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。     

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.     

DNA损伤修复过程表观遗传学改变

多种化学、物理及生物因素可诱发细胞DNA损伤,损伤后DNA损伤位点被相关损伤感受器识别,激活相应的修复通路进行DNA修复。越来越多的证据表明DNA甲基化状态、蛋白翻译后修饰、染色质重塑、miRNA等修饰方式参与了DNA的损伤修复。文章通过不同损伤修复通路中这些修饰的特点,阐述表观遗传学改变在DNA损伤修复发展过程中的作用机制。     

PCNA泛素化修饰对DNA损伤应答途径的调控

机体细胞在多种化学物质和内外环境不断攻击下会诱发DNA损伤。为了维持基因组的稳定性,细胞内拥有一系列完善而精确的细胞应答机制来保护基因组DNA的完整性。细胞首先通过DNA损伤检测点,然后通过一系列细胞信号转导通路,启动细胞周期阻滞,进而介导细胞修复或凋亡。大量研究表明泛素化作为一种重要的蛋白质翻译后修饰方式,参与调控了多种细胞生理过程。近期研究表明,DNA损伤导致复制应激可诱发PCNA的翻译后泛素化修饰,泛素化修饰的PCNA可能参与了多种DNA损伤应激过程,影响细胞选择不同的DNA损伤应答途径,导致细胞截然不同的转归。因此,更好地了解PCNA泛素化的作用及其影响DNA损伤应答通路可为我们更深入地了解人类细胞如何调控异常的DNA代谢过程和癌症的发生和发展机制提供依据。     

PCNA泛素化修饰对DNA损伤应答途径的调控

机体细胞在多种化学物质和内外环境不断攻击下会诱发DNA损伤。为了维持基因组的稳定性,细胞内拥有一系列完善而精确的细胞应答机制来保护基因组DNA的完整性。细胞首先通过DNA损伤检测点,然后通过一系列细胞信号转导通路,启动细胞周期阻滞,进而介导细胞修复或凋亡。大量研究表明泛素化作为一种重要的蛋白质翻译后修饰方式,参与调控了多种细胞生理过程。近期研究表明,DNA损伤导致复制应激可诱发PCNA的翻译后泛素化修饰,泛素化修饰的PCNA可能参与了多种DNA损伤应激过程,影响细胞选择不同的DNA损伤应答途径,导致细胞截然不同的转归。因此,更好地了解PCNA泛素化的作用及其影响DNA损伤应答通路可为我们更深入地了解人类细胞如何调控异常的DNA代谢过程和癌症的发生和发展机制提供依据。     

泛素化与SUMO化对DNA损伤应答的调控作用

蛋白质翻译后修饰是实现蛋白质多样化功能的一种重要的调控方式,泛素化和SUMO化作为重要的蛋白质翻译后修饰在转录调节、染色质结构及基因组稳定性维持以及DNA修复中扮演重要角色。由于泛素(ubiquitin,Ub)、小泛素相关修饰物(small ubiquitin-related modifier,SUMO)都是修饰目标蛋白质上的赖氨酸,因此在通常情况下,二者对于同一个蛋白质的翻译后修饰存在拮抗或协同作用,但具体调控机理目前研究还不多。DNA损伤与肿瘤的发生发展密切相关。DNA损伤若未能得到及时修复或者修复过程中出现异常,将会导致肿瘤的发生,甚至会产生致死型突变。近年来,对于DNA损伤修复过程中涉及到的蛋白质翻译后修饰的研究已成为研究热点。本文旨在阐明泛素化、SUMO化对DNA损伤修复过程中关键因子的调控作用,为了解多种翻译后修饰对DNA修复过程的调控提供新视角。     

蛋白质SUMO化修饰与肿瘤调控

SUMO化修饰是一种重要的蛋白质翻译后修饰方式,在细胞周期调控、细胞代谢、基因转录、DNA损伤和修复等众多细胞生物学过程中,对底物蛋白质的表达、定位和活性进行调控。蛋白质SUMO化修饰是动态可逆的过程,去SUMO化修饰由SUMO特异性蛋白酶(SENPs)家族成员所催化。由于受到SUMO化修饰的底物蛋白种类众多、功能多样,SUMO化修饰能够在整体和特定蛋白质修饰层面,参与调控肿瘤的发生发展,并且这种调控机制非常复杂,比如调控细胞周期的进程、DNA损伤和基因组不稳定性、肿瘤代谢与生长、抗肿瘤免疫等。SENPs家族成员是底物蛋白质SUMO化修饰程度的决定者,该研究团队对SENPs家族成员在肿瘤中的作用开展了系列研究,因此该文也将以SENP1和SENP3为例,对SENPs在肿瘤进程中的作用及其作用机制展开介绍。     

