cAMP-responding element-binding protein and c-Ets1 interact in the regulation of ATP-dependent MUC5AC gene expression

The interplay of inflammation and remodeling in the pathogenesis of chronic rhinosinusitis: current understanding and future directions

Chronic rhinosinusitis (CRS), a common clinical condition characterized by persistent mucosal inflammation and tissue remodeling, has a complex pathogenesis that is intricately linked to innate and adaptive immunity. A number of studies have demonstrated that a variety of immune cells and cytokines that play a vital role in mediating inflammation in CRS are also involved in remodeling of the nasal mucosa and the cells as well as different cytokines involved in remodeling in CRS are also able to exert some influence on inflammation, even though the exact relationship between inflammation and remodeling in CRS has not yet been fully elucidated. In this review, the potential role of immune cells and cytokines in regulating inflammation and remodeling of CRS mucosa has been described, starting with the immune cells and cytokines that act together in inflammation and remodeling. The goal is to aid researchers in understanding intimate connection between inflammation and remodeling of CRS and to offer novel ideas for future research.

Expression and Clinical Significance of Mucin Gene in Chronic Rhinosinusitis

PURPOSE OF REVIEW

This review highlights the expression and regulation of mucin in CRS and discusses its clinical implications.

RECENT FINDINGS

Chronic rhinosinusitis (CRS) is common chronic nasal disease; one of its main manifestations and important features is mucus overproduction. Mucin is the major component of mucus and plays a critical role in the pathophysiological changes in CRS. The phenotype of CRS affects the expression of various mucins, especially in nasal polyps (NP). Corticosteroids(CS), human neutrophil elastase (HNE), and transforming growth factor-β1 (TGF-β1) are closely related to the tissue remodeling of CRS and regulate mucin expression, mainly MUC1, MUC4, MUC5AC, and MUC5B. "It is expected that CS, HNE and TGF - β could be used to regulate the expression of mucin in CRS." However, at present, the research on mucin is mainly focused on mucin 5AC and mucin 5B, which is bad for finding new therapeutic targets. Investigating the expression and location of mucin in nasal mucosa and understanding the role of various inflammatory factors in mucin expression are helpful to figure out regulatory mechanisms of airway mucin hypersecretion. It is of great significance for the treatment of CRS.

Natural inhibitors on airway mucin: Molecular insight into the therapeutic potential targeting MUC5AC expression and production

Airway mucin overproduction is the hallmark risk factor of asthma, which is associated with the reduction of lung function. An aberrant mucin expression is responsible for airway obstruction due to its high viscous characteristics. Among the mucins discovered, MUC5AC is the prime mucin of airway epithelia. Nowadays, mucins induced asthma and chronic obstructive pulmonary disease (COPD) are a great concern all over the world. This review focuses on the effects of natural compounds that can be beneficial to explore new drugs to halt MUC5AC secretion and production in airway epithelial, and also their underlying molecular mechanisms based on recent studies. Several researchers are seeking natural sources to identify a new potent MUC5AC inhibitory agent for clinical applications, because of countable limitations of existing synthetic drugs. Currently, flavonoids, glycoside and steroids like natural compounds have acquired great attention due to their anti-inflammatory and mucoregulatory effects. Most importantly, many natural compounds have shown their potential effects as the modulator of mucin expression, secretion, and production. Therefore, targeting airway MUC5AC expression and production represents an auspicious area of research for the development of drugs against various respiratory diseases.

MiR-532-5p suppresses renal cancer cell proliferation by disrupting the ETS1-mediated positive feedback loop with the KRAS-NAP1L1/P-ERK axis

Background

Despite the fact that miRNAs play pivotal roles in various human malignancies, their molecular mechanisms influencing RCC are poorly understood.

Methods

The expression of miRNAs from RCC and paired normal renal specimens was analysed by a combined computational and experimental approach using two published datasets and qRT-PCR assays. The functional role of these miRNAs was further identified by overexpression and inhibition assays in vivo and in vitro. Western blots, luciferase assays, and chromatin immunoprecipitation were performed to investigate the potential mechanisms of these miRNAs.

