Objective:The epithelial-mesenchymal transition(EMT)is an important factor in the invasion and metastasis of gastric cancer,and increasing evidences have demonstrated that Sp1 play critical roles in EMT of some cancer.However,few studies indicated whether Sp1 is involved in the EMT of gastric cancer,whether abnormal expression of Sp1 in gastric cancer EMT is regulated in apost-transcriptional manner,and whether miRNAs are key players in this regulation.The purpose of this study is to identify miRNAs targeting Sp1 and determine theirexpression and function in gastric cancer.Methods and Results:we examined the expression of Sp1 in gastric cancers,their liver metastases and para-carcinoma tissues to determine the relationship between Sp1 expression and metastasis.Quantification of Sp1 mRNA and protein levels revealed that abnormal Sp1 expression in gastric cancer and metastatic tissues is attributed toalterations in post-transcriptional regulation.We next investigated the mechanism by which miRNA regulates Sp1.Using bioinformatics we identified a putative miRNA-223target site in the 3’-UTR of the SP1 gene.This target site was validated using aluciferase reporter system and miRNA-223 expression was found to negatively correlate with Sp1 protein levels.A TGF-beta1-dependent model of EMT was established for gastric cancer cell lines and used in conjunction with miRNA-223 and Sp1 over expression studies to determine the role of miRNA-223 in gastric cancer cell proliferation,apoptosis and invasion.The expression of EMT-associated proteins was analyzed in parallel to investigate at the molecular level the role of miRNA-223/Sp1/EMT in the regulation of gastric cancer invasion.Conclusions:We demonstrate that miRNA-223,through suppression of Sp1 expression,inhibits the proliferation and invasion of tumor cells and promotes apoptosis,and thereby suppresses the EMT-associated metastasis of cancer cells. Objective: The epithelial-mesenchymal transition (EMT) is an important factor in the invasion and metastasis of gastric cancer, and increasing evidences have demonstrated that Sp1 play critical roles in EMT of some cancer. However few studies show whether Sp1 is involved in the EMT of gastric cancer, whether abnormal expression of Sp1 in gastric cancer EMT is regulated in apost-transcriptional manner, and whether miRNAs are key players in this regulation. The purpose of this study is to identify miRNAs targeting Sp1 and determine theirexpression and function in gastric cancer. Methods and Results: we examined the expression of Sp1 in gastric cancers, their liver metastases and para-carcinoma tissues to determine the relationship between Sp1 expression and metastasis. Quantification of Sp1 mRNA and protein levels revealed that abnormal Sp1 expression in gastric cancer and metastatic tissues is attributed toalterations in post-transcriptional regulation. We next investigated the mechanism by whi ch miRNA regulates Sp1.Using bioinformatics we identified a putative miRNA-223 target site in the 3’-UTR of the SP1 gene. This target site was validated using a luciferase reporter system and miRNA-223 expression was found to negatively correlate with Sp1 protein levels. A TGF-beta1-dependent model of EMT was established for gastric cancer cell lines and used in conjunction with miRNA-223 and Sp1 over expression studies to determine the role of miRNA-223 in gastric cancer cell proliferation, apoptosis and invasion. The expression of EMT-associated proteins was analyzed in parallel to investigate at the molecular level the role of miRNA-223 / Spl / EMT in the regulation of gastric cancer invasion. Conclusions: We demonstrate that miRNA-223, through suppression of Spl expression, inhibits proliferation and invasion of tumor cells and promotes apoptosis, and thereby suppresses the EMT-associated metastasis of cancer cells.