Regulation of CCSP (PCB-BP/uteroglobin) expression in primary cultures of lung cells: involvement of C/EBP

Functional roles of C/EBPα and SUMO‑modification in lung development

CCAAT enhancer binding protein alpha (C/EBPα) is a transcription factor regulating the core aspects of cell growth and differentiation. The present study investigated the level and functional role of C/EBPα during the development of the rat lung. C/EBPα protein exhibits a dynamic expression pattern. The correlation between the expression of C/EBPα protein and the content of glycogen during lung maturation was analyzed to understand the function of C/EBPα in lung differentiation. The high expression of C/EBPα coincides with the reduction of glycogen in the fetal lung. In addition, the authors identified that changes in the level of C/EBPα are associated with the secretion of pulmonary surfactant. C/EBPα is modified by small ubiquitin-related modifier (SUMO) post-translationally. The results of double immunofluorescence staining and immunoprecipitation demonstrated that SUMO-modified C/EBPα was present in the lung. The sumoylated C/EBPα gradually decreased during lung differentiation and was negatively correlated with pulmonary surfactant secretion, thereby suggesting that the SUMO modification may participate in C/EBPα-mediated lung growth and differentiation. These results indicated that C/EBPα played a role in lung development and provided the insight into the mechanism underlying SUMO-modification.

Club Cell Protein 16 (CC16) Augmentation: A Potential Disease-modifying Approach for Chronic Obstructive Pulmonary Disease (COPD)

INTRODUCTION

Club cell protein 16 (CC16) is the most abundant protein in bronchoalveolar lavage fluid. CC16 has anti-inflammatory properties in smoke-exposed lungs, and chronic obstructive pulmonary disease (COPD) is associated with CC16 deficiency. Herein, we explored whether CC16 is a therapeutic target for COPD.

AREAS COVERED

We reviewed the literature on the factors that regulate airway CC16 expression, its biologic functions and its protective activities in smoke-exposed lungs using PUBMED searches. We generated hypotheses on the mechanisms by which CC16 limits COPD development, and discuss its potential as a new therapeutic approach for COPD.

EXPERT OPINION

CC16 plasma and lung levels are reduced in smokers without airflow obstruction and COPD patients. In COPD patients, airway CC16 expression is inversely correlated with severity of airflow obstruction. CC16 deficiency increases smoke-induced lung pathologies in mice by its effects on epithelial cells, leukocytes, and fibroblasts. Experimental augmentation of CC16 levels using recombinant CC16 in cell culture systems, plasmid and adenoviral-mediated over-expression of CC16 in epithelial cells or smoke-exposed murine airways reduces inflammation and cellular injury. Additional studies are necessary to assess the efficacy of therapies aimed at restoring airway CC16 levels as a new disease-modifying therapy for COPD patients.

Recombinant rat CC16 protein inhibits LPS-induced MMP-9 expression via NF-κB pathway in rat tracheal epithelial cells

