XRCC1 Prevents Replication Fork Instability during Misincorporation of the DNA Demethylation Bases 5-Hydroxymethyl-2'-Deoxycytidine and 5-Hydroxymethyl-2'-Deoxyuridine

• Published in: International journal of molecular sciences Vol. 23; no. 2; p. 893
• Main Authors: Peña-Gómez, María José, Suárez-Pizarro, Marina, Rosado, Iván V
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 14.01.2022; MDPI
• Subjects: 5-Methylcytosine - pharmacology; 5hmU-mediated genomic instability; Base excision repair; Catalytic oxidation; Cell cycle; Cell differentiation; Cell Line; Cell Survival - drug effects; Cell Survival - genetics; Chromatin; Cytosine; Deamination; Demethylation; Deoxycytidine - analogs & derivatives; Deoxyribonucleic acid; DNA; DNA biosynthesis; DNA Damage; DNA Demethylation; DNA Replication - drug effects; Enzymes; Epigenesis, Genetic; epigenetic DNA bases; Epigenetics; Exposure; Genomes; Genomic Instability; Genotoxicity; Humans; Impairment; Mutation; Phenotypes; Pluripotency; Poly(ADP-ribose) polymerase; Recruitment; Repair; Replication; replication fork instability by 5hmC; Replication Origin; Retention; Stability; Stem cells; Thymidine - analogs & derivatives; X-ray Repair Cross Complementing Protein 1 - genetics; X-ray Repair Cross Complementing Protein 1 - metabolism; XRCC1; XRCC1 protein; XRCC1; 5hmU-mediated genomic instability; epigenetic DNA bases; replication fork instability by 5hmC
• DOI: 10.3390/ijms23020893
• ISSN: 1422-0067; 1661-6596

Whilst avoidance of chemical modifications of DNA bases is essential to maintain genome stability, during evolution eukaryotic cells have evolved a chemically reversible modification of the cytosine base. These dynamic methylation and demethylation reactions on carbon-5 of cytosine regulate several cellular and developmental processes such as embryonic stem cell pluripotency, cell identity, differentiation or tumourgenesis. Whereas these physiological processes are well characterized, very little is known about the toxicity of these cytosine analogues when they incorporate during replication. Here, we report a role of the base excision repair factor XRCC1 in protecting replication fork upon incorporation of 5-hydroxymethyl-2'-deoxycytosine (5hmC) and its deamination product 5-hydroxymethyl-2'-deoxyuridine (5hmU) during DNA synthesis. In the absence of XRCC1, 5hmC exposure leads to increased genomic instability, replication fork impairment and cell lethality. Moreover, the 5hmC deamination product 5hmU recapitulated the genomic instability phenotypes observed by 5hmC exposure, suggesting that 5hmU accounts for the observed by 5hmC exposure. Remarkably, 5hmC-dependent genomic instability and replication fork impairment seen in cells were exacerbated by the trapping of Parp1 on chromatin, indicating that XRCC1 maintains replication fork stability during processing of 5hmC and 5hmU by the base excision repair pathway. Our findings uncover natural epigenetic DNA bases 5hmC and 5hmU as genotoxic nucleosides that threaten replication dynamics and genome integrity in the absence of XRCC1.