SIRT1功能的研究进展

SIRT1(si1ent mating-type information regulation 2 homologue 1)是Sirtuins去乙酰化酶家族中的一员,是酵母沉默信息调节因子Sir2(silence information regulator)的同源物.它参与了众多基因转录、能量代谢以及细胞衰老过程的调节...     

靶向Sirt3对脑卒中影响的研究进展

脑卒中是当今世界范围内主要致死性疾病之一,其发病机制与线粒体功能障碍密切相关。沉默调节蛋白（SIRT）家族是NAD+依赖性赖氨酸去乙酰化酶和ADP核糖转移酶的进化保守家族,Sirtuin家族的成员——沉默信息调节因子2同源蛋白3(Sirt3),是主要的线粒体去乙酰化酶,其通过调控相关蛋白的乙酰化水平发挥调节线粒体代谢、抗氧化应激、改善线粒体功能等重要作用。发生脑卒中后会使Sirt3的表达量下降,导致其调控线粒体正常生理过程及改善脑缺血再灌注损伤的作用被削弱。     

SIRT1在神经退行性疾病中的作用研究新进展

SIRT1是高度保守的去乙酰化酶家族成员,是酵母沉默信息调节因子Sir2的同源物。SIRT1具有组蛋白/非组蛋白去乙酰化酶活性,通过其可逆的乙酰化—去乙酰化循环反应参与调节多种细胞功能,可参与抗凋亡、抗炎、抗氧化应激、调节能量代谢、调控细胞周期等过程。近年来,其在神经退行性疾病中的作用受到越来越广泛关注,本文就SIRT1在神经退行性疾病中的作用研究新进展作一综述。     

氧化应激与染色质重构

越来越多的研究发现染色质结构的变化与基因转录的调控有密切的关系,基因转录前高度凝集的染色质必须去凝集,转录有关的酶和因子才能集结到目的基因区启动转录过程,染色质的这种结构变化称为染色质重构。氧化应激能够通过抑制组蛋白去乙酰化酶(HDAC)的活性,增加组蛋白乙酰化酶(HAT)活性造成组蛋白乙酰化/去乙酰化失衡,引起染色质重构,来调控部分基因的表达。染色质重构机制在氧化应激相关的病理生理变化中发挥重要作用。     

Sirt1 功能的研究进展

Sirt1是迄今为止在哺乳动物细胞中发现的与沉默调控基因Sir2同源性最高的同系物,是一个NAD依赖的去乙酰化酶。它参与了众多基因转录、能量代谢以及细胞衰老过程的调节。Sirt1不仅可以促进脂质动员与肝脏糖异生,还能调控胰岛β细胞的胰岛素分泌功能。此外,Sirt1还是一个内源性的凋亡抑制因子。     

组蛋白去乙酰化酶与新生血管形成的关系

真核细胞中染色质的基本单位是核小体,它是由核心组蛋白(H2A、H2B、H3和H4)、H1及DNA组成.核心蛋白的乙酰化和去乙酰化是基因表达过程中重要的调控方式,负责组蛋白乙酰化和去乙酰化的是一对功能相互拮抗的蛋白酶家族组蛋白乙酰基转移酶(HAT)和组蛋白去乙酰化酶(HDAC).HAT激活基因转录,而HDAC的功能相反,抑制基因的转录.HDAC的功能异常被证实与肿瘤的发生和发展及缺氧和病理状态下的血管增生有直接关系.本文就HDAC与新生血管形成之间的关系作一综述.     

组蛋白乙酰化、细胞周期与消化系肿瘤

在真核细胞中 ,ＤＮＡ与组蛋白是染色质的主要成分。染色质结构与基因活性密切相关 ,通过组蛋白乙酰化和去乙酰化来修饰染色质的结构 ,在ＤＮＡ复制、基因转录及细胞周期的调控等方面有重要作用[1 ] 。各种肿瘤的发生过程中常伴有乙酰化紊乱 ,干预组蛋白乙酰化可影响肿瘤的进程。一、组蛋白乙酰化酶和去乙酰化酶染色质的乙酰化可使核小体结构改变 ,乙酰化作用主要发生在组蛋白分子Ｎ端赖氨酸残基上。由于乙酰化减弱了组蛋白与ＤＮＡ的结合 ,从而使染色质构象处于开放状态 ,有利于ＤＮＡ的基因转录和表达。一般情况下 ,转录活跃区的核小体组…     

SIRT3特性与心、脑血管疾病关系研究进展

正哺乳动物体内的Sirtuins蛋白家族分别参与多种细胞代谢和生理调节,包括基因的稳定性,大部分的氧化应激过程,细胞的增殖、代谢、存活、衰老以及器官的寿命等~([1])。Sirtuins(SIRT1-7)是一类NAD依赖的去乙酰化蛋白和ADP核糖基转移酶,为非组蛋白乙酰化主要调节因子,其酶活性受细胞中NAD+和NADH含量的调节。沉默信息调节因子3(SIRT3)是哺乳动物7个SIRTuins家族成员之一,通过调节新陈代谢以稳定细胞的能量以及调节酶的活性来平衡细胞的氧化还原状态~([2])。蛋白质翻译后修饰过程中乙酰化是一个重要的过程,乙酰化作用于线粒体蛋白的翻译后修饰,     

