The DNA damage repair complex MoMMS21-MoSMC5 is required for infection-related development and pathogenicity of Magnaporthe oryzae

The conserved DNA damage repair complex,MMS21-SMC5/6(Methyl methane sulfonate 21-Structural maintenance of chromosomes 5/6),has been extensively studied in yeast,animals,and plants.However,its role in phytopathogenic fungi,particularly in the highly destructive rice blast fungus Magnaporthe oryzae,remains unknown.In this study,we functionally characterized the homologues of this complex,MoMMS21 and MoSMC5,in M.oryzae.We first demonstrated the importance of DNA damage repair in M.oryzae by showing that the DNA damage inducer phleomycin inhibited vegetative growth,infection-related development and pathogenicity in this fungus.Additionally,we discovered that MoMMS21 and MoSMC5 interacted in the nuclei,suggesting that they also function as a complex in M.oryzae.Gene deletion experiments revealed that both MoMMS21 and MoSMC5 are required for infection-related development and pathogenicity in M.oryzae,while only MoMMS21 deletion affected growth and sensitivity to phleomycin,indicating its specific involvement in DNA damage repair.Overall,our results provide insights into the roles of MoMMS21 and MoSMC5 in M.oryzae,highlighting their functions beyond DNA damage repair.

In Vivo Improvements in Facial Appearance and in Vitro Changes in Gene Expression Using a Topical Formulation Designed to Repair Environmentally Induced DNA Damage

Background: While sunscreen has been accepted as a mainline defence against photodamage from ultraviolet, visible light and near-infrared radiation, there appears to be a lack of research into photorepair. The concept of protecting the skin during the day and repairing cellular damage at night is intuitive, yet specific strategies revolving around combinations of proven reparative active ingredients remain unelucidated. Purpose: To investigate the efficacy of a solar repair Formulation following ultraviolet and environmental exposure in order to improve overall skin health and appearance through three hypotheses: The Formulation increases expression of DNA repair mechanisms markers;The Formulation enhances overall skin appearance through reducing signs of inflammation, elevating hydration, reinforcing skin firmness and amplifying radiance;In-Vivo efficacy test results are aligned with measured gene expression changes. Methods: The Formulation (#6NIC1.V1.1-1) was tested for: In-vitro LDH cytotoxicity activity, In-vitro qPCR gene expression with and without ultraviolet exposure on a reconstructed 3-dimensional skin model, and In-Vivo efficacy study on a panel of 22 participants objectively and subjectively. Results: Skin radiance, firmness, hydration, redness, and inflammation are significantly improved after In-Vivo skin exposure to the Formulation and environmental challenges such as ultraviolet radiation. These outcomes were confirmed by in-vitro genetic testing on a reconstructed human skin model. Conclusion: The studies allowed us to identify and group results in four main skin functions that were significantly enhanced following the application of the Formulation: firmness, hydration, radiance and soothing.

DNA损伤修复相关通路的合成致死靶点研究及其在卵巢癌中的应用和前景

DNA损伤引发细胞启动一系列DNA损伤应答(DNA damage response,DDR),包括DNA损伤修复、细胞周期检查点激活、细胞周期阻滞、各种细胞内信号转导途径的活化和细胞凋亡等。DNA损伤修复(DNA damage repair)是细胞维持基因组稳定性的重要机制,于2015年获得诺贝尔化学奖。DNA损伤修复途径主要包括:碱基切除修复(base-excision repair,BER)、核苷酸切除修复(nucleotide excision repair,NER)、错配修复(mismatch repair,MMR)、同源重组(homologous recombination,HR)和非同源末端连接(non-homologous end joining,NHEJ)等,分别在DNA单链断裂(single-strand break,SSB)或双链断裂(double-strand break,DSB)等损伤修复中发挥重要作用。DNA损伤修复缺陷与肿瘤发生发展密切相关,同时也是肿瘤治疗的重要靶点。DNA损伤修复通路的多聚ADP核糖聚合酶(poly-ADP-ribose polymerase,PARP)与乳腺癌易感基因BRCA 1/2等存在合成致死(synthetic lethality)作用,使PARP抑制剂(PARP inhibitor,PARPi)成为第一个也是目前唯一上市的肿瘤治疗合成致死靶药。PARPi在卵巢癌及多种实体瘤治疗中疗效良好,使DNA损伤修复及相关DDR通路的合成致死靶药研发成为热点,其他在研靶点主要包括:共济失调毛细血管扩张突变蛋白(ataxia telangiectasia-mutated protein,ATM)、共济失调毛细血管扩张与RAD3相关蛋白(ataxia telangiectasia and Rad3 related protein,ATR)、DNA依赖性蛋白质激酶催化亚单位(DNA-dependent protein kinase catalytic subunit,DNA-PKcs)、细胞周期检测点激酶1(checkpoint kinase1,CHK1)、细胞周期检测点激酶2(checkpoint kinase 2,CHK2)、阻止有丝分裂的蛋白质激酶WEE1等。PARPi与其他DDR靶药、抗血管生成药物及免疫检查点抑制剂的联用,有可能成为克服PARPi耐药、提高疗效的有效手段和发展前景。本文针对DNA损伤修复及相关DDR通路的关键分子和潜在肿瘤治疗靶点进行综述,阐述了DNA损伤修复相关通路的合成致死靶点研究及在卵巢癌的应用和前景,为基础研究及临床应用提供指导。

