Glucocorticoid receptor and histone deacetylase-2 mediate dexamethasone-induced repression of MUC5AC gene expression

Corticosteroid resistance in asthma: Cellular and molecular mechanisms

Inhaled glucocorticoids (GCs) are drugs widely used as treatment for asthma patients. They prevent the recruitment and activation of lung immune and inflammatory cells and, moreover, have profound effects on airway structural cells to reverse the effects of disease on airway inflammation. GCs bind to a specific receptor, the glucocorticoid receptor (GR), which is a member of the nuclear receptor superfamily and modulates pro- and anti-inflammatory gene transcription through a number of distinct and complementary mechanisms. Targets genes include many pro-inflammatory mediators such as chemokines, cytokines, growth factors and their receptors. Inhaled GCs are very effective for most asthma patients with little, if any, systemic side effects depending upon the dose. However, some patients show poor asthma control even after the administration of high doses of topical or even systemic GCs. Several mechanisms relating to inflammation have been considered to be responsible for the onset of the relative GC resistance observed in these patients. In these patients, the side-effect profile of GCs prevent continued use of high doses and new drugs are needed. Targeting the defective pathways associated with GC function in these patients may also reactivate GC responsiveness.

The seven constitutive respiratory defense barriers against SARS-CoV-2 infection

Before eliciting an adaptive immune response, SARS-CoV-2 must overcome seven constitutive respiratory defense barriers. The first is the mucus covering the respiratory tract's luminal surface, which entraps inhaled particles, including infectious agents, and eliminates them by mucociliary clearance. The second barrier comprises various components present in the airway lining fluid, the surfactants. Besides providing low surface tension that allows efficient gas exchange at the alveoli, surfactants inhibit the invasion of epithelial cells by respiratory viruses, enhance pathogen uptake by phagocytes, and regulate immune cells' functions. The respiratory tract microbiota constitutes the third defense barrier against SARS-CoV-2. It activates the innate and adaptive immune cells and elicits anti-infectious molecules such as secretory IgA antibodies, defensins, and interferons. The fourth defense barrier comprises the antimicrobial peptides defensins, and lactoferrin. They show direct antiviral activity, inhibit viral fusion, and modulate the innate and adaptive immune responses. Secretory IgA antibodies, the fifth defense barrier, besides protecting the local microbiota against noxious agents, also inhibit SARS-CoV-2 cell invasion. If the virus overcomes this barrier, it reaches its target, the respiratory epithelial cells. However, these cells also act as a defense barrier, the sixth one, since they hinder the virus' access to receptors and produce antiviral and immunomodulatory molecules such as interferons, lactoferrin, and defensins. Finally, the sensing of the virus by the cells of innate immunity, the last constitutive defense barrier, elicits a cascade of signals that activate adaptive immune cells and may inhibit the development of productive infection. The subject of the present essay is discussing these mechanisms.

Application of glucocorticoids in patients with novel coronavirus infection: From bench to bedside

Glucocorticoids (GCs) have potential anti-inflammatory and immunosuppressive effects. There is plenty of controversy about the application of glucocorticoids in the treatment of coronavirus disease 2019 (COVID-19). This paper briefly summarizes the mechanism of glucocorticoids and their receptors and clinical applications in COVID-19. Through reviewing the current literature, our aim is to have a deeper understanding of the mechanism of GCs and their clinical applications, so as to find possible ways to enhance their efficacy and reduce drug resistance or side effects.

Bisacodyl Suppresses TGF-α-Induced MUC5AC Production in NCI-H292 Cells

MUC5AC overproduction is commonly observed in chronic inflammatory lung diseases and worsens these conditions. Therefore, drugs that inhibit MUC5AC production are urgently needed. To identify novel drugs directly inhibiting MUC5AC production, 640 already approved drugs were screened. We found that the laxative bisacodyl suppressed transforming growth factor (TGF)-α-induced MUC5AC production in a concentration-dependent manner. Additionally, bisacodyl also suppressed TGF-α-induced MUC5AC mRNA expression in the same concentration range. These results suggested that bisacodyl could be a new drug for treating mucin overproduction.

Expression of cPLA2γ mRNA and protein differs the response of PBMC from severe and non-severe asthmatics to bacterial lipopolysaccharide and house dust mite allergen

Chronic inflammation in asthmatics is initiated/exacerbated by many environmental factors, such as bacterial lipopolysaccharide and allergens. Phospholipase A₂ and histone acetyltransferase/deacetylases are enzymes involved in inflammatory process, particularly in lipid inflammatory mediators production and control of transcription of many inflammatory genes, respectively. The aim of the study was to identify differences in the inflammatory process in patients with severe and non-severe asthma, taking as a criterion expression of two groups of enzymes: phospholipases A₂ and histone acetyltransferases/deacetylases. Thirty-two patients with severe, non-severe atopic to house dust mite asthmatics and 14 healthy volunteers were recruited. Peripheral blood mononuclear cells were stimulated with Dermatophagoides pteronyssinus allergen (nDer p1) and bacterial lipopolysaccharide (LPS). The expression of phospholipases A₂ and histone acetyltransferases and deacetylases were assessed using TaqMan Low Density Array Cards. The protein expression was analyzed with immunoblot. Increased expression of phospholipase A2 Group IVC (PLA2G4C) and cytosolic phospholipase A2 gamma (cPLA₂γ) protein was observed in peripheral blood mononuclear cells (PBMC) from severe asthmatics in response to LPS and nDer p1, compared to non-severe asthmatics. nDer p1-stimulated PBMC from severe asthmatics exhibit induced expression of HDAC1 and similar trend was observed in protein concentration. Decreased expression of EP300 occurred in PBMC of severe asthmatics. PBMC from non-severe asthmatics showed decreased expression of HDAC2 and PLA2G15 after LPS treatment. In conclusion, in response to LPS and dust mite allergen, PBMC from severe and non-severe asthmatics modulate expression of selected phospholipase A₂, histone acetyltransferases and deacetylases, while increased expression of cPLA₂γ characterizes PBMC response from severe asthmatics.

