Mutagenic Potentials of DNA Interstrand Cross-Links Induced by 7,8-Dihydro-8-Oxoadenine

DNA interstrand cross-links (ICLs) are among the most cytotoxic forms of DNA damage, arising when the two strands of the DNA helix are covalently linked by crosslink-inducing agents such as bifunctional alkylating agents and reactive aldehydes. Several studies have demonstrated that ICLs can also be induced by reactive oxygen and nitrogen species. We previously reported that under oxidative conditions, the major oxidative adenine lesion 7,8-dihydro-8-oxoadenine (oxoA) can efficiently generate a novel class of oxoA-G ICLs, structurally resembling guanine-guanine (G-G) cross-links that can be induced by reactive nitrogen species. To investigate the mutagenic potential of these oxidation-induced ICLs in cells, we employed a SupF-based mutagenesis assay using bacterial cells. A single site-specific oxoA-G ICL was synthesized and incorporated into a plasmid, which was then introduced into an E. coli reporter strain to assess mutation profiles induced by both oxoA and oxoA-G ICLs. Our results show that oxoA-G ICLs cause A-to-C/T and G-to-C transversion mutations at the oxoA-G cross-link site, demonstrating highly promutagenic nature of the lesion in bacterial cells. We propose that the oxoA-G ICL may promote transversion mutations, likely driven by a syn conformer of unhooked oxoA-G ICL repair intermediates during translesion synthesis.