胃癌弱差异基因表达谱中DNMT3A基因表达和生物学作用的探讨

目的:明确胃癌差异基因表达谱中弱差异表达基因的敏感性和特异性;探讨胃癌弱差异表达基因DNMT3A在胃癌发生发展中的生物学作用和意义.方法:利用半定量RT/PCR方法验证了胃癌弱差异基因表达谱中DNMT3A基因的表达水平,并利用GoMiner软件研究了DNMT3A的生物学功能.结果:DNMT3A基因在胃癌组织中比癌旁正常组织表达微弱升高,基因表达变化倍数为1.13,与基因芯片的表达变化(1.10)一致GoMiner软件功能注释表明DNMT3A在甲基化和转录调控等方面具有重要生物学功能.结论:可以在实验室中利用分子生物学方法验证胃癌差异基因表达谱中的弱差异表达基因;弱差异表达基因DNMT3A的异常表达与多种肿瘤的发生有密切的联系,并且可能在胃癌的发生发展中具有重要的生物学作用.     

乳腺癌组织中DNA甲基化转移酶与多药耐药基因ABCG2表达的关系

背景与目的:研究乳腺癌组织中DNA甲基化转移酶(DNA methyltransferase,DNMT)与多药耐药基因ABCG2表达的关系,以进一步探讨ABCG2表达的表观遗传学机制.材料与方法:用实时定量RT-PCR法检测22例乳腺癌及其匹配的癌旁组织中DNMT1、DNMT3A、DNMT3B和ABCG2的表达.并采用Spearman等级相关分析DNMTs与ABCG2基因表达的相关性.结果:乳腺癌组织中ABCG2、DNMT1、DNMT3A、DNMT3B mRNA表达量显著高于癌旁组织(P<0.01),并且DNMT3B表达量显著高于DNMT1和DNMT3A(P<0.01),与ABCG2基因表达呈负相关性(r=-0.664,P<0.01). 结论:乳腺癌组织中DNMT3B可能参与了ABCG2基因的表达调控,这为寻找药物靶点并逆转其介导的药物耐受提供了新的科学依据.     

微RNA-143在肿瘤研究中的新进展

微RNA-143(miR-143)在多种人类肿瘤中低表达,目前研究发现其参与了细胞发育、分化、增殖、凋亡等一系列重要生物学进程.miR-143可能的靶基因有细胞外信号调节激酶5(ERK5)、含3B的纤维连接蛋白Ⅲ型结构域(FNDC3B)、DNA甲基转移酶3A(DNMT3A)、K-ras等.miR-143通过对靶基因的调控参与肿瘤细胞的生长、侵袭、转移和耐药.miR-143与抗肿瘤药物联合应用将是肿瘤治疗的一个新方向.     

黄曲霉毒素B1诱导性大鼠肝癌超微结构观察及DNA甲基化转移酶3表达变化

由DNA甲基化转移酶(DNA methyltransferase,DNMT)活性改变诱导的DNA甲基化模式改变是肿瘤异常表观遗传修饰的重要机制,主要表现为基因组整体的低甲基化和区域性高甲基化,通过改变癌基因、抑癌基因的表达和基因组的稳定性,诱导正常细胞癌性转变[1-2].DNMT3基因是DNMT家系重要成员,在建立组织特异性甲基化模式方面发挥关键作用.黄曲霉毒素B1(aflatoxin B1,AFB1)为公认的原发性肝癌(hepatocellular carcinoma,HCC)致癌因素之一,其致癌过程中同样涉及DNA甲基化模式异常改变[3-6].DNMT3在肝细胞癌变过程中动态变化的研究少见报道,本研究旨在分析AFB1诱导性大鼠肝细胞癌变不同阶段DNMT3a mRNA和DNMT3b mRNA变化特征,初步研究AFB1诱导性大鼠HCC发生的表观遗传学机制.     

