Effect of glucocorticoid on the MUC4 gene in nasal polyps

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.

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.

A Comprehensive Systematic Review of the Association Between Airway Mucins and Chronic Rhinosinusitis

Objective

Airway mucins are the major constituents of mucus and one of the first lines of host defense against inhaled pathogens. However, aberrant expression of mucins is associated with mucus hypersecretion resulting in chronic nasal drainage, a common complaint from patients with chronic rhinosinusitis (CRS). Our goal in this systematic review was to determine (1) expression profiles, (2) regulatory mechanisms, and (3) the pathologic roles of mucins associated with CRS.

Methods

MEDLINE, Cochrane Library, Embase, Scopus, Web of Science, and ClinicalTrials.gov were searched for studies focused on the role of mucins in CRS. Quality was assessed using the Cochrane Risk of Bias tool. The full text articles selected were then categorized into 3 study groups: (1) clinical, (2) animal, and (3) in vitro cultures. Data regarding study design, population/setting, methods, and bias were extracted and synthesized.

Results

Our initial search generated 392 titles/abstracts. After the primary review, 111 articles underwent secondary review. The final review included 53 articles, including 34 articles (64%) in the clinical study group, 3 articles (6%) in the animal study group, and 16 articles (30%) in the in vitro study group. In total, aberrant expression of 8 mucins—6 secreted-mucins (MUC2, -5AC, -5B, -6, -7, and -8) and 2 membrane-bound mucins (MUC1 and -4)—were identified in CRS tissues compared to healthy controls. Mucin expression was associated with bacterial sinusitis, inflammatory markers, and the response to steroid therapy in patients with CRS with nasal polyposis.

Conclusion

There is a strong correlation between alterations in mucin expression profiles and CRS. This systematic review highlights the most recent literature on the role of mucins in CRS. The analysis of these studies is limited by the heterogeneity in study designs, relatively few numbers of clinical samples, and lack of mechanistic studies in animal models and in vitro cultures.

MUC4 mucin- a therapeutic target for pancreatic ductal adenocarcinoma

INTRODUCTION

Pancreatic cancer (PC) is characterized by mucin overexpression. MUC4 is the most differentially overexpressed membrane-bound mucin that plays a functional role in disease progression and therapy resistance. Area covered: We describe the clinicopathological significance of MUC4, summarize mechanisms contributing to its deregulated expression, review preclinical studies aimed at inhibiting MUC4, and discuss how MUC4 overexpression provides opportunities for developing targeted therapies. Finally, we discuss the challenges for developing MUC4-based therapeutics, and identify areas where efforts should be directed to effectively exploit MUC4 as a therapeutic target for PC. Expert opinion: Studies demonstrating that abrogation of MUC4 expression reduces proliferation and metastasis of PC cells and enhances sensitivity to therapeutic agents affirm its utility as a therapeutic target. Emerging evidence also supports the suitability of MUC4 as a potential immunotherapy target. However, these studies have been limited to in vitro, ex vivo or in vivo approaches using xenograft tumors in immunodeficient murine models. For translational relevance, MUC4-targeted therapies should be evaluated in murine models with intact immune system and accurate tumor microenvironment. Additionally, future studies evaluating MUC4 as a target for immunotherapy must entail characterization of immune response in PC patients and investigate its association with immunosuppression and survival.

MUC4 impairs the anti-inflammatory effects of corticosteroids in patients with chronic rhinosinusitis with nasal polyps

BACKGROUND

Current evidence suggests that membrane-tethered mucins could mediate corticosteroid efficacy, interacting with glucocorticoid receptor (GR) in patients with chronic rhinosinusitis with nasal polyps (CRSwNP). Mucin 4 (MUC4)-tethered mucin is expressed in nasal polyp (NP) epithelial cells and upregulated under inflammatory conditions. Moreover, MUC4β has the capacity to interact with other intracellular proteins. We hypothesized that MUC4 modulates corticosteroid efficacy of patients with CRSwNP.

OBJECTIVE

We sought to analyze the role of MUC4 in corticosteroid effectiveness in different cohorts of patients with CRSwNP and elucidate the possible mechanisms involved.

METHODS

Eighty-one patients with CRSwNP took oral corticosteroids for 15 days. Corticosteroid resistance was evaluated by using nasal endoscopy. Expression of MUC4 and MUC4β was evaluated by means of real-time PCR, Western blotting, and immunohistochemistry. BEAS-2B knockdown with RNA interference for MUC4 (small interfering RNA [siRNA]-MUC4) was used to analyze the role of MUC4 in the anti-inflammatory effects of dexamethasone.

RESULTS

Twenty-two patients had NPs resistant to oral corticosteroids. MUC4 expression was upregulated in these patients. In siRNA-MUC4 BEAS-2B airway epithelial cells dexamethasone produced higher anti-inflammatory effects, increased inhibition of phospho-extracellular signal-regulated kinase 1/2, increased mitogen-activated protein kinase phosphatase 1 expression, and increased glucocorticoid response element activation. Immunoprecipitation and immunofluorescence experiments revealed that MUC4β forms a complex with GRα in the nuclei of NP epithelial cells from corticosteroid-resistant patients.

