Localization of prohormone convertases 1/3 and 2 in the human pituitary gland and pituitary adenomas: analysis by immunohistochemistry, immunoelectron microscopy, and laser scanning microscopy.

Prohormone convertase (PC) 1/3 and PC2 are involved in post-translational processing of endocrine tissues, including the pancreatic islets and pituitary glands. Our immunohistochemical studies disclosed the presence of PC1/3 and PC2 in non-neoplastic pituitary glands, especially in corticotrophs, gonadotrophs, and thyrotrophs. Among 58 pituitary adenomas obtained by trans-sphenoidal surgery, adrenocorticotropin (ACTH)-secreting adenomas showed a high incidence of the presence of PC1/3 and PC2, i.e., nine of nine cases were positive for ACTH. Five of nine cases showed consistency between PC2 localization and alpha-melanocyte stimulating hormone immunoreactivity, which suggests the functional correlation between PC2 and the processing of ACTH. In four cases, we observed inconsistency in immunolocalization, which suggested the possibility of inactive PC2 and abnormal processing of alpha-melanocyte stimulating hormone. The high incidence of PC1/3 and PC2 in nonfunctioning adenomas might be related to the processing of chromogranin A.