Clara cell protein (CC16) is a well-known anti-inflammatory protein secreted by the epithelial Clara cells of the airways. It is involved in the development of airway inflammatory diseases such as chronic obstructive pulmonary disease and asthma. Previous studies suggest that CC16 gene transfer suppresses expression of interleukin (IL)-8 in bronchial epithelial cells. However, its role in the function of these cells during inflammation is not well understood. In this study, we evaluated the effect of CC16 on the expression of matrix metalloproteinase (MMP)-9 in lipopolysaccharide (LPS)-stimulated rat tracheal epithelial cells and its underlying molecular mechanisms. We generated recombinant rat CC16 protein (rCC16) which was bioactive in inhibiting the activity of phospholipase A2. rCC16 inhibited LPS-induced MMP-9 expression at both mRNA and protein levels in a concentration-dependent (0-2 µg/mL) manner, as demonstrated by real time RT-PCR, ELISA, and zymography assays. Gene transcription and DNA binding studies demonstrated that rCC16 suppressed LPS-induced NF-κB activation and its binding of gene promoters as identified by luciferase reporter and gel mobility shift assays, respectively. Western blotting and immunofluorescence staining analyses further revealed that rCC16 concentration dependently inhibited the effects of LPS on nuclear increase and cytosol reduction of NF-κB, on the phosphorylation and reduction of NF-κB inhibitory IκBα, and on p38 MAPK-dependent NF-κB activation by phosphorylation at Ser276 of its p65 subunit. These data indicate that inhibition of LPS-mediated NF-κB activation by rCC16 involves both translocation- and phosphorylation-dependent signaling pathways. When the tracheal epithelial cells were pretreated with chlorpromazine, an inhibitor of clathrin-mediated endocytosis, cellular uptake of rCC16 and its inhibition of LPS-induced NF-κB nuclear translocation and also MMP-9 production were significantly abolished. Taken together, our data suggest that clathrin-mediated uptake of rCC16 suppresses LPS-mediated inflammatory MMP-9 production through inactivation of NF-κB and p38 MAPK pathways in tracheal epithelial cells.

CCAAT/enhancer binding protein-α regulates the protease/antiprotease balance required for bronchiolar epithelium regeneration

Many transcription factors that regulate lung morphogenesis during development are reactivated to mediate repairs of the injured adult lung. We hypothesized that CCAAT/enhancer binding protein-α (C/EBPα), a transcription factor critical for perinatal lung maturation, regulates genes required for the normal repair of the bronchiolar epithelium after injury. Transgenic Cebpα(Δ/Δ) mice, in which Cebpa was conditionally deleted from Clara cells and Type II cells after birth, were used in this study. Airway injury was induced in mice by the intraperitoneal administration of naphthalene to ablate bronchiolar epithelial cells. Although the deletion of C/EBPα did not influence lung structure and function under unstressed conditions, C/EBPα was required for the normal repair of terminal bronchiolar epithelium after naphthalene injury. To identify cellular processes that are influenced by C/EBPα during repair, mRNA microarray was performed on terminal bronchiolar epithelial cells isolated by laser-capture microdissection. Normal repair of the terminal bronchiolar epithelium was highly associated with the mRNAs regulating antiprotease activities, and their induction required C/EBPα. The defective deposition of fibronectin in Cebpα(Δ/Δ) mice was associated with increased protease activity and delayed differentiation of FoxJ1-expressing ciliated cells. The fibronectin and ciliated cells were restored by the intratracheal treatment of Cebpα(Δ/Δ) mice with the serine protease inhibitor. In conclusion, C/EBPα regulates the expression of serine protease inhibitors that are required for the normal increase of fibronectin and the restoration of ciliated cells after injury. Treatment with serine protease inhibitor may aid in the recovery of injured bronchiolar epithelial cells, and prevent common chronic lung diseases.

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.

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.

Eosinophilic Inclusions in Rat Clara Cells and the Effect of an Inhaled Corticosteroid

Large eosinophilic cytoplasmic inclusions (ECIs) are occasionally seen in untreated rat Clara cells. Following inhalation exposure to a corticosteroid, the number of ECIs was increased. This is the first histopathological description of rat ECIs and attempted characterization by immunohistochemistry, in situ hybridization, and electron microscopy. ECIs were strongly positive for surfactant protein D (SP-D) and weakly positive for Clara cell specific protein (CCSP). Clara cell cytoplasm was positive for CCSP mRNA regardless of ECIs, but not within ECIs. Corticosteroid treatment and ECI presence did not affect the immunohistochemistry and in situ hybridization staining intensities. Electron microscopy revealed large intracytoplasmic granules with an irregular limiting membrane. The ECI number was microscopically quantified in rats from three-, six-, and twenty-four-month studies. The mean ECI counts in treated rats increased from three- to fifty-four-fold with a positive dose-related trend, when compared with vehicle controls. Although the mechanism is unclear, SP-D and to a lesser extent CCSP accumulate in the ECIs. As human bronchial epithelium does not appear to contain structures analogous to the ECI, it is suggested that the observation of an increased number of ECIs in the treated rats is not likely to be relevant for human clinical risk assessment.

