Extracellular NAD + enhances PARP-dependent DNA repair capacity independently of CD73 activity

Sci Rep. 2020 Jan 20;10(1):651. doi: 10.1038/s41598-020-57506-9.


Changes in nicotinamide adenine dinucleotide (NAD+) levels that compromise mitochondrial function trigger release of DNA damaging reactive oxygen species. NAD+ levels also affect DNA repair capacity as NAD+ is a substrate for PARP-enzymes (mono/poly-ADP-ribosylation) and sirtuins (deacetylation). The ecto-5'-nucleotidase CD73, an ectoenzyme highly expressed in cancer, is suggested to regulate intracellular NAD+ levels by processing NAD+ and its bio-precursor, nicotinamide mononucleotide (NMN), from tumor microenvironments, thereby enhancing tumor DNA repair capacity and chemotherapy resistance. We therefore investigated whether expression of CD73 impacts intracellular NAD+ content and NAD+-dependent DNA repair capacity. Reduced intracellular NAD+ levels suppressed recruitment of the DNA repair protein XRCC1 to sites of genomic DNA damage and impacted the amount of accumulated DNA damage. Further, decreased NAD+ reduced the capacity to repair DNA damage induced by DNA alkylating agents. Overall, reversal of these outcomes through NAD+ or NMN supplementation was independent of CD73. In opposition to its proposed role in extracellular NAD+ bioprocessing, we found that recombinant human CD73 only poorly processes NMN but not NAD+. A positive correlation between CD73 expression and intracellular NAD+ content could not be made as CD73 knockout human cells were efficient in generating intracellular NAD+ when supplemented with NAD+ or NMN.

Publication types

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

MeSH terms

  • 5'-Nucleotidase / genetics
  • 5'-Nucleotidase / metabolism*
  • 5'-Nucleotidase / physiology*
  • DNA Damage*
  • DNA Repair*
  • Gene Expression
  • Gene Expression Regulation, Neoplastic
  • Humans
  • MCF-7 Cells
  • Mitochondria / physiology
  • NAD / metabolism*
  • NAD / physiology*
  • Poly ADP Ribosylation*
  • Poly(ADP-ribose) Polymerases / physiology*
  • Reactive Oxygen Species / metabolism
  • Sirtuins
  • Tumor Microenvironment / genetics*
  • Tumor Microenvironment / physiology*
  • X-ray Repair Cross Complementing Protein 1 / metabolism


  • Reactive Oxygen Species
  • X-ray Repair Cross Complementing Protein 1
  • XRCC1 protein, human
  • NAD
  • Poly(ADP-ribose) Polymerases
  • 5'-Nucleotidase
  • Sirtuins