组蛋白泛素化修饰及其在DNA损伤应答中的作用

泛素化修饰是真核生物细胞内重要的翻译后修饰类型,通过调节蛋白质活性、稳定性和亚细胞定位广泛参与细胞内各项信号传导与代谢过程,对维持正常生命活动具有重要意义。组蛋白作为染色质中主要的蛋白成分,与DNA复制转录、修复等行为密切相关,是研究翻译后修饰的热点。DNA损伤后,组蛋白泛素化修饰通过调节核小体结构、激活细胞周期检查点、影响修复因子的招募与装配等诸多途径参与损伤应答。同时,组蛋白泛素化修饰还能调节其他位点翻译后修饰,并通过这种串扰(crosstalk)作用调节DNA损伤应答。本文介绍了组蛋白泛素化修饰的主要位点和相关组分(包括E3连接酶、去泛素化酶与效应分子),以及这些修饰作用共同编译形成的信号网络在DNA损伤应答中的作用,最后总结了目前该领域研究所面临的一些问题,以期为科研人员进一步探索组蛋白密码在DNA损伤应答中的作用提供参考。     

SUMO化修饰与DNA损伤修复

蛋白质的翻译后修饰在很大程度上决定了蛋白质的活性、细胞定位、稳定性及蛋白质之间的相互作用.而在DNA损伤修复过程中,通过调控不同修复蛋白的翻译后修饰来影响他们的活性及细胞定位,进而导致DNA损伤修复途径的不同和修复结果的差异.新近研究表明,蛋白质的SUMO化修饰在DNA损伤修复和基因组稳定性的维护方面发挥重要作用.本文将对SUMO化修饰对DNA损伤修复的调控的最新研究进展做一综述.     

去泛素化酶与基因表达调控

泛素化是常见的蛋白质翻译后修饰方式之一,其参与了生物体内细胞分裂与分化、生长发育、转录调节、损伤应激、免疫应答等多方面的生理活动.近年来,泛素研究领域的重要成员之一——去泛素化酶(deubiquitylating enzymes)被不断发现和报道.作为一类可以移除泛素的异肽酶类,去泛素化酶具有结构和功能的多样性.基因表达调控一直是分子遗传学的研究热点,系统整理和总结去泛素化酶与基因表达调控的关系具有重要意义.本文综述了去泛素化酶与基因表达调控的关系,包括去泛素化酶与染色质稳态维持、细胞周期调控和DNA损伤修复等三个方面,并对该领域未来的研究方向进行了预测和讨论.     

组蛋白翻译后修饰与DNA损伤响应蛋白招募的调控

组蛋白翻译后修饰是细胞DNA损伤早期应答反应的重要内涵,一方面是松弛、开放染色质结构的必要分子调节事件,以便DNA损伤响应蛋白能接近DNA损伤位点;另一方面直接参与DNA损伤修复蛋白招募过程的调控。综述了在DNA损伤信号激发下,发生的组蛋白主要修饰类型,异组蛋白H2AX、H2A.Z在DNA损伤部位与组蛋白置换,及其对DNA损伤响应蛋白招募的调节作用和机制。     

SUMO化修饰在DNA损伤响应中的作用

物理或化学等多种因素均可以引起DNA损伤。为维持机体基因组的稳定性,机体形成了精确完整的机制来修复损伤的／DNA。SUMO（smallubiquitin-relatedmodifier,SUMO）化修饰与其他蛋白翻译后修饰一样,具有多种生物学功能。近年来的研究表明,其在DNA损伤修复中也具有非常重要的作用。该文就DNA损伤修复、SUMO,96修饰系统及其二者关系的最新研究进展作了较为全面的介绍和总结。     

DNA修复的表观遗传学调控

表观遗传学信息的改变是导致人类肿瘤形成的重要因素之一．基因组的稳定性经常会受到DNA损伤的威胁．然而,高度致密的染色质结构却极大地妨碍了DNA修复的进行．因此,真核生物细胞中必须有一个精确的机制来克服染色质这一天然的屏障．其中,组蛋白的共价修饰和ATP-依赖的染色质重塑通过改变染色质的结构,对DNA修复进程起着关键的调控作用．介绍了DNA修复过程中,发生在表观遗传学方面的主要调控过程,特别阐述了在DNA双链断裂损伤应答和修复过程中,组蛋白修饰和染色质重塑方面最新的研究进展,并对今后的发展方向进行了讨论．     