拟南芥多聚ADP核糖水解酶在ATM和ATR依赖的DNA损伤信号途径中的作用分析

DNA损伤响应是生物体感知DNA断裂并启动DNA修复过程的重要机制,对维护遗传物质的稳定性具有重要的意义.DNA损伤响应机制中有多种蛋白的参与.多聚ADP核糖水解酶(PARG)是参与蛋白质多聚ADP核糖化(poly(ADP-ribosyl)ation)修饰调控过程的一种重要酶,它通过水解去除蛋白质上的多聚ADP核糖来调节靶蛋白质的生理生化活性.目前已知多聚ADP核糖修饰相关蛋白可能通过修饰DNA修复相关蛋白参与DNA损伤反应,但其影响的信号途径和上下游关系并不清楚.本研究通过双突变体构建、遗传以及表达谱分析,揭示了PARG1可能在DNA损伤响应途径关键激酶ATM和ATR的上游,通过调节ATM和ATR的活性来反馈调节DNA损伤信号途径.     

SUMO化修饰在核受体功能调控中的作用

小泛素相关修饰蛋白(small ubiquitin related modifier,SUMO)修饰作用是蛋白质翻译后修饰的重要方式。SUMO化修饰与泛素化作用极为相似,并且在某些靶蛋白上可以与泛素竞争结合位点,从而起到稳定靶蛋白的作用,并参与调节靶蛋白的细胞定位、膜离子通道功能、DNA损伤修复以及转录活性等。核受体是一类在生物体内广泛分布的、配体依赖的转录因子超家族,参与机体生长发育、细胞分化,以及体内许多生理、病理过程中的基因表达调控。最近研究发现,核受体的SU-MO修饰可通过影响核受体的稳定性、转录活性、亚细胞定位等多重途径影响核受体的功能,并影响机体炎症反应及相关疾病的发生发展。本文对核受体的SUMO修饰在核受体功能调控中的作用,以及与机体相关疾病之间的关系做一简要综述。     

一种新型SUMO E3连接酶CBX4的化学修饰作用

多梳蛋白家族（polycomb group proteins,PcG）是一类在染色质水平上通过表观遗传修饰抑制靶基因转录的调节因子,它在调节细胞周期、DNA修复、细胞分化、衰老和死亡中起到重要作用。CBX4作为PcG家族中唯一具有SUMO E3 连接酶活性的成员,可以作用于多种底物,包括HIPK2、SIP1、CtBP、CTCF、Dnmt3a和HIF-1α等。底物的SUMO化修饰依赖于特定的结构基础,而且SUMO化的底物功能也会相应发生改变。同时,CBX4还可以被其它分子,如HIPK2, SENP2等进行磷酸化以及去SUMO化等修饰。本篇综述详细阐述了CBX4对底物的SUMO化修饰、自身被修饰及其生物学功能的变化。     

SUMOylation and PARylation cooperate to recruit and stabilize SLX4 at DNA damage sites

SUMOylation plays important roles in the DNA damage response. However, whether it is important for interstrand crosslink repair remains unknown. We report that the SLX4 nuclease scaffold protein is regulated by SUMOylation. We have identified three SUMO interaction motifs (SIMs) in SLX4, mutating all of which abrogated the binding of SLX4 to SUMO-2 and covalent SLX4 SUMOylation. An SLX4 mutant lacking functional SIMs is not recruited to PML nuclear bodies nor stabilized at laser-induced DNA damage sites. Additionally, we elucidated a novel role for PARylation in the recruitment of SLX4 to sites of DNA damage. Combined, our results uncover how SLX4 is regulated by post-translational modifications.     

SUMOylation of Nuclear γ-Actin by SUMO2 supports DNA Damage Repair against Myocardial Ischemia-Reperfusion Injury

