The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Danesh Moazed - One of the best experts on this subject based on the ideXlab platform.
-
assembly of the sir complex and its regulation by o acetyl adp ribose a product of nad dependent histone deacetylation
Cell, 2005Co-Authors: Gunnguang Liou, Jason C Tanny, Ryan G Kruger, Thomas Walz, Danesh MoazedAbstract:Assembly of silent chromatin domains in budding yeast involves the deacetylation of histone tails by Sir2 and the association of the Sir3 and Sir4 proteins with hypoacetylated histone tails. Sir2 couples deacetylation to NAD hydrolysis and the synthesis of a metabolite, O-acetyl-ADP-ribose (AAR), but the functional significance of NAD hydrolysis or AAR, if any, is unknown. Here we examine the association of the Sir2, Sir3, and Sir4 proteins with each other and histone tails. Our analysis reveals that deacetylation of histone H4-lysine 16 (K16), which is critical for silencing in vivo, is also critical for the binding of Sir3 and Sir4 to histone H4 peptides in vitro. Moreover, AAR itself promotes the association of multiple copies of Sir3 with Sir2/Sir4 and induces a dramatic structural rearrangement in the SIR complex. These results suggest that Sir2 activity modulates the assembly of the SIR complex through both histone deacetylation and AAR synthesis.
-
budding yeast silencing complexes and regulation of Sir2 activity by protein protein interactions
Molecular and Cellular Biology, 2004Co-Authors: Jason C Tanny, Donald S Kirkpatrick, Scott A Gerber, Steven P Gygi, Danesh MoazedAbstract:Gene silencing in the budding yeast Saccharomyces cerevisiae requires the enzymatic activity of the Sir2 protein, a highly conserved NAD-dependent deacetylase. In order to study the activity of native Sir2, we purified and characterized two budding yeast Sir2 complexes: the Sir2/Sir4 complex, which mediates silencing at mating-type loci and at telomeres, and the RENT complex, which mediates silencing at the ribosomal DNA repeats. Analyses of the protein compositions of these complexes confirmed previously described interactions. We show that the assembly of Sir2 into native silencing complexes does not alter its selectivity for acetylated substrates, nor does it allow the deacetylation of nucleosomal histones. The inability of Sir2 complexes to deacetylate nucleosomes suggests that additional factors influence Sir2 activity in vivo. In contrast, Sir2 complexes show significant enhancement in their affinities for acetylated substrates and their sensitivities to the physiological inhibitor nicotinamide relative to recombinant Sir2. Reconstitution experiments showed that, for the Sir2/Sir4 complex, these differences stem from the physical interaction of Sir2 with Sir4. Finally, we provide evidence that the different nicotinamide sensitivities of Sir2/Sir4 and RENT in vitro could contribute to locus-specific differences in how Sir2 activity is regulated in vivo.
-
association of the rent complex with nontranscribed and coding regions of rdna and a regional requirement for the replication fork block protein fob1 in rdna silencing
Genes & Development, 2003Co-Authors: Julie Huang, Danesh MoazedAbstract:Silencing within the yeast rDNA repeats inhibits hyperrecombination, represses transcription from foreign promoters, and extends replicative life span. rDNA silencing is mediated by a Sir2-containing complex called RENT (regulator of nucleolar silencing and telophase exit). We show that the Net1 (also called Cfi1) and Sir2 subunits of RENT localize primarily to two distinct regions within rDNA: in one of the nontranscribed spacers (NTS1) and around the Pol I promoter, extending into the 35S rRNA coding region. Binding to NTS1 overlaps the recombination hotspot and replication fork barrier elements, which have been shown previously to require the Fob1 protein for their activities. In cells lacking Fob1, silencing and the association of RENT subunits are abolished specifically at NTS1, while silencing and association at the Pol I promoter region are unaffected or increased. We find that Net1 and Sir2 are physically associated with Fob1 and subunits of RNA polymerase I. Together with the localization data, these results suggest the existence of two distinct modes for the recruitment of the RENT complex to rDNA and reveal a role for Fob1 in rDNA silencing and in the recruitment of the RENT complex. Furthermore, the Fob1-dependent associations of Net1 and Sir2 with the recombination hotspot region strongly suggest that Sir2 acts directly at this region to carry out its inhibitory effect on rDNA recombination and accelerated aging.
