Detection of somatic beta-catenin mutations in primary pigmented nodular adrenocortical disease (PPNAD).

BACKGROUND: Primary pigmented nodular adrenocortical disease (PPNAD) leads to Cushing syndrome (CS) and is often associated with Carney complex (CNC). Genetic alterations of the type 1-alpha regulatory subunit of cAMP-dependent protein kinase A (PRKAR1A) and phosphodiesterase 11A4 (PDE11A) genes have been found in PPNAD. Recent studies have demonstrated that beta-catenin mutations are frequent in adrenocortical adenomas and carcinomas and that the Wnt-signalling pathway is involved in PPNAD tumorigenesis. We hypothesized that adrenocortical adenomas that form in the context of PPNAD may harbour beta-catenin mutations. METHODS: We studied 18 patients with CS secondary to PPNAD who were screened for germline PRKAR1A and PDE11A mutations. Tumor DNA was extracted from pigmented adrenocortical adenoma and nodular adrenal hyperplasia. Mutation analysis of exons 3 and 5 of beta-catenin was performed using polymerase chain reaction and direct sequencing. Sections from formalin-fixed, paraffin-embedded tumour samples were studied by immunohistochemistry with an antibody against beta-catenin. RESULTS: Nine patients were carrying germline PRKAR1A mutations and one patient had a PDE11A mutation. We found somatic beta-catenin mutations in 2 of 18 patients (11%). In both cases, the mutations occurred in relatively large adenomas that had formed in the background of PPNAD. Tumor DNA analysis revealed a heterozygous ACC-to-GCC missense mutation in codon 41 (T41A) and a TCT-to-CCT missense mutation in codon 45 (S45P) of exon 3 of the beta-catenin gene that was confirmed at the cDNA level. There were no alterations in the DNA of PPNAD-adjacent tissues and lymphocytes from the patients, indicating somatic events. Immunohistochemistry showed nuclear accumulation of beta-catenin in more than 90% of cells in adenomatous tissue whereas no nuclear immunoreactivity was detected in adjacent PPNAD nodular cells. Nuclear translocation of beta-catenin protein in the PPNAD adenoma suggests activation of the Wnt-beta-catenin pathway in PPNAD. CONCLUSIONS: We report, for the first time, beta-catenin mutations in adenomas associated with PPNAD, further implicating Wnt-beta-catenin signalling in tumorigenesis linked to bilateral adrenal hyperplasias.

Frequent mutations of beta-catenin gene in sporadic secreting adrenocortical adenomas.

OBJECTIVE: Molecular alterations remain largely unknown in most sporadic adrenocortical tumours and hyperplasias. In our previous work, we demonstrated the differential expression of several Wnt/beta-catenin signalling-related genes implicated in ACTH-independent macronodular adrenal hyperplasias (AIMAH). To better understand the role of Wnt/beta-catenin signalling in adrenocortical tumours, we performed mutational analysis of the beta-catenin gene. METHODS: We studied 53 human adrenocortical samples (33 adenomas, 4 carcinomas, 13 AIMAH, 3 ACTH-dependent adrenal hyperplasias) and the human adrenocortical cancer cell line NCI-H295R. All samples were screened for somatic mutations in exons 3 and 5 of the beta-catenin gene. Eleven and six samples were analysed for beta-catenin protein expression by Western blotting and immunohistochemistry, respectively. RESULTS: No mutations were detected in adrenocortical carcinomas, AIMAH and ACTH-dependent hyperplasias. Genetic alterations were found in 5 (15%) out of 33 adenomas: three cortisol-secreting adenomas, one aldosterone-secreting adenoma and one nonfunctional adenoma. Two-point mutations occurred at serine residues of codons 37 and 45 (S37C and S45F). The remaining three tumours contained deletions of 6, 55 and 271 bp. H295R cells carry an activating S45P mutation. Western blot analysis of samples with 55- and 271-bp deletions showed an additional shorter and more intense band representing an accumulation of the mutated form of beta-catenin protein. In addition, cytoplasmic and/or nuclear accumulation of beta-catenin was observed in mutated adenomas by immunohistochemistry. CONCLUSIONS: Activating mutations of exon 3 of the beta-catenin gene are frequent in adrenocortical adenomas, and further characterization of the Wnt/beta-catenin signalling pathway should lead to a better understanding of adrenal tumourigenesis.

Adrenocorticotropic hormone-independent Cushing's syndrome.

PURPOSE OF REVIEW: Endogenous Cushing's syndrome is adrenocorticotropic hormone (or corticotropin)-independent in 15-20% of cases. Primary Cushing's syndrome is most often secondary to adrenocortical adenomas or carcinomas, and more rarely to bilateral adrenal hyperplasias. Corticotropin-independent cortisol-producing hyperplasia is caused by micronodular diseases, including primary pigmented nodular adrenocortical disease and nonpigmented micronodular hyperplasia and adrenocorticotropic hormone-independent macronodular adrenal hyperplasia. Primary pigmented nodular adrenocortical disease can be found either alone or in the context of Carney complex, a multiple endocrine neoplasia syndrome. RECENT FINDINGS: In recent years, the pathophysiology of adrenocortical tumors and hyperplasias became better understood following the identification of genes responsible for syndromes associated with corticotropin-independent Cushing's syndrome and the demonstration of aberrant expression and function of various hormone receptors in adrenocortical adenomas and adrenocorticotropic hormone-independent macronodular adrenal hyperplasia. This article reviews findings on the molecular and genetic aspects of corticotropin-independent Cushing's syndrome including recent gene expression profiling studies of adrenocortical tumors and hyperplasias and animal models that provided clues on the pathogenesis of primary Cushing's syndrome. SUMMARY: A better understanding of molecular mechanisms involved in adrenocortical tumors and hyperplasias may lead to improved diagnostic and prognostic markers and treatment strategies to assist clinicians in the management of corticotropin-independent Cushing's syndrome.