DNA甲基化在肿瘤无创性分子诊断中的研究进展

DNA甲基化是真核细胞基因组最常见的一种表观遗传学修饰.DNA甲基化异常在肿瘤的发生、发展过程中扮演重要角色.研究显示DNA甲基化是一类潜力很大的肿瘤标志物.肿瘤特异性的DNA甲基化标志物可从肿瘤患者血清/血浆、尿液、粪便和支气管肺泡灌洗液中检出,为进行肿瘤无创性诊断DNA甲基化检测提供了新思路.本文对DNA甲基化在恶性肿瘤早期诊断的研究进展作一综述.     

DNA甲基化与乳腺癌

DNA甲基化是人类基因组发生的最为常见的一种表观遗传学事件,在乳腺癌发生相关机制中具有重要意义.本文主要对乳腺癌肿瘤细胞内DNA甲基化异常、DNA甲基化及其与乳腺癌诊治和预后判断的研究进展作一综述,并对去甲基化治疗的前景进行展望.     

DNA甲基化与肺癌

DNA异常甲基化是人类肿瘤中常见的改变。发生在启动子区的CpG岛的异常甲基化是基因失活的最常见机制。某些基因甲基化与肺癌发生密切相关,且是肺癌发生中的早期事件。     

DNA甲基化与妇科肿瘤

DNA甲基化是肿瘤抑制基因失活的第3种机制,DNA甲基化造成的基因异常对肿瘤的发生及发展有着重要影响.许多肿瘤相关基因启动子区域CpG岛过甲基化与妇科肿瘤的形成密切相关,DNA甲基化研究将广泛应用于妇科肿瘤的分类、肿瘤的早期发现、治疗以及预测肿瘤转移复发等.     

循环肿瘤DNA甲基化在卵巢癌中的研究进展

卵巢癌是最致命的妇科恶性肿瘤，对卵巢癌的早期诊断、治疗监测和预后判断尤为重要。越来越多的证据表明DNA甲基化在致癌过程中发挥重要的作用。肿瘤中发现的基因启动子异常甲基化，可以反映在从肿瘤释放到外周血的循环肿瘤DNA（circulating tumor DNA,ctDNA），与原发肿瘤有一致性改变,从而使ctDNA甲基化成为基于血液检测的非侵入性分子标志物。本文将介绍ctDNA甲基化及其检测方法，卵巢癌中常见的ctDNA甲基化标志物，并重点阐述ctDNA甲基化在卵巢癌中的研究进展。     

DNA甲基化在肿瘤诊断和治疗中的研究进展

DNA甲基化在基因表达调控、基因突变、细胞增殖、分化以及基因印迹等方面与肿瘤的发生发展有着密切的联系.抑癌基因的高甲基化和特异癌基因的低甲基化是目前肿瘤中DNA甲基化异常的主要形式.通过诱导癌基因和抑癌基因的DNA甲基化可抑制肿瘤的生长及癌基因的表达,是目前抗肿瘤治疗和诊断的新思路.本文就癌基因及抑癌基因的甲基化治疗和诊断在临床前的研究进展做一综述.     

DNA甲基化在肿瘤中的研究进展

DNA甲基化是调节真核生物基因表达的重要方式之一.DNA甲基化在正常细胞癌变过程中发挥重要的作用.在多种肿瘤类型中,控制细胞周期、增殖、凋亡、转移、耐药性以及细胞内信号传导的相关基因存在异常甲基化.     

DNA甲基化与肿瘤发生及治疗

DNA甲基化对肿瘤相关基因表达的调控起重要的作用,肿瘤细胞中的基因甲基化异常主要表现为基因组整体水平的低甲基化、癌基因的低甲基化以及抑癌基因、错配修复基因等高甲基化等。近期,关于DNA甲基化在肿瘤的诊断、治疗及预后等方面的作用及意义的研究正深入展开。现综述肿瘤基因的异常甲基化及DNA甲基化在肿瘤临床中应用的研究进展。     

DNA甲基化与肿瘤发生及治疗

DNA甲基化对肿瘤相关基因表达的调控起重要的作用,肿瘤细胞中的基因甲基化异常主要表现为基因组整体水平的低甲基化、癌基因的低甲基化以及抑癌基因、错配修复基因等高甲基化等。近期,关于DNA甲基化在肿瘤的诊断、治疗及预后等方面的作用及意义的研究正深入展开。现综述肿瘤基因的异常甲基化及DNA甲基化在肿瘤临床中应用的研究进展。     

