粪便DNA中MGMT、XAF1基因启动子甲基化联合检测在结直肠癌筛查中的应用研究

目的使用甲基化特异性PCR(MSP)方法检测粪便DNA中O6-甲基鸟嘌呤-DNA甲基转移酶(MGMT)、X染色体连锁凋亡抑制蛋白相关因子1(XAF1)基因启动子甲基化情况,并探讨其在结直肠肿瘤诊断中的意义。方法收集40例结直肠腺癌、40例腺瘤性息肉、52例正常对照住院患者粪便标本,使用试剂盒提取其粪便中肠道脱离细胞DNA,通过MSP方法检测其MGMT、XAF1基因启动子甲基化情况。结果 MGMT、XAF1基因启动子甲基化在结直肠腺癌中的阳性率分别为50.0%、55.9%;在腺瘤性息肉中的阳性率分别为42.1%、52.6%;二者联合检测在结直肠腺癌及腺瘤性息肉中的阳性率分别为73.5%、68.4%;特异性为52.0%。结直肠腺癌患者粪便中粪便潜血阳性率为35.3%,CEA阳性率为35.3%。结论通过试剂盒提取粪便DNA具有较高成功率;粪便DNA中MGMT、XAF1基因启动子甲基化状态用于检测结直肠腺癌及腺瘤性息肉具有较高的敏感性。检测粪便基因甲基化有望成为CRC高风险人群筛查的一个重要途径。     

实时荧光定量PCR和甲基化特异性PCR检测结直肠癌APC、MLH1基因甲基化状态

背景：启动子区甲基化致肿瘤抑制基因失活在结直肠癌的发生、发展中起重要作用,检测肿瘤相关基因的甲基化状态,可能为寻找新的结直肠癌诊断、预后相关标记物提供依据.目的：比较实时荧光定量PCR（FO-PCR）与甲基化特异性PCR（MSP）检测基因甲基化状态的差异.方法：以FQ-PCR检测66例结直肠癌组织和20例癌旁组织中与结直肠癌的发生、发展相关的抑癌基因APC和错配修复基因MLH1的甲基化状态,同时以MSP检测结直肠癌组织中APC基因的甲基化状态.结果：根据FQ-PCR结果,结直肠癌组织中APC、MLH1基因甲基化阳性率显著高于癌旁组织（48.5%和54.5%对0%和0%,P=0.000）.FQ-PCR和MSP可检出的甲基化阳性对照DNA最低浓度分别为0.015 ng/μl和1.5 ng/μl,两者对APC基因甲基化状态的检测结果差异有统计学意义（P＜0.05）.结论：在DNA甲基化的检测手段中,FQ-PCR的敏感度优于MSP.     

大肠癌APC基因研究进展

肿瘤的发生发展除了与饮食、环境等因素有关外,还与多个癌基因的激活和肿瘤抑制基因的失活有关。结直肠癌的发生发展为肿瘤分子生物学的研究提供了极好的模式。遗传性结直肠癌包括家族性腺瘤性息肉病结直肠癌及遗传性非息肉性结直肠癌,总发病率约占结直肠癌的15%左右。遗传性结直肠癌的基因定位是     

大肠癌APC基因研究进展

肿瘤的发生发展除了与饮食、环境等因素有关外，还与多个癌基因的激活和肿瘤抑制基因的失活有关。结直肠癌的发生发展为肿瘤分子生物学的研究提供了极好的模式。遗传性结直肠癌包括家族性腺瘤性息肉病结直肠癌及遗传性非息肉性结直肠癌，总发病率约占结直肠癌的15％左右。遗传性结直肠癌的基因定位是近年来结直肠癌分子生物学研究的重大进展，对预防、早期诊断、早期治疗及术后随访具有重大意义。本复习近年来发现的家族性腺瘤性息肉病基因改变的一些献，并就它与结直肠癌的关系做一综述。     

粪便SDC2基因甲基化检测在结直肠癌早期诊断中的应用价值

目的 探讨粪便SDC2基因甲基化检测在结直肠癌早期诊断中的应用价值。方法 采用定量甲基化特异性PCR技术检测接受结直肠癌（CRC）筛查的患者粪便样本中SDC2的甲基化（mSDC2）,SDC2基因甲基化检测阳性患者进一步行结肠镜检查,患者均通过结肠镜检查或术后病理检查腺癌（CRC）明确诊断,病理区分为结直肠癌、进展型腺瘤、非腺瘤性息肉、炎症。采用Pearson相关法分析SDC2基因甲基化检测结直肠肿瘤阳性预测值（PPV）与年龄的相关性。结果 纳入268例mSDC2阳性患者,其中确诊结直肠癌23例、进展型腺瘤42例、非腺瘤息肉20例、炎症18例,余下患者结肠镜检查未发现明显异常。<60岁结直肠癌患者SDC2基因甲基化检测PPV为7.04%(10/142),≥60岁者为30.23%(13/43);mSDC2在结直肠癌患者中的PPV随着年龄增长而增加,差异有统计学意义（P<0.05）。随年龄增长,mSDC2循环阈值与年龄呈负相关（r=-0.68,P<0.05）。结直肠癌患者mSDC2的Ct值比进展型腺瘤、非腺瘤息肉、炎症病变均低,差异有统计学意义（P均<0.05）。按m...     

Lynch综合征相关结直肠癌的遗传基因及分子病理筛查策略

Lynch综合征（Lynch syndrom）是结直肠癌中最常见的遗传性肿瘤综合征,约占全部大肠癌的2~3%。该病患者同时增加了罹患肠外及第二肿瘤的风险。现已证明,Lynch综合征是由于编码错配修复基因（mismatch repair,MMR）——MLH1,MSH2,MSH6和PMS2的种系突变、失活导致的一类显性遗传性疾病,近年发现EPCAM的突变与MSH2表达缺失相关。尽管有Amsterdan及Bethesda等临床诊断标准,利用分子遗传学检测在MMR基因中发现致病性胚系突变仍为目前诊断Lynch综合征的金标准。对于发病年龄小于70岁的结直肠癌患者,均应进行Lynch综合征的筛查。首先需进行微卫星不稳定性（microsatellites instability,MSI）检测,检测手段包括PCR扩增微卫星位点及免疫组化（IHC）检测,而后对相应的MMR基因进行胚系突变的检测以明确是否为Lynch综合征以及相应的致病位点。对于MLH1表达缺失患者需进行BRAF基因突变检测和（或）MLH1启动子区域甲基化检测以除外散发性结直肠癌。对于确诊的患者建议进行家系筛查并进行规律的监测和随访。     

遗传性胃肠道息肉病和非息肉病综合征

胃肠道息肉病和非息肉病综合征 散发性结肠癌占所有结肠癌的90％以上,此类癌多数起自于腺瘤性息肉的癌前期。遗传性息肉病综合征可分为腺瘤性息肉病和错构瘤性息肉病综合征,每年发生率约占结肠癌的1％。遗传性非息肉性结直肠癌综合征也称Lynch或家族性癌综合征,占每年结肠癌发生率的5％～10％。 腺瘤性息肉病 家族性腺瘤性息内病家族性腺瘤性息肉病为常染色体显性遗传病,以腺瘤性息肉病综合征最为常见,据估测其基因发生率为1/     

多基因甲基化检测对结直肠癌早期诊断的意义

目的 通过对结直肠癌（CRC）组织中多基因甲基化水平的检测,探讨多基因甲基化对CRC早期诊断的意义.方法 选取25例CRC患者胃镜采集标本组织,通过甲基化特异性PCR（MSP）检测CRC和炎性组织中甲基化水平,分析其与CRC患者临床各指标的关系.结果 在CRC患者中,APC、P16、MLH1、DCC甲基化率分别为52.0%（13/25）、32.0%（8/25）、44.0%（11/25）、60.0%（15/25）.炎性组织中仅有1例DCC甲基化异常表达,甲基化率为10.0%（1/10）,甲基化阳性率显著高于炎性组织（P＜0.05）,4种基因甲基化联合检测诊断CRC的阳性率为92.0%（23/25）,高于单个基因检测的甲基化阳性率,差异有统计学意义（P＜0.01）.结论 APC、P16、MLH1、DCC基因在CRC患者中甲基化水平异常表达,联合检测APC、P16、MLH1、DCC可能作为CRC早期诊断的标志物.     

慢性粒细胞白血病ZO-1基因启动子区甲基化状态分析及临床意义探讨

目的通过对慢性期及急变期慢性粒细胞白血病（CML）患者骨髓标本中人紧密连接蛋白1（ZO-1）基因启动子区甲基化状态的分析,初步探讨其在CML病情发展变化中的临床意义。方法应用甲基化特异性聚合酶链反应（MS-PCR）检测5例CML慢性期和10例CML急变期患者骨髓标本中ZO-1基因启动子区的甲基化状态。结果在5例CML-CP患者中ZO-1基因启动子区呈非甲基化状态;在7例CML-BP患者中ZO-1基因启动子区呈高甲基化状态,甲基化阳性率为70%（7/10）;1例CML患者其慢性期骨髓标本ZO-1基因启动子区呈非甲基化状态,而急变期则呈甲基化状态,经治疗恢复到慢性期时,则又表现为非甲基化状态。结论 ZO-1基因启动子区甲基化状态可能与CML病情发展变化密切相关,可能是一个提示CML急变的分子标志物。     

人源DNA错配修复基因和微卫星不稳定与老年结肠癌的相关性

目的探讨老年结肠癌患者肿瘤组织的人源DNA错配修复基因(h MLH)1和微卫星不稳定性型情况。方法通过甲基化特异性聚合酶链反应(PCR)检测老年结肠癌样本中基因h MLH1启动子甲基化修饰的异常;研究结肠癌样本中微卫星标志物杂合型丢失频率;确定结肠癌患者中的变异与结肠癌的相关性。结果 18.0%的老年结肠癌样本中出现h MLH1启动子高甲基化;51.2%出现微卫星标记D22S280或D22S929的杂合型缺失,25.6%出现D22S280和D22S929的杂合型缺失,并且杂合型缺失与基因h MLH1启动子高甲基化状态相互独立。基因h MLH1启动子甲基化可作为独立的变量预测肿瘤的预后。结论根据h MLH1启动子甲基化状态对高甲基化状态结肠癌进行分类,基因h MLH1可作为微卫星不稳定型老年结肠癌潜在预后标志物之一。     

Germline promoter hypermethylation of tumor suppressor genes in gastric cancer

AIM: To explore germline hypermethylation of the tumor suppressor genes MLH1, CDH1 and P16^INK4a in suspected cases of hereditary gastric cancer (GC).METHODS: A group of 140 Chinese GC patients in whom the primary cancer had developed before the age of 60 or who had a familial history of cancer were screened for germline hypermethylation of the MLH1, CDH1 and P16^INK4a tumor suppressor genes. Genomic DNA was extracted from peripheral blood leukocytes and modified by sodium bisulfite. The treated DNA was then subjected to bisulfite DNA sequencing for a specific region of the MLH1 promoter. The methylation status of CDH1 or P16^INK4a was assayed using methylation-specific PCR. Clonal bisulfite allelic sequencing in positive samples was performed to obtain a comprehensive analysis of the CpG island methylation status of these promoter regions.RESULTS: Methylation of the MLH1 gene promoter was detected in the peripheral blood DNA of only 1/140 (0.7%) of the GC patient group. However, this methylation pattern was mosaic rather than the allelic pattern which has previously been reported for MLH1 in hereditary non-polyposis colorectal cancer (HNPCC) patients. We found that 10% of the MLH1 alleles in the peripheral blood DNA of this patient were methylated, consistent with 20% of cells having one methylated allele. No germline promoter methylation of the CDH1 or P16^INK4a genes was detected.CONCLUSION: Mosaic germline epimutation of the MLH1 gene is present in suspected hereditary GC patients in China but at a very low level. Germline epimutation of the CDH1 or P16^INK4a gene is not a frequent event.     