DNA甲基化与基因表达调控研究进展

表观遗传修饰是指不改变DNA序列的、可遗传的对碱基和组蛋白的化学修饰,主要包括DNA甲基化、组蛋白修饰、染色质重塑以及非编码RNA等.表观遗传修饰是更高层次的基因表达调控手段.DNA甲基化是一种重要的表观遗传修饰,参与基因表达调控、基因印记、转座子沉默、X染色体失活以及癌症发生等重要生物学过程.近年来随着研究方法和技术的进步,全基因组DNA甲基化的研究广泛兴起,多个物种全基因组甲基化图谱被破译,全局水平对DNA甲基化的研究不仅利于在宏观层面上了解DNA甲基化的特性与规律,同时也为深入分析DNA甲基化的生物学功能与调控奠定了基础.结合最新研究进展综述DNA甲基化在基因组中的分布模式、规律以及和基因转录的关系等.     

植物组蛋白赖氨酸化修饰参与基因表达调控的机理

组蛋白共价修饰作为表观遗传修饰的重要部分,主要包括乙酰化和甲酰化、甲基化、磷酸化、泛素化和SUMO化等,它们形成一个复杂的网络共同调控基因的表达,其中组蛋白甲基化修饰成为研究的热点,甲基化主要发生在赖氨酸残基上。近年来,随着有关植物组蛋白赖氨酸甲基化修饰研究的不断深入,发现其通过改变自身赖氨酸残基的甲基化状态和甲基化程度,形成转录激活或者转录抑制标记,调控基因的表达,在植物开花和逆境胁迫的响应过程中起着至关重要的作用。H3组蛋白的赖氨酸甲基化修饰能够调控FLC基因和有关抗性基因的表达,具体表现为:H3K4的三甲基化促进FLC的表达,H3K27的三甲基化则抑制FLC的表达;H3K4me3作为转录激活标记,可激活PtdIns5P基因的表达,启动响应干旱的脂质合成信号通路,响应干旱胁迫;相反,H3K27me3作为一种转录抑制标记,低水平的H3K27me3诱导COR15A和ATGOLS3基因表达,它们分别编码叶绿体低温保护蛋白Cor15am和肌醇半乳糖合成酶GOLS,以抵抗寒冷胁迫。文章主要综述了植物组蛋白赖氨酸甲基化修饰参与DNA甲基化、开花过程以及应答逆境胁迫的分子机制。     

组蛋白H2B单泛素化参与DNA损伤修复的调控机制

作为一种重要的组蛋白修饰形式,H2B的单泛素化(uH2B)广泛地参与DNA复制、基因的表达与转录、DNA损伤修复及异染色质维持等生物学事件.在裂殖酵母中,H2B的单泛素化发生在其羧基端的119位赖氨酸(K119),并依赖于Rhp6/Bre1泛素连接酶复合体.研究表明,uH2B通过破坏H2A/H2B二聚体的结构促进mRNA在转录过程中的延伸,同时促进H3K4的三甲基化激活基因的表达及参与DNA损伤修复.本研究发现,Rhp6能够对核糖核苷酸还原酶抑制基因(Spd1)位点进行活跃的染色质修饰,促进H2B的单泛素化并抑制基因表达,从而促进dNTP的合成并调控DNA复制及损伤修复.重要的是,本研究发现,该过程不依赖于H3K4而决定于H3K9的三甲基化.同时uH2B直接在DNA双链断裂位点富集,通过改变染色质的结构参与DNA损伤修复,该过程中可能存在其他更为复杂的分子机制.     

