title: Cycloheximide and lipopolysaccharide downregulate αENaC mRNA via different mechanisms in alveolar epithelial cells.
abstract: Active Na(+) transport mediated by epithelial Na(+) channel (ENaC) is vital for fetal lung fluid reabsorption at birth and pulmonary edema resolution. Previously, we demonstrated that αENaC expression and activity are downregulated in alveolar epithelial cells by cycloheximide (Chx) and Pseudomonas aeruginosa. The regulatory mechanisms of αENaC mRNA expression by Chx and lipopolysaccharide (LPS) from P. aeruginosa were further studied in the present work. Both agents decreased αENaC mRNA expression to 50% of control values after 4 h. Chx repressed αENaC expression in a dose-dependent manner independently of protein synthesis. Although extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) pathways were activated by the two treatments, their mechanisms of ENaC mRNA modulation were different. First, activation of the signaling pathways was sustained by Chx but only transiently by LPS. Second, ERK1/2 or p38 MAPK inhibition attenuated the effects of Chx on αENaC mRNA, whereas suppression of both signaling pathways was necessary to alleviate the outcome of LPS on αENaC mRNA. The molecular mechanisms involved in the decrease of αENaC expression were investigated in both conditions. LPS, but not Chx, significantly reduced αENaC promoter activity via the ERK1/2 and p38 MAPK pathways. These results suggest that LPS attenuates αENaC mRNA expression via diminution of transcription, whereas Chx could trigger some posttranscriptional mechanisms. Although LPS and Chx downregulate αENaC mRNA expression similarly and with similar signaling pathways, the mechanisms modulating ENaC expression are different depending on the nature of the cellular stress.
authors.affiliation: IRCM, 110 Ave. des Pins Ouest, Montreal (QuebecCanada H2W 1R7. yves.berthiaume@umontreal.ca.
authors.forename: Francis
authors.initials: F
authors.lastname: Migneault
authors.forename: Emilie
authors.initials: E
authors.lastname: Boncoeur
authors.forename: Frédéric
authors.initials: F
authors.lastname: Morneau
authors.forename: Mihai
authors.initials: M
authors.lastname: Pascariu
authors.forename: André
authors.initials: A
authors.lastname: Dagenais
authors.forename: Yves
authors.initials: Y
authors.lastname: Berthiaume
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology*; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008156:Luciferases / Q000378:metabolism; D008297:Male; D011401:Promoter Regions, Genetic / Q000235:genetics; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D053503:Epithelial Sodium Channels; D008070:Lipopolysaccharides; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D003513:Cycloheximide; D008156:Luciferases; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases
keywords: cellular stress; epithelial sodium channel; inflammation; messenger ribonucleic acid; signal transduction