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An ATM-independent S-phase checkpoint response involves CHK1 pathway
Xiang-Yang Zhou1, Xiang Wang, Baocheng Hu
1Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Abstract:
After exposure to genotoxic stress, proliferating cells actively slow down the DNA replication through a S-phase checkpoint to provide time for repair. We report that in addition to the ataxia-telangiectasia mutated (ATM)-dependent pathway that controls the fast response, there is an ATM-independent pathway that controls the slow response to regulate the S-phase checkpoint after ionizing radiation in mammalian cells. The slow response of S-phase checkpoint, which is resistant to wortmannin, sensitive to caffeine and UCN-01, and related to cyclin-dependent kinase phosphorylation, is much stronger in CHK1 overexpressed cells, and it could be abolished by Chk1 antisense oligonucleotides. These results provide evidence that the ATM-independent slow response of S-phase checkpoint involves CHK1 pathway.
Insights
Proliferating cells use DNA replication checkpoints to repair genotoxic stress. A newly identified ATM-independent pathway involving CHK1 regulates the slow S-phase checkpoint response to ionizing radiation in mammalian cells.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- DNA Damage Response
Background:
- Proliferating cells employ S-phase checkpoints to halt DNA replication during genotoxic stress, allowing for DNA repair.
- The ataxia-telangiectasia mutated (ATM)-dependent pathway is known to mediate the rapid response to DNA damage.
Purpose of the Study:
- To investigate the existence and characteristics of an ATM-independent pathway regulating the S-phase checkpoint after ionizing radiation.
- To elucidate the role of CHK1 in the slow response of the S-phase checkpoint.
Main Methods:
- Exposure of mammalian cells to ionizing radiation.
- Analysis of S-phase checkpoint regulation, including sensitivity to wortmannin, caffeine, and UCN-01.
- Assessment of CHK1 overexpression and the effect of Chk1 antisense oligonucleotides.
Main Results:
- Identified an ATM-independent pathway controlling the slow S-phase checkpoint response to ionizing radiation.
- The slow response is resistant to wortmannin but sensitive to caffeine and UCN-01, involving cyclin-dependent kinase phosphorylation.
- Overexpression of CHK1 significantly enhanced the slow S-phase checkpoint response, which was abolished by Chk1 antisense oligonucleotides.
Conclusions:
- The ATM-independent slow response of the S-phase checkpoint is mediated by the CHK1 pathway.
- This finding reveals a parallel regulatory mechanism for the S-phase checkpoint, distinct from the ATM-dependent fast response.