-
Sir2 regulates histone h3 lysine 9 methylation and heterochromatin assembly in fission yeast
Current Biology, 2003Co-Authors: Gurumurthy D Shankaranarayana, Danesh Moazed, Mohammad R Motamedi, Shiv I S GrewalAbstract:Hypoacetylated histones are a hallmark of heterochromatin in organisms ranging from yeast to humans. Histone deacetylation is carried out by both NAD(+)-dependent and NAD(+)-independent enzymes. In the budding yeast Saccharomyces cerevisiae, deacetylation of histones in heterochromatic chromosomal domains requires Sir2, a phylogenetically conserved NAD(+)-dependent deacetylase. In the fission yeast Schizosaccharomyces pombe, NAD(+)-independent histone deacetylases are required for the formation of heterochromatin, but the role of Sir2-like deacetylases in this process has not been evaluated. Here, we show that spSir2, the S. pombe Sir2-like protein that is the most closely related to the S. cerevisiae Sir2, is an NAD(+)-dependent deacetylase that efficiently deacetylates histone H3 lysine 9 (K9) and histone H4 lysine 16 (K16) in vitro. In Sir2 Delta cells, silencing at the donor mating-type loci, telomeres, and the inner centromeric repeats (imr) is abolished, while silencing at the outer centromeric repeats (otr) and rDNA is weakly reduced. Furthermore, Sir2 is required for hypoacetylation and methylation of H3-K9 and for the association of Swi6 with the above loci in vivo. Our findings suggest that the NAD(+)-dependent deacetylase Sir2 plays an important and conserved role in heterochromatin assembly in eukaryotes.
-
steps in assembly of silent chromatin in yeast sir3 independent binding of a Sir2 sir4 complex to silencers and role for Sir2 dependent deacetylation
Molecular and Cellular Biology, 2002Co-Authors: Georg J Hoppe, Jason C Tanny, Scott A Gerber, Steven P Gygi, Adam D Rudner, Sherwin Danaie, Danesh MoazedAbstract:Transcriptional silencing at the budding yeast silent mating type (HM) loci and telomeric DNA regions requires Sir2, a conserved NAD-dependent histone deacetylase, Sir3, Sir4, histones H3 and H4, and several DNA-binding proteins. Silencing at the yeast ribosomal DNA (rDNA) repeats requires a complex containing Sir2, Net1, and Cdc14. Here we show that the native Sir2/Sir4 complex is composed solely of Sir2 and Sir4 and that native Sir3 is not associated with other proteins. We further show that the initial binding of the Sir2/Sir4 complex to DNA sites that nucleate silencing, accompanied by partial Sir2-dependent histone deacetylation, occurs independently of Sir3 and is likely to be the first step in assembly of silent chromatin at the HM loci and telomeres. The enzymatic activity of Sir2 is not required for this initial binding, but is required for the association of silencing proteins with regions distal from nucleation sites. At the rDNA repeats, we show that histone H3 and H4 tails are required for silencing and rDNA-associated H4 is hypoacetylated in a Sir2-dependent manner. However, the binding of Sir2 to rDNA is independent of its histone deacetylase activity. Together, these results support a stepwise model for the assembly of silent chromatin domains in Saccharomyces cerevisiae.
Matt Kaeberlein - One of the best experts on this subject based on the ideXlab platform.
-
The SAGA Histone Deubiquitinase Module Controls Yeast Replicative Lifespan via Sir2 Interaction
Cell reports, 2014Co-Authors: Mark A. Mccormick, Matt Kaeberlein, Amanda G. Mason, Stephan J. Guyenet, Weiwei Dang, Renee M. Garza, Marc K. Ting, Rick M. Moller, Shelley L. Berger, Lorraine PillusAbstract:We have analyzed the yeast replicative lifespan of a large number of open reading frame (ORF) deletions. Here, we report that strains lacking genes SGF73, SGF11, and UBP8 encoding SAGA/SLIK complex histone deubiquitinase module (DUBm) components are exceptionally long lived. Strains lacking other SAGA/SALSA components, including the acetyltransferase encoded by GCN5, are not long lived; however, these genes are required for the lifespan extension observed in DUBm deletions. Moreover, the Sir2-encoded histone deacetylase is required, and we document both a genetic and physical interaction between DUBm and Sir2. A series of studies assessing Sir2-dependent functions lead us to propose that DUBm strains are exceptionally long lived because they promote multiple prolongevity events, including reduced rDNA recombination and altered silencing of telomere-proximal genes. Given that ataxin-7, the human Sgf73 ortholog, causes the neurodegenerative disease spinocerebellar ataxia type 7, our findings indicate that the genetic and epigenetic interactions between DUBm and Sir2 will be relevant to neurodegeneration and aging.
