Expression of O⁶-Methylguanine-DNA Methyltransferase Examined by Alkyl-Transfer Assays, Methylation-Specific PCR and Western Blots in Tumors and Matched Normal Tissue

The tumor selectivity of alkylating agents that produce guanine O6-chloroethyl (laromustine and carmustine) and O6-methyl (temozolomide) lesions depends upon O6-methylguanine-DNA methyltransferase (MGMT) activity being lower in tumor than in host tissue. Despite the established role of MGMT as a tumor resistance factor, consensus on how to assess MGMT expression in clinical samples is unsettled. The aim of this study is to examine the relationship between the values derived from distinctive MGMT measurements in 13, 12, 6 and 2 pairs of human tumors and matched normal adjacent tissue from the colon, kidney, lung and liver, respectively, and in human cell lines. The MGMT measurements included 1) alkyl-transfer assays using [benzene-3H]O6-benzylguanine as a substrate to assess functional MGMT activity, 2) methylation-specific PCR (MSP) to probe MGMT gene promoter CpG methylations as a measure of gene silencing, and 3) western immunoblots to analyze the MGMT protein. In human cell lines, a strict negative correlation existed between MGMT activity and the extent of promoter methylation. In tissue specimens, by contrast, the correlation between these two variables was low. Moreover, alkyl-transfer assays identified 3 pairs of tumors and normal tissue with tumor-selective reduction in MGMT activity in the absence of promoter methylation. Cell line MGMT migrated as a single band in western analyses, whereas tissue MGMT was heterogeneous around its molecular size and at much higher molecular masses, indicative of multi-layered post-translational modifications. Malignancy is occasionally associated with a mobility shift in MGMT. Contrary to the prevalent expectation that MGMT expression is governed at the level of gene silencing, these data suggest that other mechanisms that can lead to tumorselective reduction in MGMT activity exist in human tissue.

Different denaturation rates between methylated and non-methylated genomic DNA can result in allele-specific PCR amplification

We analysed a DNA sample from a father and child who were both heterozygous for a 7 base pair insertion in the MEST gene differentially-methylated promoter region, previously shown by PCR analysis of bisulphite-treated DNA to be on the methylated allele in the unaffected father and the unmethylated allele in the affected child. PCR from genomic DNA was then carried out using a commercial PCR kit with its recommended initial DNA denaturation step of 2 minutes. Subsequent sequence analysis showed that only the non-methylated allele had been amplified, the father appearing to be homozygous normal and the child appearing to have a homozygous 7 b.p. insertion. The PCR protocol was then modified in order to use a longer DNA denaturation stage prior to the addition of the polymerase enzyme. Upon doing so, both the methylated and non-methylated alleles were then identifiable by sequencing with the mutation appearing in its expected heterozygous form. These results highlight the fact that the methylation status of DNA can affect the denaturation rate prior to PCR and result in allele drop-out, showing that the standard protocols of commercial kits should be used with caution when working with methylated regions of DNA.

基于甲基化特异性PCR的外周血循环游离DNA甲基化检测对乳腺癌诊断价值的荟萃分析

目的通过Meta分析系统评估基于甲基化特异性PCR(MSP)的外周血循环游离DNA(cfDNA)甲基化检测对乳腺癌的诊断价值。方法检索PubMed、Embase、Cochrane数据库,检索时间为2011年1月至2021年12月,以“Breast neoplasms”“Breast cancer”“Methylation”“Cell-free DNA”等为检索词,检索有关血液循环cfDNA甲基化用于乳腺癌诊断的文献,根据纳入及排除标准筛选文献。使用QUADAS-2对纳入文献进行质量评价,提取研究数据并使用Stata 16.0对各效应量进行合并,分析异质性及来源,以Deek’s法检验发表偏倚。结果共检索318篇文献,最终纳入12篇文献的27项研究进行Meta分析,患者2195例,纳入研究存在高度异质性(I^(2)>50.00%)。采用随机效应模型合并灵敏度为0.43[95%CI(0.31~0.56)],合并特异度为0.97[95%CI(0.94~0.99)],合并阳性似然比(LR+)为16.30[95%CI(7.00~37.80)],合并阴性似然比(LR-)为0.59[95%CI(0.47~0.73)],合并诊断比值比(DOR)为28.00[95%CI(11.00~70.00)],合并AUC为0.85[95%CI(0.82~0.88)]。结论基于MSP的外周血cfDNA甲基化检测对乳腺癌有较高的辅助诊断价值。

