Glucocorticoid induction of epithelial sodium channel expression in lung and renal epithelia occurs via trans-activation of a hormone response element in the 5'-flanking region of the human epithelial sodium channel alpha subunit gene.
In airway and renal epithelia, the glucocorticoid-mediated stimulation of amiloride-sensitive Na+ transport is associated with increased expression of the epithelial Na+ channel alpha subunit (alphaENaC). In H441 lung cells, 100 nM dexamethasone increases amiloride-sensitive short-circuit current (3.3 microA/cm2 to 7.5 microA/cm2), correlating with a 5-fold increase in alphaENaC mRNA expression that could be blocked by actinomycin D. To explore transcriptional regulation of alphaENaC, the human alphaENaC 5'-flanking region was cloned and tested in H441 cells. By deletion analysis, a approximately 150-base pair region 5' to the upstream promoter was identified that, when stimulated with 100 nM dexamethasone, increased luciferase expression 15-fold. This region, which contains two imperfect GREs, also functioned when coupled to a heterologous promoter. When individually tested, only the downstream GRE functioned in cis and bound GR in a gel mobility shift assay. In the M-1 collecting duct line Na+ transport, malphaENaC expression and luciferase expression from alphaENaC genomic fragments were also increased by 100 nM dexamethasone. In a colonic cell line, HT29, trans-activation via a heterologously expressed glucocorticoid receptor restored glucocorticoid-stimulated alphaENaC gene transcription. We conclude that glucocorticoids stimulate alphaENaC expression in kidney and lung via activation of a hormone response element in the 5'-flanking region of halphaENaC and this response, in part, is the likely basis for the up-regulation of Na+ transport in these sites.
Sayegh
R
R
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa 52246, USA.
Auerbach
S D
SD
Li
X
X
Loftus
R W
RW
Husted
R F
RF
Stokes
J B
JB
Thomas
C P
CP
D000584:Amiloride / Q000494:pharmacology; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D003907:Dexamethasone / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D053503:Epithelial Sodium Channels; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D017136:Ion Transport; D007672:Kidney Cortex / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics*; D015533:Transcriptional Activation / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D017931:DNA Primers; D053503:Epithelial Sodium Channels; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D015222:Sodium Channels; D000584:Amiloride; D003907:Dexamethasone