Transforming Growth Factor β Inhibits MUC5AC Expression by Smad3/HDAC2 Complex Formation and NF-κB Deacetylation at K310 in NCI-H292 Cells

Airway mucus secretion is an essential innate immune response for host protection. However, overproduction and hypersecretion of mucus, mainly composed of the gel- forming MUC5AC protein, are significant risk factors for patients with asthma and chronic obstructive pulmonary disease (COPD). The transforming growth factor β (TGFβ) signaling pathway negatively regulates MUC5AC expression; however, the underlying molecular mechanism is not fully understood. Here, we showed that TGFβ significantly reduces the expression of MUC5AC mRNA and its protein in NCI-H292 cells, a human mucoepidermoid carcinoma cell line. This reduced MUC5AC expression was restored by a TGFβ receptor inhibitor (SB431542), but not by the inhibition of NF-κB (BAY11-7082 or Triptolide) or PI3K (LY294002) activities. TGFβ-activated Smad3 dose-dependently bound to MUC5AC promoter. Notably, TGFβ-activated Smad3 recruited HDAC2 and facilitated nuclear translocation of HDAC2, thereby inducing the deacetylation of NF-κB at K310, which is essential for a reduction in NF-κB transcriptional activity. Both TGFβ-induced nuclear translocation of Smad3/HDAC2 and deacetylation of NF-κB at K310 were suppressed by a Smad3 inhibitor (SIS3). These results suggest that the TGFβ-activated Smad3/HDAC2 complex is an essential negative regulator for MUC5AC expression and an epigenetic regulator for NF-κB acetylation. Therefore, these results collectively suggest that modulation of the TGFβ1/Smad3/HDAC2/NF-κB pathway axis can be a promising way to improve lung function as a treatment strategy for asthma and COPD.

Chemocentric Informatics Analysis: Dexamethasone Versus Combination Therapy for COVID-19

COVID-19 is a biphasic infectious disease with no approved vaccine or pharmacotherapy. The first drug that has shown promise in reducing COVID-19 mortality in severely-ill patients is dexamethasone, a cheap, well-known anti-inflammatory glucocorticoid, approved for the treatment of inflammatory conditions including respiratory diseases such as asthma and tuberculosis. However, about 80% of COVID-19 patients requiring oxygenation, and about 67% of patients on ventilators, are not responsive to dexamethasone therapy mainly. Additionally, using higher doses of dexamethasone for prolonged periods of time can lead to severe side effects and some patients may develop corticosteroid resistance leading to treatment failure. In order to increase the therapeutic efficacy of dexamethasone in COVID-19 patients, while minimizing dexamethasone-related complications that could result from using higher doses of the drug, we applied a chemocentric informatics approach to identify combination therapies. Our results indicated that combining dexamethasone with fast long-acting beta-2 adrenergic agonists (LABAs), such as formoterol and salmeterol, can ease respiratory symptoms hastily, until dexamethasone's anti-inflammatory and immunosuppressant effects kick in. Our studies demonstrated that LABAs and dexamethasone (or other glucocorticoids) exert synergistic effects that will augment both anti-inflammatory and fibronectin-mediated anticoagulant effects. We also propose other alternatives to LABAs that are supported by sound systems biology evidence, such as nitric oxide. Other drugs such as sevoflurane and treprostinil interact with the SARS-CoV-2 interactome and deserve further exploration. Moreover, our chemocentric informatics approach provides systems biology evidence that combination therapies for COVID-19 will have higher chances of perturbing the SARS-CoV-2 human interactome, which may negatively impact COVID-19 disease pathways.

Recent Advances in the Development of Novel Drug Candidates for Regulating the Secretion of Pulmonary Mucus

Hypersecretion of pulmonary mucus is a major pathophysiological feature in allergic and inflammatory respiratory diseases including asthma and chronic obstructive pulmonary disease (COPD). Overproduction and/or oversecretion of mucus cause the airway obstruction and the colonization of pathogenic microbes. Developing a novel pharmacological agent to regulate the production and/or secretion of pulmonary mucus can be a useful strategy for the effective management of pathologic hypersecretion of mucus observed in COPD and asthma. Thus, in the present review, we tried to give an overview of the conventional pharmacotherapy for mucus-hypersecretory diseases and recent research results on searching for the novel candidate agents for controlling of pulmonary mucus hypersecretion, aiming to shed light on the potential efficacious pharmacotherapy of mucus-hypersecretory diseases.

