胃癌中DNA聚合酶β的突变及与胃癌分化程度的关系

肿瘤的发生是多个基因突变积累的结果。这些突变包括参与DNA复制和修复以及维持基因稳定性和完整性的基因，其中DNA聚合酶β（polβ）和肿瘤的关系受到越来越多的关注。polβ是一种修复酶，其突变的存在与一些肿瘤的发生有关。胃癌病因起源复杂，推测在其发生发展过程中一定伴有DNA损伤修复，然而有关胃癌中有无polβ突变国内尚少见报道。本研究对胃癌及癌旁组织标本进行ploβ突变检测。     

线粒体DNA ND1基因nt3394 T→C突变与老年人2型糖尿病

目的：了解线粒体烟酰胺腺嘌呤脱氧核苷酸（NADH）脱氢酶第一亚单位（ND1）基因中339位点T→C突变与我国老年人2型糖尿病的关系。方法：收集无血缘关系的208例老年2型糖尿病患者，同时以180例无糖尿病家族史的老年糖耐量正常者作为对照，用聚合酶链反应扩增。限糖尿病患者，同时以180例无糖尿病家族史的老年糖耐量正常者作为对照，用聚合酶链反应扩增、限制性内切酶HaeⅢ消化进行点突变筛选。结果：发现9例患者存在线粒体DNA ND1基因3394位点T→C突变（4．3％），非糖尿病者中仅有1例突变（0．6％），两组比较差异有显著性（P＜0．05）。结论：线粒体DNA ND1基因中3394位点T→C突变可能与我国老年人2型糖尿病的发病有关。     

线粒体DNA突变与原发性高血压相关性的研究进展

原发性高血压（EH）作为心脑血管疾病的主要危险因素,严重危害人类健康。前期研究发现,EH在许多家系中都存在母系遗传特性;因此,线粒体DNA（mtDNA）突变成为了探索EH发病机制的新目标。目前已发现多个与EH相关的mtDNA突变位点,这些突变被证实能够导致线粒体氧化磷酸化缺陷,ATP 合成降低,反应活性氧（ROS）增加和诱导线粒体介导的细胞死亡。据此推断,对线粒体功能障碍的深入研究将有望诠释母系遗传性高血压的分子发病机制,而且EH相关的mtDNA突变将有望成为母系遗传性EH诊断的遗传学标志物。鉴于此,本文将对EH相关的mtDNA突变和功能机制进行全面综述。     

线粒体基因突变与妊娠糖尿病

妊娠糖尿病(gestational diabetes mellitus,GDM)常伴随着妊娠不良结局的发生,对孕妇和胎儿均有严重影响。线粒体是真核细胞的重要细胞器之一,具有独立遗传物质及遗传体系。线粒体DNA突变主要影响线粒体能量代谢,导致ATP的合成减少,活性氧产生增加,从而导致一系列疾病,包括糖尿病或可能导致妊娠糖尿病。该文就线粒体DNA基因的相关突变位点与妊娠糖尿病关系进行综述。     

线粒体tRNA突变与高血压关系的研究进展

线粒体基因突变与多种疾病的发生有关，虽然转移RNA（tRNA）基因只占整个线粒体基因组的10%，但它们却是研究线粒体基因突变与疾病发生关系的热点。既往高血压遗传学的研究主要集中在核基因方面，近年来研究发现线粒体DNA突变可能参与原发性高血压（EH）的发生与发展，且越来越多的线粒体tRNA也被报道与EH的发生和发展密切相关。本文对线粒体tRNA突变与高血压发病的关系及其机制进行了综述。     

前列腺癌特异突变DNA聚合酶β真核表达载体构建及鉴定

目的 构建前列腺癌(PCa)特异突变DNA聚合酶β(polβ)真核表达载体.方法 提取有特异DNA polβ突变的PCa组织的总RNA,通用引物逆转录成cDNA;用设计带有接头的DNA polβ全基因引物,PCR扩增PCa组织中呈现的突变型DNA polβ全基因;构建T-A克隆并进行重组体的筛选鉴定;亚克隆入表达载体pcDNA3.1并进行重组体的筛选和鉴定.结果 PCa特异突变DNA polβ基因扩增选择出P4(MI-polβ)和P5(M2-polβ)两个标本,构建重组有特定突变位点的polβ目的 基因的pcDNA3.1真核表达载体,经PCR扩增获得2个阳性集落.结论 经鉴定成功构建2例PCa特异突变DNA polβ真核表达载体(pcDNA3.1-M1 and peDNA3.1-M2).     

