The Mechanism Of PPIs Inhibit STAT3Phosphorylation As Well As The Expression Of Snail In Gastric Cancer Cells,and Increase Their Sensitivity To Chemotherapy Drugs

Background and Aims:Gastric cancer is a worldwide common malignant tumor. According to the report from the World Health Organization published in2008, gastric cancer had a secondary mortality rate which was just behind the lung cancer. China is one of the countries with a high incidence of gastric cancer. Nowadays the main treatments for gastric cancer are surgery and chemotherapy. Since many drug-resistant gastric cancer strains has appeared, the sensitivity to chemotherapy drugs of gastric cancer reduces a lot which results in chemotherapy ineffective. Therefore, increasing the sensitivity of gastric cancer chemotherapy becomes an important process in the treatment of gastric cancer. Proton pump inhibitors (PPIs) are widely used in digestive system diseases. It is an urgent problem to be solved whether or not PPIs could enhance the sensitivity to chemotherapy drugs of gastric cancer. The aim of present study were to study the correlation between PPIs with STAT3and Snail and explore the possible mechanisms about how PPIs increase gastric cancer chemosensitivity.Methods:(1) Western blotting analysed the expression of STAT3, pSTAT3and Snail using different concentrations of PPI (omeprazole sodium for injection) to treat SGC7901cells.(2) Constructed the pEGFP-Cl-STAT3recombinant eukaryotic expression vector and transfected it into SGC7901which was named SGC7901/STAT3. A fluorescence microscope was used to detect the expression of STAT3in transfected cells. Western blotting was used to detect the expression changes of STAT3、pSTAT3、Snail and its downstream resistance gene ERCC1in SGC7901/STAT3. Transfected targeting STAT3small interfering RNA(siSTAT3) into SGC7901cells then detected the expression of STAB、pSTAT3and Snail by Western blotting.(3) The IL-6secreted by gastric cancer cells after treatment by PPI was detected by ELISA.(4) The SGC7901、SGC7901/STAT3cell apoptosis were determined by Annexin V-FITC-PI with cisplatin pretreatment.Results:(1) The level of STAT3has no significant change at all with PPI treatment, but the expression of pSTAT3and Snail began to decrease and decreased significantly with120μg/ml PPI treatment.(2) Successfully constructed the pEGFP-Cl-STAT3recombinant eukaryotic expression vector and transfect it into SGC7901cell line. The expression of EGFP was observed in transfected SGC7901cells by fluorescent microscopy. The results of Western blotting indicated that the expression of STAT3、Snail and ERCC1were significantly higher in SGC7901/STAT3cells. Western blotting showed the expression of Snail decreased as the expression of STAT3and pSTAT3were inhibited after transfecting siSTAT3into SGC7901cells.(3) ELISA method was used to detect the level of IL-6in gastric cancer cells supernatant after treated by different concentration of PPI, and we found that the concentration of IL-6in the cell supernatant increased as time went on. PPI40μg/ml could significantly reduced the level of IL-6and it had a downward trend with the increasing concentration of PPI.(4) Flow cytometry found that early apoptosis rate of SGC7901/STAT3cells induced by cisplatin was lower than SGC7901group.Conclusions:PPI inhibition of STAT3phosphorylation as well as the expression of Snail in SGC7901cell lines. The recombinant STAT3plasmid was transfected into SGC7901and the expression of STAT3、Snail and its downstream resistance gene ERCC1were raised. The expression of pSTAT3and Snail were decreased after transfected siRNA to interfer the expression of STAT3which further validated the corelation between STAT3and Snail. After24hours pretreatment by20μg/ml PPI. Since PPI can inhibit the expression of IL-6in SGC7901cells and IL-6is the activator of STAT3, so we infer that PPI may inhibit STAT3phosphorylation through the inhibition of IL-6levels in SGC7901cells, and further inhibit the expression of Snail. The apoptosis rate of SGC7901/STAT3declined compared with SGC7901cells under the induction of cisplatin which indicated that the presence of STAT3reduced SGC7901cells sensitivity to cisplatin. In summary, PPI possibly inhibits the expression of Snail through the inhibition of STAT3phosphorylation, and increased the sensitivity of SGC7901cells to chemotherapy drugs represented by cisplatin. The discovery of this pathway provided a new theoretical foundation for PPI auxiliary sensitizing chemotherapy.