Clinical PARP inhibitors do not abrogate PARP1 exchange at DNA damage sites in vivo

Nucleic Acids Res. 2020 Sep 25;48(17):9694-9709. doi: 10.1093/nar/gkaa718.


DNA breaks recruit and activate PARP1/2, which deposit poly-ADP-ribose (PAR) to recruit XRCC1-Ligase3 and other repair factors to promote DNA repair. Clinical PARP inhibitors (PARPi) extend the lifetime of damage-induced PARP1/2 foci, referred to as 'trapping'. To understand the molecular nature of 'trapping' in cells, we employed quantitative live-cell imaging and fluorescence recovery after photo-bleaching. Unexpectedly, we found that PARP1 exchanges rapidly at DNA damage sites even in the presence of clinical PARPi, suggesting the persistent foci are not caused by physical stalling. Loss of Xrcc1, a major downstream effector of PAR, also caused persistent PARP1 foci without affecting PARP1 exchange. Thus, we propose that the persistent PARP1 foci are formed by different PARP1 molecules that are continuously recruited to and exchanging at DNA lesions due to attenuated XRCC1-LIG3 recruitment and delayed DNA repair. Moreover, mutation analyses of the NAD+ interacting residues of PARP1 showed that PARP1 can be physically trapped at DNA damage sites, and identified H862 as a potential regulator for PARP1 exchange. PARP1-H862D, but not PARylation-deficient PARP1-E988K, formed stable PARP1 foci upon activation. Together, these findings uncovered the nature of persistent PARP1 foci and identified NAD+ interacting residues involved in the PARP1 exchange.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Catalytic Domain
  • Cell Line, Tumor
  • DNA Damage*
  • DNA Repair / drug effects*
  • DNA Repair / physiology
  • Fluorescence Resonance Energy Transfer
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Humans
  • Indazoles / pharmacology
  • Kinetics
  • Molecular Imaging
  • NAD / metabolism
  • Piperidines / pharmacology
  • Poly (ADP-Ribose) Polymerase-1 / genetics*
  • Poly (ADP-Ribose) Polymerase-1 / metabolism*
  • Poly(ADP-ribose) Polymerase Inhibitors / pharmacology*
  • Poly(ADP-ribose) Polymerases / genetics
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • X-ray Repair Cross Complementing Protein 1 / genetics
  • X-ray Repair Cross Complementing Protein 1 / metabolism


  • Indazoles
  • Piperidines
  • Poly(ADP-ribose) Polymerase Inhibitors
  • Recombinant Proteins
  • X-ray Repair Cross Complementing Protein 1
  • XRCC1 protein, human
  • NAD
  • Green Fluorescent Proteins
  • PARP1 protein, human
  • PARP2 protein, human
  • Poly (ADP-Ribose) Polymerase-1
  • Poly(ADP-ribose) Polymerases
  • niraparib