Dexamethasone Treatment Increases the Intracellular Calcium Level Through TRPV6 in A549 Cells

This study investigated the effect of dexamethasone (DEX) on intracellular calcium levels and the expressions of transient receptor potential cation channel subcomponent V member 6 (TRPV6), sodium-calcium exchanger 1 (NCX1), and plasma membrane calcium ATPase 1 (PMCA1) in A549 cells. The intracellular calcium level, by using the calcium indicator pGP-CMV-GCaMP6f, increased following DEX treatment for 6, 12, and 24 h in A549 cells. In addition, Rhod-4 assay after DEX treatment for 24 h showed that DEX increased the level of intracellular calcium. The expression of the calcium influx TRPV6 gene significantly increased, whereas the expressions of the calcium outflow NCX1 and PMCA1 genes significantly decreased with DEX treatment. The mRNA levels of surfactant protein genes SFTPA1, SFTPB, SFTPC, and SFTPD and the secreted airway mucin genes MUC1 and MUC5AC were investigated by treating cells with DEX. The DEX treatment decreased the mRNA levels of SFTPA1 and SFTPB but increased the mRNA levels of SFTPC and SFTPD. The MUC1 mRNA level was increased by DEX treatment, whereas MUC5AC mRNA was significantly decreased. These results indicate that DEX influences the intracellular calcium level through TRPV6, and affects pulmonary surfactant genes and secreted airway mucin genes in A549 cells.

Fluorometholone modulates gene expression of ocular surface mucins

PURPOSE

Mucins are vital to keep the ocular surface hydrated. Genes encoding for mucins contain a glucocorticoid response element. The purpose of this study was to evaluate the effect of fluorometholone, a glucocorticoid receptor agonist used in the management of dry eye, on the gene expression of conjunctival and corneal epithelial cell mucins.

METHODS

Stratified cultures of human conjunctival and corneal epithelial cells were exposed to 25, 50 and 100 nM of fluorometholone alone or in presence of mifepristone, a glucocorticoid receptor antagonist. The mRNA was isolated from the cells and reverse transcribed to cDNA. The cDNA was used for quantification of gene expression of mucin (MUC) 1, 4, 16 and 19 using real-time PCR.

RESULTS

Fluorometholone caused a dose- and time-dependent increase in the gene expression of MUC1, MUC4, MUC16 and MUC19 in the conjunctival as well as corneal epithelial cells. Mifepristone, a glucocorticoid receptor antagonist, inhibited fluorometholone-mediated increase in the gene expression of conjunctival and corneal mucins. At the tested concentration, neither fluorometholone nor mifepristone caused any notable changes in the cellular phenotype or viability of conjunctival and corneal epithelial cells.

CONCLUSION

Fluorometholone increases the gene expression of MUC1, MUC4, MUC16 and MUC19 in the conjunctival and corneal epithelial cells through activation of glucocorticoid receptors. The increased expression of mucins can be an additional possible mechanism contributing to the beneficial effects of fluorometholone in dry eye in addition to its well-known anti-inflammatory effects.

Strategies for measuring airway mucus and mucins

Mucus secretion and mucociliary transport are essential defense mechanisms of the airways. Deviations in mucus composition and secretion can impede mucociliary transport and elicit airway obstruction. As such, mucus abnormalities are hallmark features of many respiratory diseases, including asthma, cystic fibrosis and chronic obstructive pulmonary disease (COPD). Studying mucus composition and its physical properties has therefore been of significant interest both clinically and scientifically. Yet, measuring mucus production, output, composition and transport presents several challenges. Here we summarize and discuss the advantages and limitations of several techniques from five broadly characterized strategies used to measure mucus secretion, composition and mucociliary transport, with an emphasis on the gel-forming mucins. Further, we summarize advances in the field, as well as suggest potential areas of improvement moving forward.

The Gata2 repression during 3T3-L1 preadipocyte differentiation is dependent on a rapid decrease in histone acetylation in response to glucocorticoid receptor activation

The transcription factor GATA2 is an anti-adipogenic factor whose expression is downregulated during adipocyte differentiation. The present study attempted to clarify the molecular mechanism underlying the GATA2 repression and found that the repression is dependent on the activation of the glucocorticoid receptor (GR) during 3T3-L1 preadipocyte differentiation. Although several recognition sequences for GR were found in both the proximal and distal regions of the Gata2 locus, the promoter activity was not affected by the GR activation in the reporter assays, and the CRISPR-Cas9-mediated deletion of the two distal regions of the Gata2 locus was not involved in the GR-mediated Gata2 repression. Notably, the level of histone acetylation was markedly reduced at the Gata2 locus during 3T3-L1 differentiation, and the GR-mediated Gata2 repression was significantly relieved by histone deacetylase inhibition. These results suggest that GR regulates the Gata2 gene by reducing histone acetylation in the early phase of adipogenesis.

Mucin 1 downregulation impairs the anti-necroptotic effects of glucocorticoids in human bronchial epithelial cells

AIMS

To investigate whether mucin 1 (MUC1) downregulation reduced the sensitivity of tumor necrosis factor-alpha (TNF-α)-induced bronchial epithelial cells to glucocorticoid-mediated necroptosis and explore the underlying mechanisms.

