Shen, MR; Jones, IM; Mohrenweiser, H; et al.

Variation in DNA repair is a factor in cancer susceptibility: A paradigm for the promises and perils of individual and population risk estimation?

Mohrenweiser, HW; Jones, IM

Polymorphisms of DNA repair geneXRCC1in squamous cell carcinoma of the head and neck

Sturgis, EM; Castillo, EJ; Li, L; et al.

DNA損傷修復基本方式的研究進展

朱守民，夏昭林

（復旦大學公共衛(wèi)生學院勞動衛(wèi)生學教研室，上海 200032）

螺旋藻多糖對核酸內(nèi)切酶活性和DNA修復合成的增強作用

龐啟深，郭寶江，阮繼紅

熱點追蹤

DNA修復

·編者按·

DNA修復（DNA repair）是細胞對DNA受損傷后的一種反應，這種反應可能使DNA結構恢復原樣，重新執(zhí)行它原來的功能；但有時并非能完全消除DNA的損傷，只是使細胞能夠耐受DNA的損傷而能繼續(xù)生存。也許這未能完全修復而存留下來的損傷會在適合的條件下顯示出來（如細胞的癌變等），但如果細胞不具備這修復功能，就無法對付經(jīng)常發(fā)生的DNA損傷事件，甚至不能生存。DNA持續(xù)受到來自環(huán)境的攻擊，但它們的結構完整程度卻出人意料。托馬斯·林達爾（Tomas Lindahl）、保羅·莫德里奇（Paul Modrich）以及阿齊茲·桑賈爾（Aziz Sancar）因為描述并解釋了細胞修復DNA的機制以及對遺傳信息的保護措施，而被授予了2015年的諾貝爾化學獎。

DNA損傷可分為內(nèi)源性損傷（endogenous）和外源性損傷（exogenous）兩大類型。其中，內(nèi)源性損傷一般是指被正常代謝的副產(chǎn)物活性氧分子（自由基）攻擊導致的損傷（自發(fā)突變）；外源性損傷則是由外部因素引起的損傷，這些外部因素包括來自太陽的紫外射線（UV 200～300 nm）、其他頻率的輻射、水解和熱解、某些植物毒素、人造的突變物質以及腫瘤的化學療法和放射線療法等。

由于DNA損害來源無法避免，細胞就必須對這些DNA損害的形式采取適當?shù)拇胧?。對一個細胞來說，消極的做法是暫時容忍損害的存在，等到細胞的基因體受損到一定程度，細胞自然無法再持續(xù)進行運作；而積極的做法則是針對所有可能的DNA損害發(fā)展出相對應的修復補救措施，以確?；蝮w內(nèi)遺傳訊息的正確性。根據(jù)分子生物學近幾年來的研究發(fā)展，科學家已經(jīng)發(fā)現(xiàn)從以單細胞形式存活的酵母菌到人類的細胞，都可以找到相對應的DNA修復機制，這說明DNA修復機制在各物種間的高度保守性，更充分顯示了DNA損害所造成的危害，在生物演化初期就無可避免。

在現(xiàn)存細胞內(nèi)的DNA修復機制中，由DNA損害斷裂的程度可以分為兩種類型，一種是單鏈損害，另一種則是DNA雙鏈斷裂。前者修復機制通常需要借助其對應的另一條DNA鏈當模板，而后者在缺乏另一條DNA序列當模板的情況下，則是轉而透過同源的染色體序列或姊妹染色單體來尋求支持。在高等生物中，有時候DNA雙鏈斷裂的修復有可能無須任何序列當模板，而徑行將斷裂部分直接接合，然而這種DNA修復方式可能隱含錯誤的機率。DNA損傷修復的3種基本方式分別是堿基切除修復（base excision repair，BER）、核苷酸切除修復（nucleotide excision repair，NER）和錯配修復（mismatch repair，MMR）。

研究DNA修復也是探索生命的一個重要方面，在軍事醫(yī)學、腫瘤學等研究中有著廣泛的應用前景。

本專題得到了黃德軍副教授（蘭州大學生命科學學院）的大力支持。

·熱點數(shù)據(jù)排行·

截至2015年10月20日，中國知網(wǎng)（CNKI）和Web of Science（WOS）的數(shù)據(jù)報告顯示，以“DNA修復”為詞條檢索到的期刊文獻分別為1075與7648條，本專題將相關數(shù)據(jù)按照：研究機構發(fā)文數(shù)、作者發(fā)文數(shù)、期刊發(fā)文數(shù)、被引用頻次進行排行，結果如下。

研究機構發(fā)文數(shù)量排名（CNKI）

研究機構發(fā)文數(shù)量排名（WOS）

作者發(fā)文數(shù)量排名（CNKI）

作者發(fā)文數(shù)量排名（WOS）

期刊發(fā)文數(shù)量排名（CNKI）

期刊發(fā)文數(shù)量排名（WOS）

根據(jù)中國知網(wǎng)（CNKI）數(shù)據(jù)報告，以“DNA修復”為詞條檢索到的高被引論文排行結果如下。

國內(nèi)數(shù)據(jù)庫高被引論文排行

根據(jù)Web of Science統(tǒng)計數(shù)據(jù)，以“DNA修復”為詞條檢索到的高被引論文排行結果如下。

國外數(shù)據(jù)庫高被引論文排行

·經(jīng)典文獻推薦·

基于Web of Science檢索結果，利用Histcite軟件選取LCS（Local Citation Score，本地引用次數(shù)）TOP 30文獻作為節(jié)點進行分析，得到本領域推薦的經(jīng)典文獻如下。

本領域經(jīng)典文獻

來源出版物：Cancer Research, 1996, 56(18): 4103-4107

Nonconservative amino acid substitution variants exist at polymorphic frequency in DNA repair genes in healthy humans

Shen, MR; Jones, IM; Mohrenweiser, H; et al.

Abstract:The removal or repair of DNA damage has a key role in protecting the genome of the cell from the insults of cancer-causingagents, This was originally demonstrated in individuals with the rare genetic disease xeroderma pigmentosum, the paradigm of cancer genes, and subsequently in the relationship between mismatch repair and colon cancer, Recent reports suggest that individuals with less dramatic reductions in the capacity to repair DNA damage are observed at polymorphic frequency in the population; these individuals have an increased susceptibility to breast, lung, and skin cancer. We report initial results from a study to estimate the extent of DNA sequence variation among individuals in genes encoding proteins of the DNA repair pathways, Nine different amino acid substitution variants have been identified in resequencing of the exons of three nucleotide excision repair genes (ERCC1,XPD, andXPF), a gene involved in double-strand break repair/recombination genes (XRCC3), and a gene functioning in base excision repair and the repair of radiation-induced damage (XRCC1), The frequencies for the nine different variant alleles range from 0.04 to 0.45 in a group of 12 healthy individuals; the average allele frequency is 0.17, The potential that this variation, and especially the six nonconservative amino acid substitutions occurring at residues that are identical in human and mouse, may cause reductions in DNA repair capacity or the fidelity of DNA repair is intriguing; the role of the variants as cancer risk factors or susceptibility alleles remains to be addressed.

來源出版物：Cancer Research, 1998, 58(4): 604-608

Variation in DNA repair is a factor in cancer susceptibility: A paradigm for the promises and perils of individual and population risk estimation?

Mohrenweiser, HW; Jones, IM

Abstract:The repair of DNA damage protects the genome of the cell from the insults of cancer causing agents. This was originally demonstrated in individuals with the rare genetic disease, xeroderma pigmentosum, the prototype of cancer genes, and subsequently in the relationship of mismatch repair to colon cancer. Recent studies suggest that individuals with less dramatic reductions in the capacity to repair DNA damage are observed at polymorphic frequency and these individuals have an increased susceptibility to several types of cancer. Screening of individuals for DNA sequence variation in the exons of 9 DNA repair genes has resulted in identification of 15 different polymorphic amino acid substitution variants. Although the studies to relate these variants to reduced DNA repair capacity and cancer status have not been completed, the available information is sufficient to suggest that DNA repair genes should be incorporated into molecular epidemiology and cancer susceptibility studies. The availability of molecular epidemiology data presents exciting opportunities for refinement of risk estimation models and identification of individuals at increased risk of disease, with resultant opportunities for effective surveillance and early intervention and treatment. The opportunities to acquire susceptibility data are associated with possible perils for establishment of regulations for permissible exposures to carcinogenic agents and also stigmatization of 'at risk' individuals that may result in decreased access to employment opportunities and health care.

來源出版物：Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, 1998, 400(1): 15-24

Polymorphisms of DNA repair geneXRCC1in squamous cell carcinoma of the head and neck

Sturgis, EM; Castillo, EJ; Li, L; et al.

Abstract:Because reduced DNA repair capacity (phenotype) has been suggested as a risk factor for squamous cell carcinoma of the head and neck (SCCHN), newly-identified DNA repair gene polymorphisms (genotype) may also be implicated in risk. To test this hypothesis, we conducted a case-control study of 203 SCCHN patients and 424 control subjects (matched for age, sex and ethnicity) to investigate the role of twoXRCC1polymorphisms (XRCC126304 T andXRCC128152 A, respectively) in SCCHN. Multivariate logistic regression analysis was performed to calculate the adjusted odds ratio (OR) and 95% confidence interval (CI), A total of 180 cases (88.7%) and 363 controls (85.6%) lacked theXRCC126304 T allele [adjusted OR=1.34 (CI, 0.80-2.25)]. Lack of this polymorphism was a significant risk factor specifically for cancers of the oral cavity and pharynx [adjusted OR=2.46 (CI, 1.22-4.97)]. Thirty-two cases (15.8%) and 46 controls (10.8%) were homozygous for theXRCC128152 A allele [adjusted OR=1.59 (CI, 0.97-2.61) for all cases, and 1.41 (CI, 0.80-2.48) for oral and pharyngeal cancer only]. Furthermore, when the two genotypes were combined into a three-level model of risk, a polymorphismpolymorphism interaction of increasing risk (trend test,P=0.049) was evident: OR=1.0 for those with neither risk genotype (referent group), adjusted OR=1.51 (CI, 0.87-2.61) for those with either risk genotype, and 2.02 (CI, 1.00-4.05) for those with both risk genotypes, For oral and pharyngeal cancer, this trend was even more pronounced with the adjusted OR=2.68 (CI, 1.28-5.61) for those with either risk genotype, and 3.22 (CI, 1.33-7.81) for those with both risk genotypes, The findings support the hypothesis that a polymorphicXRCC1DNA repair gene contributes to risk of developing SCCHN.

