The Paradoxical Increase in Cortisol Secretion Induced by Dexamethasone in Primary Pigmented Nodular Adrenocortical Disease Involves a Glucocorticoid Receptor-Mediated Effect of Dexamethasone on Protein Kinase A Catalytic Subunits

Abstract

Primary pigmented nodular adrenocortical disease (PPNAD) results in most cases from mutations of the protein kinase A (PKA) regulatory subunit 1A (PRKAR1A) gene. Patients with PPNAD exhibit a paradoxical increase in cortisol secretion in response to dexamethasone. The aim was to investigate the mechanism of the action of dexamethasone on adrenocortical cells removed from patients with PPNAD and a transgenic model of PPNAD [Tg(tTA/X2AS) mice]. We performed an in vitro study in an academic research laboratory. Eleven patients with histologically proven PPNAD were included in the study. Cultured PPNAD cells were incubated with dexamethasone in the presence of various modulators of the cAMP/PKA pathway and the glucocorticoid receptor antagonist RU486. Cortisol and corticosterone were measured by radioimmunological assays in cell culture supernatants. Dexamethasone stimulated in vitro cortisol secretion from PPNAD tissues in six patients. The stimulatory effect of dexamethasone on cortisol release was not reduced by the adenylyl cyclase inhibitor SQ22536 or potentiated by the phosphodiesterase inhibitor IMBX and the cAMP analog 8Br-cAMP. Conversely, the PKA inhibitor H89 and RU486 inhibited the cortisol response to dexamethasone. Dexamethasone had no effect on cortisol production from normal human adrenocortical cells but stimulated corticosteroidogenesis in the presence of RU486. Similarly, dexamethasone failed to influence corticosterone release by adrenocortical cells removed from Tg(tTA/X2AS) mice but stimulated corticosteroidogenesis in the presence of RU 486. These results indicate that, in human PPNAD tissues, dexamethasone paradoxically stimulates cortisol release through a glucocorticoid receptor-mediated effect on PKA catalytic subunits.