Transactivation of the reporter construct was abrogated by deletion of sequences upstream of -205. Independent site-directed mutagenesis of the sites at -432, -340, and -319 reduced C/EBP-mediated activation by approximately 50%, and mutagenesis of the site at -432 in combination with either of the tandem sites at -340 and -319 blocked activation. The conserved AP-1 element at -109 was required for maximal promoter activity, but not for the transactivation of SS698 by C/EBPs. Thus, interactions among C/EBP elements in the near-distal promoter can modulate the promoter activity of SP-D.

Different regulation of the LXRalpha promoter activity by isoforms of CCAAT/enhancer-binding proteins

LXRs have recently been shown to regulate key enzymes in cholesterol degradation, reverse transport of cholesterol from peripheral cells, cholesterol uptake and lipogenesis. The LXRalpha promoter was thus studied to investigate if LXRalpha gene expression is under the regulation of transcription factors involved in adipogenesis. We report that the C/EBP transcription factor interacts with the promoter of the LXRalpha gene. In in vitro footprinting experiments, protein extracts from several tissues gave footprints covering a putative C/EBP recognition site. Transfection experiments and EMSA showed a direct effect of these transcription factors on the LXRalpha promoter. C/EBPalpha upregulated expression of the reporter gene in an NIH 3T3-L1 preadipocyte cell line, while C/EBPbeta and C/EBPdelta had no effect. In liver hepatoma Fao II and Cos-7 kidney cells, both C/EBPalpha and C/EBPbeta downregulated expression of the reporter gene while C/EBPdelta induced activity, indicating that the functional consequences of C/EBP isoform interactions with the LXRalpha promoter are dependent on the cellular context. Monitoring of the LXR mRNA levels during adipose tissue differentiation showed that LXRbeta is constitutively expressed during the entire differentiation process while LXRalpha is induced upon addition of differentiation mix.

Glucocorticoids regulate the CCSP and CYP2B1 promoters via C/EBPbeta and delta in lung cells

Glucocorticoids have several important roles in the lung and play a key role in lung development and maturation. However, the specific molecular mechanisms of glucocorticoid action in lung are unclear. In this study, we have investigated two glucocorticoid-regulated genes expressed in the lung epithelium, the secretory protein CCSP, and the P450-enzyme CYP2B1. In transient transfections of lung epithelial cells, glucocorticoids increased expression from the CCSP and CYP2B1 promoters and we demonstrated that induction was dependent on the integrity of C/EBP-binding sites in both promoters. Electrophoretic mobility shift assays revealed increased DNA-binding of C/EBPbeta and C/EBPdelta after glucocorticoid treatment, which was not correlated to altered protein levels. The results of this study indicate a previously unknown role for C/EBP transcription factors in glucocorticoid signaling in the lung epithelium.

Regulation of the Clara cell secretory protein/uteroglobin promoter in lung

Clara cell secretory protein/uteroglobin (CCSP/UG) is specifically expressed in the conducting airway epithelium of the lung in a differentiation-dependent manner. The proximal promoter region of the rodent CCSP/UG gene directs Clara cell specificity. Previously, it was shown that the forkhead transcription factors HNF-3 alpha and beta and the homeodomain factor TTF-1 are important transcription factors acting through this region, suggesting that they contribute to cell specificity of the CCSP/UG gene. Members of the C/EBP family of transcription factors can also interact with elements of the proximal rat and mouse CCSP/UG promoters. The onset of C/EBP alpha expression in Clara cells correlates with the strong increase of CCSP/UG expression. Thus, C/EBP alpha may play a crucial role for differentiation-dependent CCSP/UG expression. Transfection studies demonstrate that C/EBP alpha and TTF-1 can synergistically activate the murine CCSP/UG promoter. Altogether, these results suggest that C/EBP alpha, TTF-1, and HNF-3 determine the Clara cell-specific, differentiation-dependent expression of the CCSP/UG gene in murine lung. The relative importance of these three transcription factors, however, differs in rabbits and humans.