DNA聚合酶θ:易错的多功能DNA末端修复分子

DNA聚合酶θ(DNA polymerase theta,Polθ)是一种广泛存在于动植物中的DNA修复酶。它在选择性末端连接(alternative end-joining,Alt-EJ)途径中发挥着关键作用,常参与DNA双链断裂(DNA double-strand breaks,DSB)损伤修复。在正常生理状态下,Polθ主要调控基因组稳定性。然而,在恶性肿瘤发生时,Polθ表现出异常高表达水平,并参与调控肿瘤细胞的恶性转变过程。研究表明,抑制Polθ活性可导致同源重组(homologous recombination,HR)缺陷的肿瘤细胞发生合成致死(synthetic lethality,SL)。因此,已经开发出多种针对Polθ的小分子抑制剂,可与其他化疗药物联合使用以抑制恶性肿瘤的发展。此外,敲除或抑制Polθ活性还能增加HR修复效率,从而提高外源基因靶向整合效果。本文综述了Polθ及其介导的Alt-EJ修复机制在生物学功能方面的最新研究进展,为靶向Polθ在肿瘤治疗和基因编辑方面的应用提供理论基础。

RNF20对紫外线诱导的胃癌细胞DNA损伤修复的影响

目的探究在紫外线暴露下环指蛋白20(ring finger protein 20,RNF20)低表达对胃癌细胞DNA损伤修复的影响及其相关作用机制。方法实验采用慢病毒载体构建稳定低表达胃癌细胞系,分为对照组和RNF20敲低组,用CCK-8法检测两组细胞的增殖情况,用总共照射剂量为20 J/m^(2)紫外线照射胃癌MGC803细胞,采用Western blotting及免疫荧光技术检测两组细胞γ-H2AX、RAD51和p21的情况。结果荧光显微镜观察两组细胞均有绿色荧光蛋白表达;CCK-8显示RNF20表达降低会促进胃癌细胞增殖;敲低组细胞中RNF20蛋白较对照组表达降低。与对照组相比,经20 J/m^(2)紫外线照射细胞后,敲低组γ-H2AX消失更加迟缓,RAD51蛋白表达降低,p21蛋白表达下降趋势更慢。结论RNF20敲低会抑制紫外线诱导的胃癌细胞DNA损伤修复过程。

Targeting DNA repair for cancer treatment: Lessons from PARP inhibitor trials

Ionizing radiation is frequently used to treat solid tumors,as it causes DNA damage and kill cancer cells.However,damaged DNA is repaired involving poly-(ADP-ribose)polymerase-1(PARP-1)causing resistance to radiation therapy.Thus,PARP-1 represents an important target in multiple cancer types,including prostate cancer.PARP is a nuclear enzyme essential for single-strand DNA breaks repair.Inhibiting PARP-1 is lethal in a wide range of cancer cells that lack the homologous recombination repair(HR)pathway.This article provides a concise and simplified overview of the development of PARP inhibitors in the laboratory and their clinical applications.We focused on the use of PARP inhibitors in various cancers,including prostate cancer.We also discussed some of the underlying principles and challenges that may affect the clinical efficacy of PARP inhibitors.

