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

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Polycyclic aromatic hydrocarbons (PAHs) are environmental carcinogens metabolized into reactive diol epoxides.
• These metabolites form DNA adducts, which can lead to mutations and cancer if not repaired by cellular mechanisms.
• Nucleotide excision repair (NER) is crucial for removing bulky DNA adducts, with structural features influencing repair efficiency.

Purpose of the Study:

• To investigate the differential repair rates of various polycyclic aromatic hydrocarbon (PAH) DNA adducts within an actively transcribing gene.
• To assess the impact of adduct structure on repair by the global genomic repair (GGR) subpathway of nucleotide excision repair (NER).
• To compare repair capacities in normal B-lymphocytes and those from patients with distinct DNA repair deficiencies (XP-A, XP-C, CS-B).

Main Methods:

• Host cell reactivation assay using a luciferase reporter plasmid damaged with specific PAH diol epoxides (B[a]P-DE, DB[a,l]P-DE, B[g]Ch-DE, B[c]Ph-DE).
• Transfection of damaged plasmids into B-lymphocytes with normal repair function and those from XP-A, XP-C, and CS-B patients.
• Quantification of luciferase gene expression to measure DNA adduct repair rates and transcriptional bypass.

Main Results:

• XPA cells exhibited slow transcriptional bypass of benzo[g]chrysene diol epoxide (B[g]Ch-DE) adducts, but not other PAH adducts.
• In repair-proficient and XP-C cells, relative repair rates of PAH adducts in the transcribing gene were: B[a]P-DE > DB[a,l]P-DE, B[g]Ch-DE > B[c]Ph-DE.
• Transcriptional bypass and DNA repair of PAH adducts depend on distinct structural characteristics of the adducts.

Conclusions:

• Structural features of polycyclic aromatic hydrocarbon (PAH) DNA adducts significantly influence their repair rates via nucleotide excision repair (NER).
• The ability of cells to transcribe past PAH adducts is distinct from the efficiency of their repair, highlighting complex cellular responses.
• Differential repair kinetics of PAH adducts, particularly in actively transcribing genes, have implications for understanding mutation induction and cancer initiation by these carcinogens.