Aberrantly methylated MGMT, hMLH1 and hMSH2 in tumor and serum DNA of gliomas patients

OBJECTIVE This study is to investigate the prevalence of promoter CpG island methylation of O6-methylguananine-DNA methyltransferase （MGMT）, mismatch repair genes （hMLH1 and hMSH2） in both tumor and serum samples of gliomas. METHODS Methylation-specific PCR （MSP） was employed to detect promoter CpG island methylation of the MGMT, hMLH1 and hMSH2 genes in 39 samples taken from surgery and 32 samples of pretreatment serum all from the patients with gliomas. RESULTS Promoter CpG island methylation of MGMT, hMLH1 and hMSH2 was detected and the results were 46.2%, 10.3% and 20.5%, respectively in tumor DNA of the cases with gliomas, and 40.6%, 9.4% and 18.8%, respectively in serum DNA of the cases. The methylation pattern in primary tumor and serum was found to be concordant in matched tissue and serum samples of 21 patients. In the cases with positive result of methylation for MGMT, hMLH1 and hMSH2 in tumor tissues, the results of detection for those in the paired serum sample were 77.8% （7/9）, 66.7% （2/3） and 75.0 % （3/4）, respectively. False positive results were not obtained in any of the patients who did not exhibit methylation. No association was found between the promoter methylation of MGMT, hMLH1, and hMSH2 genes in primary gliomas and gender, age, localization, grade of malignant or tumor stage. CONCLUSION Promoter CpG island methylation is a frequent event in gliomagenesis. Methylation analysis appears to be a promising predictive factor of the prognosis for the glioma patients treated with alkylating drugs and a noninvasive tumor marker in serum DNA.     

Aberrant DNA Methylation of P16, MGMT,hMLH1 and hMSH2 Genes in Combination with the MTHFR C677T Genetic Polymorphism in Gastric Cancer

Associations of P16, MGMT, hMLH1 and hMLH2 with gastric cancer and their relation with MTHFR statusin gastric patients who were confirmed with pathological diagnosis were assessed. Aberrant DNA methylationof P16, MGMT, hMLH1 and hMLH2 and polymorphisms of MTHFR C677T were assayed. The proportionalDNA hypermethylation in P16, MGMT, hMLH1 and hMLH2 in cancer tissues was significantly higher than inremote normal-appearing tissues. DNA hypermethylation of P16 and MGMT was correlated with the T and Nstages. Individuals with homozygotes (TT) of MTHFR C677T had significant risk of hypermethylation of MGMTin cancer tissues [OR (95% CI)= 3.47(1.41-7.93)]. However, we did not find association between polymorphismin MTHFR C677T and risk of hypermethylation in P16, MGMT, hMLH1 and hMLH2 genes either in canceror remote normal-appearing tissues. Aberrant hypermethylation of P16, MGMT, hMLH1 and hMLH2 couldbe predictive of gastric cancer.     

Population carrier frequency of hMSH2 and hMLH1 mutations

Knowledge of population carrier frequency for DNA mismatch repair (MMR) gene mutations would contribute to understanding the burden of cancer due to genetic susceptibility, but robust prevalence estimates are lacking. To estimate carrier frequency, we genotyped a cohort of relatives of mutation carriers and determined their colorectal cancer prevalence. Systematic Finnish and US data were combined with Scottish genotype and cancer prevalence data in a Bayesian calculation. The estimated carrier prevalence in the population aged 15-74 years is 1:3139 (95% Cl = 1:1247-1:7626) and these carriers are at high risk of colorectal and other cancers.     

