Expression and promoter methylation status of mismatch repair gene hMLH1 and hMSH2 in epithelial ovarian cancer.
OBJECTIVE
The purpose of this study is to determine the relationship between methylation and loss of hMLH1 and hMSH2 expression in ovarian cancer.


METHODS
We examined the methylation status of hMLH1 and hMSH2 promoter region by methylation-specific polymerase chain reaction (MSP) in 56 primary ovarian cancer tissues and 20 normal ovarian tissues, the relationship between the methylation status of these two genes and clinicopathological characteristics were analysed. We then treated SKOV3 and 3AO ovarian cancer cell lines with the demethylating agent 5-aza-2'-deoxycytidine (5-aza-dc). The hMLH1 and hMSH2 methylation was further assessed by MSP, and their mRNA expression was compared by reverse transcription polymerase chain reaction (RT-PCR) before and after 5-aza-dc treatment in these two cell lines.


RESULTS
The methylation frequency of hMLH1 and hMSH2 was 30.4% (17 of 56) and 51.7% (29 of 56) in ovarian cancers, respectively, while no methylation was detected in normal ovarian tissues (P=0.015). There is a significant correlation between hMLH1 promoter hypermethylation and histological grade (P=0.028) as well as lymphatic metastasis (P=0.003). Methylation of hMSH2 correlated with histological grade (P=0.035) and lymphatic metastasis (P=0.015). Besides, the methylation rates of hMSH2 were significantly higher in endometrioid adenocarcinoma tissues than in other pathological types of ovarian cancer. After 5-aza-dc treatment, the expression of hMLH1 and hMSH2 was reversed in two cell lines.


CONCLUSIONS
Our results indicate that promoter hypermethylation is an important mechanism for loss of hMLH1 and hMSH2 expression in human ovarian cancer and may be a potential prognostic factor in ovarian cancer.
Zhang
Hui
H
Department of Obstetrics and Gynecology, Qilu Hospital of Shandong University, Ji'nan, China.
Zhang
Shiqian
S
Cui
Jing
J
Zhang
Aifeng
A
Shen
Liang
L
Yu
Hao
H
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics* / Q000378:metabolism; D001374:Azacitidine / Q000494:pharmacology; D020137:Base Pair Mismatch / Q000235:genetics*; D016022:Case-Control Studies; D045744:Cell Line, Tumor; D019175:DNA Methylation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D000070956:MutL Proteins; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D009367:Neoplasm Staging; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000235:genetics*; D011379:Prognosis; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods
D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C088996:PMS1 protein, human; D012333:RNA, Messenger; D000070957:MutL Protein Homolog 1; D000070956:MutL Proteins; D001374:Azacitidine