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Objective: To explore the role of S100A4 in the epithelial-mesenchymal transition (EMT) in esophageal squamous cell carcinoma and its possible molecular mechanism., Methods: Three chemically synthesized S100A4 siRNA sequences were transiently transfected into esophageal carcinoma EC9706 cells. EC9706 cells transfected with negative siRNA, lipofectamine 2000, and vacant EC9706 cells were used as control. Fluorescence quantitative RT-PCR and Western blot were used to detect the inhibition rate of S100A4 siRNA. S100A4 siRNA2 with the best inhibition rate was chosen to transiently transfect into EC9706 cells under the same conditions. The EC9706 cells transfected with negative siRNA, lipofectamine 2000 and vacant EC9706 cells were also used as control. Fluorescence quantitative RT-PCR and Western blot were used to detect the mRNA and protein expressions of E-cadherin, vimentin and snail. The morphology of EC9706 cells was observed under an inverted microscope. Boyden chamber and scratch test were used to detect the invasion and migration ability of EC9706 cells, and CCK8 assay was used to detect the proliferation ability of EC9706 cells. EC9706 cells transfected with S100A4 siRNA2 were further transfected with snail eukaryotic expression vector. The EC9706 cells transfected with S100A4 siRNA, EC9706 cells transfected with snail eukaryotic expression vector and vacant EC9706 cells were used as control. The above indexes of all the groups were observed, too., Results: The S100A4 mRNA and protein expression levels of the S100A4 siRNA2 group were 0.417 ± 0.041 and 0.337 ± 0.039, the transmembrane cell number was 61.608 ± 8.937, the scratch healing distance was (0.216 ± 0.064) mm, the A value was 0.623 ± 0.084, the E-cadherin mRNA and protein levels were 0.619 ± 0.032 and 0.495 ± 0.034, the vimentin mRNA and protein levels were 0.514 ± 0.032 and 0.427 ± 0.028, the snail mRNA and protein levels were 0.573 ± 0.029 and 0.429 ± 0.041. These data were significantly different with the liposome group, the negative control group and the blank group (P < 0.05 for all). After the S100A4 siRNA2 treatment for 24 h, the appearance of EC9706 cells changed to epithelial cell morphology. The transmembrane cell number and the scratch healing distance of the S100A4 siRNA2+snail eukaryotic expression vector group were (69.382 ± 9.666) cells and (0.274 ± 0.029) mm, the A value was 0.823 ± 0.101, the snail mRNA and protein levels were 0.704 ± 0.037 and 0.625 ± 0.031, the vimentin mRNA and protein levels were 0.712 ± 0.046 and 0.609 ± 0.038, and these data were significantly higher than those of the Sl00A4 siRNA2 group (P < 0.05 for all). The E-cadherin mRNA and protein levels of the S100A4 siRNA2+eukaryotic expression vector group were 0.437 ± 0.038 and 0.381 ± 0.031, significantly lower than those of the S100A4 siRNA2 group (P < 0.05 for all). However, snail had no effect on the morphology of EC9706 cells., Conclusions: S100A4 may be involved in the EMT process of esophageal squamous-cell carcinoma by regulating the expression of snail and then plays a role in the invasion and metastasis of esophageal carcinoma.