Tumor Buds Show Reduced Expression of Laminin-5 Gamma 2 Chain in DNA Mismatch Repair Deficient Colorectal Cancer

Purpose Tumor budding at the invasive margin of colorectal cancer is an important adverse prognostic factor. The subset of colorectal cancer that is deficient in DNA mismatch repair has been associated with a good prognosis. It is hypothesized that tumor budding in this subset may lack biologic aggressiveness because it is not associated with aberrant expression of the independent prognostic factor, laminin-5 gamma 2. Methods Eighty colorectal cancers with high-grade tumor budding were studied, including nine sporadic colorectal cancers with immunohistochemical loss of expression of MLH1 (MLH1(−)), seven colorectal cancers from patients with hereditary nonpolyposis colorectal cancer, and 64 sporadic colorectal cancers expressing both MLH1 and MSH2 (MLH1(+)). Two regulatory mechanisms for laminin-5 gamma 2 expression were explored, including aberrant nuclear expression of β-catenin by immunohistochemistry and promoter methylation of laminin-5 gamma 2 by methylation-specific polymerase chain reaction. Results Only three of nine MLH1(−) colorectal cancers showed expression of laminin-5 gamma 2 compared with 46 of 64 MLH1(+) colorectal cancers (P = 0.05). Only two of seven hereditary nonpolyposis colorectal cancers expressed laminin-5 gamma2 compared with MLH1(+) colorectal cancers (P= 0.03). Expression of nuclear β-catenin was more frequent (58 percent) in MLH1(+) colorectal cancers compared with MLH1(−) colorectal cancers (11 percent, P = 0.01). Methylation of laminin-5 gamma 2 was found in 5 of 38 (13 percent) cases but did not differ among colorectal cancer subsets. Four of five colorectal cancers with methylation of laminin-5 gamma 2 were scored as negative for laminin-5 gamma 2 by immunohistochemistry. Conclusions The reduced expression of laminin-5 gamma 2in colorectal cancers with deficient DNA mismatch repair may underlie a variant of tumor budding that is relatively nonaggressive. Supported by a grant from the Canadian Institutes of Health Research (grant no. MOP-67206).     

结直肠癌组织及细胞株中分泌型卷曲相关蛋白家族的甲基化研究

目的 研究分泌型卷曲相关蛋白(SFRP)基因启动子区CpG岛甲基化与结直肠癌的关系.方法 采用甲基化特异性PCR(MSP)技术检测20对结直肠癌及相应癌旁组织中SFRP基因启动子区CpG岛甲基化状况,T-A克隆测序验证MSP产物.5-氮杂-2'-脱氧胞苷对结直肠癌细胞株HCT116、SW480进行去甲基化处理,MSP和Western印迹法分别检测细胞株中SFRP基因甲基化和蛋白表达.结果 SFRP 1、2、4、5在结直肠癌中甲基化率分别为19/20、17/20、3/20、13/20,癌旁组织中分别为12/20、8/12、1/20、7/20.结直肠癌中SFRP 1、2、5甲基化率均高于癌旁组织,差异有统计学意义(P<0.05).HCT116细胞株SFRP 1、2、4、5基因均发生甲基化,而SW480细胞株中仅SFRP1和SFRP2出现启动子甲基化.SFRP蛋白表达与启动子甲基化呈明显负相关,经5-氮杂-2'-脱氧胞苷处理后能有效恢复SFRP蛋白表达.结论 SFRP 1、2、5甲基化可能与结直肠癌的发生有关,SFRP基因甲基化与其表达失活密切相关.     

MLH1 promoter germline-methylation in selected probands of Chinese hereditary non-polyposis colorectal cancer families

AIM： To detect the MLH1 gene promoter germline- methylation in probands of Chinese hereditary non- polyposis colorectal cancer （HNPCC）, and to evaluate the role of methylation in MLH1 gene promoter and molecular genetics in screening for HNPCC.METHODS： The promoter germline methylation of MLH1 gene was detected by methylation-specific PCR （MSP） in 18 probands from unrelated HNPCC families with high microsatellite-instability （MSI-H） phenotype but without germline mutations in MSH2, MLH1 and MSH6 genes. At the same time, 6 kindreds were col- lected with microsatellite-stability （MSS） phenotype but without germline mutations in MSH2, MIH1 and MSH6 genes as controls. The results of MSP were confirmed by clone sequencing. To ensure the reliability of the results, family H65 with nonsense germline mutation at c.2228C 〉 A in MSH2 gene was used as the negative control and the cell line sw48 was used as the known positive control along with water as the blank control. Immunochemical staining of MIH1 protein was performed with Envision two-step method in those patients with aberrant methylation to judge whether the status of MLH1 gene methylation affects the expression of MLH1 protein.RESULTS： Five probands with MIH1 gene promoter methylation were detected in 18 Chinese HNPCC families with MSI-H phenotype but without germline mutations in MSH2, MLH1 and MSH6 genes. Two of the five probands from families H10 and H29 displayed exhaustive-methylation, fulfilling the Japanese criteria （JC） and the Amsterdam criteria （AC）, respectively. The other 3 probands presented part-methylation fulfilling the AC. Of the 13 probands with unmethylation phenotype, 8 fulfilled the JC and the Bethesda guidelines （BG）, 5 fulfilled the AC. The rate of aberrant methylation in MLH1 gene in the AC group （22.2%, 4/18） was higher than that in the JC/BG groups （5.6%, 1/18） in all HNPCC families with MSI-H phenotype but without germline mutations in PISH2, PIIH1 and MSH6 genes. However, no proband with methy     

