Translesion synthesis of 6-nitrochrysene-derived 2ʹ-deoxyadenosine adduct in human cells

Abstract

6-Nitrochrysene (6-NC) is a potent mutagen in bacteria and carcinogenic in animals. It is the most potent carcinogen ever tested in newborn mouse assay. DNA lesions resulting from 6-NC modification are likely to induce mutations if they are not removed by cellular defense pathways prior to DNA replication. Earlier studies showed that 6-NC-derived C8−2'-deoxyadenosine adduct, N-(dA-8-yl)-6-AC, is very slowly repaired in human cells. In this study, we have investigated replication of N-(dA-8-yl)-6-AC in human embryonic kidney (HEK 293T) cells and the roles of translesion synthesis (TLS) DNA polymerases in bypassing it. Replication of a plasmid containing a single site-specific N-(dA-8-yl)-6-AC adduct in HEK 293 T cells showed that human DNA polymerase (hPol) η and hPol κ played important roles in bypassing the adduct, since TLS efficiency was reduced to 26 % in the absence of these two polymerases compared to 83 % in polymerase-competent HEK 293T cells. The progeny from HEK 293T cells provided 12.7 % mutants predominantly containing A→T transversions. Mutation frequency (MF) was increased to 17.8 % in hPol η-deficient cells, whereas it was decreased to 3.3 % and 3.9 % when the adduct containing plasmid was replicated in hPol κ- and hPol ζ-deficient cells, respectively. The greatest reduction in MF by more than 90 % (to MF 1.2 %) was observed in hPol ζ-knockout cells in which hPol κ was knocked down. Taken together, these results suggest that hPol κ and hPol ζ are involved in the error-prone TLS of N-(dA-8-yl)-6-AC, while hPol η performs error-free bypass.