Vicinal abasic site impaired processing of a Tg:G mismatch and 8-oxoguanine lesions in three-component bistranded clustered DNA damage

Abstract

The occurrence of 7,8-dihydro-8-oxo-2 0 deoxyguanosine (8-oxodG), thymine glycol:guanine (Tg:G) mismatch and abasic site DNA damage lesions in close proximity induce repair refractive multicomponent clustered DNA damage. Herein, the influence of abasic sites in the processing of 8-oxodG lesion and Tg:G mismatch bistranded cluster is evaluated. Abasic sites are found to impart conformational destabilization that appreciably hinders the repair activity of the other lesions whenever present in a cluster combination. The repair process reduces the formation of double strand breaks (DSBs) and renders this three-lesion combination a non-DSB forming cluster. The stability of the DNA duplex harbouring these three lesions is highly compromised due to altered base helicity and base stacking phenomena leading to impaired repair.Damaged lesions in deoxyribonucleic acid (DNA) are ubiquitous due to the exposure of cells to various exogenous sources, including ionizing radiation and toxins, as well as endogenous metabolism. 1,2 5-Methyl cytosine (5-mC) residues in DNA are vulnerable to radiation-induced oxidation that could generate a Tg:G mismatch.3 In addition, stripping of purine or pyrimidine bases giving rise to potentially mutagenic abasic sites is a familiar event.4 8-oxodG is one of the most common DNA damage lesions that plays a critical role in mutagenesis and carcinogenesis.5 However, the present understanding of the repair pattern of three-component multilesion clustered DNA damage is very limited, particularly in clusters containing a Tg:G mismatch and 8-oxodG in the vicinity of abasic sites. Herein, for the rst time, we demonstrate the role of abasic sites in the repair of a Tg:G mismatch and 8-oxodG present in a three component bistranded cluster environment.The DNA repair machinery in our cells has the huge responsibility of repairing chemically unrelated lesions in order to ensure the smooth functioning of cellular processes and maintain genomic integrity.6 Evidently, the challenge for the DNA repair machinery is even greater when multiple lesions are present in close proximity to one another giving rise to multicomponent clustered DNA damage, oen reported as a major outcome of exposure to ionizing radiation.7-12 Subsequent repair takes place through the intervention of various well recruited enzymes of the base excision repair (BER) pathway. 13Specically, in human cells, the repair of abasic sites, 8-oxodG and Tg lesions involves apurinic/apyrimidic endonuclease (APE1), oxoguanine glycosylase (hOGG1) and hNTH1 enzymes, respectively, in the initial stages following the BER pathway. 14,15The attempted repair of bistranded clusters oen leads to the generation of potentially lethal double strand breaks (DSBs) that could lead to deletions, translocations, and fusions. 16Reportedly, bistranded clustered abasic sites are processed to yield DSBs in E. coli leading to cytotoxicity.17 In contrast, most clustered damage systems adopt a hierarchal repair strategy to lessen the DSB formation while attempting repair.18...

Reactive Oxygen Species and Their Consequences on the Structure and Function of Mammalian Spermatozoa

“…It has also been shown elsewhere that in a cluster containing an AP site or SSB, DNA repair activity is greatly reduced when 8-oxodG residues are in close proximity. It is hypothesized that 8-oxodG lesions in the vicinity of SSB and AP sites introduce conformational destabilization of DNA that prevents proper interaction of the repair machinery (96,97). Therefore, one consequence of the presence of clusters of 8-oxodG residues on sperm chromosomes next to AP sites and SSBs will be to delay oocyte-driven DNA repair of the paternal nucleus and potentially increase the occurrence of mutagenic DSBs that are more difficult to repair (74,163).…”