Increased expression of cyclin D1, cyclin E and p21(Cip1) associated with decreased expression of p27(Kip1) chemically induced rat mammary carcinogenesis

We induced rat mammary tumors in 7-week-old female Sprague-Dawley rats by i ntragastric administration of 7,12-dimethylbenz(a)anthracene (DMBA), and an alyzed by immunohistochemistry the expression of cyclin D1, cyclin E, p21(C ip1), and p27(Kip1) in carcinomas, atypical tumors, and benign tumors as we ll as normal mammary glands from the control group. Proliferation status wa s assessed by immunohistochemistry using bromodeoxyuridine (BrdU). A sequen tial increase in cyclin D1-, cyclin E-, and p21(Cip1)-positive epithelial c ells was observed from normal mammary glands, to atypical tumors, to carcin omas. In contrast, carcinomas showed a significantly lower number of epithe lial cells immunoreactive to p27(Kip1) when compared with atypical tumors, benign tumors and normal mammary glands. The immunoreactivities of BrdU, cy clin D1, cyclin E, and p21(Cip1) were positively correlated, whereas that o f p27(Kip1) appeared inversely correlated to those of the others. Reverse t ranscriptase-polymerase chain reaction (RT-PCR) and western blot analysis w ere also performed to determine the mRNA and protein levels of cyclins and cyclin-dependent kinase inhibitors in tumors and normal mammary glands. The protein levels for cyclin D1, cyclin E and p21(Cip1) in carcinomas and aty pical tumors were significantly higher than those in benign tumors, while n ormal mammary glands showed negligible expression. On RT-PCR, tumors showed higher mRNA levels of cyclin D1 and cyclin E than those of normal mammary glands. Our results suggest that rat mammary carcinogenesis involves increa sed expression of cyclin D1, cyclin E, and p21(Cip1), associated with decre ased expression of p27(Kip1).