title: Mechanism of dexamethasone-mediated interleukin-8 gene suppression in cultured airway epithelial cells.
abstract: The effects of dexamethasone, a glucocorticoid analog, on interleukin 8 (IL-8) gene expression were studied in cultures of primary human tracheobronchial epithelial cells and an immortalized human bronchial epithelial cell line, HBE1 cells. Dexamethasone inhibited IL-8 mRNA and protein expression in a concentration- and time-dependent manner. The inhibition did not occur at the transcriptional level since both nuclear run-on activity and IL-8 promoter-reporter gene expression assay revealed no significant effect. Instead, there was a change in IL-8 mRNA stability in dexamethasone-treated cultures. Under actinomycin D treatment, IL-8 mRNA was quite stable in dexamethasone-depleted cultures, while in dexamethasone-pretreated cultures, IL-8 message was rapidly degraded within the first hour, then leveled off. When dexamethasone and actinomycin D were added simultaneously to dexamethasone-depleted cultures, IL-8 mRNA remained rather stable. When cycloheximide was used to inhibit new protein synthesis, dexamethasone-dependent inhibition was not observed. These results suggest that a posttranscriptional mechanism, which requires dexamethasone-dependent new protein synthesis, is involved in the regulation of IL-8 mRNA by dexamethasone in airway epithelial cells.
authors.affiliation: Center for Comparative Respiratory Biology and Medicine, School of Medicine, University of California, Davis, California 95616, USA. mjchang@ucdavis.edu
authors.forename: M M
authors.initials: MM
authors.lastname: Chang
authors.forename: M
authors.initials: M
authors.lastname: Juarez
authors.forename: D M
authors.initials: DM
authors.lastname: Hyde
authors.forename: R
authors.initials: R
authors.lastname: Wu
mesh_terms: D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D016209:Interleukin-8 / Q000235:genetics*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects / Q000276:immunology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects / Q000276:immunology
chemical_list: D005938:Glucocorticoids; D016209:Interleukin-8; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D003907:Dexamethasone; D003513:Cycloheximide