title: Carcinogenic lead chromate induces DNA double-strand breaks in human lung cells.
abstract: Hexavalent chromium (Cr(VI)) is a widespread environmental contaminant and a known human carcinogen, generally causing bronchial cancer. Recent studies have shown that the particulate forms of Cr(VI) are the potent carcinogens. Particulate Cr(VI) is known to induce a spectrum of DNA damage such as DNA single strand breaks, Cr-DNA adducts, DNA-protein crosslinks and chromosomal aberrations. However, particulate Cr(VI)-induced DNA double strand breaks (DSBs) have not been reported. Thus, the aim of this study was to determine if particulate Cr(VI)-induces DSBs in human bronchial cells. Using the single cell gel electrophoresis assay (comet assay), showed that lead chromate-induced concentration dependent increases in DSBs with 0.1, 0.5, 1 and 5 microg/cm2 lead chromate inducing a 20, 50, 67 and 109% relative increase in the tail integrated intensity ratio, respectively. Sodium chromate at concentrations of 1, 2.5 and 5 microM induced 38, 78 and 107% relative increase in the tail integrated intensity ratio, respectively. We also show that genotoxic concentrations of lead chromate activate the ataxia telangiectasia mutated (ATM) protein, which is thought to play a central role in the early stages of DSB detection and controls cellular responses to this damage. The H2A.X protein becomes rapidly phosphorylated on residue serine 139 in cells when DSBs are introduced into the DNA by ionizing radiation. By using immunofluorescence, we found that lead chromate-induced concentration-dependent increases in phosphorylated H2A.X (r-H2A.X) foci formation with 0.1, 0.5, 1, 5 and 10 microg/cm2 lead chromate inducing a relative increase in the number of cells with r-H2A.X foci formation of 43, 51, 115 and 129%, respectively.
authors.affiliation: Wise Laboratory of Environmental and Genetic Toxicology, University of Southern Maine, 96 Falmouth St., P.O. Box 9300, Portland, ME 04104-9300, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Xie
authors.forename: Sandra S
authors.initials: SS
authors.lastname: Wise
authors.forename: Amie L
authors.initials: AL
authors.lastname: Holmes
authors.forename: Bo
authors.initials: B
authors.lastname: Xu
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Wakeman
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Pelsue
authors.forename: Narendra P
authors.initials: NP
authors.lastname: Singh
authors.forename: John Pierce
authors.initials: JP
authors.lastname: Wise
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D002840:Chromates / Q000633:toxicity*; D020552:Comet Assay; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000378:metabolism; D006801:Humans; D007854:Lead / Q000633:toxicity*; D008168:Lung / Q000166:cytology* / Q000187:drug effects*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017670:Sodium Compounds / Q000633:toxicity; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D018797:Cell Cycle Proteins; D002840:Chromates; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D017670:Sodium Compounds; D025521:Tumor Suppressor Proteins; D007854:Lead; C028982:sodium chromate(VI); C031895:lead chromate; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases