title: Excision repair is required for genotoxin-induced mutagenesis in mammalian cells.
abstract: 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.
authors.affiliation: Department of Pharmacology and Physiology, The George Washington University Medical Center, 2300 Eye Street Northwest, Washington, DC 20037, USA.
authors.forename: Bradford
authors.initials: B
authors.lastname: Brooks
authors.forename: Travis J
authors.initials: TJ
authors.lastname: O'Brien
authors.forename: Susan
authors.initials: S
authors.lastname: Ceryak
authors.forename: John Pierce
authors.initials: JP
authors.lastname: Wise
authors.forename: Sandra S
authors.initials: SS
authors.lastname: Wise
authors.forename: John Pierce
authors.initials: JP
authors.lastname: Wise
authors.forename: Edward
authors.initials: E
authors.lastname: Defabo
authors.forename: Steven R
authors.initials: SR
authors.lastname: Patierno
mesh_terms: D000818:Animals; D016466:CHO Cells; D002470:Cell Survival / Q000187:drug effects*; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000187:drug effects / Q000235:genetics; D004260:DNA Repair / Q000187:drug effects* / Q000235:genetics; D007041:Hypoxanthine Phosphoribosyltransferase / Q000187:drug effects / Q000235:genetics; D008322:Mammals; D016296:Mutagenesis; D009153:Mutagens / Q000633:toxicity*
chemical_list: D009153:Mutagens; D004247:DNA; D007041:Hypoxanthine Phosphoribosyltransferase