It has long been understood that many of the same manipulations that increase longevity in Caenorhabditis elegans also increase resistance to various acute stressors, and vice-versa; moreover these findings hold in more complex organisms as well. Nevertheless, the mechanistic relationship between these phenotypes remains unclear, and in many cases the overlap between stress resistance and longevity is inexact. Here we review the known connections between stress resistance and longevity, discuss instances in which these connections are absent, and summarize the theoretical explanations that have been posited for these phenomena. deletions in Caenorhabditis elegans alter the localization of intracellular reactive oxygen species and show molecular compensation. J Gerontol A Biol Sci Med Sci. 2009; 64:530-539. 30. McCord JM, Fridovich I. Superoxide dismutase. an enzymic function for erythrocuprein (hemocuprein). J Biol Chem. 1969; 244:6049-6055. 31. Walker TK, Tosic J. The ;catalase test', with special reference to acetobacter species. Biochem J. 1943; 37:10-12. 32. Mills GC. The purification and properties of glutathione peroxidase of erythrocytes. J Biol Chem. 1959; 234:502-506. 33. Brenot A, King KY, Janowiak B, Griffith O, Caparon MG. Contribution of glutathione peroxidase to the virulence of streptococcus pyogenes. Infect Immun. 2004; 72:408-413. 34. Larsen PL. Aging and resistance to oxidative damage in. A redox-sensitive peroxiredoxin that is important for longevity has tissue-and stress-specific roles in stress resistance.

A major cause of aging is thought to result from the cumulative effects of cell loss over time. In yeast, caloric restriction (CR) delays aging by activating the Sir2 deacetylase. Here we show that expression of mammalian Sir2 (SIRT1) is induced in CR rats as well as in human cells that are treated with serum from these animals. Insulin and insulin-like growth factor 1 (IGF-1) attenuated this response. SIRT1 deacetylates the DNA repair factor Ku70, causing it to sequester the proapoptotic factor Bax away from mitochondria, thereby inhibiting stress-induced apoptotic cell death. Thus, CR could extend life-span by inducing SIRT1 expression and promoting the long-term survival of irreplaceable cells.

The Saccharomyces cerevisiae Sir2 protein is an NAD ؉ -dependent histone deacetylase that plays a critical role in transcriptional silencing, genome stability, and longevity. A human homologue of Sir2, SIRT1, regulates the activity of the p53 tumor suppressor and inhibits apoptosis. The Sir2 deacetylation reaction generates two products: O-acetyl-ADP-ribose and nicotinamide, a precursor of nicotinic acid and a form of niacin/vitamin B 3 . We show here that nicotinamide strongly inhibits yeast silencing, increases rDNA recombination, and shortens replicative life span to that of a sir2 mutant. Nicotinamide abolishes silencing and leads to an eventual delocalization of Sir2 even in G 1 -arrested cells, demonstrating that silent heterochromatin requires continual Sir2 activity. We show that physiological concentrations of nicotinamide noncompetitively inhibit both Sir2 and SIRT1 in vitro. The degree of inhibition by nicotinamide (IC 50 < 50 M) is equal to or better than the most effective known synthetic inhibitors of this class of proteins. We propose a model whereby nicotinamide inhibits deacetylation by binding to a conserved pocket adjacent to NAD ؉ , thereby blocking NAD ؉ hydrolysis. We discuss the possibility that nicotinamide is a physiologically relevant regulator of Sir2 enzymes.Transcriptional silencing involves the heritable modification of chromatin at distinct sites in the genome. Silencing is referred to as long range repression as it is promoter nonspecific and often encompasses an entire genomic locus (1, 2). In yeast these silent regions, which are similar to the heterochromatin of higher eukaryotes, are subject to a wide variety of modifications (3). Among the best studied of these modifications is the reversible acetylation of histones (reviewed by Refs. 4 and 5).There are two types of enzymes that affect the acetylation state of histones: histone acetyltransferases and the opposing histone deacetylases (HDACs).1 Compared with more transcriptionally active areas of the genome, histones within silent regions of chromatin are known to be hypoacetylated, specifically on the NH 2 -terminal tails of core histones H3 and H4 (6). Three classes of histone deacetylases have been described and classified based on homology to yeast proteins. Proteins in class I (Rpd3-like) and class II (Hda1-like) are characterized by their sensitivity to the inhibitor trichostatin A (TSA) (7,8). Studies using this inhibitor have provided a wealth of information regarding the biochemistry and cellular function of these proteins (reviewed by Ref. 9).Yeast Sir2 is the founding member of Class III HDACs. Sir2-like deacetylases are not inhibited by TSA and have the unique characteristic of being NAD ϩ -dependent (10 -13). Proteins of this class are found in a wide array of organisms, ranging from bacteria to humans. At least two Sir2 homologues, yeast Hst2 and human SIRT2, are localized to the cytoplasm and human SIRT1, a nuclear protein, has recently been shown to target p53 for deacetylation (11,(13)(14)(15). These results i...