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.

C/EBPalpha: a tumour suppressor in multiple tissues?

The CCATT/enhancer binding protein alpha, C/EBPalpha, is a key transcription factor involved in late differentiation events of several cell types. Besides acting as a classical transcription factor, C/EBPalpha is also a well-characterized inhibitor of mitotic growth in most cell lines tested. In line with its anti-mitotic properties, C/EBPalpha has been shown to interact with, and alter the activities of, several cell cycle related proteins and a number of models as to the mechanistics of C/EBPalpha-mediated growth repression have been proposed. More recently, several reports have indicated that C/EBPalpha acts as a tumour suppressor in the hematopoietic system and that mutation within C/EBPalpha is sufficient to induce tumourigenesis. Here, we will review these data and probe the possibility that C/EBPalpha also act as a tumour suppressor in other C/EBPalpha-expressing tissues.

C/EBPalpha is required for lung maturation at birth

Epithelial cells lining the peripheral lung synthesize pulmonary surfactant that reduces surface tension at the air-liquid interface. Lack of surfactant lipids and proteins in the lungs causes respiratory distress syndrome, a common cause of morbidity and mortality in preterm infants. We show that C/EBPalpha plays a crucial role in the maturation of the respiratory epithelium in late gestation, being required for the production of surfactant lipids and proteins necessary for lung function. Deletion of the Cebpa gene in respiratory epithelial cells in fetal mice caused respiratory failure at birth. Structural and biochemical maturation of the lung was delayed. Normal synthesis of surfactant lipids and proteins, including SP-A, SP-B, SP-C, SP-D, ABCA3 (a lamellar body associated protein) and FAS (precursor of fatty acid synthesis) were dependent upon expression of the C/EBPalpha in respiratory epithelial cells. Deletion of the Cebpa gene caused increased expression of Tgfb2, a growth factor that inhibits lung epithelial cell proliferation and differentiation. Normal expression of C/EBPalpha required Titf1 and Foxa2, transcription factors that also play an important role in perinatal lung differentiation. C/EBPalpha participates in a transcriptional network that is required for the regulation of genes mediating perinatal lung maturation and surfactant homeostasis that is necessary for adaptation to air breathing at birth.

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.

Sp1: regulation of gene expression by phosphorylation

As the prototype of a family of transcription factors, Sp1 has been extensively studied and widely reported for its role in gene regulation. The first evidence of Sp1 phosphorylation was reported more than a decade ago. Since then, an increasing number of Sp1 phosphorylation events have been characterized. Recent data demonstrate an important role for the phosphorylation state of Sp1 in the regulation of multiple genes. In this article, we review published literature in four specific areas relating to the phosphorylation of Sp1: (1) signal transduction pathways for Sp1 phosphorylation, (2) mechanisms of Sp1 dephosphorylation, (3) the functional implications of Sp1 phosphorylation, and (4) Sp1 phosphorylation in the 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.

Maturational factors modulate transcription factors CCAAT/enhancer-binding proteins alpha, beta, delta, and peroxisome proliferator-activated receptor-gamma in fetal rat lung epithelial cells

