Differential expression of cyclin-dependent kinase inhibitors, p27Kip1 and p57Kip2, by corticotropin in rat adrenal cortex

An important role for the cyclin-dependent kinase inhibi-tors (CDKIs), p27Kip1 and p57Kip2, in the proliferation and differentiation of adrenal cells has been suggested by their knockout mice, which display adrenal hyperplasia. Adrenal development and function are primarily regulated by ACTH. In the present study, we investigated the effects of ACTH on the expression of p27Kip1, p57Kip2 and proliferating cell nuclear antigen (PCNA) in rat adrenals. Male Wistar rats were treated with dexametha-sone (Dex) to inhibit endogenous ACTH secretion. ACTH was then administered to the rats, and the adrenals were examined by Western blot and immunohisto-chemical analyses. Dex treatment induced shrinkage of adrenals where no PCNA-expressing cells were detected