title: Glucocorticoid-stimulated lung epithelial Na(+) transport is associated with regulated ENaC and sgk1 expression.
abstract: H441 cells, a bronchiolar epithelial cell line, develop a glucocorticoid-regulated amiloride-sensitive Na(+) transport pathway on permeable supports (R. Sayegh, S. D. Auerbach, X. Li, R. Loftus, R. Husted, J. B. Stokes, and C. P. Thomas. J Biol Chem 274: 12431-12437, 1999). To understand its molecular basis, we examined the effect of glucocorticoids (GC) on epithelial Na(+) channel (ENaC)-alpha, -beta, and -gamma and sgk1 expression and determined the biophysical properties of Na(+) channels in these cells. GC stimulated the expression of ENac-alpha, -beta, and -gamma and sgk1 mRNA, with the first effect seen by 1 h. These effects were abolished by actinomycin D, but not by cycloheximide, indicating a direct stimulatory effect on ENaC and sgk1 mRNA synthesis. The GC effect on transcription of ENaC-alpha mRNA was accompanied by a significant increase in ENaC-alpha protein levels. GC also stimulated ENaC-alpha, -beta, and -gamma and sgk1 mRNA expression in A549 cells, an alveolar type II cell line. To determine the biophysical properties of the Na(+) channel, single-channel currents were recorded from cell-attached H441 membranes. An Na(+)-selective channel with slow kinetics and a slope conductance of 10.8 pS was noted, properties similar to ENaC-alpha, -beta, and -gamma expressed in Xenopus laevis oocytes. These experiments indicate that amiloride-sensitive Na(+) transport is mediated through classic ENaC channels in human lung epithelia and that GC-regulated Na(+) transport is accompanied by increased transcription of each of the component subunits and sgk1.
authors.affiliation: Department of Internal Medicine, University of Iowa College of Medicine, 200 Hawkins Drive, Iowa City, IA 52242, USA.
authors.forename: Omar A
authors.initials: OA
authors.lastname: Itani
authors.forename: Scott D
authors.initials: SD
authors.lastname: Auerbach
authors.forename: Russell F
authors.initials: RF
authors.lastname: Husted
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Volk
authors.forename: Shana
authors.initials: S
authors.lastname: Ageloff
authors.forename: Mark A
authors.initials: MA
authors.lastname: Knepper
authors.forename: John B
authors.initials: JB
authors.lastname: Stokes
authors.forename: Christie P
authors.initials: CP
authors.lastname: Thomas
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D004232:Diuretics / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism; D053503:Epithelial Sodium Channels; D015633:Extravascular Lung Water / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D017874:Immediate-Early Proteins; D009687:Nuclear Proteins; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D021122:Protein Subunits; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D015056:1-Methyl-3-isobutylxanthine; D000584:Amiloride; D005576:Colforsin; D000242:Cyclic AMP; D003907:Dexamethasone; D004232:Diuretics; D053503:Epithelial Sodium Channels; D005938:Glucocorticoids; D017874:Immediate-Early Proteins; D009687:Nuclear Proteins; D010726:Phosphodiesterase Inhibitors; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits; D012333:RNA, Messenger; D012964:Sodium; D015222:Sodium Channels; D000099184:Serum-Glucocorticoid Regulated Kinases