title: Cdc6 determines utilization of p21(WAF1/CIP1)-dependent damage checkpoint in S phase cells.
abstract: 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.
authors.affiliation: Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, University of Tokyo, Tokyo, Japan.
authors.forename: Qiuming
authors.initials: Q
authors.lastname: Kan
authors.forename: Shigeki
authors.initials: S
authors.lastname: Jinno
authors.forename: Kohei
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Hanako
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Hiroto
authors.initials: H
authors.lastname: Okayama
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology*; D002945:Cisplatin / Q000494:pharmacology; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D004249:DNA Damage; D006801:Humans; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D051379:Mice; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D034622:RNA Interference; D016196:S Phase; D014466:Ultraviolet Rays; D020687:cdc25 Phosphatases / Q000378:metabolism
chemical_list: C103706:CDC6 protein, human; C502132:CDC6 protein, mouse; C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D009687:Nuclear Proteins; D008741:Methyl Methanesulfonate; C517005:Cdc25a protein, mouse; D020687:cdc25 Phosphatases; D002945:Cisplatin