DNA甲基转移酶在妇科肿瘤中的研究进展

大量研究表明，许多种类的肿瘤细胞都有异常的DNA甲基化行为，抑癌基因常常被过量地甲基化而失去活性，而基因的DNA序列并不发生改变。DNA甲基化是由DNA甲基转移酶（DNMT）催化并维持的。DNMT通过调节细胞内甲基化过程而参与肿瘤的发生与发展，在有5′端调控区胞嘧啶．鸟嘌呤（CpG）岛甲基化异常参与的肿瘤细胞中常表现为过度表达，其活性增高是肿瘤细胞具有特征的早期分子改变。     

DNA甲基转移酶在肿瘤形成中的研究进展

DNA甲基化是基因表达调控中重要的调节方式之一,可通过影响癌基因和抑癌基因的表达以及基因组的稳定性而参与肿瘤形成。DNA甲基化是由DNA甲基转移酶(DNMT)催化发生并维持的,并认为DNMT活性增高是肿瘤细胞具有特征的早期分子改变,因而受到越来越多的学者关注。     

DNMT1高表达与beta-catenin蓄积及肺鳞癌、腺癌的恶性表型相关

背景与目的 DNA甲基转移酶1(DNA methyltransferase 1,DNMT1)是调控DNA甲基化的重要分子之一,DNMT1的异常表达与抑癌基因的甲基化、失活和多种肿瘤的发生发展有关.本研究旨在分析阐明DNMT1在正常肺组织和肺癌组织中表达的差异及其与肺鳞癌和腺癌临床病理因素的关系,并探讨DNMT1与β-catenin在肺癌中表达的相关性.方法采用组织芯片和免疫组化方法检测DNMT1和β-catenin在84例肺鳞癌、腺癌和相应癌旁正常肺组织中的表达情况.结果 DNMT1在84例肺癌组织中的平均阳性率为(58.04±35.07)%,显著高于癌旁正常肺组织[(6.88±10.26)%](t=12.835,P<0.001).DNMT1的高表达与肺癌组织的腺癌组织学分型(r=0.365,P=0.001)、低 分化程度(r=0.253,P=0.021)和淋巴结转移(r=0.246,P=0.024)正相关.DNMT1 与β-catenin的细胞浆表达显著正相关(r=0.571,P<0.001).结论 DNMT1的高表达是肺鳞癌和腺癌的普遍现象,DNMT1的高表达与肺癌的腺癌组织学类型和恶性表型有关;DNMT1在肺癌中可能与β-catenin协同表达.     

DNA甲基转移酶在肿瘤形成中的研究进展

DNA甲基化是基因表达调控中重要的调节方式之一，可通过影响癌基因和抑癌基因的表达以及基因组的稳定性而参与肿瘤形成。DNA甲基化是由DNA甲基转移酶（DNMT）催化发生并维持的，并认为DNMT活性增高是肿瘤细胞具有特征的早期分子改变，因而受到越来越多的学者关注。     

肿瘤相关基因NDRG2的研究进展

NDRG2隶属于NDRG家族（N-myc down-stream regulated gene family）,是一种与细胞增殖和分化相关的基因,参与了肿瘤的发生、发展和转归,目前功能定位于抑癌候选基因。将NDRG2基因转染入U373和U138胶质瘤细胞系后,明显抑制了胶质瘤细胞的增殖;在结肠癌及高危腺瘤中,NDRG2mRNA表达量明显低于正常组织,同时随着Dukes′分级的增高,NDRG2表达有下降趋势。随着相关研究的不断深入,该基因的其他功能也逐渐被揭示：与组织胚胎的发育和细胞的分化密切相关,与神经系统的发育及其疾病的发生相关,参与了醛固酮对肾远曲小管和集合管的水钠代谢调节作用,以及多种应激反应例如：DNA损伤、缺氧等。目前其转录调控机制及其相互作用分子研究表明,NDRG2受c-Myc负调控且该调控需要Miz-1参与,同时NDRG2还是HIF-1的靶基因。维尔姆斯肿瘤基因（WT1）可以直接或间接诱导NDRG2表达等。但NDRG2生物学功能至今还尚未完全明确,值得进一步探索。     

下调DNMT1对食管鳞癌EC9706增殖、迁移的影响及相关机制的研究

背景与目的：已有研究显示在多种肿瘤组织或细胞中均能检测出特异性DNA甲基转移酶1（DNA methyltransferase 1,DNMT1）的高表达,提示DNMT1的高表达与肿瘤的发生发展密切相关。本研究旨在通过下调DNMT1基因的表达,研究其对食管鳞癌EC9706细胞的增殖及浸润转移能力的影响,并探讨相关的分子作用机制。方法：利用CCK-8试剂盒研检测下调DNMT1对EC9706细胞增殖能力的影响,并利用Boyden室法检测下调DNMT1对EC9706细胞浸润转移能力,进一步通过Real-time PCR和Western印迹法检测转染DNMT1 siRNA后细胞中DNMT1及MMP-2基因的转录及其蛋白表达。结果：DNMT1 siRNA转染后,能明显抑制食管鳞癌EC9706细胞的增殖,降低其浸润转移能力,引起MMP-2表达下调,提示DNMT1下调引起的浸润转移能力的降低可能与MMP-2表达下调密切相关。结论：DNMT1可能成为食管鳞癌治疗新的分子靶点。     

