Work

PARP1 auto-modification promotes faithful Okazaki fragment processing and limits replication fork speed

Year: 2025

Type: article

Abstract: PARP-inhibitors have proven their efficacy for treating tumors defective in homologous recombination via synthetic lethality. In response to DNA breaks, PARP1 is the major writer of ADP-ribosylation, targeting itself (auto-modification) and other targets, which is critical for DNA repair. However, PARP-inhibitors prevent modification of both PARP1 itself and other substrates, which has made it challenging to dissect the relative contributions of self and non-self ADPr for DNA repair. Here we use our site-specific proteomics strategy to identify a new auto-modification site on PARP1, allowing us to generate a PARP1 mutant unable to undergo self ADP-ribosylation, yet it remains catalytically active. This separation of function mutant uncovered that PARP1 auto-modification alone restricts the speed of the DNA replication fork. Surprisingly, we found that PARP1 auto-modification is dispensable for recruitment of DNA repair factors, yet it is required for the timely repair of DNA breaks and its subsequent release. Simultaneous inhibition of FEN1 and loss of PARP1 auto-modification gives rise to synthetic lethality, implicating auto-modification in Okazaki fragment processing. Finally, we characterize the ADP-ribosylation targets at the DNA replication fork contingent on PARP1 activation. Our results demonstrate that trapping of PARP at DNA breaks impedes repair factor accessibility, constituting an important dimension of PARP-inhibitor driven cytotoxicity.

Source: Molecular Cell

DOI: 10.1016/j.molcel.2025.09.006