乙型肝炎病毒前C区和核心启动子区突变与慢性乙型肝炎病情的关系

乙型肝炎病毒（HBV）感染能导致急、慢性肝病，其中全球慢性乙型肝炎感染者近4亿。每年由于HBV慢性感染引起的肝硬化，肝细胞癌死亡患者超过47万人。而由于HBV病毒复制过程缺乏校对机制，在慢性感染的过程中发生基因突变的概率很高，相关研究最多的HBV突变株主要有：发生在翻译水平的前C区突变（G1896A）；发生在核心启动子（BCP）区，即A1762T和G1764A的联合突变；发生在HBV DNA聚合酶区的变异包括P区528、552位点的突变。研究表明，HBV前C区1896位突变以及BCP区突变普遍存在于CHB患者中，     

DNA聚合酶β基因启动子在食管癌组织中的突变分析

目的:研究人食管癌组织、癌旁组织及其远端正常黏膜组织中DNA聚合酶β(DNA polymerase beta,polβ)基因启动子的突变情况.方法:采用聚合酶链反应(PCR)、DNA序列分析技术对25例食管癌患者手术切除的病变标本进行DNA pol β基因启动子序列检测,并利用DNASIS、OMIGA等软件分析测序数据.结果:25例中,食管癌组织、癌旁组织和正常黏膜组织中DNA polβ基因启动子发生突变者分别为8、6、5例,三组问突变率差异无统计学意义.在三组标本中共有35个突变点(癌组织包括18个突变点,癌旁组织包括9个突变点,正常黏膜组织8个突变点),25个点在polβ核心启动子区域,其中,-37位C→A突变出现8次;.-5位G→T突变出现7次;29位T→C突变出现2次;-19位出现C的缺失和插入C突变各1次.结论:DNA polβ基因启动子突变可能与食管癌的发生和发展有关.     

缺血性卒中患者线粒体DNA点突变研究

对56例缺血性卒中患者及38例正常对照者检测粒体（mt）的A3243G和G13513A点突变，提取外周血淋巴细胞总DNA。经热启动聚合酶链反应扩增线粒体相关的DNA片段，ApaI酶切后电泳检测长工片段多肽（RFLP），采用敏感性较高的非放射性银梁单链构象多态性（SSCP）技术分析扩增产物。结果显示，7例患者SSCP出现额外条带，具有显著性差异（Fisher确切概率法，P=0．039）。在2例患者中检出mtRNAA3243G突变，未见G1513A点突变ApaI酶切片段的长度片段多态性显示，A3243G突变率较低（3．57％），认为线粒体DNA突变异致的呼吸链功能障碍与缺血性卒中的发生相关。     

家族性高胆固醇血症患者低密度脂蛋白受体基因新的突变类型一例

目的：分析一例家庭性高胆固醇血症患的低密度脂蛋白受体基因突变位点。方法：以患儿的基因组DNA为模板，用聚合酶链反应（PCR）扩增该基因的18个外显子。用单链构象多态性（SSCP）方法分析检测PCR产物，对电泳结果异常进行DNA测序。结果：单链构象多态性分析发现患儿第10外显子存在一异常条带。DNA测序证实患儿第10外显子发生N515S纯合错义突变。结论：该病例为一个新的LDLR突变位点；聚合酶链反应－单链构象多态性分析（PCR－SSCP）可用于该突变位点的诊断。     

Polymerase γ gene POLG determines the risk of sodium valproate-induced liver toxicity