Results

Bioinformatics analysis and qRT-PCR revealed that miR-532-5p was one of the most heavily downregulated miRNAs. Overexpression of miR-532-5p inhibited RCC cell proliferation, while knockdown of miR-532-5p promoted cell proliferation. Mechanistic analyses indicated that miR-532-5p directly targets KRAS and NAP1L1. Interestingly, ETS1 suppressed the transcription of miR-532-5p by directly binding a special region of its promoter. Moreover, high levels of ETS1, as an oncogene in RCC, were significantly associated with poor survival in a large cohort of RCC specimens.

Conclusions

Our work presents a road map for the prediction and validation of a miR-532-5p/KRAS-NAP1L1/P-ERK/ETS1 axis feedback loop regulating cell proliferation, which could potentially provide better therapeutic avenues for treating RCC.

Airborne particulate matter increases MUC5AC expression by downregulating Claudin-1 expression in human airway cells

CLB_2.0, a constituent of PM, induces secretion of multiple cytokines and chemokines that regulate airway inflammation. Specifically, IL-6 upregulates CLB_2.0-induced MUC5AC and MUC1 expression. Interestingly, of the tight junction proteins examined, claudin-1 expression was inhibited by CLB_2.0. While the overexpression of claudin-1 decreased CLB_2.0-induced MUC5AC expression, it increased the expression of the anti-inflammatory mucin, MUC1. CLB_2.0-induced IL-6 secretion was mediated by ROS. The ROS scavenger N-acetylcysteine inhibited CLB_2.0-induced IL-6 secretion, thereby decreasing the CLB_2.0-induced MUC5AC expression, whereas CLB_2.0-induced MUC1 expression increased. CLB_2.0 activated the ERK1/2 MAPK via a ROS-dependent pathway. ERK1/2 downregulated the claudin-1 and MUC1 expressions, whereas it dramatically increased CLB_2.0-induced MUC5AC expression. These findings suggest that CLB_2.0-induced ERK1/2 activation acts as a switch for regulating inflammatory conditions though a ROS-dependent pathway. Our data also suggest that secreted IL-6 regulates CLB_2.0-induced MUC5AC and MUC1 expression via ROS-mediated downregulation of claudin-1 expression to maintain mucus homeostasis in the airway.

Effect of MUC8 on Airway Inflammation: A Friend or a Foe?

In this review, we compile identifying molecular mechanisms of MUC8 gene expression and studies characterizing the physiological functions of MUC8 in the airway and analyzing how altered MUC8 gene expression in the lung is affected by negative regulators.

A novel dissociative steroid VBP15 reduces MUC5AC gene expression in airway epithelial cells but lacks the GRE mediated transcriptional properties of dexamethasone

Overproduction of secretory mucins contributes to morbidity/mortality in inflammatory lung diseases. Inflammatory mediators directly increase expression of mucin genes, but few drugs have been shown to directly repress mucin gene expression. IL-1β upregulates the MUC5AC mucin gene in part via the transcription factors NFκB while the glucocorticoid Dexamethasone (Dex) transcriptionally represses MUC5AC expression by Dex-activated GR binding to two GRE cis-sites in the MUC5AC promoter in lung epithelial cells. VBP compounds (ReveraGen BioPharma) maintain anti-inflammatory activity through inhibition of NFκB but exhibit reduced GRE-mediated transcriptional properties associated with adverse side-effects and thus have potential to minimize harmful side effects of long-term steroid therapy in inflammatory lung diseases. We investigated VBP15 efficacy as an anti-mucin agent in two types of airway epithelial cells and analyzed the transcription factor activity and promoter binding associated with VBP15-induced MUC5AC repression. VBP15 reduced MUC5AC mRNA abundance in a dose- and time-dependent manner similar to Dex in the presence or absence of IL-1β in A549 and differentiated human bronchial epithelial cells. Repression was abrogated in the presence of RU486, demonstrating a requirement for GR in the VBP15-induced repression of MUC5AC. Inhibition of NFκB activity resulted in reduced baseline expression of MUC5AC indicating that constitutive activity maintains MUC5AC production. Chromatin immunoprecipitation analysis demonstrated lack of GR and of p65 (NFκB) binding to composite GRE domains in the MUC5AC promoter following VBP15 exposure of cells, in contrast to Dex. These data demonstrate that VBP15 is a novel anti-mucin agent that mediates the reduction of MUC5AC gene expression differently than the classical glucocorticoid, Dex.

