How (5′S) and (5′R) 5′,8-Cyclo-2′-Deoxypurines Affect Base Excision Repair of Clustered DNA Damage in Nuclear Extracts of xrs5 Cells? A Biochemical Study

Abstract

The clustered DNA lesions (CDLs) are a characteristic feature of ionizing radiation’s impact on the human genetic material. CDLs impair the efficiency of cellular repair machinery, especially base excision repair (BER). When CDLs contain a lesion repaired by BER (e.g., apurinic/apyrimidinic (AP) sites) and a bulkier 5′,8-cyclo-2′-deoxypurine (cdPu), which is not a substrate for BER, the repair efficiency of the first one may be affected. The cdPus’ influence on the efficiency of nuclear BER in xrs5 cells have been investigated using synthetic oligonucleotides with bi-stranded CDL (containing (5′S) 5′,8-cyclo-2′-deoxyadenosine (ScdA), (5′R) 5′,8-cyclo-2′-deoxyadenosine (RcdA), (5′S) 5′,8-cyclo-2′-deoxyguanosine (ScdG) or (5′R) 5′,8-cyclo-2′-deoxyguanosine (RcdG) in one strand and an AP site in the other strand at different interlesion distances). Here, for the first time, the impact of ScdG and RcdG was experimentally tested in the context of nuclear BER. This study shows that the presence of RcdA inhibits BER more than ScdA; however, ScdG decreases repair level more than RcdG. Moreover, AP sites located ≤10 base pairs to the cdPu on its 5′-end side were repaired less efficiently than AP sites located ≤10 base pairs on the 3′-end side of cdPu. The strand with an AP site placed opposite cdPu or one base in the 5′-end direction was not reconstituted for cdA nor cdG. CdPus affect the repair of the other lesion within the CDL. It may translate to a prolonged lifetime of unrepaired lesions leading to mutations and impaired cellular processes. Therefore, future research should focus on exploring this subject in more detail.

(5′S) 5′,8-cyclo-2′-deoxyadenosine Cannot Stop BER. Clustered DNA Lesion Studies

“…Moreover, in the recent article by Boguszewska et al it was shown that, for bi-stranded CDL, when the distance between (5′ S )cdA and AP-site is bigger than seven nucleotides, the activity of AP-site repair via the BER system was unchanged [ 45 ]. Additionally, this was also noted for (5′ R )cdA and both diastereomeric forms of 5′,8-cyclo-2′-deoxyguanosine (5′ S and 5′ R ).…”

The Influence of 5′R and 5′S cdA and cdG on the Activity of BsmAI and SspI Restriction Enzymes

“…This study showed the potential of cdPus to diminish RE activity. Since it is known that cdPus may affect eukaryotic DNA repair [ 11 , 13 , 14 ], it is advisable to investigate the impact of cdPus on the maintenance of the bacterial genome in more detail. Moreover, current findings on the influence of cdPus on eukaryotic DNA repair are based on research performed in vitro or using pure enzymes [ 13 , 14 ].…”

“…Since it is known that cdPus may affect eukaryotic DNA repair [ 11 , 13 , 14 ], it is advisable to investigate the impact of cdPus on the maintenance of the bacterial genome in more detail. Moreover, current findings on the influence of cdPus on eukaryotic DNA repair are based on research performed in vitro or using pure enzymes [ 13 , 14 ]. Studies on bacterial models may lead to a further in vivo approach to unveil the mechanism of cdPus action [ 34 , 35 , 36 , 37 ].…”

“…Furthermore, cdPus gained attention due to their potential medical usefulness in cancer diagnosis and evaluation of treatment effectiveness [ 11 , 12 ]. When unrepaired, they can inhibit or block gene expression, replication, and the activity of proteins involved in DNA repair and trigger subsequent mutagenesis [ 7 , 9 , 13 , 14 ].…”

“…CdPus may potentially lower the activity of REs, thus impairing the ability of prokaryotes to defend against external genetic material [ 17 , 20 ]. CdPus may also lower the ability of eukaryotic cells to manage DNA lesions by inhibition of proteins responsible for genome repair [ 13 , 14 , 21 ].…”