Previous investigations have evidenced the importance of CCAAT/enhancer-binding proteins (C/EBPs) and peroxisome proliferator-activated receptor (PPAR)gamma for lung development, especially for alveolar type II cells (ATII). This prompted us to explore whether ATII maturation-promoting mediators controlled their expression in isolated ATII. In whole rat lung, C/EBPalpha, beta, delta, and PPARgamma mRNAs increased 3-5 times between gestational day 18 and term (Day 22), dropped around birth, then reincreased. C/EBPbeta and delta, but not PPARgamma, displayed similar profile in isolated ATII; C/EBPalpha transcript disappeared and the protein became hardly detectable in isolated cells. In cultured ATII, dexamethasone increased C/EBPbeta and PPARgamma mRNAs 2-4 times, and cyclic AMP increased C/EBPbeta and delta mRNAs approximately 1.5 times. Whereas retinoic acid increased C/EBPbeta and PPARgamma mRNAs 1.5 times in ATII in vitro, vitamin-A deficiency strongly decreased fetal lung C/EBPalpha, beta, and PPARgamma transcripts in vivo. C/EBPbeta, delta, and PPARgamma mRNAs were also increased in vitro by epidermal growth factor and keratinocyte growth factor, whereas they were unchanged by the maturation inhibitor transforming growth factor-beta. C/EBPalpha expression was not reinduced by any mediator. Changes in transcripts were reflected in protein levels analyzed through Western blotting. These results argue for a role of these factors in ATII functional maturation, and indicate a multifactorial control of their ontogeny.

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.

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.

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.

A role for C/EBP delta in human surfactant protein A (SP-A) gene expression

C/EBP delta, a member of the leucine zipper transcription factor family, is expressed at higher levels in the lung than in any other tissue. We detected C/EBP delta mRNA and protein in NCI-H441 cells, a cell line derived from a human adenocarcinoma that produces surfactant protein A (SP-A). NCI-H441 cells were exposed to phosphorothioate-substituted antisense oligonucleotides directed against C/EBP delta. After exposure to the oligonucleotides, cells were harvested, total RNA prepared, and levels of mRNA for C/EBP delta, SP-A and a control, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), were quantified from Northern blots. An oligonucleotide that overlapped the translational start was effective in reducing C/EBP delta mRNA. Oligonucleotides that corresponded to regions upstream and downstream from the translational start were not as effective. The loss of C/EBP delta was accompanied by a decrease in the level of SP-A mRNA. The overlapping oligonucleotide was tested more extensively. After 72 h, antisense oligonucleotide at 3 and 5 microM reduced the level of C/EBP delta mRNA and protein by 50% or more as compared with sense and scrambled controls. The SP-A mRNA level was reduced even more, by about 75%. GAPDH mRNA was not affected. We conclude that C/EBP delta plays a role in the regulation of SP-A gene expression.

Pseudomonas aeruginosa and tumor necrosis factor-alpha attenuate Clara cell secretory protein promoter function

The Clara cell secretory protein (CCSP, also CC-10/uterglobin) is a 16-kD homodimeric protein abundantly expressed in the airways of mammals. Although the molecular function is unknown, gene-targeting studies indicate CCSP as a regulator of lung inflammation following acute respiratory infection or injury. CCSP is decreased in the lungs of mice following acute Pseudomonas aeruginosa (P.a.) infection. In the present study, the role of decreased promoter function in the regulation of CCSP by P.a. was assessed using an in vitro co-culture system and in vivo studies of transgenic mice. CCSP promoter activity in lung epithelial cells was markedly decreased by P.a. or tumor necrosis factor-alpha (TNF-alpha) in a dose-dependent manner. Regulation of CCSP promoter function by either P.a. or TNF-alpha was localized to the proximal 166 bp flanking region of the CCSP promoter activity. Decreased regulation of the CCSP promoter by P.a. or TNF-alpha was specific to CCSP, as human surfactant protein D (SP-D) promoter activity was unaffected or increased by P.a. or TNF-alpha, respectively. A neutralizing antibody against human TNF-alpha was able to reverse both the TNF-alpha- mediated as well as P.a.-mediated decrease in CCSP promoter function in lung epithelial cells. TNF-alpha secretion by lung epithelial cells coincided with the decrease in CCSP promoter function following P.a. administration. Using a transgenic mouse model, P.a. administration to the lung markedly attenuated CCSP promoter-conferred gene expression in vivo. The attenuation of CCSP promoter activity in lung epithelial cells by P.a. involves, in part, autocrine/paracrine secretion of TNF-alpha, which in turn regulates CCSP transcription through cis-active elements in the proximal promoter region.

