title: Enhancement of camptothecin-induced topoisomerase I cleavage complexes by the acetaldehyde adduct N2-ethyl-2'-deoxyguanosine.
abstract: The activity of DNA topoisomerase I (Top1), an enzyme that regulates DNA topology, is impacted by DNA structure alterations and by the anticancer alkaloid camptothecin (CPT). Here, we evaluated the effect of the acetaldehyde-derived DNA adduct, N2-ethyl-2'-deoxyguanosine (N2-ethyl-dG), on human Top1 nicking and closing activities. Using purified recombinant Top1, we show that Top1 nicking-closing activity remains unaffected in N2-ethyl-dG adducted oligonucleotides. However, the N2-ethyl-dG adduct enhanced CPT-induced Top1-DNA cleavage complexes depending on the relative position of the N2-ethyl-dG adduct with respect to the Top1 cleavage site. The Top1-mediated DNA religation (closing) was selectively inhibited when the N2-ethyl-dG adduct was present immediately 3' from the Top1 site (position +1). In addition, when the N2-ethyl-dG adduct was located at the -5 position, CPT enhanced cleavage at an alternate Top1 cleavage site immediately adjacent to the adduct, which was then at position +1 relative to this new alternate Top1 site. Modeling studies suggest that the ethyl group on the N2-ethyl-dG adduct located at the 5' end of a Top1 site (position +1) sterically blocks the dissociation of CPT from the Top1-DNA complex, thereby inhibiting further the religation (closing) reaction.
authors.affiliation: Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA.
authors.forename: Smitha
authors.initials: S
authors.lastname: Antony
authors.forename: Jacob A
authors.initials: JA
authors.lastname: Theruvathu
authors.forename: P J
authors.initials: PJ
authors.lastname: Brooks
authors.forename: Diem-Thu
authors.initials: DT
authors.lastname: Lesher
authors.forename: Matt
authors.initials: M
authors.lastname: Redinbo
authors.forename: Yves
authors.initials: Y
authors.lastname: Pommier
mesh_terms: D002166:Camptothecin / Q000494:pharmacology*; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D018736:DNA Adducts / Q000737:chemistry*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D046911:Macromolecular Substances; D008958:Models, Molecular
chemical_list: D018736:DNA Adducts; D004791:Enzyme Inhibitors; D046911:Macromolecular Substances; C492934:N2-ethyl-2'-deoxyguanosine; D004247:DNA; D004264:DNA Topoisomerases, Type I; D003849:Deoxyguanosine; D002166:Camptothecin