DNA甲基化在细胞衰老中的作用

衰老是一种不可抗拒的生理现象,衰老过程伴随着复杂的生理生化改变,经常伴有一系列基因表达的变化。DNA甲基化作为哺乳动物细胞基因组修饰和表达调控的后遗传方式,在细胞的衰老过程中其总体水平降低,但同时又伴随着某些基因的高甲基化。衰老细胞的DNA甲基化改变可能是多种蛋白质参与的复杂过程。其甲基化模式与肿瘤细胞具有相似性,提示二者联系密切。     

非编码RNA与基因表达调控

近年来,随着对基因组的深入研究,发现真核生物中存在许多形态和功能各异的非编码RNA分子,这类RNA分子并不表达蛋白质,但它们在基因转录水平、转录后水平及翻译水平起了重要的调控作用。具有调控作用的RNA分子种类非常丰富,如长链非编码RNA(long non-coding RNA,lncRNA)、miRNA、PIWI相互作用RNA(PIWI-interacting RNA,piRNA)、内源性小干扰RNA(endogenous small interfering RNA,endo-siRNA)、竞争性内源RNA(competitive endogenous RNA,ceRNA)等,它们使基因表达过程更为丰富、严谨和有序。本文综述几类典型的非编码RNA对基因表达的调节作用,以助于理解细胞中RNA分子调节网络的功能和机制。     

Histone methyltransferase Dot1 and Rad9 inhibit single-stranded DNA accumulation at DSBs and uncapped telomeres

Cells respond to DNA double-strand breaks (DSBs) and uncapped telomeres by recruiting checkpoint and repair factors to the site of lesions. Single-stranded DNA (ssDNA) is an important intermediate in the repair of DSBs and is produced also at uncapped telomeres. Here, we provide evidence that binding of the checkpoint protein Rad9, through its Tudor domain, to methylated histone H3-K79 inhibits resection at DSBs and uncapped telomeres. Loss of DOT1 or mutations in RAD9 influence a Rad50-dependent nuclease, leading to more rapid accumulation of ssDNA, and faster activation of the critical checkpoint kinase, Mec1. Moreover, deletion of RAD9 or DOT1 partially bypasses the requirement for CDK1 in DSB resection. Interestingly, Dot1 contributes to checkpoint activation in response to low levels of telomere uncapping but is not essential with high levels of uncapping. We suggest that both Rad9 and histone H3 methylation allow transmission of the damage signal to checkpoint kinases, and keep resection of damaged DNA under control influencing, both positively and negatively, checkpoint cascades and contributing to a tightly controlled response to DNA damage.     

BRCA1和BRCA2与DNA损伤修复及转录调控

乳腺癌和卵巢癌敏感基因BRCA1和BRCA2与同源重组,DNA损伤修复,胚胎生长,转录调控及遍在蛋白化有关,其中,BRCA1和BRCA2在DNA损伤修复和转录调控中功能的确定,将有助于探讨和阐明两者的肿瘤抑制功能及其机理,作者将综述近年来有关BRCA1和BRCA2在DNA损伤修复和转录调控中功能研究的最新进展。     

Interplay between H3K36me3, methyltransferase SETD2, and mismatch recognition protein MutSα facilitates processing of oxidative DNA damage in human cells

Oxidative DNA damage contributes to aging and the pathogenesis of numerous human diseases including cancer. 8-hydroxyguanine (8-oxoG) is the major product of oxidative DNA lesions. Although OGG1-mediated base excision repair is the primary mechanism for 8-oxoG removal, DNA mismatch repair has also been implicated in processing oxidative DNA damage. However, the mechanism of the latter is not fully understood. Here, we treated human cells defective in various 8-oxoG repair factors with H₂O₂ and performed biochemical, live cell imaging, and chromatin immunoprecipitation sequencing analyses to determine their response to the treatment. We show that the mismatch repair processing of oxidative DNA damage involves cohesive interactions between mismatch recognition protein MutSα, histone mark H3K36me3, and H3K36 trimethyltransferase SETD2, which activates the ATM DNA damage signaling pathway. We found that cells depleted of MutSα or SETD2 accumulate 8-oxoG adducts and fail to trigger H₂O₂-induced ATM activation. Furthermore, we show that SETD2 physically interacts with both MutSα and ATM, which suggests a role for SETD2 in transducing DNA damage signals from lesion-bound MutSα to ATM. Consistently, MutSα and SETD2 are highly coenriched at oxidative damage sites. The data presented here support a model wherein MutSα, SETD2, ATM, and H3K36me3 constitute a positive feedback loop to help cells cope with oxidative DNA damage.     

