期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：48
页码：13774-13779
DOI：10.1073/pnas.1609024113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceHuman dietary exposures to foods contaminated with fungi that synthesize aflatoxins present major health concerns and are associated with increased risk of hepatocellular carcinomas. Previous biochemical analyses revealed a prominent role for DNA polymerase {zeta} in replication bypass and mutagenesis of the long-lived aflatoxin DNA adduct. This investigation reveals an essential role for polymerase {zeta} in cell survival after aflatoxin exposure and that polymerase {zeta} limits aflatoxin-induced genomic instability and associated nuclear defects. Routine dietary consumption of foods that contain aflatoxins is the second leading cause of environmental carcinogenesis worldwide. Aflatoxin-driven mutagenesis is initiated through metabolic activation of aflatoxin B1 (AFB1) to its epoxide form that reacts with N7 guanine in DNA. The resulting AFB1-N7-dG adduct undergoes either spontaneous depurination or imidazole-ring opening yielding formamidopyrimidine AFB1 (AFB1-Fapy-dG). Because this latter adduct is known to persist in human tissues and contributes to the high frequency G-to-T mutation signature associated with many hepatocellular carcinomas, we sought to establish the identity of the polymerase(s) involved in processing this lesion. Although our previous biochemical analyses demonstrated the ability of polymerase {zeta} (pol {zeta}) to incorporate an A opposite AFB1-Fapy-dG and extend from this mismatch, biological evidence supporting a unique role for this polymerase in cellular tolerance following aflatoxin exposure has not been established. Following challenge with AFB1, survival of mouse cells deficient in pol {zeta} (Rev3L-/-) was significantly reduced relative to Rev3L+/- cells or Rev3L-/- cells complemented through expression of the wild-type human REV3L. Furthermore, cell-cycle progression of Rev3L-/- mouse embryo fibroblasts was arrested in late S/G2 following AFB1 exposure. These Rev3L-/- cells showed an increase in replication-dependent formation of {gamma}-H2AX foci, micronuclei, and chromosomal aberrations (chromatid breaks and radials) relative to Rev3L+/- cells. These data suggest that pol {zeta} is essential for processing AFB1-induced DNA adducts and that, in its absence, cells do not have an efficient backup polymerase or a repair/tolerance mechanism facilitating survival.
