Chromium (VI) induces both bulky DNA adducts and oxidative DNA damage at adenines and guanines in the p53 gene of human lung cells

摘要

Chromium (VI) [Cr(VI)], a ubiquitous environmental carcinogen, is generally believed to induce mainly mutagenic binary and ternary Cr(III)–deoxyguanosine (dG)-DNA adducts in human cells. However, both adenine (A) and guanine (G) mutations are found in the p53 gene in Cr exposure-related lung cancer. Using UvrABC nuclease and formamidopyrimidine glycosylase (Fpg), and ligation-mediated PCR methods, we mapped the distribution of bulky DNA adducts (BDA) and oxidative DNA damage (ODD) in the p53 gene in Cr(VI)-treated human lung cells. We found that both BDA and ODD formed at 2ʹ-deoxyadenosine (dA) and dG bases. To understand the causes for these Cr-induced DNA damages, we mapped the distribution of BDA adducts and ODD in the p53 gene DNA fragments induced by Cr(III), Cr(VI) and Cr(V), the three major cellular Cr forms. We found that (i) dA at –CA- is a major Cr(VI) binding site followed by -GG- and –G-. Cr(VI) does not bind to –GGG-, (ii) Cr(VI)–DNA binding specificity is distinctly different from the Cr(III)–DNA binding in which –GGG- and –GG- are preferential sites, (iii) Cr(V) binding sites include all of Cr(VI) and Cr(III)–DNA binding sites and (iv) Cr(VI) and Cr(V) induce Fpg-sensitive sites at –G-. Together, these results suggest that Cr(VI) induction of BDA and ODD at dA and dG residues is through Cr(V) intermediate. We propose that these Cr(VI)-induced BDA and ODD contribute to mutagenesis of the p53 gene that leads to lung carcinogenesis.