title: Cyclin A-Cdk1 regulates the origin firing program in mammalian cells.
abstract: Somatic mammalian cells possess well-established S-phase programs with specific regions of the genome replicated at precise times. The ATR-Chk1 pathway plays a central role in these programs, but the mechanism for how Chk1 regulates origin firing remains unknown. We demonstrate here the essential role of cyclin A2-Cdk1 in the regulation of late origin firing. Activity of cyclin A2-Cdk1 was hardly detected at the onset of S phase, but it was obvious at middle to late S phase under unperturbed condition. Chk1 depletion resulted in increased expression of Cdc25A, subsequent hyperactivation of cyclin A2-Cdk1, and abnormal replication at early S phase. Hence, the ectopic expression of cyclin A2-Cdk1AF (constitutively active mutant) fusion constructs resulted in abnormal origin firing, causing the premature appearance of DNA replication at late origins at early S phase. Intriguingly, inactivation of Cdk1 in temperature-sensitive Cdk1 mutant cell lines (FT210) resulted in a prolonged S phase and inefficient activation of late origin firing even at late S phase. Our results thus suggest that cyclin A2-Cdk1 is a key regulator of S-phase programs.
authors.affiliation: Department of Cell Biology, Graduate School of Medical Sciences, Nagoya City University, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Katsuno
authors.forename: Ayumi
authors.initials: A
authors.lastname: Suzuki
authors.forename: Kazuto
authors.initials: K
authors.lastname: Sugimura
authors.forename: Katsuzumi
authors.initials: K
authors.lastname: Okumura
authors.forename: Doaa H
authors.initials: DH
authors.lastname: Zineldeen
authors.forename: Midori
authors.initials: M
authors.lastname: Shimada
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Niida
authors.forename: Takeshi
authors.initials: T
authors.lastname: Mizuno
authors.forename: Fumio
authors.initials: F
authors.lastname: Hanaoka
authors.forename: Makoto
authors.initials: M
authors.lastname: Nakanishi
mesh_terms: D000818:Animals; D016203:CDC2 Protein Kinase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D019925:Cyclin A / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation / Q000187:drug effects; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016196:S Phase
chemical_list: D019925:Cyclin A; D011993:Recombinant Fusion Proteins; D016203:CDC2 Protein Kinase