Carcinogenesis Advance Access originally published online on March 10, 2008
Carcinogenesis 2008 29(5):1064-1069; doi:10.1093/carcin/bgn058
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Excision repair is required for genotoxin-induced mutagenesis in mammalian cells
1 Department of Pharmacology and Physiology
2 GW Cancer Institute
3 Department of Environmental and Occupational Health, The George Washington University Medical Center, 2300 Eye Street Northwest, Washington, DC 20037, USA
4 Wise Laboratory of Environmental and Genetic Toxicology
5 Maine Center for Toxicology and Environmental Health
6 Department of Applied Medical Sciences, University of Southern Maine, Portland, ME 04104, USA
* To whom correspondence should be addressed. Tel: 202-994-3286; Fax: 202-994-2870;Email: cansrp{at}gwumc.edu
Certain hexavalent chromium [Cr(VI)] compounds are human lung carcinogens. Although much is known about Cr-induced DNA damage, very little is known about mechanisms of Cr(VI) mutagenesis and the role that DNA repair plays in this process. Our goal was to investigate the role of excision repair (ER) pathways in Cr(VI)-mediated mutagenesis in mammalian cells. Repair-proficient Chinese hamster ovary cells (AA8), nucleotide excision repair (NER)-deficient (UV-5) and base excision repair (BER)-inhibited cells were treated with Cr(VI) and monitored for forward mutation frequency at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus. BER was inhibited using methoxyamine hydrochloride (Mx), which binds to apurinic/apyrimidinic sites generated during BER. Notably, we found that both NER-deficient (UV-5 and UV-41) and BER-inhibited (AA8 + Mx) cells displayed attenuated Cr(VI) mutagenesis. To determine whether this was unique to Cr(VI), we included the alkylating agent, methylmethane sulfonate (MMS) and ultraviolet (UV) radiation (260 nm) in our studies. Similar to Cr(VI), UV-5 cells exhibited a marked attenuation of MMS mutagenesis, but were hypermutagenic following UV exposure. Moreover, UV-5 cells expressing human xeroderma pigmentosum complementation group D displayed similar sensitivity to Cr(VI) and MMS-induced mutagenesis as AA8 controls, indicating that the genetic loss of NER was responsible for attenuated mutagenesis. Interestingly, Cr(VI)-induced clastogenesis was also attenuated in NER-deficient and BER-inhibited cells. Taken together, our results suggest that NER and BER are required for Cr(VI) and MMS-induced genomic instability. We postulate that, in the absence of ER, DNA damage is channeled into an error-free system of DNA repair or damage tolerance.
Abbreviations: AP, apurinic/apyrimidinic; BER, base excision repair; CHO, Chinese hamster ovary; Cr(III), trivalent chromium; Cr(VI), hexavalent chromium; ER, excision repair; ICL, interstrand cross-link; MEM, minimal Eagle’s medium; MMS, methylmethane sulfonate; Mx, methoxyamine hydrochloride; NER, nucleotide excision repair; TLS, translesion synthesis; UV, ultraviolet; XP, xeroderma pigmentosum; XPD, xeroderma pigmentosum complementation group D; XPF, xeroderma pigmentosum complementation group F
These authors contributed equally to this work. Received November 26, 2007; revised February 6, 2008; accepted February 12, 2008.