Novel DNA Polymerases and Novel Genotoxicity Assays

Abstract

Human genome is continuously exposed to exogenous and endogenous genotoxic agents. The most hazardous and ubiquitous exogenous mutagen may be cigarette smoke, which contains more than 4,000 chemicals including about 60 known carcinogens. About 1% of oxygen metabolism leads to production of reactive oxygen species, a major source of endogenous mutagens. These genotoxic agents induce a variety of lesions in DNA, which results in mutations and chromosome aberrations upon replication. If such genetic alterations occurred in the genes involved in cell proliferations and/or maintenance of genome stability, the cells would proceed in multi-steps of carcinogenesis. The goal of environmental mutagenesis and genetic toxicology is to elucidate the mechanistic links between exposure to genotoxic agents and the health consequences, and to prevent the health hazard associated with DNA damage. To this end, we have investigated the mechanisms of mutagenesis induced by environmental chemicals and contributed to establish the paradigm that Y-family DNA polymerases play central roles in mutagenesis via translesion DNA synthesis across damaged bases in DNA. We also developed genotoxicity assays with bacteria and mice to evaluate the potential risk of environmental chemicals. Here, I review the roles of Y-family DNA polymerases in mutagenesis and introduce features of the novel bacterial and rodent genotoxicity assays. Future directions of environmental mutagenesis and carcinogenesis are also discussed.

Comparative mutagenic activity of atmospheric particulate matter from limeira, stockholm, and kyoto

“…The relatively higher sensitivity of the strains that overproduce NR and/or OAT enzymes, YG1041, YG1024, and YG1021, in relation to the parental strain TA98 (with background levels of both enzymes), indicates a major contribution of nitroarenes and aromatic amines (Watanabe et al, ; Watanabe et al, ; Hagiwara et al, ) to the mutagenicity observed in all sample extracts. Nitroarenes and aromatic amines are recognized as two important classes of environmental mutagens ubiquitously present in atmospheric PM samples (Claxton et al, ; Nohmi, ; Umbuzeiro et al, ; IARC, ). The NR enzyme has been shown to be a limiting factor for the metabolic activation of nitroarenes in the Salmonella strains (Watanabe et al, ), while OAT is a key enzyme for the activation of both nitroarenes and aromatic amines (Watanabe et al, ).…”

“…Aromatic amines usually require exogenous metabolic activation (+S9) to be mutagenic in the Salmonella /microsome assay (Nohmi, ; Umbuzeiro et al, ). The International Agency for Research on Cancer (IARC, ) observed the same behavior of our samples in relation to the YG1021 and YG1024, where in the absence of S9, the mutagenicity usually was higher for YG1024, highlighting the important contribution of mutagens that depend on OAT activation.…”

In vivo evidence that DNA polymerase kappa is responsible for error-free bypass across DNA cross-links induced by mitomycin C

“…We crossed the Polk D197A-E198A mice with gpt delta mice [41], which possess reporter genes for mutations in vivo. The gpt delta mice have been extensively employed in chemical mutagenesis, carcinogenesis, and radiation biology [42][43][44]. We exposed the resulting mice, namely, inactivated Polk mutant and gpt delta double transgenic mice (hereafter, referred to as inactivated Polk KI mice, and their counterparts, the Polk wild-type gpt delta mice, as Polk + mice) to mitomycin C (MMC).…”

Possible Mechanisms of Practical Thresholds for Genotoxicity

“…TLS is a process where DNA Pols continues DNA synthesis across lesions (11). If correct bases are inserted opposite the lesions, TLS will reduce the chance of induction of mutations and contribute to DNA damage tolerance.…”

“…In addition to endogenous genotoxic agents, human DNA is damaged by exogenous chemical and physical genotoxic insults (11). These include ultraviolet light (UV), radiation, cigarette smoke, polluted air, mutagenic heterocyclic amines, asbestos and so on.…”