title: Evidence that a burst of DNA depurination in SENCAR mouse skin induces error-prone repair and forms mutations in the H-ras gene.
abstract: Treatment of SENCAR mouse skin with dibenzo[a,l]pyrene results in abundant formation of abasic sites that undergo error-prone excision repair, forming oncogenic H-ras mutations in the early preneoplastic period. To examine whether the abundance of abasic sites causes repair infidelity, we treated SENCAR mouse skin with estradiol-3,4-quinone (E(2)-3,4-Q) and determined adduct levels 1 h after treatment, as well as mutation spectra in the H-ras gene between 6 h and 3 days after treatment. E(2)-3,4-Q formed predominantly (> or =99%) the rapidly-depurinating 4-hydroxy estradiol (4-OHE(2))-1-N3Ade adduct and the slower-depurinating 4-OHE(2)-1-N7Gua adduct. Between 6 h and 3 days, E(2)-3,4-Q induced abundant A to G mutations in H-ras DNA, frequently in the context of a 3'-G residue. Using a T.G-DNA glycosylase (TDG)-PCR assay, we determined that the early A to G mutations (6 and 12 h) were in the form of G.T heteroduplexes, suggesting misrepair at A-specific depurination sites. Since G-specific mutations were infrequent in the spectra, it appears that the slow rate of depurination of the N7Gua adducts during active repair may not generate a threshold level of G-specific abasic sites to affect repair fidelity. These results also suggest that E(2)-3,4-Q, a suspected endogenous carcinogen, is a genotoxic compound and could cause mutations.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 986805 Nebraska Medical Center, Omaha, Nebraska 68198-6805, USA. dchakrav@unmc.edu
authors.forename: D
authors.initials: D
authors.lastname: Chakravarti
authors.forename: P C
authors.initials: PC
authors.lastname: Mailander
authors.forename: K M
authors.initials: KM
authors.lastname: Li
authors.forename: S
authors.initials: S
authors.lastname: Higginbotham
authors.forename: H L
authors.initials: HL
authors.lastname: Zhang
authors.forename: M L
authors.initials: ML
authors.lastname: Gross
authors.forename: J L
authors.initials: JL
authors.lastname: Meza
authors.forename: E L
authors.initials: EL
authors.lastname: Cavalieri
authors.forename: E G
authors.initials: EG
authors.lastname: Rogan
mesh_terms: D000818:Animals; D016477:Artifacts; D001483:Base Sequence; D018736:DNA Adducts / Q000737:chemistry / Q000187:drug effects / Q000235:genetics*; D004249:DNA Damage / Q000187:drug effects / Q000235:genetics*; D004252:DNA Mutational Analysis; D004260:DNA Repair / Q000187:drug effects / Q000235:genetics*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D005260:Female; D011905:Genes, ras / Q000235:genetics*; D051379:Mice; D018632:Mice, Inbred SENCAR; D016296:Mutagenesis / Q000235:genetics*; D009153:Mutagens / Q000737:chemistry / Q000494:pharmacology; D009692:Nucleic Acid Heteroduplexes / Q000187:drug effects / Q000235:genetics; D017354:Point Mutation / Q000235:genetics; D016133:Polymerase Chain Reaction; D012867:Skin / Q000187:drug effects / Q000378:metabolism*
chemical_list: D018736:DNA Adducts; D009153:Mutagens; D009692:Nucleic Acid Heteroduplexes; C049872:estradiol-2,3-O-quinone; D004958:Estradiol