Extensive but hemiallelic methylation of the hMLH1 promoter region in early-onset sporadic colon cancers with microsatellite instability.

BACKGROUND AND AIMS: Methylation of the hMLH1 promoter region is frequently observed in microsatellite instability (MSI)-positive sporadic colorectal carcinomas. We studied hMLH1 promoter methylation in peripheral blood lymphocytes of 87 index patients representing 29 cases of hereditary nonpolyposis colorectal cancers (HNPCCs), 28 cases of atypical HNPCCs, and 30 sporadic cases of the development of early-onset colorectal carcinomas or multiple primary cancers. METHODS: Methylation of the hMLH1 promoter region was analyzed by Na-bisulfite polymerase chain reaction/single-strand conformation polymorphism analysis or methylation-specific polymerase chain reaction. MSI, allelic status of the hMLH1 locus, and loss of hMLH1 protein expression were examined in cases for which tumor tissues were available. RESULTS: Extensive methylation of the hMLH1 promoter was detected in peripheral blood lymphocytes of 4 of 30 patients with sporadic early-onset colon cancer, among whom multiple primary cancers (1 colon and 1 endometrial cancer) developed in 2 cases. This methylation was not detected in analyses of HNPCC or atypical HNPCC groups or healthy control subjects. MSI was positive, and extensive methylation was detected in both cancers (colon and endometrial cancer) and normal tissues (colon, gastric mucosa, endometrium, and bone marrow) in all of the examined cases (3 of 3). Analysis of a polymorphic site in the hMLH1 promoter in 2 informative cases showed that methylation was hemiallelic. In 1 case, the unmethylated allele was lost in the colon cancer but not in the metachronous endometrial cancer. CONCLUSIONS: Constitutive, hemiallelic methylation of the hMLH1 promoter region was shown to be associated with carcinogenesis in sporadic, early-onset MSI-positive colon cancers.     

Hypermethylation and expression regulation of secreted frizzled-related protein genes in colorectal tumor

INTRODUCTION Secreted frizzled-related proteins (sFRPs) comprise a family of five secreted glycoproteins that antagonize Wnt canonical and noncanonical signaling by different mechanisms directly or indirectly[1]. Wnt signaling regulates cell growth, motil…     

Histologic comparison of hereditary nonpolyposis colorectal cancer associated with MSH2 and MLH1 and colorectal cancer from the general population

PURPOSE: Hereditary nonpolyposis colorectal cancer is reported to have special histologic features. This study compares the histologic features of hereditary nonpolyposis colorectal cancer to colorectal cancers from the general population when hereditary nonpolyposis colorectal cancer cases are restricted to families with known MSH2 and MLH1 mutations. METHODS: Thirty-seven cancers from kindreds carrying MSH2 mutations, 27 cancers from kindreds carrying MLH1 mutations, and 37 colorectal cancers from the general population were reviewed by a pathologist blinded to hereditary nonpolyposis colorectal cancer gene status. Tumor grade, growth pattern, Crohn's-like lymphoid reaction, mucin production, extent of disease in the bowel wall, and lymph node status were evaluated. RESULTS: Poor differentiation and Crohn's-like reaction were a feature of 44 and 49 percent of hereditary nonpolyposis colorectal cancer compared with 14 percent (P=0.002) and 27 percent (P=0.049) of colorectal cancers from the general population, respectively. There was no difference in growth pattern, mucin production, lymph node involvement, or local extent of disease between hereditary nonpolyposis colorectal cancer and colorectal cancers from the general population. Poor differentiation and lymph node metastases were found in 57 and 49 percent of MSH2 compared with 26 percent (P=0.002) and 10 percent (P=0.03) of MLH1-associated cancers, respectively. There was no difference in growth pattern, mucin production, Crohn's-like lymphoid reaction, or local extent of disease between subgroups of hereditary nonpolyposis colorectal cancer. CONCLUSIONS: Poor differentiation and Crohn's-like reaction are more common in hereditary nonpolyposis colorectal cancer than colorectal cancers from general population. Poor differentiation and lymph node metastases are more commonly seen in MSH2-associated cancers than MLH1. Evaluation of the natural history, pathogenesis, and prognosis of colorectal cancer in hereditary nonpolyposis colorectal cancer should include consideration of which mismatch repair genes are mutated and what the specific mutations are.Poster presentation at the meeting of The American Society of Colon and Rectal Surgeons, Philadelphia, Pennsylvania, June 22 to 27, 1997.     