Promoter hypermethylation profile of tumor-associated genes p16, p15, hMLH1, MGMT and E-cadherin in oral squamous cell carcinoma

Aberrant promoter hypermethylation of tumor-associated genes leading to their inactivation is a common event in many cancer types. Using a sensitive restriction-multiplex PCR method, we studied the promoter hypermethylation profile of the p16, p15, hMLH1, MGMT and E-cad genes in oral squamous cell carcinoma (OSCC) of Indians. We analyzed a total of 51 samples for the p15 tumor-suppressor gene and 99 samples for each of the remaining genes. Our studies indicate an incidence of promoter hypermethylation of 23% each for p16 and p15, 8% for hMLH1, 41% for MGMT and 35% for E-cad. We observed aberrant hypermethylation of the promoter region of at least 1 of these genes in 74.5% of cases (n = 51) for which all the 5 genes were studied. Abnormal methylation was detected in tumors irrespective of stage and location in the oral cavity, whereas no abnormal methylation was detectable in normal oral squamous tissues obtained from 25 OSCC patients. Detection of aberrant hypermethylation patterns of cancer-associated genes listed above is therefore suitable for diagnosis of OSCC in individuals at high risk for this disease.     

散发性结直肠癌组织中hMSH2和hMLH1的表达研究

[目的]分析散发性结直肠癌中的hMLH1和hMSH2蛋白表达情况。[方法]选取经病理学确诊并在术前未接受过放疗或化疗的结直肠癌手术切除标本127例,以及内镜活检无肿瘤患者肠黏膜上皮20例。用免疫组化方法检测hMLH1和hMSH2蛋白表达情况。[结果]结直肠癌组织中hMSH2蛋白表达缺失率为65.4%（83/127）,高于对照肠组织（20.0%,4/20）（χ2=14.714,P〈0.001）。结直肠癌组织中hMSH2蛋白缺失率随T分期增加而增加（χ2=8.233,P=0.041）;与N分期有关（χ2=20.235,P〈0.001）,有淋巴结转移者患者中hMSH2蛋白表达缺失率达87.1%（27/31）,高于无淋巴结转移患者（54.2%）（χ2=9.250,P=0.002）。hMLH1蛋白表达缺失率为74.0%,与T分期（χ2=29.115,P〈0.001）、N分期（χ2=9.807,P=0.006）、M分期（χ2=7.363,P=0.007）有关。[结论]结直肠癌组织中存在hMLH1和hMLH2蛋白表达缺失,通过免疫组化方法检测,可以简便、准确地发现错配修复基因的突变,可为后期的治疗和预后判断提供参考。     

hMLH1与MGMT蛋白在非小细胞肺癌的表达及病理意义

目的：探讨hMLH1与MGMT蛋白在非小细胞肺癌的表达及病理意义。方法：应用免疫组织化学方法检测110例非小细胞肺癌和42例癌旁组织标本的hMLH1与MGMT蛋白表达情况,在SPSS 13.0统计软件上应用卡方检验、Spearman相关分析和Fisher＇s精确概率法分析蛋白表达与患者的性别、年龄、吸烟、组织类型、淋巴结转移和分化程度的相关性。结果：hMLH1蛋白表达阳性率在非小细胞肺癌组织为54.5%,显著高于癌旁组织的14.3%（P〈0.05）;其表达与淋巴结转移显著相关（P〈0.05）,但与患者的性别、年龄、吸烟、组织类型均无显著相关关系（P〉0.05）。MGMT蛋白表达阳性率在癌组织为41.8%,显著高于癌旁组织的16.7%（P〈0.05）;但其表达与患者的性别、年龄、吸烟、组织类型、淋巴结转移及分化程度均无显著相关关系（P〉0.05）。hMLH1与MGMT蛋白表达无显著相关关系（P〉0.05）。结论：检测hMLH1与MGMT蛋白的表达可能有助于非小细胞肺癌的诊断。     

Aberrant DNA Methylation of P16, MGMT,and hMLH1 Genes in Combination with MTHFR C677T Genetic Polymorphism and Folate Intake in Esophageal Squamous Cell Carcinoma

