Heat stress induced Cup9 dependent transcriptional regulation of Sir2
15 Jan 2015-Molecular and Cellular Biology (American Society for Microbiology)-Vol. 35, Iss: 2, pp 437-450
TL;DR: The mechanism by which Sir2 is regulated under heat stress is demonstrated, which reveals that a transient heat shock causes a drastic reduction in the SIR2 transcript which results in sustained failure to initiate silencing for as long as 90 generations.
Abstract: The epigenetic writer Sir2 maintains the heterochromatin state of chromosome in three chromosomal regions, namely, the silent mating type loci, telomeres, and the ribosomal DNA (rDNA). In this study, we demonstrated the mechanism by which Sir2 is regulated under heat stress. Our study reveals that a transient heat shock causes a drastic reduction in the SIR2 transcript which results in sustained failure to initiate silencing for as long as 90 generations. Hsp82 overexpression, which is the usual outcome of heat shock treatment, leads to a similar downregulation of SIR2 transcription. Using a series of genetic experiments, we have established that heat shock or Hsp82 overexpression causes upregulation of CUP9 that, in turn, represses SIR2 transcription by binding to its upstream activator sequence. We have mapped the cis regulatory element of SIR2. Our study shows that the deletion of cup9 causes reversal of the Hsp82 overexpression phenotype and upregulation of SIR2 expression in heat-induced Hsp82-overexpressing cells. On the other hand, we found that Cup9 overexpression represses SIR2 transcription and leads to a failure in the establishment of heterochromatin. The results of our study highlight the mechanism by which environmental factors amend the epigenetic configuration of chromatin.
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TL;DR: The role of Hsp90 is discussed in all the three aforementioned mechanisms of transcriptional control, taking examples from various model organisms with a special emphasis on cancer progression.
Abstract: In the last decade Hsp90 has emerged as a major regulator of cancer cell growth and proliferation In cancer cells, it assists in giving maturation to oncogenic proteins including several kinases and transcription factors Recent studies have shown that apart from its chaperone activity, it also imparts regulation of transcription machinery and thereby alters the cellular physiology Hsp90 and its co-chaperones modulate transcription at-least at three different levels In the first place, they alter the steady-state levels of certain transcription factors in response to various physiological cues Secondly, they modulate the activity of certain epigenetic modifiers, such as histone deacetylases or DNA methyl transferases, and thereby respond to the change in the environment Thirdly, they participate in the eviction of histones from the promoter region of certain genes and thereby turn on gene expression In this review, we discuss the role of Hsp90 in all the three aforementioned mechanisms of transcriptional control, taking examples from various model organisms with a special emphasis on cancer progression
54 citations
01 Aug 2012
TL;DR: The results establish HSP90 client recognition as a combinatorial process: CDC37 provides recognition of the kinase family, whereas thermodynamic parameters determine client binding within the family.
Abstract: National Institutes of Health (U.S.). Genomics Based Drug Discovery-Driving Medical Project (Grant UL1-DE019585)
28 citations
TL;DR: The recent advancements that for the first time provide a mechanistic understanding of how heterochromatin, dictated by histone modifications specifically, is preserved during S-phase are discussed.
Abstract: Saccharomyces cerevisiae (budding yeast) and Schizosaccharomyces pombe (fission yeast) are two of the most recognised and well-studied model systems for epigenetic regulation and the inheritance of chromatin states. Their silent loci serve as a proxy for heterochromatic chromatin in higher eukaryotes, and as such both species have provided a wealth of information on the mechanisms behind the establishment and maintenance of epigenetic states, not only in yeast, but in higher eukaryotes. This review focuses specifically on the role of histone modifications in governing telomeric silencing in S. cerevisiae and centromeric silencing in S. pombe as examples of genetic loci that exemplify epigenetic inheritance. We discuss the recent advancements that for the first time provide a mechanistic understanding of how heterochromatin, dictated by histone modifications specifically, is preserved during S-phase. We also discuss the current state of our understanding of yeast nucleosome dynamics during DNA replication, an essential component in delineating the contribution of histone modifications to epigenetic inheritance.
25 citations
TL;DR: The model organism Saccharomyces cerevisiae is used to establish that a transient heat shock and particularly the concomitant induction of Hsp90 lead to increased genomic instability via transcriptional regulation of the major checkpoint kinase Rad53.
Abstract: It is well documented that elevated body temperature causes tumors to regress upon radiotherapy. However, how hyperthermia induces DNA damage sensitivity is not clear. We show that a transient heat shock and particularly the concomitant induction of Hsp90 lead to increased genomic instability under DNA-damaging conditions. Using Saccharomyces cerevisiae as a model eukaryote, we demonstrate that elevated levels of Hsp90 attenuate efficient DNA damage signaling and dictate preferential use of the potentially mutagenic double-strand break repair pathway. We show that under normal physiological conditions, Hsp90 negatively regulates RAD53 transcription to suppress DNA damage checkpoint activation. However, under DNA damaging conditions, RAD53 is derepressed, and the increased level of Rad53p triggers an efficient DNA damage response. A higher abundance of Hsp90 causes increased transcriptional repression on RAD53 in a dose-dependent manner, which could not be fully derepressed even in the presence of DNA damage. Accordingly, cells behave like a rad53 loss-of-function mutant and show reduced NHEJ efficiency, with a drastic failure to up-regulate RAD51 expression and manifestly faster accumulation of CLN1 and CLN2 in DNA-damaged G1, cells leading to premature release from checkpoint arrest. We further demonstrate that Rad53 overexpression is able to rescue all of the aforementioned deleterious effects caused by Hsp90 overproduction.