Sodium valproate (VPA) is widely used throughout the world to treat epilepsy, migraine, chronic headache, bipolar disorder, and as adjuvant chemotherapy. VPA toxicity is an uncommon but potentially fatal cause of idiosyncratic liver injury. Rare mutations in POLG, which codes for the mitochondrial DNA polymerase γ (polγ), cause Alpers-Huttenlocher syndrome (AHS). AHS is a neurometabolic disorder associated with an increased risk of developing fatal VPA hepatotoxicity. We therefore set out to determine whether common genetic variants in POLG explain why some otherwise healthy individuals develop VPA hepatotoxicity. We carried out a prospective study of subjects enrolled in the Drug Induced Liver Injury Network (DILIN) from 2004 to 2008 through five US centers. POLG was sequenced and the functional consequences of VPA and novel POLG variants were evaluated in primary human cell lines and the yeast model system Saccharomyces cerevisiae. Heterozygous genetic variation in POLG was strongly associated with VPA-induced liver toxicity (odds ratio = 23.6, 95% confidence interval [CI] = 8.4-65.8, P = 5.1 × 10??). This was principally due to the p.Q1236H substitution which compromised polγ function in yeast. Therapeutic doses of VPA inhibited human cellular proliferation and high doses caused nonapoptotic cell death, which was not mediated through mitochondrial DNA depletion, mutation, or a defect of fatty acid metabolism. CONCLUSION: These findings implicate impaired liver regeneration in VPA toxicity and show that prospective genetic testing of POLG will identify individuals at high risk of this potentially fatal consequence of treatment.     

Molecular diagnosis of Alpers syndrome

BACKGROUND/AIMS: Alpers syndrome is a developmental mitochondrial DNA depletion syndrome leading to fatal brain and liver disease in children and young adults. Mutations in the gene for the mitochondrial DNA polymerase (POLG) have recently been shown to cause this disorder. METHODS: The POLG locus was sequenced in 15 sequential probands diagnosed with Alpers syndrome. In addition, the POLG mutations found to cause Alpers syndrome in the 20 cases published to date were analyzed. RESULTS: POLG DNA testing accurately diagnosed 87% (13/15=87%: 95% confidence interval=60-98%) of cases. Five new POLG amino acid substitutions (F749S, R852C, T914P, L966R, and L1173fsX) were found that were associated with Alpers syndrome in five unrelated kindreds, and 14 different allelic combinations of POLG mutations were found to cause Alpers syndrome in the 20 probands published to date. The most common Alpers-causing mutation was the A467T substitution, located in the linker region of the pol gamma protein, which accounted for about 40% of the alleles and was present in 65% of the patients. All patients with POLG mutations had either the A467T or the W748S substitution in the linker region. CONCLUSIONS: Screening for A467T and W748S substitutions in POLG now constitutes the most rapid and sensitive test available for confirming the clinical diagnosis of Alpers syndrome.     

Lack of correlation between length variation in the DNA polymerase gamma gene CAG repeat and lactic acidosis or neuropathy during antiretroviral treatment

Antiretroviral therapy, although successful in reducing HIV load and accordingly decreasing the incidence of HIV infection-related symptoms, has its drawbacks in the form of severe side effects. Recognized drug-related side effects are, for example, nausea, fatigue, lactic acidosis, neuropathy, lipodystrophy, and myopathy. Because not all patients experience these side effects, genetic factors could be involved. It is believed that the main toxicity of nucleoside analog drugs is due to a decrease in mitochondrial function, possibly by inhibition of mitochondrial DNA (mtDNA) replication. mtDNA is replicated by a multienzyme complex, the main component of which is the nuclear-encoded DNA polymerase gamma. Presently, the only known variation in the DNA polymerase gamma gene is variation in the number of CAG repeats in the second exon. To investigate whether CAG repeat expansion or mutations in the DNA polymerase gamma (POLG) gene could predispose to peripheral neuropathy or lactic acidosis, we have sequenced part of the second exon of the DNA polymerase gamma gene, containing the CAG repeat, of 59 drug-treated HIV-infected patients, 11 of whom experienced drug-induced neuropathy, and 3 of whom died from lactic acidosis. No correlation was found between numbers of CAG repeats and any of the symptoms. The coding regions of the POLG gene from the three lactic acidosis patients were then completely sequenced, but no mutations were found. In addition, no variation was detected in exons 3, 8, and 19 of seven neuropathy patients and three control subjects without symptoms. These exons were the only sites of amino acid changes between human and chimpanzee POLG genes, and were chosen as targets of tolerated variation.     

