Repair of Oxidative DNA Damage: Mechanisms and Functions

Abstract

Cellular genomes suffer extensive damage from exogenous agents and reactive oxygen species formed during normal metabolism. The MutT homologs (MutT/MTH) remove oxidized nucleotide precursors so that they cannot be incorporated into DNA during replication. Among many repair pathways, the base excision repair (BER) pathway is the most important cellular protection mechanism responding to oxidative DNA damage. The 8-oxoG glycosylases (Fpg or MutM/OGG) and the MutY homologs (MutY/MYH) glycosylases along with MutT/MTH protect cells from the mutagenic effects of 8-oxoG, the most stable and deleterious product known caused by oxidative damage to DNA. The key enzymes in the BER process are DNA glycosylases, which remove different damaged bases by cleavage of the N-glycosylic bonds between the bases and the deoxyribose moieties of the nucleotide residues. Biochemical and structural studies have demonstrated the substrate recognition and reaction mechanism of BER enzymes. Cocrystal structures of several glycosylases show that the substrate base flips out of the sharply bent DNA helix and the minor groove is widened to be accessed by the glycosylases. To complete the repair after glycosylase action, the apurinic/apyrimidinic (AP) site is further processed by an incision step, DNA synthesis, an excision step, and DNA ligation through two alternative pathways. The short-patch BER (1-nucleotide patch size) and long-patch BER (2-6-nucleotide patch size) pathways need AP endonuclease to generate a 3' hydroxyl group but require different sets of enzymes for DNA synthesis and ligation. Protein-protein interactions have been reported among the enzymes involved in BER. It is possible that the successive players in the repair pathway are assembled in a complex to perform concerted actions. The BER pathways are proposed to protect cells and organisms from mutagenesis and carcinogenesis.

NADPH Oxidase-generated Hydrogen Peroxide Induces DNA Damage in Mutant FLT3-expressing Leukemia Cells

“…Repair of 8-OHdG results in a removal of the oxidized base that produces a single strand break (55). When the latter one is encountered by the replication fork, it can result in a DSB (37). We suggest that a similar phenomenon may be occurring in the FLT3-ITD AML.…”

BCR/ABL oncogenic kinase promotes unfaithful repair of the reactive oxygen species–dependent DNA double-strand breaks

“…15,16,62,63 Usually, oxidized bases are repaired by base excision repair, which requires the activity of a DNA glycosylase and an AP endonuclease to generate gaps in singlestranded DNA. 64 Such interruptions, if encountered by a replication fork, can cause DSBs, 62 which can be detected experimentally as ␥-H2AX foci. 65 We hypothesize that ROS-mediated oxidative DNA lesions in BCR/ABL cells produce numerous DNA repair intermediates, which do not induce the G 1 /S checkpoint in BCR/ ABL cells, 5,66 resulting in DSBs at the replication forks.…”

Mitochondrial 8-oxoguanine glycosylase decreases mitochondrial fragmentation and improves mitochondrial function in H9C2 cells under oxidative stress conditions

“…8-Hydroxy 2=-deoxyguanine (8-OHdG) is one of the most common ROS-induced DNA lesions and is considered an index of DNA damage (19,27). High levels of mitochondrial 8-OHdG have been correlated with increased mutation, deletion, fragmentation, and loss of mtDNA (28,31,42). 8-Oxoguanine DNA glycosylase 1 (OGG1), an enzyme in the initial steps of the base excision repair (BER) pathway, is present in the nucleus as well as in the mitochondria.…”