MAIN METHODS

The human lung bronchial epithelial cell line (16HBE) was transfected with small interfering RNA (siRNA) against MUC1 and then stimulated by TNF-α, where some cells were pretreated with dexamethasone. Flow cytometry was performed to analyze necroptosis in 16HBE cells, and western blot analysis was used to detect protein expression levels of MUC1, glucocorticoid receptor (GR)α, GRβ, NF-κB p65, phospho-p65 (p-p65), and histone deacetylase-2 (HDAC2). Additionally, nuclear translocation of MUC1 and GRα was assessed by immunofluorescence.

KEY FINDINGS

We observed that MUC1 downregulation by siRNA significantly augmented TNF-α-induced necroptosis in 16HBE cells, and that dexamethasone showed impaired anti-necroptotic effects of MUC1 downregulation. Furthermore, we found that GRα nuclear translocation was inhibited in 16HBE cells with MUC1 downregulation, and that dexamethasone-mediated inhibition of p65 phosphorylation was lower in cells transfected with MUC1-siRNA compared to those transfected with negative control siRNA.

SIGNIFICANCE

Impaired GRα nuclear translocation and inhibited p-p65 expression might contribute to glucocorticoid resistance caused by MUC1 deficiency in TNF-α-induced necroptosis in 16HBE cells, and should be considered as a potential target for the development of novel therapeutics for asthma.

Glucocorticoid receptor activation selectively influence performance of Wistar rats in Y-maze

Glucocorticoid receptors (GR) are ubiquitously expressed in metazoans. Different and contrasting phenotypes have been reported upon their activation. This study investigated the behavioral phenotypes characteristic of GR stimulation in male Wistar rats. Rats in each of the four groups of rats received one of the following treatments: distilled water (control) or one of three doses of dexamethasone (treatment) injected intraperitoneally for 7 days. The Rats were afterwards subjected to the Y maze, the elevated plus maze (EPM), the Morris water maze (MWM), and the novel object recognition (NOR) test. At the end of the study, the animals were anesthetized and neural activity from the prefrontal cortex recorded. Blood was collected via cardiac puncture to evaluate the levels of plasma insulin and glucose, and the prefrontal cortexes excised to determine the levels of insulin, markers of oxidative stress, and calcium in the homogenate. This study showed that treatment with dexamethasone significantly reduced the total and percentage alternation in the Y maze, but had no significant effect on object recognition in the NOR test, long-term and short-term spatial memory in the MWM, or anxiety-like behavior in the EPM. Plasma and brain insulin and calcium levels were elevated moderately following treatment with the lowest dose of dexamethasone. All doses of dexamethasone decreased brain superoxide dismutase and increased lactate dehydrogenase levels. No significant change in neural activity was observed. This study shows that activation of glucocorticoid receptors differentially affects different behavioral paradigms and provides evidence for a role for glucocorticoids in mediating insulin function in the brain.

Glucocorticoids

The most effective anti-inflammatory drugs used to treat patients with airways disease are topical glucocorticosteroids (GCs). These act on virtually all cells within the airway to suppress airway inflammation or prevent the recruitment of inflammatory cells into the airway. They also have profound effects on airway structural cells to reverse the effects of disease on their function. Glucorticosteroids act via specific receptors-the glucocorticosteroid receptor (GR)-which are a member of the nuclear receptor family. As such, many of the important actions of GCs are to modulate gene transcription through a number of distinct and complementary mechanisms. Targets genes include most inflammatory mediators such as chemokines, cytokines, growth factors and their receptors. GCs delivered by the inhaled route are very effective for most patients and have few systemic side effects. However, in some patients, even high doses of topical or even systemic GCs fail to control their disease. A number of mechanisms relating to inflammation have been reported to be responsible for the failure of these patients to respond correctly to GCs and these provide insight into GC actions within the airways. In these patients, the side-effect profile of GCs prevent continued use of high doses and new drugs are needed for these patients. Targeting the defective pathways associated with GC function in these patients may also reactivate GC responsiveness.

Astragalus polysaccharide modulates ER stress response in an OVA-LPS induced murine model of severe asthma

Endoplasmic reticulum (ER) stress has been recently revealed to play a pivotal role in the pathogenesis of severe asthma. Astragalus polysaccharide (APS), a major bioactive component from Astragalus membranaceus, exerts immunomodulatory and anti-inflammatory effects and has been shown to suppress ER stress in chronic diseases such as type-2 diabetes. However, the pharmaceutical application of APS in the treatment of severe asthma is unknown. The results obtained here indicate that APS significantly attenuates eosinophils and neutrophil-dominant airway inflammation by reducing the mRNA levels of Cxcl5, Il8, and chemokine (C-C motif) ligand 20 (Ccl20) and the protein levels of IL13RA and IL17RA. APS also inhibits the activation of unfolded protein response by decreasing the levels of ER stress markers such as C/EBP homologous protein (CHOP), which was associated with a reduction of PERK phosphorylation. Moreover, APS substantially blocks the nuclear translocation of ATF6 and NF-κB p65. Interestingly, we observed that APS markedly suppresses mucus hypersecretion by decreasing the levels of mucin (MUC) 5AC and MUC5B, which might be due to inhibition of goblet cells differentiation by suppressing the expression of IRE1β-correlated genes. In summary, APS can have potential pharmaceutical application in treatment of severe asthma.

