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Evidence for the DNA binding and adduct formation of estrone and 17beta-estradiol after dimethyldioxirane activation
1Department of Biomedical Sciences, University of Illinois, College of Medicine at Rockford, 61107, USA. Fuliyu@uic.edu
Abstract:
Estrogens, used widely from hormone replacement therapy to cancer treatment, are themselves carcinogenic, causing uterine and breast cancers. However, the mechanism of their carcinogenic action is still not known. Recently, we found that estrone (E1) and 17beta-estradiol (E2) could be activated by the versatile epoxide-forming oxidant dimethyldioxirane (DMDO), resulting in the inhibition of rat liver nuclear and nucleolar RNA synthesis in a dose-dependent manner in vitro. Since epoxidation is often required for the activation of chemical carcinogens, we proposed that estrogen epoxidation is the underlying mechanism for the initiation of estrogen carcinogenesis (Carcinogenesis 17 (1996) 1957-1961). It is known that initiation requires the binding of a carcinogen to DNA with the formation of DNA adducts. One of the critical tests of our hypothesis is therefore to determine whether E1 and E2 after activation are able to bind DNA. This paper reports that after DMDO activation, [3H]E1 and [3H]E2 were able to bind to both A-T and G-C containing DNAs. Furthermore. the formation of E1-DNA and E2-DNA adducts was detected by 32P-postlabeling analysis.
Insights
Estrogen epoxidation by dimethyldioxirane (DMDO) activates estrone (E1) and 17beta-estradiol (E2). Activated estrogens bind to DNA, forming adducts, supporting their role in initiating estrogen carcinogenesis.
Area of Science:
- Endocrinology
- Molecular Biology
- Carcinogenesis
Background:
- Estrogens are widely used but are known carcinogens, particularly for uterine and breast cancers.
- The precise mechanism behind estrogen-induced carcinogenesis remains largely unknown.
- Epoxidation is a known activation pathway for chemical carcinogens.
Purpose of the Study:
- To investigate the hypothesis that estrogen epoxidation is the initiating mechanism for estrogen carcinogenesis.
- To determine if activated estrogens (E1 and E2) can bind to DNA.
- To detect the formation of estrogen-DNA adducts.
Main Methods:
- Activation of [3H]estrone (E1) and [3H]17beta-estradiol (E2) using dimethyldioxirane (DMDO).
- In vitro incubation of activated estrogens with DNA (both A-T and G-C rich).
- Detection of DNA adducts using 32P-postlabeling analysis.
Main Results:
- DMDO-activated [3H]E1 and [3H]E2 demonstrated binding to DNA.
- Binding occurred with both A-T and G-C containing DNA sequences.
- Formation of E1-DNA and E2-DNA adducts was confirmed via 32P-postlabeling.
Conclusions:
- Estrogen epoxidation by DMDO leads to the formation of DNA adducts.
- This DNA binding supports the hypothesis that estrogen epoxidation is a key step in initiating estrogen carcinogenesis.
- Further research into estrogen-DNA adducts is warranted to understand their role in cancer development.