Aim: The present case-control study was conducted to explore the association of MTHFR gene polymorphismand relations of P16, MGMT and HMLH1 to MTHFR and folate intake. Methods: A total of 257 cases ofesophageal squamous cell carcinoma confirmed by histopathological examination were collected. Genotypingof P16, MGMT and HMLH1 was accomplished by methylation-specific polymerase chain reaction (PCR) aftersodium bisulfate modification of DNA and the MTHFR C677T genetic polymorphism was detected by PCRrestrictionfragment-length polymorphism (PCR-RFLP). Results: The proportions of DNA hypermethylation inP16, MGMT and hMLH1 in cancer tissues were significantly higher than in paracancerous normal tissue. Theproportion of hypermethylation in at least one gene was 88.5% in cancer tissue, and was also significantly higherthan that in paracancerous normal tissue. Our finding showed individuals with homozygotes (TT) of MTHFRC677T had significant risk of DNA hypermethylation of MGMT in cancer tissues, with an OR (95% CI) of 3.15(1.12-6.87). Similarly, patients with high intake of folate also showed a slight high risk of DNA methylation ofMGMT, with OR (95% CI) of 2.03 (1.05-4.57). Conclusion: Our study found the P16, MGMT and hMLH1demonstrate a high proportion of hypermethylation in esophageal squamous cell cancer cancer tissues, whichmight be used as biomarkers for cancer detection.     

hMLH1与MGMT蛋白在非小细胞肺癌的表达及病理意义

目的:探讨hMLH1与MGMT蛋白在非小细胞肺癌的表达及病理意义。方法:应用免疫组织化学方法检测110例非小细胞肺癌和42例癌旁组织标本的hMLH1与MGMT蛋白表达情况,在SPSS 13.0统计软件上应用卡方检验、Spearman相关分析和Fisher’s精确概率法分析蛋白表达与患者的性别、年龄、吸烟、组织类型、淋巴结转移和分化程度的相关性。结果:hMLH1蛋白表达阳性率在非小细胞肺癌组织为54.5%,显著高于癌旁组织的14.3%(P<0.05);其表达与淋巴结转移显著相关(P<0.05),但与患者的性别、年龄、吸烟、组织类型均无显著相关关系(P>0.05)。MGMT蛋白表达阳性率在癌组织为41.8%,显著高于癌旁组织的16.7%(P<0.05);但其表达与患者的性别、年龄、吸烟、组织类型、淋巴结转移及分化程度均无显著相关关系(P>0.05)。hMLH1与MGMT蛋白表达无显著相关关系(P>0.05)。结论:检测hMLH1与MGMT蛋白的表达可能有助于非小细胞肺癌的诊断。     

Analysis of Inactivation of hMLH1 by Promoter Hypermethylation and Microsatellite Instability in Gastric Carcinogenesis

OBJECTIVE To study the microsatellite instability (MSI) and methylation state of the hMLH1 gene promoter and their mechanisms underlying the development of gastric cancer. METHODS Forty-one gastric cancer samples were obtained from patients undergoing surgery and 46 chronic atrophic gastritis tissues with dysplasia or intestinal metaplasia (IM) were obtained from patients undergoing gastro-endoscopy. Fourteen normal gastric mucosal samples were used as controls. Genomic DNA was extracted from the samples and 5 microsatellite markers were used to measure MSI. Methylation-specific PCR (MSP) was used to screen the methylation state of the samples. DNA sequencing and immunohistochemistry were performed to verify the results. RESULTS MSI was identified in 22 out of the 41 (53.7%) gastric cancers, of which 8 cases showed high-level MSI (2 or more loci altered) and 14 showed low-level MSI (1 locus altered). MSI was also detected in 12 out of 46 (26.1%) pre-cancerous lesions of the stomach, whereas it was not seen in the normal tissue. Moreover, hMLH1 hypermethylation was detected in 17 out of the 41 (41.5%) gastric cancers, 9 out of the 46 (19.6%) pre-cancerous lesions and 0 out of the 14 normal tissue. Significant differences in frequency of MSI and hMLH1 promoter methylation were observed among gastric cancers, precancerous lesions and normal gastric tissue. Gastric samples with MSI had a tendency to be hypermethylated in the hMLH1 promoter. DNA sequencing and immunohistochemistry results also confirmed that hMLH1 promoter methylation could lead to loss of the hMLH1 protein and gene silence which sequentely resulted in gene mismatch and MSI. CONCLUSION Accumulation of MSI and hMLH1 promoter methylation may be important early molecular events during gastric carcinogenesis and may contribute to the acquisition of a transformed cell phenotype and the development of gastric cancer.     

