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Benzo[alpha]pyrene diol epoxide I binds to DNA at replication forks
R S Paules1, M Cordeiro-Stone, M J Mass
1Department of Pathology, University of North Carolina, Chapel Hill 27599.
Summary
Benzo[a]pyrene diol epoxide-I carcinogen adducts preferentially bind to DNA replication fork junctions. These DNA adducts block DNA synthesis, impacting cell replication and potentially leading to mutations.
Area of Science:
- Biochemistry
- Molecular Biology
- Carcinogenesis
Background:
- Polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, are environmental carcinogens.
- DNA adducts formed by carcinogens can lead to mutations and cancer.
- Understanding the distribution of DNA adducts during replication is crucial for carcinogenicity studies.
Purpose of the Study:
- To investigate the distribution of benzo[a]pyrene diol epoxide-I (B[alpha]P diol epoxide-I) adducts in DNA during replication.
- To determine if DNA adducts affect DNA replication fork progression.
Main Methods:
- Synchronized C3H/10T1/2 cells were treated with B[alpha]P diol epoxide-I during the S phase.
- Polyclonal antibodies against B[alpha]P diol epoxide-I modified DNA were used to identify adducts.
- Electron microscopy was employed to visualize DNA replication forks and bound antibodies.
Main Results:
- DNA adducts were found to be 8-fold more frequent at replication fork junctions than expected.
- The proportion of replication forks blocked by B[alpha]P diol epoxide-I adducts increased after allowing replication post-exposure.
- The study identified trans-(7R)-N2-[10-(7 beta,8 alpha,9 alpha-trihydroxy-7,8,9,10-tetrahydrobenzo[alpha]pyrene)-yl]-deoxyguanosine as the primary adduct.
Conclusions:
- The DNA replication fork junction is a preferred site for B[alpha]P diol epoxide-I adduction.
- B[alpha]P diol epoxide-I adducts impede DNA replication fork progression in intact cells.
- This suggests a mechanism by which B[alpha]P diol epoxide-I contributes to mutagenesis and carcinogenesis.