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Updated: Aug 14, 2026
Two- and Three-Dimensional Live Cell Imaging of DNA Damage Response Proteins
Published on: September 28, 2012
Chk1 and p21 cooperate to prevent apoptosis during DNA replication fork stress
1Institute for Cancer Studies, School of Medicine and Biomedical Sciences, University of Sheffield, Sheffield S10 2RX, United Kingdom.
Abstract:
Cells respond to DNA replication stress by triggering cell cycle checkpoints, repair, or death. To understand the role of the DNA damage response pathways in determining whether cells survive replication stress or become committed to death, we examined the effect of loss of these pathways on cellular response to agents that slow or arrest DNA synthesis. We show that replication inhibitors such as excess thymidine, hydroxyurea, and camptothecin are normally poor inducers of apoptosis. However, these agents become potent inducers of death in S-phase cells upon small interfering RNA-mediated depletion of the checkpoint kinase Chk1. This death response is independent of p53 and Chk2. p21-deficient cells, on the other hand, produce a more robust apoptotic response upon Chk1 depletion. p21 is normally induced only late after thymidine treatment. In Chk1-depleted cells p21 induction occurs earlier and does not require p53. Thus, Chk1 plays a primary role in the protection of cells from death induced by replication fork stress, whereas p21 mediates through its role in regulating entry into S phase. These findings are of potential importance to cancer therapy because we demonstrate that the efficacy of clinically relevant agents can be enhanced by manipulation of these signaling pathways.
Insights
Checkpoint kinase 1 (Chk1) depletion enhances cancer cell death from replication stress, independent of p53. Manipulating DNA repair pathways like p21 may improve cancer therapy efficacy.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Cells activate DNA damage response pathways to manage replication stress, involving checkpoints, repair, or cell death.
- Replication inhibitors typically induce apoptosis poorly, but their role in cell fate determination under stress is not fully understood.
Purpose of the Study:
- To investigate the role of DNA damage response pathways in cellular survival versus death following replication stress.
- To determine how loss of specific pathways affects cellular responses to agents that impede DNA synthesis.
Main Methods:
- Utilized small interfering RNA (siRNA) to deplete checkpoint kinase 1 (Chk1).
- Examined cellular responses to replication inhibitors like excess thymidine, hydroxyurea, and camptothecin.
- Assessed apoptosis induction and the involvement of p53, Chk2, and p21.
Main Results:
- Replication inhibitors are weak apoptosis inducers unless Chk1 is depleted, which then triggers potent S-phase cell death.
- This Chk1-depletion-induced death is independent of p53 and Chk2.
- p21-deficient cells show enhanced apoptosis upon Chk1 depletion; p21 induction is accelerated and p53-independent in Chk1-depleted cells.
- Chk1 protects cells from replication fork stress-induced death, while p21 regulates S-phase entry.
Conclusions:
- Chk1 is crucial for preventing cell death caused by replication fork stress.
- p21 influences cell fate by regulating entry into S phase.
- Targeting these pathways, particularly Chk1 and p21, can potentially enhance the effectiveness of cancer therapies.
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