Glucocorticoids stimulate human sgk1 gene expression by activation of a GRE in its 5′-flanking region

Abstract

In lung and collecting duct epithelia, glucocorticoid (GC)-stimulated Na+ transport is preceded by an increase in the protein kinase sgk1, which in turn regulates the activity of the epithelial Na+ channel (ENaC). We investigated the mechanism for GC-regulated human sgk1 expression in lung and renal epithelia. sgk1 mRNA was increased in these epithelia by GCs, and this was inhibited by actinomycin D and superinduced by cycloheximide, consistent with a transcriptional effect that did not require protein synthesis. To understand the basis for transcriptional regulation, the transcription initiation site was mapped and the 5'-flanking region cloned by PCR. A 3-kb fragment of the upstream region was coupled to luciferase and transfected into A549 cells. By deletion analysis, an imperfect GC response element (GRE) was identified that was necessary and sufficient for GC responsiveness. When tested with cell extracts, a specific protein recognized by an anti-GC receptor (GR) antibody bound the GRE in gel mobility shift assays. We conclude that GCs stimulate sgk1 expression in human epithelial cells via activation of a GRE in the 5'-flanking region of sgk1.