Published ahead of print on October 20, 2005, doi:10.1165/rcmb.2005-0176OC Am. J. Respir. Cell Mol. Biol., Volume 34, Number 3, March 2006, 338-347 A more recent version of this article appeared on March 1, 2006
Submitted on May 10, 2005 Dexamethasone-mediated Repression of MUC5AC Gene Expression in Human Lung Epithelial CellsYajun Chen1,1 Center for Genetic Medicine Research, Children's Research Institute, Children's National Medical Center, Washington, DC, USA, 2 Department of Pediatrics, George Washington University School of Medicine and Health Sciences, Washington, DC, USA; Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, DC, USA, 3 Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, Washington, DC, USA; Department of Pediatrics, George Washington University School of Medicine and Health Sciences, Washington, DC, USA; Department of Biochemistry and Molecular Biology, George Washington University School of Medicine and Health Sciences, Washington, DC, USA, 4 Center for Genetic Medicine Research, Children's Research Institute, Children's National Medical Center, Washington, DC, USA; Department of Pediatrics, George Washington University School of Medicine and Health Sciences, Washington, DC, USA; Department of Biochemistry and Molecular Biology, George Washington University School of Medicine and Health Sciences, Washington, DC, USA * To whom correspondence should be addressed. E-mail: Mrose{at}cnmcresearch.org.
Glucocorticoids regulate gene expression via binding of the ligand-activated glucocorticoid receptor (GR) to glucocorticoid responsive cis-elements (GRE) in target gene promoters. The MUC5AC gene, which encodes the protein backbone of an abundant secreted airway mucin, has several putative GRE cis-elements in its 5' sequence. Mechanism(s) whereby glucocorticoids regulate mucin genes have not previously been described. In this study, the glucocorticoid dexamethasone (Dex) decreased MUC5AC mRNA abundance in A549, NCI-H292 cell lines and primary differentiated normal bronchial epithelial cells by 50-80%, suggesting a common mechanism of MUC5AC gene repression in human lung epithelial cells. Kinetic analyses showed that MUC5AC mRNA was not significantly decreased until 6h following Dex exposure, and that nuclear translocation of GR was biphasic, suggesting that Dex-mediated cis-repression of MUC5AC gene expression was a delayed response of GR translocation. Transfection analyses demonstrated that Dex transcriptionally repressed the MUC5AC promoter. Electrophoretic mobility shift assays with wild type and mutant oligonucleotide probes showed that GR bound to two GRE cis-sites (nucleotides -930 to -912 and -369 to -351) in the MUC5AC promoter. Analyses of mutated MUC5AC promoter constructs demonstrated that NF
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B cis-sites were not involved in Dex-mediated repression of MUC5AC. Dex did not alter mRNA stability of MUC5AC transcripts. Taken together, the data indicates that Dex transcriptionally mediates repression of MUC5AC gene expression in human lung epithelial cells at quiescent states following binding of GR to one or more GRE cis-elements in the MUC5AC promoter.