IL-1ra Secreted by ATP-Induced P2Y2 Negatively Regulates MUC5AC Overproduction via PLCβ3 during Airway Inflammation

Mucus secretion is often uncontrolled in many airway inflammatory diseases of humans. Identifying the regulatory pathway(s) of mucus gene expression, mucus overproduction, and hypersecretion is important to alleviate airway inflammation in these diseases. However, the regulatory signaling pathway controlling mucus overproduction has not been fully identified yet. In this study, we report that the ATP/P2Y2 complex secretes many cytokines and chemokines to regulate airway inflammation, among which IL-1 receptor antagonist (IL-1ra) downregulates MUC5AC gene expression via the inhibition of Gαq-induced Ca(2+) signaling. IL-1ra inhibited IL-1α protein expression and secretion, and vice versa. Interestingly, ATP/P2Y2-induced IL-1ra and IL-1α secretion were both mediated by PLCβ3. A dominant-negative mutation in the PDZ-binding domain of PLCβ3 inhibited ATP/P2Y2-induced IL-1ra and IL-1α secretion. IL-1α in the presence of the ATP/P2Y2 complex activated the ERK1/2 pathway in a greater degree and for a longer duration than the ATP/P2Y2 complex itself, which was dramatically inhibited by IL-1ra. These findings suggest that secreted IL-1ra exhibits a regulatory effect on ATP/P2Y2-induced MUC5AC gene expression, through inhibition of IL-1α secretion, to maintain the mucus homeostasis in the airway. Therefore, IL-1ra could be an excellent modality for regulating inflamed airway microenvironments in respiratory diseases.

Induction of MUC5AC mucin expression by histamine through the activation of its core promoter region

CONCLUSION

This study provides evidence that histamine induced MUC5AC mRNA expression through the activation of the core region of its promoter. It may also help in approaching new therapeutic strategies in airway mucins hypersecretory diseases.

OBJECTIVE

Mucin hypersecretion characterizes several respiratory diseases. Production of MUC5AC, a major gel forming mucin secreted by airway epithelia, can be induced by various inflammatory mediators. Histamine is associated with MUC5AC up-regulation during the early phase of allergic respiratory diseases. The goal of the present study was to identify whether histamine may induce MUC5AC gene expression both at mRNA and protein levels and to elucidate its mechanism.

METHODS

Guinea pigs were sensitized and challenged with dermatophagoides farinae (Der f) extract. Human lung mucoepidermoid carcinoma cell line (NCI-H292) was used. The regulatory mechanism of MUC5AC by histamine and H1R was investigated using RT-PCR, immunofluorescence, and MUC5AC promoter-driven luciferase reporter assay.

RESULTS

The MUC5AC expression levels were increased by histamine treatment in either nasal tissues of Der f challenged guinea pigs or NCI-H292 cells, whereas the MUC5AC protein over-production induced by histamine administration was significantly inhibited by H1R antagonist chlorpheniramine. It was found that histamine enhanced the activation of the proximal core region of the MUC5AC promoter, which was significantly blocked by chlorpheniramine, as indicated by luciferase reporter assays.

A long-acting β2-adrenergic agonist increases the expression of muscarine cholinergic subtype‑3 receptors by activating the β2-adrenoceptor cyclic adenosine monophosphate signaling pathway in airway smooth muscle cells