肝细胞癌复发进程中DNA修复调节的蛋白质组学分析及验证

目的分析肝细胞癌(HCC)复发进程中DNA修复调节的作用及机制。方法串联质量标签(TMT)标记的定量蛋白质组学方法分析HCC 2年内复发和5年预后良好的肝癌组织样本,分析富集在DNA复制、错配修复、碱基切除修复、核苷酸切除修复4条通路的蛋白表达差异,分析在HCC复发进程中起主要作用的调控通路及靶点,预测可能的调控机制。计量资料2组间比较采用成组t检验;多组间比较采用单因素方差分析,进一步两两比较采用LSD-t检验。结果真核生物复制复合体通路MCM2(P=0.018)、MCM3(P=0.047)、MCM4(P=0.014)、MCM5(P=0.008)、MCM6(P=0.006)、MCM7(P=0.007)、PCNA(P=0.019)、RFC4(P=0.002)、RFC5(P<0.001)、LIG1(P=0.042)蛋白表达均显著降低;核苷酸切除修复通路中PCNA(P=0.019)、RFC4(P=0.002)、RFC5(P<0.001)、LIG1(P=0.042)共4个蛋白表达水平均显著减少;碱基切除修复通路PCNA(P=0.019)和LIG1(P=0.042)在HCC复发组中均显著降低;错配修复富集通路中MSH2(P=0.026)、MSH6(P=0.006)、RFC4(P=0.002)、RFC5(P<0.001)、PCNA(P=0.019)、LIG1(P=0.042)共6个蛋白在肝癌复发组织中均显著减少。差异蛋白涉及MCM复合体、DNA聚合酶复合体ε、连接酶LIG1、长补丁碱基剪切修复复合体(long patch BER)、DNA错配修复蛋白复合体的重要组分。对DNA修复调节的重要差异蛋白进行临床样本验证分析,结果表明复发组中除MCM6表现出下降趋势外,MCM5(P=0.008)、MCM7(P=0.007)、RCF4(P=0.002)、RCF5(P<0.001)和MSH6(P=0.006)蛋白相对表达量均显著降低。结论HCC复发过程中,DNA修复进程中多个复合体蛋白组分存在显著减少或缺失。

UbcH5a调控DNA损伤修复蛋白表达对食管癌细胞放射敏感性的影响

目的:构建过表达人泛素交联酶UbcH5a基因的稳定转染食管鳞癌EC109细胞株,研究UbcH5a影响食管癌放射敏感性的机制。方法:将EC109细胞分为空白对照组(不处理)、阴性对照组(转染pEGFP-C1质粒)和过表达组(转染pEGFP-UbcH5a质粒)。分别采用实时荧光定量PCR(RT-qPCR)和western blotting法检测UbcH5a mRNA及蛋白表达以验证转染效率,克隆形成实验检测2 Gy X线照射后的细胞存活分数(SF2),免疫荧光检测DNA损伤灶点,western blotting法检测DNA损伤修复相关蛋白(ATM、ATR、p-ATM、p-ATR、Chk1、Chk2和BRCA1)表达。结果:与空白对照组相比,过表达组UbcH5a mRNA及蛋白表达水平升高,SF2降低,DNA损伤灶点增多(均P<0.05),而阴性对照组无明显变化(P>0.05)。与阴性对照组相比,过表达组经X线照射前、后ATM、ATR、p-ATM、p-ATR、Chk1、Chk2和BRCA1表达均显著下调(均P<0.05)。结论:UbcH5a通过抑制DNA损伤修复相关蛋白表达来增强食管癌细胞的放射敏感性。