Autocrine Acetylcholine, Induced by IL-17A via NFκB and ERK1/2 Pathway Activation, Promotes MUC5AC and IL-8 Synthesis in Bronchial Epithelial Cells

IL-17A is overexpressed in the lung during acute neutrophilic inflammation. Acetylcholine (ACh) increases IL-8 and Muc5AC production in airway epithelial cells. We aimed to characterize the involvement of nonneuronal components of cholinergic system on IL-8 and Muc5AC production in bronchial epithelial cells stimulated with IL-17A. Bronchial epithelial cells were stimulated with recombinant human IL-17A (rhIL-17A) to evaluate the ChAT expression, the ACh binding and production, the IL-8 release, and the Muc5AC production. Furthermore, the effectiveness of PD098,059 (inhibitor of MAPKK activation), Bay11-7082 (inhibitor of IkBα phosphorylation), Hemicholinium-3 (HCh-3) (choline uptake blocker), and Tiotropium bromide (Spiriva®) (anticholinergic drug) was tested in our in vitro model. We showed that rhIL-17A increased the expression of ChAT, the levels of ACh binding and production, and the IL-8 and Muc5AC production in stimulated bronchial epithelial cells compared with untreated cells. The pretreatment of the cells with PD098,059 and Bay11-7082 decreased the ChAT expression and the ACh production/binding, while HCh-3 and Tiotropium decreased the IL-8 and Muc5AC synthesis in bronchial epithelial cells stimulated with rhIL-17A. IL-17A is involved in the IL-8 and Muc5AC production promoting, via NFκB and ERK1/2 pathway activation, the synthesis of ChAT, and the related activity of autocrine ACh in bronchial epithelial cells.

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.

Glucocorticoids and the Lung

The lung is a major clinical target of glucocorticoid-based therapeutics, and GR signaling has broad effects on respiratory physiology and inflammation. During lung development, expression of GR in the mesenchyme is required for normal terminal alveolar epithelial differentiation. Prenatal administration of exogenous glucocorticoids (GCs) to prevent neonatal respiratory distress syndrome, however, promotes alveolar maturation and accelerates surfactant expression in a manner consistent with direct effects on the developing alveolar epithelium. Likewise, cell autonomous effects of GCs in regulating gene expression and phenotype of the airway epithelium and airway smooth muscle have been demonstrated to control important therapeutic effects of GCs in treating asthma and chronic obstructive pulmonary disease. Here, mechanisms and consequences of GR signaling in the developing lung and in treating obstructive lung disease are reviewed, with a focus on direct effects of GR signaling on alveolar differentiation, surfactant expression, and airway epithelial and smooth muscle pathophysiology.

Mucins in lung cancer: diagnostic, prognostic, and therapeutic implications

Aberrant expression of mucins is associated with cancer development and metastasis. An overexpression of few mucins contributes to oncogenesis by enhancing cancer cell growth and providing constitutive survival signals. This review focuses on the importance of mucins both in the normal bronchial epithelial cells and the malignant tumors of the lung and their contribution in the diagnosis and prognosis of lung cancer patients. During lung cancer progression, mucins either alone or through their interaction with many receptor tyrosine kinases mediate cell signals for growth and survival of cancer cells. Also, stage-specific expression of certain mucins, like MUC1, is associated with poor prognosis from lung cancer. Thus, mucins are emerging as attractive targets for developing novel therapeutic approaches for lung cancer. Several strategies targeting mucin expression and function are currently being investigated to control lung cancer progression.

Exploring the role and diversity of mucins in health and disease with special insight into non-communicable diseases

Mucins are major glycoprotein components of the mucus that coats the surfaces of cells lining the respiratory, digestive, gastrointestinal and urogenital tracts. They function to protect epithelial cells from infection, dehydration and physical or chemical injury, as well as to aid the passage of materials through a tract i.e., lubrication. They are also implicated in the pathogenesis of benign and malignant diseases of secretory epithelial cells. In Human there are two types of mucins, membrane-bound and secreted that are originated from mucous producing goblet cells localized in the epithelial cell layer or in mucous producing glands and encoded by MUC gene. Mucins belong to a heterogeneous family of high molecular weight proteins composed of a long peptidic chain with a large number of tandem repeats that form the so-called mucin domain. The molecular weight is generally high, ranging between 0.2 and 10 million Dalton and all mucins contain one or more domains which are highly glycosylated. The size and number of repeats vary between mucins and the genetic polymorphism represents number of repeats (VNTR polymorphisms), which means the size of individual mucins can differ substantially between individuals which can be used as markers. In human it is only MUC1 and MUC7 that have mucin domains with less than 40% serine and threonine which in turn could reduce number of PTS domains. Mucins can be considered as powerful two-edged sword, as its normal function protects from unwanted substances and organisms at an arm's length while, malfunction of mucus may be an important factor in human diseases. In this review we have unearthed the current status of different mucin proteins in understanding its role and function in various non-communicable diseases in human with special reference to its organ specific locations. The findings described in this review may be of direct relevance to the major research area in biomedicine with reference to mucin and mucin associated diseases.

