title: Differential impact of ionic and coordinate covalent chromium (Cr)-DNA binding on DNA replication.
abstract: The reactive species produced by the reduction of Cr(VI), particularly Cr(III), can form both ionic and coordinate covalent complexes with DNA. These Cr(III)-DNA interactions consist of Cr-DNA monoadducts, Cr-DNA ternary adducts, and Cr-DNA interstrand cross-links (Cr-ICLs), the latter of which are DNA polymerase arresting lesions (PALs). We sought to determine the impact of Cr-DNA interactions on the formation of replication blocking lesions in S. cerevisiae using a PCR-based method. We found that target sequence (TS) amplification using DNA isolated from Cr(VI)-treated yeast actually increased as a function of Cr(VI) concentration. Moreover, the enhanced TS amplification was reproduced in vitro using Cr(III)-treated DNA. In contrast, PCR amplification of TS from DNA isolated from yeast exposed to equitoxic doses of the inorganic DNA cross-linking agent cisplatin (CDDP), was decreased in a concentration-dependent manner. This paradox suggested that a specific Cr-DNA interaction, such as an ionic Cr-DNA complex, was responsible for the enhanced TS amplification, thereby masking the replication-blocking effect of certain ternary Cr-DNA adducts (i.e. interstrand cross-links). To test this possibility, we removed ionically associated Cr from the DNA using salt extraction prior to PCR analysis. This procedure obviated the increased amplification and revealed a dose-dependent decrease in TS amplification and an increase in Cr-PALs. These data from DNA analyzed ex vivo after treatment of intact cells indicate that ionic interactions of Cr with DNA result in increased DNA amplification whereas coordinate-covalent Cr-DNA complexes lead to formation of Cr-PALs. Thus, these results suggest that treatment of living cells with Cr(VI) leads to two modes of Cr-binding, which may have conflicting effects on DNA replication.
authors.affiliation: Department of Pharmacology and Physiology, The George Washington University Medical Center, Washington, DC 20037, USA.
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Fornsaglio
authors.forename: Travis J
authors.initials: TJ
authors.lastname: O'Brien
authors.forename: Steven R
authors.initials: SR
authors.lastname: Patierno
mesh_terms: D002273:Carcinogens / Q000737:chemistry / Q000378:metabolism; D002712:Chlorides / Q000737:chemistry / Q000378:metabolism; D002840:Chromates / Q000737:chemistry / Q000378:metabolism; D002857:Chromium / Q000737:chemistry* / Q000378:metabolism; D017608:Chromium Compounds / Q000737:chemistry / Q000378:metabolism; D018736:DNA Adducts / Q000737:chemistry* / Q000378:metabolism; D004249:DNA Damage; D004261:DNA Replication; D004271:DNA, Fungal / Q000737:chemistry* / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019384:Nucleic Acid Synthesis Inhibitors; D012441:Saccharomyces cerevisiae; D017670:Sodium Compounds / Q000737:chemistry / Q000378:metabolism
chemical_list: D002273:Carcinogens; D002712:Chlorides; D002840:Chromates; D017608:Chromium Compounds; D018736:DNA Adducts; D004271:DNA, Fungal; D019384:Nucleic Acid Synthesis Inhibitors; D017670:Sodium Compounds; D002857:Chromium; C028982:sodium chromate(VI); D004259:DNA-Directed DNA Polymerase; C022990:chromic chloride