Cdc6 determines utilization of p21(WAF1/CIP1)-dependent damage checkpoint in S phase cells

• Published in: The Journal of biological chemistry 2008-06, Vol.283 (26), p.17864
• Main Authors: Kan, Qiuming, Jinno, Shigeki, Kobayashi, Kohei, Yamamoto, Hanako, Okayama, Hiroto
• Format: Article
• Language: English
• Subjects: Animals; cdc25 Phosphatases - metabolism; Cell Cycle Proteins - metabolism; Cell Cycle Proteins - physiology; Cisplatin - pharmacology; Cyclin-Dependent Kinase Inhibitor p21 - metabolism; DNA Damage; Humans; Methyl Methanesulfonate - pharmacology; Mice; Models, Biological; Nuclear Proteins - metabolism; Nuclear Proteins - physiology; RNA Interference; S Phase; Ultraviolet Rays
• ISSN: 0021-9258
• DOI: 10.1074/jbc.M802055200

When cells traversing G(1) are irradiated with UV light, two parallel damage checkpoint pathways are activated: Chk1-Cdc25A and p53-p21(WAF1/CIP1), both targeting Cdk2, but the latter inducing a long lasting arrest. In similarly treated S phase-progressing cells, however, only the Cdc25A-dependent checkpoint is active. We have recently found that the p21-dependent checkpoint can be activated and induce a prolonged arrest if S phase cells are damaged with a base-modifying agent, such as methyl methanesulfonate (MMS) and cisplatin. But the mechanistic basis for the differential activation of the p21-dependent checkpoint by different DNA damaging agents is not understood. Here we report that treatment of S phase cells with MMS but not a comparable dose of UV light elicits proteasome-mediated degradation of Cdc6, the assembler of pre-replicative complexes, which allows induced p21 to bind Cdk2, thereby extending inactivation of Cdk2 and S phase arrest. Consistently, enforced expression of Cdc6 largely eliminates the prolonged S phase arrest and Cdk2 inactivation induced with MMS, whereas RNA interference-mediated Cdc6 knockdown not only prolongs such arrest and inactivation but also effectively activates the p21-dependent checkpoint in the UV-irradiated S phase cells.