The Flavonoid 7,4'-Dihydroxyflavone Inhibits MUC5AC Gene Expression, Production, and Secretion via Regulation of NF-κB, STAT6, and HDAC2

Mucus overproduction is a significant component of the pathophysiology of obstructive lung diseases. Currently, there are only a few medications available that inhibit mucus production. Previous studies showed that glycyrrhizin, a triterpenoid in Glycyrrhiza uralensis inhibits mucin 5AC (MUC5AC) mRNA and protein expression. Other potential mucus production inhibitory compounds contained within in G. uralensis have not been fully investigated. The aim of the present study was to determine if the G. uralensis flavonoid 7,4'-dihydroxyflavone (7,4'-DHF) inhibits MUC5AC gene expression, mucus production, and secretion, and if so, to elucidate the mechanism of this inhibition. 7,4'-Dihydroxyflavone significantly decreased phorbol 12-myristate 13-acetate-stimulated NCI-H292 human airway epithelial cell MUC5AC gene expression and mucus production, at a 28-fold lower concentration than glycyrrhizin (The half maximal inhibitory concentration IC50 value of 1.4 μM vs 38 μM, respectively); 7,4'-DHF also inhibited MUC5AC mucus secretion. Inhibition was associated with the suppression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), signal transducer and activator of transcription 6 (STAT6) activation, and enhanced histone deacetylase 2 (HDAC2) expression. In a murine model of asthma, 7,4'-DHF-treated mice exhibited a marked reduction in MUC5AC secretion in the bronchoalveolar lavage fluid compared with control mice. These findings, together with previous findings linking NF-κB, STAT6, and HDAC2 modulation to the control of MUC5AC expression, demonstrate that 7,4'-DHF is a newly identified component of G. uralensis that regulates MUC5AC expression and secretion via regulation of NF-κB, STAT6, and HDAC2.

Molecular mechanisms of repeated social defeat-induced glucocorticoid resistance: Role of microRNA

Glucocorticoid (GC) resistance is a severe problem associated with various inflammatory diseases. Previous studies have shown that repeated social stress induces GC resistance in innate immune cells, but the underlying molecular mechanisms have not been fully elucidated. Therefore, the purpose of this study was to examine potential underlying molecular mechanism(s) of repeated social defeat (RSD) stress on GC resistance in splenic macrophages. It was hypothesized that mRNA expression of receptors for GC and nuclear translocating-associated regulators in splenic macrophages would be affected by RSD, and that these changes would be associated with epigenetic modification. The data showed that the mRNA expression of GC and mineralocorticoid receptors were significantly decreased in splenic macrophages by RSD. RSD also induced a significantly decreased mRNA expression in FK506-binding protein 52 (FKBP52), consequently resulting in a significantly increased ratio of FKBP51 to FKBP52. Moreover, DNA methyltransferases 3a and 3b showed a significant decrease in their mRNA expression in the RSD group as did mRNA expression of histone deacetyltransferase 2. The RSD group also showed a significantly reduced quantity of methylated DNA in splenic macrophages. Based on microRNA (miRNA) profiling data, it was determined that RSD induced significantly increased expression of 9 different miRNAs that were predicted to interact with mRNAs of the GC receptor (6 miRNAs), mineralocorticoid receptor (3 miRNAs) and FKBP52 (2 miRNAs). Spearman correlation analysis revealed significantly strong correlations between the expression of 2 miRNAs and their target mRNA expression for GC receptors. Among these miRNAs, we verified direct effects of miRNA-29b and -340 overexpression on mRNA expression of GC receptors in L929 cells. The overexpression of miRNA-29b or -340 in L929 cells significantly reduced LPS-induced overexpression of GC receptors. In conclusion, this study provides evidence that epigenetic regulation, such as DNA methylation and miRNA expression, may play a role in the RSD-induced GC resistance that we have observed in splenic macrophages.

Histone deacetylases and their inhibitors: new implications for asthma and chronic respiratory conditions

PURPOSE OF REVIEW

The importance of the role of histone deacetylase enzymes in the pathogenesis of asthma and chronic respiratory diseases is increasingly being recognized. Similarly, the potential clinical utility of histone deacetylase enzymes in the treatment of disease is emerging. In this review, the role of histone deacetylases (HDAC) and their inhibitors in asthma and chronic obstructive pulmonary disease is discussed.

RECENT FINDINGS

HDAC are able to catalyze the hydrolysis of acetyl groups on lysine residues of histones, causing the condensation and coiling of chromosomal DNA around histones, and therefore regulating gene expression. Histone deacetylase inhibitors act specifically or broadly on HDAC and also on nonhistone targets. Some have been used in the oncology therapeutic field for some years, but it is only more recently that they have been suggested in the treatment of asthma and other inflammatory lung diseases.

SUMMARY

Important developments have been made in the understanding of histone deacetylase expression in normal and diseased airways and pulmonary tissue as well as effects of histone deacetylase inhibitors on structural and inflammatory cells in the lung, including cell proliferation, differentiation and apoptosis and senescence. Many of these discoveries may have implications in addressing airway inflammation, airway remodeling and airway hyperresponsiveness in asthma.

