乳腺癌易感蛋白1在DNA损伤修复中的作用

人类乳腺癌易感基因1(breast cancer susceptibility gene 1,BRCA1)首先是在乳腺癌家族中发现的,是具有遗传倾向的乳腺癌和卵巢癌易感基因,其基因的突变与家族性乳腺癌及卵巢癌的发生有密切联系。BRCA1是一种抑癌基因,其基因产物可以参与维持基因组稳定性的多条细胞信号通路,例如DNA损伤诱导的细胞周期调控、DNA损伤修复、基因转录调节、细胞凋亡、泛素化等重要的细胞活动。本文就近几年来BRCA1在DNA损伤修复中的作用的研究进展作一综述,包括DNA损伤诱导的细胞周期检查点的激活和DNA损伤修复两方面。     

BRCA1蛋白参与DNA双链损伤应答

BRCA1是乳腺癌易感基因,负责维持细胞基因组的稳定性,防止调控细胞增殖和肿瘤生长的基因突变的积累。BRCA1基因蛋白产物结构复杂,功能多样,是细胞内重要的多功能蛋白,参与执行多种生理代谢过程。本主要探讨了BRCA1蛋白应答DNA双链损伤过程中所伴随的一系列信号传导的历程,阐述了连续的生理生化反应中BRCA1蛋白所发挥的作用。     

BRCA2的BRC4基元与RAD51相互作用位点的研究进展

乳腺癌易感基因2(breast cancer susceptibility gene 2,BRCA2),是人体内一种与乳腺、卵巢、胰腺等部位的肿瘤有关的抑癌基因。人的RAD51(h RAD51)是参与DNA同源重组修复过程的关键蛋白。BRCA2蛋白通过其结构中8个高度保守的BRC重复基元来调控h RAD51通过同源重组对DNA损伤进行的修复,从而阻止细胞癌变。在BRCA2的8个BRC重复基元中,BRC4与同源重组酶h RAD51的相互作用较为明显。综述了BRCA2的BRC4基元与h RAD51相互作用位点的研究进展,为了解BRCA2与RAD51相互作用的分子机理提供基础。     

BRCA1基因与乳腺癌

乳腺癌易感基因1(BRCA1)是具有遗传倾向的乳腺癌和卵巢癌的易感基因,且是一种抑癌基因.BRCA1基因的突变与家族性乳腺癌及它在细胞周期的调节,DNA损伤修复,基因的转录调控和诱导细胞凋亡方面起着重要作用.BRCA1基因的突变与家族性乳腺癌及卵巢癌的发生密切相关,对BRCA1分子功能的研究,将有利于阐明肿瘤发生的机理关.BRCA1的启动子甲基化与散发性乳腺癌有关.本文拟对BRCA1的结构,功能以及它的甲基化,突变,杂合性丢失对乳腺癌的影响作一综述.     

乳腺癌易感基因BRCA1的研究进展

BRCA1基因是目前发现的外显率最高的乳腺癌易感基因之,编码一个相对分子质量为220000的多功能核蛋白,作用于一系列维持基因组稳定性的细胞通路,包括DNA损伤修复、细胞周期检验点激活、蛋白泛素化、染色质重组,以及转录调控和凋亡等。BRCA1丢失将导致显著的遗传不稳定性和生长停滞。着重介绍近年来BRCA1基础研究方面的进展,并讨论BRCA1与乳腺癌的临床关联性。     

乳腺癌易感基因BRCA1研究进展

BRCA1是目前所发现的最重要的乳腺癌易感基因之一,它在DNA损伤修复,细胞周期调节,基因的转录激活,染色质稳定性,细胞增殖等方面都起着重要作用。该文着重介绍近几年来BRCA1基础研究方面的进展,并讨论BRCA1在肿瘤发生、发展过程的作用。为BRCA1在临床上的应用提供理论依据。     

BRCA1相互作用蛋白的分离及鉴定

乳腺癌易感基因(breast cancer susceptibility gene-1,BRCAl)在DNA损伤修复、细胞周期调控、染色质的稳定、基因转录激活以及细胞凋亡等方面起着重要作用。BRCAI C-末端是富含酸性氨基酸的转录激活结构域(AD),AD核心结构为两个串联的BRCT结构域(BRCTl和BRCT2)。应用酵母双杂交技术,以BRCT2为诱饵蛋白,从卵巢文库中筛选到了与BRCT2结构域相互作用蛋白FHL2(four and half LIM domains)。利用酵母交配的方法证明FHL2与BRCAlBRCT2特异结合,而不与BRCAl BRCTl、Rapl BRCT结构域结合。GST沉淀实验表明,FHL2在体外特异地与BRCT2结构域相结合;免疫共沉淀实验表明,FHL2在体内特异地与BRCT2结构域结合;FHL2可与全长BRCAl结合。BRCAl与FHL2相互作用的发现为研究BRCAl以及FHL2在肿瘤发生、发展中的作用打下了坚实的基础。     