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.

Uteroglobin gene transcription: what's the RUSH?

Prolactin enhances progesterone-dependent transcription of the rabbit uteroglobin gene. RUSH transcription factors are implicated in the signal transduction pathway. The RUSH acronym identifies key features of these nuclear phosphoproteins, that is, RING-finger motif, binds the uteroglobin promoter, structurally related to the SWI/SNF family of transcription factors, and helicase-like. Cloned by recognition site screening, RUSH proteins bind to an 85-bp region (-170/-85) of the uteroglobin promoter that was subsequently identified as a novel prolactin-responsive region by promoter deletion analysis. Gel shift and linker-scanning assays further reduced the RUSH target site to -160/-110. A hexameric core of MCWTDK was identified as the RUSH-specific DNA-binding site (-126/-121) by CASTing. This site overlaps authentic HNF3 beta and OCT-1 binding sites. A unique Type IV P-type ATPase that is embedded in the inner nuclear membrane binds the RING domain of RUSH. The conformationally flexible loop portion of this RING-finger binding protein (RFBP) extends into the nucleoplasm to contact euchromatin. The physical association of RFBP with transcriptionally active chromatin supports the speculation that RFBP targets RUSH transcription factors to the active uteroglobin promoter.

Uteroglobin reverts the transformed phenotype in the endometrial adenocarcinoma cell line HEC-1A by disrupting the metabolic pathways generating platelet-activating factor

Uteroglobin, originally named blastokinin, is a protein synthesized and secreted by most epithelia, including the endometrium. Uteroglobin has strong anti-inflammatory properties that appear to be due, at least in part, to its inhibitory effect on the activity of the enzyme phospholipase A(2). In addition, recent experimental evidence indicates that uteroglobin exerts antiproliferative and antimetastatic effects in different cancer cells via a membrane receptor. The human endometrial adenocarcinoma cell line HEC-1A does not express uteroglobin. Thus, we transfected HEC-1A cells with human uteroglobin cDNA. The transfectants showed a markedly reduced proliferative potential as assessed by impaired plating efficiency as well as by reduced growth in soft agar. Cytofluorimetric analysis clearly indicated that in uteroglobin-transfected cells the time for completion of the cell cycle was increased. We previously demonstrated that HEC-1A cells actively synthesize platelet-activating factor, one of the products of phospholipase A(2) activity. In addition, we demonstrated that platelet-activating factor stimulates the proliferation of these cells through an autocrine loop. In uteroglobin transfectants, the activity of phospholipase A(2) and platelet-activating factor acetyl-transferase, which are involved in the synthesis of platelet-activating factor, was significantly reduced compared with wild-type and vector-transfected cells (p < 0.05). Our results indicate that enforced expression of uteroglobin in HEC-1A cells markedly reduced their growth potential and significantly impaired the synthesis of platelet-activating factor, an autocrine growth factor for these cells. These data suggest that one possible mechanism for the recently observed antineoplastic properties of uteroglobin may be the inhibition of the synthesis of platelet-activating factor.

