書誌： J Biol Chem ,2012
Lee AY, Chiba T, Truong LN, Cheng AN, Do J, Cho MJ, Chen L, Wu X. J Biol Chem. 2012, 287(4):2531-43.
Background: S-phase checkpoint is important for maintaining genome stability upon DNA damage in S-phase. Results: A replication essential protein Dbf4 is phosphorylated by checkpoint kinases when DNA is damaged. Conclusion: Dbf4 is a downstream target of the S-phase checkpoint to mediate DNA damage responses. Significance: These studies help understand how the genome is protected from DNA damage to prevent tumorigenesis.
Dbf4/Cdc7 (Dbf4-dependent kinase (DDK)) is activated at the onset of S-phase, and its kinase activity is required for DNA replication initiation from each origin. We showed that DDK is an important target for the S-phase checkpoint in mammalian cells to suppress replication initiation and to protect replication forks. We demonstrated that ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3-related (ATR) proteins directly phosphorylate Dbf4 in response to ionizing radiation and replication stress. We identified novel ATM/ATR phosphorylation sites on Dbf4 and showed that ATM/ATR-mediated phosphorylation of Dbf4 is critical for the intra-S-phase checkpoint to inhibit DNA replication. The kinase activity of DDK, which is not suppressed upon DNA damage, is required for fork protection under replication stress. We further demonstrated that ATM/ATR-mediated phosphorylation of Dbf4 is important for preventing DNA rereplication upon loss of replication licensing through the activation of the S-phase checkpoint. These studies indicate that DDK is a direct substrate of ATM and ATR to mediate the intra-S-phase checkpoint in mammalian cells.