Bypass of a 5′,8-cyclopurine-2′-deoxynucleoside by DNA polymerase β during DNA replication and base excision repair leads to nucleotide misinsertions and DNA strand breaks

Abstract

5′,8-cyclopurine-2′-deoxynucleosides including 5′,8-cyclo-dA (cdA) and 5′,8-cyclo-dG (cdG) are induced by hydroxyl radicals resulting from oxidative stress such as ionizing radiation. 5′,8-cyclopurine-2′-deoxynucleoside lesions are repaired by nucleotide excision repair with low efficiency, thereby leading to their accumulation in the human genome and lesion bypass by DNA polymerases during DNA replication and base excision repair (BER). In this study, for the first time, we discovered that DNA polymerase β (pol β) efficiently bypassed a 5′R-cdA, but inefficiently bypassed a 5′S-cdA during DNA replication and BER. We found that cell extracts from pol β wild-type mouse embryonic fibroblasts exhibited significant DNA synthesis activity in bypassing a cdA lesion located in replication and BER intermediates. However, pol β knock-out cell extracts exhibited little DNA synthesis to bypass the lesion. This indicates that pol β plays an important role in bypassing a cdA lesion during DNA replication and BER. Furthermore, we demonstrated that pol β inserted both a correct and incorrect nucleotide to bypass a cdA at a low concentration. Nucleotide misinsertion was significantly stimulated by a high concentration of pol β, indicating a mutagenic effect induced by pol β lesion bypass synthesis of a 5′,8-cyclopurine-2′-deoxynucleoside. Moreover, we found that bypass of a 5′S-cdA by pol β generated an intermediate that failed to be extended by pol β, resulting in accumulation of single-strand DNA breaks. Our study provides the first evidence that pol β plays an important role in bypassing a 5′,8-cyclo-dA during DNA replication and repair, as well as new insight into mutagenic effects and genome instability resulting from pol β bypassing of a cdA lesion.

Translesion DNA polymerases in eukaryotes: what makes them tick?

“…Thus, replicative pols δ and ε are also involved in all major DNA excision-repair pathways, where they act to maintain the integrity of the genome by restoring the DNA sequence after damaged bases, or nucleotides, are removed. Both, replicative pol δ (Choi et al , 2010; Daube et al , 2000; Hirota et al , 2016; Meng et al , 2009; Narita et al , 2010; O’Day et al , 1992; Schmitt et al , 2009) and the base excision repair polymerase, pol β (Jiang et al , 2015; Vaisman and Woodgate, 2004; Villani et al , 2011; Villani et al , 2014; Xu et al , 2014) have been implicated in TLS. Even though the discovery of pol ζ hinted that cells might contain more enzymes specializing in the replication of damaged DNA, a prevailing idea was that replicative polymerases could perform this function themselves with the assistance of accessory proteins.…”

Association Studies Between XRCC1, XRCC2, XRCC3 Polymorphisms and Differentiated Thyroid Carcinoma

“…Since genetic variations within DNA repair genes may increase cancer risk [12,13], DNA repair genes have been surmised as a candidate gene that is related to cancer susceptibility. Among various DNA repair pathways, the base excision repair (BER) could particularly eliminate methylation, oxidation or alteration of a single base, which further restore DNA single-strand breaks [14], while the homologous recombination repair (HRR) could restore DNA double-strand breaks [15]. Therefore, variations in the BER pathway or the HRR pathway may trigger thyroid cancer.…”

COST Action CM1201 “Biomimetic Radical Chemistry”: free radical chemistry successfully meets many disciplines

“…Evidence that a cdA can effect TNR deletion by inducing the formation of various sizes of loop structures with the lesion in the template strand of a TNR repeat tract were obtained. DNA pol b efficiently bypasses 5'R-cdA, but inefficiently bypasses 5 0 S-cdA during DNA replication and base excision repair (BER) [50]. This result highlights that the diastereomeric nature of purine cyclonucleoside lesions can play a crucial role in DNA repair mechanisms.…”