HDAC2 expression and variable number of repeats in exon 1 of the HDAC2 gene in corticotroph adenomas.

Objectives: Alterations in protein expression of histone deacetylase 2 (HDAC2) have been demonstrated in various neoplasms, and lack of nuclear expression of HDAC2 has previously been shown in some human and canine corticotroph adenomas. This study aimed to examine HDAC2 expression in a Norwegian cohort of corticotroph adenomas, screen for exonic HDAC2 gene variants in the adenomas and correlate the results with clinical data.
Patients and Design: Forty-four patients with verified Cushing's disease or Nelson's syndrome, positive ACTH staining and tissue available for immunohistochemistry and/or DNA sequencing were included. Ninety-four controls were chosen from the Norwegian Bone Marrow Registry.
Results: Histone deacetylase 2 expression examined by immunohistochemistry was strongly reduced in 3/30 adenomas. There were no association between HDAC2 expression and clinical variables. A previously unidentified insertion of three bases in a region coding for a polyserine cluster in exon 1 of the HDAC2 gene was identified in 6/32 adenomas. No other mutations in HDAC2 exons were found. Examination of DNA extracted from peripheral blood confirmed germ-line origin of the exon 1 insertion. The same insertion was also found in 28/94 of the controls (i.e., not significantly different from the patients).
Conclusions: Strongly reduced HDAC2 protein expression was confirmed in a small portion of corticotroph tumours. Mutations in HDAC2 exons are unlikely to play an important role in the development of corticotroph adenomas.