title: Inhibition of Ape1 nuclease activity by lead, iron, and cadmium.
abstract: Many environmental metals are co-carcinogens, eliciting their effects via inhibition of DNA repair. Apurinic/apyrimidinic (AP) endonuclease 1 (Ape1) is the major mammalian abasic endonuclease and initiates repair of this cytotoxic/mutagenic lesion by incising the DNA backbone via a Mg(2+)-dependent reaction. In this study we examined the effects of arsenite [As(III)], cadmium [Cd(II)], cobalt [Co(II)], iron [Fe(II)], nickel [Ni(II)], and lead [Pb(II)] at concentrations ranging from 0.3 to 100 microM on the incision activity of Ape1 in the presence of 1 mM MgCl(subscript)2(/subscript). Pb(II) and Fe(II) inhibited Ape1 activity at each of the concentrations tested, with an IC(subscript)50(/subscript) (half-maximal inhibitory concentration) of 0.61 and 1.0 microM, respectively. Cd(II) also inhibited Ape1 activity but only at concentrations > 10 microM. No inhibition was seen with As(III), Co(II), or Ni(II). A similar inhibition pattern was observed with the homologous Escherichia coli protein, exonuclease III, but no inhibition was seen with the structurally distinct AP endonuclease E. coli endonuclease IV, indicating a targeted effect of Pb(II), Fe(II), and Cd(II) on the Ape1-like repair enzymes. Excess nonspecific DNA did not abrogate the metal inactivation, suggesting a protein-specific effect. Notably, Cd(II), Fe(II), and Pb(II) [but not As(III), Co(II), or Ni(II)] inhibited AP endonuclease activity in whole-cell extracts but had no significant effect on single nucleotide gap filling, 5'-flap endonuclease, and nick ligation activities, supporting the idea of selective inactivation of Ape1 in cells. Our results are the first to identify a potential DNA repair enzyme target for lead and suggest a means by which these prevalent environmental metals may elicit their deleterious effects.
authors.affiliation: Laboratory of Molecular Gerontology, Gerontology Research Center, National Institute on Aging, Intramural Research Program, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland 21224-6825, USA.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: McNeill
authors.forename: Avinash
authors.initials: A
authors.lastname: Narayana
authors.forename: Heng-Kuan
authors.initials: HK
authors.lastname: Wong
authors.forename: David M
authors.initials: DM
authors.lastname: Wilson
mesh_terms: D002104:Cadmium / Q000633:toxicity*; D018929:Cell Culture Techniques; D004249:DNA Damage; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000201:enzymology; D020869:Gene Expression Profiling; D006801:Humans; D007501:Iron / Q000633:toxicity*; D007854:Lead / Q000633:toxicity*; D019216:Metals, Heavy / Q000633:toxicity*
chemical_list: D019216:Metals, Heavy; D002104:Cadmium; D007854:Lead; D007501:Iron; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase