Role of DNA repair gene MGMT, hMLHI and hMSH2 in oncogenesis and progression of human gastrointestinal, hepatobiliary carcinoma

O^6-甲基鸟嘌呤-DNA甲基转移酶（MGMT）是一种DNA修复酶，当MGMT表达受损时，O^6-甲基鸟嘌呤在DNA复制过程中与胸腺嘧啶错配，导致DNA中G：C→A：T过渡突变。我们先前在免疫组化研究中证实，MGMT表达缺陷与胆道癌、肝细胞癌和胃癌患者的不良预后相关。因此，我们提出了两种可能的假设，即MGMT丢失如何促进肿瘤进展。一是肿瘤中MGMT的缺失可能导致癌基因和抑癌基因DNA突变的积累，从而导致肿瘤进展，导致预后不良。因此，我们使用胆囊癌标本研究K-ras、p53和β-catenin基因突变是否与MGMT状态相关，并评估基因突变是否表现出G：C→A：T转换起源， ...更多信息 从MGMT的损失。DNA测序结果显示K-ras基因突变率为11.5%，p53基因突变率为40%，β catenin基因突变率为10%。虽然MGMT缺失与候选基因的DNA突变密切相关，但在部分MGMI缺失的标本中，K-ras基因发生了G：C→A：T的突变。另一个可能的机制是通过表观遗传DNA修饰，启动子区域的高甲基化可能同时发生在MGMT和其他基因中。事实上，我们发现MGMT基因沉默是由肝细胞癌中MGMT启动子的CpG甲基化引起的。我们用甲基化特异性PCR方法检测GB癌中MGMT、E-cadherin和p16基因启动子区是否发生高甲基化。目前，我们已经发现MGMT（-）hMLH 1（+）的GB癌细胞系对烷化剂具有高敏感性和凋亡。在这项研究中，我们提出除了MGMT丧失之外，失败的错配修复功能也有助于烷基化剂的细胞毒性作用。我们正在尝试基于MGMT和hMLH 1状态使用烷化剂的分子靶向化疗。少

O^6-Methylguanine-DNA methyltansferase(MGMT) is a DNA repair enzyme that transfers methyl groups from O^6-Methylguanine to itself When MGMT expression is impaired, the O^6-Methylguanine mispairs with thymine during DNA replication, resulting in G:C→A:T transitional mutation in DNA. We have previously demonstrated that the deficient expression of MGMT was correlated with a poor prognosis of patients with biliary tract, hepatocellular and gastric carcinoma in immunohistochemical study. We consequently prompted two possible hypotheses how MGMT loss contributes to tumor progression. One is that MGMT loss in carcinoma may cause an accumulation of DNA mutation in oncogenes and tumor suppressor genes, which brings about tumor progression leading to poor prognosis. Thus, we investigated using gall bladder (GB) carcinoma specimens whether or not gene mutation including K-ras, p53 and β-catenin correlates with MGMT status, and assessed whether the gene mutation exhibit a G:C→A:T transition origi … More nated from MGMT loss. DNA seguencing study defined that frequency of gene mutations were 11.5% in K-ras, 40% in p53 and 10% in β catenin. Although significant correlation between MGMT loss and DNA mutation in the candidate genes, G:C→A:T transition in K-ras gene was observed in several specimens with MGMI loss. Another possible mechanism is by epigenetic DNA modification, that hypermethylation on promoter region may simultaneously occur in MGMT as well as other genes. Indeed, we found that MGMT gene silencing was caused by CpG methylation of the MGMT promoter in Hepatocellular carcinoma. We are examining in GB carcinoma whether promoter hypermetylation may occur in MGMT, E-cadherin and p16 genes by methylation specific PCR method. Currently, we have revealed that GB carcinoma cell line with MGMT(-)hMLH1(+) exerted high sensitivity and apoptosis to alkylating drug. In this study, we propose that abortive mismatch repair function in addition to MGMT loss contributes to cytotoxic effects of alkylating agents. We are attempting molecular targetting chemotherapy using alkylating agents based on MGMT and hMLH1 status. Less