PTTG1 expression analysis and ACTH plasma levels in dogs with corticotroph adenomas

Abstract

Pituitary tumor transforming gene 1 (PTTG1), a oncogene, is recently analyzed in canine corticotroph adenomas1. High PTTG1 RNA levels were correlated with poor prognosis. However, PTTG1 mRNA expression was not correlated with PTTG1 protein expression in canine corticotroph adenomas. Furthermore it was reported that there was no difference in PTTG1 protein expression between tumor and healthy pituitary. It was suggested that PTTG1 activity may have a species dependent effect on pituitary tumorigenesis and may also have secretory functions. Therefore, further research was necessary to understand the function of PTTG1 in healthy pituitary and corticotroph adenomas in canine. The correlation between PTTG1 expression in canine corticotroph adenomas and ACTH plasma levels was studied in 20 dogs. Corticotroph adenomas were collected during transsphenoidal hypophysectomy. Blood samples for ACTH determination were taken preoperatively with a commercially available two-site immunoradiometreic assay. Besides, immunohistochemistry was performed in 1 healthy canine pituitary to evaluate immunohistochemical localization for PTTG1 and ACTH. The percentage of immunopositive cells was assessed as the percentage of cells exhibiting reactivity in each field; the labelling index (LI). PTTG1 expression was positive in 19 out of 20 canine corticotroph adenomas and positivity ranged from 0% to 94%. There was no correlation found between PTTG1 expression and ACTH levels in plasma. Immunohistochemistry staining for PTTG1 and ACTH showed cytoplasmic staining in corresponded areas, this corroborated the assumption that PTTG1 is a secretory protein in the canine pituitary.