Abstract
PARP1 regulates the repair of DNA single-strand breaks generated directly, or during base excision repair (BER). However, the role of PARP2 in these and other repair mechanisms is unknown. Here, we report a requirement for PARP2 in stabilising replication forks that encounter BER intermediates through Fbh1-dependent regulation of Rad51. Whereas PARP2 is dispensable for tolerance of cells to SSBs or homologous recombination dysfunction, it is redundant with PARP1 in BER. Therefore, combined disruption of PARP1 and PARP2 leads to defective BER, resulting in elevated levels of replication-associated DNA damage owing to an inability to stabilise Rad51 at damaged replication forks and prevent uncontrolled DNA resection. Together, our results demonstrate how PARP1 and PARP2 regulate two independent, but intrinsically linked aspects of DNA base damage tolerance by promoting BER directly, and by stabilising replication forks that encounter BER intermediates.
Highlights
PARP1 regulates the repair of DNA single-strand breaks generated directly, or during base excision repair (BER)
We identify that PARP1 and PARP2 are redundant in BER and allow cells to tolerate DNA base damage induced by methyl methanesulfonate (MMS)
In order to understand the contributions of different poly(ADP-ribose) polymerases (PARPs) family members in regulating DNA repair, we generated a number of cell lines deficient for PARPs in U2OS cells, starting with PARP1 (Fig. 1a and Supplementary Fig. 1)
Summary
PARP1 regulates the repair of DNA single-strand breaks generated directly, or during base excision repair (BER). PARP1, the founding member of the ARTD family, senses DNA single-strand breaks (SSBs) induced either directly, or as a consequence of processing DNA lesions during the base excision repair (BER) pathway[6]. Given PARP1 and PARP2 are both targets for inhibitors being used to treat tumours with defects in homologous recombination (HR)[22,23], unravelling these complexities will be important for understanding the mechanistic basis of DNA repair, and refining the use of PARP inhibitors (PARPi) in the clinic and guiding the development of novel PARPi with new mechanisms of action We address these questions by disrupting PARP1 and PARP2 alone or in combinations and assessing the impact of these manipulations on the repair of DNA base damage. In the absence of PARP1, PARP2 is required for optimal resolution of MMS-induced DNA damage during DNA replication, independent of its role in BER, by stabilising HR proteins at sites of replication stress to protect stalled and/or damaged forks against uncontrolled nucleolytic resection
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