Cellular necrosis has long been regarded as an incidental and uncontrolled form of cell death. However, a regulated form of cell death termed necroptosis has been identified recently. Necroptosis can be induced by extracellular cytokines, pathogens and several pharmacological compounds, which share the property of triggering the formation of a RIPK3-containing molecular complex supporting cell death. Of interest, most ligands known to induce necroptosis (including notably TNF and FASL) can also promote apoptosis, and the mechanisms regulating the decision of cells to commit to one form of cell death or the other are still poorly defined. We demonstrate herein that intracellular nicotinamide adenine dinucleotide (NAD +) has an important role in supporting cell progression to necroptosis. Using a panel of pharmacological and genetic approaches, we show that intracellular NAD + promotes necroptosis of the L929 cell line in response to TNF. Use of a pan-sirtuin inhibitor and shRNA-mediated protein knockdown led us to uncover a role for the NAD + -dependent family of sirtuins, and in particular for SIRT2 and SIRT5, in the regulation of the necroptotic cell death program. Thus, and in contrast to a generally held view, intracellular NAD + does not represent a universal pro-survival factor, but rather acts as a key metabolite regulating the choice of cell demise in response to both intrinsic and extrinsic factors.
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Acknowledgements. We thank Iain Welsby and Muriel Moser for reviewing the manuscript and providing helpful suggestions. We wish to acknowledge the support of the Belgian Program in Interuniversity Poles of Attraction initiated by Science Policy Programming, Belgium, the Research Concerted Action and the ‘Fonds pour la formation à la Recherche dans l’Industrie et l’Agriculture’ (F.R.I.A.) of the ‘Fédération Wallonie-Bruxelles’, the ‘Fonds David et Alice Van Buuren’, and the ‘Fonds Brachet’ for financial support. We wish to thank Adrian Ting (Mount Sinai School of Medicine, NY, USA) and Christine Hawkins (La Trobe University, Victoria, Australia) for sharing plasmids encoding respectively for IκBαSR and CrmA. We also wish to thank Vishva M. Dixit (Genentech, South San Francisco, CA, USA) for sharing RIPK3-KO mice.