The effect of oxidative stress and RNA interferance on expression of matrix metalloproteinase (MMP) genes at gastric cancer

Gastric cancer is the fourth leading cancer type of all cancers and although there has been a decline in the incidence of this cancer in recent years, it is still one of the most common cause of deaths. Although the role of oxidative stress on cancer formation has long been known, its mechanism has not been elucidated yet. The invasiveness and metastasis of tumor cells are the result of degradation of connective tissue by matrix metalloproteinases (MMP). MMPs play a profound role on aggressiveness of tumor cells and their spread.This study was undertaken to understand the role of MMP genes and ß-catenin in gastric cancer biopsies and gastric cancer cell lines in relation to oxidative stress. Further, the aim of the study here was to determine the effect of MMP-3 dependent RNA interference on AGS cell line. The gene expression profiles of gastric cancer biopsies were investigated with RT-PCR, while the gene expression profiles of cell lines under stress conditions were determined through a Q-RT PCR study. The localization of ß-catenin and 8-OHdG in tissue samples and cell lines was determined by an immunohistochemical method. To determine MMP-3 expression level, MMP-3 siRNA was introduced into AGS cell line expressing MMP-3 protein and expression level was determined by a method utilizing Q-RT PCR.MMP and ß-catenin genes were determined to have a higher expression level in tumor tissues studied. Localization studies showed that, 85 % of ß-catenin was present in cytoplasm and membrane, while the rest was localized in nucleus. The toxicity of H2O2 on gastric cancer cell lines was similar to that of on normal cells but the response of cells to stress was different. One other striking finding was that MKN-45 cell line was determined to go to apoptosis upon treatment with H2O2, the other cell lines did not show such behavior. While the infection by H. pylori did not cause a change in the expression leveles of ß-catenin and MMP genes, H2O2 stress resulted an increased level of expression in MMP-1, MMP-7, MMP-14, MMP-15, MMP-17 and ß-catenin genes. Down-regulation of the expression of these genes under no H2O2 conditions showed that the difference in gene expression profiles was due to oxidative stress.The silencing of MMP-3 gene in AGS cell line caused a decrease MMP-15, but an increase in MMP-10 expression. It is assumed that, in gastric cancer the effect of MMP-3 expression has a key role on regulation of other MMPs.