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

2008; Baishideng Publishing Group; Volume: 14; Issue: 48 Linguagem: Inglês

10.3748/wjg.14.7329

2219-2840

Heng-Hua Zhou, Shi-Yan Yan, Xiao-Yan Zhou, Du Xiang, Tai-Ming Zhang, Cai Xu, Yong-Ming Lu, San-Jun Cai, Da-Ren Shi,

Epigenetics and DNA Methylation

control and the cell line sw48 was used as the known positive control along with water as the blank control.Immunochemical staining of MLH1 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 MLH1 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 MSH2 , MLH1 and MSH6 genes.However, no proband with methylation in MLH1 gene was found in the families with MSS phenotype and without germline mutations in MSH2 , MLH1 and MSH6 genes.No expression of MLH1 protein was found in tumor tissues from two patients with exhaustive-methylation phenotype, whereas positive expression of MLH1 protein was observed in tumor tissues from patients with partial methylation phenotype (excluding family H42 without tumor tissue), indicating that exhaustive-methylation of MLH1 gene can cause defective expression of MLH1 protein.CONCLUSION: Methylation phenotype of MLH1 gene is correlated with microsatellite phenotype of MMR genes, especially with MSI-H.Exhaustive-methylation of MLH1 gene can silence the expression of MLH1 protein.MLH1 promoter methylation analysis is a promising tool for molecular genetics screening for HNPCC.