Journal
JOURNAL OF STEROID BIOCHEMISTRY AND MOLECULAR BIOLOGY
Volume 101, Issue 4-5, Pages 204-215Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsbmb.2006.06.019
Keywords
estrogen mutagenesis; erroneous repair; ACI rat; mammary gland
Funding
- NCI NIH HHS [P01 CA49210, P30 CA36727] Funding Source: Medline
- NCRR NIH HHS [P20RR17675] Funding Source: Medline
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Evidence suggests that the genotoxic mechanism of estrogens (estrone/estradiol) in breast cancer involves their oxidation to 3,4-quinones and reaction with DNA to form depurinating N3Ade and N7Gua adducts. We examined whether estrogen genotoxicity is mutagenic in the mammary gland of the female ACI rat, a model for estrogen-dependent breast cancer. Mutagenesis was studied by PCR amplification of the H-ras1 gene (exons 1-2), cloning in pUC18, transforming Escherichia coli, and sequencing the inserts in plasmids from individual colonies. Mammary glands of both estrogen-responsive (ACI and DA) and resistant (Sprague-Dawley) rats contained pre-existing mutations at frequencies of (39.8-58.8) x 10(-5), the majority (62.5-100%) of which were A-T to G-C transitions. Estradiol-3,4-quinone (200 nmol) treatment of ACI rats caused rapid (6 h to 1 day) mutagenesis (frequency (83.3-156.1) x 10(-5); AT to G-C 70-73.3%). The estrogen-induced A center dot T to G center dot C mutations were detected as G center dot T heteroduplexes, as would be expected if N3Ade depurinations caused Gua misincorporations by erroneous repair. These heteroduplexes were identified by the T center dot G-DNA glycosylase (TDG) assay. TDG converts G center dot T heteroduplexes to G.abasic sites, rendering DNA templates refractory to PCR amplification. Consequently, A center dot T to G center dot C mutations present as G center dot T heteroduplexes in the DNA are eliminated from the spectra. TDG treatment of mammary DNA from estradiol-3,4-quinone-treated ACI rats brought A center dot T to G center dot C mutations down to pre-existing frequencies. Our results demonstrate that treatment with estradiol-3,4-quinone, an important metabolite of estrogens, produced A center dot T to G center dot C mutations in the DNA of the mammary gland of ACI rats. (c) 2006 Elsevier Ltd. All rights reserved.
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