Immunohistochemical analysis of p27 (Kip1) in human pituitary glands and in various types of pituitary adenomas

p27 (Kip1) plays regulatory roles in the cell cycle by inhibiting the activ ity of cyclin dependent kinases (CDKs). This immunohistochemical study is a imed at elucidating the expression of p27 in human pituitary and in various types of pituitary adenomas in order to clarify its role in the regulation of proliferation. Sixteen normal pituitary glands and 179 human pituitary adenomas were used for immunohistochemical studies. The tissues were fixed in 10% formalin and embedded in paraffin. Indirect peroxidase method was performed after heat- induced antigen retrieval using a monoclonal antibody against p27 protein. p27 protein was expressed in the nuclei of all 16 normal human pituitary gl ands. p27 protein was also expressed in 128 of 179 cases of pituitary adeno mas (71.5%). A marked decrease of p27 expression was noted in ACTH-secreting adenomas, 8 /20 (40.0%), compared with other types of pituitary adenomas-GH-secreting a denomas, 35/46 (76.1%); PRL-secreting adenomas, 22/33 (66.7%); TSH-secretin g adenomas, 8/11 (72.7%); and nonfunctioning adenomas, 55/69 (79.7%). These results suggest that p27 may play some role in the regulation of prol iferation in all types of pituitary adenomas. The lower levels of p27 in AC TH-secreting adenoma is of particular interest with respect to the intermed iate lobe-derived pituitary tumor developed in p27 knockout mice.