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 a miloride-sensitive Na+ transport is associated with increased expression of the epithelial Na+ channel Lu subunit (alpha ENaC), In H441 lung cells, 10 0 nM dexamethasone increases amiloride-sensitive short-circuit current (3.3 mu A/cm(2) to 7.5 mu A/cm(2)), correlating with a 5-fold increase in aENaC mRNA expression that could be blocked by actinomycin D, To explore transcr iptional regulation of alpha ENaC, the human alpha ENaC 5'-flanking region was cloned and tested in H441 cells. By deletion analysis, a similar to 150 -base pair region 5' to the upstream promoter was identified that, when sti mulated with 100 nM dexamethasone, increased luciferase expression 15-fold. This region, which contains two imperfect GREs, also functioned when coupl ed to a heterologous promoter. When individually tested, only the downstrea m GRE functioned in cis and bound GR in a gel mobility shift assay. In the M-l collecting duct line Na+ transport, m alpha ENaC expression and lucifer ase expression from alpha ENaC genomic fragments were also increased by 100 nM dexamethasone. In a colonic cell line, HT29, trans-activation via a het erologously expressed glucocorticoid receptor restored glucocorticoid-stimu lated alpha ENaC gene transcription. We conclude that glucocorticoids stimu late alpha ENaC expression in kidney and lung via activation of a hormone r esponse element in the 5'-flanking region of h alpha ENaC and this response , in part, is the likely basis for the up-regulation of Na+ transport in th ese sites.