p16 promoter hypermethylation:A useful serum marker for early detection of gastric cancer

AIM： TO determine p15 promoter hypermethylation in gastric tumoral tissue and serum samples, its impact on p16-protein expression, and correlation with clinical and histological features. METHODS： Samples were obtained from 52 histologically confirmed cases of gastric adenocarcinoma. Gastric tissue and serum of 50 age- and sex-matched individuals with normal gastroscopy and biopsy were obtained as control samples. Methylation-specific polymerase chain reaction （MSP） was used to evaluate methylation status of p16 promoter, p16-protein expression was analyzed by immunohistochemical staining on paraffin-embedded sections. RESULTS： Methylation was detected in 44.2% （23/52） of tumoral tissues. 60.9% of them were also methylated in serum, i.e., 26.9% of all patients （14/52）. Methylation was not detected in tissue and sera of control samples. p16-protein expression was decreased in 61.5% of cases （32/52）, and was significantly associated with promoter hypermethylation （P 〈 0.001）. Methylation was significantly more frequent in higher pathological grades （P 〈 0.05）. Methylation was not associated with other clinicopathological features and environmental factors including Hpylori infection and smoking. CONCLUSION： p16 promoter hypermethylation is an important event in gastric carcinogenesis. It is the principle mechanism of p16 gene silencing. It is related to malignant tumor behavior. Detection of DNA methylation in serum may be a biomarker for early detection of gastric cancer.

Methylation profiling of twenty four genes and the concordant methylation behaviours of nineteen genes that may contribute to hepatocellular carcinogenesis

To determine the possible role of the epigenetic mechanisms in carcinogenesis of the hepatocellular carcinoma, we methylation-profiled the promoter CpG islands of twenty four genes both in HCC tumors and the neighboring non-cancerous tissues of twenty eight patients using the methylation-specific PCR (MSP) method in conjunction with the DNA sequencing. In comparison with the normal liver tissues from the healthy donors, it was found that while remained unmethylated the ABL, CAV, EPO, GATA3, LKB1, NEP, NFL, NIS and p27^(KIP1) genes, varying extents of the HCC specific hypermethylation were found associated with the ABO, AR, CSPG2, cyclin al, DBCCR1, GALR2, IRF7, MGMT, MT1A, MYOD1, OCT6, p57^(KIP2), p73, WT1 genes, and demethylation with the MAGEA1 gene, respectively. Judged by whether the hypermethylated occurred in HCC more frequently than in their neighboring normal tissues, the hypermethylation status of the AR, DBCCR1, IRF7, OCT6, and p73 genes was considered as the event specific to the late stage, while that the rest that lacked such a distinguished contrast, as the event specific to the early stage of HCC carcinogenesis. Among all the clinical pathological parameters tested for the association with, the hypermethylation of the cyclin al gene was more prevalent in the non-cirrhosis group (P=0.021) while the hypermethylated p16^(INK4a) gene was more common in the cirrhosis group (P=0.017). The concordant methylation behaviors of nineteen genes, including the four previously studied and their association with cirrhosis has been evaluated by the best subgroup selection method. The data presented in this report would enable us to shape our understanding of the mechanisms for the HCC specific loss of the epigenetic stability of the genome, as well as the strategy of developing the novel robust methylation based diagnostic and prognostic tools.