范可尼贫血:从遗传疾病到癌症关联的DNA修复通路探索与治疗展望

范可尼贫血(FA)是一种遗传性疾病,其特征包括骨髓衰竭、发育异常和易患癌症。这种疾病是由基因突变引起的,导致修复DNA链间交联(ICLs)异常。DNA损伤反应失调会导致基因组不稳定,增加突变率和致癌风险。FA通路是DNA损伤应答的重要组成部分,在DNA链间交联修复和基因组稳定性方面发挥着关键作用。任何一个编码FA蛋白的基因胚系突变都会导致FA。随着体细胞癌中FA基因表达异常的普遍发生和不断开展的FA通路激活与化疗耐药相关性的研究,FA通路与癌症之间的联系得到了进一步确认,并且基于FA通路基因缺陷的靶向治疗也在逐步开发和应用。本文综述了FA蛋白在ICLs修复、FA信号网络调节以及其在癌症发病和预后中的重要作用,并探讨了靶向FA途径的小分子抑制剂的潜在应用。

基于DNA损伤修复基因的膀胱癌预后风险模型构建及其在免疫治疗效果预测中的应用

目的本研究旨在探索构建一个基于DNA损伤修复相关基因(DDRGs)的预测膀胱癌患者生存预后及免疫治疗效果的风险模型。方法首先,从TCGA⁃BLCA数据集下载的RNA序列及临床信息,通过单变量Cox、最小绝对收缩与选择算法(LASSO)及多变量Cox分析,筛选出与DNA损伤修复相关的基因(DDRGs),构建预后风险模型;利用Kaplan⁃Meier生存曲线评估生存差异,通过接收者操作特征(ROC)曲线验证模型性能,并结合临床特征构建列线图进行验证。最后,对临床特征进行了分层分析,并进一步通过基因集富集分析(GSEA)、评估免疫状态和免疫检查点抑制剂(ICIs)的治疗效果。结果通过构建11个DNA损伤修复相关基因的风险模型,显示高风险得分的膀胱癌患者生存率明显低于低风险得分患者。免疫状态的分析揭示了高风险与低风险组之间存在显著差异,且低风险组患者对免疫检查点抑制剂的治疗效果更佳。结论基于DNA损伤修复构建的预后风险模型能有效预测膀胱癌患者的生存预后及其对免疫检查点抑制剂治疗的响应性。

Tislelizumab in previously treated,locally advanced unresectable/metastatic microsatellite instability-high/mismatch repair-deficient solid tumors

Objective:The open-label,phase II RATIONALE-209 study evaluated tislelizumab(anti-programmed cell death protein 1 antibody)as a tissue-agnostic monotherapy for microsatellite instability-high(MSI-H)/mismatch repair-deficient(dMMR)tumors.Methods:Adults with previously treated,locally advanced unresectable or metastatic MSI-H/dMMR solid tumors were enrolled.Patients received tislelizumab 200 mg intravenously every 3 weeks.Objective response rate(ORR;primary endpoint),duration of response(DoR),and progression-free survival(PFS)were assessed by independent review committee(Response Evaluation Criteria in Solid Tumors v1.1).Results:Eighty patients were enrolled and treated;75(93.8%)patients had measurable disease at baseline.Most had metastatic disease and received at least one prior therapy for advanced/metastatic disease(n=79;98.8%).At primary analysis(data cutoff July 8,2021;median follow-up 15.2 months),overall ORR[46.7%;95%confidence interval(95%CI),35.1−58.6;one-sided P<0.0001]and ORR across tumor-specific subgroups[colorectal(n=46):39.1%(95%CI,25.1–54.6);gastric/gastroesophageal junction(n=9):55.6%(95%CI,21.2−86.3);others(n=20):60.0%(95%CI,36.1−80.9)]were significantly greater with tislelizumab vs.a prespecified historical control ORR of 10%;five(6.7%)patients had complete responses.Median DoR,PFS,and overall survival were not reached with long-term follow-up(data cutoff December 5,2022;median follow-up 28.9 months).Tislelizumab was well tolerated with no unexpected safety signals.Treatment-related adverse events(TRAEs)of grade≥3 occurred in 53.8%of patients;7.5%of patients discontinued treatment due to TRAEs.Conclusions:Tislelizumab demonstrated a significant ORR improvement in patients with previously treated,locally advanced unresectable or metastatic MSI-H/dMMR tumors and was generally well tolerated.

