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.