Glucocorticoid Receptor and Histone Deacetylase–2 Mediate Dexamethasone-Induced Repression of MUC5AC Gene Expression

Abstract

Airway occlusion in obstructive airway diseases is caused in part by the overproduction of secretory mucin glycoproteins through the up-regulation of mucin (MUC) genes by inflammatory mediators. Some pharmacological agents, including the glucocorticoid dexamethasone (Dex), repress mucin concentrations in lung epithelial cancer cells. Here, we show that Dex reduces the expression of MUC5AC, a major airway mucin gene, in primary differentiated normal human bronchial epithelial (NHBE) cells in a dose-dependent and time-dependent manner, and that the Dex-induced repression is mediated by the glucocorticoid receptor (GR) and two glucocorticoid response elements (GREs) in the MUC5AC promoter. The preexposure of cells to RU486, a GR antagonist, and mutations in either the GRE3 or GRE5 cis-sites abolished the Dex-induced repression. Chromatin immunoprecipitation (ChIP) assays showed a rapid temporal recruitment of GR to the GRE3 and GRE5 cis-elements in the MUC5AC promoter in NHBE and in A549 cells. Immunofluorescence showed nuclear colocalization of GR and histone deacetylase-2 (HDAC2) in MUC5AC-expressing NHBE cells. ChIP also showed a rapid temporal recruitment of HDAC2 to the GRE3 and GRE5 cis-elements in the MUC5AC promoter in both cell types. The knockdown of HDAC2 by HDAC2-specific short interfering RNA prevented the Dex-induced repression of MUC5AC in NHBE and A549 cells. These data demonstrate that GR and HDAC2 are recruited to the GRE3 and GRE5 cis-sites in the MUC5AC promoter and mediate the Dexinduced cis repression of MUC5AC gene expression. A better understanding of the mechanisms whereby glucocorticoids repress MUC5AC gene expression may be useful in formulating therapeutic interventions in chronic lung diseases.Keywords: MUC5AC; HDAC2; dexamethasone; gene repression; glucocorticoid receptor Mucus covers and protects the epithelium in the mammalian respiratory, gastrointestinal, and reproductive tracts, and contributes to the mucosal defense barrier (1, 2). In the respiratory tract, secreted mucin glycoproteins (mucins), the major macromolecular components of lung mucus, are part of the innate immune defense system and mucociliary escalator that protect the airways against airborne challenges (3). Mucin production is increased in chronic lung diseases and contributes to the occlusion of the conducting airways by mucus, thereby significantly affecting disease morbidity and mortality in patients with asthma, cystic fibrosis, bronchopulmonary dysplasia, and chronic obstructive pulmonary diseases (4).Mucin (MUC) genes encode the protein backbone of human mucins, and exhibit a selective tissue and cell specificity that is frequently altered in inflammatory diseases and in cancer (5, 6). Two polymeric mucins (MUC5AC and MUC5B) are normally expressed and secreted in the lungs by secretory cells in the conducting airway epithelium and submucosal glands, respectively. Increased production of MUC5AC mRNA and protein occurs in the airway epithelium and secretions of patients with asthma (7-10), and MUC5B concentrati...

CFTR, Mucins, and Mucus Obstruction in Cystic Fibrosis

“…Studies to investigate mechanisms, especially under conditions in which lung epithelial cells are exposed to inflammatory mediators, are underway in several laboratories. The glucocorticoid dexamethasone (Dex) transcriptionally represses MUC5AC gene expression following binding of Dex-activated GR to two GRE cis-sites on the MUC5AC promoter in A549 (Chen et al 2006) and in differentiated HBE cells (Chen et al 2012) and is mediated by histone deacetylase 2 (Chen et al 2012).…”

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

“…Therefore, the cytoplasm contains Dex, GR, Imα, Imα-GR, Imα-GR-Dex and GR-GR-Dex, in a dynamic balance. Dex promotes GR import, thus resulting in the nuclear retention of GR (7,(16)(17)(18). Subsequently, the GR-GR dimer changes into GR in order to bind GRE, triggering LV gene transcription modulation (19).…”

Glucocorticoids and the Lung

“…Corroborating these fi ndings, repression of NF-kB activity in airway epithelial cells has been associated with changes in histone acetylation to marks consistent with gene repression at several loci [ 75 ]. For example, work from Rose and colleagues encompassed in several publications established that GR directly represses MUC5AC expression through recruiting HDAC2 [ 76 ]. Moreover, stimulation of MUC5AC expression by IL-1b, which occurs through induction of NF-kB activity, is antagonized by dexamethasone [ 77 ], implicating GR-mediated recruitment of HDAC2 as a mechanism through which NF-kB activity is repressed by GCs in the airway epithelium.…”