Topoisomerase I poisoning results in PARP-mediated replication fork reversal

Nat Struct Mol Biol. 2012 Mar 4;19(4):417-23. doi: 10.1038/nsmb.2258.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Camptothecin / pharmacology*
  • Cell Line
  • DNA / chemistry
  • DNA / metabolism
  • DNA Repair / drug effects
  • DNA Replication / drug effects*
  • DNA Topoisomerases, Type I / metabolism*
  • Humans
  • Nucleic Acid Conformation / drug effects
  • Poly(ADP-ribose) Polymerases / metabolism*
  • Saccharomyces cerevisiae / cytology
  • Saccharomyces cerevisiae / drug effects
  • Topoisomerase I Inhibitors / pharmacology*
  • Xenopus laevis / metabolism


  • Topoisomerase I Inhibitors
  • DNA
  • Poly(ADP-ribose) Polymerases
  • DNA Topoisomerases, Type I
  • Camptothecin