Abstract
BACKGROUND: 8-Oxo-7,8-dihydroguanine (8-hydroxyguanine, G(O)) is a major damaged base caused by oxidation. Misincorporation of dATP opposite G(O) by DNA polymerases leads to a G:C→T:A transversion at the damaged site via G(O):A intermediate formation. The G(O):A pair is also formed by 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate incorporation opposite A. The G(O):C and G(O):A pairs are both repaired through the base excision repair (BER) pathway to suppress the G:C→T:A mutations. G(O):C also induces action-at-a-distance mutations around the damaged base. These untargeted mutations seem to be induced through the excision of G(O) from G(O):C by DNA glycosylases, such as OGG1 and NEIL1, in the BER pathway. The adenine base of G(O):A is excised by a specific adenine DNA glycosylase, MUTYH, and this excision potentially induces action-at-a-distance mutations. RESULTS: In this study, plasmid DNA bearing a G(O):A pair was introduced into human U2OS cells to investigate the untargeted mutations by the G(O):A pair. The G(O):A pair induced action-at-a-distance mutations at C bases in 5'-TpC-3' of the G(O)-strand, in contrast to those by G(O):C, which elicit mutations at G bases of 5'-GpA-3'. Furthermore, the untargeted mutations were suppressed by the MUTYH knockdown. CONCLUSION: The G(O):A pair induced the action-at-a-distance mutations through base excision by the MUTYH glycosylase.