DNA甲基转移酶3A基因与肿瘤发生的分子调控机制研究进展

DNA甲基化是最重要的表观遗传修饰之一,在基因表达、基因组印记、X染色体失活和肿瘤发生的调节中发挥关键作用。DNA甲基转移酶3A（DNMT3A）被称为从头甲基转移酶,负责在胚胎发生期间建立DNA甲基化模式并在生殖细胞发育期间建立基因组印记,其异常表达与肿瘤的发生发展密切相关。本文就DNA甲基转移酶3A基因与肿瘤发生的分子调控机制作一综述。     

MicroRNA-342 inhibits colorectal cancer cell proliferation and invasion by directly targeting DNA methyltransferase 1

Overexpressed DNA methyltransferase 1 (DNMT1) strongly contributes to tumor suppressor gene silencing in colorectal cancer (CRC). However, the underlying mechanism of DNMT1 overexpression is still unclear. MicroRNAs (miRNA) have been implicated as gene regulators controlling diverse biological processes, including carcinogenesis. In this study, we investigated whether some miRNA is involved in the regulation of DNMT1 and thus play a functional role in CRC. Our results showed that miR-342 was downregulated in CRC tissues and cell lines. Restoration of miR-342 resulted in a dramatic reduction of the expression of DNMT1 at both messenger RNA and protein levels by directly targeting its 3' untranslated region. This in turn reactivated ADAM23, Hint1, RASSF1A and RECK genes via promoter demethylation. Furthermore, the enhanced expression of miR-342 could significantly inhibit SW480 cell proliferation in vitro (P = 0.006). Further investigation demonstrated G(0)/G(1) cell cycle arrest in SW480 cells, which was associated with an upregulation of p21 and downregulation of cyclinE and CDK2. Overexpression of miR-342 also inhibited SW480 cell invasion. The in vivo antitumor effect was evaluated in SW480 cells with lentivirus-mediated expression of miR-342. Results showed that overexpression of miR-342 significantly inhibited tumor growth and lung metastasis in nude mice (P = 0.034). Our findings describe a new mechanism for the regulation of DNMT1 and aberrant DNA hypermethylation in CRC. This is also the first report to demonstrate that miR-342 may act as a tumor suppressor gene in CRC development. The newly identified miR-342/DNMT1 link provides a new, potential therapeutic target for the treatment of CRC.     

A DNA methylation signature associated with aberrant promoter DNA hypermethylation of DNMT3B in human colorectal cancer

Altered promoter DNA methylation, one of the most important molecular alterations in cancer, is proposed to correlate with deregulation of DNA methyltransferases, although the molecular mechanisms implicated are still poorly understood. Here we show that the de novo DNA methyltransferase DNMT3B is frequently repressed in human colorectal cancer cell lines (CCL) and primary tumours by aberrant DNA hypermethylation of its distal promoter. At the epigenome level, DNMT3B promoter hypermethylation was associated with the hypomethylation of gene promoters usually hypermethylated in the healthy colon. Forced DNMT3B overexpression in cancer cells restored the methylation levels of these promoters in the healthy colon. Our results show a new molecular mechanism of aberrant DNMT3B regulation in colon cancer and suggest that its expression is associated with the methylation of constitutively hypermethylated promoters in the healthy colon.     