The persistent administration of β₂-adrenergic (β₂AR) agonists has been demonstrated to increase the risk of severe asthma, partly due to the induction of tolerance to bronchoprotection via undefined mechanisms. The present study investigated the potential effect of the long-acting β₂-adrenergic agonist, formoterol, on the expression of muscarinic M3 receptor (M₃R) in rat airway smooth muscle cells (ASMCs). Primary rat ASMCs were isolated and characterized following immunostaining with anti-α-smooth muscle actin antibodies. The protein expression levels of M₃R and phospholipase C-β₁ (PLCβ₁) were characterized by western blot analysis and the production of inositol 1,4,5-trisphosphate (IP₃) was determined using an enzyme-linked immunosorbent assay. Formoterol increased the protein expression of M₃R in rat ASMCs in a time- and dose-dependent manner, which was significantly inhibited by the β₂AR antagonist, ICI118,551 and the cyclic adenosine monophosphate (cAMP) inhibitor, SQ22,536. The increased protein expression of M₃R was positively correlated with increased production of PLCβ₁ and IP₃. Furthermore, treatment with the glucocorticoid, budesonide, and the PLC inhibitor, U73,122, significantly suppressed the formoterol-induced upregulated protein expression levels of M₃R and PLCβ₁ and production of IP₃. The present study demonstrated that formoterol mediated the upregulation of M₃R in the rat ASMCs by activating the β₂AR-cAMP signaling pathway, resulting in increased expression levels of PLCβ₁ and IP₃, which are key to inducing bronchoprotection tolerance. Administration of glucocorticoids or a PLC antagonist prevented formoterol-induced bronchoprotection tolerance by suppressing the protein expression of M₃R.

Silencing of MUC8 by siRNA increases P2Y₂-induced airway inflammation

Mucin hypersecretion and overproduction are frequent manifestations of respiratory disease. Determining the physiological function of airway mucin is presently considered more important than identifying the relevant signaling pathways. The lack of a full-length human mucin 8 (MUC8) cDNA sequence has hindered the generation of a Muc8 knockout mouse line. Thus, the precise physiological functions of MUC8 are unclear. Herein, we investigated the function of MUC8 using a small-interfering RNA (siRNA)-mediated genetic silencing approach in human airway epithelial cells. Herein, intracellular IL-1α production was stimulated by an ATP/P2Y2 complex. While ATP/P2Y₂ increased IL-1α secretion in a time-dependent manner, treatment with P2Y₂-specific siRNA significantly decreased IL-1α secretion. Moreover, ATP increased P2Y₂-mediated upregulation of MUC8 expression; however, IL-1α significantly decreased the extent to which ATP/P2Y₂ upregulated MUC8 expression. Interestingly, treatment with MUC8-specific siRNA decreased the production of anti-inflammatory cytokines (TGF-β and IL-1 receptor antagonist) and increased the production of inflammatory cytokines (IL-1α and IL-6) in our system. In addition, siRNA-mediated knockdown of MUC8 expression dramatically increased the secretion of inflammatory chemokines and resulted in an approximately threefold decrease in cell chemotaxis. We propose that MUC8 may function as an anti-inflammatory mucin that participates in inflammatory response by attracting immune cells/cytokines to the site of inflammation. Our results provide new insight into the physiological function of MUC8 and enhance our understanding of mucin overproduction during airway inflammation.

IL-1β induction of MUC5AC gene expression is mediated by CREB and NF-κB and repressed by dexamethasone

Chronic airway diseases are characterized by inflammation and mucus overproduction. The MUC5AC mucin gene is upregulated by the proinflammatory cytokine interleukin-1 β (IL-1β) via activation of cAMP response element-binding protein (CREB) in the NCI-H292 cancer cell line and nuclear factor-κB (NF-κB) in the HBE1 transformed cell line, with each transcription factor binding to a cognate cis site in the proximal or distal region, respectively, of the MUC5AC promoter. We utilized primary differentiated human bronchial epithelial (HBE) and A549 lung adenocarcinoma cells to further investigate the contributions of CREB and NF-κB subunits to the IL-1β-induced upregulation of MUC5AC. Data show that ligand binding of IL-1β to the IL-1β receptor is required to increase MUC5AC mRNA abundance. Chromatin immunoprecipitation analyses show direct binding of CREB to the previously identified cAMP response element site and binding of p65 and p50 subunits to a novel NF-κB site in a mucin-regulatory domain in the proximal promoter and to a previously identified NF-κB site in the distal promoter. P50 binds to both NF-κB sites at 1 h following IL-1β exposure, but is replaced at 2 h by p65 in A549 cells and by a p50/p65 heterodimer in HBE cells. Thus IL-1β activates multiple domains in the MUC5AC promoter but exhibits some cell-specific responses, highlighting the complexity of MUC5AC transcriptional regulation. Data show that dexamethasone, a glucocorticoid that transcriptionally represses MUC5AC gene expression under constitutive conditions, also represses IL-1β-mediated upregulation of MUC5AC gene expression. A further understanding of mechanisms mediating MUC5AC regulation should lead to a honing of therapeutic approaches for the treatment of mucus overproduction in inflammatory lung diseases.

