Action-at-a-distance mutations induced by 8-oxo-7,8-dihydroguanine are dependent on APOBEC3

DNA oxidation is a serious threat to genome integrity and is involved in mutations and cancer initiation. The G base is most frequently damaged, and 8-oxo-7,8-dihydroguanine (GO, 8-hydroxyguanine) is one of the predominant damaged bases. In human cells, GO causes a G:C→T:A transversion mutation at the modified site, and also induces untargeted substitution mutations at the G bases of 5'-GpA-3' dinucleotides (action-at-a-distance mutations). The 5'-GpA-3' sequences are complementary to the 5'-TpC-3' sequences, the preferred substrates for apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3 (APOBEC3) cytosine deaminases, and thus their contribution to mutagenesis has been considered. In this study, APOBEC3B, the most abundant APOBEC3 protein in human U2OS cells, was knocked down in human U2OS cells, and a GO-shuttle plasmid was then transfected into the cells. The action-at-a-distance mutations were reduced to ~25% by the knockdown, indicating that GO-induced action-at-a-distance mutations are highly dependent on APOBEC3B in this cell line.