Methylation of RAR-β2, RASSF1A, and CDKN2A Genes Induced by Nickel Subsulfide and Nickel-carcinogenesis in Rats

Objective To investigate the expression variation of RAR‐β2, RASSF1A, and CDKN2A gene in the process of nickel‐induced carcinogenesis. Methods Nickel subsulfide （Ni 3 S 2 ） at dose of 10 mg was given to Wistar rats by intramuscular injection. The mRNA expression of the three genes in induced tumors and their lung metastasis were examined by Real‐time PCR. The methylation status of the 5’ region of these genes were detected by Quantitative Real‐time methylation specific PCR. Results The mRNA expressions of the three genes both in muscle and lung tumor were decreased distinctly in comparison with normal tissue. But hypermethylation was found only in muscle tumor. Conclusion These findings suggest that loss of function or decrease of RAR‐β2, RASSF1A, and CDKN2A, as well as the hypermethylation of 5’ region of these genes, are related with nickel exposure.

The methylation status of the TMS1/ASC gene in cholangiocarcinoma and its clinical significance

BACKGROUND: TMS1/ASC is a bipartite protein comprising two protein-protein interactive domains: pyrin (PYD) and caspase recruitment domain (CARD). Proteins containing these domains play pivotal roles in regulating apoptosis and immune response pathways. The absence of TMS1/ ASC expression in some tumors is because methylation of the TMS1/ASC gene contributes to carcinogenesis and cancer development. We studied the methylation status of the TMS1/ASC gene and its clinical significance in cholangiocarcinoma. METHODS: Target DNA was modified by sodium bisulfite, coverting all unmethylated, but not methylated, cytosines to uracil, and subsequently by a nested amplification with primers specific for methylated versus unmethylated DNA. The PCR product was detected by gel electrophoresis and combined with the clinical records of patients. RESULTS: Aberrant methylation of the TMS1/ASC gene was detected in specimens of colorectal cancer tissues from 13 (36.1%) of 36 patients, and specimens of adjacent normal tissues from 3 patients (8.3%). No statistical differences were seen in the extent of differentiation and invasion, lymph node metastasis, and pathologic type between the methylated and unmethylated tissues (P】0.05). CONCLUSIONS: The frequency of TMS1/ASC gene methylation in cholangiocarcinoma is high, but it is not related to pathologic changes. The TMS1/ASC gene is probably suppressed by methylation, and is resistant to apoptosis and immunological surveillance. The gene epigenetically affected in methylated tissues could be associated with carcinogenesis of cholangiocarcinoma.

Prognostic Value of Promoter Hypermethylation of Retinoic Acid Receptor Beta (RARB) and CDKN2 (p16/MTS1) in Prostate Cancer

Objective: The molecular mechanism of prostate cancer is poorly understood. The aim of the study was to investigate the prevalence and prognostic value of promoter hypermethylation of retinoic acid receptor beta (RARB) and p16 among benign prostatic hyperplasia (BPH) and prostate cancer patients. Methods: In this case-control study, 63 patients were included in three groups; 21 with BPH as the control group, 21 with prostate cancer and good prognostic factors (based on prostate-specific antigen, Gleason score and stage) as good prognosis group, and 21 with prostate cancer and poor prognostic features as poor prognosis group. The prostate biopsy specimen of each individual was examined for hypermethylation of RARB and p16 promoters by methylation specific PCR (MSPCR). Results: Seven (33.3%) patients with good prognosis and 15 (71.4%) patients with poor prognosis were positive for RARB methylation, which were significantly higher than controls (P <0.0001). p16 promoter methylation was shown in 19.0% and 47.6% patients with good and poor prognosis, respectively. The RARB and p16 promoter methylation in the poor prognosis group was significantly higher than that in the good prognosis group (P =0.02 for RARB and P<0.0001 for p16). Conclusion: Hypermethylation of RARB and p16 promoters may predict prognosis in prostate cancer.

