17q22–24 Chromosomal Losses and Alterations of Protein Kinase A Subunit Expression and Activity in Adrenocorticotropin-Independent Macronodular Adrenal Hyperplasia

Abstract

Primary adrenocortical hyperplasias leading to Cushing syndrome include primary pigmented nodular adrenocortical disease and ACTH-independent macronodular adrenal hyperplasia (AIMAH). Inactivating mutations of the 17q22-24-located PRKAR1A gene, coding for the type 1A regulatory subunit of protein kinase A (PKA), cause primary pigmented nodular adrenocortical disease and the multiple endocrine neoplasia syndrome Carney complex. PRKAR1A mutations and 17q22-24 chromosomal losses have been found in sporadic adrenal tumors and are associated with aberrant PKA signaling. The objective of the study was to examine whether somatic 17q22-24 changes, PRKAR1A mutations, and/or PKA abnormalities are present in AIMAH. We studied fourteen patients with Cushing syndrome due to AIMAH. Fluorescent in situ hybridization with a PRKAR1A-specific probe was used for investigating chromosome 17 allelic losses. The PRKAR1A gene was sequenced in all samples, and tissue was studied for PKA activity, cAMP responsiveness, and PKA subunit expression. We found 17q22-24 allelic losses in 73% of the samples. There were no PRKAR1A-coding sequence mutations. The RIIbeta PKA subunit was overexpressed by mRNA, whereas the RIalpha, RIbeta, RIIalpha, and Calpha PKA subunits were underexpressed. These findings were confirmed by immunohistochemistry. Total PKA activity and free PKA activity were higher in AIMAH than normal adrenal glands, consistent with the up-regulation of the RIIbeta PKA subunit. PRKAR1A mutations are not found in AIMAH. Somatic losses of the 17q22-24 region and PKA subunit and enzymatic activity changes show that PKA signaling is altered in AIMAH in a way that is similar to that of other adrenal tumors with 17q losses or PRKAR1A mutations.