| Objective: Gastric cancer is in the forefornt of the cancer pathogenesis in the world, and its morbidity and mortality in China are twice more than the world average. More than half of patients with gastric cancer are found in advanced cancer, or even lose the chance of dissection, while treatments are more rely on chemotherapy and so on. There is no gold standard for gastric cancer chemotherapy,and the efficacy improvement was limited. Cisplatin is basic for gastric cancer chemotherapy, but the efficacy of cisplatin alone or combination therapy is no more than 20%. The primary or acquired drug resistance to cisplatin is the cause of its poor efficacy or its invalid. Gastric cancer resistance to cisplatin is a multi-gene, multi-step and complex process of multiple factors. Clarify the mechanism of drug resistance to cisplatin, improve its clinical application, and improve patient outcomes and survival are important in gastric cancer.E-cadherin is number of the adhesion molecule superfamily, which can mediate the tight junction between cell–cell and cell–matrix. E-cadherin is participate in the epithelial to mesenchymal transition (EMT), and it can be involved a variety of tumor biological behavior such as proliferation, apoptosis, invasion and metastasis. Now it has been confirmed as an invasion suppressor. Recent studies revealed that E-cadherin can also affect drug sensitivity of tumor cells to various cytotoxic agents including cisplatin and targeted therapy. Its related mechanism is focused on regulation of antiapoptosis gene BCL-2, but the conclusion is not yet uniform.It has observed that E-cadherin low expression or absence in gastric cancer, and expression of E-cadherin can inhibit local invasion and distant metastasis. Therefor, E-cadherin may play a role as a tumor suppressor in the deveopment of gastric cancer. The relationship between E-cadherin and cisplatin resistance in gastric cancer has not been reported.Gastric cancer SGC7901/DDP and SGC7901 cells are used as models in this study, which have the same genetic background. We found that E-cadherin mRNA and protein expressions were different between the two cell lines, and its expression in SGC7901/DDP cell was significantly lower. Therefore, we applied siRNA interference in SGC7901 cell for loss-of-function studies, which in the high level of E-cadherin expression, aiming to discuse the influence of E-cadherin in gastric cancer cisplatin drug resistance and its related mechanism, which can provide further theoretical basis for understanding the mechanism of cisplatin drug resistance and have important significance in the discovery of intervention and treatment of gastric cancer therapeutic targets.Methods: Cisplatin-resistant gastric cancer cell SGC7901/DDP and its sensitive cell line SGC7901 were in cultured. Drug sensitivity to ciaplatin of these cells were tested using MTT assay, and mRNA and protein changes between the cell lines of E-cadherin were detected by RT-PCR and Western blot. Design and synthese of E-cadherin-specific interference siRNA sequence and its negative control sequence, SGC7901 cell line were transiently transfected with E-cadherin siRNA and its negative control by means of Lipofectamine 2000. RT-PCR and Western blot were used to detect E-cadherin mRNA and protein expression after transfection 24, 48, 72h in SGC7901 cell to detected the interference effects. SGC7901 cell after transfection 24h used for drug sensitivity study by means of MTT assay. Total protein was extracted after transfection 72h, and protein expression changes of BCL-2 and BAX were tested using Western blot.Results:1 The IC50 of cisplatin in SGC7901/DDP cell line was 11.245±0.272 mg/L, while in the sensitive strain was 2.206±0.256 mg/L. SGC7901/DDP resistance to ciaplatin was significantly higher than that of SGC7901 cell (P <0.05). 2 E-cadherin mRNA relative expression in SGC7901/DDP cell was 0.029±0.018, while in the SGC7901 cell was 0.364±0.040. E-cadherin protein relative expression in SGC7901/DDP cell was 0.098±0.029, while in the SGC7901 cell was 0.385±0.025. Compared with the SGC7901 cell, E-cadherin mRNA and protein expressions in SGC7901/DDP cell were significantly lower (P <0.05).3 E-cadherin mRNA relative expressions in SGC7901 cell 24, 48, 72h after transfection were 0.168±0.016, 0.109±0.020 and 0.048±0.014, while in negative control group was 0.414±0.025. E-cadherin protein relative expressions in SGC7901 cell 24, 48, 72h after transfection were 0.244±0.006, 0.155±0.007 and 0.118±0.014, while in negative control group was 0.527±0.006. E-cadherin mRNA and protein levels was significant lower than the negative control group after siRNA transfection, E-cadherin siRNA interference silencing sequence could achieve good results.4 The IC50 of cisplatin in SGC7901 cell after transfection was 4.375±0.199mg / L, while in negative control group was 2.882±0.166mg / L. Cisplatin sensitivity in SGC7901 cell after E-cadherin siRNA transfection was significantly lower than the negative control group (P <0.05), and the resistant phenotype was change after transfection.5 Compared with negative control group, the BCL-2 protein expression was significantly increased in SGC701 cell 72h after E-cadherin siRNA trasfection(0.114±0.012 vs 0.328±0.014 ), while the BAX protein was significantly decreased(0.369±0.016 vs 0.139±0.013 ) (P <0.05).Conclusion:1 The process of gastric cancer cell resistant to cisplatin may be related to lack of E-cadherin expression. E-cadherin may be the new mechanism of drug resistance in gastric cancer.2 Inhibition of E-cadherin expression in gastric cancer SGC7901 cell may promot drug resistance for cisplatin.3 E-cadherin siRNA induced gastric cancer cell drug resistance phenotypes may relate to increasing antiapoptotic BCL-2 gene expression and inhibiting apoptotic gene BAX expression.
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