血中循环DNA启动子甲基化与妇科肿瘤的关系

妇科恶性肿瘤患者外周血中存在着循环DNA,其含量明显高于健康人水平且具有与肿瘤原发灶相一致的基因异常改变,DNA基因启动子甲基化是基因异常中一项重要的表观遗传学改变,是导致肿瘤抑癌基因、DNA错配修复基因、转移抑制基因等表达沉默的重要分子生物学基础.目前已检测到妇科恶性肿瘤患者外周血循环DNA中有多种基因存在异常甲基化,且与肿瘤患者的临床病理特征存在不同程度的相关性.这使得非创伤性早期诊断肿瘤、及时发现肿瘤的复发或转移、监测疗效、预测预后成为可能.     

Detection of methylated apoptosis-associated genes in urine sediments of bladder cancer patients.

PURPOSE: There is increasing evidence for a fundamental role for epigenetic silencing of apoptotic pathways in cancer. Changes in DNA methylation can be detected with a high degree of sensitivity, so we used the MethyLight assay to determine how methylation patterns of apoptosis-associated genes change during bladder carcinogenesis and whether DNA methylation could be detected in urine sediments. EXPERIMENTAL DESIGN: We analyzed the methylation status of the 5' regions of 12 apoptosis-associated genes (ARF, FADD, TNFRSF21, BAX, LITAF, DAPK, TMS-1, BCL2, RASSF1A, TERT, TNFRSF25, and EDNRB) in 18 bladder cancer cell lines, 127 bladder cancer samples, and 37 samples of adjacent normal bladder mucosa using the quantitative MethyLight assay. We also analyzed the methylation status in urine sediments of 20 cancer-free volunteers and 37 bladder cancer patients. RESULTS: The 5' regions of DAPK, BCL2, TERT, RASSFIA, and TNFRSF25 showed significant increases in methylation levels when compared with nonmalignant adjacent tissue (P < or = 0.01). Methylation levels of BCL2 were significantly associated with tumor staging and grading (P < or = 0.01), whereas methylation levels of RASSF1A and ARF were only associated with tumor stage (P < or = 0.04), and TERT methylation and EDNRB methylation were predictors of tumor grade (P < or = 0.02). To investigate clinical usefulness for noninvasive bladder cancer detection, we further analyzed the methylation status of the markers in urine samples of patients with bladder cancer. Methylation of DAPK, BCL2, and TERT in urine sediment DNA from bladder cancer patients was detected in the majority of samples (78%), whereas they were unmethylated in the urine sediment DNA from age-matched cancer-free individuals. CONCLUSIONS: Our results indicate that methylation of the 5' region of apoptosis-associated genes is a common finding in patients with bladder carcinoma. The ability to detect methylation not only in bladder tissue, but also in urine sediments, suggests that methylation markers are promising tools for noninvasive detection of bladder cancers. Our results also indicate that some methylation markers, such as those in regions of RASSF1A and TNFRSF25, might be of limited use for detection because they are also methylated in normal bladder tissues.     

LINE-1 hypomethylation is associated with bladder cancer risk among nonsmoking Chinese

Reduced levels of global DNA methylation, assessed in peripheral blood, have been associated with bladder cancer risk in European and American populations. Similar data are lacking in Asian populations where genetic differences, lifestyle factors and different environmental exposures may affect DNA methylation and its risk relationship with bladder cancer. The association between global DNA methylation measured at long interspersed nuclear element (LINE-1) repeat regions through bisulfite pyrosequencing in lymphocyte DNA and bladder cancer risk was examined in a case-control study of 510 bladder cancer patients and 528 healthy control subjects in Shanghai, China. In an initial analysis restricted to control subjects, LINE-1 methylation was elevated among men, those who frequently consumed cruciferous vegetables and those with a null genotype for either glutathione S-transferase M1 (GSTM1) or GSTT1. In contrast, reduced LINE-1 methylation was found in current smokers with a high-cytochrome P450 1A2 (CYP1A2) phenotype index. In a case-control analysis, there was no significant association of LINE-1 methylation with case status, although reduced LINE-1 methylation was associated with increased risk of bladder cancer among never smokers (p for trend = 0.03); analysis by tertile revealed odds ratios (ORs) of 1.91 (lowest tertile; 95% CI = 1.17-3.13) and 1.34 (middle tertile; 95% CI = 0.79-2.28) when compared with the highest tertile. This association was strongest among nonsmokers null for either the GSTM1 or GSTT1 genotype (p for trend = 0.006). Further research is needed to understand the relationships between methyl group availability and LINE-1 methylation in relation to bladder cancer risk.     