MBD蛋白家族研究进展

甲基化CpG结合域(methyl-CpG-binding domain,MBD)蛋白家族在基因的转录调控中发挥重要作用。MBD蛋白功能的实现需要蛋白的MBD结构域和基因组的甲基化CpG位点,它们通过异染色质的形成,组蛋白去乙酰化以及DNA甲基化修饰,进而产生基因表达抑制作用。但是,一些MBD蛋白也可以结合非甲基化DNA,并通过蛋白其他的结构域或者与核小体重塑及去乙酰化酶(nucleosome remodeling deacetylase,NuRD)/Mi-2复合物的相互作用来发挥转录激活作用和多向分化潜能。MBD蛋白发生基因突变或异常表达会引起多种疾病,包括神经系统疾病、癌症和慢性乙型肝炎。本文总结了MBD蛋白家族核心成员的主要功能及与相关疾病的关系。     

SIRT1的神经保护机制

Sirtuin是一类作用于组蛋白的去乙酰化酶,Sirtuin-1(SIRT1)是哺乳动物中与沉默调控基因SIR2同源性最高的同系物.SIRT1的主要功能是调控机体能最代谢、细胞衰老以及对应激的反应.SIRT1通过与多种参与应激反应中的转录因子相互作用抑制细胞凋亡,是一种神经保护药.     

Sir2 mediates apoptosis through JNK-dependent pathways in Drosophila

Increased expression of the histone deacetylase sir2 has been reported to extend the life span of diverse organisms including yeast, Caenorhabditis elegans, and Drosophila melanogaster. A small molecule activator of Sir2, resveratrol, has also been suggested to extend the fitness and survival of these simple model organisms as well as mice fed high calorie diets. However, other studies in yeast have shown that Sir2 itself may prevent life extension, and high expression levels of Sir2 can be toxic to yeast and mouse cells. This conflicting evidence highlights the importance of understanding the mechanisms by which Sir2 expression or activation affects survival of organisms. To investigate the downstream signaling pathways affected by Sir2 in Drosophila, we generated transgenic flies expressing sir2. Here, we show that overexpression of sir2 in Drosophila promotes caspase-dependent but p53-independent apoptosis that is mediated by the JNK and FOXO signaling pathways. Furthermore, we find that a loss-of-function sir2 mutant partially prevents apoptosis induced by UV irradiation in the eye. Together, these results suggest that Sir2 normally participates in the regulation of cell survival and death in Drosophila.     

Transcriptional silencing functions of the yeast protein Orc1/Sir3 subfunctionalized after gene duplication

The origin recognition complex (ORC) defines origins of replication and also interacts with heterochromatin proteins in a variety of species, but how ORC functions in heterochromatin assembly remains unclear. The largest subunit of ORC, Orc1, is particularly interesting because it contains a nucleosome-binding BAH domain and because it gave rise to Sir3, a key silencing protein in Saccharomyces cerevisiae, through gene duplication. We examined whether Orc1 possessed a Sir3-like silencing function before duplication and found that Orc1 from the yeast Kluyveromyces lactis, which diverged from S. cerevisiae before the duplication, acts in conjunction with the deacetylase Sir2 and the histone-binding protein Sir4 to generate heterochromatin at telomeres and a mating-type locus. Moreover, the ability of KlOrc1 to spread across a silenced locus depends on its nucleosome-binding BAH domain and the deacetylase Sir2. Interestingly, KlOrc1 appears to act independently of the entire ORC, as other subunits of the complex, Orc4 and Orc5, are not strongly associated with silenced domains. These findings demonstrate that Orc1 functioned in silencing before duplication and suggest that Orc1 and Sir2, both of which are broadly conserved among eukaryotes, may have an ancient history of cooperating to generate chromatin structures, with Sir2 deacetylating histones and Orc1 binding to these deacetylated nucleosomes through its BAH domain.     

Identification of a small molecule inhibitor of Sir2p

Sir2p is an NAD(+)-dependent histone deacetylase required for chromatin-dependent silencing in yeast. In a cell-based screen for inhibitors of Sir2p, we identified a compound, splitomicin, that creates a conditional phenocopy of a sir2 deletion mutant in Saccharomyces cerevisiae. Cells grown in the presence of the drug have silencing defects at telomeres, silent mating-type loci, and the ribosomal DNA. In addition, whole genome microarray experiments show that splitomicin selectively inhibits Sir2p. In vitro, splitomicin inhibits NAD(+)-dependent histone deacetylase activity (HDA) of the Sir2 protein. Mutations in SIR2 that confer resistance to the drug map to the likely acetylated histone tail binding domain of the protein. By using splitomicin as a chemical genetic probe, we demonstrate that continuous HDA of Sir2p is required for maintaining a silenced state in nondividing cells.     

