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Mechanism of DNA replication fork breakage and PARP1 hyperactivation during replication catastrophe
Pedro Ortega1,2,3, Elodie Bournique1,2,3, Junyi Li1,2,3
1Department of Biological Chemistry, School of Medicine, University of California Irvine, Irvine, CA, USA.
Science Advances
|April 16, 2025
Summary
Ataxia telangiectasia and Rad3-related (ATR) inhibition causes replication catastrophe by leaving single-stranded DNA (ssDNA) unprotected. APOBEC3B targets this ssDNA, leading to DNA breaks and synthetic lethality with PARP inhibitors.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- ATR inhibition increases origin firing, leading to ssDNA accumulation and replication catastrophe.
- The precise mechanism of ssDNA breakage under ATR inhibition is not fully understood.
Purpose of the Study:
- To elucidate the mechanism of ssDNA breakage following ATR inhibition.
- To identify key enzymes involved in replication catastrophe and PARP1 hyperactivation.
- To explore therapeutic strategies based on these findings.
Main Methods:
- Cell-based assays to monitor DNA damage and replication stress.
- Enzyme activity assays to assess the role of APOBEC3B, UNG2, and APE1.
- PARP inhibitor sensitivity assays.
Main Results:
- APOBEC3B was identified as the key enzyme targeting unprotected ssDNA at replication forks.
- APOBEC3B initiates a cascade involving uracil generation, removal by UNG2, and cleavage by APE1 endonuclease.
- APE1-mediated DNA cleavage is critical for PARP1 hyperactivation.
- APOBEC3B-induced DNA damage and PARP1 trapping sensitize cells to ATR inhibition, creating synthetic lethality with PARP inhibitors.
Conclusions:
- APOBEC3B is a critical mediator of replication catastrophe induced by ATR inhibition.
- Targeting APOBEC3B or its downstream effectors may offer novel therapeutic strategies.
- The findings establish a synthetic lethal interaction between ATR inhibition and PARP inhibition via APOBEC3B-mediated DNA damage.
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