PDK1 controls upstream PI3K expression and PIP3 generation

The PI3K/PDK1/Akt signaling axis is centrally involved in cellular homeostasis and controls cell growth and proliferation. Due to its key function as regulator of cell survival and metabolism, the dysregulation of this pathway is manifested in several human pathologies including cancers and immunological diseases. Thus, current therapeutic strategies target the components of this signaling cascade. In recent years, numerous feedback loops have been identified that attenuate PI3K/PDK1/Akt-dependent signaling. Here, we report the identification of an additional level of feedback regulation that depends on the negative transcriptional control of phosphatidylinositol 3-kinase (PI3K) class IA subunits. Genetic deletion of 3-phosphoinositide-dependent protein kinase 1 (PDK1) or the pharmacological inhibition of its downstream effectors, that is, Akt and mammalian target of rapamycin (mTOR), relieves this suppression and leads to the upregulation of PI3K subunits, resulting in enhanced generation of phosphatidylinositol-3,4,5-trisphosphate (PIP3). Apparently, this transcriptional induction is mediated by the concerted action of different transcription factor families, including the transcription factors cAMP-responsive element-binding protein and forkhead box O. Collectively, we propose that PDK1 functions as a cellular sensor that balances basal PIP3 generation at levels sufficient for survival but below a threshold being harmful to the cell. Our study suggests that the efficiency of therapies targeting the aberrantly activated PI3K/PDK1/Akt pathway might be increased by the parallel blockade of feedback circuits.

CFTR, mucins, and mucus obstruction in cystic fibrosis

Mucus pathology in cystic fibrosis (CF) has been known for as long as the disease has been recognized and is sometimes called mucoviscidosis. The disease is marked by mucus hyperproduction and plugging in many organs, which are usually most fatal in the airways of CF patients, once the problem of meconium ileus at birth is resolved. After the CF gene, CFTR, was cloned and its protein product identified as a cAMP-regulated Cl(-) channel, causal mechanisms underlying the strong mucus phenotype of the disease became obscure. Here we focus on mucin genes and polymeric mucin glycoproteins, examining their regulation and potential relationships to a dysfunctional cystic fibrosis transmembrane conductance regulator (CFTR). Detailed examination of CFTR expression in organs and different cell types indicates that changes in CFTR expression do not always correlate with the severity of CF disease or mucus accumulation. Thus, the mucus hyperproduction that typifies CF does not appear to be a direct cause of a defective CFTR but, rather, to be a downstream consequence. In organs like the lung, up-regulation of mucin gene expression by inflammation results from chronic infection; however, in other instances and organs, the inflammation may have a non-infectious origin. The mucus plugging phenotype of the β-subunit of the epithelial Na(+) channel (βENaC)-overexpressing mouse is proving to be an archetypal example of this kind of inflammation, with a dehydrated airway surface/concentrated mucus gel apparently providing the inflammatory stimulus. Data indicate that the luminal HCO(3)(-) deficiency recently described for CF epithelia may also provide such a stimulus, perhaps by causing a mal-maturation of mucins as they are released onto luminal surfaces. In any event, the path between CFTR dysfunction and mucus hyperproduction has proven tortuous, and its unraveling continues to offer its own twists and turns, along with fascinating glimpses into biology.

