Glucocorticoid-stimulated lung epithelial Na(+) transport is associated with regulated ENaC and sgk1 expression.
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.
Itani
Omar A
OA
Department of Internal Medicine, University of Iowa College of Medicine, 200 Hawkins Drive, Iowa City, IA 52242, USA.
Auerbach
Scott D
SD
Husted
Russell F
RF
Volk
Kenneth A
KA
Ageloff
Shana
S
Knepper
Mark A
MA
Stokes
John B
JB
Thomas
Christie P
CP
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
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