title: Topoisomerase I poisoning results in PARP-mediated replication fork reversal.
abstract: Topoisomerase I (Top1) releases torsional stress during DNA replication and transcription and is inhibited by camptothecin and camptothecin-derived cancer chemotherapeutics. Top1 inhibitor cytotoxicity is frequently linked to double-strand break (DSB) formation as a result of Top1 being trapped on a nicked DNA intermediate in replicating cells. Here we use yeast, mammalian cell lines and Xenopus laevis egg extracts to show that Top1 poisons rapidly induce replication-fork slowing and reversal, which can be uncoupled from DSB formation at sublethal inhibitor doses. Poly(ADP-ribose) polymerase activity, but not single-stranded break repair in general, is required for effective fork reversal and limits DSB formation. These data identify fork reversal as a means to prevent chromosome breakage upon exogenous replication stress and implicate proteins involved in fork reversal or restart as factors modulating the cytotoxicity of replication stress-inducing chemotherapeutics.
authors.affiliation: Institute of Molecular Cancer Research, University of Zurich, Zurich, Switzerland.
authors.forename: Arnab
authors.initials: A
authors.lastname: Ray Chaudhuri
authors.forename: Yoshitami
authors.initials: Y
authors.lastname: Hashimoto
authors.forename: Raquel
authors.initials: R
authors.lastname: Herrador
authors.forename: Kai J
authors.initials: KJ
authors.lastname: Neelsen
authors.forename: Daniele
authors.initials: D
authors.lastname: Fachinetti
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Bermejo
authors.forename: Andrea
authors.initials: A
authors.lastname: Cocito
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Costanzo
authors.forename: Massimo
authors.initials: M
authors.lastname: Lopes
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000494:pharmacology*; D002460:Cell Line; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D006801:Humans; D009690:Nucleic Acid Conformation / Q000187:drug effects; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology*; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D059004:Topoisomerase I Inhibitors; D004247:DNA; D011065:Poly(ADP-ribose) Polymerases; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin