p27 (Kip1) plays regulatory roles in the cell cycle by inhibiting the activity of
cyclin dependent kinases (CDKs). This immunohistochemical study is aimed 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 glands. p27
protein was also expressed in 128 of 179 cases of
pituitary adenomas (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 adenomas, 35/46 (76.1%); PRL-secreting
adenomas, 22/33 (66.7%); TSH-secreting
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 proliferation in all types of
pituitary adenomas. The lower levels of p27 in
ACTH-secreting
adenoma is of particular interest with respect to the intermediate lobe-derived
pituitary tumor developed in p27 knockout mice.