用尿沉淀细胞DNA甲基化状态的分析检测膀胱癌

目的：确定尿沉淀细胞DNA中的13个肿瘤相关基因启动子的甲基化谱式分析在膀胱癌诊断中的价值。方法：用定性甲基化特异性（methylation specific polymerase chain reaction，MSP）的方法，对92例临床确诊的膀胱癌患者、23例非肿瘤性尿路疾病患者、6例脑外科患者、7例健康志愿者检测了尿沉淀细胞DNA中肿瘤相关基因启动子的甲基化状态。结果：在临床确诊的92例膀胱癌患者中被检测的13个基因的高甲基化状态出现频率显著高于23例非肿瘤性尿路疾病患者，差异有统计学意义（P〈0．05）。而6例脑外科患者和7例正常健康人的尿沉淀细胞DNA中，上述基因均为去甲基化状态。若以任一个基因高甲基化为膀胱癌的指征，88．0％（81／92例）的膀胱癌可被检出。结论：MSP法分析尿沉淀细胞DNA中肿瘤相关基因启动子的甲基化状态可有效地检出膀胱癌。     

High Detection Rate for Non–Muscle-Invasive Bladder Cancer Using an Approved DNA Methylation Signature Test

IntroductionCystoscopy and transurethral resection are the current reference standard tests to diagnose and histologically confirm non–muscle-invasive bladder cancer (NMIBC). In other tumor entities (ie, colon carcinoma, cervical cancer), DNA methylation markers have been approved as diagnostic tests with high diagnostic power. In our case-control study, we used an approved molecular cervical cancer diagnostics test that includes 6 DNA methylation markers (GynTect) for the detection of bladder cancer.Patients and MethodsWe included samples from 40 patients with bladder cancer and 34 control subjects. In a pilot study, we analyzed DNA methylation in 38 tumor tissues and 4 healthy ureters using methylation-specific polymerase chain reaction. Subsequently, we determined the sensitivity and specificity of the GynTect for the detection of bladder cancer in urine sediments from 40 patients with bladder cancer and 30 control subjects with benign prostatic hyperplasia or urolithiasis.ResultsThe markers showed very different methylation rates in the NMIBC tissues, ranging from 2.6% to 78.9%. No methylation of any of the markers was detectable in the healthy ureters. Using the urine sediments from the patients with cancer and control subjects, we found surprisingly high sensitivity and specificity for the GynTect assay (60% and 96.7%, respectively). The application of different algorithms for evaluation of the markers included in GynTect resulted in a sensitivity of ≤ 90% and specificity of ≤ 100%.ConclusionThe GynTect assay, originally designed for cervical cancer diagnostics, showed unexpectedly high diagnostic accuracy for bladder cancer detection. The inclusion of additional methylation markers might allow for the development of a suitable diagnostic marker set based on the GynTect test for NMIBC diagnostics.     

RUNX3 methylation reveals that bladder tumors are older in patients with a history of smoking

Exposure to tobacco smoke is associated with increased DNA methylation at certain genes in both lung and bladder tumors. We sought to identify interactions in bladder cancer between DNA methylation and a history of smoking, along with any possible effect of aging. We measured DNA methylation in 342 transitional cell carcinoma tumors at BCL2, PTGS2 (COX2), DAPK, CDH1 (ECAD), EDNRB, RASSF1A, RUNX3, TERT, and TIMP3. The prevalence of methylation at RUNX3, a polycomb target gene, increased as a function of age at diagnosis (P = 0.031) and a history of smoking (P = 0.015). RUNX3 methylation also preceded methylation at the other eight genes (P < 0.001). It has been proposed that DNA methylation patterns constitute a "molecular clock" and can be used to determine the "age" of normal tissues (i.e., the number of times the cells have divided). Because RUNX3 methylation increases with age, is not present in normal urothelium, and occurs early in tumorigenesis, it can be used for the first time as a molecular clock to determine the age of a bladder tumor. Doing so reveals that tumors from smokers are "older" than tumors from nonsmokers (P = 0.009) due to tumors in smokers either initiating earlier or undergoing more rapid cell divisions. Because RUNX3 methylation is acquired early on in tumorigenesis, then its detection in biopsy or urine specimens could provide a marker to screen cigarette smokers long before any symptoms of bladder cancer are present.     

