Activation of cyclin E-dependent kinase activity in colorectal cancer

Although cyclin E gene amplification is reported to be an important event i n various cancers, it is rarely found in human colorectal cancers. As one o f the candidate factors of other mechanisms relating to cyclin E, we analyz ed cyclin E-dependent kinase activity in colorectal cancer. Protein levels of cyclin E, its catalytic subunit, cyclin-dependent kinase 2 (Cdk2), and p 21 and p27 were determined by western blot or immunohistochemistry in 27 co lorectal cancers and 10 colorectal adenomas, and compared with adjacent nor mal colonic mucosa. Enzymatic activity of cyclin E-Cdk2 complex in the colo rectal neoplasm was measured using in-gel kinase assay using glutathione S- transferase-retinoblastoma (GST-Rb) fusion protein as substrate, and compar ed with that of normal mucosa. We clearly showed that although the protein level of cyclin E in colorectal cancer and adenoma was similar to that of a djacent normal mucosa, cylin E-dependent kinase activity was increased in a ll the cases of colorectal cancers and 90% of colorectal adenomas. The rela tive kinase activity was significantly higher in colorectal cancer (3.7 +/- 1.7 -fold) than colorectal adenomas (2.0 +/- 0.8-fold) (P < 0.004). The re lative expression level of Cdk2 protein in cancer was significantly higher than adenoma (4.4 +/- 2.4 vs 2.7 +/- 1.3, P < 0.04), and p21 and p27 were n ot detected in colorectal cancer and notably decreased in adenoma. The resu lts of this study strongly suggest that activation of cyclin E-dependent ki nase activity may play an important role in colorectal cancer, and its leve l appears to be related to increased Cdk2 and decreased p21 and p27 amounts rather than cyclin E protein level.