來源出版物：Carcinogenesis, 1999, 20(11): 2125-2129

·推薦綜述·

DNA損傷修復基本方式的研究進展

朱守民，夏昭林

（復旦大學公共衛(wèi)生學院勞動衛(wèi)生學教研室，上海 200032）

1997年10月，美國國立環(huán)境衛(wèi)生科學研究所（NIEHS）提出環(huán)境基因組計劃，闡明基因和環(huán)境對疾病的影響和它們之間的相互作用，列舉了11大類共76種再測序的環(huán)境應答基因，DNA修復基因被列為第一位，其中21種DNA修復酶基因被列為重點研究對象[1]。人類基因與其它物種的基因的功能均是編碼遺傳信息從而保護其完整性。DNA修復酶始終監(jiān)視染色體并修復癌基因和細胞化學物所致的核苷酸殘基的破壞，若沒有DNA修復，那么由多種多樣的DNA損傷因素所引起的染色體不穩(wěn)定性將對細胞和生物體產(chǎn)生致命的影響。

本文分別闡述了DNA損傷修復3種基本方式，即堿基切除修復（base excision repair，BER）、核苷酸切除修復（nucleotide excision repair，NER）和錯配修復（mismatch repair，MMR），并討論DNA鏈斷裂的重組和重接合修復及DNA聚合酶繞道修復DNA損傷。

1 堿基切除修復

堿基切除修復是指切除和替換由內(nèi)源性化學物作用產(chǎn)生的DNA堿基損傷，DNA糖基化酶參與此過程，隨后糖-磷酸鍵斷裂，切去堿基殘基，DNA鏈連接修復損傷。有3種不同的核DNA糖基化酶參與修復氧化作用產(chǎn)生的DNA損傷，還有1種主要切除烷基化嘌呤。已發(fā)現(xiàn)的DNA糖基化酶中的4種均可切除DNA上的尿嘧啶。尿嘧啶糖基化酶上的Ala被Tyr147取代，或Cys、Ser、Asn204取代Asp（外顯子5），尿嘧啶糖基化酶轉變?yōu)榘奏ぬ腔富蛐叵汆奏ぬ腔?，尿嘧啶糖基化酶選擇性降低，可誤切除去正常的嘧啶，出現(xiàn)突變型細胞[2]，其中第3外顯子點突變可導致編碼子143錯意突變，導致神經(jīng)膠質瘤發(fā)生[3]。

O6-甲基鳥嘌呤-DNA甲基轉移酶（O6-methylguanine-DNAmethy l transferase，MGMT）可同時發(fā)揮轉移酶和甲基接受體的作用，是DNA損傷修復的重要的酶，將甲基從O6-甲基鳥嘌呤轉移到自身的半胱氨酸殘基上，使DNA鏈上的鳥嘌呤復原，同時自身不可逆的失活，目前還沒有發(fā)現(xiàn)其它蛋白質參與此過程。它可切除甲基和其它小的烷基，對保護細胞免受烷化劑損害、防止細胞癌變和死亡起重要作用。神經(jīng)膠質瘤的MGMT啟動子甲基化可抑制其表達。由于MGMT存在于體內(nèi)多個組織中，DNA烷基化損傷導致的致突變、致癌效應并沒有組織特異性，當正常DNA修復功能變化時，人體內(nèi)各種器官組織都有可能發(fā)生突變的積累，腫瘤的易感性升高[4]。已發(fā)現(xiàn)DNA修復基因表達變異如MGMT和MSH6是起源上漸成的。神經(jīng)膠質瘤MGMT啟動子甲基化抑制其表達，烷化劑治療后表達增加。人類基因組研究使確定啟動子區(qū)域成為可能，進而可研究CpG島的DNA甲基化情況[3]。

X線修復交叉互補基團1（x-ray repair crosscomplementing group 1，XRCC1）和DNA聚合酶β、DNA連接酶Ⅲ相互作用，共同參與堿基切除修復。對XRCC1基團的分析顯示，有3個會導致氨基酸發(fā)生變化的基因多態(tài)性分別發(fā)生在密碼子194，280，399位[8]，其中尤以399位值得引起重視，399位密碼子位于PARP [poly (ADP-ribose) polymerase]的結合閾-BRCT-1上，而許多有BRCT閾的蛋白質參與細胞周期和DNA損傷修復[6]。有研究表明DNA修復能力和XRCC1399Arg-Gln基因表型的變化有關[7]。另外Arg194和399Arg-Gln多態(tài)與吸煙有交互作用，需進行流行病學調(diào)查和功能研究以確定XRCC1在腫瘤發(fā)生中的重要作用[8]。雖然報道了許多DNA修復基因的多態(tài)性，但因此出現(xiàn)的氨基酸改變的功能等信息卻很少。發(fā)現(xiàn)確實影響蛋白質功能的多態(tài)，然后進行流行病學和臨床研究是很重要的，例如特殊的多態(tài)純合體的DNA連接酶亞單位XRCC1在吸煙者中姐妹染色體交換的頻率較高，表明該等位基因對煙草和年齡等DNA損傷因素有較高的風險。需進一步拓展有關多態(tài)的生物作用的研究[9]。

許多生物體具光裂解酶，修復由紫外線誘導的環(huán)丁烷嘧啶二聚體和光產(chǎn)物等的損傷。人類基因組2個CRT基因具相同的光裂解酶序列，編碼與生理節(jié)奏有關的藍光受體而與DNA損傷修復無關。人類基因中沒發(fā)現(xiàn)DNA光裂解酶的其它同源基因，這與以往認為脊椎動物包括魚、爬行動物及有袋類哺乳動物廣泛存在，而有胎盤的哺乳動物并不廣泛存在光裂解酶是一致的。

2 核苷酸切除修復

核苷酸切除修復主要切除由環(huán)境因素作用產(chǎn)生的大的加合物。人有精密的核苷酸切除修復基因，它至少有4種核苷酸切除修復因子可連接DNA損傷位點，有兩種切開鏈的DNA螺旋酶，切口則由核苷酸酶連接。

著色性干皮病基因C（xeroderma pigmentosum pomplementary group C，XPC）其等位基因XPC、XPC-PAT+突變，XPC-PAT+/-和XPC-PAT+/+基因型顯著增加了患頭頸部鱗狀細胞癌的風險，DNA修復基因多態(tài)性可致其修復功能改變，故推測遺傳性DNA修復基因多態(tài)性可增加癌癥的遺傳易感性[10]。暴露于內(nèi)源性或外源性的致癌因素或遺傳毒物可引起細胞周期延遲，影響細胞DNA損傷修復。XPC的內(nèi)含子9與外顯子15單核苷酸多態(tài)連接失衡，導致氨基酸改變，改變的XPC蛋白連接HR23B形成復合物，作用可能是激活NER損傷的早期識別因子[11]。另外發(fā)現(xiàn)XPC雜合子與純合子相比，轉錄和蛋白表達沒發(fā)現(xiàn)數(shù)量明顯改變，提示存在可能的監(jiān)視XPC蛋白表達水平的機制[12]。

著色性干皮病基因D（xeroderma pigmentosum complementary group D，XPD）是ATP依賴的5′→3′解旋酶，可編碼核苷酸切除修復成分，可切除由香煙煙霧導致的DNA加合物，一個有關鱗狀細胞癌的病例—對照研究表明，312和751位點多態(tài)可增加與吸煙有關的鱗狀細胞肺癌的發(fā)病風險[13]。非西班牙裔白種美國人XPD的23047和23051位點的突變與頭頸部鱗狀細胞癌（SCCHN）無關，提示從復雜的修復過程中識別由單一基因的單一位點突變導致的DNA修復能力微弱的改變是很困難的，需進行重組過程的蛋白結構和體外功能研究。XPD參與核苷酸切除修復及P53介導的凋亡反應，其312和751位點具多態(tài)，研究表明312位點進化上高度保守，在維持XPD蛋白功能上起一定作用；而751Gln位于XPD蛋白的N端，保守性差，可作為反映DNA修復能力的指標[14]。

科凱恩綜合征（Cockayne syndrome，CS）等位基因CSB 發(fā)生突變，導致單氨基酸改變，使C-端2/3蛋白質失活；缺乏CSB基因，不能修復UV照射導致的基因損傷，是科克因綜合征發(fā)生的原因[15]。轉錄相關的修復過程已知與CSA、CSB 和XAB的產(chǎn)物有關，且轉錄鏈修復速度快于非轉錄鏈，但轉錄修復的機制還不很清楚，需進一步研究揭示參與的其它物質。

X線修復交叉互補基因（x-ray repair cross-complementing group 3，XRCC3）是Rad-51蛋白家族的成員。XRCC3 241位點多態(tài)導致表達氨基酸改變，影響DNA修復能力[16]。其外顯子7（18067位點）T等位基因與黑色素瘤的發(fā)生明顯相關[17]，此基因編碼參與雙鏈DNA同源重組修復，可修復染色體斷裂、異位和缺失，在抑制UV誘導的腫瘤的發(fā)生過程起一定作用。

3 錯配修復

錯配修復可校正DNA復制和重組過程中非同源染色體偶爾出現(xiàn)的DNA堿基錯配。錯配的堿基可被錯配修復酶識別后進行修復，人DNA鏈識別基因定位于DNA復制復合物或是其它未了解的因子，DNA雙鍵斷裂可能通過同源或非同源重組的方式修復。實驗證實MMR缺失的細胞對烷基化化療藥物有較高的耐受性。

遺傳性非息肉型結腸癌（hereditary nonpolyposis colorectal cancer，HNPCC），與DNA的錯配修復基因突變有關，特別是hMSH2和hMLH1基因易發(fā)生突變[18]，HNPCC患者MMR基因hMSH2、hMSH1、pMSH1和pMSH2遺傳缺陷，使結腸癌潛伏期縮短為3～5年，而正常人為20～30年。hMSH2的5′端大約4.4 kb內(nèi)富含CpG島，并有許多參與表達的成分，但在轉錄起始位點附近沒有TATA盒，為許多看家基因啟動子典型結構。缺失分析發(fā)現(xiàn)少于300 bp的堿基足以引發(fā)轉錄，該區(qū)聚集Alu序列和單核苷酸重復序列，并有兩個轉錄起始位點。此區(qū)域內(nèi)發(fā)現(xiàn)一個多態(tài)位點，雖然沒發(fā)現(xiàn)此區(qū)域多態(tài)影響啟動子功能，但可作為檢測等位基因缺失的標志[19]。

DNA雙鍵斷裂可能通過同源或非同源重組的方式修復。值得注意的是，人類至少有7種編碼蛋白質的基因[1]。人類細胞同源重組可能包括分枝轉移酶和分解酶，后者與細菌RuvABC系統(tǒng)功能相似。近來的生化實驗支持分枝轉移和分解酶的存在，但仍未發(fā)現(xiàn)相應的基因產(chǎn)物。