miR-194通过靶定DNMT3A基因调控肝癌细胞的生长

目的:探讨miR-194对肝癌细胞增殖和细胞周期的影响及其潜在的作用机制。方法:实时定量聚合酶链式反应检测肝癌细胞系HepG2和正常肝细胞系L-O2中miR-194的表达水平。构建miR-194过表达质粒,采用MTT法检测细胞增殖活力,流式细胞术检测细胞周期;双荧光素酶报告基因分析法预测和验证miR-194可能的靶基因。结果:实时定量PCR结果显示,miR-194在肝癌细胞中的表达明显低于肝脏正常细胞。在肝癌细胞中过表达miR-194抑制细胞生长。而流式细胞术检测发现细胞周期进程减慢,G1期比例增加,S期比例相应的减少。靶基因筛选得到DNMT3A为miR-194的候选靶基因。荧光报告载体实验证实,miR-194能够通过作用于靶基因3' 非翻译区的特定位点,对其表达在转录后进行负性调节。而在miR-194表达增加的肝癌细胞中,靶基因的mRNA表达水平和蛋白表达水平都有明显降低。在肝癌细胞HepG2中,敲除靶基因DNMT3A后,细胞的增殖能力减弱,相反,当把DNMT3A过表达后,细胞的增殖能力增强,可以挽救miR-194对细胞的表型影响。结论:miR-194可通过靶定DNMT3A基因抑制肝癌细胞的生长。     

骨髓增生异常综合征患者DNMT3A基因突变的情况及临床意义

目的:了解DNMT3A基因突变在骨髓增生异常综合征（MDS）患者中的发生率、分布情况及临床意义。方法:选取2012年 4月至2018年6月在湘雅二医院和湘潭市中心医院住院的85例MDS患者为研究对象。提取患者外周血基因组DNA,针对DNMT3A基因突变热点R882位点设计合成引物,采用聚合酶链式反应法扩增DNMT3A基因23号外显子整个编码区基因片段,再将扩增产物纯化后测序,分析DNMT3A基因突变在本组患者中的发生率、分布情况及临床意义。结果:85例MDS患者中检测到5例DNMT3A基因突变,突变阳性率5.9%,其中R882H和R882C基因突变各2例,R882P基因突变1例,未见R882S基因突变。常规化疗联合去甲基化药物地西他滨治疗后,1例患者一度获得血液学完全缓解,复杂染色体核型恢复正常,但是1月后转为急性白血病并发严重感染死亡,1例治疗后稳定,2例治疗后疾病进展,1例死于肺部感染。结论:MDS中DNMT3A基因突变率低,其突变多预示预后较差,并可能更快地向急性髓性白血病转化,选择去甲基化药物治疗可能获益。     

Carcinogen-induced gene promoter hypermethylation is mediated by DNMT1 and causal for transformation of immortalized bronchial epithelial cells

A better understanding of key molecular changes during transformation of lung epithelial cells could affect strategies to reduce mortality from lung cancer. This study uses an in vitro model to identify key molecular changes that drive cell transformation and the likely clonal outgrowth of preneoplastic lung epithelial cells that occurs in the chronic smoker. Here, we show differences in transformation efficiency associated with DNA repair capacity for two hTERT/cyclin-dependent kinase 4, immortalized bronchial epithelial cell lines after low-dose treatment with the carcinogens methylnitrosourea, benzo(a)pyrene-diolepoxide 1, or both for 12 weeks. Levels of cytosine-DNA methyltransferase 1 (DNMT1) protein increased significantly during carcinogen exposure and were associated with the detection of promoter hypermethylation of 5 to 10 genes in each transformed cell line. Multiple members of the cadherin gene family were commonly methylated during transformation. Stable knockdown of DNMT1 reversed transformation and gene silencing. Moreover, stable knockdown of DNMT1 protein before carcinogen treatment prevented transformation and methylation of cadherin genes. These studies provide a mechanistic link between increased DNMT1 protein, de novo methylation of tumor suppressor genes, and reduced DNA repair capacity that together seem causal for transformation of lung epithelial cells. This finding supports the development of demethylation strategies for primary prevention of lung cancer in smokers.     

DNMT1 and DNMT3b silencing sensitizes human hepatoma cells to TRAIL‐mediated apoptosis via up‐regulation of TRAIL‐R2/DR5 and caspase‐8

