Ubiquitin immunoreactivity in corticotrophs following glucocorticoid treatment and in pituitary adenomas.

Ubiquitin involved in nonlysosomal protein degradation was studied in 31 nontumorous pituitary glands and 133 pituitary adenomas by immunocytochemical techniques. Normal nontumorous hypophyses were immunonegative for ubiquitin. Ubiquitin immunoreactivity was present in 3% to 30% of corticotrophs containing Crooke's hyaline in 10 of 12 glucocorticoid-treated patients. Fifty-eight adenomas showed ubiquitin-immunoreactive cells. Ubiquitin immunoreactivity was found in cytokeratin immunopositive filamentous inclusions of Crooke's cell adenomas and in fibrous bodies of somatotroph adenomas. Forty-five adenomas showed a diffuse cytoplasmic immunopositivity. No correlation was revealed between ubiquitin immunoreactivity, hormone content, and bromocriptine and octreotide treatments. The results are consistent with the interpretation that ubiquitin immunoreactivity in nontumorous corticotrophs containing Crooke's hyaline and in various adenomas is secondary to glucocorticoid excess or to altered metabolic activity. Whether ubiquitin expression reflects increased ubiquitin synthesis or decreased breakdown of ubiquitinated conjugates remains to be elucidated.