CtIP-BRCA1 complex and MRE11 maintain replication forks in the presence of chain terminating nucleoside analogs

• Published in: Nucleic acids research Vol. 47; no. 6; pp. 2966 - 2980
• Main Authors: Mohiuddin, Mohiuddin, Rahman, Md Maminur, Sale, Julian E, Pearson, Christopher E
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 08-04-2019
• Subjects: BRCA1 Protein - genetics; Carrier Proteins - genetics; DNA Replication - genetics; DNA-Directed DNA Polymerase - genetics; Genome Integrity, Repair and; Humans; MRE11 Homologue Protein - genetics; Nuclear Proteins - genetics; Nucleosides - analogs & derivatives; Nucleosides - genetics; Peptide Chain Termination, Translational
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/gkz009

Abstract
Chain-terminating nucleoside analogs (CTNAs), which cannot be extended by DNA polymerases, are widely used as antivirals or anti-cancer agents, and can induce cell death. Processing of blocked DNA ends, like camptothecin-induced trapped-topoisomerase I, can be mediated by TDP1, BRCA1, CtIP and MRE11. Here, we investigated whether the CtIP-BRCA1 complex and MRE11 also contribute to cellular tolerance to CTNAs, including 2’,3’-dideoxycytidine (ddC), cytarabine (ara-C) and zidovudine (Azidothymidine, AZT). We show that BRCA1−/−, CtIPS332A/−/− and nuclease-dead MRE11D20A/− mutants display increased sensitivity to CTNAs, accumulate more DNA damage (chromosomal breaks, γ-H2AX and neutral comets) when treated with CTNAs and exhibit significant delays in replication fork progression during exposure to CTNAs. Moreover, BRCA1−/−, CtIPS332A/−/− and nuclease-dead MRE11D20A/− mutants failed to resume DNA replication in response to CTNAs, whereas control and CtIP+/−/− cells experienced extensive recovery of DNA replication. In summary, we provide clear evidence that MRE11 and the collaborative action of BRCA1 and CtIP play a critical role in the nuclease-dependent removal of incorporated ddC from replicating genomic DNA. We propose that BRCA1-CTIP and MRE11 prepare nascent DNA ends, blocked from synthesis by CTNAs, for further repair.