WIP1 mutations suppress DNA damage triggered bypass of the mitotic timer
Tomoaki Sobajima1, Luke J Fulcher1, Caleb Batley1
1Department of Biochemistry, University of Oxford, South Parks Road, OX1 3QU, Oxford, UK.
Abstract:
Prolonged mitosis results in the destruction of MDM2, initiating a p53-dependent G1 cell-cycle arrest in the absence of DNA damage. Here, we investigate how DNA damage earlier in the cell cycle affects this mitotic-timer response. We find that G2-DNA damage triggers highly penetrant bypass of mitosis and of the mitotic timer, generating tetraploid cells arrested in G1. Collapse of G2 to G1 after DNA damage is initiated by p21-mediated CDK2 inhibition and rendered irreversible by the destruction of G2/M-cyclins A and B. This behaviour is altered in cells with cancer-associated mutations in the p53-phosphatase WIP1 (PPM1D), which increase the threshold for DNA-damage signalling, enabling DNA-damaged G2 cells to enter mitosis with elevated levels of MDM2, thereby suppressing mitotic-timer-dependent G1 cell-cycle arrest. Importantly, neither WIP1 mutations nor knockout prevent p53-dependent G1-arrest in response to prolonged mitosis in the absence of DNA damage. Prolonged mitosis and G2-DNA damage thus promote p53-dependent G1 cell-cycle exit through discrete routes with differential requirements for WIP1 and genotoxic stress.
Insights
DNA damage in G2 phase bypasses mitosis, leading to tetraploid cells. Cancer-associated WIP1 mutations alter this response by suppressing cell-cycle arrest, impacting cancer progression.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Prolonged mitosis normally triggers MDM2 destruction and p53-dependent G1 arrest.
- The cell's response to DNA damage during G2 phase and its interaction with mitotic regulation are not fully understood.
Purpose of the Study:
- To investigate how G2-phase DNA damage affects the mitotic timer and subsequent cell-cycle arrest.
- To elucidate the role of WIP1 (PPM1D) mutations in modulating the response to DNA damage and mitotic stress.
Main Methods:
- Cell culture and synchronization.
- Analysis of cell-cycle progression and ploidy.
- Western blotting for key cell-cycle regulators (MDM2, cyclins A/B, p21).
- Assessment of p53-dependent and independent cell-cycle arrest.
Main Results:
- G2-DNA damage causes bypass of mitosis and the mitotic timer, resulting in tetraploid G1-arrested cells.
- This G2 to G1 collapse is mediated by p21-induced CDK2 inhibition and cyclin destruction.
- Cancer-associated WIP1 mutations elevate the DNA damage signaling threshold, allowing damaged G2 cells to enter mitosis and evade arrest.
- WIP1 mutations do not prevent G1 arrest following prolonged mitosis without DNA damage.
Conclusions:
- G2-DNA damage and prolonged mitosis induce p53-dependent G1 arrest via distinct pathways.
- WIP1 mutations disrupt the G2-DNA damage response, promoting genomic instability and potentially contributing to cancer development.
- The differential regulation highlights the complexity of cell-cycle checkpoints in response to various cellular stresses.
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