Promoter hypermethylation of death-associated protein kinase gene in cholangiocarcinoma

BACKGROUND: Death-associated protein kinase (DAPK) is a Ca2+/calmodulin-regulated Ser/Thr kinase which is involved in apoptosis. The aberrant methylation of its promoter region CpG islands may be one of the important mechanisms of carcinogenesis. We studied the relationship of methylation status and expression of the DAPK gene with the clinical findings in cholangiocarcinoma. METHODS: Target DNA was modified by sodium bisulfite, coverting all unmethylated, but not methylated, cytosines to uracil, and subsequently detected by methylation-specific PCR. Moreover, mRNA expression of the DAPK gene was assessed by RT-PCR. RESULTS: Aberrant methylation of the DAPK gene was detected in 11 (30.6%) of 36 tissue specimens of cholangiocarcinoma, and in 2 (5.6%) of 36 specimens of adjacent normal tissues. DAPK mRNA was not expressed in tumor and adjacent tissues with hypermethylation of the DAPK promoter. There were no statistical differences in the extent of differentiation and invasion, lymph node metastasis or pathologic type between the methylated and unmethylated tissues. CONCLUSIONS: The frequency of DAPK gene methylation in cholangiocarcinoma is high and it may offer an effective means for earlier auxiliary diagnosis of the malignancy. The DAPK gene is probably suppressed by methylation, and it could become resistant to apoptosis and immunological surveillance. The DAPK gene epigenetically affected by methylation may be associated with the carcinogenesis of cholangiocarcinoma.

Alteration of oncogenic IGF-II gene methylation status associates with hepatocyte malignant transformation

Background: Oncogenic insulin-like growth factor-II(IGF-II) is overexpressed in hepatocellular carcinoma(HCC). The present study aimed to analyze the dynamic alteration of IGF-II CpG site methylation status and its molecular mechanism in HCC progression. Methods: IGF-II alterations were observed in rat hepatocarcinogenesis models induced by 2-acetylaminofluorene. Liver IGF-II expression was compared by immunohistochemistry or tissue IGF-II specific concentration(nmol/mg protein). Status of human IGF-II promoter 3(P3) or rat IGF-II P2 CpG site methylation was amplified by methylation-specific polymerase chain reaction(MSP). Serum IGF-II levels were quantitatively detected by an enzyme-linked immunosorbent assay. Results: The levels of hepatic IGF-II expression were significantly elevated in the HCC group( P < 0.001). The unmethylation rate of IGF-II P3 CpG sites was 100% in the HCC-, 52.5% in the paracancerous-, and none(0%) in the distal noncancerous-tissues. Abnormal IGF-II expression was related to differentiation degree, tumor invasion, and positive HBV-DNA(all P < 0.001), with a negative correlation between P3 methylation degree and IGF-II expression. There was a positive correlation between liver IGF-II specific concentration and circulating IGF-II level( r = 0.97, P < 0.001). Significantly negative correlation was found between IGF-II P2 CpG site methylation and circulating IGF-II( r s =-0.89, P < 0.001) or liver IGF-II level( r s =-0.84, P < 0.001). Conclusions: The increase of serum IGF-II and the alteration of oncogenic gene IGF-II methylation may be biomarkers for HCC diagnosis and DNA methylation may be the therapeutic target of HCC.

Promoter Hypermethylation of DNA Repair Gene MGMT in Laryngeal Squamous Cell Carcinoma

The relationship between hypermethylation of CpG islands in the promoter regions of O^6- methylguanine DNA methyhransferase （MGMT） genes and laryngeal squamous cell carcinoma was explored. Methylation-specific PCR and semi-quantitative RT-PCR were used to study the promoter methylation and mRNA expression of the MGMT gene in laryngeal carcinoma tissues, tissues adjacent to the tumor and normal laryngeal tissues. Hypermethylation of MGMT gene was detected in 16 samples of 46 （34.8 %） laryngeal squamous cell carcinoma samples. However, the MGMT hypermethylation was not detected in all tissues adjacent to the tumors and normal tissues. No significant difference in MGMT gene hypermethylation was found in samples with different histological grades （χ^2= 3. 130, P=0. 077） or in samples from patients with different TNM status （χ^2= 3. 957, P=0. 138）. No expression of MGMT mRNA was detected in all hypermethylated laryngeal carcinoma tissues. The expression of MGMT mRNA was detected in all unmethylated laryngeal carcinoma tissues, tissues adjacent to the tumors and normal tissues. It suggests that MGMT gene promoter hypermethylation is associated with MGMT gene transcription loss in laryngeal carcinoma tissues and possibly plays an important role in carcinogenesis of laryngeal tissues.