4 其他

對不同人群進行的研究顯示，不同位點的基因表型的分布存在種族和地區(qū)的差異，提示遺傳差異性的存在及基因和環(huán)境的相互作用，值得進一步研究[20]。DNA修復系統(tǒng)在維持機體的遺傳穩(wěn)定性方面起關鍵作用，它可以逆轉由機體內(nèi)外環(huán)境因素所致的DNA突變。一些修復基因的某些位點的多態(tài)性會導致DNA修復能力的改變，致使某些疾病發(fā)生的危險性增加。DNA修復基因是一類易感性基因，其多態(tài)性為人群中普遍存在的現(xiàn)象，對人群中腫瘤發(fā)生的影響較大。XRCC1、XRCC3、XPD是3種常見的DNA修復基因，分別參與不同的DNA修復途徑，在一定程度上可反映機體的DNA修復能力，但僅僅單一基因的點突變不能決定吸煙者的肺癌易感性[16]。

人類基因組研究發(fā)現(xiàn)許多以前未識別的DNA聚合酶。人類現(xiàn)在至少有15種DNA聚合酶，多于其它物種[1]。修復核DNA時，BER主要使用的酶為Polβ而NER和MMR分別為Polδ和Polε。遺傳與生化研究闡明了新發(fā)現(xiàn)的聚合酶在DNA損傷時的功能。隨著新的生化分析方法應用于修復研究的不同方面，將發(fā)現(xiàn)新基因例如可修復兩條DNA鏈間交聯(lián)的新的基因。天然化學物及用于癌癥治療的藥物以及電磁和紫外輻射均可導致鏈內(nèi)交聯(lián)，修復這種交聯(lián)需NER基因和與重組有關的XRCC2和XRCC3，并猜測DNA聚合酶POLQ也參與其中，另外對范科尼貧血個體（FA）敏感細胞的研究指出，F(xiàn)ANC基因組在交換修復中起一定的作用。但鏈內(nèi)交聯(lián)修復機制仍不清楚[3]。

目前注意力多集中于探明細胞損傷信號傳遞到細胞周期檢查點的機制和控制細胞凋亡的監(jiān)視系統(tǒng)的研究。近來研究這一復雜的網(wǎng)絡已取得了一定的進展，它包括損傷識別因子、蛋白激酶、轉錄因子如p53[21]。已經(jīng)嘗試獲取DNA修復組成圖中起信號作用的部分，這是一個令人感興趣的方向，一些人類遺傳病由于缺乏與損傷識別有關的功能（如ATM）而對DNA損傷因素敏感。

·高被引論文摘要·

被引頻次：101

螺旋藻多糖對核酸內(nèi)切酶活性和DNA修復合成的增強作用

龐啟深，郭寶江，阮繼紅

本文用核酸內(nèi)切酶實驗和放射自顯影術研究了螺旋藻水溶性多糖對DNA切除修復的效應。結果表明，該多糖能顯著增強輻射引起DNA損傷的切除修復活性和程序外DNA合成（UDS）?？疾烨谐迯偷臅r程，發(fā)現(xiàn)螺旋藻多糖的存在不但能加快損傷DNA切除反應和UDS的初時速度，而且能延緩以上兩個重要修復反應的飽和。

螺旋藻；多糖；內(nèi)切酶活性；DNA修復合成

來源出版物：遺傳學報, 1988, 15(5): 374-374

被引頻次：86

北京地區(qū)漢族人群DNA修復基因XPD單核苷酸多態(tài)性與肺癌及食管癌風險的研究

邢德印，齊軍，譚文，等

摘要：功能化DNA修復氯化1-（2-羥乙基）-3-甲基咪唑鹽是纖維素的新型良溶劑，在70℃時微晶纖維素的溶解能力達到5%～7%。向DNA修復纖維素溶液中加入去離子水可獲得再生纖維素。用XRD，F(xiàn)T-IR和TGA對再生纖維素進行了表征，IR和XRD數(shù)據(jù)表明，功能化DNA修復是纖維素的直接溶劑，但TGA數(shù)據(jù)則表明再生纖維素的熱穩(wěn)定性有所降低，熱失重殘留物有所增加。對溶解機理進行了初步討論。

關鍵詞：肺癌；食管癌；XPD基因；遺傳多態(tài)性

來源出版物：中華醫(yī)學遺傳學雜志, 2003, 20(1): 35-38

被引頻次：85

中國人DNA修復基因XRCC1單核苷酸多態(tài)及其與食管癌風險的關系

宋春英，譚文，林東昕

摘要：目的：研究堿基切除修復基因XRCC1單核苷酸多態(tài)與食管癌易感性的關系?方法：以PCR-RFLP方法分析了食管癌病例（n=222）和按性別、年齡頻數(shù)配對的正常對照者（n=433）XRCC1基因C26304T和G28152A多態(tài)，并比較不同基因型與食管癌風險的關系以及基因多態(tài)與吸煙之間的交互作用對食管癌風險的影響。結果：在食管癌病人中XRCC126304TT變異基因型頻率為12.6%，高于對照組的6.7%（P＜0.05）；攜帶此種基因型個體發(fā)生食管癌的風險比攜帶其他基因型者高1.8倍（校正的OR=1.83，95%CI1.03～3.24）?G28152A基因型頻率在對照組和病例組中的分布無顯著性差異（P＞0.05），因而與食管癌風險無關。XRCC1基因這兩個位點多態(tài)之間沒有聯(lián)合作用，但26304TT基因型與吸煙之間有一定的協(xié)同作用，在吸煙與否和吸煙量兩個層次，26304TT基因型均與之有聯(lián)合作用而增高食管癌風險。結論：DNA堿基切除修復基因XRCC1多態(tài)可能在食管癌的發(fā)生過程中起一定作用。

關鍵詞：XRCC1基因；DNA修復；食管腫瘤；基因多態(tài)；分子流行病學

來源出版物：癌癥, 2001, 20(1): 28-31

被引頻次：84

甘草甜素抑制致癌過程中對DNA損傷修復的影響

嚴瑞琪，李俊麗，黃玫玲，等

摘要：本文檢測外周淋巴細胞非程序DNA合成（UDS），探討甘草甜素（GL）在抑制二乙基亞硝胺（DEN）致肝癌前病變發(fā)生過程中，對DNA損傷修復的影響。結果顯示：大鼠腹腔注射DEN（100 mg/kg）后5小時，UDS值（168.5±36.5cpm/5×105LC）顯著低于正常大鼠（226.7±47.0）（P＜0.05）；在加用GL的影響下，UDS值（212.3±69.2）顯著提高，與正常者相接近（P＞0.05）。在注射DEN后4周，肝癌前病變的發(fā)生受到GL抑制，同時UDS值（501.0±140.0）也顯著高于不用GL者（367.0±36.3）（P＜0.01），而與正常者（606.8±83.85）無明顯差別（P＞0.05）。提示GL抑制DEN致肝癌作用與GL保護DNA損傷修復有關。

關鍵詞：甘草甜素；二乙基亞硝胺（DEN）；非程序DNA合成

來源出版物：癌癥: 英文版, 1995, 14(4): 245-248

被引頻次：81

增殖細胞核抗原（PCNA）的分子結構及其生物學功能研究進展

宋楠萌，桑建利，徐恒，等

摘要：增殖細胞核抗原（PCNA）是真核生物復制復合體的核心成分，具有特殊的環(huán)狀三級結構。作為真核細胞DNA聚合酶δ的推動因子，與不同復制相關蛋白結合，協(xié)調(diào)DNA復制過程。同時PCNA還作為功能轉換因子，通過不同調(diào)控方式與多種細胞因子作用，參與了DNA損傷修復、細胞周期調(diào)控及凋亡等許多重要的細胞事件。另外作為細胞增殖的指標，PCNA與腫瘤等細胞增殖性疾病的發(fā)生和發(fā)展存在相關性，因此在臨床上對PCNA的深入研究有重要意義。文中就PCNA的“功能性”結構及其在不同細胞事件中的功能轉換（Function Switch）進行簡要綜述。

關鍵詞：PCNA功能轉換；PCNA結合區(qū)域；細胞周期；DNA復制；DNA修復

來源出版物：自然科學進展, 2006, 16(10): 1201-1209

被引頻次：80

乳寧沖劑對乳腺增生病神經(jīng)內(nèi)分泌免疫網(wǎng)絡及淋巴細胞DNA修復功能調(diào)節(jié)作用的觀察

闕華發(fā)，陳紅風，陸德銘，等

摘要：目的：探討乳寧沖劑治療乳腺增生病臨床療效和作用機制，闡明乳腺增生病的發(fā)病機理。方法：對187例乳腺增生病患者分別采用乳寧沖劑（147例）和三苯氧胺（40例）治療，療程均為3個月，觀察兩組臨床療效及治療前后神經(jīng)遞質、內(nèi)分泌激素，T細胞亞群和淋巴細胞DNA損傷修復功能的變化。結果：乳腺增生病患者存在去甲腎上腺素（NE）、催乳素（PRL）、T輔助及誘導細胞（OKT4+）、T抑制或細胞毒細胞（OKT+8）異常升高（P＜0.01），孕酮（P）、睪酮（T）、總T細胞（OKT+3）、OKT+4 /OKT+8、淋巴細胞DNA損傷修復能力（UDS）值明顯低下（P＜0.05，P＜0.01），5 -色胺（5 -HT）、腎上腺素（E）、雌二醇（E2）、卵泡刺激素（FSH）、黃體生成素（LH）呈分泌紊亂狀態(tài)，乳寧沖劑對此有明顯的調(diào)整作用。通過與三苯氧胺組對比觀察，結果顯示乳寧沖劑組臨床痊愈率優(yōu)于三苯氧胺組（P＜0.05），其調(diào)節(jié)5 -HT/NE、E2/P、T、OKT+3作用亦優(yōu)于三苯氧胺組（P＜0.05），并且在治療過程中未發(fā)現(xiàn)明顯毒副作用。結論：乳腺增生病的發(fā)生是以神經(jīng)內(nèi)分泌免疫網(wǎng)絡功能失調(diào)或紊亂為中心的多因素共同作用的結果；乳寧沖劑治療乳腺增生病有良好療效的重要機制可能在于從整體上多環(huán)節(jié)、多途徑、多層次的調(diào)整了失調(diào)或紊亂的神經(jīng)內(nèi)分泌免疫網(wǎng)絡狀態(tài)，提高了機體內(nèi)環(huán)境的穩(wěn)定能力。