-
Increased life span due to calorie restriction in respiratory‐deficient yeast
2013Co-Authors: Matt Kaeberlein, Mitsuhiro Tsuchiya, Nick Dang, Emily O Kerr, Stanley Fields, Eric A Westman, Brian K KennedyAbstract:A model for replicative life span extension by calorie restriction (CR) in yeast has been proposed whereby reduced glucose in the growth medium leads to activation of the NAD þ –dependent histone deacetylase Sir2. One mechanism proposed for this putative activation of Sir2 is that CR enhances the rate of respiration, in turn leading to altered levels of NAD þ or NADH, and ultimately resulting in enhanced Sir2 activity. An alternative mechanism has been proposed in which CR decreases levels of the Sir2 inhibitor nicotinamide through increased expression of the gene coding for nicotinamidase, PNC1. We have previously reported that life span extension by CR is not dependent on Sir2 in the longlived BY4742 strain background. Here we have determined the requirement for respiration and the effect of nicotinamide levels on life span extension by CR. We find that CR confers robust life span extension in respiratorydeficient cells independent of strain background, and moreover, suppresses the premature mortality associated with loss of mitochondrial DNA in the short-lived PSY316 strain. Addition of nicotinamide to the medium dramatically shortens the life span of wild type cells, due to inhibition of Sir2. However, even in cells lacking both Sir2 and the replication fork block protein Fob1, nicotinamide partially prevents life span extension by CR. These findings (1) demonstrate that respiration is not required for the longevity benefits of CR in yeast, (2) show that nicotinamide inhibits life span extension by CR through a Sir2-independent mechanism, and (3) suggest that CR acts through a conserved, Sir2-independent mechanism in both PSY316 and BY4742
-
Increased Life Span due to Calorie Restriction in Respiratory-Deficient Yeast
2013Co-Authors: Matt Kaeberlein, Mitsuhiro Tsuchiya, Nick Dang, Emily O Kerr, Stanley Fields, Eric A Westman, Brian K KennedyAbstract:A model for replicative life span extension by calorie restriction (CR) in yeast has been proposed whereby reduced glucose in the growth medium leads to activation of the NAD+–dependent histone deacetylase Sir2. One mechanism proposed for this putative activation of Sir2 is that CR enhances the rate of respiration, in turn leading to altered levels of NAD+ or NADH, and ultimately resulting in enhanced Sir2 activity. An alternative mechanism has been proposed in which CR decreases levels of the Sir2 inhibitor nicotinamide through increased expression of the gene coding for nicotinamidase, PNC1. We have previously reported that life span extension by CR is not dependent on Sir2 in the long-lived BY4742 strain background. Here we have determined the requirement for respiration and the effect of nicotinamide levels on life span extension by CR. We find that CR confers robust life span extension in respiratory-deficient cells independent of strain background, and moreover, suppresses the premature mortality associated with loss of mitochondrial DNA in the short-lived PSY316 strain. Addition of nicotinamide to the medium dramatically shortens the life span of wild type cells, due to inhibition of Sir2. However, even in cells lacking both Sir2 and the replication fork block protein Fob1, nicotinamide partially prevents life span extension by CR. These findings (1) demonstrate that respiration is not required for the longevity benefits of CR in yeast, (2) show that nicotinamide inhibits life span extension by CR through a Sir2-independent mechanism, and (3) suggest that CR acts through a conserved, Sir2-independent mechanism in both PSY316 and BY4742.
-
Sir2 and calorie restriction in yeast a skeptical perspective
Ageing Research Reviews, 2007Co-Authors: Matt Kaeberlein, Wilson R PowersAbstract:Activation of Sir2-family proteins in response to calorie restriction (CR) has been proposed as an evolutionarily conserved mechanism for life span extension. This idea has been called into question with the discovery that Sir2-family proteins are not required for life span extension from CR in yeast. We present here a historical perspective and critical evaluation of the model that CR acts through Sir2 in yeast, and interpret prior reports in light of more recent discoveries. Several specific cases where the Sir2 model of CR is inconsistent with experimental data are noted. These shortcomings must be considered along with evidence supporting a role for Sir2 in CR in order to fully evaluate the validity of this model.