Melatonin inhibits MUC5AC production via suppression of MAPK signaling in human airway epithelial cells

Mucus acts as a primary defense system in the airway against various stimuli. However, excess mucus production causes a reduction in lung function via limitation of the airflow in the airway of patients suffering from asthma or chronic obstructive pulmonary disease (COPD). In this study, we evaluated the effects of melatonin on the production of MUC5AC, a major constituent of the mucin that is secreted from the airway, using epidermal growth factor (EGF)-stimulated NCI-H292 cells, a human mucoepidermoid carcinoma cell line, and an ovalbumin (OVA)-induced asthma murine model. Melatonin treatment significantly reduced the mRNA and protein levels of MUC5AC and reduced interleukin (IL)-6 production in EGF-stimulated H292 cells. Melatonin markedly decreased the phosphorylation of MAPKs, including ERK1/2, JNK, and p-38, induced by EGF stimulation. These findings were consistent with the results using MAPK inhibitors. Particularly, co-treatment with melatonin and a MAPK inhibitor more effectively suppressed MAPK phosphorylation than treatment with a MAPK inhibitor alone, which resulted in a reduction in MUC5AC expression. In the asthma murine model, melatonin-treated mice exhibited a marked reduction in MUC5AC expression in the airway compared with the OVA-induced mice. These reductions were accompanied by reductions in proinflammatory cytokine production and inflammatory cell infiltration. Collectively, these findings indicate that melatonin effectively inhibits MUC5AC expression. These effects may be closely associated with the inhibition of MAPK phosphorylation. Furthermore, our study suggests that melatonin could represent a potential therapeutic for chronic airway diseases, such as asthma and COPD.

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.

Minireview: The versatile roles of lysine deacetylases in steroid receptor signaling

Lysine deacetylases have been known to regulate nuclear receptor function for many years. In the unliganded state, nuclear receptors that form heterodimers with retinoid X receptors, such as the retinoic acid and thyroid hormone receptors, associate with deacetylases to repress target genes. In the case of steroid receptors, binding of an antagonist ligand was initially reported to induce association of deacetylases to prevent activation of target genes. Since then, deacetylases have been shown to have diverse functions in steroid receptor signaling, from regulating interactions with molecular chaperones to facilitating their ability to activate transcription. The purpose of this review is to summarize recent studies on the role of deacetylases in steroid receptor signaling, which show deacetylases to be highly versatile regulators of steroid receptor function.

Glucocorticoid dexamethasone regulates the differentiation of mouse conducting airway epithelial progenitor cells

Inhaled glucocorticoid dexamethasone is the most effective treatment of asthma currently available. Epithelial damage and shedding represents a clear manifestation of asthmatic pathologies. However it remains unknown if dexamethasone regulates functions of airway progenitor cells that are responsible for epithelial repair. In present study Secretoglobin1a1 (Scgb1a1) lineage tracing mice were injected intraperitoneally with tamoxifen to induce the expression of green fluorescence protein (GFP) in Scgb1a1-expressing conducting airway progenitor cells. Scgb1a1-expressing progenitor cells were isolated from lungs of Scgb1a1 lineage tracing mice via flow activated cell sorting. In vitro three-dimensional matrigel culture of these progenitor cells revealed that dexamethasone has little effect on the colony forming ability of airway epithelial progenitor cells, but exhibits significant effects on the differentiation of the progenitor cells. Compared to the untreated group, dexamethasone treatment inhibited the expression of forkhead box J1 (FoxJ1) and mucin subtype A & C (Muc5Ac), but promoted the expression of calcium activated chloride channel 3 (Clca3) and cystic fibrosis transmembrane conductance regulator (Cftr). Dexamethasone-induced effects on the expression of FoxJ1, Muc5Ac and Clca3 were abolished or even reversed in the presence of RU486, an antagonist of glucocorticoid receptor, indicating that glucocorticoid receptor plays a role in the regulation of airway epithelial progenitor cells by dexamethasone. These data suggested that, though effective to reduce airway inflammation, dexamethasone treatment alone fails to fully restore the mucociliary clearance function in the treatment of asthma patients.

The effect of dexamethasone on lentiviral vector infection is associated with importin α

Importin α (Imα) plays an important role during the shuttling of the HIV-1 preintegration complex (PIC) from the cytoplasm to the nucleus. Imα may bind to the glucocorticoid receptor (GR), which is localized to nucleus following hormone binding. However, it remains unclear whether the binding of dexamethasone (Dex) to GR affects the Imα redistribution and, thus, alters PIC import. In our study, 293T cells were transfected with the lentiviral vector (LV) carrying the luciferase (Luci) gene following Dex or RU486 pretreatment. The Luci activity (LucA) in the Dex or RU486 group was significantly higher compared to that in the control group (P≤0.01). The effects of Dex and RU486 were inhibited by the Imα inhibitor Bimax1 (P≤0.01), although the inhibitory effect of Bimax1 was alleviated by increasing the Dex dose. Furthermore, it was observed that the LucA in the 30-min Dex treatment group was lower compared to that in the 30-min Dex pretreatment group (P≤0.01). These results suggested that Dex may improve PIC import via increasing the cytoplasmic Imα levels. Kunming mice were transfected in vivo with the LV, either 30 min or 15 h following an intraperitoneal injection of Dex. The LucA in the liver of the 30-min group mice was significantly lower compared to that of the 15-h group mice (P≤0.01), suggesting that the effect of Dex on LV infection depends mainly on the suppression of immune and inflammatory responses in vivo. Taken together, our data indicated that the effect of Dex on LV infection may be associated with Imα, constituting a novel signaling pathway mediating the effects of Dex on HIV-1 infection.