DNA聚合酶η小分子抑制剂筛选

DNA损伤修复以及基因组稳定性维持对于动植物正常生长和防御逆境至关重要。针对DNA聚合酶错误掺入导致的基因组不稳定性,本研究以DNA聚合酶η为研究对象,通过计算分子模拟对接的方式,对其可能的小分子抑制剂进行筛选,并对其酶动力学参数进行测定。结果显示:脱氧腺苷三磷酸(deoxyadenosine triphosphate,d ATP)对DNA聚合酶η的活性具有抑制效果,使其延伸的相对效率为36%~42%。分子模拟对接和体外实验结果表明,相较于dATP(亲和力为-26.7 kJ/mol),环鸟苷酸-腺苷酸(cyclic GMP-AMP,cGAMP)与DNA聚合酶η具有更低的结合能(亲和力为-35.1 kJ/mol)。酶动力学参数测定结果也表明,相较于dATP,cGAMP具有更强的抑制能力且在浓度为0.5 mmol/L时达到最强(相对延伸效率为13%)。因此,本研究筛选获得了针对DNA聚合酶η的一种潜在的小分子抑制剂。同时,鉴于该蛋白质高表达导致细胞对抗肿瘤药物(DNA损伤剂)的耐受性,这为新型药物的开发提供了依据。

靶向DNA损伤修复通路的胰腺癌治疗策略

随着新的免疫治疗和靶向治疗的发展,其他肿瘤的预后明显得到改善。但胰腺癌的5年生存率一直维持在10%以下,是极具挑战性的恶性肿瘤,亟待寻找新的治疗策略。DNA损伤修复通路形成复杂的调控网络,其功能缺陷将导致肿瘤的发生,但同时增加对基因毒性药物及放射治疗的敏感性。DNA损伤修复通路的异常与恶性肿瘤的发展和肿瘤的耐药密切相关,而PARP抑制剂在BRCA1/2缺陷肿瘤中的成功应用,极大地促进了针对DNA损伤修复缺陷肿瘤的分子靶向治疗研究。除PARP抑制剂外,针对ATR、CHK1、WEE1、DNA-PK等DNA损伤修复的抑制剂均已进入临床试验。在转移性胰腺导管癌中发现,15%~20%的患者存在DNA损伤修复基因的体细胞突变或种系突变,然而其中的部分突变并不影响基因的功能。DNA损伤修复基因在胰腺癌等肿瘤中频繁发生表观遗传异常改变,深入研究其对DNA修复调控网络的影响,有望获得新的“协同致死”治疗策略。

RNA甲基化修饰调控DNA损伤修复过程及其在肿瘤耐药中的作用

DNA损伤修复是指纠正DNA两条单链间错配的碱基、清除DNA链上受损的碱基、恢复DNA正常结构的过程。细胞内存在多种机制来应对不同类型的DNA损伤,同源重组修复便是重要的修复机制之一。在同源重组修复过程中,RNA的合成发挥着重要作用,而RNA甲基化修饰作为一个普遍存在于真核细胞中的调控机制,也参与了这一复杂的修复过程。肿瘤发生过程中普遍存在RNA甲基化修饰失调导致的DNA损伤累积,从而引起肿瘤的恶性转化。此外,RNA甲基化修饰还可以影响放化疗后细胞对DNA损伤的修复能力,使肿瘤细胞的放化疗敏感性发生改变,进而影响治疗效果。本文综述了目前已知的不同类型RNA甲基化修饰在DNA损伤修复过程中的作用,并进一步分析RNA甲基化修饰介导的DNA损伤修复异常在肿瘤临床诊断、预后判断和作为治疗靶点等方面的应用前景。

川芎嗪通过RAD52调控乳腺癌细胞DNA损伤修复

目的:探究TMP对乳腺癌BT474细胞增殖、细胞周期及其调控蛋白表达与DNA双链断裂修复通路的相关性。方法:CCK8法测定TMP对乳腺癌BT474细胞的增殖抑制情况;流式细胞术测定TMP对细胞周期的影响;单细胞凝胶电泳测定分析TMP对损伤后细胞DSBs累积情况的影响;Isce-I内切酶系统检测TMP对修复通路活性的影响;Western blotting检测DSBs修复通路相关染色体结合蛋白表达水平变化。结果:TMP通过使细胞阻滞在G_(1)期呈浓度依赖性抑制BT474细胞增殖,显著减少体内由Zeocin导致的细胞拖尾DNA含量(P<0.05);TMP显著增加BT474细胞对RAD52、ERCC1、XRCC4以及DNA LigⅣ蛋白募集,减少对KU80蛋白募集,促进了SSA以及NHEJ通路修复活性(P<0.05)。结论:TMP通过阻滞BT474细胞停留在G_(1)期使其发挥增殖抑制作用的机制之一;TMP通过增强损伤缺口对各个通路的关键染色体结合蛋白募集,促进SSA与NHEJ修复通路活性从而减少DNA损伤。

