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Updated: May 24, 2026
Visualizing and Quantifying Endonuclease-Based Site-Specific DNA Damage
Published on: August 21, 2021
Mechanism-based screen establishes signalling framework for DNA damage-associated G1 checkpoint response
Elizabeth Richardson1, Simon R Stockwell, He Li
1Department of Cancer Biology, UCL Cancer Institute, London, United Kingdom.
Abstract:
DNA damage activates checkpoint controls which block progression of cells through the division cycle. Several different checkpoints exist that control transit at different positions in the cell cycle. A role for checkpoint activation in providing resistance of cells to genotoxic anticancer therapy, including chemotherapy and ionizing radiation, is widely recognized. Although the core molecular functions that execute different damage activated checkpoints are known, the signals that control checkpoint activation are far from understood. We used a kinome-spanning RNA interference screen to delineate signalling required for radiation-mediated retinoblastoma protein activation, the recognized executor of G(1) checkpoint control. Our results corroborate the involvement of the p53 tumour suppressor (TP53) and its downstream targets p21(CIP1/WAF1) but infer lack of involvement of canonical double strand break (DSB) recognition known for its role in activating TP53 in damaged cells. Instead our results predict signalling involving the known TP53 phosphorylating kinase PRPK/TP53RK and the JNK/p38MAPK activating kinase STK4/MST1, both hitherto unrecognised for their contribution to DNA damage G1 checkpoint signalling. Our results further predict a network topology whereby induction of p21(CIP1/WAF1) is required but not sufficient to elicit checkpoint activation. Our experiments document a role of the kinases identified in radiation protection proposing their pharmacological inhibition as a potential strategy to increase radiation sensitivity in proliferating cancer cells.
Insights
DNA damage triggers cell cycle checkpoints, offering cancer therapy resistance. This study identifies novel kinases, PRPK/TP53RK and STK4/MST1, crucial for G1 checkpoint activation, suggesting new therapeutic targets for enhancing radiation sensitivity.
Area of Science:
- Cell Biology
- Molecular Oncology
- Cancer Therapeutics
Background:
- DNA damage response pathways activate cell cycle checkpoints, crucial for preventing genomic instability.
- Checkpoint activation confers resistance to genotoxic cancer therapies like chemotherapy and ionizing radiation.
- The precise signaling networks controlling DNA damage-induced G1 checkpoint activation remain incompletely understood.
Purpose of the Study:
- To identify novel signaling molecules involved in DNA damage-induced G1 checkpoint activation using a comprehensive RNA interference screen.
- To elucidate the signaling pathways regulating retinoblastoma protein (Rb) activation following radiation exposure.
- To explore the potential of targeting identified kinases for enhancing cancer therapy sensitivity.
Main Methods:
- A kinome-wide RNA interference screen was employed to identify kinases regulating radiation-mediated Rb activation.
- Experimental validation of candidate kinases and their downstream targets, including p53 (TP53) and p21(CIP1/WAF1).
- Assessment of the role of identified kinases in cellular radiation protection and checkpoint control.
Main Results:
- The screen identified PRPK/TP53RK and STK4/MST1 as novel kinases involved in G1 checkpoint signaling following DNA damage.
- While p53 (TP53) and p21(CIP1/WAF1) were confirmed to be involved, canonical double-strand break (DSB) recognition pathways were found to be dispensable for this specific checkpoint activation.
- A network model was proposed where p21(CIP1/WAF1) induction is necessary but not sufficient for checkpoint activation, with PRPK/TP53RK and STK4/MST1 playing critical roles.
- These kinases were found to mediate radiation protection, indicating their importance in cellular survival post-irradiation.
Conclusions:
- PRPK/TP53RK and STK4/MST1 are novel regulators of the DNA damage-induced G1 checkpoint, distinct from canonical DSB sensing pathways.
- The identified kinases play a significant role in cellular radiation resistance.
- Pharmacological inhibition of these kinases presents a promising strategy to sensitize proliferating cancer cells to radiation therapy.
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