Translesion DNA Synthesis across the heptanone--etheno-2'-deoxycytidine adduct in cells

4-Oxo-2(E)-nonenal, a lipid peroxidation-derived product, reacts with dG, dA, and dC in DNA to form heptanone (H)-etheno (epsilon) adducts. Among the three adducts, H-epsilondC is formed in the greatest abundance in in vitro reactions, and it has been detected in the C57BL/6JAPC(min) mouse model of colorectal cancer. To establish the genotoxic properties of this adduct, a site-specifically modified oligonucleotide was synthesized and incorporated into a shuttle vector. The modified vector was replicated in Escherichia coli and human cells. Analysis of the progeny plasmid has revealed that H-epsilondC strongly blocks DNA synthesis and markedly miscodes in both hosts. The miscoding frequency was 40-50% in bacteria and more than 90% in three human cell lines (xeroderma pigmentosum A and variant cells, and DNA repair wild-type cells). There was a drastic difference in coding events in these two hosts: dG and dC were almost exclusively inserted opposite the lesion in E. coli, while dA and dT were the preferential choices in human cells. These results indicate that this endogenous DNA adduct is very genotoxic to both organisms.