Identification of signaling pathways mediating cell cycle arrest and apoptosis induced by Porphyromonas gingivalis in human trophoblasts

Epidemiological and interventional studies of humans have revealed a close association between periodontal diseases and preterm delivery of low-birth-weight infants. Porphyromonas gingivalis, a periodontal pathogen, can translocate to gestational tissues following oral-hematogenous spread. We previously reported that P. gingivalis invades extravillous trophoblast cells (HTR-8) derived from the human placenta and inhibits proliferation through induction of arrest in the G(1) phase of the cell cycle. The purpose of the present study was to identify signaling pathways mediating cellular impairment caused by P. gingivalis. Following P. gingivalis infection, the expression of Fas was induced and p53 accumulated, responses consistent with response to DNA damage. Ataxia telangiectasia- and Rad3-related kinase (ATR), an essential regulator of DNA damage checkpoints, was shown to be activated together with its downstream signaling molecule Chk2, while the p53 degradation-related protein MDM2 was not induced. The inhibition of ATR prevented both G(1) arrest and apoptosis caused by P. gingivalis in HTR-8 cells. In addition, small interfering RNA (siRNA) knockdown of p53 abrogated both G(1) arrest and apoptosis. The regulation of apoptosis was associated with Ets1 activation. HTR-8 cells infected with P. gingivalis exhibited activation of Ets1, and knockdown of Ets1 with siRNA diminished both G(1) arrest and apoptosis. These results suggest that P. gingivalis activates cellular DNA damage signaling pathways that lead to G(1) arrest and apoptosis in trophoblasts.

Lipopolysaccharides induces MUC5AC overproduction in human nasal epithelium

Hyperproduction of mucin in the nasal epithelium is an important feature of nasal inflammatory diseases. We investigated the mechanism of lipopolysaccharides (LPS) involvement in mucin 5 subtype AC (MUC5AC) expression in human nasal epithelial cells. The primary human nasal epithelial cells were cultured in vitro, which were treated with LPS (10 nM/ml or 1 μM/ml) for 12 and 24 h. LPS-induced MUC5AC protein was determined in nasal epithelial cells. The levels of nuclear factor kappa B p65 (NF-κBp65) and its inhibitor kappa Bα (IκBα) protein were also detected, and interleukin-1β (IL-1β) mRNA was detected by real-time PCR. LPS up-regulated MUC5AC protein in human nasal epithelial cells, and we determined that the up-regulation of MUC5AC expression was due to a time- and dose-dependent degradation of IκBα protein, which resulted in the increase of NF-κBp65 nuclear translocation. Subsequently, we also determined that LPS can induce IL-1β mRNA in a time- and dose-dependent manner. These data show that LPS treatment activated NF-κB by promoting the degradation of IκBα and the nuclear localization of NF-κBp65, which induced MUC5AC overproduction.

c-Ets1 inhibits the interaction of NF-κB and CREB, and downregulates IL-1β-induced MUC5AC overproduction during airway inflammation

Mucin hypersecretion is frequently observed in many inflammatory diseases of the human respiratory tract. As mucin hypersecretion refers to uncontrolled mucin expression and secretion during inflammation, studies examining the negative control mechanisms of mucin hypersecretion are vital in developing novel therapeutic medications. We hypothesized that the c-Ets1 induced by interleukin (IL)-1β would decrease MUC5AC overproduction by inhibiting the interaction of NF-κB with cAMP response element-binding protein (CREB) in vivo. Stimulation with IL-1β caused the direct binding of NF-κB and CREB to the MUC5AC promoter, thus increasing MUC5AC gene expression. However, IL-1β-induced MUC5AC messenger RNA levels were surprizingly downregulated by c-Ets1 (located -938 to -930). Interestingly, c-Ets1 also suppressed IL-1β-induced MUC5AC gene expression in vitro and in vivo by disrupting the interaction of NF-κB with CREB on the MUC5AC promoter. In addition, c-Ets1 also inhibited significant morphologic changes and inflammatory cell infiltration after IL-1β exposure in mouse lungs infected with either wild-type or shRNA-c-Ets1. Moreover, reactive oxygen species produced by NOX4 increased c-Ets1 gene expression and MUC5AC gene expression in alveolar macrophages from bronchoalveolar lavage fluid. These results suggest a molecular paradigm for the establishment of a novel mechanism underlying the negative regulation of mucin overproduction, thus enhancing our understanding of airway inflammation.

