title: Low concentration of arsenite exacerbates UVR-induced DNA strand breaks by inhibiting PARP-1 activity.
abstract: Epidemiological studies have associated arsenic exposure with many types of human cancers. Arsenic has also been shown to act as a co-carcinogen even at low concentrations. However, the precise mechanism of its co-carcinogenic action is unknown. Recent studies indicate that arsenic can interfere with DNA-repair processes. Poly(ADP-ribose) polymerase (PARP)-1 is a zinc-finger DNA-repair protein, which can promptly sense DNA strand breaks and initiate DNA-repair pathways. In the present study, we tested the hypothesis that low concentrations of arsenic could inhibit PAPR-1 activity and so exacerbate levels of ultraviolet radiation (UVR)-induced DNA strand breaks. HaCat cells were treated with arsenite and/or UVR, and then DNA strand breaks were assessed by comet assay. Low concentrations of arsenite (<or=2 microM) alone did not induce significant DNA strand breaks, but greatly enhanced the DNA strand breaks induced by UVR. Further studies showed that 2 microM arsenite effectively inhibited PARP-1 activity. Zinc supplementation of arsenite-treated cells restored PARP-1 activity and significantly diminished the exacerbating effect of arsenite on UVR-induced DNA strand breaks. Importantly, neither arsenite treatment, nor zinc supplementation changed UVR-triggered reactive oxygen species (ROS) formation, suggesting that their effects upon UVR-induced DNA strand breaks are not through a direct free radical mechanism. Combination treatments of arsenite with PARP-1 inhibitor 3-aminobenzamide or PARP-1 siRNA demonstrate that PARP-1 is the target of arsenite. Together, these findings show that arsenite at low concentration exacerbates UVR-induced DNA strand breaks by inhibiting PARP-1 activity, which may represent an important mechanism underlying the co-carcinogenicity of arsenic.
authors.affiliation: Program of Toxicology, College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131-0001, USA.
authors.forename: Xu-Jun
authors.initials: XJ
authors.lastname: Qin
authors.forename: Laurie G
authors.initials: LG
authors.lastname: Hudson
authors.forename: Wenlan
authors.initials: W
authors.lastname: Liu
authors.forename: Graham S
authors.initials: GS
authors.lastname: Timmins
authors.forename: Ke Jian
authors.initials: KJ
authors.lastname: Liu
mesh_terms: D018053:Arsenites / Q000633:toxicity*; D001549:Benzamides / Q000494:pharmacology; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D002712:Chlorides / Q000494:pharmacology; D020552:Comet Assay; D053960:DNA Breaks; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000633:toxicity*; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects* / Q000201:enzymology / Q000528:radiation effects; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species / Q000378:metabolism; D017670:Sodium Compounds / Q000633:toxicity*; D014162:Transfection; D014466:Ultraviolet Rays; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D018053:Arsenites; D001549:Benzamides; D002273:Carcinogens; D002712:Chlorides; D004791:Enzyme Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D017670:Sodium Compounds; D017967:Zinc Compounds; C017947:sodium arsenite; C016837:zinc chloride; C025160:3-aminobenzamide; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases