Cyclin A-Cdk1 regulates the origin firing program in mammalian cells.
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.
Katsuno
Yuko
Y
Department of Cell Biology, Graduate School of Medical Sciences, Nagoya City University, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan.
Suzuki
Ayumi
A
Sugimura
Kazuto
K
Okumura
Katsuzumi
K
Zineldeen
Doaa H
DH
Shimada
Midori
M
Niida
Hiroyuki
H
Mizuno
Takeshi
T
Hanaoka
Fumio
F
Nakanishi
Makoto
M
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
D019925:Cyclin A; D011993:Recombinant Fusion Proteins; D016203:CDC2 Protein Kinase