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Disruption of the checkpoint kinase 1/cell division cycle 25A pathway abrogates ionizing radiation-induced S and G2
Hui Zhao1, Janis L Watkins, Helen Piwnica-Worms
1Department of Cell Biology and Physiology, Howard Hughes Medical Institute, Washington University School of Medicine, Box 8228, 660 South Euclid Avenue, St. Louis, MO 63110-1093, USA.
Abstract:
Checkpoint kinase (Chk)1 is an evolutionarily conserved protein kinase that was first identified in fission yeast as an essential component of the DNA damage checkpoint. In mice, Chk1 provides an essential function in the absence of environmentally imposed genotoxic stress. Here we show that human cells lacking Chk1 exhibit defects in both the ionizing radiation (IR)-induced S and G(2) checkpoints. In addition, loss of Chk1 resulted in the accumulation of a hypophosphorylated form of the Cdc25A protein phosphatase, and Chk1-deficient cells failed to degrade Cdc25A after IR. The IR-induced S and G(2) checkpoints were partially restored in Chk1-deficient cells when Cdc25A accumulation was interfered with. Finally, Cdc25A was phosphorylated by Chk1 in vitro on similar sites phosphorylated in vivo, including serine-123. These findings indicate that Chk1 directly phosphorylates Cdc25A during an unperturbed cell cycle, and that phosphorylation of Cdc25A by Chk1 is required for cells to delay cell cycle progression in response to double-strand DNA breaks.
Insights
Checkpoint kinase 1 (Chk1) is essential for DNA damage checkpoints. Human cells lacking Chk1 show cell cycle defects after DNA damage, as Chk1 directly phosphorylates Cdc25A to regulate cell cycle progression.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Checkpoint kinase 1 (Chk1) is a conserved protein kinase crucial for DNA damage response.
- Chk1 plays an essential role in cell cycle regulation, even without external genotoxic stress.
- Previous studies identified Chk1 as a key component of the DNA damage checkpoint in yeast and mice.
Purpose of the Study:
- To investigate the role of Chk1 in human cells, particularly in response to ionizing radiation (IR).
- To elucidate the mechanism by which Chk1 regulates cell cycle checkpoints.
- To determine the relationship between Chk1 and Cdc25A protein phosphatase in DNA damage response.
Main Methods:
- Studied human cells lacking Chk1.
- Utilized ionizing radiation (IR) to induce DNA damage.
- Analyzed cell cycle progression (S and G2 checkpoints).
- Assessed Cdc25A protein levels and phosphorylation status.
- Performed in vitro phosphorylation assays.
Main Results:
- Human cells deficient in Chk1 exhibit defects in IR-induced S and G2 checkpoints.
- Loss of Chk1 leads to accumulation of hypophosphorylated Cdc25A and impaired Cdc25A degradation post-IR.
- Interfering with Cdc25A accumulation partially restored IR-induced checkpoints in Chk1-deficient cells.
- Chk1 directly phosphorylates Cdc25A in vitro at sites including serine-123.
Conclusions:
- Chk1 directly phosphorylates Cdc25A during normal cell cycles.
- Phosphorylation of Cdc25A by Chk1 is critical for delaying cell cycle progression after double-strand DNA breaks.
- Chk1 is a key regulator of the DNA damage response through its interaction with Cdc25A.