甲基转移酶基因甲基化在结直肠肿瘤中的作用

目的探讨6氧甲基鸟嘌呤DNA甲基转移酶(MGMT)基因启动子CpG岛高甲基化在结直肠肿瘤发生、发展中的作用。方法用甲基特异性PCR检测20例正常大肠黏膜、27例散发性结直肠腺瘤和62例散发性结直肠腺癌组织DNA中MGMT基因启动子的甲基化,同时用免疫组化方法检测MGMT蛋白的表达情况。结果正常大肠黏膜组织均未显示甲基化条带,分别有40.7%(11/27)的腺瘤组织和43.5%(27/62)的腺癌组织存在MGMT基因启动子CpG岛高甲基化。正常大肠黏膜胞核和胞质表达MGMT蛋白,22.2%(6/27)的腺瘤和45.2%(28/62)的腺癌MGMT蛋白表达缺失,其差异有显著性(P=0.041)。6例MGMT表达缺失的腺瘤中5例存在甲基化(P=0.027),28例表达缺失的腺癌中24例存在甲基化(P<0.001)。结论结直肠肿瘤中存在高频率MGMT基因启动子高甲基化和蛋白表达缺失,腺癌中蛋白表达缺失比腺瘤中更常见。MGMT蛋白表达缺失与MGMT基因启动子区域高甲基化有关。MGMT基因表型遗传性失活可能在结直肠肿瘤发生过程中起重要作用。     

Mechanisms of Microsatellite Instability in Colorectal Cancer Patients in Different Age Groups

PURPOSE The proportion of colorectal cancers located proximal to the splenic flexure increases with age. Colorectal cancers of the microsatellite instability phenotype are preferentially located in the proximal colon. We investigated the location of colorectal cancer with this phenotype in different age groups to determine whether different molecular mechanisms could account for the changes in distribution of colorectal cancers. METHODS A representative sample of 230 colorectal cancers from three age groups (<45 years, 60–70 years, >87 years) was selected from a subset of The Upper Midwest Oncology Medical Registries database. Microsatellite instability was determined by polymerase chain reaction using a panel of five microsatellite markers. The presence of new microsatellite alleles at two or more loci was scored as microsatellite instability. Tumors were otherwise considered microsatellite stable. MLH1 and MSH2 expression was determined by immunohistochemistry. Methylation of the MLH1 gene promotor was determined by methylation-specific polymerase chain reaction assay. RESULTS The proportion of tumors of the microsatellite instability phenotype was 21 percent in the young group, 15 percent in the middle group, and 33 percent in the old group. More tumors of the microsatellite instability phenotype were proximal compared with microsatellite-stable tumors in all three age groups, but the differences were significant only for the old group. Tumors of the microsatellite instability phenotype in the older group were associated with MLH1 inactivation (24/29 or 83 percent), MLH1 promoter methylation (18/29 or 62 percent), and proximal location (25/29 or 86 percent), while tumors in the young group were associated with MSH2 inactivation (8/18 or 44 percent) and distal location (11/18 or 62 percent). CONCLUSION The age-related proximal shift of colorectal cancers is associated with the microsatellite instability phenotype, MLH1 inactivation, and MLH1 promoter hypermethylation. Presented at the Research Forum of The American Society of Colon and Rectal Surgeons, San Diego, California, June 3 to 8, 2001.