Involvement of Daphnia pulicaria Sir2 in regulating stress response and lifespan

The ability to appropriately respond to proteotoxic stimuli is a major determinant of longevity and involves induction of various heat shock response (HSR) genes, which are essential to cope with cellular and organismal insults throughout lifespan. The activity of NAD+-dependent deacetylase Sir2, originally discovered in yeast, is known to be essential for effective HSR and longevity. Our previous work on HSR in Daphnia pulicaria indicated a drastic reduction of the HSR in older organisms. In this report we investigate the role of Sir2 in regulating HSR during the lifespan of D. pulicaria. We cloned Daphnia Sir2 open reading frame (ORF) to characterize the enzyme activity and confirmed that the overall function of Sir2 was conserved in Daphnia. The Sir2 mRNA levels increased while the enzyme activity declined with age and considering that Sir2 activity regulates HSR, this explains the previously observed age-dependent decline in HSR. Finally, we tested the effect of Sir2 knockdown throughout adult life by using our new RNA interference (RNAi) method by feeding. Sir2 knockdown severely reduced both the median lifespan as well as significantly increased mortality following heat shock. Our study provides the first characterization and functional study of Daphnia Sir2.     

Heterochromatin protein Sir3 induces contacts between the amino terminus of histone H4 and nucleosomal DNA

The regulated binding of effector proteins to the nucleosome plays a central role in the activation and silencing of eukaryotic genes. How this binding changes the properties of chromatin to mediate gene activation or silencing is not fully understood. Here we provide evidence that association of the budding yeast silent information regulator 3 (Sir3) silencing protein with the nucleosome induces a conformational change in the amino terminus of histone H4 that promotes interactions between the conserved H4 arginines 17 and 19 (R17 and R19) and nucleosomal DNA. Substitutions of H4R17 and R19 with alanine abolish silencing in vivo, but have little or no effect on binding of Sir3 to nucleosomes or histone H4 peptides in vitro. Furthermore, in both the previously reported crystal structure of the Sir3-bromo adjacent homology (BAH) domain bound to the Xenopus laevis nucleosome core particle and the crystal structure of the Sir3-BAH domain bound to the yeast nucleosome core particle described here, H4R17 and R19 make contacts with nucleosomal DNA rather than with Sir3. These results suggest that Sir3 binding generates a more stable nucleosome by clamping H4R17 and R19 to nucleosomal DNA, and raise the possibility that such induced changes in histone–DNA contacts play major roles in the regulation of chromatin structure.     

dSir2 and longevity in Drosophila

The silent information regulator 2 (Sir2 or Sirtuin) family of proteins is highly conserved and has been implicated in the extension of longevity for several species. Mammalian Sirtuins have been shown to affect various aspects of physiology including metabolism, the stress response, cell survival, replicative senescence, inflammation, the circadian rhythm, neurodegeneration, and even cancer. Evidence in Drosophila implicates Sir2 in at least some of the beneficial effects of caloric restriction (CR). CR delays age-related pathology and extends life span in a wide variety of species. Here we will review the evidence linking Drosophila Sir2 (dSir2) to longevity regulation and the pathway associated with CR in Drosophila, as well as the effects of the Sir2 activator resveratrol and potential interactions between dSir2 and p53.     

Histone deacetylase 2 is required for chromatin condensation and subsequent enucleation of cultured mouse fetal erythroblasts

Background

During the final stages of differentiation of mammalian erythroid cells, the chromatin is condensed and enucleated. We previously reported that Rac GTPases and their downstream target, mammalian homolog of Drosophila diaphanous 2 (mDia2), are required for enucleation of in vitro cultured mouse fetal liver erythroblasts. However, it is not clear how chromatin condensation is achieved and whether it is required for enucleation.

Design and Methods

Mouse fetal liver erythroblasts were purified from embryonic day 14.5 pregnant mice and cultured in erythropoietin-containing medium. Enucleation was determined by flow-cytometry based analysis after treatment with histone deacetylase inhibitors or infection with lentiviral short harirpin RNA.

Results

We showed that histone deacetylases play critical roles in chromatin condensation and enucleation in cultured mouse fetal liver erythroblasts. Enzymatic inhibition of histone deacetylases by trichostatin A or valproic acid prior to the start of enucleation blocked chromatin condensation, contractile actin ring formation and enucleation. We further demonstrated that histone deacetylases 1, 2, 3 and 5 are highly expressed in mouse fetal erythroblasts. Short hairpin RNA down-regulation of histone deacetylase 2, but not of the other histone deacetylases, phenotypically mimicked the effect of trichostatin A or valproic acid treatment, causing significant inhibition of chromatin condensation and enucleation. Importantly, knock-down of histone deacetylase 2 did not affect erythroblast proliferation, differentiation, or apoptosis.

Conclusions

These results identify histone deacetylase 2 as an important regulator, mediating chromatin condensation and enucleation in the final stages of mammalian erythropoiesis.