Studies on the initiation and elongation reactions in the simian virus 40 DNA replication system.

The synthesis of oligoribonucleotides by DNA primase in the presence of duplex DNA containing the simian virus 40 (SV40) origin of replication was examined. Small RNA chains (10-15 nucleotides) were synthesized in the presence of the four common ribonucleoside triphosphates, SV40 large tumor antigen (T antigen), the human DNA polymerase alpha (pol alpha)-DNA primase complex, the human single-stranded DNA-binding protein (HSSB), and topoisomerase I isolated from HeLa cells. The DNA primase-catalyzed reaction showed an absolute requirement for T antigen, HSSB, and pol alpha. The requirement for HSSB was not satisfied by other SSBs that can support the T-antigen-catalyzed unwinding of DNA containing the SV40 origin of replication. Oligoribonucleotide synthesis occurred with a lag that paralleled the lag observed in DNA synthesis. These results indicate that the specificity for the HSSB in the SV40 replication reaction is due to the pol alpha-primase-mediated synthesis of the Okazaki fragments. In contrast to this specificity, the elongation of Okazaki fragments can be catalyzed by a variety of different DNA polymerases, including high levels of pol alpha, the polymerase delta holoenzyme, T4 polymerase holoenzyme, the Escherichia coli polymerase III holoenzyme, and other polymerases. These observations suggest that leading-strand synthesis in the in vitro SV40 replication system can be nonspecific.     

Mitochondrial disease

Defects of mitochondrial metabolism cause a wide range of human diseases that include examples from all medical subspecialties. This review updates the topic of mitochondrial diseases by reviewing the most important recent advances in this area. The factors influencing inheritance, maintenance and replication of mtDNA are reviewed and the genotype-phenotype of mtDNA disorders has been expanded, with new insights into epidemiology, pathogenesis and its role in ageing. Recently identified nuclear gene mutations of mitochondrial proteins include mutations of frataxin causing Friedreich's ataxia, PINK1, DJ1 causing Parkinson's disease and POLG causing infantile mtDNA depletion syndrome, ophthalmoplegia, parkinsonism, male subfertility and, in a transgenic mouse model, premature senescence. Mitochondrial defects in neurodegenerative diseases include Parkinson's, Alzheimer's and Huntington's disease. Improved understanding of mtDNA inheritance and mutation penetrance patterns, and novel techniques for mtDNA modification offer significant prospects for more accurate genetic counselling and effective future therapies.     

Functional interaction between the Werner Syndrome protein and DNA polymerase delta

Werner Syndrome (WS) is an inherited disease characterized by premature onset of aging, increased cancer incidence, and genomic instability. The WS gene encodes a 1,432-amino acid polypeptide (WRN) with a central domain homologous to the RecQ family of DNA helicases. Purified WRN unwinds DNA with 3'-->5' polarity, and also possesses 3'-->5' exonuclease activity. Elucidation of the physiologic function(s) of WRN may be aided by the identification of WRN-interacting proteins. We show here that WRN functionally interacts with DNA polymerase delta (pol delta), a eukaryotic polymerase required for DNA replication and DNA repair. WRN increases the rate of nucleotide incorporation by pol delta in the absence of proliferating cell nuclear antigen (PCNA) but does not stimulate the activity of eukaryotic DNA polymerases alpha or epsilon, or a variety of other DNA polymerases. Moreover, we show that functional interaction with WRN is mediated through the third subunit of pol delta: i.e., Pol32p of Saccharomyces cerevisae, corresponding to the recently identified p66 subunit of human pol delta. Absence of the third subunit abrogates stimulation by WRN, and stimulation is restored by reconstituting the three-subunit enzyme. Our findings suggest that WRN may facilitate pol delta-mediated DNA replication and/or DNA repair and that disruption of WRN-pol delta interaction in WS cells may contribute to the previously observed S-phase defects and/or the unusual sensitivity to a limited number of DNA damaging agents.     

