Mutagenicity of Ochratoxin A: Role for a Carbon-Linked C8-Deoxyguanosine Adduct?
Richard A Manderville1, Stacey D Wetmore2
1Departments of Chemistry and Toxicology, University of Guelph , Guelph, Ontario, Canada N1G 2W1.
Abstract:
Ochratoxin A (OTA) is a fungal toxin that is considered to be a potent kidney carcinogen in rodent models. The toxin produces double strand breaks and has a propensity for deletions, single-base substitutions, and insertions. The toxin reacts covalently with DNA to afford a C8-2'-deoxyguanosine carbon-linked adduct (OT-dG) as the major lesion in animal tissues. Incorporation of model C-linked C8-aryl-dG adducts into the G3 site of the NarI sequence demonstrates a tendency to induce base substitutions and deletion mutations in primer extension assays using model polymerases. The degree of misincorporation induced by the C-linked C8-dG adducts correlates with an ability to adopt the promutagenic syn conformation within the NarI duplex as predicted by molecular dynamics (MD) simulations. MD simulations of the OT-dG adduct within the NarI duplex predict an even greater degree of conformational flexibility, suggesting enhanced in vitro mutagenicity compared to the simpler model C-linked C8-dG adducts. Together these findings support the role of OT-dG in promoting OTA-mediated mutagenicity and carcinogenicity in animal studies.
Insights
Ochratoxin A (OTA), a fungal toxin, causes kidney cancer in rodents by damaging DNA. The major DNA lesion, OT-dG, promotes mutations and carcinogenicity, as supported by molecular dynamics simulations.
Area of Science:
- Toxicology
- Molecular Biology
- Genetics
Background:
- Ochratoxin A (OTA) is a mycotoxin recognized as a potent kidney carcinogen in rodent models.
- OTA induces DNA damage, including double-strand breaks and various mutations like deletions, substitutions, and insertions.
Purpose of the Study:
- To investigate the mutagenic mechanisms of OTA, focusing on the role of the major DNA adduct, C8-2'-deoxyguanosine (OT-dG).
- To assess the mutagenic potential of OT-dG and related adducts using in vitro assays and molecular dynamics simulations.
Main Methods:
- Primer extension assays with model polymerases using DNA sequences containing C-linked C8-aryl-dG adducts.
- Molecular dynamics (MD) simulations to predict the conformational flexibility of adducts within DNA duplexes.
Main Results:
- Model C-linked C8-aryl-dG adducts induced base substitutions and deletions in primer extension assays.
- Adduct-induced misincorporation correlated with the adoption of a promutagenic syn conformation.
- MD simulations predicted greater conformational flexibility for the OT-dG adduct, suggesting enhanced in vitro mutagenicity.
Conclusions:
- The OT-dG adduct plays a significant role in promoting OTA-mediated mutagenicity.
- Findings support the contribution of OT-dG to OTA's carcinogenicity observed in animal studies.
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