Glucocorticoids rapidly activate cAMP production via Gαs to initiate non-genomic signaling that contributes to one-third of their canonical genomic effects.

Abstract

Glucocorticoids are widely used for the suppression of inflammation, but evidence is growing that they can have rapid, non‐genomic actions that have been unappreciated. Diverse cell signaling effects have been reported for glucocorticoids, leading us to hypothesize that glucocorticoids alone can swiftly increase the 3′,5′‐cyclic adenosine monophosphate (cAMP) production. We found that prednisone, fluticasone, budesonide, and progesterone each increased cAMP levels within 3 minutes without phosphodiesterase inhibitors by measuring real‐time cAMP dynamics using the cAMP difference detector in situ assay in a variety of immortalized cell lines and primary human airway smooth muscle (HASM) cells. A membrane‐ impermeable glucocorticoid showed similarly rapid stimulation of cAMP, implying that responses are initiated at the cell surface. siRNA knockdown of Gαs virtually eliminated glucocorticoid‐stimulated cAMP responses, suggesting that these drugs activate the cAMP production via a G protein‐coupled receptor. Estradiol had small effects on cAMP levels but G protein estrogen receptor antagonists had little effect on responses to any of the glucocorticoids tested. The genomic and non‐genomic actions of budesonide were analyzed by RNA‐Seq analysis of 24 hours treated HASM, with and without knockdown of Gαs. A 140‐gene budesonide signature was identified, of which 48 genes represent a non‐genomic signature that requires Gαs signaling. Collectively, this non‐genomic cAMP signaling modality contributes to one‐third of the gene expression changes induced by glucocorticoid treatment and shifts the view of how this important class of drugs exerts its effects.