SUMO化修饰与DNA损伤修复

由于体内外因素的影响,DNA损伤是生物生命周期中的常见现象,如果得不到及时的修复,DNA损伤的积累将导致基因组的不稳定及染色质的异常,并可能导致肿瘤的发生发展。SUMO化修饰是体内一个重要的蛋白质翻译后修饰,越来越多的研究发现SUMO化修饰与多个参与DNA损伤反应、维持基因组稳定的蛋白质相关,有可能参与肿瘤的发生。本文将阐述SUMO化修饰与DNA损伤修复的关系。     

甲基化修饰在细菌表观调控中的功能

为了适应复杂多变的生存环境,微生物通常需要在保证基因组序列不变的前提下不断调整胞内代谢网络。表观调控可以在不改变DNA序列的情况下对基因表达进行调控,因此成为细菌中重要的调控方式。作为一种DNA修饰,DNA甲基化修饰是生物体中最常见的表观调控工具。在本文中我们全面、深入解析了两种孤儿甲基转移酶:DNA腺嘌呤甲基转移酶(DNA adenine methyltransferase,Dam)和细胞周期调控甲基转移酶(Cell cycle-regulated methyltransferase,Ccr M)在原核生物中的表观调控功能。我们主要探讨了DNA甲基化参与的细胞生理过程包括DNA复制起始、DNA错配修复、基因表达调控、致病性和相变异等方面。同时,我们结合三维基因组研究技术基因组结构捕获(Chromosome conformation capture,3C)技术和新型DNA磷硫酰化修饰讨论了该领域的发展前景。     

Simulated microgravity decreases DNA repair capacity and induces DNA damage in human lymphocytes

The effect of simulated microgravity on DNA damage and apoptosis is still controversial. The objective of this study was to test whether simulated microgravity conditions affect the expression of genes for DNA repair and apoptosis. To achieve this objective, human lymphocyte cells were grown in a NASA‐developed rotating wall vessel (RWV) bioreactor that simulates microgravity. The same cell line was grown in parallel under normal gravitational conditions in culture flasks. The effect of microgravity on the expression of genes was measured by quantitative real‐time PCR while DNA damage was examined by comet assay. The result of this study revealed that exposure to simulated microgravity condition decreases the expression of DNA repair genes. Mismatch repair (MMR) class of DNA repair pathway were more susceptible to microgravity condition‐induced gene expression changes than base excision repair (BER) and nucleotide excision repair (NER) class of DNA repair genes. Downregulation of genes involved in cell proliferation (CyclinD1 and PCNA) and apoptosis (Bax) was also observed. Microgravity‐induced changes in the expression of some of these genes were further verified at the protein level by Western blot analysis. The findings of this study suggest that microgravity may induce alterations in the expression of these DNA repair genes resulting in accumulation of DNA damage. Reduced expression of cell‐cycle genes suggests that microgravity may cause a reduction in cell growth. Downregulation of pro‐apoptotic genes further suggests that extended exposure to microgravity may result in a reduction in the cells' ability to undergo apoptosis. Any resistance to apoptosis seen in cells with damaged DNA may eventually lead to malignant transformation of those cells. J. Cell. Biochem. 107: 723–731, 2009. © 2009 Wiley‐Liss, Inc.     

Triplex technology in studies of DNA damage, DNA repair, and mutagenesis

Triplex-forming oligonucleotides (TFOs) can bind to the major groove of homopurine-homopyrimidine stretches of double-stranded DNA in a sequence-specific manner through Hoogsteen hydrogen bonding to form DNA triplexes. TFOs by themselves or conjugated to reactive molecules can be used to direct sequence-specific DNA damage, which in turn results in the induction of several DNA metabolic activities. Triplex technology is highly utilized as a tool to study gene regulation, molecular mechanisms of DNA repair, recombination, and mutagenesis. In addition, TFO targeting of specific genes has been exploited in the development of therapeutic strategies to modulate DNA structure and function. In this review, we discuss advances made in studies of DNA damage, DNA repair, recombination, and mutagenesis by using triplex technology to target specific DNA sequences.