Promoter methylation and expression of MGMT and the DNA mismatch repair genes MLH1, MSH2, MSH6 and PMS2 in paired primary and recurrent glioblastomas

Epigenetic silencing of the O(6) -methylguanine-DNA methyltransferase (MGMT) gene promoter is associated with prolonged survival in glioblastoma patients treated with temozolomide (TMZ). We investigated whether glioblastoma recurrence is associated with changes in the promoter methylation status and the expression of MGMT and the DNA mismatch repair (MMR) genes MLH1, MSH2, MSH6 and PMS2 in pairs of primary and recurrent glioblastomas of 80 patients, including 64 patients treated with radiotherapy and TMZ after the first operation. Among the primary tumors, the MGMT promoter was methylated in 31 patients and unmethylated in 49 patients. In 71 patients (89%), the MGMT promoter methylation status of the primary tumor was retained at recurrence. MGMT promoter methylation, but not MGMT protein expression, was associated with longer progression-free survival, overall survival and postrecurrence survival (PRS). Moreover, PRS was increased under salvage chemotherapy. Investigation of primary and recurrent glioblastomas of 43 patients did not identify promoter methylation in any of the four MMR genes. However, recurrent glioblastomas demonstrated significantly lower MSH2, MSH6 and PMS2 protein expression as detected by immunohistochemistry. In conclusion, reduced expression of MMR proteins, but not changes in MGMT promoter methylation, is characteristic of glioblastomas recurring after the current standards of care.     

胃癌环氧化酶-2 、hMLH1 及hMSH2 微卫星不稳定与基因调控的关系

 目的 检测临床手术切除43例胃癌及相应正常组织COX-2、hMLH1和hMSH2微卫星不稳定状态MSI及三种基因启动子甲基化情况，并进一步探讨它们与胃癌发生的关系。方法 采用聚合酶链反应（PCR）技术检测5个位点的MSI状态；甲基化特异性PCR（Methylation specific PCR，MSP）方法检测胃癌及正常组织COX-2、hMLH1及hMSH2三种基因启动子CpG岛甲基化状态。结果 43例胃癌中MSI总检出率为48．84％（21／43），五个位点的MSI检出率无显著差别。COX-2和hMLH1基因启动子CpG岛甲基化在43例胃癌中分别有8例和13例，正常组织中未检测到。hMSH2基因启动子CpG岛在胃癌及正常组织中均未检测到甲基化。在MSI-H组hMLH1基因启动子CpG岛甲基化率显著高于MSS组（P〈0．01）；而在MSI-H和MSI-L组间以及MSI-L和MSS无差别。MSI-H组中COX-2基因启动子CpG岛甲基化8例，且有7例胃癌同时出现hMLH1和COX-2基因启动子CpG岛甲基化。结论 在MSI胃癌（尤其是MSI-H型胃癌）的发生、发展过程中可能同时出现了hMLH1和COX-2基因启动子CpG岛的甲基化（即表型遗传修饰）。MSI胃癌hMLH1基因启动子CpG岛甲基化率高于MSS胃癌，提示检测hMLH1基因启动子CpG岛甲基化对于判断肿瘤类型有一定意义。     

hMLH1和hMSH2蛋白在梨状窝癌手术切缘中的表达

目的:探讨梨状窝癌手术切缘的安全范围。方法:采用免疫组化法检测50例梨状窝癌组织、癌旁3mm、5mm、10mm和20例正常喉组织中hMLH1和hMSH2蛋白的表达。结果:hMLH1和hMSH2蛋白的阳性表达按癌组织、癌旁3mm、5mm、10mm和正常喉组织的顺序依次递增,越靠近正常组织,阳性表达越高。差异具有显著性(P<0.05)。结论:梨状窝癌手术可以选择距肿瘤10mm作为安全切缘参考标准。     

Methylated DNA sequences for early cancer detection,molecular classification and chemotherapy response prediction

