title: Nicotinamide clearance by Pnc1 directly regulates Sir2-mediated silencing and longevity.
abstract: The Saccharomyces cerevisiae Sir2 protein is an NAD(+)-dependent histone deacetylase (HDAC) that functions in transcriptional silencing and longevity. The NAD(+) salvage pathway protein, Npt1, regulates Sir2-mediated processes by maintaining a sufficiently high intracellular NAD(+) concentration. However, another NAD(+) salvage pathway component, Pnc1, modulates silencing independently of the NAD(+) concentration. Nicotinamide (NAM) is a by-product of the Sir2 deacetylase reaction and is a natural Sir2 inhibitor. Pnc1 is a nicotinamidase that converts NAM to nicotinic acid. Here we show that recombinant Pnc1 stimulates Sir2 HDAC activity in vitro by preventing the accumulation of NAM produced by Sir2. In vivo, telomeric, rDNA, and HM silencing are differentially sensitive to inhibition by NAM. Furthermore, PNC1 overexpression suppresses the inhibitory effect of exogenously added NAM on silencing, life span, and Hst1-mediated transcriptional repression. Finally, we show that stress suppresses the inhibitory effect of NAM through the induction of PNC1 expression. Pnc1, therefore, positively regulates Sir2-mediated silencing and longevity by preventing the accumulation of intracellular NAM during times of stress.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia Health System, Charlottesville, Virginia 22908, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Gallo
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Smith
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Smith
mesh_terms: D004275:DNA, Ribosomal / Q000378:metabolism; D020868:Gene Silencing / Q000502:physiology*; D006655:Histone Deacetylases / Q000378:metabolism*; D009536:Niacinamide / Q000378:metabolism*; D009535:Nicotinamidase / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000378:metabolism*; D056565:Sirtuin 2; D037761:Sirtuins / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism; D013997:Time Factors
chemical_list: D004275:DNA, Ribosomal; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D009536:Niacinamide; C103934:HST1 protein, S cerevisiae; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D009535:Nicotinamidase; C474330:PNC1 protein, S cerevisiae; D006655:Histone Deacetylases