The study on DNA methylation of p53-Bax mitochondrial apoptosis pathway in cholangiocarcinoma

Objective： To study the methylation status of several genes on p53-Bax mitochondrial apoptosis pathway and clinical significance in cholangiocarcinoma. Methods： Promoter hypermethylation of DAPK, p14 and ASC genes were detected by methylation-specific PCR. p53 gene status （exon 5-8） were examined by automated sequencing, combined with the clinical documents of patients by statistics analysis. Results： （1） We found 66.7% of 36 cases cholangiocarcinoma had methylation of at least one tumor suppressor gene. The frequency of tumor suppressor gene methylation in cholangiocarcinoma was： p14 （24%）, DAPK （30.6%）, TMSI/ASC （36.1%）. The frequency of tumor suppressor gene methylation in tissues near cancer was： DAPK （5.6%）, TMS1/ASC （8.3%）. （2） p53 gene mutations were found in 22 of 36 patients （61.1%）. （3） There were no statistically relationship among the methylation of DAPK, p14 and ASC genes. There were negative relationship differences between the methylation of p14 and p53 gene mutation （P 〈 0.05）. （4） p53 gene mutation combined with the methylation of tumor suppressor were 14 cases （38.9%）. There were statistically differences on extent of pathologic biology, differentiation and invasion （P 〈 0.05）. Conclusion： Our study indicated that methylation of p53-Bax mitochondrial apoptosis pathway in cholangiocarcinoma was a common epigenetic event. Although the methylation of ASC, DAPK genes was low, it might be significance for early diagnosis, p53 gene mutation combined with the methylation of tumor suppressor might be relationship with pathologic biology, it trended to more malignancy.

急性白血病细胞中ID4基因甲基化的PCR定量检测系统的建立及其特异性和敏感性

ID4基因启动子区甲基化发生率在急性白血病中极高,甲基化程度与急性白血病关系密切。因缺少合适的研究方法,其具体的甲基化量化水平与疾病的关系,人们一直缺乏认识。本研究旨在建立ID4甲基化定量PCR体系,同时验证该方法的特异性及敏感性,并初步尝试在初治急性白血病骨髓样本中评估ID4的甲基化水平。首先构建质粒并建立体系标准曲线,分别使用MSP和定量MSP对细胞系样本进行检测,以传统MSP的结果为对照,验证新方法的特异性;按不同比例将甲基化阴性和阳性细胞混合,用甲基化定量PCR扩增验证新方法敏感性。结果表明,本研究成功建立了符合绝对定量要求的标准曲线;通过细胞系验证,MSP结果与定量MSP结果完全一致;同时在甲基化阴性细胞背景下,定量MSP可以稳定的检测到1∶10-5水平的ID4甲基化阳性细胞。在急性白血病骨髓样本检测中,定量MSP甲基化阳性检出率高于MSP。结论:本研究成功建立了完整的ID4基因甲基化定量PCR体系,该方法特异性好、敏感性高。