基于DNA损伤修复基因构建AML预后预测模型

目的构建基于DNA损伤修复(DNA Damage Response,DDR)基因的急性髓系白血病(Acute Myeloid Leukemia,AML)预后模型,为探索AML基因稳定性和精准治疗提供理论依据。方法利用TCGA和GEO数据库分别下载训练集和验证集;利用MSigDB数据库的DDR通路基因,根据训练集中DDR基因表达水平与总生存(Overall survival,OS)相关系数,构建Lasso回归模型并得出特征基因;多因素COX回归得出每个基因的相关系数,并计算DDR评分(risk score);在训练集和验证集中分别根据DDR评分截断值,将2组病例分为高危组(high risk)和低危组(low risk),并对2组临床特征和预后进行比较;绘制受试者工作特征曲线(receiver operating characteristic curve,ROC)评价该DDR基因集的DDR评分预测OS的灵敏度和特异度。结果以TCGA(n=157)AML数据集作为训练集,建立Lasso回归模型后得到10个特征基因,将这10个特征基因合集命名为“DDR基因集”;高危组和低危组比较发现,高危组含ELN2017不良组(Adverse)病例比例更高(P<0.05);高危组OS较低危组明显缩短(P<0.05);年龄≥60岁(HR:2.853;95%CI:1.909~4.263),ELN2017危险度分层为不良组(HR:1.63;95%CI:1.059~2.511)以及高DDR评分(HR:3.137;95%CI:2.075~4.744)是影响OS的独立危险因素;验证集中发现高危组OS较低危组明显缩短(P<0.05);绘制TCGA数据集的ROC曲线显示:1年AUC=0.709,3年AUC=0.755和5年AUC=0.759。结论DDR基因集灵敏和稳健,DDR评分可用于临床预测AML的预后。

靶向DNA损伤应答在肿瘤放射增敏治疗的研究进展

放射治疗是恶性肿瘤治疗的重要手段,但是,肿瘤放射抗拒是限制放疗疗效、肿瘤复发转移的主要因素。在DNA受损的情况下,细胞内DNA损伤应答随之被激活。研究发现DNA损伤应答不仅影响肿瘤发生,还与肿瘤放射治疗敏感性密切相关,这使其成为肿瘤临床治疗极具前景的靶点。一些针对DNA损伤应答的小分子抑制剂的临床一期实验也正在进行中。本文将对DNA损伤应答在肿瘤中的作用以及DNA损伤应答关键基因和重要路径作为生物标志物和治疗靶点在肿瘤放射增敏治疗中的潜在应用作一综述。

KRAS and BRAF gene mutations and DNA mismatch repair status in Chinese colorectal carcinoma patients