Calorie restriction extends lifespan in a broad range of organisms, from yeasts to mammals. Numerous hypotheses have been proposed to explain this phenomenon, including decreased oxidative damage and altered energy metabolism. In Saccharomyces cerevisiae, lifespan extension by calorie restriction requires the NAD+-dependent histone deacetylase, Sir2 (ref. 1). We have recently shown that Sir2 and its closest human homologue SIRT1, a p53 deacetylase, are strongly inhibited by the vitamin B3 precursor nicotinamide. Here we show that increased expression of PNC1 (pyrazinamidase/nicotinamidase 1), which encodes an enzyme that deaminates nicotinamide, is both necessary and sufficient for lifespan extension by calorie restriction and low-intensity stress. We also identify PNC1 as a longevity gene that is responsive to all stimuli that extend lifespan. We provide evidence that nicotinamide depletion is sufficient to activate Sir2 and that this is the mechanism by which PNC1 regulates longevity. We conclude that yeast lifespan extension by calorie restriction is the consequence of an active cellular response to a low-intensity stress and speculate that nicotinamide might regulate critical cellular processes in higher organisms.

Apoptosis is a key tumor suppression mechanism that can be initiated by activation of the proapoptotic factor Bax. The Ku70 DNA end-joining protein has recently been shown to suppress apoptosis by sequestering Bax from mitochondria. The mechanism by which Bax is regulated remains unknown. Here, we identify eight lysines in Ku70 that are targets for acetylation in vivo. Five of these, K539, K542, K544, K533, and K556, lie in the C-terminal linker domain of Ku70 adjacent to the Bax interaction domain. We show that CBP and PCAF efficiently acetylate K542 in vitro and associate with Ku70 in vivo. Mimicking acetylation of K539 or K542 or treating cells with deacetylase inhibitors abolishes the ability of Ku70 to suppress Bax-mediated apoptosis. We demonstrate that increased acetylation of Ku70 disrupts the Ku70-Bax interaction and coincides with cytoplasmic accumulation of CBP. These results shed light on the role of acetyltransferases as tumor suppressors.

Yeast deprived of nutrients exhibit a marked life span extension that requires the activity of the NAD ؉ -dependent histone deacetylase, Sir2p. Here we show that increased dosage of NPT1, encoding a nicotinate phosphoribosyltransferase critical for the NAD ؉ salvage pathway, increases Sir2-dependent silencing, stabilizes the rDNA locus, and extends yeast replicative life span by up to 60%. Both NPT1 and SIR2 provide resistance against heat shock, demonstrating that these genes act in a more general manner to promote cell survival. We show that Npt1 and a previously uncharacterized salvage pathway enzyme, Nma2, are both concentrated in the nucleus, indicating that a significant amount of NAD ؉ is regenerated in this organelle. Additional copies of the salvage pathway genes, PNC1, NMA1, and NMA2, increase telomeric and rDNA silencing, implying that multiple steps affect the rate of the pathway. Although SIR2-dependent processes are enhanced by additional NPT1, steady-state NAD ؉ levels and NAD ؉ /NADH ratios remain unaltered. This finding suggests that yeast life span extension may be facilitated by an increase in the availability of NAD ؉ to Sir2, although not through a simple increase in steady-state levels. We propose a model in which increased flux through the NAD ؉ salvage pathway is responsible for the Sir2-dependent extension of life span.

When it was first proposed that the budding yeast Saccharomyces cerevisiae might serve as a model for human aging in 1959, the suggestion was met with considerable skepticism. Although yeast had proved a valuable model for understanding basic cellular processes in humans, it was difficult to accept that such a simple unicellular organism could provide information about human aging, one of the most complex of biological phenomena. While it is true that causes of aging are likely to be multifarious, there is a growing realization that all eukaryotes possess surprisingly conserved longevity pathways that govern the pace of aging. This realization has come, in part, from studies of S. cerevisiae, which has emerged as a highly informative and respected model for the study of life span regulation. Genomic instability has been identified as a major cause of aging, and over a dozen longevity genes have now been identified that suppress it. Here we present the key discoveries in the yeast-aging field, regarding both the replicative and chronological measures of life span in this organism. We discuss the implications of these findings not only for mammalian longevity but also for other key aspects of cell biology, including cell survival, the relationship between chromatin structure and genome stability, and the effect of internal and external environments on cellular defense pathways. We focus on the regulation of replicative life span, since recent findings have shed considerable light on the mechanisms controlling this process. We also present the specific methods used to study aging and longevity regulation in S. cerevisiae

PAGE 18883:During preparation of the manuscript, the same images of yeast colonies were inadvertently shown for two different wild type controls in Fig. 2A. The panel is for visual purposes only. The quantification of three independent experiments is shown in Fig. 2B. The error does not affect the results or conclusions of the study.