Fig. 1.

Cyclin E up-regulation and loss of p27^Kip1 expression in corticotroph adenomas. A, A panel of 25 human corticotroph adenomas was studied by immunohistochemistry for Brg1, cyclin E, and p27^Kip1 expression. All samples were also positive for ACTH, Tpit, and GR expression. Normal pituitary tissue is always positive for nuclear Brg1 and p27^Kip1 and negative for cyclin E. The upper panels represent data for adenomas that are Wt for Brg1 (i.e. positive) whereas the lower panels represent data for the Brg1-negative subset. For each, the left panel indicates percentage of tumors that are either cyclin E negative (Wt) or cyclin E positive, and the right panels indicate the proportion of each tumor group that has lost expression of p27^Kip1. No tumor was ever observed to be Brg1 negative and cyclin E negative. B, Immunohistochemical analyses for a representative human Brg1-negative, cyclin E-positive, p27^Kip1-negative adenoma. Normal pituitary is shown for comparison. C, The putative repressor activity of Brg1 on cyclin E expression was verified in AtT-20 cells using RNA interference with a short hairpin loop RNA target against Brg1 (shpBrg1) in comparison with a scrambled-sequence control RNA (shpCTRL). Western blot analysis of Brg1, cyclin E, and GAPDH indicated successful knockdown of Brg1 resulting in up-regulation of cyclin E. D, Sections from two representative tumors of the Brg1-negative, cyclin E-positive, and p27^Kip1-negative group showing colabeling of POMC-positive cells with pHH3. All tumor samples of this group showed similar double-positive cells, but no pHH3-positive, ACTH-negative cells. IB, Immunoblotting.