-
sirtuin independent effects of nicotinamide on lifespan extension from calorie restriction in yeast
Aging Cell, 2006Co-Authors: Mitsuhiro Tsuchiya, Nick Dang, Emily O Kerr, Kristan K Steffen, Jonathan A Oakes, Brian K Kennedy, Matt KaeberleinAbstract:Summary Two models have been proposed for how calorie restriction (CR) enhances replicative longevity in yeast: (i) suppression of rDNA recombination through activation of the sirtuin protein deacetylase Sir2 or (ii) decreased activity of the nutrient-responsive kinases Sch9 and TOR. We report here that CR increases lifespan independently of all Sir2-family proteins in yeast. Furthermore, we demonstrate that nicotinamide, an inhibitor of Sir2-mediated deacetylation, interferes with lifespan extension from CR, but does so independent of Sir2, Hst1, Hst2, and Hst4. We also find that 5 mm nicotinamide, a concentration sufficient to inhibit other sirtuins, does not phenocopy deletion of HST3. Thus, we propose that lifespan extension by CR is independent of sirtuins and that nicotinamide has sirtuin-independent effects on lifespan extension by CR.
Jef D. Boeke - One of the best experts on this subject based on the ideXlab platform.
-
Yeast heterochromatin regulators Sir2 and Sir3 act directly at euchromatic DNA replication origins
PLOS Genetics, 2018Co-Authors: Timothy Hoggard, Fu-jung Chang, Kelsey Rae Perry, Sandya Subramanian, Jessica Kenworthy, Julie Chueng, Erika Shor, Edel M. Hyland, Jef D. Boeke, Michael WeinreichAbstract:Most active DNA replication origins are found within euchromatin, while origins within heterochromatin are often inactive or inhibited. In yeast, origin activity within heterochromatin is negatively controlled by the histone H4K16 deacetylase, Sir2, and at some heterochromatic loci also by the nucleosome binding protein, Sir3. The prevailing view has been that direct functions of Sir2 and Sir3 are confined to heterochromatin. However, growth defects in yeast mutants compromised for loading the MCM helicase, such as cdc6-4, are suppressed by deletion of either Sir2 or SIR3. While these and other observations indicate that Sir2,3 can have a negative impact on at least some euchromatic origins, the genomic scale of this effect was unknown. It was also unknown whether this suppression resulted from direct functions of Sir2,3 within euchromatin, or was an indirect effect of their previously established roles within heterochromatin. Using MCM ChIP-Seq, we show that a Sir2 deletion rescued MCM complex loading at ~80% of euchromatic origins in cdc6-4 cells. Therefore, Sir2 exhibited a pervasive effect at the majority of euchromatic origins. Using MNase-H4K16ac ChIP-Seq, we show that origin-adjacent nucleosomes were depleted for H4K16 acetylation in a Sir2-dependent manner in wild type (i.e. CDC6) cells. In addition, we present evidence that both Sir2 and Sir3 bound to nucleosomes adjacent to euchromatic origins. The relative levels of each of these molecular hallmarks of yeast heterochromatin–Sir2-dependent H4K16 hypoacetylation, Sir2, and Sir3 –correlated with how strongly a Sir2 deletion suppressed the MCM loading defect in cdc6-4 cells. Finally, a screen for histone H3 and H4 mutants that could suppress the cdc6-4 growth defect identified amino acids that map to a surface of the nucleosome important for Sir3 binding. We conclude that heterochromatin proteins directly modify the local chromatin environment of euchromatic DNA replication origins.