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

The Clara cell secretory protein (CCSP) gene is a cell-specific differentiation marker for the bronchiolar Clara cell. Previous studies suggest that CCAAT/enhancer binding protein (C/EBP)alpha is involved in controlling differentiation-dependent gene expression in the distal lung. In this study, immunofluorescence studies demonstrated high level expression of C/EBPdelta in the bronchiolar epithelium as well as lower levels of C/EBPalpha. Cotransfection studies in the lung epithelial cell line A549 showed that both C/EBPalpha and C/EBPdelta activate the murine CCSP gene and that a C/EBP-response element resides in the proximal CCSP promoter. C/EBPdelta exhibits an approximately 2-fold higher transactivation potential than does C/EBPalpha. DNase I footprint analyses revealed a footprint region located at -100 to -62 bp, corresponding to two C/EBP-binding sites. Mutation of either site resulted in abolished or strikingly reduced transactivation of the CCSP promoter by C/EBPalpha and C/EBPdelta, as well as impaired binding of both factors, indicating that the two C/EBP-binding sites form a compound response element. In electrophoretic mobility shift assays, it was shown that C/EBPalpha and C/EBPdelta can bind to both C/EBP sites, whereas in DNase I footprint analyses, the interaction of C/EBPalpha with the proximal site was weak. Furthermore, electrophoretic mobility shift assays demonstrated that C/EBPalpha and C/EBPdelta preferentially form heterodimers at both binding sites. Cotransfections with C/EBPalpha and C/EBPdelta together resulted in a superinduction of the CCSP promoter, indicating a regulatory role for the C/EBPalpha-C/EBPdelta heterodimers. Our findings demonstrate that C/EBPalpha and C/EBPdelta regulate the CCSP gene through a compound response element and suggest that these factors are important for the differentiation-dependent expression of CCSP.

CYP2B1 is regulated by C/EBP alpha and C/EBP delta inlung epithelial cells

Pulmonary expression of several cytochrome P450 (CYP) monooxygenases is detected late in gestation. Little is known of the factors involved in this differentiation-dependent expression. C/EBP factors are known regulators of differentiation and differentiation-dependent gene expression in several tissues. In this study we demonstrate the importance of C/EBP alpha and C/EBP delta in pulmonary epithelial CYP2B1 gene expression. A 1.3 kb CYP2B1 promoter fragment which recently has been shown to confer lung tissue- and cell-specific expression of CYP2B1 in transgenic mice was used in transient transfection studies. Both C/EBP alpha and C/EBP delta transactivated the CYP2B1 promoter in the lung epithelial cell lines A549 and NCI-H441. C/EBP alpha in nuclear extracts from isolated rat primary bronchiolar Clara cells was capable of interacting with a C/EBP-binding site in the proximal CYP2B1 promoter. Site-directed mutagenesis studies showed that this proximal C/EBP-binding site is necessary for transactivation of the CYP2B1 gene by C/EBP alpha and C/EBP delta. Thi study shows that C/EBP factors have a role in pulmonary CYP2B1 expression and suggests that these transcription factors may be important for the differentiation-dependent expression of CYP2B1 in the lung.

Cis-acting sequences from the rat cytochrome P450 2B1 gene confer pulmonary and phenobarbital-inducible expression in transgenic mice

Specific cytochrome P450 enzymes show tissue-specific induction, and different regulatory units for expression of these enzymes have been identified. The regulation of the phenobarbital (PB)-inducible P450 genes has been relatively well characterized in terms of PB induction, but less so with regard to tissue-specific expression. CYP2B2 is not expressed in the rat lung, whereas cytochrome P450 2B1 (CYP2B1) is a dominating enzyme in the same tissue. The constitutive expression of CYP2B1 and CYP2B2 in liver is low, but inducible by PB, whereas the pulmonary expression of CYP2B1 is not induced by PB. This indicates utilization of different regulating mechanisms in the two organs. A gene construct consisting of the structural gene for LacZ coupled to a 1.3-kb 5' fragment of the rat CYP2B1 gene was used to generate transgenic mice in order to further elucidate the mechanism behind tissue-specific expression and PB induction of the CYP2B1 gene. Using reverse transcriptase-polymerase chain reaction on total RNA extracted from lung and liver tissue, a lung-specific transcription of the transgene was observed. Transcription of the construct was also observed in livers from PB-treated transgenic animals. By histochemical staining of lung sections with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal), we demonstrated expression at the protein level in bronchiolar cells. In conclusion, our results revealed that the region extending to -1. 3 kb in the 5' flanking region of the CYP2B1 gene included sequences that could partly account for the lung-specific transcription of CYP2B1 and the hepatic induction of CYP2B1 transcription by PB.