ID4基因甲基化定量PCR检测在急性白血病中的临床意义

尽管治疗的进步极大地改善了急性白血病患者的预后和生存,但时至今日多数类型的急性白血病没有特异性的生物标记,因此对于多数白血病患者,影响生存的复发这一重要因素缺少有效的预警机制。ID4基因启动子区甲基化广泛发生于各类型急性白血病。本研究在前期建立的甲基化定量PCR体系的基础上,用该方法检测患者骨髓样本,探讨ID4甲基化定量指标(percentage of methylated reference,PMR)的临床意义。采集我院门诊及住院确诊的初治、完全缓解、复发3个阶段的急性白血病患者骨髓样本及正常对照者骨髓样本。应用ID4甲基化定量PCR体系对样本进行检测。按初治、完全缓解、复发分组比较PMR值。比较相同病例不同疾病状态的PMR的动态变化。结果表明,初治组PMR最高,其次为复发组,而完全缓解组最低。初治组PMR与完全缓解组比较存在统计学差异。4例随访病例的PMR值波动与病情变化一致。在1例复发病例中,PMR升高早于骨髓细胞学检查确认复发1.7个月。结论:本研究通过ID4基因启动子区甲基定量检测的方法初步验证:甲基化水平的量化指标PMR值与急性白血病患者肿瘤细胞负荷关系密切。PMR动态监测波动与疾病变化一致,可能具有预测复发的作用,但ID4甲基化定量指标的临床价值还有待进一步研究证据的支持。

甲基化特异性PCR方法诊断Prader-Willi综合征

目的Prader-Willi综合征(PWS)是多系统异常的复杂临床综合征,仅根据临床症状很难诊断,国外已建立快速、高效、特异性、敏感性均佳的甲基化特异性PCR(MS-PCR)方法用于临床诊断,但我国还未有系统的对照研究。该研究目的便是建立PWS的MS-PCR诊断方法,并对临床疑似患者进行筛查。方法将44例受试者,分为正常对照组(16例)、临床确诊患者组(7例)及临床疑似患者组(21例)。采用盐析法提取基因组DNA;应用CpGemoneTMFast Modification试剂盒行亚硫酸盐修饰;以正常人为阴性对照,未修饰的基因组DNA为系统对照,以M(母源)、P(父源)两对引物同时对修饰产物行PCR;扩增产物以琼脂糖凝胶电泳分离。结果①16例正常对照的PCR结果同时显示M,P两条带,7例临床确诊的PWS患者均只显示一条M带;②经MS-PCR筛查的21例临床疑似患者,2例确诊为PWS,其他19例排除PWS。结论该研究成功建立MS-PCR,并对疑似患者进行了筛查确诊。MS-PCR为特异高效的PWS确诊方法且方便易行。

甲基化特异性PCR检测FMR1和XIST基因甲基化实验方法的建立

建立一种快速、灵敏的检测脆性X智障基因(fragile X mental retardation,FMR1)、X染色体失活基因(Xchromosome inactivation,XIST)甲基化的方法.用亚硫酸氢钠和对苯二酚对基因组DNA进行脱氨基修饰.以修饰后的DNA为模板,用两套不同的引物对:1对甲基化特异性引物和1对非甲基化特异性引物扩增FMR1基因(CGG)n重复序列区、FMR1和XIST基因的启动子区.PCR产物进一步克隆、测序.以亚硫酸氢钠和对苯二酚脱氨基修饰后的DNA为模板进行PCR扩增后的产物与预期基因目的基因片段大小相符合,无非特异性扩增产物.测序结果表明,FMR1、XIST基因中的非甲基化的C碱基转变为U碱基,而CpG岛被甲基化的C碱基不改变.成功地建立了检测FMR1、XIST甲基化的方法,为实验室诊断脆性X综合征提供了新的方法.

巢式甲基化特异性PCR检测肺癌病人WIF-1基因启动子区异常甲基化

为了检测肺癌患者血浆中WIF-1基因启动子区的甲基化状态,收集肺癌患者及健康对照者的血浆标本,采用巢式甲基化特异性PCR(nMSP)法检测WIF-1基因启动子区甲基化状态,并与普通甲基化特异性PCR(MSP)法进行了比较,结果在58例肺癌患者血浆样品中经nMSP法发现20例WIF-1基因启动子的过甲基化,用MSP法只检出10例,有吸烟史组WIF-1基因的甲基化率高于无吸烟史组(P<0.05).而20例正常对照血浆中都未检测到WIF-1基因启动子的过甲基化;表明利用巢式MSP(nMSP)法检测外周血血浆中WIF-1基因启动子的甲基化,可为非损伤性筛选和早期诊断肺癌提供有价值的信息.