關鍵詞：乳腺增生??；神經(jīng)內(nèi)分泌免疫網(wǎng)絡；DNA修復功能；乳寧沖劑

來源出版物：中國中西醫(yī)結合雜志, 1999, 19(9): 529-532

被引頻次：60

DNA修復基因XPD多態(tài)性和肝細胞肝癌危險性的病例-對照研究

許麗，吳一遷，金晏，等

摘要：目的：探討DNA修復基因XPD多態(tài)性和肝細胞肝癌（Hepatocellular carcinoma，HCC）發(fā)生的關系。方法：應用病例-對照研究方法，選擇了江蘇啟東地區(qū)72例HCC患者以及137例正常對照，以年齡（±3歲）和性別為配對因素進行了配對，對XPD-751位點基因多態(tài)性作PCR-RFLP分析。結果：XPD-751位點的Gln/Lys或Gln/Gln基因型的發(fā)生頻率在病例組中明顯高于對照組，差別有顯著性（OR= 3.13，95%CI= 1.16～8.47），在調(diào)整了HBV感染因素后，差別的顯著性雖然消失，但可信限下限位于臨界處（OR= 2.70，95%CI= 0.98～7.42）。對HBV感染患者并同時伴有XPD-751位點為Gln/Lys或Gln/Gln基因型的個體，其HCC發(fā)生的危險性是HBV陰性及XPD-751位點為Lys/Lys野生型基因型個體的6.68倍，差別有顯著性（OR= 6.68，95%CI=3.4313.01）。結論：本次研究的結果首次應用病例-對照研究發(fā)現(xiàn)XPD-751位點基因多態(tài)性可能影響HCC的發(fā)生，同時指出XPD-751位點基因多態(tài)性和HBV感染之間可能存在基因）環(huán)境交互作用。

關鍵詞：肝腫瘤/流行病學；癌，肝細胞；病例-對照研究；DNA修復；XPD基因；遺傳多態(tài)性

來源出版物：腫瘤, 2004, 24(6): 526-529

被引頻次：60

DNA斷裂檢測方法——單細胞凝膠電泳法

秦椿華，沈建英，黃仕和，等

摘要：單細胞凝膠電泳（single cell gel electrophoresis assay, SCGE）也叫彗星試驗（comet assay），是一種快速、敏感、簡便、廉價的檢測單個哺乳動物細胞DNA斷裂的技術，目前已用于檢測氧化、紫外線和電離輻射引起的損傷，以及三氯乙烷、丙烯酞胺等化學物及老化、吸煙所致?lián)p害的研究。文章介紹SCGE的發(fā)展、檢測分析方法、原理及其在DNA損傷與修復、生物監(jiān)測、遺傳毒理研究、腫瘤治療方案優(yōu)化和療效研究方面的應用前景。

關鍵詞：DNA斷裂；單細胞凝膠電泳；DNA損傷；DNA修復；腫瘤治療

來源出版物：生物化學與生物物理進展, 1995, 22(6): 517-520

被引頻次：55

DNA損傷修復基因XRCC1和XPD遺傳多態(tài)與晚期非小細胞肺癌對鉑類藥物的敏感性

袁芃，繆小平，張雪梅，等

摘要：目的：探討DNA損傷修復基因XRCC1和XPD的遺傳多態(tài)與晚期非小細胞肺癌（NSCLC）對以鉑類為主化療藥物敏感性的關系。方法：以聚合酶鏈反應（PCR）結合限制性片段長度多態(tài)性（RFLP），檢測200例以順鉑（DDP）或卡鉑（CBP）為主要化療方案的NSCLC患者XRCC1Arg194Trp和XPDLys751Gln多態(tài)基因型，并比較不同基因型與化療敏感性的關系。結果化療總有效（CR+PR）率為36.0%，其中CR1例，PR71例，SD94例，PD34例。攜帶XRCC1第194位密碼子Arg/Trp或Trp/Trp基因型的個體化療敏感性是XRCC1第194位密碼子Arg/Arg基因型攜帶者的2.48倍（95%CI為1.36～4.51，P=0.003）；未發(fā)現(xiàn)XPDLys751Gln多態(tài)與化療敏感性的相關性。聯(lián)合分析這兩個遺傳多態(tài)發(fā)現(xiàn)，XRCC1Arg194Trp和XPDLys751Gln多態(tài)在NSCLC對鉑類藥物敏感性中存在一定的聯(lián)合作用（趨勢檢驗，P=0.004）。結論：XRCC1Arg194Trp和XPDLys 751Gln遺傳多態(tài)可能與NSCLC鉑類藥物敏感性有關。

關鍵詞：基因遺傳變異；XRCC1；XPD；非小細胞肺癌；化療敏感性

來源出版物：中華腫瘤雜志, 2006, 28(3): 196-199

被引頻次：53

DNA損傷修復與鉑類耐藥研究進展

林莉，劉曉晴，宋三泰

摘要：鉑類是非小細胞肺癌化療的基本藥物，它的耐藥機制復雜，其中DNA損傷修復能力改變是鉑類耐藥的重要分子基礎。全文綜述DNA損傷修復機制——堿基切除修復、核苷酸切除修復、酶修復及DNA雙鏈斷裂修復等研究進展。

關鍵詞：DNA損傷；耐藥；修復；XPD；ERCC1

來源出版物：中國腫瘤, 2006, 15(1): 29-31

被引頻次：1765

Targeting the DNA repair defect in BRCA mutant cells as a therapeutic strategy

Farmer, H; McCabe, N; Lord, CJ; et al.

Abstract:BRCA1 and BRCA2 are important for DNA double-strand break repair by homologous recombination, and mutations in these genes predispose to breast and other cancers. Poly(ADP-ribose) polymerase (PARP) is an enzyme involved in base excision repair, a key pathway in the repair of DNA single-strand breaks. We show here that BRCA1 or BRCA2 dysfunction unexpectedly and profoundly sensitizes cells to the inhibition of PARP enzymatic activity, resulting in chromosomal instability, cell cycle arrest and subsequent apoptosis. This seems to be because the inhibition of PARP leads to the persistence of DNA lesions normally repaired by homologous recombination. These results illustrate how different pathways cooperate to repair damage, and suggest that the targeted inhibition of particular DNA repair pathways may allow the design of specific and less toxic therapies for cancer.

來源出版物：Nature, 2005, 434(7035): 917-921

被引頻次：1671

Mutation in the DNA mismatch repair gene homolog hmlh1 is associated with hereditary nonpolyposis colon-cancer

Bronner, CE; Baker, SM; Morrison, PT; et al.

Abstract:The human DNA mismatch repair gene homologue, hMSH2, on chromosome 2p is involved in hereditary non-polyposis colon cancer (HNPCC). On the basis of linkage data, a second HNPCC locus was assigned to chromosome 3p21-23 (ref. 3). Here we report that ahuman gene encoding a protein, hMLH1 (human MutL homologue), homologous to the bacterial DNA mismatch repair protein MutL, is located on human chromosome 3p21.3-23. We propose that hMLH1 is the HNPCC gene located on 3p because of the similarity of the hMLH1 gene product to the yeast DNA mismatch repair protein, MLH1, the coincident location of the hMLH1 gene and the HNPCC locus on chromosome 3, and hMLH1 missense mutations in affected individuals from a chromosome 3-linked HNPCC family.

來源出版物：Nature, 1994, 368(6468): 258-261

被引頻次：1217

RAD6-dependent DNA repair is linked to modification of PCNA by ubiquitin and SUMO

Hoege, C; Pfander, B; Moldovan, GL; et al.

Abstract:TheRAD6pathway is central to post-replicative DNA repair in eukaryotic cells; however, the machinery and its regulation remain poorly understood. Two principal elements of this pathway are the ubiquitin-conjugating enzymesRAD6and the MMS2-UBC13 heterodimer, which are recruited to chromatin by the RING-finger proteins RAD18 and RAD5, respectively. Here we show that UBC9, a small ubiquitin-related modifier (SUMO)-conjugating enzyme, is also affiliated with this pathway and that proliferating cell nuclear antigen (PCNA)-a DNA-polymerase sliding clamp involved in DNA synthesis and repair-is a substrate. PCNA is monoubiquitinated throughRAD6and RAD18, modified by lysine-63-linked multi-ubiquitination-which additionally requires MMS2, UBC13 and RAD5-and is conjugated to SUMO by UBC9. All three modifications affect the same lysine residue of PCNA, suggesting that they label PCNA for alternative functions. We demonstrate that these modifications differentially affect resistance to DNA damage, and that damage-induced PCNA ubiquitination is elementary for DNA repair and occurs at the same conserved residue in yeast and humans.

來源出版物：Nature, 2002, 419(6903): 135-141

被引頻次：1058

Inactivation of the DNA-repair gene MGMT and the clinical response of gliomas to alkylating agents

Esteller, M; Garcia-Foncillas, J; Andion, E; et al.

Abstract:Background: The DNA-repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) inhibits the killing of tumor cells by alkylating agents.MGMTactivity is controlled by a promoter; methylation of the promoter silences the gene in cancer, and the cells no longer produce MGMT. We examined gliomas to determine whether methylation of theMGMTpromoter is related to the responsiveness of the tumor to alkylating agents. Methods: We analyzed theMGMTpromoter in tumor DNA by a methylation-specific polymerase-chainreaction assay. The gliomas were obtained from patients who had been treated with carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea, or BCNU). The molecular data were correlated with the clinical outcome. Results: The MGMT promoter was methylated in gliomas from 19 of 47 patients (40 percent). This finding was associated with regression of the tumor and prolonged overall and disease-free survival. It was an independent and stronger prognostic factor than age, stage, tumor grade, or performance status. Conclusions: Methylation of theMGMTpromoter in gliomas is a useful predictor of the responsiveness of the tumors to alkylating agents.

來源出版物：New England Journal of Medicine, 2000, 343(19): 1350-1354

被引頻次：1000

DNA-repair in an active gene - Removal of pyrimidine dimers from the dhfr gene of cho cells is much more efficient than in the genome overall

Bohr, VA; Smith, CA; Okumoto, DS; et al.

Abstract:DNA repair was measured in the dihydrofolate reductase gene in Chinese hamster ovary cells, amplified for the gene, by quantitating pyrimidine dimers with a specific UV-endonuclease. More than two thirds of the dimers had been removed from a 14.1 kb restriction fragment of the gene by 26 hr after irradiation (20 J/m2), while little removal was detected in fragments upstream of the gene and only 15% were removed from the genome overall. This suggests that damage processing can vary according to function or activity of affected sequences, which has general implications for correlations of DNA repair with survival and mutagenesis. Perhaps preferential repair of vital sequences facilitates UV-resistance of these cells despite low overall repair levels.