CONCLUSION

MUC4β participates in the corticosteroid resistance process, inhibiting normal GRα nuclear function. The high expression of MUC4 in patients with CRSwNP might participate in corticosteroid resistance.

Transcriptional regulation of human MUC4 gene: identification of a novel inhibitory element and its nuclear binding protein

The human mucin 4 (MUC4) is aberrantly expressed in pancreatic adenocarcinoma and tumor cell lines, while remaining undetectable in normal pancreas, indicating its important role in pancreatic cancer development. Although its transcriptional regulation has been investigated in considerable detail, some important elements remain unknown. The aim of the present study was to demonstrate the existence of a novel inhibitory element in the MUC4 promoter and characterize some of its binding proteins. By luciferase reporter assay, we located the inhibitory element between nucleotides -2530 and -2521 in the MUC4 promoter using a series of deletion and mutant reporter constructs. Electrophoretic mobility shift assay (EMSA) with Bxpc-3 cell nuclear extracts revealed that one protein or protein complex bind to this element. The proteins binding to this element were purified and identified as Yin Yang 1 (YY1) by mass spectrometry. Supershift assay and chromatin immunoprecipitation (ChIP) assay confirmed that YY1 binds to this element in vitro and in vivo. Moreover, transient YY1 overexpression significantly inhibited MUC4 promoter activity and endogenous MUC4 protein expression. In conclusion, we reported here a novel inhibitory element in the human MUC4 promoter. This provides additional data on MUC4 gene regulation and indicates that YY1 may be a potential target for abnormal MUC4 expression.

Effects of Asian sand dust on mucin gene expression and activation of nasal polyp epithelial cells

BACKGROUND

Asian sand dust (ASD) contains a variety of chemical and microbiological materials such as lipopolysaccharide (LPS) and beta-glucan that can cause inflammation. The increase in the atmospheric concentration of ASD has been associated with asthma severity and adverse effects on respiratory function. The aim of this study was to evaluate the effect of ASD on the inflammatory process and mucin gene expression in nasal epithelial cells.

METHODS

Primary nasal polyp epithelial cells were exposed to ASD for 72 hours, and then the supernatants were collected. To determine the activation of the epithelial cells, IL-6, IL-8, and granulocyte-macrophage colony-stimulating factor were measured. In addition, the potential cytotoxic effects of ASD on the epithelial cells were evaluated. Quantitative reverse-transcription polymerase chain reaction for MUC4, MUC5AC, MUC5B, and MUC8 mRNA expression, in the nasal epithelial cells, was performed.

RESULTS

ASD stimulated the production of chemical mediators in a time-dependent manner. The cytokine production was highest at 100 micrograms/mL of ASD. MUC4 and MUC5B mRNA expression was significantly increased at 10 and 50 micrograms/mL of ASD.

CONCLUSION

Atomospheric exposure to various chemical species and microbiological materials carrying ASD may affect upper airway inflammation through the production of inflammatory cytokines and mucin.

Leptin up-regulates MUC5B expression in human airway epithelial cells via mitogen-activated protein kinase pathway

Leptin, an adipocyte-secreted hormone that regulates food intake and metabolic response, has been recently reported to increase in the serum during inflammatory airway disease associated with mucus-hypersecretion. We investigated the effects of leptin on mucin expression in human airway epithelial cells and the signaling pathways. The expression of the leptin receptor was evaluated in human nasal mucosa and NCI-H292 cells. Leptin-induced expression of major respiratory mucins in NCI-H292 cells was analyzed. Mutant leptin, which acts as a receptor antagonist, and specific inhibitors of extracellular signal-regulated kinase (ERK1/2), p38 and Janus kinase-2 (JAK2)/signal transducer and activator of transcription-3 (STAT3) were used. Leptin receptors were expressed in the nasal mucosa and NCI-H292 cells. Treatment with leptin significantly increased the expression of MUC5AC and MUC5B in NCI-H292 cells; these effects were blocked by mutant leptin. The cells activated by leptin showed increased ERK1/2, p38, and STAT3 phosphorylation. Leptin-induced MUC5B expression was blocked by the ERK1/2 and p38 pathway inhibitors, but not by the JAK2/STAT3 pathway inhibitor. Leptin might significantly contribute to the production of major gel-forming mucins by direct stimulation of airway epithelial cells and the activation of leptin receptors coupled with the activation of ERK1/2 or p38, but not the JAK2/STAT3 pathway.

Significance of susceptible gene expression profiles in nasal polyposis

Nasal polyposis (NP) is a common chronic inflammatory disease of the rhinosinus mucosa and a complex disease with strong genetic and environmental components. During the past 10 to 20 yr, many studies have been performed to determine differential gene expression profiles between NP and normal nasal tissues, in order to identify susceptible genes that are associated with NP-related traits. Despite achievement in the identification of candidate genes and their associated pathogenic pathways, the large challenges remain as the genetic and molecular alterations required for its development and progression are still unclear. Therefore, the development of novel, powerful tools for gene discovery, and a closer integration of genetics and medical biology would provide valuable insight into the pathogenesis of NP.