Molecular studies of many types of cancer have revealed that clinically evident tumours carry multiple genetic and epigenetic abnormalities, including DNA sequence alterations, chromosome copy number changes and aberrant promoter hypermethylation. Together, these aberrant changes result in the activation of oncogenes and inactivation of tumour-suppressor genes (TSG). In many cases these abnormalities can be found in premalignant lesions and even in histological normal adjacent cells. Many tumour types are difficult to detect early and are frequently resistant to available chemotherapy and radiotherapy. Therefore, the early detection, chemoprevention and the design of new therapeutic strategies based on the increased understanding of cancer molecular changes are one of the great challenges nowadays. Insertions of a methyl group at the fifth carbon of cytosines within the dinucleotide 5'- CpG-3' is the best studied epigenetic mechanism. DNA methylation acts together with others mechanisms like histone modification, chromatin remodelling and microRNAs to mould the DNA structure according to the functional state required. The aberrant methylation of the CpG islands located at the promoter region of specific genes is a common and early event involved in cancer development. Thus, hypermethylated DNA sequences from tumours are one of the most promising markers for early detection screenings as well as tumour classification and chemotherapy response in many types of cancer.     

胃癌个体化免疫治疗新策略研究

目的 探讨程序性死亡配体 1（PD L1）、程序性死亡受体 1（PD 1）、错配修复基因hMSH2、hMLH1在胃癌表达及其与临床病理特征的关系。 方法 应用免疫组化法检测76例胃癌组织中PD L1、PD 1和hMSH2、hMLH1蛋白表达。 结果 胃癌组织中,PD L1表达水平与TNM分期、分化程度、淋巴结转移情况及脉管癌栓相关（均P＜005）;PD 1表达与各临床病例特征均无相关（P＞005）。hMSH2、hMLH1表达与TNM分期相关（P＜005）。PD L1与hMSH2、hMLH1蛋白表达相关（均P＜005）,PD 1与hMSH2、hMLH1蛋白表达均无相关,PD L1表达与PD 1无相关（P＞005）。 结论 依据错配修复缺陷基因及PD L1表达水平选择性阻断PD L1／PD 1免疫检查点有望成为胃癌个体化免疫治疗的新策略。     

CpG methylation of MGMT and hMLH1 promoter in hepatocellular carcinoma associated with hepatitis viral infection

Inactivations of DNA repair genes, O(6)-methylguanine-DNA methyltransferase (MGMT) and hMLH1, by promoter hypermethylation have been reported in several types of primary human neoplasia. This epigenetic inactivation mechanism remains elusive in hepatocellular carcinoma (HCC). To investigate the relation between the expression of MGMT and hMLH1 and the CpG methylation within their promoters in HCCs with or without hepatitis viral infection, we performed immunohistochemistry and urea/bisulphite sequencing on 46 HCCs, corresponding noncancerous tissues, and 20 normal liver tissues. MGMT- and hMLH1-negative HCCs were 60.9% (28 out of 46) and 21.8% (10 out of 46), respectively. HCCs lacking both proteins were 10.9% (five out of 46). The frequency and extent of CpG methylation in the MGMT promoter increased along with hepatitis viral infection and pathological progression. MGMT-negative tumours showed very frequent and widespread methylation in the promoter compared with MGMT-positive tumours. Half of the hMLH1-negative HCCs showed promoter hypermethylation. These data suggested that MGMT gene silencing in a subset of HCCs was likely caused by epigenetic alteration, such as promoter hypermethylation, and that the promoter hypermethylation silenced the hMLH1 gene in half of the hMLH1-negative tumours. A correlation between the promoter methylation status and viral infection, although it was weak, intimated that hepatitis viral infections could play a role in the CpG methylation of the MGMT promoter.     