The transcription factor ETS-1 regulates angiotensin II-stimulated fibronectin production in mesangial cells

Angiotensin II (ANG II) produced as result of activation of the renin-angiotensin system (RAS) plays a critical role in the pathogenesis of chronic kidney disease via its hemodynamic effects on the renal microcirculation as well as by its nonhemodynamic actions including the production of extracellular matrix proteins such as fibronectin, a multifunctional extracellular matrix protein that plays a major role in cell adhesion and migration as well as in the development of glomerulosclerosis. ETS-1 is an important transcription factor essential for normal kidney development and glomerular integrity. We previously showed that ANG II increases ETS-1 expression and is required for fibronectin production in mesangial cells. In these studies, we determined that ANG II induces phosphorylation of ETS-1 via activation of the type 1 ANG II receptor and that Erk1/2 and Akt/PKB phosphorylation are required for these effects. In addition, we characterized the role of ETS-1 on the transcriptional activation of fibronectin production in mesangial cells. We determined that ETS-1 directly activates the fibronectin promoter and by utilizing gel shift assays and chromatin immunoprecipitation assays identified two different ETS-1 binding sites that promote the transcriptional activation of fibronectin in response to ANG II. In addition, we identified the essential role of CREB and its coactivator p300 on the transcriptional activation of fibronectin by ETS-1. These studies unveil novel mechanisms involved in RAS-induced production of the extracellular matrix protein fibronectin in mesangial cells and establish the role of the transcription factor ETS-1 as a direct mediator of these effects.

Peptidoglycan from Staphylococcus aureus increases MUC5AC gene expression via RSK1-CREB pathway in human airway epithelial cells

Respiratory tract exposure to viruses, air pollutants, or bacterial pathogens can lead to pulmonary diseases. The molecular mechanism of mucous overproduction increased by these pathogens provides the knowledge for developing new therapeutic strategies. There is established in vitro data demonstrating that the overexpression of MUC5AC is induced by peptidoglycan (PGN) derived from Staphylococcus aureus. However, the mechanisms by which PGN activates MUC5AC gene expression in the airway remain unclear. The aim of this study was to identify the mechanism of PGN-induced MUC5AC gene expression. We found that PGN could induce MUC5AC gene expressions in a time- and dose-dependent manner. Moreover, activations of ERK1/2 and JNK increased after treatment of cells with PGN, whereas phosporylation of p38 was undetected. Of these MAPKs, pharmacologic inhibition of ERK1/2 decreased PGN-induced MUC5AC gene expression. In addition, we checked the activation of p90 ribosomal S6 kinase 1 (RSK1) as a downstream signaling target of ERK1/2 in PGN signaling. The activation of RSK1 was prevented by pretreatment with PD98059. We also found that RSK1 mediated the PGN-induced phosphorylation of cAMP response element-binding protein (CREB) and the transcription of MUC5AC. Furthermore, the cAMP-response element (CRE) in the MUC5AC promoter appears to be important for PGN-induced MUC5AC gene expression in NCI-H292 cells.

Activation of c-Myb transcription factor is critical for PMA-induced lysozyme expression in airway epithelial cells

Lysozyme is a major component of airway epithelial secretions, acts as cationic anti-microbial protein for innate immunity. Although lysozyme plays an important role in airway defense and is a key component of airway secretions under inflammatory conditions, little is understood about the regulation of its expression and the associated signaling pathway. We wanted to examine whether Phorbol 12-myristate 13-acetate (PMA), one of PKC activators, treatment of the airway epithelial cell line NCI-H292 increases lysozyme gene expression. In this study, we sought to determine which signal molecules are involved in PMA-induced lysozyme gene expression. We found that PKC and mitogen-activating protein/ERK2 kinase are essential for PMA-induced lysozyme expression and also mediate the PMA-induced activation of c-Myb protein. We identified a proximal region of the lysozyme promoter essential for promoter activity containing c-Myb transcription factor binding site. Additionally, by site-directed promoter mutagenesis, we identified that c-Myb preferred the CAA motif of the -85/-73 region of the lysozyme promoter. Finally, we showed that overexpression of c-Myb without PMA treatment increased the lysozyme promoter activity and protein expression. From these results, we conclude that PMA induces overexpression of lysozyme via ERK1/2 MAP kinase-c-Myb signaling pathways in NCI-H292 cells.

