Mutations in the protein kinase A (PKA) regulatory subunit type 1A (PRKAR1A) and armadillo repeat-containing 5 (ARMC5) genes cause Cushing‘s syndrome (CS) due to primary pigmented nodular adrenocortical disease (PPNAD) and primary bilateral macronodular adrenocortical hyperplasia (PBMAH), respectively. Between the two genes, ARMC5 is highly polymorphic with several variants in the population, whereas PRKAR1A has very little, if any, non-pathogenic variation in its coding sequence. We tested the hypothesis that ARMC5 variants may affect the clinical presentation of PPNAD and CS among patients with PRKAR1A mutations. In this study, 91 patients with PPNAD due to PRKAR1A mutations were tested for abnormal cortisol secretion or CS and for ARMC5 sequence variants. Abnormal cortisol secretion was present in 71 of 74 patients with ARMC5 variants, whereas 11 of 17 patients negative for ARMC5 variants did not have hypercortisolemia. The presence of ARMC5 variants was a statistically strong predictor of CS among patients with PRKAR1A mutations (P < 0.001). Among patients with CS due to PPNAD, ARMC5 variants were associated with lower cortisol levels at baseline (P = 0.04) and after high dose dexamethasone administration (P = 0.02). The ARMC5 p.I170V variant increased ARMC5 protein accumulation in vitro and decreased viability of NCI-H295 cells (but not HEK 293T cells). PPNAD tissues with ARMC5 variants showed stronger ARMC5 protein expression than those that carried a normal ARMC5 sequence. Taken together, our results suggest that ARMC5 variants among patients with PPNAD due to PRKAR1A defects may play the role of a genetic modifier for the presence and severity of hypercortisolemia.
Andrea Gutierrez Maria, Christina Tatsi, Annabel Berthon, Ludivine Drougat, Nikolaos Settas, Fady Hannah-Shmouni, Jerome Bertherat, Fabio R Faucz, and Constantine A Stratakis
Stéphanie Espiard, Ludivine Drougat, Nikolaos Settas, Sara Haydar, Kerstin Bathon, Edra London, Isaac Levy, Fabio R Faucz, Davide Calebiro, Jerome Bertherat, Dong Li, Michael A. Levine, and Constantine A Stratakis
Genetic variants in components of the protein kinase A (PKA) enzyme have been associated with various defects and neoplasms in the context of Carney complex (CNC) and in isolated cases, such as in primary pigmented nodular adrenocortical disease (PPNAD), cortisol-producing adrenal adenomas (CPAs), and various cancers. PRKAR1A mutations have been found in subjects with impaired cAMP-dependent signaling and skeletal defects; bone tumors also develop in both humans and mice with Prkar1a abnormalities. We studied the PRKACB gene in 148 subjects with PPNAD and related disorders, who did not have other PKA-related defects and identified two subjects with possibly pathogenic PRKACB gene variants and unusual bone and endocrine phenotypes. The first presented with bone and other abnormalities, and carried a de novo c.858_860GAA (p.K286del) variant. The second subject carried the c.899 C>T (p.T300M) variant and had a PPNAD-like phenotype. Both variants are highly conserved in the PRKACB gene. In functional studies, the p.K286del variant affected PRKACB protein stability and led to increased PKA signaling. The p.T300M variant did not affect protein stability or response to cAMP and its pathogenicity remains uncertain. We conclude that PRKACB germline variants are uncommon but may be associated with phenotypes that resemble those of other PKA-related defects. However, detailed investigation of each variant is needed as PRKACB appears to be only rarely affected in these conditions, and variants such as p.T300M maybe proven to be clinically insignificant, whereas others (such as p.K286del) are clearly pathogenic and may lead to a novel skeletal syndrome phenotype.
Isadora Pontes Cavalcante, Anna Vaczlavik, Ludivine Drougat, Claudimara Ferini Pacicco Lotfi, Karine Perlemoine, Christopher Ribes, Marthe Rizk-Rabin, Eric Clauser, Maria Candida Barisson Villares Fragoso, Jérôme Bertherat, and Bruno Ragazzon
ARMC5 (Armadillo repeat containing 5 gene) was identified as a new tumor suppressor gene responsible for hereditary adrenocortical tumors and meningiomas. ARMC5 is ubiquitously expressed and encodes a protein which contains a N-terminal Armadillo repeat domain and a C-terminal BTB (Bric-a-Brac, Tramtrack and Broad-complex) domain, both docking platforms for numerous proteins. At present, expression regulation and mechanisms of action of ARMC5 are almost unknown. In this study, we showed that ARMC5 interacts with CUL3 requiring its BTB domain. This interaction leads to ARMC5 ubiquitination and further degradation by the proteasome. ARMC5 alters cell cycle (G1/S phases and cyclin E accumulation) and this effect is blocked by CUL3. Moreover, missense mutants in the BTB domain of ARMC5, identified in patients with multiple adrenocortical tumors, are neither able to interact and be degraded by CUL3/proteasome nor alter cell cycle. These data show a new mechanism of regulation of the ARMC5 protein and open new perspectives in the understanding of its tumor suppressor activity.