Anti-inflammatory effects of budesonide in human lung fibroblast are independent of histone deacetylase 2

Objective and design

Reduced expression of histone deacetylase 2 (HDAC2) in alveolar macrophages and epithelial cells may account for reduced response of chronic obstructive pulmonary disease (COPD) patients to glucocorticoids. HDAC2 expression and its role in mediating glucocorticoid effects on fibroblast functions, however, has not been fully studied. This study was designed to investigate whether HDAC2 mediates glucocorticoid effects on release of inflammatory cytokines and matrix metalloproteinases (MMPs) from human lung fibroblasts.

Methods

Human lung fibroblasts (HFL-1 cells) were stimulated with interleukin (IL)-1 β plus tumor necrosis factor (TNF)-α in the presence or absence of the glucocorticoid budesonide. Cytokines (IL-6 and IL-8) were quantified by enzyme linked immunosorbent assay (ELISA) and MMPs (MMP-1 and MMP-3) by immunoblotting in culture medium. The role of HDAC2 was investigated using a pharmacologic inhibitor as well as a small interfering ribonucleic acid (siRNA) targeting HDAC2.

Results

We have demonstrated that budesonide concentration-dependently (10⁻¹⁰–10⁻⁷ M) inhibited IL-6, IL-8, MMP-1, and MMP-3 release by HFL-1 cells in response to IL-1β plus TNF-α. While an HDAC inhibitor significantly blocked the inhibitory effect of budesonide on human bronchial epithelial cells (HBECs) and monocytes (THP-1 cells), it did not block the inhibitory effect of budesonide on release of cytokines and MMPs from HFL-1 cells. Similarly, an HDAC2-siRNA blocked budesonide inhibition of cytokine release in HBECs, but it did not block the inhibitory effect of budesonide on HFL-1 cytokine and MMP release. Furthermore, budesonide significantly blocked release of cytokines and MMPs to a similar degree in normal and COPD lung fibroblasts as well as in HFL-1 cells exposed or not exposed to cigarette smoke extract.

Conclusion

These findings suggest that, in contrast to airway epithelial cells and monocytes/macrophages, HDAC2 is not required for budesonide to inhibit MMP and cytokine release by lung fibroblasts and this inhibitory pathway appears to be intact in cultured fibroblasts from COPD patients. These results also suggest that budesonide has the potential to modulate fibroblast-mediated tissue remodeling following airway inflammation in COPD, which is mediated via an HDAC2 independent pathway.

Chronic cough and sputum production are associated with worse clinical outcomes in stable asthma

BACKGROUND

Chronic cough and sputum production (chronic mucus hypersecretion) is a poorly described clinical feature of asthma. Our objective was to identify clinical, immunological and computed tomography (CT) measures of airway wall dimensions associated with these symptoms in smokers and never smokers with asthma.

METHODS

Cross-sectional data was analysed from 120 smokers and never smokers with asthma. Participants with and without a history of chronic mucus hypersecretion were compared for clinical outcomes, sputum differential cell counts and CT measures of airway dimensions (wall thickness, luminal area and percent wall area).

RESULTS

Chronic mucus hypersecretion occurred in a higher proportion of smokers with asthma (56%) than never smokers with asthma (20%), (p < 0.001) and the proportion of patients with these symptoms increased with asthma severity (p = 0.003). Smokers with asthma and chronic mucus hypersecretion had worse current clinical control than smokers without those symptoms [ACQ score 2.3 versus 1.6, p = 0.002]. A greater proportion of never smokers with chronic mucus hypersecretion required short courses of oral corticosteroids in the last year (58% versus 19%, p = 0.011). Sputum neutrophil and eosinophil counts were similar in asthma patients with or without chronic mucus hypersecretion. Of those with severe asthma and chronic mucus hypersecretion, a CT measure of airway lumen area was reduced in smokers compared to never smokers (11.4 mm(2) versus 18.4 mm(2); p = 0.017).

CONCLUSIONS

Chronic mucus hypersecretion occurs frequently in adults with stable asthma, particularly in smokers with severe disease and is associated with worse current clinical control in smokers and more exacerbations in never smokers.

Cellular and molecular biology of airway mucins

Airway mucus constitutes a thin layer of airway surface liquid with component macromolecules that covers the luminal surface of the respiratory tract. The major function of mucus is to protect the lungs through mucociliary clearance of inhaled foreign particles and noxious chemicals. Mucus is comprised of water, ions, mucin glycoproteins, and a variety of other macromolecules, some of which possess anti-microbial, anti-protease, and anti-oxidant activities. Mucins comprise the major protein component of mucus and exist as secreted and cell-associated glycoproteins. Secreted, gel-forming mucins are mainly responsible for the viscoelastic property of mucus, which is crucial for effective mucociliary clearance. Cell-associated mucins shield the epithelial surface from pathogens through their extracellular domains and regulate intracellular signaling through their cytoplasmic regions. However, neither the exact structures of mucin glycoproteins, nor the manner through which their expression is regulated, are completely understood. This chapter reviews what is currently known about the cellular and molecular properties of airway mucins.