乳腺癌与卵巢癌易感基因BRCA1和BRCA2

BRCA1和BRCA2是近年来发现的遗传性乳腺癌和卵巢癌易感基因,分别位于第17号和第13号染色体上。目前所知,两者与细胞周期调控、胚胎生 长发育、DNA损伤修复和转录调控等生命活动有关。随着BRCA1和BRCA2研究的不断深入和其确切生物学功能的阐明,将在临床上帮助早期诊断和有效治疗乳腺癌和卵巢癌患者。     

BRCA-1 基因与神经干细胞

乳腺癌易感基因(Breast cancer susceptibility gene,Brca-1)是肿瘤抑制基因家族中的一员,它是乳腺癌特异性抑癌基因,1994年Miki等[1]采用定位克隆方法首次将Brca-1分离出来。Brca-1能防止细胞过快地或失去控制地生长和分化,在调节细胞进程、DNA损伤修复、细胞生长与凋亡及转录活化和抑制等多种生物学途径都发挥重要作用,Korhonen等2003年报道Brca-1基因可促进体外培养的大鼠来源的神经干细胞的增殖。     

泛素E3连接酶接头蛋白SPOP和MDM2在DNA损伤修复中的作用

DNA损伤修复是维持细胞基因组稳定性和完整性的基础,越来越多的研究发现,E3泛素连接酶在DNA损伤修复中起着重要的作用.该文将介绍DNA损伤修复的机制、DNA损伤修复与疾病的关系、及E3泛素连接酶接头蛋白MDM2和SPOP在DNA损伤修复中的作用.重点围绕DNA损伤修复的两条通路:E3泛素连接酶接头蛋白SPOP与ATM...     

BRCA2 is ubiquitinated in vivo and interacts with USP11, a deubiquitinating enzyme that exhibits prosurvival function in the cellular response to DNA damage

Individuals carrying a germ line mutation of the breast cancer susceptibility gene BRCA2 are predisposed to breast, ovarian, and other types of cancer. The BRCA2 protein has been proposed to function in the repair of DNA double-strand breaks. Using an immunopurification-mass spectrometry approach to identify novel proteins that associate with the BRCA2 gene product, we found that a deubiquitinating enzyme, USP11, formed specific complexes with BRCA2. Moreover, BRCA2 was constitutively ubiquitinated in vivo in the absence of detectable proteasomal degradation. Mitomycin C (MMC) led to decreased BRCA2 protein levels associated with increased ubiquitination, consistent with proteasome-dependent degradation. While BRCA2 could be deubiquitinated by USP11 in transient overexpression assays, a catalytically inactive USP11 mutant had no effect on BRCA2 ubiquitination or protein levels. Antagonism of USP11 function either through expression of this mutant or through RNA interference increased cellular sensitivity to MMC in a BRCA2-dependent manner. All of these results imply that BRCA2 expression levels are regulated by ubiquitination in the cellular response to MMC-induced DNA damage and that USP11 participates in DNA damage repair functions within the BRCA2 pathway independently of BRCA2 deubiquitination.     

Emerging functions of BRCA2 in DNA recombination

Mutations in the breast cancer susceptibility protein BRCA2 cause inherited susceptibility to breast, ovarian and other cancers. There is now compelling experimental evidence that a major biological function of BRCA2 is the maintenance of chromosome structure stability in dividing cells by regulation of steps in recombination between homologous DNA strands. Recent experimental findings shape the current models for BRCA2 function, and structural and biochemical advances shed new light on the interactions between BRCA2, the RAD51 recombinase and single-stranded DNA during DNA recombination.     

Plasticity of BRCA2 function in homologous recombination: genetic interactions of the PALB2 and DNA binding domains

The breast cancer suppressor BRCA2 is essential for the maintenance of genomic integrity in mammalian cells through its role in DNA repair by homologous recombination (HR). Human BRCA2 is 3,418 amino acids and is comprised of multiple domains that interact with the RAD51 recombinase and other proteins as well as with DNA. To gain insight into the cellular function of BRCA2 in HR, we created fusions consisting of various BRCA2 domains and also introduced mutations into these domains to disrupt specific protein and DNA interactions. We find that a BRCA2 fusion peptide deleted for the DNA binding domain and active in HR is completely dependent on interaction with the PALB2 tumor suppressor for activity. Conversely, a BRCA2 fusion peptide deleted for the PALB2 binding domain is dependent on an intact DNA binding domain, providing a role for this conserved domain in vivo; mutagenesis suggests that both single-stranded and double-stranded DNA binding activities in the DNA binding domain are required for its activity. Given that PALB2 itself binds DNA, these results suggest alternative mechanisms to deliver RAD51 to DNA. In addition, the BRCA2 C terminus contains both RAD51-dependent and -independent activities which are essential to HR in some contexts. Finally, binding the small peptide DSS1 is essential for activity when its binding domain is present, but not when it is absent. Our results reveal functional redundancy within the BRCA2 protein and emphasize the plasticity of this large protein built for optimal HR function in mammalian cells. The occurrence of disease-causing mutations throughout BRCA2 suggests sub-optimal HR from a variety of domain modulations.     