散发性胆囊肿瘤错配修复基因hMLH1、hMSH2和nm23H1基因蛋白表达的研究

目的探讨hMLH1和hMSH22种错配修复基因和抑癌基因nm23H1蛋白在胆囊肿瘤组织中的表达,评估其在胆囊肿瘤发生、发展和预后判断中的临床意义,为揭示肿瘤发生的病理机制提供实验依据。方法采用Envision免疫组织化学方法,检测70例胆囊肿瘤组织和10例胆囊炎症组织hMLH1、hMSH2和nm23H1蛋白表达变化。结果①在胆囊癌、胆囊良性肿瘤和炎症组织中,hMLH1、hMSH2和nm23H1蛋白表达阳性率差异显著(P<0.05);②在胆囊癌组织中,hMLH1、hMSH2蛋白表达阳性率分别为51.06%、42.55%;有淋巴结转移者hMLH1蛋白表达阳性率(25.00%)和NevinⅣ Ⅴ期表达阳性率(29.17%)分别低于无淋巴结转移者(70.37%)和NevinⅠ Ⅱ Ⅲ期(73.91%),P<0.01,伴肝脏浸润者(27.78%)低于无肝脏浸润者(65.51%),P<0.05;但hMSH2蛋白表达阳性率无显著性差异;③在胆囊癌组织中,nm23H1蛋白表达阳性率为46.81%,有淋巴结转移者(25.00%)低于无淋巴结转移者(62.96%),P<0.01;NevinⅣ Ⅴ期(29.17%)低于Ⅰ Ⅱ Ⅲ期(65.22%),P<0.05;④在胆囊癌组织中,hMSH2蛋白表达阳性者中nm23H1蛋白表达阳性率(65.00%)显著高于hMSH2蛋白表达阴性者(33.33%),P<0.05。结论实验结果提示,DNA错配修复基因hMLH1、hMSH2和nm23H1基因相互协同,参与了胆囊肿瘤发生、发展和转移的过程,可能是胆囊肿瘤发生的1个重要分子机制。     

Mutational Analysis of Mismatch Repair Genes, hMLH1 and hMSH2, in Sporadic Endometrial Carcinomas with Microsatellite Instability

Microsatellite instability, monitored by replication error (RER), bas been observed in both sporadic and hereditary types of endometrial carcinoma. In the hereditary tumors, this instability is considered to be caused by a germline defect in the DNA mismatch-repair system. We previously reported that nearly one-quarter of sporadic endometrial carcinomas examined revealed an RER-positive phenotype at multiple microsatellite loci. To investigate the role of genetic alterations of DNA mismatch-repair genes in sporadic endometrial carcinomas, we screened 18 RER(+) endometrial carcinomas for mutations of hMLH1 and hMSH2 . Although we found no germline mutations, we detected two somatic mutations of hMLH1 in a single endometrial cancer; these two mutations had occurred on different alleles, suggesting that two separate mutational events had affected both copies of hMLH1 in this particular tumor. These data implied that mutations of hMLH1 or hMSH2 play limited roles in the development of sporadic endometrial carcinomas, and that the tumors with genetic instability might have alterations of other mismatch-repair genes, such as hPMS1 and hPMS2 , or of unknown genes related to the mismatch-repair system.     

错配修复蛋白hMSH2 hMLH1表达在胃癌发生中的作用及临床意义

目的：探讨错配修复蛋白hMSH2、hMLH1表达及其在细胞内表达位置对胃癌发生的影响及临床意义.方法：收集大连医科大学附属第一医院胃癌标本172例、癌旁胃粘膜标本151例，非癌患者胃粘膜标本34例．应用免疫组织化学方法检测每例胃粘膜标本hMSH2、hMLH1蛋白的表达情况（包括其在细胞内表达位置），应用χ^2检验，Speannan等级相关分析在SPSS13．0统计软件上作相关统计结果：胃癌、癌旁胃粘膜和非癌患者胃粘膜hMSH2蛋白表达率分别为69．8％（120／172）、49．7％（75／151）和32．4％（11／34），胃癌组显著高于后两组（P=0．000），而后两组间无显著性差异（P=0．067）；hMLH1蛋白表达率分别为73.3％（126／172）、57．6％（87／151）和41．2％（14／34），胃癌组显著高于后两组（P=0．000），而后两组间无显著性差异（P=-0．082）．hMSH2和hMLH1蛋白表达率与胃癌患者的性别、年龄及胃癌分化程度均无显著相关关系．胃癌、癌旁胃粘膜和非癌患者胃粘膜hMSH2蛋白细胞核表达率分别为70．0％（84／120）、58．7％（44／75）和36．4％（4／11），细胞浆表达率分别为30．0％（36／120）、41.3％（31／75）和63．6％（7／11）；胃癌、癌旁胃粘膜、非癌患者胃粘膜中，hMSH2蛋白细胞核表达率逐渐降低，而细胞浆表达率则逐渐增高（r=0．161，P=0．020）。三种不同胃粘膜间，hMLH1蛋白在细胞内表达位置无显著性差异（P=0．878）。结论：同时检测胃粘膜错配修复蛋白hMSH2和hMLH1的表达及其细胞内表达位置可能有助于胃癌的早期预警。     