A phenotype for enigmatic DNA polymerase II: A pivotal role for pol II in replication restart in UV-irradiated Escherichia coli

DNA synthesis in Escherichia coli is inhibited transiently after UV irradiation. Induced replisome reactivation or "replication restart" occurs shortly thereafter, allowing cells to complete replication of damaged genomes. At the present time, the molecular mechanism underlying replication restart is not understood. DNA polymerase II (pol II), encoded by the dinA (polB) gene, is induced as part of the global SOS response to DNA damage. Here we show that pol II plays a pivotal role in resuming DNA replication in cells exposed to UV irradiation. There is a 50-min delay in replication restart in mutant cells lacking pol II. Although replication restart appears normal in DeltaumuDC strains containing pol II, the restart process is delayed for >90 min in cells lacking both pol II and UmuD'(2)C. Because of the presence of pol II, a transient replication-restart burst is observed in a "quick-stop" temperature-sensitive pol III mutant (dnaE486) at nonpermissive temperature. However, complete recovery of DNA synthesis requires the concerted action of both pol II and pol III. Our data demonstrate that pol II and UmuD'(2)C act in independent pathways of replication restart, thereby providing a phenotype for pol II in the repair of UV-damaged DNA.     

程新刘宝玲王海滨金壮张杰林CrumpackerClyde人刘宝玲王海滨金壮张杰林CrumpackerClyde巨细胞病毒临床分离株感染血管内皮细胞伴肾素基因表达

目的探讨巨细胞病毒（Cytomegalovirus,CMV）是否感染血管内皮细胞伴肾素表达。方法（1）用10^7pfu（空斑形成单位）／mlCMV临床分离株BI-5和实验室型CMVAD169分别与10^6腹主动脉内皮细胞和人脐静脉内皮细胞共同孵育,在23小时后、第3天、第7天、第10天和第14天分别收集培养上清200μl,第14天用PBS缓冲液洗细胞3次,收获细胞。每组实验均设培养液代替病毒液的无感染对照;（2）COBAS定量PCR检测培养上清中CMVDNA拷贝数;（3）PCR检测感染细胞中CMVpol基因;（4）RT—PCR、RealtimeRT—PCR和Westernblot检测肾素在感染细胞内的表达。结果（1）BI-5和AD169感染静脉和动脉细胞后,其形态学变化相似,无细胞裂解病理效应;（2）ADl69感染细胞不同时间培养上清中CMVDNA拷贝数无明显增加,BI-5呈增殖趋势;（3）BI-5感染动脉细胞CMVDNA拷贝数和肾素表达量均大于静脉细胞。结论临床分离株CMV以非裂解形式在血管内皮细胞持续存在并诱导肾素基因表达,血管内皮细胞分泌肾素可能是CMV感染引起心血管疾病的新机制。     

Functional roles of DNA polymerases beta and gamma.

The physiological functions of DNA polymerases (deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) beta and gamma were investigated by using neuronal nuclei and synaptosomes isolated from rat brain. UV irradiation of neuronal nuclei from 60-day-old rats resulted in a 7- to 10-fold stimulation of DNA repair synthesis attributable to DNA polymerase beta which, at this developmental stage, is virtually the only DNA polymerase present in the nuclei. No repair synthesis could be elicited by treating the nuclei with N-methyl-N-nitrosourea, but this way probably due to the inability of brain tissues to excise alkylated bases from DNA. The role of DNA polymerase gamma was studied in synaptosomes by using a system mimicking in vivo mitochondrial DNA synthesis. By showing that, under these conditions, DNA replication occurs in mitochondria, and exploiting the fact that DNA polymerase gama is the only DNA polymerase present in mitochondria, evidence was obtained for a role of DNA polymerase gamma in mitochondrial DNA replication. Based on these results and on the wealth of literature on DNA polymerase alpha, we conclude that DNA polymerase alpha is mainly responsible for DNA replication in nuclei, DNA polymerase beta is involved in nuclear DNA repair, and DNA polymerase gamma is the mitochondrial replicating enzyme. However, minor roles for DNA polymerase alpha in DNA repair or for DNA polymerase beta in DNA replication cannot be excluded.