Focus: 50 Years of DNA Repair: The Yale Symposium Reports: BRCA2: One Small Step for DNA Repair,One Giant Protein Purified

DNA damage, malfunctions in DNA repair, and genomic instability are processes that intersect at the crossroads of carcinogenesis. Underscoring the importance of DNA repair in breast and ovarian tumorigenesis is the familial inherited cancer predisposition gene BRCA2. The role of BRCA2 in DNA double-strand break repair was first revealed based on its interaction with RAD51, a central player in homologous recombination. The RAD51 protein forms a nucleoprotein filament on single-stranded DNA, invades a DNA duplex, and initiates a search for homology. Once a homologous DNA sequence is found, the DNA is used as a template for the high-fidelity repair of the DNA break. Many of the biochemical features that allow BRCA2 to choreograph the activities of RAD51 have been elucidated and include: targeting RAD51 to single-stranded DNA while inhibiting binding to dsDNA, reducing the ATPase activity of RAD51, and facilitating the displacement of the single-strand DNA binding protein, Replication Protein A. These reinforcing activities of BRCA2 culminate in the correct positioning of RAD51 onto a processed DNA double-strand break and initiate its faithful repair by homologous recombination. In this review, I will address current biochemical data concerning the BRCA2 protein and highlight unanswered questions regarding BRCA2 function in homologous recombination and cancer.     

Mediator of DNA damage checkpoint protein 1 regulates BRCA1 localization and phosphorylation in DNA damage checkpoint control

BRCA1 is a tumor suppressor involved in DNA repair and damage-induced checkpoint controls. In response to DNA damage, BRCA1 relocalizes to nuclear foci at the sites of DNA lesions. However, little is known about the regulation of BRCA1 relocalization following DNA damage. Here we show that mediator of DNA damage checkpoint protein 1 (MDC1), previously named NFBD1 or Kiaa0170, is a proximate mediator of DNA damage responses that regulates BRCA1 function. MDC1 regulates ataxia-telangiectasia-mutated (ATM)-dependent phosphorylation events at the site of DNA damage. Importantly down-regulation of MDC1 abolishes the relocalization and hyperphosphorylation of BRCA1 following DNA damage, which coincides with defective G(2)/M checkpoint control in response to DNA damage. Taken together these data suggest that MDC1 regulates BRCA1 function in DNA damage checkpoint control.     

Identification and functional characterization of a PP1-binding site in BRCA1

The phosphorylation state of the tumor suppressor protein BRCA1 is tightly associated with its functions including cell cycle control and DNA repair. Protein kinases involved in the DNA damage checkpoint control, such as ATM, ATR, and hCds1/Chk2, have been shown to phosphorylate and activate BRCA1 upon DNA damage. We reported previously that protein phosphatase 1alpha (PP1alpha) interacts with and dephosphorylates hCds1/Chk2-phosphorylated BRCA1. This study demonstrates the identification of a PP1-binding motif 898KVTF901 in BRCA1. Mutation or deletion of critical residues in this PP1-binding motif substantially reduces the interaction between BRCA1 and PP1alpha. PP1alpha can also dephosphorylate ATM and ATR phosphorylation sites in BRCA1 and may serve as a general regulator for BRCA1 phosphorylation. Unlike wild-type BRCA1, expression of the PP1 non-binding mutant BRCA1 protein in BRCA1-deficient cells failed to enhance survival after DNA damage. Taken together, these results suggest that interaction with PP1alpha is important for BRCA1 function.     

CCDC98 targets BRCA1 to DNA damage sites

Breast cancer-1 (BRCA1) participates in the DNA damage response. However, the mechanism by which BRCA1 is recruited to DNA damage sites remains elusive. Recently, we have demonstrated that a ubiquitin-binding protein, RAP80, is required for DNA damage-induced BRCA1 translocation. Here we identify another component, CCDC98, in the BRCA1-RAP80 complex. CCDC98 mediates BRCA1's association with RAP80. Moreover, CCDC98 controls both DNA damage-induced formation of BRCA1 foci and BRCA1-dependent G2/M checkpoint activation. Together, our results demonstrate that CCDC98 is a BRCA1 binding partner that mediates BRCA1 function in response to DNA damage.     

Control of BRCA2 cellular and clinical functions by a nuclear partner, PALB2

BRCA2 mutations predispose carriers to breast and ovarian cancer and can also cause other cancers and Fanconi anemia. BRCA2 acts as a "caretaker" of genome integrity by enabling homologous recombination (HR)-based, error-free DNA double-strand break repair (DSBR) and intra-S phase DNA damage checkpoint control. Described here is the identification of PALB2, a BRCA2 binding protein. PALB2 colocalizes with BRCA2 in nuclear foci, promotes its localization and stability in key nuclear structures (e.g., chromatin and nuclear matrix), and enables its recombinational repair and checkpoint functions. In addition, multiple, germline BRCA2 missense mutations identified in breast cancer patients but of heretofore unknown biological/clinical consequence appear to disrupt PALB2 binding and disable BRCA2 HR/DSBR function. Thus, PALB2 licenses key cellular biochemical properties of BRCA2 and ensures its tumor suppression function.