Preferential DNA damage in the p53 gene by benzo[a]pyrene metabolites in cytochrome P4501A1-expressing xeroderma pigmentosum group A cells

Gene-specific DNA damage levels were determined by quantitative polymerase chain reaction (QPCR) after treating cytochrome P450 (CYP) 1A1-expressing xeroderma pigmentosum fibroblasts with [3H]benzo[a]pyrene-trans-7,8-dihydrodiol ([3H]BPD) or [3H]benzo[a]pyrene-trans-7,8-dihydrodiol-9, 10-epoxide([3H]BPDE). DNA damage in the p53 gene (which is transcriptionally active) and the β-globin gene (which is transcriptionally inactive) was measured in cells treated with [3H](±)-anti-BPDE, [3H](±)-BPD, and [3H](−)-BPD. DNA adduct formation in the genome overall was determined by measuring the incorporation of 3H into DNA. DNA damage in a p53 gene fragment (exons 8–9, 445 bp) was readily detected by QPCR. DNA damage was either not detected or much reduced in a similarly sized target in the β-globin gene (exons 1–2, 551 bp). At equivalent levels of genomic DNA adducts, BPD treatment induced more damage in the p53 gene than BPDE treatment did. The lesion frequencies in the p53 and β-globin genes in purified DNA treated with BPDE in vitro were the same, indicating that there was no sequence-specific basis for preferential lesion formation in the p53 gene in treated cells. DNA damage in both the p53 and β-globin genes showed a dose response to [3H](−)-BPD. The frequency of BPD-induced lesions in the p53 gene was sixfold to sevenfold greater than in the β-globin gene and 200- to 300-fold greater than in bulk DNA. The BPD-induced lesion frequency in the β-globin gene was 30- to 50-fold greater than in bulk DNA. The data indicate that the distribution of BPDE-induced DNA lesions is dramatically nonrandom and suggest that the nonrandomness is governed by DNA sequence composition, chromatin structure, and dose rate. © 1996 Wiley-Liss, Inc.