Differential repair of polycyclic aromatic hydrocarbon DNA adducts from an actively transcribed gene

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are carcinogens with varying potencies. These compounds are metabolized to diol epoxides that react to form DNA adducts. Nucleotide excision repair is a critical cellular defense against these bulky DNA adducts which, if not repaired, can lead to mutations and the initiation of cancer. The structural features of the PAH-adducts play a role in differential repair of these adducts by the global genomic repair subpathway of nucleotide excision repair. DNA adducts derived from the PAHs containing bay-regions are repaired more rapidly than adducts derived from PAHs containing fjord-regions. We have employed the host cell reactivation assay to examine the rate of repair of these adducts in an actively transcribing gene. The pGL3 plasmid containing a luciferase gene was damaged with diol epoxides of benzo[ a]pyrene (B[ a]P-DE), dibenzo[ a,l]pyrene (DB[ a,l]P-DE), benzo[g]chrysene (B[g]Ch-DE), and benzo[ c]phenanthrene (B[ c]Ph-DE). The plasmids were transfected into B-lymphocytes with normal repair capacity as well as lymphocytes derived from patients with the XP-A, XP-C and CS-B syndromes. We found that XPA cells were able to transcribe slowly past B[g]Ch-adducts but not the other PAHs. Using the amount of luciferase produced as a measure of DNA repair, we found that the relative rates of repair in the actively transcribing luciferase gene was B[ a]P-DE > DB[ a,l]P-DE, B[ g]Ch-DE, >B[ c]Ph-DE in repair proficient and XP-C cells. These results indicate that the abilities to transcribe past and to repair the PAH adducts are dependent on different structural features of the DNA adducts.