Reversed distribution of calpains and calpastatin in human pituitary gland and selective localization of calpastatin in adrenocorticotropin-producing cells as demonstrated by immunohistochemistry.

The immunohistochemical distribution of Ca2+-dependent cysteine proteinases (calpains I and II) and their endogenous inhibitor calpastatin in normal and adenomatous human pituitary tissue was studied using specific antibodies. The distributions of calpain and calpastatin were dissimilar in human pituitary gland, i.e. ACTH-immunoreactive cells were strongly positive for calpastatin and negative for calpains. PRL-, GH-, FSH-, and TSH-producing cells were negative for calpastatin, but moderately positive for calpains, especially for calpain II, the high Ca2+-requiring form of the enzyme. Similar results were found in pituitary adenoma tissue. These findings indicate that each type of cells producing a specific hormone is equipped with a different balance of the enzyme-inhibitor system involved in the Ca2+-dependent degradation of intracellular proteins.