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Localization of aflatoxin B1--nucleic acid adducts in mitochondria and nuclei
Abstract:
The reaction of chemical carcinogens with cellular macromolecules, particularly DNA, is considered to be an important event during chemical carcinogenesis. Until recently, most studies have dealt primarily with nuclear DNA (nDNA). Mitochondrial DNA (mtDNA) is increasingly being investigated for its possible role during chemical carcinogenesis. Using monoclonal antibodies against aflatoxin B1 (AFB1)-modified guanosine and ultrastructural immunocytochemistry, we have localized the AFB1-guanosine adducts predominantly in mitochondria and nuclei. Morphometric analysis of the electron micrographs demonstrates that localization of the AFB1-guanosine adducts is several-fold greater in mitochondria than in the nuclei. However, biochemical analysis demonstrates that 77% of the covalent binding was detected in nucleic acids of the mitochondria relative to the nuclear fractions. In RNA-free preparations, the extent of covalent modification of mt circular DNA was less than 50% of that of nuclear DNA. Our results indicate that 67% of AFB1 binding to mitochondrial nucleic acids is associated primarily with mtRNA.
Insights
Aflatoxin B1 (AFB1) primarily binds to mitochondrial RNA (mtRNA), not DNA, within cells. This finding highlights the importance of studying mitochondrial nucleic acids in chemical carcinogenesis research.
Area of Science:
- Biochemistry
- Molecular Biology
- Toxicology
Background:
- Chemical carcinogens react with cellular macromolecules like DNA, a key event in carcinogenesis.
- Research has historically focused on nuclear DNA (nDNA), but mitochondrial DNA (mtDNA) is gaining attention for its role.
Purpose of the Study:
- To investigate the localization and binding of aflatoxin B1 (AFB1)-modified guanosine adducts in cellular macromolecules.
- To compare the binding of AFB1 adducts in mitochondria versus nuclei.
Main Methods:
- Utilized monoclonal antibodies against AFB1-modified guanosine.
- Employed ultrastructural immunocytochemistry and morphometric analysis.
- Conducted biochemical analysis of nucleic acid binding, including RNA-free preparations.
Main Results:
- AFB1-guanosine adducts were predominantly found in mitochondria and nuclei.
- Mitochondria showed several-fold greater localization of AFB1-guanosine adducts than nuclei.
- Biochemical analysis revealed 77% of covalent binding in mitochondrial nucleic acids, with 67% of this binding associated with mtRNA.
- Covalent modification of mitochondrial DNA was less than 50% of nuclear DNA in RNA-free preparations.
Conclusions:
- Mitochondrial RNA (mtRNA) is the primary target for AFB1 binding within mitochondria.
- These findings emphasize the significance of mtRNA in the context of AFB1-induced cellular damage and chemical carcinogenesis.