-
Yeast heterochromatin regulators Sir2 and Sir3 act directly at euchromatic DNA replication origins
bioRxiv, 2018Co-Authors: Timothy Hoggard, Fu-jung Chang, Kelsey Rae Perry, Sandya Subramanian, Jessica Kenworthy, Julie Chueng, Erika Shor, Michael S. Cosgrove, Jef D. BoekeAbstract:Most active DNA replication origins are found within euchromatin, while origins within heterochromatin are often inactive or inhibited. In yeast, origin activity within heterochromatin is negatively controlled by the histone H4K16 deacetylase, Sir2, and at some heterochromatic loci also by the nucleosome binding protein, Sir3. The prevailing view has been that direct functions of Sir2 and Sir3 are confined to heterochromatin. However, growth defects in yeast mutants compromised for loading the MCM helicase, such as cdc6-4, are robustly suppressed by deletion of either Sir2 or SIR3. While this and other observations indicate that Sir2,3 can have a negative impact on at least some euchromatic origins, the genomic scale of this effect was unknown. It was also unknown whether this suppression resulted from direct functions of Sir2,3 within euchromatin, or was an indirect effect of their previously established roles within heterochromatin. Using both MCM ChIP-Seq and MNase-H4K16ac ChIP-Seq data, we show that a Sir2 deletion rescues MCM complex loading at ~80% of euchromatic origins in cdc6-4 cells. Therefore, Sir2 exhibits a pervasive effect at the majority of euchromatic origins. Importantly, in wild type (i.e. CDC6) cells, origin-adjacent nucleosomes were depleted for H4K16 acetylation in a Sir2-dependent manner. In addition, both Sir2 and Sir3 directly bound to nucleosomes adjacent to euchromatic origins. The relative levels of each of these molecular hallmarks of yeast heterochromatin, Sir2-dependent H4K16 hypoacetylation, Sir2, and Sir3, correlated with how strongly a Sir2 deletion suppressed the MCM loading defect in cdc6-4 cells. Finally, a screen for histone H3 and H4 mutants that could suppress the cdc6-4 growth defect identified amino acids that map to a surface of the nucleosome important for Sir3 binding. We conclude that heterochromatin proteins directly bind euchromatic DNA replication origins and modify their local chromatin environment.
-
structural basis for the mechanism and regulation of Sir2 enzymes
Molecular Cell, 2004Co-Authors: Jose L Avalos, Jef D. Boeke, Cynthia WolbergerAbstract:Sir2 proteins form a family of NAD + -dependent protein deacetylases required for diverse biological processes, including transcriptional silencing, suppression of rDNA recombination, control of p53 activity, regulation of acetyl-CoA synthetase, and aging. Although structures of Sir2 enzymes in the presence and absence of peptide substrate or NAD + have been determined, the role of the enzyme in the mechanism of deacetylation and NAD + cleavage is still unclear. Here, we present additional structures of Sir2Af2 in several differently complexed states: in a productive complex with NAD + , in a nonproductive NAD + complex with bound ADP-ribose, and in the unliganded state. We observe a new mode of NAD + binding that seems to depend on acetyl-lysine binding, in which the nicotinamide ring of NAD + is buried in the highly conserved "C" pocket of the enzyme. We propose a detailed structure-based mechanism for deacetylation and nicotinamide inhibition of Sir2 consistent with mutagenesis and enzymatic studies.
-
short chain fatty acid activation by acyl coenzyme a synthetases requires Sir2 protein function in salmonella enterica and saccharomyces cerevisiae
Genetics, 2003Co-Authors: Vincent J Starai, Jef D. Boeke, Hidekazu Takahashi, Jorge C EscalantesemerenaAbstract:Sir2 proteins have NAD(+)-dependent histone deacetylase activity, but no metabolic role has been assigned to any of these proteins. In Salmonella enterica, Sir2 function was required for activity of the acetyl-CoA synthetase (Acs) enzyme. A greater than two orders of magnitude increase in the specific activity of Acs enzyme synthesized by a sirtuin-deficient strain was measured after treatment with homogeneous S. enterica Sir2 protein. Human Sir2A and yeast Sir2 proteins restored growth of Sir2-deficient S. enterica on acetate and propionate, suggesting that eukaryotic cells may also use Sir2 proteins to control the synthesis of acetyl-CoA by the level of acetylation of acetyl-CoA synthetases. Consistent with this idea, growth of a quintuple Sir2 hst1 hst2 hst3 hst4 mutant strain of the yeast Saccharomyces cerevisiae on acetate or propionate was severely impaired. The data suggest that the Hst3 and Hst4 proteins are the most important for allowing growth on these short-chain fatty acids.
-
structure of a Sir2 enzyme bound to an acetylated p53 peptide
Molecular Cell, 2002Co-Authors: Jose L Avalos, Ivana Celic, Shabazz Muhammad, Jef D. Boeke, Michael S. Cosgrove, Cynthia WolbergerAbstract:Abstract Sir2 proteins are NAD + -dependent protein deacetylases that play key roles in transcriptional regulation, DNA repair, and life span regulation. The structure of an archaeal Sir2 enzyme, Sir2-Af2, bound to an acetylated p53 peptide reveals that the substrate binds in a cleft in the enzyme, forming an enzyme-substrate β sheet with two flanking strands in Sir2-Af2. The acetyl-lysine inserts into a conserved hydrophobic tunnel that contains the active site histidine. Comparison with other structures of Sir2 enzymes suggests that the apoenzyme undergoes a conformational change upon substrate binding. Based on the Sir2-Af2 substrate complex structure, mutations were made in the other A. fulgidus sirtuin, Sir2-Af1, that increased its affinity for the p53 peptide.
Leonard Guarente - One of the best experts on this subject based on the ideXlab platform.
-
Sir2 a potential target for calorie restriction mimetics
Trends in Molecular Medicine, 2007Co-Authors: Danica Chen, Leonard GuarenteAbstract:Calorie restriction (CR) extends lifespan in a wide variety of species and mitigates diseases of aging in mammals. Here, we describe the evidence that the silent information regulator 2 (Sir2) gene, which encodes a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, regulates lifespan and mediates CR in lower species such as Saccharomyces cerevisiae and Caenorhabditis elegans. We discuss the emerging roles of mammalian Sir2 homologs in regulating physiological changes triggered by CR and their potential connections to diseases of aging. We conclude with the recent advances on small molecules that activate the enzymatic activity of Sir2 as potential CR mimetics. The Sir2 family represents an evolutionarily conserved lifespan regulator. Modulating the activity of Sir2 might provide effective CR mimetics to combat diseases of aging.
-
mammalian sirtuins emerging roles in physiology aging and calorie restriction
Genes & Development, 2006Co-Authors: Marcia C Haigis, Leonard GuarenteAbstract:: Sir2 is an NAD-dependent deacetylase that connects metabolism with longevity in yeast, worms and flies. Mammals contain seven homologs of yeast Sir2, SIRT1-7. Here, we review recent findings demonstrating the role of these mammalian sirtuins as regulators of physiology, calorie restriction, and aging. The current findings sharpen our understanding of sirtuins as potential pharmacological targets to treat the major diseases of aging.
-
the Sir2 family of protein deacetylases
Annual Review of Biochemistry, 2004Co-Authors: Gil Blander, Leonard GuarenteAbstract:▪ Abstract The yeast SIR protein complex has been implicated in transcription silencing and suppression of recombination. The Sir complex represses transcription at telomeres, mating-type loci, and ribosomal DNA. Unlike SIR3 and SIR4, the Sir2 gene is highly conserved in organisms ranging from archaea to humans. Interestingly, Sir2 is active as an NAD+-dependent deacetylase, which is broadly conserved from bacteria to higher eukaryotes. In this review, we discuss the role of NAD+, the unusual products of the deacetylation reaction, the Sir2 structure, and the Sir2 chemical inhibitors and activators that were recently identified. We summarize the current knowledge of the Sir2 homologs from different organisms, and finally we discuss the role of Sir2 in caloric restriction and aging.
-
calorie restriction extends yeast life span by lowering the level of nadh
Genes & Development, 2004Co-Authors: Su Ju Lin, Ethan Ford, Marcia C Haigis, Greg Liszt, Leonard GuarenteAbstract:Calorie restriction (CR) extends life span in a wide variety of species. Previously, we showed that calorie restriction increases the replicative life span in yeast by activating Sir2, a highly conserved NAD-dependent deacetylase. Here we test whether CR activates Sir2 by increasing the NAD/NADH ratio or by regulating the level of nicotinamide, a known inhibitor of Sir2. We show that CR decreases NADH levels, and that NADH is a competitive inhibitor of Sir2. A genetic intervention that specifically decreases NADH levels increases life span, validating the model that NADH regulates yeast longevity in response to CR.
-
hSir2sirt1 functions as an nad dependent p53 deacetylase
Cell, 2001Co-Authors: Homayoun Vaziri, Leonard Guarente, Shinichiro Imai, Scott K Dessain, Elinor Ng Eaton, Roy A Frye, Tej K Pandita, Robert A WeinbergAbstract:Abstract DNA damage-induced acetylation of p53 protein leads to its activation and either growth arrest or apoptosis. We show here that the protein product of the gene hSir2 SIRT1 , the human homolog of the S. cerevisiae Sir2 protein known to be involved in cell aging and in the response to DNA damage, binds and deacetylates the p53 protein with a specificity for its C-terminal Lys382 residue, modification of which has been implicated in the activation of p53 as a transcription factor. Expression of wild-type hSir2 in human cells reduces the transcriptional activity of p53. In contrast, expression of a catalytically inactive hSir2 protein potentiates p53-dependent apoptosis and radiosensitivity. We propose that hSir2 is involved in the regulation of p53 function via deacetylation.
David A Sinclair - One of the best experts on this subject based on the ideXlab platform.
-
Sir2 histone deacetylase prevents programmed cell death caused by sustained activation of the hog1 stress activated protein kinase
EMBO Reports, 2011Co-Authors: Alexandre Vendrell, David A Sinclair, Mar Martinezpastor, Alberto Gonzaleznovo, Amparo Pascualahuir, Markus Proft, Francesc PosasAbstract:Exposure of yeast to high osmolarity induces a transient activation of the Hog1 stress-activated protein kinase (SAPK), which is required for cell survival under these conditions. However, sustained activation of the SAPK results in a severe growth defect. We found that prolonged SAPK activation leads to cell death, which is not observed in nma111 cells, by causing accumulation of reactive oxygen species (ROS). Mutations of the SCFCDC4 ubiquitin ligase complex suppress cell death by preventing the degradation of Msn2 and Msn4 transcription factors. Accumulation of Msn2 and Msn4 leads to the induction of PNC1, which is an activator of the Sir2 histone acetylase. Sir2 is involved in protection against Hog1-induced cell death and can suppress Hog1-induced ROS accumulation. Therefore, cell death seems to be dictated by the balance of ROS induced by Hog1 and the protective effect of Sir2.
-
response to comment on hst2 mediates Sir2 independent life span extension by calorie restriction
Science, 2006Co-Authors: Dudley W Lamming, Magda Latorreesteves, Oliver Medvedik, Stacy N Wong, Felicia Tsang, Chen Wang, Su Ju Lin, David A SinclairAbstract:Our two labs and others have shown that Sir2 controls the life span of diverse species, including Saccharomyces cerevisiae and Drosophila melanogaster, and that deleting Sir2 blocks life-span extension by calorie restriction. The methods of Kaeberlein et al . allow yeast to bypass the requirement for Sir2 and its homologs, which brings into question their suitability for modeling the physiology of more complex organisms.
-
hst2 mediates Sir2 independent life span extension by calorie restriction
Science, 2005Co-Authors: Dudley W Lamming, Magda Latorreesteves, Oliver Medvedik, Stacy N Wong, Felicia Tsang, Chen Wang, Su Ju Lin, David A SinclairAbstract:Calorie restriction (CR) extends the life span of numerous species, from yeast to rodents. Yeast Sir2 is a nicotinamide adenine dinucleotide (NAD+-dependent histone deacetylase that has been proposed to mediate the effects of CR. However, this hypothesis has been challenged by the observation that CR can extend yeast life span in the absence of Sir2. Here, we show that Sir2-independent life-span extension is mediated by Hst2, a Sir2 homolog that promotes the stability of repetitive ribosomal DNA, the same mechanism by which Sir2 extends life span. These findings demonstrate that the maintenance of DNA stability is critical for yeast life-span extension by CR and suggest that, in higher organisms, multiple members of the Sir2 family may regulate life span in response to diet.
-
inhibition of silencing and accelerated aging by nicotinamide a putative negative regulator of yeast Sir2 and human sirt1
Journal of Biological Chemistry, 2002Co-Authors: Kevin J Bitterman, Magda Latorreesteves, Rozalyn M Anderson, Haim Y Cohen, David A SinclairAbstract: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 microm) 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.
-
manipulation of a nuclear nad salvage pathway delays aging without altering steady state nad levels
Journal of Biological Chemistry, 2002Co-Authors: Rozalyn M Anderson, Jason G Wood, Oliver Medvedik, Kevin J Bitterman, Haim Y Cohen, Stephen S Lin, Jill K Manchester, Jeffrey I Gordon, David A SinclairAbstract: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.