12 citations
Cites background or methods from "Heat stress induced Cup9 dependent ..."
...was then cross-linked with 1% formaldehyde at 30C for 15 minutes and the experiment was performed as mentioned earlier (Laskar et al., 2014)....
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...It modulates the activity of chromatin modifiers and thereby alters gene expression (Laskar et al., 2011; Laskar et al., 2014; Tariq et al., 2009; Khurana and Bhattacharyya, 2015)....
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TL;DR: This work proposes a new model where the increase of entropy leads to the formation of double strand breaks, resulting in an aging phenotype, which not only offers a new perspective on aging research and facilitates experimental validation, but could also serve as a useful explanatory tool.
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References
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TL;DR: An understanding of the mechanism for ligand-induced repression and how this differs from activation has proven elusive, and a number of recent studies have directly or indirectly addressed this problem.
Abstract: Nuclear receptors are arguably the best understood transcriptional regulators. We know a great deal about the mechanisms through which they activate transcription in response to ligand binding and about the mechanisms through which they repress transcription in the absence of ligand. However, endocrine regulation often requires that ligand-bound receptors repress transcription of a subset of genes. An understanding of the mechanism for ligand-induced repression and how this differs from activation has proven elusive. A number of recent studies have directly or indirectly addressed this problem. Yet it seems the more evidence that accumulates, the more complex the mystery becomes.
84 citations
77 citations
"Heat stress induced Cup9 dependent ..." refers background in this paper
...Sir2-mediated telomere silencing plays a major role in mutually exclusive expression of virulent multigene family in protozoan parasites such as Plasmodium and trypanosomes (50, 51)....
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TL;DR: Gen expression analysis revealed induction of the heat shock protein (HSP) genes HSP12, HSP82, and especially HSP26 and HSP104, under acetaldehyde stress in most of the strains.
Abstract: In the production of sherry wines, the process of biological aging is essential for the development of their organoleptic properties. This process involves velum formation by "flor" yeasts. Several of these yeast strains have been isolated and characterized with regard to their genetic, physiological and metabolic properties. In this work, we studied their resistance to cold-, osmotic-, oxidative-, ethanol- and acetaldehyde-stress, and found, in most cases, a correlation between resistance to acetaldehyde stress and ethanol stress and isolation from "soleras." Moreover, gene expression analysis revealed induction of the heat shock protein (HSP) genes HSP12, HSP82, and especially HSP26 and HSP104, under acetaldehyde stress in most of the strains. In strain C, there was a clear correlation between resistance to ethanol and acetaldehyde, the high induction of HSP genes by these compounds and its presence as the predominant strain in most levels of several soleras.
76 citations
TL;DR: It is reported that for this yeast, heme uptake is induced under conditions of heme starvation, and a role for Pug1p in inducible protoporphyrin IX influx and heme efflux is reported.
Abstract: Unlike pathogenic fungi, the budding yeast Saccharomyces cerevisiae is not efficient at using heme as a nutritional source of iron. Here we report that for this yeast, heme uptake is induced under conditions of heme starvation. Heme synthesis requires oxygen, and yeast grown anaerobically exhibited an increased uptake of hemin. Similarly, a strain lacking aminolevulinate synthase exhibited a sixfold increase in hemin uptake when grown without 2-aminolevulinic acid. We used microarray analysis of cells grown under reduced oxygen tension or reduced intracellular heme conditions to identify candidate genes involved in heme uptake. Surprisingly, overexpression of PUG1 (protoporphyrin uptake gene 1) resulted in reduced utilization of exogenous heme by a heme-deficient strain and, conversely, increased the utilization of protoporphyrin IX. Pug1p was localized to the plasma membrane by indirect immunofluorescence and subcellular fractionation. Strains overexpressing PUG1 exhibited decreased accumulation of [55Fe]hemin but increased accumulation of protoporphyrin IX compared to the wild-type strain. To measure the effect of PUG1 overexpression on intracellular heme pools, we used a CYC1-lacZ reporter, which is activated in the presence of heme, and we monitored the activity of a heme-containing metalloreductase, Fre1p, expressed from a constitutive promoter. The data from these experiments were consistent with a role for Pug1p in inducible protoporphyrin IX influx and heme efflux.
62 citations
TL;DR: This review discusses how the loss of important heterochromatin proteins, including HP1, in the budding yeast lineage presented an evolutionary opportunity for the development and diversification of alternative varieties of heterochROMatin, in which the conserved deacetylase Sir2 and the replication protein Orc1 play key roles.
Abstract: The transcriptional silencing of the cryptic mating-type loci in Saccharomyces cerevisiae is one of the best-studied models of repressive heterochromatin. However, this type of heterochromatin, which is mediated by the Sir proteins, has a distinct molecular composition compared to the more ubiquitous type of heterochromatin found in Schizosaccharomyces pombe, other fungi, animals, and plants and characterized by the presence of HP1 (heterochromatin protein 1). This review discusses how the loss of important heterochromatin proteins, including HP1, in the budding yeast lineage presented an evolutionary opportunity for the development and diversification of alternative varieties of heterochromatin, in which the conserved deacetylase Sir2 and the replication protein Orc1 play key roles. In addition, we highlight how this diversification has been facilitated by gene duplications and has contributed to adaptations in lifestyle.
55 citations
"Heat stress induced Cup9 dependent ..." refers background in this paper
...Sir3 and Sir4 recruit additional Sir2, and thus, the renewal of this cycle causes the spread of the Sir complex along the chromosome (9)....
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