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 α Subunit Gene

Abstract

In airway and renal epithelia, the glucocorticoid-mediated stimulation of amiloride-sensitive Na ؉ transport is associated with increased expression of the epithelial Na ؉ channel ␣ subunit (␣ENaC). In H441 lung cells, 100 nM dexamethasone increases amiloride-sensitive shortcircuit current (3.3 A/cm 2 to 7.5 A/cm 2 ), correlating with a 5-fold increase in ␣ENaC mRNA expression that could be blocked by actinomycin D. To explore transcriptional regulation of ␣ENaC, the human ␣ENaC 5-flanking region was cloned and tested in H441 cells. By deletion analysis, a ϳ150-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, m␣ENaC expression and luciferase expression from ␣ENaC 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 ␣ENaC gene transcription. We conclude that glucocorticoids stimulate ␣ENaC expression in kidney and lung via activation of a hormone response element in the 5-flanking region of h␣ENaC and this response, in part, is the likely basis for the up-regulation of Na ؉ transport in these sites.

Aldosterone Modulates Steroid Receptor Binding to the Endothelin-1 Gene (edn1)

“…Similarly, the aldosterone response gene scnn1a also contains two HREs in different orientations. Only the inverted HRE was capable of stimulating transcription (69).…”

Anti-inflammatory functions of glucocorticoid-induced genes

“…On the other hand, GILZ stimulated rather than suppressed the expression and activity of the epithelial sodium channel α (ENaCα) (Bhalla et al, 2006;Soundararajan et al, 2005), possibly via inhibition of the ERK pathway (Ayroldi et al, 2002;Soundararajan et al, 2005). ENaCα expression is thought to contribute to GC-induced hypertension (Fuller et al, 2000;Itani et al, 2002;Sayegh et al, 1999;Stokes and Sigmund, 1998). This raises the interesting possibility that a GCinduced gene could contribute to both anti-inflammatory and harmful effects in a single cell type.…”

Clinical implication of lung fluid balance in the perinatal period

“…The beneficial effect of corticosteroids on fetal lung maturation is believed to be induced by surfactant synthesis and secretion; [53][54][55][56] however, in some part, the beneficial effect of corticosteroids on minimizing respiratory distress especially in late preterm infants may well be mediated by enhancing ENaC activity and thus improving fetal lung fluid removal. Indeed, glucocorticosteroids have been shown to induce a-ENaC transcription, 57,58 and in human fetal lung explant cultures all three ENaC subunits were upregulated by glucocorticosteroids. 59,60 Glucocorticosteroids also increase the number of available sodium channels by increasing ENaC trafficking and decreasing the rate of degradation of existing channels 61,62 and improving lung responsiveness to b2 stimulants and thyroid hormones.…”