title: Interdependent genotoxic mechanisms of monomethylarsonous acid: role of ROS-induced DNA damage and poly(ADP-ribose) polymerase-1 inhibition in the malignant transformation of urothelial cells.
abstract: Exposure of human bladder urothelial cells (UROtsa) to 50 nM of the arsenic metabolite, monomethylarsonous acid (MMA(III)), for 12 weeks results in irreversible malignant transformation. The ability of continuous, low-level MMA(III) exposure to cause an increase in genotoxic potential by inhibiting repair processes necessary to maintain genomic stability is unknown. Following genomic insult within cellular systems poly(ADP-ribose) polymerase-1 (PARP-1), a zinc finger protein, is rapidly activated and recruited to sites of DNA strand breaks. When UROtsa cells are continuously exposed to 50 nM MMA(III), PARP-1 activity does not increase despite the increase in MMA(III)-induced DNA single-strand breaks through 12 weeks of exposure. When UROtsa cells are removed from continuous MMA(III) exposure (2 weeks), PARP-1 activity increases coinciding with a subsequent decrease in DNA damage levels. Paradoxically, PARP-1 mRNA expression and protein levels are elevated in the presence of continuous MMA(III) indicating a possible mechanism to compensate for the inhibition of PARP-1 activity in the presence of MMA(III). The zinc finger domains of PARP-1 contain vicinal sulfhydryl groups which may act as a potential site for MMA(III) to bind, displace zinc ion, and render PARP-1 inactive. Mass spectrometry analysis demonstrates the ability of MMA(III) to bind a synthetic peptide representing the zinc-finger domain of PARP-1, and displace zinc from the peptide in a dose-dependent manner. In the presence of continuous MMA(III) exposure, continuous 4-week zinc supplementation restored PARP-1 activity levels and reduced the genotoxicity associated with MMA(III). Zinc supplementation did not produce an overall increase in PARP-1 protein levels, decrease the levels of MMA(III)-induced reactive oxygen species, or alter Cu-Zn superoxide dismutase levels. Overall, these results present two potential interdependent mechanisms in which MMA(III) may increase the susceptibility of UROtsa cells to genotoxic insult and/or malignant transformation: elevated levels of MMA(III)-induced DNA damage through the production of reactive oxygen species, and the direct MMA(III)-induced inhibition of PARP-1.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, The University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Shawn M
authors.initials: SM
authors.lastname: Wnek
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Kuhlman
authors.forename: Jeannie M
authors.initials: JM
authors.lastname: Camarillo
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Medeiros
authors.forename: Ke J
authors.initials: KJ
authors.lastname: Liu
authors.forename: Serrine S
authors.initials: SS
authors.lastname: Lau
authors.forename: A J
authors.initials: AJ
authors.lastname: Gandolfi
mesh_terms: D015153:Blotting, Western; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D020552:Comet Assay; D004249:DNA Damage / Q000187:drug effects*; D005434:Flow Cytometry; D006801:Humans; D009942:Organometallic Compounds / Q000633:toxicity*; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D001743:Urinary Bladder / Q000166:cytology / Q000187:drug effects*; D001749:Urinary Bladder Neoplasms / Q000139:chemically induced; D019459:Urothelium / Q000166:cytology / Q000187:drug effects*; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002273:Carcinogens; D002712:Chlorides; D009942:Organometallic Compounds; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D017382:Reactive Oxygen Species; D017967:Zinc Compounds; C406082:monomethylarsonous acid; C016837:zinc chloride; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases