NIH Research Festival
Oxidative stress and reactive oxygen species damage DNA and bases in the nucleotide pool, and this can promote genome instability. The oxidized guanine base 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) is a well known promutagenic lesion in DNA and the nucleotide pool, and this lesion can be introduced into DNA during replication and repair from 8-oxodGTP in the pool. Base excision repair (BER), a main repair system for removing oxidative agent-induced lesions, involves a coordinated sequence of steps, including channeling of the repair intermediate from the DNA polymerase β (pol β) nucleotide insertion to the final DNA ligation step. Here we found that the ligation step is compromised after pol β inserts the oxidized nucleotide 8-oxodGMP. These results are consistent with recent pol β X-ray crystallography study that revealed inserted 8-oxodGMP in a distorted position stacked over the template base; this distortion suggested the ligation step of BER would be compromised. A deficiency in ligation of nicked DNA with a pre-formed 3'-end 8-oxoG lesion also was confirmed. We observed more oxidative agent KBrO3-induced cytotoxicity in wild-type cells than in pol β null cells, and co-treatment with an agent that increases 8-oxodGTP in the pool increased KBrO3 cytotoxicity. Finally, we observed an increase in γH2AX formation in the cells after KBrO3 treatment in wild-type cells than in null cells. We conclude that the oxidative agent-induced cytotoxicity observed was due, in part, to pol β insertion of oxidized nucleotide into BER intermediates. This could result in accumulation of strand breaks and cell death.
Scientific Focus Area: Molecular Biology and Biochemistry
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