Purinergic signaling in wound healing and airway remodeling

Airway epithelia are continuously damaged by airborne pollutants, pathogens and allergens, and they rely on intrinsic mechanisms to restore barrier integrity. Epithelial repair is a multi-step process including cell migration into the wounded area, proliferation, differentiation and matrix deposition. Each step requires the secretion of various molecules, including growth factors, integrins and matrix metalloproteinases. Evidence is emerging that purinergic signaling promotes repair in human airway epithelia. An injury induces ATP release, which binds P2Y(2) receptors (P2Y(2)Rs) to initiate protein kinase C (PKC)-dependent oxidative activation of TNFα-converting enzyme (TACE), which then releases the membrane-bound ligands of the epidermal growth factor receptor (EGFR). The P2Y(2)R- and EGFR-dependent signaling cascades converge to induce mediator release, whereas the latter also induces cytoskeletal rearrangement for cell migration and proliferation. Similar roles for purinergic signaling are reported in pulmonary endothelial cells, smooth muscle cells and fibroblasts. In chronic airway diseases, the aberrant regulation of extracellular purines is implicated in the development of airway remodeling by mucus cell metaplasia and hypersecretion, excess collagen deposition, fibrosis and neovascularization. This chapter describes the crosstalk between these signaling cascades and discusses the impact of deregulated purinergic signaling in chronic lung diseases.

Upregulation of MUC5AC gene expression by IL-4 through CREB in human airway epithelial cells

Mucus hypersecretion is an important characteristic feature of the pathogenesis of allergy. Although interleukin (IL)-4 is known to be an inflammatory mediator in respiratory diseases, the mechanism by which IL-4 induces MUC5AC gene expression has not been fully explored. The aim of this study was to investigate the mechanism by which IL-4 induces MUC5AC gene expression in the airway. We examined the role of mitogen-activated protein kinase (MAPK) signaling on MUC5AC gene expression in airway epithelium. We showed that phosphorylation of ERK1/2 increased after treatment of cells with IL-4, whereas phosphorylation of p38 and JNK was not detected. In addition, pharmacologic and genetic inhibition of ERK1/2 abolished IL-4-induced MUC5AC gene expression. Moreover, we investigated the activation of p90 ribosomal S6 kinase 1 (RSK1) as a downstream signaling target of ERK1/2 in IL-4 signaling. The activation of RSK1 was prevented by pretreatment with PD98059 or plasmid expressing a MEK1 dominant-negative mutant. We also found that RSK1 mediated the IL-4-induced phosphorylation of cAMP response element-binding protein (CREB) and the transcription of MUC5AC. Furthermore, the cAMP-response element (CRE) in the MUC5AC promoter appears to be important for IL-4-induced MUC5AC gene expression in NCI-H292 cells.

NGFI-B nuclear orphan receptor Nurr1 interacts with p53 and suppresses its transcriptional activity

Nurr1 is a member of the NGFI-B nuclear orphan receptor family which includes two other members, Nur77 and Nor-1. Nurr1 is essential for the development and survival of dopaminergic neurons. It was reported that Nurr1 has antiapoptotic functions, however, the mechanisms by which Nurr1 mediates these effects remain unknown. Here, we show that overexpression of Nurr1 decreases Bax expression whereas knockdown of Nurr1 increases Bax expression. Nurr1 also interacts with p53 and represses its assembly. Furthermore, Nurr1 represses p53 transcriptional activity in interaction-dependent and dose-dependent manners. Moreover, Nurr1 protects cells from doxorubicin-induced apoptosis. These findings provide evidence that Nurr1 promotes cell survival through its interacting with and repressing p53, thus implicating that Nurr1 may play an important role in carcinogenesis and other diseases.