Examination of IGF2 and H19 loss of imprinting in bladder cancer

Loss of imprinting (LOI) is a common epigenetic event in cancer and may serve as an early biomarker in some cancers. To obtain a better understanding of LOI, we studied 41 bladder tumors and their adjacent normal bladder mucosa. We found 2/9 (22.2%) cases that displayed LOI of IGF2 and 2/16 (12.5%) that had LOI of H19, as determined by the evaluation of mRNA for biallelic expression. In addition, we examined allele-specific methylation of the differentially methylated regions (DMR) of IGF2 and H19 using a new allele-specific pyrosequencing assay. We found that DNA methylation changes were a common finding (21/30, 70%) in the DMR regions, but could not clearly link DNA methylation changes with LOI as measured by biallelic expression. LOI and allele-specific DNA methylation changes are present in bladder cancer; however, a better understanding of the biology of LOI and its relationship to DNA methylation changes is needed before its use as an epigenetic biomarker.     

抗凋亡基因bcl-2启动子CpG岛的高甲基化状态见于28.3%(13/46例)的膀胱癌患者尿沉淀细胞DNA

目的:检测上海地区膀胱癌患者尿沉淀细胞中3个肿瘤相关基因启动子CpG岛的甲基化谱式异常频率,继而评估其应用前景。方法:采用甲基化特异性PCR方法分析尿沉淀细胞DNA中DAPK1、bcl2和hTERT3个基因的启动子CpG岛甲基化状态,并通过RTPCR方法评估DAPK1基因在膀胱癌细胞系中的表达状态。结果:对膀胱癌细胞系中DAPK1基因的启动子CpG岛甲基化状态及其表达(mRNA水平上)所做的分析,确立了高甲基化状态与表达静息化之间的相关性。对46例临床确诊的膀胱癌患者和84例非膀胱癌对照(包括前46例术后的36例)的尿沉淀细胞中DNA甲基化的分析发现,仅bcl2基因的高甲基化见之于28.3%(13/46例)的膀胱癌患者,而84例的对照中均为去甲基化状态。结论:在美国膀胱癌患者尿沉淀细胞中频发DNA高甲基化的靶点在上海地区膀胱癌患者人群中频率很低,因此寻找在后者中频发DNA高甲基化的新靶点实属必要。     

Fragile genes as biomarkers: epigenetic control of WWOX and FHIT in lung, breast and bladder cancer

This study aimed to (a) determine if DNA methylation is a mechanism of WWOX (WW domain containing oxidoreductase) and FHIT (fragile histidine triad) inactivation in lung, breast and bladder cancers; (b) examine distinct methylation patterns in neoplastic and adjacent tissues and (c) seek correlation of methylation patterns with disease status. Protein expression was detected by immunohistochemistry, and methylation status by methylation-specific PCR (MSP) and sequencing, in lung squamous cell carcinomas and adjacent tissues, invasive breast carcinomas, adjacent tissues and normal mammary tissues and bladder transitional cell carcinomas. Wwox and Fhit expression was reduced in cancers in association with hypermethylation. Differential patterns of WWOX and FHIT methylation were observed in neoplastic vs adjacent non-neoplastic tissues, suggesting that targeted MSP amplification could be useful in following treatment or prevention protocols. WWOX promoter MSP differentiates DNA of lung cancer from DNA of adjacent lung tissue. WWOX and FHIT promoter methylation is detected in tissue adjacent to breast cancer and WWOX exon 1 MSP distinguishes breast cancer DNA from DNA of adjacent and normal tissue. Differential methylation in cancerous vs adjacent tissues suggests that WWOX and FHIT hypermethylation analyses could enrich a panel of DNA methylation markers.