肺癌组织、支气管肺泡灌洗液及痰标本中p16基因甲基化特异性PCR检测

目的 :探讨肺癌组织、支气管灌洗液及痰标本中p16基因甲基化特异性PCR检测的临床应用价值。方法 :选取 5 6例肺部疾病住院患者手术切除的病变肺组织和相应的支气管肺泡灌洗液 (BALF)及痰标本 ,其中 32例为肺癌 ,2 4例为良性肺部疾病。标本经一般处理 ,PCR扩增后 ,产物经电泳EB染色 ,紫外灯下观察。结果 :32例肺癌组织标本中 ,14例 (4 3.8% )在p16基因启动子区域呈现异常甲基化 ,其中 9例 (6 4 .3% )在相应的BALF中检出甲基化存在 ,5例 (35 .8% )在相应的痰标本中也检出甲基化存在。 2 4例良性肺部疾病 ,其中肺囊肿 10例 ,肺结核 14例 ,无论在手术切除标本还是BALF和痰标本中均未检出p16基因甲基化存在。结论 :MSP技术对肺癌患者BALF及痰标本中P16基因的异常甲基化检测具有高度特异性 ,是一项很有潜力的肺癌早期诊断新技术。

死亡相关蛋白激酶基因启动子甲基化特异性PCR法的建立与初步应用

目的:建立甲基化特异性PCR(MSP)技术检测死亡相关蛋白激酶(DAPK)基因启动子甲基化。方法:设计针对DAPK基因启动子的MSP引物,建立MSP检测体系对甲基化阳性模板进行检测,评价其特异性、重复性和灵敏性,并经测序鉴定。结果:所建立的甲基化MSP方法仅能扩增出甲基化阳性模板,不能扩增出未甲基化阳性模板和未硫化处理的DNA模板;对不同梯度稀释的甲基化阳性模板进行检测,其最大敏感性可达2%;在不同时间进行甲基化MSP检测的结果均一致。结论:成功建立的DAPK基因启动子甲基化MSP检测方法具有良好的特异性、灵敏性和重复性,可用于肿瘤标本的批量检测。

限制性内切酶结合半巢式PCR法检测人肝癌P16抑癌基因启动子区甲基化研究

目的建立甲基化敏感的限制性内切酶结合半巢式降落PCR方法,研究原发性肝癌P 16基因启动子区甲基化状态。方法针对P 16基因启动子区富含CpG的序列,设计3条引物,进行半巢式降落PCR扩增,检测原发性肝癌P 16基因启动子区甲基化状态;并将P 16基因启动子区340 bp片段克隆到pM D 18-T载体,E.coli JM 109扩增此质粒后经CpG甲基化酶M.S ssⅠ处理,再用Hp aⅡ酶切验证获得P 16基因启动子区甲基化阳性的质粒P 16Pm+并进行特异性和灵敏度实验。以此甲基化敏感的限制性内切酶结合半巢式降落PCR方法检测40例人原发性肝癌和3例正常人肝组织DNA样品的P 16基因启动子区甲基化状态。结果所采用的Hp aⅡ酶切后半巢式PCR方法的特异性强,灵敏度达100 fg;对40例人原发性肝癌组织DNA样品P 16基因的启动子区甲基化状态检测显示甲基化阳性率为30%(12/40),3例正常人肝组织均为阴性(0/3)。结论P 16抑癌基因启动子区甲基化可能与肝癌发生发展有关。本实验方法简便、成本低廉,并有高度的特异性与灵敏度,在大规模检查中有实际应用价值。