Targeting Nuclear NAD+ Synthesis Inhibits DNA Repair, Impairs Metabolic Adaptation and Increases Chemosensitivity of U-2OS Osteosarcoma Cells

Alexandra Kiss; Arnold Péter Ráduly; Zsolt Regdon; Zsuzsanna Polgár; Szabolcs Tarapcsák; Isotta Sturniolo; Tarek El-Hamoly; László Virág; Csaba Hegedűs

doi:10.3390/cancers12051180

Targeting Nuclear NAD⁺ Synthesis Inhibits DNA Repair, Impairs Metabolic Adaptation and Increases Chemosensitivity of U-2OS Osteosarcoma Cells

Cancers (Basel). 2020 May 7;12(5):1180. doi: 10.3390/cancers12051180.

Authors

Affiliations

¹ Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, H-4032 Debrecen, Hungary, kissalexandra@med.unideb.hu (A.K.).
² Doctoral School of Molecular Medicine, University of Debrecen, H-4032 Debrecen, Hungary.
³ Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, H-4032 Debrecen, Hungary, tarapcsakszabolcs@gmail.com.
⁴ Drug Radiation Research Department, National Center for Radiation Research and Technology, Atomic Energy Authority, 113701 Cairo, Egypt.
⁵ MTA-DE Cell Biology and Signaling Research Group, H-4032 Debrecen, Hungary.

Abstract

Osteosarcoma (OS) is the most common bone tumor in children and adolescents. Modern OS treatment, based on the combination of neoadjuvant chemotherapy (cisplatin + doxorubicin + methotrexate) with subsequent surgical removal of the primary tumor and metastases, has dramatically improved overall survival of OS patients. However, further research is needed to identify new therapeutic targets. Here we report that expression level of the nuclear NAD synthesis enzyme, nicotinamide mononucleotide adenylyltransferase-1 (NMNAT1), increases in U-2OS cells upon exposure to DNA damaging agents, suggesting the involvement of the enzyme in the DNA damage response. Moreover, genetic inactivation of NMNAT1 sensitizes U-2OS osteosarcoma cells to cisplatin, doxorubicin, or a combination of these two treatments. Increased cisplatin-induced cell death of NMNAT1^-/- cells showed features of both apoptosis and necroptosis, as indicated by the protective effect of the caspase-3 inhibitor z-DEVD-FMK and the necroptosis inhibitor necrostatin-1. Activation of the DNA damage sensor enzyme poly(ADP-ribose) polymerase 1 (PARP1), a major consumer of NAD⁺ in the nucleus, was fully blocked by NMNAT1 inactivation, leading to increased DNA damage (phospho-H2AX foci). The PARP inhibitor, olaparib, sensitized wild type but not NMNAT1^-/- cells to cisplatin-induced anti-clonogenic effects, suggesting that impaired PARP1 activity is important for chemosensitization. Cisplatin-induced cell death of NMNAT1^-/- cells was also characterized by a marked drop in cellular ATP levels and impaired mitochondrial respiratory reserve capacity, highlighting the central role of compromised cellular bioenergetics in chemosensitization by NMNAT1 inactivation. Moreover, NMNAT1 cells also displayed markedly higher sensitivity to cisplatin when grown as spheroids in 3D culture. In summary, our work provides the first evidence that NMNAT1 is a promising therapeutic target for osteosarcoma and possibly other tumors as well.

Keywords: NAD+; NMNAT1; PARP1; apoptosis; cancer; chemotherapy; cisplatin; osteosarcoma.

Abstract

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