Reduced expression of the CDK inhibitor p27(KIP1) in rat two-stage bladdercarcinogenesis and its association with expression profiles of p21(WAF1/Cip1) and p53

The cyclin-dependent kinase (CDK) inhibitor p27(KIP1) exerts its growth sup pressive effects by targeting the cyclin-CDK complexes. Reduced protein lev els of p27(KIP1) have been reported in numerous human cancers and this has been attributed to increased degradation. However, few reports have address ed the significance of p27(KIP1) expression in chemical carcinogenesis of r odents. In a rat two-stage urinary bladder carcinogenesis model, with N-but yl-N-(4-hydroxybutyl)nitrosamine (BBN) initiation followed by promotion wit h sodium L-ascorbate (Na-AsA), we evaluated the expression of p27(KIP1) pro tein using immunohistochemistry during various stages of urinary bladder ca rcinogenesis. In addition, we evaluated the mRNA expression profiles for p2 7(KIP1), P21(WAF1/Cip1) and p53 in tumors. Fisher 344 rats were initiated w ith 0.05% BBN in the drinking water for 4 weeks and then administered 5% Na -AsA in the diet. Immunohistochemical examination revealed p27(KIP1) protei n to be constitutively expressed in normal urothelium, simple hyperplasia a nd in most papillary and nodular (PN) hyperplasias and small papillomas, bu t diminished or absent in large papillomas and in transitional cell carcino mas, An inverse correlation between expression of p27(KIP1) and cell prolif eration was generally observed. Quantitation of mRNA by multiplex reverse t ranscription-PCR showed a significant downregulation of p27(KIP1) p21(WAF1/ Cip1) and p53 mRNA in tumors. More than 50% reduction in p27(KIP1) mRNA exp ression was observed in 42 and 47% of tumors at weeks 18 and 24, respective ly; similar reduction in p21(WAF1/Cip1) mRNA expression was observed in 58 and 73% of tumors at weeks 18 and 24, and in p53 mRNA expression in 50 and 73% of tumors at weeks 18 and 24, respectively. None of the 25 tumors we ex amined by PCR-single-strand conformational polymorphism analysis had p53 mu tations. These data imply that abnormal down-regulation of p27(KIP1), P21(W AF1/Cip1) and/or p53 in tumor cells may contribute to the malignant progres sion of tumors during rat two-stage bladder carcinogenesis.