Effects of dietary intake and genetic factors on hypermethylation of the hMLH1 gene promoter in gastric cancer

Relationship between Helicobacter pylori and DNA mismatch repair system

Helicobacter pylori infection causes the defect of mismatch repair (MMR) in eucaryotes, and microsatellite instability (MSI) in gastric epithelial cells, which increases the spontaneous mutation of relative genes, and finally results in the susceptibility to tumors in human bodies. DNA MMR can prevent the excessive proliferation of mutant cells and development of tumors by correcting mismatched bases, which occur in the process of duplication and recombination, and inducing apoptosis of the cells in which DNA had been seriously impaired. The majority of the mutation in mismatch repair gene is the gene mutation in which substitution exceeds the absence or insertion of the single basic group. In MMR, hMLH1 and hMSH2 gene are the main controlling genes. Current research showed that H pylori infection might lead to functional defect of MMR, which had played an important role in the development of gastric carcinomas. In this article, we reviewed the correlations between H pylori infection and DNA mismatch repair system.

Molecular epidemiology of gastric cancer: current status and future prospects

Gene-environment interaction appears to contribute to the etiology of gastric cancer, as suggested by the varying geographic patterns of gastric cancer incidence. Even in areas with a high rate Helicobacter pylori (H. pylori) infection, only a small proportion of infected individuals develop gastric cancer. It is likely that genetic factors, particularly relatively common genetic variants, such as single nucleotide polymorphisms (SNPs), may modulate the effects of environmental risk factors by regulating multiple biologic pathways involved in gastric carcinogenesis. Thus, common genetic variants can pose a substantial influence on the population attributable risk, even though the absolute risk associated with each of these variants may be low. Remarkable progress has been made in the field of molecular epidemiology, but it appears that an initial view on the magnitude of the effects of inherited variants was overestimated. Nevertheless, evidence suggests that genetic variants may contribute to the etiology of gastric cancer, particularly those SNPs in genes that are involved in inflammatory response, metabolism of chemical carcinogens, DNA repair, and tumor suppression. Although previous molecular epidemiologic studies of potentially functional polymorphisms in candidate genes and gastric cancer susceptibility lack consistency, they have advanced our knowledge of the role of genetic susceptibility in the etiology of gastric cancer. Future, welldesigned large population-based studies will validate current findings and provide the rationale for identifying at-risk subpopulations for primary prevention of gastric cancer.

Epigenetic effects of ethanol on liver and gastrointestinal injury

Alcohol consumption causes cellular injury. Recent developments indicate that ethanol induces epigenetic alterations, particularly acetylation, methylation of histones, and hypo- and hypermethylation of DNA. This has opened up a new area of interest in ethanol research and is providing novel insight into actions of ethanol at the nucleosomal level in relation to gene expression and patho-physiological consequences. The epigenetic effects are mainly attributable to ethanol metabolic stress (Emess), generated by the oxidative and non-oxidative metabolism of ethanol, and dysregulation of methionine metabolism. Epigenetic changes are important in ethanol-induced hepatic steatosis, fibrosis, carcinoma and gastrointestinal injury. This editorial highlights these new advances and its future potential.

Methylation and expression of tumor-related genes and their associations with folate and MTHFR gene polymorphisms in gastric cancerous tissues

AIM: To investigate the methylation and expression of c-myc oncogenes, p16^INK4A, p21^WAF1, hMLH1 and hMSH2 tumor suppressor genes, and their associations with folate and methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms in gastric cancerous tissues.

METHODS: Paired samples of primary gastric cancer and corresponding para-cancerous, non-cancerous gastric mucosa were obtained from surgically resected specimens of 38 patients, and the latter were used as controls. Folate concentration was detected by FOL ACS: 180 automated chemiluminescence system. Two common polymorphisms of MTHFR gene were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The mRNA expression of tumor-related gene was detected by real-time reverse transcription-PCR (RT-PCR). The methylation status of gene promoter was determined by methylation-specific PCR (MSP).

RESULTS: Up-regulation of c-myc, down-regulation of p16^INK4A, hMLH1 and hMSH2 expression were associated with the aberrant methylation of gene promoters in gastric canceous mucosae, while p21^WAF1 expression was not. Down-regulation of p21^WAF1 and hMSH2 expression, hypermethylation of p16^INK4A were associated with low folate level. Over-expression and hypomethylation of c-myc coexisted with low folate level. 677CC genotype of MTHFR showed hypermethylation and down-regulation of p16^INK4A expression, and there was no significant relationship between the two common polymorphisms of MTHFR and the methylation and expression of the other tumor-related genes.

CONCLUSION: DNA methylation plays an important role in human gastric carcinogenesis. Folate level and MTHFR gene polymorphisms may regulate the expression of tumor-related genes by affecting the methylation status.

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