來源出版物：Cell, 1985, 40(2): 359-369

被引頻次：975

DNA repair byERCC1in non-small-cell lung cancer and cisplatin-based adjuvant chemotherapy

Olaussen, KA; Dunant, A; Fouret, P; et al.

Abstract:Background: Adjuvant cisplatin-based chemotherapy improves survival among patients with completely resected non-small-celllung cancer, but there is no validated clinical or biologic predictor of the benefit of chemotherapy. Methods: We used immunohistochemical analysis to determine the expression of the excision repair cross-complementation group 1 (ERCC1) protein in operative specimens of non-small-cell lung cancer. The patients had been enrolled in the International Adjuvant Lung Cancer Trial, thereby allowing a comparison of the effect of adjuvant cisplatin-based chemotherapy on survival, according toERCC1expression. Overall survival was analyzed with a Cox model adjusted for clinical and pathological factors. Results: Among 761 tumors,ERCC1expression was positive in 335 (44%) and negative in 426 (56%). A benefit from cisplatin-based adjuvant chemotherapy was associated with the absence ofERCC1(test for interaction,P=0.009). Adjuvant chemotherapy, as compared with observation, significantly prolonged survival among patients withERCC1-negative tumors (adjusted hazard ratio for death, 0.65; 95% confidence interval [CI], 0.50 to 0.86;P=0.002) but not among patients withERCC1-positive tumors (adjusted hazard ratio for death, 1.14; 95%CI, 0.84 to 1.55;P=0.40). Among patients who did not receive adjuvant chemotherapy, those withERCC1-positive tumors survived longer than those withERCC1-negative tumors (adjusted hazard ratio for death, 0.66; 95%CI, 0.49 to 0.90;P=0.009). Conclusions: Patients with completely resected non-small-cell lung cancer andERCC1-negative tumors appear to benefit from adjuvant cisplatin-based chemotherapy, whereas patients withERCC1-positive tumors do not.

來源出版物：New England Journal of Medicine, 2006, 355(10): 983-991

被引頻次：892

(ADP-ribose)nparticipates in DNA excision repair

Anthony, JL; Maginn, EJ; Brennecke, JF

Abstract:Chromatin proteins are covalently modified by at least five different processes; in no case has the precise physiological function been established. One of these post-synthetic, covalent modifications is effected by the enzyme poly(ADP–ribose) polymerase, which uses the coenzyme NAD+to ADP–ribosylate chromatin proteins. The modification consists largely of mono(ADP–ribose), but long, homopolymer chains of (ADP–ribose) are also present. Various physiological functions have been suggested for (ADP–ribose)n. Here we demonstrate that one function of (ADP–ribose)nis to participate in the cellular recovery from DNA damage. Specific inhibitors of poly(ADP–ribose) polymerase prevent rejoining of DNA strand breaks caused by dimethyl sulphate and cytotoxicity is enhanced thereby. The rejoining of strand breaks is prevented also by nutritionally depleting the cells of NAD.

來源出版物：Nature, 2002, 283(5747): 593-596

被引頻次：841

Destabilization of tracts of simple repetitive DNA in yeast by mutations affecting DNA mismatch repair

Strand, M; Prolla, TA; Liskay, RM; et al.

Abstract:The genomes of all eukaryotes contain tracts of DNA in which a single base or a small number of bases is repeated. Expansions of such tracts have been associated with several human disorders including the fragile X syndrome1. In addition, simple repeats are unstable in certain forms of colorectal cancer, suggesting a defect in DNA replication or repair. We show here that mutations in any three yeast genes involved in DNA mismatch repair (PMS1,MLH1andMSH2) lead to 100- to 700-fold increases in tract instability, whereas mutations that eliminate the proof-reading function of DNA polymerases have little effect. The meiotic stability of the tracts is similar to the mitotic stability. Th results suggest that tract instability is associated with DNA polymerases slipping during replication, and that some types of colorectal cancer may reflect mutations in genes involved in DNA mismatch repair.

來源出版物: Nature, 1993, 365(6443): 274-276

被引頻次：804

Inactivation of the DNA repair gene O6-methylguanine-DNAmethyltransferaseby promoter hypermethylation is a common event in primary human neoplasia

Esteller, M; Hamilton, SR; Burger, PC; et al.

Abstract:The DNA repair protein O6-methylguanine DNA methyltransferase (MGMT) removes alkyl adducts from the O6position of guanine. MGMT expression is decreased in some tumor tissues, and lack of activity has been observed in some cell lines. Loss of expression is rarely due to deletion, mutation, or rearrangement of theMGMTgene, but methylation of discrete regions of the CpG island ofMGMThas been associated with the silencing of the gene in cell lines. We used methylation-specific PCR to study the promoter methylation of theMGMTgene. All normal tissues and expressing cancer cell lines were unmethylated, whereas nonexpressing cancer cell lines were methylated. Among the more than 500 primary human tumors examined,MGMThypermethylation was present in a subset of specific types of cancer. In gliomas and colorectal carcinomas, aberrant methylation was detected in 40% of the tumors, whereas innon-small cell lung carcinomas, lymphomas, and head and neck carcinomas, this alteration was found in 25% of the tumors.MGMTmethylation was found rarely or not at all in other tumor types. We also analyzed MGMT expression by immunohistochemistry in relation to the methylation status in 31 primary tumors. The presence of aberrant hypermethylation was associated with loss of MGMT protein, in contrast to retention of protein in the majority of tumors without aberrant hypermethylation. Our results suggest that epigenetic inactivation ofMGMTplays an important role in primary human neoplasia.

來源出版物：Cancer Research, 1999, 59(4): 793-797

被引頻次：777

Redox activation of Fos-Jun DNA binding activity is mediated by a DNA repair enzymeXanthoudakis, S; Miao, G; Wang, F; et al.

Abstract:The DNA binding activity of Fos and Jun is regulated in vitro by a post-translational mechanism involving reduction-oxidation. Redox regulation occurs through a conserved cysteine residue located in the DNA binding domain of Fos and Jun. Reduction of this residue by chemical reducing agents or by a ubiquitous nuclear redox factor (Ref-1) recently purified from Hela cells, stimulates AP-1 DNA binding activity in vitro, whereas oxidation or chemical modification of the cysteine has an inhibitory effect on DNA binding activity. Here we demonstrate that the protein product of the ref-1 gene stimulates the DNA binding activity of Fos-Jun heterodimers, Jun-Jun homodimers and Hela cell AP-1 proteins as well as that of several other transcription factors including NF-chi-B, Myb and members of the ATF/CREB family. Furthermore, immunodepletion analysis indicates that Ref-1 is the major AP-1 redox activity in Hela nuclear extracts. Interestingly, Ref-1 is a bifunctional protein; it also possesses an apurinic/apyrimidinic (AP) endonuclease DNA repair activity. However, the redox and DNA repair activities of Ref-1 can, in part, be distinguished biochemically. This study suggests a novel link between transcription factor regulation, oxidative signalling and DNA repair processes in higher eukaryotes.

Keywords:AP endonuclease; FOS; JUN; reduction oxidation; transcription factor

來源出版物：The EMBO Journal, 1992, 11(9): 3323 -3335

·推薦論文摘要·

非同源末端連接修復相關因子對DNA損傷修復調(diào)控及腫瘤治療作用的研究進展

李蔚蔚，孔金昕，漆永梅，等

摘要：細胞在內(nèi)源性或外源性因子的脅迫作用下會產(chǎn)生各種損傷，包括遺傳物質DNA的雙鏈斷裂（DSB）。非同源末端連接（NHEJ）是哺乳動物細胞中DSB損傷修復的一種主要機制。NHEJ過程中一些主要因子如DNA依賴性蛋白激酶、DNA交聯(lián)修復蛋白1C、X射線修復交叉互補蛋白4/DNA連接酶Ⅳ和X射線修復交叉互補蛋白4類似因子對DNA損傷修復（DDR）具有重要的調(diào)控作用，其中任何一種因子的改變都會影響DDR的效率。此外，NHEJ相關因子與腫瘤發(fā)生息息相關。本文針對NHEJ相關因子調(diào)控DSB修復方面的研究作一簡要綜述，并對NHEJ修復相關因子在腫瘤治療中的研究進行總結。

關鍵詞：DNA依賴性蛋白激酶；DNA雙鏈斷裂；DNA斷端接合修復；DNA損傷修復

來源出版物：中國藥理學與毒理學雜志, 2015, 29(4): 607-613聯(lián)系郵箱：黃德軍，huangdj@lzu.edu.cn

MicroRNA-7在DNA損傷修復中研究進展

陳玉婷，云林，徐龍妹，等

摘要：微小RNA（microRNA，miRNA)是一類存在于真核生物中的非編碼小RNA，由大小約19～24個核苷酸組成，通過結合在靶基因mRNA的3′非編碼區(qū)，降低mRNA穩(wěn)定性或抑制翻譯影響蛋白的表達，在轉錄后水平參與眾多生理病理過程。日常生活和職業(yè)環(huán)境中有毒有害因素可通過多種途徑進入人體產(chǎn)生遺傳毒性，直接或間接引起DNA損傷。DNA損傷的轉歸主要包括細胞周期的激活、DNA損傷修復和修復不完全導致細胞凋亡?凋亡異?；驌p傷的DNA未經(jīng)過完全修復無限制進入細胞周期，與腫瘤的發(fā)生發(fā)展密切相關。近年來microRNA-7(miR-7)對細胞凋亡和DNA損傷修復基因的調(diào)控作用也越來越受到重視。本文擬就miR-7在生物學功能、DNA損傷修復以及通過調(diào)控DNA損傷修復影響腫瘤治療等方面的研究進展進行綜述?

