Effect Of The Promoter Methylation On The Protein Expression Of HMLH1 In Gastric Cancer

Objective:Gastric cancer is one of the most common cancers in China with unclear the molecular biological mechanism of cancergenesis. Recently, the researchers pay more and more attention to the relationship between the deficiency of mismatch repair function and gastric cancer. Mismatch repair gene system is one of gene repair systems in cell with the function of maintaining the genomic stability through repairing mismatched bases during the DNA replication. hMLH1 gene is one major member of mismatch repair gene system. Its protein takes part in repairing mismatched bases, therefore its abnormal expression will affect the function of mismatch repair gene. Gene mutations and promoter methylation are the major causes of hMLH1 expression down-regulated. It has been verified by foreign researchers that hMLH1 promoter methylation can lead protein expression reduction in colorectal cancer and lung cancer and so on. We have found that the protein expressions are higher or lower in different cases, but there isn't clear explanation of this. There are few reports about the state of hMLH1 gene promoter methylation and its effect to protein expression in Chinese gastric cancers, and neither of them is clear. It is helpful to answer these questions for clarifying gastric cancergenesis and predicating the gastric cancer happening.Methods:Gastric cancers with clear pathological diagnosis and their adjacent mucosa for corresponding from 41 patients without receively radio-chemotherapys were obtained by operation. In order to analyse the difference of hMLH1 protein expression quantity and expression location between gastric cancer group and adjacent mucosa group, immunohistoche- mistry was used to examine the hMLH1 protein expression in all cases. Inorder to analyse the difference of hMLH1 promoter methylation state between gastric cancer and adjacent mucosa, methylation-specific PCR (MSP) was used to examine the hMLH1 promoter methylation state. Dividing the cases into promoter methylated and unmethylated groups according the hMLH1 promoter methylation state, we analysed the relationship between hMLH1 promoter methylation and protein expression in all cases, gastric cancers, ajacent mucosa. Dividing the cases into total-methylation group and partial-methylation group according the methylation extent, we analysed the relationship between the methylation extent and protein expression in all cases, gastric cancer, ajacent mucosa. We analysed the relationship between hMLH1 promoter methylation and patients'sex, age, tissue differentiated extent, tumor invading deepth, lymphonode transfering. SPSS 13.0 statistics soft was used to process all the data.Results: The positive expression rates of hMLH1 protein in gastric cancer group and adjacent mucosa group were 58.54%(24/41) and 80.49%(33/41) respectively (p<0.05). The expression rates of nucleus in gastric cancer group and adjacent mucosa group were 9.76%(4/41) and 34.15%(14/41) respectively (p < 0.05), the expression rates of cytoplasm were 34.15%(14/41) and 14.63%(6/41) respectively (p<0.05), the expressions rate of both nucleus and plasm were 14.63%(6/41) and 31.71%(13/41) respectively (p>0.05).The rates of hMLH1 gene promoter methylation in gastric cancer group and adjacent mucosa group were 80.49%(33/41) and 24.39%(10/41) respectively (p< 0.05); the rates of total-methylation in gastric cancer group and adjacent mucosa group were 41.46%(17/41) and 19.51%(8/41) respectively (p < 0.05), the positive rates of partial-methylation were 39.02%(16/41) and 4.88%(2/41) respectively (p<0.05).In all cases, the positive expression rate of hMLH1 protein in promoter methylated group being 41.86%(18/43) was significantly lower than that in promoter unmethylated group being 100.00%(39/39) (p<0.05).In gastric cancer cases, the positive expression rate of hMLH1 protein in promoter methylated group being 48.48%(16/43) was significantly lower than thatin promoter unmethylated group being 100.00%(8/8) (p<0.05).In adjacent mucosa cases, the positive expression rate of hMLH1protein in promoter methylated group being 20.00%(2/10) was significantly lower than that in promoter unmethylated group being 100.00%(31/31) (p<0.05).In all cases, the positive expression rate of hMLH1 protein in total-methylation group being 0%(0/25) was significantly lower than that in partial-methylation group being 100.00%(18/18) (p<0.05).In gastric cancer cases, the positive expression rate of hMLH1 protein in total-methylation group being 0%(0/17) was significantly lower than that in partial-methylation group being 100.00%(16/16) (p<0.05).In adjacent mucosa cases, the positive expression rate of hMLH1 protein in total-methylation group being 0%(0/8) was significantly lower than that in partial-methylation group being 100.00%(2/2) (p<0.05).The rates of hMLH1 promoter methylation were 81.58%(31/38) and 66.67%(2/3) in male and female gastric cancer patients respectively (p>0.05), were 50.00%(3/6) and 85.71%(30/35) in patients older than 50-year-old group and younger than 50-year-old group respectively (p>0.05), were 81.25%(13/16) and 80.00%(20/25) in differentiated and undifferentiated gastric cancer groups respectively (p > 0.05), were 77.78%(7/9) and 81.25%(26/32) in no-invading deep-muscle and invading deep-muscle groups respectively (p > 0.05), were 76.92%(10/13) and 82.14%(23/28) in groups with lymphonode metastasis and without lymphonode metastasis respectively (p>0.05).Conclusions:1. The expression of hMLH1 protein was down-regulated in gastric cancer cells;2. The expression of hMLH1 protein in gastric mucosa cell plasm may be an signal of cell malignant transformation;3 . There is hMLH1 gene promoter abnomal methylation in gastric cancer cell;4. hMLH1 gene promoter methylation is a major cause of protein expression reduction;5. It may be helpful to examine hMLH1 gene promoter methylation state for predication of gastric cancer.