Title: Extracellular NAD+ enhances PARP-dependent DNA repair capacity independently of CD73 activity.
Authors: Wilk, Anna; Hayat, Faisal; Cunningham, Richard; Li, Jianfeng; Garavaglia, Silvia; Zamani, Leila; Ferraris, Davide M; Sykora, Peter; Andrews, Joel; Clark, Jennifer; Davis, Amanda; Chaloin, Laurent; Rizzi, Menico; Migaud, Marie; Sobol, Robert W
Published In Sci Rep, (2020 01 20)
Abstract: 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.
PubMed ID: 31959836
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