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.
11 citations
References
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TL;DR: These findings suggest that the increased longevity induced by calorie restriction requires the activation of Sir2p by NAD, the oxidized form of nicotinamide adenine dinucleotide.
Abstract: Calorie restriction extends life-span in a wide variety of organisms. Although it has been suggested that calorie restriction may work by reducing the levels of reactive oxygen species produced during respiration, the mechanism by which this regimen slows aging is uncertain. Here, we mimicked calorie restriction in yeast by physiological or genetic means and showed a substantial extension in life-span. This extension was not observed in strains mutant for SIR2 (which encodes the silencing protein Sir2p) or NPT1 (a gene in a pathway in the synthesis of NAD, the oxidized form of nicotinamide adenine dinucleotide). These findings suggest that the increased longevity induced by calorie restriction requires the activation of Sir2p by NAD.
1,786 citations
"Heat stress induced Cup9 dependent ..." refers background in this paper
...NAD -induced histone deacetylase activity of Sir2 is required for increased longevity during starvation, and this effect was not observed in a sir2 mutant strain (45)....
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TL;DR: It is shown here that nicotinamide strongly inhibits yeast silencing, increases rDNA recombination, and shortens replicative life span to that of asir2 mutant, demonstrating that silent heterochromatin requires continual Sir2 activity.
985 citations
"Heat stress induced Cup9 dependent ..." refers background in this paper
...Nicotinamide (NAM), which is generated as the by-product of the enzymatic reaction, acts as a noncompetitive inhibitor of Sir2 (11)....
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TL;DR: It is shown that the SIR3 and SIR4 proteins interact with specific silencing domains of the H3 and H4 N-termini in vitro, which proposes a model for heterochromatin-mediated transcriptional silencing in yeast, which may serve as a paradigm for other eukaryotic organisms as well.
809 citations
TL;DR: It is proposed that Sirt1 regulates calorie restriction by sensing low calories and triggering physiological changes linked to health and longevity.
780 citations
"Heat stress induced Cup9 dependent ..." refers background in this paper
...Dietary restriction is proven to be an environmental factor that increases longevity from yeast to mammals (43, 44)....
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TL;DR: A statistical-mechanical selection theory for the sequence analysis of a set of specific DNA regulatory sites makes it possible to predict the relationship between individual base-pair choices in the site and specific activity (affinity), and shows that functional specificity is based on other properties in addition to primary sequence recognition.
764 citations
"Heat stress induced Cup9 dependent ..." refers methods in this paper
...The analysis for finding transcription factors was performed by the statistical method (34) employed in the widely used TRAP (transcription factor affinity prediction) web tool (35)....
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