Error-prone Replication Bypass of the Primary Aflatoxin B1 DNA Adduct, AFB1-N7-Gua

Hepatocellular carcinomas (HCCs) are the third leading cause of cancer deaths worldwide. The highest rates of early onset HCCs occur in geographical regions with high aflatoxin B-1 (AFB(1)) exposure, concomitant with hepatitis B infection. Although the carcinogenic basis of AFB1 has been ascribed to its mutagenic effects, the mutagenic property of the primary AFB(1)-DNA adduct, AFB(1)-N7-Gua, in mammalian cells has not been studied extensively. Taking advantage of the ability to create vectors containing a site-specific DNA adduct, the mutagenic potential was determined in primate cells. This adduct was highly mutagenic following replication in COS-7 cells, with a mutation frequency of 45%. The spectrum of mutations was predominantly G to T base substitutions, a result that is consistent with previous mutation data derived from aflatoxin-associated HCCs. To assess which DNA polymerases (pol) might contribute to the mutational outcome, in vitro replication studies were performed. Unexpectedly, replicative pol delta and the error-prone translesion synthesis pol sigma were able to accurately bypass AFB(1)-N7-Gua. In contrast, replication bypass using pol kappa was shown to occur with low fidelity and could account for the commonly detected G to T transversions.