Regulation of β-adrenergic receptors by 'permissive' hormones: Glucocorticoids increase steady-state levels of receptor mRNA

Incubation of DDT₁ MF-2 hamster vas deferens cells with glucocorticoids results in a marked increase in β-adrenergic receptor (βAR) number. The increase in receptor number was visualized by indirect immunofluorescence with antiserum specific for the βAR and was verified by radioligand binding. The steady-state levels of βAR mRNA were quantified in untreated (control) and glucocorticoid-treated cells by DNA-excess solution hybridization using a single-stranded probe corresponding to nucleotides +12 to 182 of the hamster β₂AR cDNA coding region. The steady-state level increased from 0.37 pg to βAR mRNA per μg of total cellular RNA in untreated cells to 1.05 pg or βAR mRNA per μg of RNA in cells treated with dexamethasone (500 nM) for 2-4 hr. After this sharp transient peak, the steady-state level of receptor mRNA declined by 6 hr to a level approximately twice that of the untreated cells. Half-maximal effects were achieved at 20-40 nM dexamethasone. Testosterone (500 nM) and 17β-estradiol (500 nM), in contrast, did not alter the steady-state levels of βAR mRNA. Actinomycin D, a potent inhibitor of transcription, abolished that the permissive hormone effect was exerted on gene transcription. The half-life of the receptor mRNA measured in the presence of actinomycin D was found to be 12 hr in both the untreated and the dexamethasone-treated cells. These studies provide a molecular explanation for the well-known regulation of GTP-binding protein (G-protein)-linked cell-surface receptors by permissive hormones.