DNA methylation plays a critical role in chromatin remodeling and gene expression. DNA methyltransferases (DNMTs) are hypothesized to mediate cellular DNA methylation status and gene expression during mammalian development and in malignant diseases. In this study, we examined the role of DNA methyltransferase 1 (DNMT1) and DNMT3b in cell proliferation and survival of hepatocellular carcinoma (HCC) cells. Gene silencing of both DNMT1 and DNMT3b by targeted siRNA knockdown reduces cell proliferation and sensitizes the cells to tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL)‐mediated cell death. The proapoptotic protein caspase‐8 demonstrated promoter hypermethylation in HCC cells and was up‐regulated by knockdown of DNMT1 and DNMT3b both at mRNA and protein levels. In addition, death receptor TRAIL‐R2/DR5 (TRAIL receptor 2/death receptor 5) did not exhibit promoter hypermethylation in HCC cells but was also up‐regulated by knockdown of DNMT1 and DNMT3b both at mRNA and protein levels. Consistent with this observation, the combined transfection of DNMT1‐siRNA plus DNMT3b‐siRNA enhanced formation of the TRAIL‐death‐inducing signaling complex formation in HCC cells. In conclusion, our data suggest that DNA methylation of specific genomic regions maintained by DNMT1 and DNMT3b plays a critical role in survival of HCC cells, and a simultaneous knockdown of both DNMT1 and DNMT3b may be a novel anticancer strategy for the treatment of HCC. (Cancer Sci 2010)     

DNMT3a通过STAT3及RAD51影响胰腺癌细胞对奥沙利铂敏感性的研究

目的:检测DNMT3a在胰腺癌细胞中的表达及对奥沙利铂（oxaliplatin，OXA）敏感性的影响，探讨DNMT3a对胰腺癌细胞奥沙利铂敏感性影响的机制。方法:MTT法检测奥沙利铂对人胰腺癌Panc-1细胞的增殖影响，及下调DNMT3a对Panc-1细胞奥沙利铂敏感性的影响。Western blot检测siDNMT3a对DNMT3a蛋白表达的影响，检测奥沙利铂及下调DNMT3a对γ-H2AX、RAD51、p-STAT3和STAT3蛋白表达的影响。流式细胞仪检测奥沙利铂及联合下调DNMT3a对Panc-1细胞凋亡的影响。结果:奥沙利铂能够以浓度依赖方式抑制胰腺癌Panc-1细胞的增殖。奥沙利铂能够引起DNA损伤、γ-H2AX上调及RAD51增高，同时引起STAT3通路的一过性活化。下调DNMT3a表达能够明显增加Panc-1细胞对奥沙利铂的敏感性，抑制STAT3一过性活化，并抑制RAD51表达，促进DNA损伤，进而增加奥沙利铂诱导Panc-1细胞的凋亡。结论:下调DNMT3a表达能够通过抑制STAT3活化及增加DNA损伤增加胰腺癌细胞对奥沙利铂的敏感性，DNMT3a有望成为胰腺癌新的治疗靶点。     

Decrease of DNA methyltransferase 1 expression relative to cell proliferation in transitional cell carcinoma

In many common cancers such as transitional cell carcinoma (TCC), specific genes are hypermethylated, whereas overall DNA methylation is diminished. Genome-wide DNA hypomethylation mostly affects repetitive sequences such as LINE-1 retrotransposons. Methylation of these sequences depends on adequate expression of DNA methyltransferase I (DNMT1) during DNA replication. Therefore, DNMT1 expression relative to proliferation was investigated in TCC cell lines and tissue as well as in renal carcinoma (RCC) cell lines, which also display hypomethylation, as indicated by decreased LINE-1 methylation. Cultured normal uroepithelial cells or normal bladder tissue served as controls. In all tumor cell lines, DNMT1 mRNA as well as protein was decreased relative to the DNA replication factor PCNA, and DNA hypomethylation was present. However, the extents of hypomethylation and DNMT1 downregulation did not correlate. Reporter gene assays showed that the differences in DNMT1 expression between normal and tumor cells were not established at the level of DNMT1 promoter regulation. Diminished DNMT1:PCNA mRNA ratios were also found in 28/45 TCC tissues but did not correlate with the extent of DNA hypomethylation. In addition, expression of the presumed de novo methyltransferases DNMT3A and DNMT3B mRNAs was investigated. DNMT3B overexpression was observed in about half of all high-stage TCC (DNMT3B vs. tumor stage, chi(2): p = 0.03), whereas overexpression of DNMT3A was rarer and less pronounced. Expression of DNMT3A and DNMT3B in most RCC lines was higher than in TCC lines. Our data indicate that DNMT1 expression does not increase adequately with cell proliferation in bladder cancer. This relative downregulation probably contributes to hypomethylation of repetitive DNA but does not determine its extent alone.