關鍵詞：microRNA-7；細胞周期；DNA損傷修復；細胞凋亡；腫瘤

來源出版物：中國職業(yè)醫(yī)學, 2015,42(5): 575-578聯(lián)系郵箱：唐煥文，gdmcthw@126.com

DNA損傷修復基因與人鼻咽癌細胞輻射耐受CNE-2R細胞的相關性研究

王亞利，馬秀龍，任宏濤，等

摘要：目的：探討射線誘導后DNA損傷修復相關基因在放射敏感性不同鼻咽癌細胞系CNE-2、CNE-2R的差異表達。方法：中性彗星分析法檢測細胞DNA的雙鏈斷鏈（DSB）；免疫熒光技術檢測磷酸化組蛋白γH2AX焦點形成、射線照射后細胞放射性損傷的時間劑量效應及放射敏感性的變化；基因芯片（OHS-029）技術檢測CNE-2及CNE-2R細胞2Gy照射前后的基因差異表達；Western blot方法驗證二者的差異表達蛋白質。結果：4Gy的9MeV-β射線照射后2 h，CNE-2R細胞與CNE-2細胞相比，細胞DNA損傷程度加重，且隨時間的延長更為明顯。熒光顯微鏡顯示，2Gy的9MeV-β射線照射后6 h，CNE-2各時間段細胞γH2AX陽性細胞率明顯高于CNE-2R組。DNA損傷相關基因表達譜分析發(fā)現(xiàn)，CNE-2和CNE-2R細胞相比，差異表達的DNA損傷修復相關基因共37個，其中上調(diào)基因24個，下調(diào)13個，其中6個位點差異6倍以上，3個位點低于0.1的差異表達；Western blot結果顯示，與CNE-2細胞相比，GADD45a、RRAD1在CNE-2R中的表達水平明顯下調(diào)，而ERCC1及PRKDC蛋白質明顯上調(diào)，與基因芯片的研究結果一致。結論：9MeV-β射線照射后CNE-2細胞DNA的損傷程度較CNE-2R細胞明顯，CNE-2R細胞放射抗拒性與DNA損傷修復能力的基因差異表達相關。通過對篩選出的靶基因進行調(diào)控，有可能改變細胞的放射敏感性。

關鍵詞：鼻咽癌；DNA損傷修復；基因表達譜；放射抗拒性

來源出版物：西安交通大學學報：醫(yī)學版, 2015, 36(2): 174-179聯(lián)系郵箱：王中衛(wèi)，wangzhongwei601@163.com

DNA損傷修復相關基因Polζ、ERCC1、ERCC2和RAD52在宮頸癌中的表達及其臨床意義

劉霏，李浩然，楊莉，等

摘要：目的：評價DNA損傷修復相關基因在宮頸癌組織中的表達及其臨床意義。方法：納入2008～2009年在復旦大學附屬腫瘤醫(yī)院行根治性手術并輔助同步放化療的113例宮頸鱗狀細胞癌患者，采用免疫組化法檢測DNA損傷修復相關基因（Polζ，ERCC1，ERCC2和RAD52）在石蠟包埋組織中的蛋白表達水平。結果：Polζ，ERCC1，ERCC2和RAD52的陽性表達率分別為22.1%，46.0%，48.7%和20.4%。Kaplan-Meier生存分析表明Polζ蛋白表達陽性的患者無進展生存期更短（32個月vs 34個月，P=0.008)。多因素生存分析顯示Polζ是腫瘤復發(fā)的重要因素（adjusted HR=7.79，95%CI:2.21～27.52，P=0.001）。結論：Polζ可作為宮頸癌判斷預后的預測因素，這可能是由于宮頸癌患者潛在的放化療抵抗導致的，該機制值得進一步研究。

關鍵詞：宮頸癌；預后；Polζ；ERCC1；ERCC2；RAD52

來源出版物：中國腫瘤, 2015, 24(10): 875-880聯(lián)系郵箱：程璽，cheng_xi1@hotmail.com

乳腺癌易感基因1在DNA損傷修復中作用的研究進展

趙錫鵬，張鳳梅，鳳志慧

摘要：乳腺癌易感基因1（BRCA1）基因突變與乳腺癌的發(fā)生密切相關。目前研究表明，BRCA1作為調(diào)節(jié)者參與了DNA損傷修復過程。DNA損傷的最嚴重的形式是雙鏈斷裂，BRCA1通過調(diào)控同源重組（HR）在修復雙鏈斷裂中發(fā)揮關鍵作用。本文從BRCA1主要功能區(qū)與HR的關系、主要功能區(qū)基因突變對修復雙鏈斷裂的影響、BRCA1與BRCA2，Rad51和CtIP復合物等蛋白之間的相互作用和蛋白的磷酸化等方面，對BRCA1調(diào)控HR的分子機制、BRCA1介導的修復機制缺失在合成致死性中的作用、及BRCA1缺失后細胞對不同DNA損傷制劑敏感性發(fā)生的變化等內(nèi)容進行了系統(tǒng)的綜述。

關鍵詞：乳腺癌易感基因1；DNA損傷；DNA修復；DNA斷裂，雙鏈；重組；遺傳

來源出版物：中國藥理學與毒理學雜志, 2014, 28(4): 606-611聯(lián)系郵箱：鳳志慧，fengzhihui@sdu.edu.cn

DNA損傷修復蛋白XRCC1的研究進展

徐誠，嚴麗鋒，王心如，等

摘要：X線修復交叉互補蛋白1（XRCC1）在堿基切除修復（BER）以及單鏈斷裂損傷修復（SSBR）中起著支架蛋白的作用。XRCC1可以與多個DNA修復相關蛋白交互作用并招募到DNA損傷部位，最終完成DNA的修復。由于XRCC1在DNA修復通路的重要作用，主要突變體Arg194Trp、Arg280His以及Arg399Gln也被深入地研究。在本文中作者對XRCC1的結構、功能以及它的突變體在人類疾病發(fā)生中的作用作一概述。

關鍵詞：X線修復交叉互補蛋白1；DNA修復；突變體；文獻綜述

來源出版物：東南大學學報：醫(yī)學版, 2014 (3): 376-380聯(lián)系郵箱：顧愛華，aihuagu@njmu.edu.cn

Celecoxib對放射所致DNA損傷修復與凋亡的影響

雷宏偉，龍成，姜永梅，等

摘要：目的：探討選擇性COX-2抑制劑celecoxib影響肺腺癌A549細胞凋亡及DNA損傷修復的放療增敏機制。方法：A549細胞分為對照組（相同體積的DMSO）、藥物組（celecoxib）、照射組（6MV X射線6 Gy）、聯(lián)合組[celecoxib+6Gy X射線（藥物作用24 h后）]。CCK-8法檢測celecoxib對肺腺癌A549細胞的IC50。RT-PCR、Western blot法檢測細胞DNA-PKcs、Ku80基因mRNA及蛋白表達。流式細胞儀檢測各組細胞凋亡率。結果：Celecoxib抑制A549細胞增殖作用呈劑量和時間依賴性，48 h的IC50值為58.74 μmol/L。聯(lián)合組DNA-PKcs、Ku80基因mRNA及蛋白表達量明顯低于對照組、藥物組、照射組（P＜0.01）。聯(lián)合組細胞凋亡率明顯高于對照組、物組和照射組（P＜0.01）。結論：Celecoxib通過抑制放射所致DNA損傷修復及促進凋亡，從而達到放療增敏作用。

關鍵詞：塞來昔布；DNA-PKcs；凋亡；放療增敏

來源出版物：實用癌癥雜志, 2014, 29(7): 733-736

DNA修復基因多態(tài)性與肺癌易感性的研究進展

周渝斌，車國衛(wèi)

摘要：肺癌的發(fā)生與個體遺傳易感性有關，其中DNA修復基因多態(tài)性可以引起不同DNA損傷反應，而機體間DNA損傷修復能力的不同與肺癌的發(fā)生有密切聯(lián)系。DNA修復基因多態(tài)性與肺癌易感性的關系已成為當前的研究熱點。本文回顧了DNA修復基因的作用機制及其多態(tài)性與肺癌易感性的國內(nèi)外研究現(xiàn)狀，就DNA損傷和修復類型、DNA不同修復途徑相關基因的作用機制及其多態(tài)性與肺癌易感性的關系、DNA修復基因多態(tài)性與肺癌化療敏感性的關系幾個方面進行綜述。

關鍵詞：DNA修復基因多態(tài)性；易感性；肺癌；化療

來源出版物：中國腫瘤臨床, 2013, 40(9): 551-554聯(lián)系郵箱：車國衛(wèi)，cheguowei@yahoo.com.cn

輻射耐受性宮頸癌細胞系的建立及DNA損傷修復相關基因的差異表達

王中衛(wèi)，王亞利，金迎迎，等

摘要：目的：篩選來源相同輻射耐受性不同的宮頸低分化鱗癌細胞DNA損傷修復相關基因的差異表達，探討宮頸癌輻射耐受的機制。方法：用9MeV-β射線反復多次間歇大劑量照射人宮頸低分化鱗癌細胞株SiHa，建立輻射耐受性細胞SiHaR，用DNA損傷修復相關PCR基因芯片檢測SiHa與SiHaR差異表達基因，并對篩選出的部分基因進行Western blot驗證。結果：SiHa及SiHaR細胞經(jīng)射線照射后呈指數(shù)性殺滅，同一劑量照射后SiHaR細胞存活分數(shù)（survival fraction，SF）值更高，SiHaR細胞在2Gy照射后細胞存活分數(shù)（SF2）是SiHa的2.26倍；二者有差異表達的DNA損傷修復相關基因41個，其中上調(diào)基因27個，下調(diào)14個。有13個位點出現(xiàn)6倍以上或低于0.1的差異。Western blot對4個差異表達蛋白質驗證結果提示，與SiHa細胞相比，糖尿病關聯(lián)Ras相關基因（ras-related associated with diabetes，RRAD1）、復制因子C2[replication factor C（activator 1）2，RCF2]在SiHaR表達水平明顯下調(diào)，而X線修復交叉互補基因1（X-ray repair complementing defective repair，XRCC1）及切除修復交叉互補基因（excision repair cross-complementing，ERCC1）蛋白質明顯上調(diào)。結論：人宮頸癌細胞系SiHa經(jīng)間歇性大劑量射線多次照射后篩選獲得的SiHaR細胞具有穩(wěn)定的輻射耐受性;這與DNA損傷修復能力在基因水平上發(fā)生了某些突變明顯相關。這為通過調(diào)控相關基因進行放射敏感性調(diào)控提供了依據(jù)。

關鍵詞：宮頸癌；DNA損傷修復；基因表達譜；輻射耐受性

來源出版物：西安交通大學學報：醫(yī)學版, 2013, 34(5): 572-576聯(lián)系郵箱：王中衛(wèi)，wanglank@126.com

Interactome analysis identifies a new paralogue of XRCC4 in non-homologous end joining DNA repair pathway

Xing, MT; Yang, MR; Huo, W; et al.

Abstract:Non-homologous end joining (NHEJ) is a major pathway to repair DNA double-strand breaks (DSBs), which can display different types of broken ends. However, it is unclear how NHEJ factors organize to repair diverse types of DNA breaks. Here, through systematic analysis of the human NHEJ factor interactome, we identify PAXX as a direct interactor of Ku. The crystal structure of PAXX is similar to those of XRCC4 and XLF. Importantly, PAXX-deficient cells are sensitive to DSB-causing agents. Moreover, epistasis analysis demonstrates that PAXX functions together with XLF in response to ionizing radiation-induced complex DSBs, whereas they function redundantly in response to Topo2 inhibitor-induced simple DSBs. Consistently, PAXX and XLF coordinately promote the ligation of complex but not simple DNA endsin vitro. Altogether, our data identify PAXX as a new NHEJ factor and provide insight regarding the organization of NHEJ factors responding to diverse types of DSB ends.

