Abstract LB-182: Constitutive activation of PRKACA in adrenal Cushing's syndrome

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Corticotropin-independent Cushing's syndrome may be caused by tumors or hyperplasia of the adrenal cortex. Until now genetic alterations explain only a small fraction of cases. The observation that a subset of adrenal adenomas is characterized by abnormal PKA activity despite the absence of mutations in candidate genes suggested as yet unknown alterations in the cAMP/PKA signaling cascade in these tumors. The aim of this study was the analysis of the genetic basis of Cushing's syndrome in order to reveal the gene/s responsible for the disease. Exome sequencing was performed in ten cortisol-producing adenomas and recurrent mutations in candidate genes were evaluated in additional 171 patients with adrenocortical tumors. Genome-wide copy number analysis was performed in 35 patients with cortisol secreting bilateral hyperplasias. The effects of these genetic defects were studied both clinically and in vitro. Exome sequencing in 8/10 adenomas revealed somatic mutations in the PRKACA gene, which encodes the main catalytic subunit of cyclic AMP-dependent protein kinase (PKA) (c.617A>C in seven and c.595_596insCAC in one). Overall, PRKACA somatic mutations were identified in a total of 22/59 (37%) adenomas from patients with overt Cushing's syndrome while these mutations were not detectable in patients with subclinical hypercortisolism (n=40) or in other adrenal tumors (n=82). Among 35 patients with cortisol producing hyperplasias, 5 (with two patients as first degree relatives) carried germline copy number gain of the chromosome 19 region including the PRKACA gene. In vitro studies demonstrated impaired inhibition of the mutant PRKACA by the PKA regulatory subunit, while cells from patients with germline chromosomal gains showed increased protein levels; in both cases, PKA activity was increased. The present study shows that more than one third of cortisol-producing adenomas associated with overt Cushing syndrome harbor unique somatic mutations of the main cAMP-dependent kinase catalytic subunit, PRKACA resulting in constitutive PKA activation. While in these patients the mutation is present only in tumor cells, germline duplication of the PRKACA gene was identified in a group of patients with bilateral adrenal hyperplasias. This is the first report of genetic alterations of the catalytic subunit of PKA linked to human disease: Germline PRKACA duplications with bilateral adrenal hyperplasias and somatic PRKACA mutations with unilateral cortisol producing adrenal adenomas. Citation Format: Fabio R. Faucz, Felix Beuschlei, Martin Fassnacht, Guilaume Assie, Davide Calebiro, Constantine Stratakis, Andrea Osswald, Cristina L. Ronchi, Thomas Wieland, Silviu Sbiera, Katrin Schaak, Anett Schmittfull, Thomas Schwarzmayr, Olivia Barreau, Delphine Vezzosi, Marthe Rizk-Rabbin, Ulrike Zabel, Eva Szarek, Paraskevi Salpea, Antonella Forlino, Annalisa Vetro, Orsetta Zuffardi, Caroline Kisker, Susanne Diener, Thomas Meitinger, Martin J. Lohse, Martin Reincke, Jerome Bertherat, Tim M. Strom, Bruno Allolio. Constitutive activation of PRKACA in adrenal Cushing's syndrome. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-182. doi:10.1158/1538-7445.AM2014-LB-182