Myocardial infarction triggers oxidative DNA damage, apoptosis and adverse cardiac remodeling in the heart. Small ubiquitin-like modifier (SUMO) proteins mediate post-translational SUMOylation of the cardiac proteins in response to oxidative stress signals. Upregulation of isoform SUMO2 could attenuate myocardial injury via increasing protein SUMOylation. The present study aimed to discover the identity and cardioprotective activities of SUMOylated proteins. A plasmid vector for expressing N-Strep-SUMO2 protein was generated and introduced into H9c2 rat cardiomyocytes. The SUMOylated proteins were isolated with Strep-Tactin^® agarose beads and identified by MALDI-TOF-MS technology. As a result, γ-actin was identified from a predominant protein band of ~42 kDa and verified by Western blotting. The roles of SUMO2 and γ-actin SUMOylation were subsequently determined in a mouse model of myocardial infarction induced by ligating left anterior descending coronary artery and H9c2 cells challenged by hypoxia-reoxygenation. In vitro lentiviral-mediated SUMO2 expression in H9c2 cells were used to explore the role of SUMOylation of γ-actin. SUMOylation of γ-actin by SUMO2 was proven to be a new cardioprotective mechanism from the following aspects: 1) SUMO2 overexpression reduced the number of TUNEL positive cells, the levels of 8-OHdG and p-γ-H2ax while promoted the nuclear deposition of γ-actin in mouse model and H9c2 cell model of myocardial infarction; 2) SUMO-2 silencing decreased the levels of nuclear γ-actin and SUMOylation while exacerbated DNA damage; 3) Mutated γ-actin (K⁶⁸R/K²⁸⁴R) void of SUMOylation sites failed to protect cardiomyocytes against hypoxia-reoxygenation challenge. The present study suggested that SUMO2 upregulation promoted DNA damage repair and attenuated myocardial injury via increasing SUMOylation of γ-actin in the cell nucleus.     

Ku70 is stabilized by increased cellular SUMO

Ku70 is a protein that finds itself at the heart of several important cellular processes. It is essential to the non-homologous end joining pathway as a part of the DNA-end binding complex, required for proper maintenance of telomeres and contributes to DNA damage recognition and regulation of apoptosis. Forces that regulate Ku70 are therefore likely to have large consequences on the physiologic state of the cell. We report here that transient expression of the small protein SUMO resulted in a dramatic increase in the abundance of Ku70. Surprisingly, the direct SUMOylation of Ku70 does not appear to be required for this effect. Rather, Ku70 appears to be stabilized through indirect effects on the rate of degradation. The same outcome was obtained by raising the expression of enzymes that promote SUMOylation. It is likely that many other proteins will be similarly regulated, providing a general control of cellular state.     

The ADP-ribosyltransferase PARP10/ARTD10 Interacts with Proliferating Cell Nuclear Antigen (PCNA) and Is Required for DNA Damage Tolerance

All cells rely on genomic stability mechanisms to protect against DNA alterations. PCNA is a master regulator of DNA replication and S-phase-coupled repair. PCNA post-translational modifications by ubiquitination and SUMOylation dictate how cells stabilize and re-start replication forks stalled at sites of damaged DNA. PCNA mono-ubiquitination recruits low fidelity DNA polymerases to promote error-prone replication across DNA lesions. Here, we identify the mono-ADP-ribosyltransferase PARP10/ARTD10 as a novel PCNA binding partner. PARP10 knockdown results in genomic instability and DNA damage hypersensitivity. Importantly, we show that PARP10 binding to PCNA is required for translesion DNA synthesis. Our work identifies a novel PCNA-linked mechanism for genome protection, centered on post-translational modification by mono-ADP-ribosylation.     

The SUMO (Small Ubiquitin-like Modifier) Ligase PIAS3 Primes ATR for Checkpoint Activation

The maintenance of genomic stability relies on the concerted action of DNA repair and DNA damage signaling pathways. The PIAS (protein inhibitor of activated STAT) family of SUMO (small ubiquitin-like modifier) ligases has been implicated in DNA repair, but whether it plays a role in DNA damage signaling is still unclear. Here, we show that the PIAS3 SUMO ligase is important for activation of the ATR (ataxia telangiectasia and Rad3 related)-regulated DNA damage signaling pathway. PIAS3 is the only member of the PIAS family that is indispensable for ATR activation. In response to different types of DNA damage and replication stress, PIAS3 plays multiple roles in ATR activation. In cells treated with camptothecin (CPT), PIAS3 contributes to formation of DNA double-stranded breaks. In UV (ultraviolet light)- or HU (hydroxyurea)-treated cells, PIAS3 is required for efficient ATR autophosphorylation, one of the earliest events during ATR activation. Although PIAS3 is dispensable for ATRIP (ATR-interacting protein) SUMOylation and the ATR-ATRIP interaction, it is required for maintaining the basal kinase activity of ATR prior to DNA damage. In the absence of PIAS3, ATR fails to display normal kinase activity after DNA damage, which accompanies with reduced phosphorylation of ATR substrates. Together, these results suggest that PIAS3 primes ATR for checkpoint activation by sustaining its basal kinase activity, revealing a new function of the PIAS family in DNA damage signaling.     

SUMOylation and de-SUMOylation in response to DNA damage

To maintain genomic integrity, a cell must utilize multiple mechanisms to protect its DNA from the damage generated by environmental agents or DNA metabolism. SUMO (small ubiquitin-like modifier) can regulate protein stability, protein cellular location, and protein-protein interactions. In this review, we summarize the current understanding of the roles of SUMOylation and de-SUMOylation in DNA damage response (DDR) and DNA repair with a specific focus on the role of RPA SUMOylation in homologous recombination (HR).     

