Identification of a Glucocorticoid Response Element in the Rat β2-Adrenergic Receptor Gene

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Abstract
Regulation of β2-adrenergic receptor (β2AR) levels by glucocorticoids is a physiologically important mechanism for altering β2AR responsiveness. Glucocorticoids increase β2AR density by increasing the rate of β2AR gene transcription, but the cis-elements involved have not been well characterized. We now show that one of six potential glucocorticoid response elements (GREs) in the 5′-flanking region of the rat β2AR gene is necessary for glucocorticoid-dependent stimulation of receptor gene expression. Using a nested set of deletion fragments of the rat β2AR gene 5′-flanking region fused to a luciferase reporter gene, glucocorticoid-dependent induction of reporter gene expression in HepG2 cells was localized to a region between positions −643 and −152, relative to the transcription initiation site. In electrophoretic mobility shift assays, a double-stranded oligonucleotide incorporating a near-consensus GRE from this region (positions −379 to −365) formed complexes with the human recombinant glucocorticoid receptor, as well as with nuclear protein from dexamethasone-treated HepG2 cells. Mutation of a single base within this GRE sequence greatly diminished interaction of the mutated oligonucleotide with the human recombinant glucocorticoid receptor. The functional activity of the GRE was characterized using a luciferase reporter construct driven by a minimal thymidine kinase promoter. In HepG2 cells transfected with constructs containing the GRE, dexamethasone increased reporter gene expression approximately 3-fold, whereas a dexamethasone effect was not observed with constructs lacking the GRE. Taken together, these findings show that a GRE located at positions −379 to −365 in the 5′-flanking region of the rat β2AR gene mediates glucocorticoid stimulation of β2AR gene transcription.

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