AIM:To investigate gene mutations and DNA mismatch repair(MMR) protein abnormality in Chinese colorectalcarcinoma(CRC) patients and their correlations with clinicopathologic features.METHODS:Clinical and pathological information for 535 patients including 538 tumors was reviewed and recorded.Mutation analyses for exon 2 of KRAS gene and exon 15 of BRAF gene were performed by Sanger sequencing except that in 9 tumors amplification refractory mutation system PCR was used.Expression of MMR proteins including MHL1,MSH2,MSH6 and PMS2 was evaluated by immunohistochemistry.Correlations of KRAS and BRAF mutation status and the expression status of MMR proteins with age,gender,cancer stage,location,and histology were analyzed.Correlations between KRAS or BRAF mutations and MMR protein expression were also explored.RESULTS:The overall frequencies of KRAS and BRAF mutations were 37.9% and 4.4%,respectively.KRAS mutations were more common in patients ≥ 50 years old(39.8% vs 22% in patients < 50 years old,P < 0.05).The frequencies of BRAF mutants were higher in tumors from females(6.6% vs males 2.8%,P < 0.05),located in the right colon(9.6% vs 2.1% in the left colon,1.8% in the rectum,P < 0.01),with mucinous differentiation(9.8% vs 2.8% without mucinous differentiation,P < 0.01),or being poorly differentiated(9.5% vs 3.4% well/moderately differentiated,P < 0.05).MMR deficiency was strongly associated with proximal location(20.5% in the right colon vs 9.2% in the left colon and 5.1% in the rectum,P < 0.001),early cancer stage(15.0% in stages Ⅰ-Ⅱ vs 7.7% in stages Ⅲ-Ⅳ,P < 0.05),and mucinous differentiation(20.2% vs 9.2% without mucin,P < 0.01).A higher frequency of MLH1/PMS2 loss was found in females(9.2% vs 4.4% in males,P < 0.05),and MSH2/MSH6 loss tended to be seen in younger(<50 years old) patients(12.0% vs 4.0% ≥ 50 years old,P < 0.05).MMR deficient tumors were less likely to have KRAS mutations(18.8% vs 41.7% in MMR proficient tumors,P < 0.05) and tumorswith abnormal MLH1/PMS2 tended to harbor BRAF mutations(15.4% vs 4.2% in MMR proficient tumors,P < 0.05).CONCLUSION:The frequency of sporadic CRCs having BRAF mutation,MLH1 deficiency and MSI in Chinese population may be lower than that in the Western population.

Epigenetic regulation of DNA repair machinery in Helicobacter pylori-induced gastric carcinogenesis

Although thousands of DNA damaging events occur in each cell every day,efficient DNA repair pathways have evolved to counteract them. The DNA repair machinery plays a key role in maintaining genomic stability by avoiding the maintenance of mutations. The DNA repair enzymes continuously monitor the chromosomes to correct any damage that is caused by exogenous and endogenous mutagens. If DNA damage in proliferating cells is not repaired because of an inadequate expression of DNA repair genes,it might increase the risk of cancer. In addition to mutations,which can be either inherited or somatically acquired,epigenetic silencing of DNA repair genes has been associated with carcinogenesis. Gastric cancer represents the second highest cause of cancer mortality worldwide. The disease develops from the accumulation of several genetic and epigenetic changes during the lifetime. Among the risk factors,Helicobacter pylori(H. pylori) infection is considered the main driving factor to gastric cancer development. Thus,in this review,we summarize the current knowledge of the role of H. pylori infection on the epigenetic regulation of DNA repair machinery in gastric carcinogenesis.

Perspectives on the combination of radiotherapy and targeted therapy with DNA repair inhibitors in the treatment of pancreatic cancer

Pancreatic cancer is highly lethal. Current research that combines radiation with targeted therapy may dramatically improve prognosis. Cancerous cells are characterized by unstable genomes and activation of DNA repair pathways, which are indicated by increased phosphorylation of numerous factors, including H2 AX, ATM, ATR, Chk1, Chk2, DNA-PKcs, Rad51, and Ku70/Ku80 heterodimers. Radiotherapy causes DNA damage. Cancer cells can be made more sensitive to the effects of radiation(radiosensitization) through inhibition of DNA repair pathways. The synergistic effects, of two or more combined non-lethal treatments, led to coadministration of chemotherapy and radiosensitization in BRCA-defective cells and patients, with promising results. ATM/Chk2 and ATR/Chk1 pathways are principal regulators of cell cycle arrest, following DNA doublestrand or single-strand breaks. DNA double-stranded breaks activate DNA-dependent protein kinase, catalytic subunit(DNA-PKcs). It forms a holoenzyme with Ku70/Ku80 heterodimers, called DNA-PK, which catalyzes the joining of nonhomologous ends. This is the primary repair pathway utilized in human cells after exposure to ionizing radiation. Radiosensitization, induced by inhibitors of ATM, ATR, Chk1, Chk2, Wee1, PP2 A, or DNA-PK, has been demonstrated in preclinical pancreatic cancer studies. Clinical trials are underway. Development of agents that inhibit DNA repair pathways to be clinically used in combination with radiotherapy is warranted for the treatment of pancreatic cancer.