Spatiotemporal regulation of posttranslational modifications in the DNA damage response

A timely and accurate cellular response to DNA damage requires tight regulation of the action of DNA damage response (DDR) proteins at lesions. A multitude of posttranslational modifications (PTMs) of chromatin and chromatin‐associated proteins coordinates the recruitment of critical proteins that dictate the appropriate DNA repair pathway and enable the actual repair of lesions. Phosphorylation, ubiquitylation, SUMOylation, neddylation, poly(ADP‐ribosyl)ation, acetylation, and methylation are among the DNA damage‐induced PTMs that have taken center stage as important DDR regulators. Redundant and multivalent interactions of DDR proteins with PTMs may not only be a means to facilitate efficient relocalization, but also a feature that allows high temporal and spatial resolution of protein recruitment to, and extraction from, DNA damage sites. In this review, we will focus on the complex interplay between such PTMs, and discuss the importance of their interconnectivity in coding DNA lesions and maintaining the integrity of the genome.     

Mechanism and function of DNA replication‐independent DNA‐protein crosslink repair via the SUMO‐RNF4 pathway

DNA‐protein crosslinks (DPCs) obstruct essential DNA transactions, posing a serious threat to genome stability and functionality. DPCs are proteolytically processed in a ubiquitin‐ and DNA replication‐dependent manner by SPRTN and the proteasome but can also be resolved via targeted SUMOylation. However, the mechanistic basis of SUMO‐mediated DPC resolution and its interplay with replication‐coupled DPC repair remain unclear. Here, we show that the SUMO‐targeted ubiquitin ligase RNF4 defines a major pathway for ubiquitylation and proteasomal clearance of SUMOylated DPCs in the absence of DNA replication. Importantly, SUMO modifications of DPCs neither stimulate nor inhibit their rapid DNA replication‐coupled proteolysis. Instead, DPC SUMOylation provides a critical salvage mechanism to remove DPCs formed after DNA replication, as DPCs on duplex DNA do not activate interphase DNA damage checkpoints. Consequently, in the absence of the SUMO‐RNF4 pathway cells are able to enter mitosis with a high load of unresolved DPCs, leading to defective chromosome segregation and cell death. Collectively, these findings provide mechanistic insights into SUMO‐driven pathways underlying replication‐independent DPC resolution and highlight their critical importance in maintaining chromosome stability and cellular fitness.     

TOPORS-mediated RAD51 SUMOylation facilitates homologous recombination repair

Homologous recombination (HR) is critical for error-free repair of DNA double-strand breaks. Chromatin loading of RAD51, a key protein that mediates the recombination, is a crucial step in the execution of the HR repair. Here, we present evidence that SUMOylation of RAD51 is crucial for the RAD51 recruitment to chromatin and HR repair. We found that topoisomerase 1-binding arginine/serine-rich protein (TOPORS) induces the SUMOylation of RAD51 at lysine residues 57 and 70 in response to DNA damaging agents. The SUMOylation was facilitated by an ATM-induced phosphorylation of TOPORS at threonine 515 upon DNA damage. Knockdown of TOPORS or expression of SUMOylation-deficient RAD51 mutants caused reduction in supporting normal RAD51 functions during the HR repair, suggesting the physiological importance of the modification. We found that the SUMOylation-deficient RAD51 reduces the association with its crucial binding partner BRCA2, explaining its deficiency in supporting the HR repair. These findings altogether demonstrate a crucial role for TOPORS-mediated RAD51 SUMOylation in promoting HR repair and genomic maintenance.     

The implication of the SUMOylation pathway in breast cancer pathogenesis and treatment

Abstract

Breast cancer is the most commonly diagnosed malignancy in woman worldwide, and is the second most common cause of death in developed countries. The transformation of a normal cell into a malignant derivate requires the acquisition of diverse genomic and proteomic changes, including enzymatic post-translational modifications (PTMs) on key proteins encompassing critical cell signaling events. PTMs occur on proteins after translation, and regulate several aspects of proteins activity, including their localization, activation and turnover. Deregulation of PTMs can potentially lead to tumorigenesis, and several de-regulated PTM pathways contribute to abnormal cell proliferation during breast tumorigenesis. SUMOylation is a PTM that plays a pivotal role in numerous aspects of cell physiology, including cell cycle regulation, protein trafficking and turnover, and DNA damage repair. Consistently with this, the deregulation of the SUMO pathway is observed in different human pathologies, including breast cancer. In this review we will describe the role of SUMOylation in breast tumorigenesis and its implication for breast cancer therapy.