來源出版物：Nature Communications, 2015, 6, 6233聯(lián)系郵箱：Xu, DY; xudongyi@pku.edu.cn

Interleukin 6 alters localization of hMSH3, leading to DNA mismatch repair defects in colorectal cancer cells

Tseng-Rogenski, SS; Hamaya, Y; Choi, DY; et al.

Abstract:BACKGROUND & AIMS: Elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) is the most common DNA mismatch repair defect in colorectal cancers, observed in approximately 60% of specimens. This acquired genotype correlates with metastasis and poor outcomes for patients, and is associated with intra-epithelial inflammation and heterogeneous nuclear levels of the mismatch repair protein hMSH3. Inflammation and accompanying oxidative stress can cause hMSH3 to change its intracellular location, but little is known about the source of oxidative stress in cancer cells. We investigated whether cytokines mediate this process. METHODS: We analyzed levels of interleukin 6 (IL6) and its receptor (IL6R) in human colon and lung cancer cell lines by flow cytometry and enzyme-linked immunosorbent assay; proteins were localized by immunofluorescence and immunoblot analyses. IL6 signaling was blocked with antibodies against IL6, soluble glycoprotein 130 Fc fragments, and the signal transducers and activators of transcription 3 inhibitor NSC74859; a constitutively active form of STAT3 was expressed in colon and lung cancer cell lines to replicate IL6R signaling. EMAST was detected by DNA fragment analysis. Immunohistochemistry was used to examine levels of IL6 in 20 colorectal tumor and adjacent nontumor tissues. RESULTS: Incubation of colon and lung cancer cell lines with IL6, but not other cytokines, caused hMSH3, but no other mismatch repair proteins, to move from the nucleus to the cytosol after generation of oxidative stress; inhibition of IL6 signaling prevented this shift. Expression of constitutively active STAT3 also caused hMSH3 to translocate from the nucleus to the cytoplasm in cancer cell lines. Incubation of cells with IL6 led to tetranucleotide frameshifts, the signature for EMAST. EMAST-positive colorectal tumors had significantly higher levels of IL6 than EMAST-negative tumors. CONCLUSIONS: IL6 signaling disrupts the nuclear localization of hMSH3 and DNA repair, leading to EMAST in cancer cell lines. Inflammatory cytokines might therefore promote genetic alterations in human cancer cells.

Keywords:CRC; mutation; cytokine; EMAST; STAT3; tetranucleotide repeat

來源出版物：Gastroenterology, 2015, 148(3): 579-589聯(lián)系郵箱：Carethers, JM；jcarethe@umich.edu

MAD2L2 controls DNA repair at telomeres and DNA breaks by inhibiting 5′ end resection

Boersma, V; Moatti, N; Segura-Bayona, S; et al.

Abstract:Appropriate repair of DNA lesions and the inhibition of DNA repair activities at telomeres are crucial to prevent genomic instability. By fuelling the generation of genetic alterations and by compromising cell viability, genomic instability is a driving force incancer and ageing. Here we identify MAD2L2 (also known as MAD2B or REV7) through functional genetic screening as a novel factor controlling DNA repair activities at mammalian telomeres. We show that MAD2L2 accumulates at uncapped telomeres and promotes non-homologous end-joining (NHEJ)-mediated fusion of deprotected chromosome ends and genomic instability. MAD2L2 depletion causes elongated 39 telomeric overhangs, indicating that MAD2L2 inhibits 59 end resection. End resection blocks NHEJ while committing to homology-directed repair, and is under the control of 53BP1, RIF1 and PTIP. Consistent with MAD2L2 promoting NHEJ-mediated telomere fusion by inhibiting 5' end resection, knockdown of the nucleases CTIP or EXO1 partially restores telomere-driven genomic instability in MAD2L2-depleted cells. Control of DNA repair by MAD2L2 is not limited to telomeres. MAD2L2 also accumulates and inhibits end resection at irradiation-induced DNA double-strand breaks and promotes end-joining of DNA double-strand breaks in several settings, including during immunoglobulin class switch recombination. These activities of MAD2L2 depend on ATM kinase activity, RNF8, RNF168, 53BP1 and RIF1, but not on PTIP, REV1 and REV3, the latter two acting with MAD2L2 in translesion synthesis. Together, our data establish MAD2L2 as a crucial contributor to the control of DNA repair activity by 53BP1 that promotes NHEJ by inhibiting 5' end resection downstream of RIF1.

來源出版物：Nature, 2015, 521(7553): 537-U291聯(lián)系郵箱：Jacobs, JJL; j.jacobs@nki.nl

BRCA1 recruitment to transcriptional pause sites is required for R-Loop-Driven DNA damage repair

Hatchi, E; Skourti-Stathaki, K; Ventz, S; et al.

Abstract:The mechanisms contributing to transcription-associated genomic instability are both complex and incompletely understood. Although R-loops are normal transcriptional intermediates, they are also associated with genomic instability. Here, we show that BRCA1 is recruited to R-loops that form normally over a subset of transcription termination regions. There it mediates the recruitment of a specific, physiological binding partner, senataxin (SETX). Disruption of this complex led to R-loop-driven DNA damage at those loci as reflected by adjacent gamma-H2AX accumulation and ssDNA breaks within the untranscribed strand of relevant R-loop structures. Genome-wide analysis revealed widespread BRCA1 binding enrichment at R-loop-rich termination regions (TRs) of actively transcribed genes. Strikingly, within some of these genes in BRCA1 null breast tumors, there are specific insertion/deletion mutations located close to R-loop-mediated BRCA1 binding sites within TRs. Thus, BRCA1/SETX complexes support a DNA repair mechanism that addresses R-loop-based DNA damage at transcriptional pause sites.

來源出版物：Molecular Cell, 2015, 57(4): 636-647聯(lián)系郵箱：Hatchi, E; elodiey_hatchi@dfci.harvard.edu

Differential DNA mismatch repair underlies mutation rate variation across the human genome

Supek, F; Lehner, B

Abstract:Cancer genome sequencing has revealed considerable variation in somatic mutation rates across the human genome, with mutation rates elevated inheterochromatic late replicating regionsand reduced in early replicating euchromatin. Multiple mechanisms have been suggested to underlie this, but the actual cause is unknown. Here we identify variable DNA mismatch repair (MMR) as the basis of this variation. Analysing similar to 17 million single-nucleotide variants from the genomes of 652 tumours, we show that regional autosomal mutation rates at megabase resolution are largely stable across cancer types, with differences related to changes in replication timing and gene expression. However, mutations arising after the inactivation of MMR are no longer enriched in late replicating heterochromatin relative to early replicating euchromatin. Thus, differential DNA repair and not differential mutation supply is the primary cause of the large-scale regional mutation rate variation across the human genome.

來源出版物：Nature, 2015, 521(7550): 81-84聯(lián)系郵箱：Lehner, B; ben.lehner@crg.eu

UvrD facilitates DNA repair by pulling RNA polymerase backwards

Epshtein, V; Kamarthapu, V; McGary, K; et al.

Abstract:UvrD helicase is required for nucleotide excision repair, although its role in this process is not well defined. Here we show thatEscherichia coliUvrD binds RNA polymerase during transcription elongation and, using its helicase/translocase activity, forces RNA polymerase to slide backward along DNA. By inducing backtracking, UvrD exposes DNA lesions shielded by blocked RNA polymerase, allowing nucleotide excision repair enzymes to gain access to sites of damage. Our results establish UvrD as a bona fide transcription elongation factor that contributes to genomic integrity by resolving conflicts between transcription and DNA repair complexes. Furthermore, we show that the elongation factor NusA cooperates with UvrD in coupling transcription to DNA repair by promoting backtracking and recruiting nucleotide excision repair enzymes to exposed lesions. Because backtracking is a shared feature of all cellular RNA polymerases, we propose that this mechanism enables RNA polymerases to function as global DNA damage scanners in bacteria and eukaryotes.

來源出版物：Nature, 2014, 505(7483): 372-377聯(lián)系郵箱：Nudler, E; evgeny.nudler@nyumc.org

RecA bundles mediate homology pairing between distant sisters during DNA break repair

Lesterlin, C; Ball, G; Schermelleh, L; et al.

Abstract:DNA double-strand break (DSB) repair by homologous recombination has evolved to maintain genetic integrity in all organisms(1). Although many reactions that occur during homologous recombination are known(1-3), it is unclear where, when and how they occur in cells. Here, by using conventional and super-resolution microscopy, we describe the progression of DSB repair in liveEscherichia coli. Specifically, we investigate whether homologous recombination can occur efficiently between distant sister loci that have segregated to opposite halves of an E. coli cell. We show that a site-specific DSB in one sister can be repaired efficiently using distant sister homology. After RecBCD processing of the DSB, RecA is recruited to the cut locus, where it nucleates into a bundle that contains many more RecA molecules than can associate with the two single-stranded DNA regions that format the DSB. Mature bundles extend along the long axis of the cell, in the space between the bulk nucleoid and the inner membrane. Bundle formation is followed by pairing, in which the two ends of the cut locus relocate at the periphery of the nucleoid and together move rapidly towards the homology of the uncut sister. After sister locus pairing, RecA bundles disassemble and proteins that act late in homologous recombination are recruited to give viable recombinants 1-2-generation-time equivalents after formation of the initial DSB. Mutated RecA proteins that do not form bundles are defective in sister pairing and in DSB-induced repair. This work reveals an unanticipated role of RecA bundles in channelling the movement of the DNA DSB ends, thereby facilitating the long-range homology search that occurs before the strand invasion and transfer reactions.

來源出版物：Nature, 2014, 506(7487): 249-253聯(lián)系郵箱：Sherratt, DJ; david.sherratt@bioch.ox.ac.uk

Mouse SLX4 is a tumor suppressor that stimulates the activity of the nucleaseXPF-ERCC1in DNA crosslink repair

Hodskinson, MRG; Silhan, J; Crossan, GP

Abstract:SLX4 binds to three nucleases (XPF-ERCC1, MUS81-EME1, and SLX1), and its deficiency leads to genomic instability, sensitivity to DNA crosslinking agents, and Fanconi anemia. However, it is not understood how SLX4 and its associated nucleases act in DNA crosslink repair. Here, we uncover consequences of mouse Slx4 deficiency and reveal its function in DNA crosslink repair. Slx4-deficient mice develop epithelial cancers and have a contracted hematopoietic stem cell pool. The N-terminal domain of SLX4 (mini-SLX4) that only binds to XPF-ERCC1 is sufficient to confer resistance to DNA crosslinking agents. Recombinant mini-SLX4 enhances XPF-ERCC1 nuclease activity up to 100-fold, directing specificity toward DNA forks. Mini-SLX4-XPF-ERCC1 also vigorously stimulates dual incisions around a DNA crosslink embedded in a synthetic replication fork, an essential step in the repair of this lesion. These observations define vertebrate SLX4 as a tumor suppressor, which activates XPF-ERCC1 nuclease specificity in DNA crosslink repair.