Changes of hMSH2 and hMLH1 Expression in Nasopharyngeal Carcinoma Cells after X-Radiation

OBJECTIVE To study the effect of X-radiation on expression of hMSH2 and hMLH1 in nasopharyngeal carcinoma （NPC） CNE-1 cells, and explore the mechanism of DNA mismatch repair after radiation. METHODS The cells were divided into experimental and control groups. Experimental cells were exposed to 10 Gy radiation administered as 2 Gy per fraction. Control cells were not radiated. The distribution of cells in the cell cycle was analyzed using flow cytometry. The expression of hMSH2 and hMLH1 was examined by RT-PCR and Western blots. RESULTS The expression of hMSH2 mRNA in experimental cells was significantly greater compared to control cells at 0-3rd weeks and decreased at the 4th week following radiation （P〈0.01）. The expression of hMSH2 protein in experimental cells was up-regulated and significantly greater compared to control cells at the 2nd-4th weeks after radiation （P〈0.01）. There were no significant differences in hMLH1 mRNA and protein expression between experimental and control cells （P 〉0.05）. CONCLUSION Radiation induces hMSH2 expression; hMSH2 has a role in the process of DNA repair, which maybe responsible for reduction of radiosensitivity after radiation.     

Differential expression of hMLH1 and hMSH2 is related to bladder cancer grade,stage and prognosis but not microsatellite instability

Defects in the DNA mismatch repair proteins result in microsatellite instability and malignancy in hereditary non-polyposis colorectal carcinoma (HNPCC). However, the role of mismatch repair (MMR) proteins and microsatellite instability (MSI) in transitional cell carcinoma of the bladder is less clear. In our study, the expression of 2 MMR proteins and the frequency of MSI in Transitional cell carcinoma of the bladder (TCC) were investigated. One hundred eleven patients with TCC of the bladder were studied, with complete clinicopathological data (median follow up of 5 years, range 5-16 years). Immunohistochemistry was used to detect the expression levels of hMLH1 and hMSH2. Microsatellite analysis for 14 loci (10 loci from the Bethesda consensus panel and the repeats in the TGFbetaR2, BAX, hMSH3 and hMSH6 genes) was performed on 84 tumors. Reduced expression of either MMR protein was seen in 26 of 111 tumors (23%). Reduced expression was seen more commonly in muscle invasive (p<0.03) and high grade TCC (p<0.03) than in superficial, low grade tumors. By 5 years, reduced expression of either MMR protein was associated with fewer recurrences of superficial tumors (p=0.015) and fewer relapses in all tumors (p=0.03), compared to tumors with normal expression. Nine tumors had reduced expression of both MMR proteins, analysis which suggests a synergistic reduction in expression (p=0.001). MMR expression was related to patient age, younger patients being more likely to have reduced MMR expression than older patients (p<0.01). MSI was seen at multiple loci in 1 tumor (1%) and at a single locus in 6 tumors (7%). MSI was not associated with MMR expression. Our findings indicate that reduced expression of the MMR proteins may have an important contribution in the development of a subset of TCCs and suggest a potential role for MMR expression as prognostic indicators.