Abstract
Benzene is a ubiquitous environmental pollutant. Recent studies have shown a link between the development of childhood leukemias and maternal benzene exposure, suggesting that these leukemias may be initiated in utero. Benzene crosses the placental barrier however the mechanisms behind in utero benzene toxicity have not been well elucidated. This study is the first to show that the benzene metabolite, benzoquinone (BQ), perturbs fetal topoisomerase IIα (Topo IIα), an enzyme essential for DNA repair. Using cultured murine CD-1 fetal liver cells, this study shows that Topo IIα activity decreases following 24 h of exposure to BQ (12.5 and 15.625 µM), with 12.5 µM confirmed to disrupt the c-kit+ Lin− Sca-1− Il7rα− population of cells in culture. Pretreatment with the antioxidant N-acetylcysteine did not prevent the inhibition of Topo IIα by BQ. An increase in Topo IIα-DNA covalent adducts was detected following 24-h exposure to BQ (12.5 and 50 µM). Interestingly, BQ (12.5 µM) exposure did not significantly increase levels of 4-hydroxynonenal (4-HNE), a marker of oxidative stress after 24 h. However, increased levels of the double-stranded DNA break marker γH2AX were detected following 24 h of BQ exposure, confirming that Topo IIα-induced breaks are increased in BQ-treated cells. This study shows that fetal Topo IIα is perturbed by BQ and suggests that this protein is a target of benzene and may be implicated with in utero benzene toxicity.
DNA Synthesis on a Double-stranded DNA Template by the T4 Bacteriophage DNA Polymerase and the T4 Gene 32 DNA Unwinding Protein