來源出版物：Molecular Cell, 2014, 54(3): 472-484聯(lián)系郵箱：Patel, KJ; kjp@mrc-lmb.cam.ac.uk

RPA antagonizes microhomology-mediated repair of DNA double-strand breaks

Deng, SK; Gibb, B; de Almeida, MJ; et al.

Abstract:Microhomology-mediated end joining (MMEJ) is a Ku- and ligase IV-independent mechanism for the repair of DNA double-strand breaks that contributes to chromosome rearrangements. Here we used a chromosomal end-joining assay to determine the genetic requirements for MMEJ inSaccharomyces cerevisiae. We found that end resection influences the ability to expose microhomologies; however, it is not rate limiting for MMEJ in wild-type cells. The frequency of MMEJ increased by up to 350-fold inrfa1hypomorphic mutants, suggesting that replication protein A (RPA) bound to the single-stranded DNA (ssDNA) overhangs formed by resection prevents spontaneous annealing between microhomologies. In vitro, the mutant RPA complexes were unable to fully extend ssDNA and were compromised in their ability to prevent spontaneous annealing. We propose that the helix-destabilizing activity of RPA channels ssDNA intermediates from mutagenic MMEJ to error-free homologous recombination, thus preserving genome integrity.

來源出版物：Nature Structural & Molecular Biology, 2014, 21(4): 405-412聯(lián)系郵箱：Symington, LS; lss5@columbia.edu

A cell cycle-dependent regulatory circuit composed of 53BP1-RIF1 and BRCA1-CtIP controls DNA repair pathway choice

Escribano-Diaz, C; Orthwein, A; Fradet-Turcotte, A; et al.

Abstract:DNA double-strand break (DSB) repair pathway choice is governed by the opposing activities of 53BP1 and BRCA1. 53BP1 stimulates nonhomologous end joining (NHEJ), whereas BRCA1 promotes end resection and homologous recombination (HR). Here we show that 53BP1 is an inhibitor of BRCA1 accumulation at DSB sites, specifically in the G1 phase of the cell cycle. ATM-dependent phosphorylation of 53BP1 physically recruits RIF1 to DSB sites, and we identify RIF1 as the critical effector of 53BP1 during DSB repair. Remarkably, RIF1 accumulation at DSB sites is strongly antagonized by BRCA1 and its interacting partner CtIP. Lastly, we show that depletion of RIF1 is able to restore end resection and RAD51 loading in BRCA1-depleted cells. This work therefore identifies a cell cycle-regulated circuit, underpinned by RIF1 and BRCA1, that governs DSB repair pathway choice to ensure that NHEJ dominates in G1and HR is favored from S phase onward.

來源出版物：Molecular cell, 2013, 49(5): 872-883聯(lián)系郵箱：Xu, DY; xudongyi@pku.edu.cn

The histone mark H3K36me3 regulates human DNA mismatch repair through its interaction with mutsα

Li, F; Mao, GG; Tong, D; et al.

Abstract:DNA mismatch repair (MMR) ensures replication fidelity by correcting mismatches generated during DNA replication. Although human MMR has been reconstituted in vitro, how MMR occurs in vivo is unknown. Here, we show that an epigenetic histone mark, H3K36me3, is required in vivo to recruit the mismatch recognition protein hMutS alpha (hMSH2-hMSH6) onto chromatin through direct interactions with the hMSH6 PWWP domain. The abundance of H3K36me3 in G1 and early S phases ensures that hMutS alpha is enriched on chromatin before mispairs are introduced during DNA replication. Cells lacking the H3K36 trimethyltransferase SETD2 display microsatellite instability (MSI) and an elevated spontaneous mutation frequency, characteristic of MMR-deficient cells. This work reveals that a histone mark regulates MMR in human cells and explains the long-standing puzzle of MSI-positive cancer cells that lack detectable mutations in known MMR genes.

來源出版物：Cell, 2013, 153(3): 590-600聯(lián)系郵箱：Gu, LY; Jlgu0@uky.edu

Nuclear PTEN controls DNA repair and sensitivity to genotoxic stress

Bassi, C; Ho, J; Srikumar, T; et al.

Abstract:Loss of function of the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) tumor suppressor gene is associated with many human cancers. In the cytoplasm, PTEN antagonizes the phosphatidylinositol 3-kinase (PI3K) signaling pathway. PTEN also accumulates in the nucleus, where its function remains poorly understood. We demonstrate that SUMOylation (SUMO, small ubiquitin-like modifier) of PTEN controls its nuclear localization. In cells exposed to genotoxic stress, SUMO-PTEN was rapidly excluded from the nucleus dependent on the protein kinase ataxia telangiectasia mutated (ATM). Cells lacking nuclear PTEN were hypersensitive to DNA damage, whereas PTEN-deficient cells were susceptible to killing by a combination of genotoxic stress and a small-molecule PI3K inhibitor both in vitro and in vivo. Our findings may have implications for individualized therapy for patients with PTEN-deficient tumors.

來源出版物：Science, 2013, 341(6144): 395-399聯(lián)系郵箱：Stambolic, V; vuks@uhnres.utoronto.ca

53BP1 mediates productive and mutagenic DNA repair through distinct phosphoprotein interactions

Callen, E; Di Virgilio, M; Kruhlak, MJ; et al.

Abstract:The DNA damage response (DDR) protein 53BP1 protects DNA ends from excessive resection in G1, and thereby favors repair by nonhomologous end-joining (NHEJ) as opposed to homologous recombination (HR). During S phase, BRCA1 antagonizes 53BP1 to promote HR. The pro-NHEJ and antirecombinase functions of 53BP1 are mediated in part by RIF1, the only known factor that requires 53BP1 phosphorylation for its recruitment to double-strand breaks (DSBs). Here, we show that a 53BP1 phosphomutant, 53BP18A, comprising alanine substitutions of the eight most N-terminal S/TQ phosphorylation sites, mimics 53BP1 deficiency by restoring genome stability in BRCA1-deficient cells yet behaves like wild-type 53BP1 with respect to immunoglobulin class switch recombination (CSR). 53BP18Arecruits RIF1 but fails to recruit the DDR protein PTIP to DSBs, and disruption of PTIP phenocopies 53BP18A. We conclude that 53BP1 promotes productive CSR and suppresses mutagenic DNA repair through distinct phosphodependent interactions with RIF1 and PTIP.

來源出版物：Cell, 2013, 153(6): 1266-1280聯(lián)系郵箱：Nussenzweig, A; andre_nussenzweig@nih.gov

RIF1 counteracts BRCA1-mediated end resection during DNA repair

Feng, L; Fong, KW; Wang, JD; et al.

Abstract:BRCA1 promotes homologous recombination repair and antagonizes 53BP1-dependent nonhomologous end joining (NHEJ) pathway. However, the molecular basis of the competition between BRCA1 and 53BP1 pathways remains elusive. Here we report that RIF1 protein translocates to damage sites via ATM-dependent 53BP1 phosphorylation. Strikingly, loss of RIF1 rescues initial DNA end resection and checkpoint activation in BRCA1-depleted cells. Interestingly RIF1 accumulation at damage sites is antagonized by BRCA1 in S and G2phases. Conversely, the translocation of BRCA1 to damage sites is inhibited by RIF1 in G1phase. However, loss of RIF1 differs from that of 53BP1 deficiency, as it cannot fully rescue RAD51 foci formation, homologous recombination defect, and radio-hypersensitivity in BRCA1-deficient cells. This is likely because RIF1, but not 53BP1, also regulates the foci formation and chromatin loading of BLM (the Bloom syndrome helicase). Thus, RIF1 not only acts downstream of 53BP1 and counteracts BRCA1-mediated end resection but also has a secondary role in promoting BLM function in DNA repair.

來源出版物：Journal of Biological Chemistry, 2013, 288(16): 11135-11143聯(lián)系郵箱：Chen, JJ; jchen8@mdanderson.org

編輯：王微

Xeroderma pigmentosum: A human disease in which an initial stage of DNA repair is defective

Cleaver, JE

Homozygous xeroderma pigmentosum fibroblasts cannot repair damage to DNA bases, but can repair damage that involves chain breaks. In xeroderma pigmentosum, therefore, there is a defect in an early step in repair at which base damage is recognized and the polynucleotide chain broken enzymatically (by an endonuclease). Heterozygous fibroblasts repair base damage to normal extents. Carcinogenesis in xeroderma pigmentosum, and perhaps in some normal individuals, may be the result of somatic mutations caused by unrepaired damage.來源出版物：Proceedings of the National Academy of Sciences, 1969, 63(2): 428-435Reduced DNA repair capacity in lung cancer patientsWei, QY; Cheng, L; Hong, WK; et al.Abstract:Although lung cancer is the paradigm of a tobacco-induced malignancy, host-specific factors modulate susceptibility to tobacco carcinogenesis, Variations in DNA repair may influence the rate of removal of DNA damage and of fixation of mutations, To test the hypothesis that genetically determined DNA repair capacity (DRC) modulates lung cancer susceptibility, we conducted a pilot case-control study of 51 patients with newly diagnosed, previously untreated lung cancer and 56 controls identified from local community centers and frequency matched to the cases on age, sex, and ethnicity, The subjects were ascertained and interviewed for an ongoing molecular epidemiological investigation of lung cancer susceptibility, We measured DRC in the subjects' peripheral blood lymphocytes by using the host-cell reactivation assay, which measures cellular reactivation of a reporter gene damaged by exposure to 75 mu M benzo(a) pyrene diol epoxide. The mean level of DRC in cases (3.3%) was significantly lower than that in controls (5.1%) (P＜ 0.01), Only nine cases (18%) had DNA repair levels greater than the median value of repair in the controls, This median level of DRC in controls was used as the cutoff value for calculating the odds ratios, After adjustment for age, sex, ethnicity, and smoking status, the cases were five times more likely than the controls to have reduced DRC (odds ratio, 5.7; 95% confidence interval, 2.1-15.7), Younger cases (＜65 years) and smokers were more likely than controls to have reduced DRC, These findings suggest that individuals with reduced DRC are at an increased risk of developing lung cancer.

kin cancer; case-control study; molecular epidemiology

摘編自《國外醫(yī)學分子生物學分冊》2003年第25卷5期：270～272頁，圖、表、參考文獻已省略。