Background: MicroRNAs could target multiple genes by regulating the translation or degradation of mRNAs, and are involved in functions such as signal transduction pathways affecting the physiological functions of normal or tumor cells. 
Methods: In this study, the expressions of miRNA-21-5p in gastric cancer tissues and SGC-7901 cells were analyzed, and the effects of miRNA-21-5p on cell proliferation, migration, invasion, and apoptosis and the expressions of target proteins SMADs in SGC-7901 cells were evaluated. Inflammatory factors interleukin 1β and tumor necrosis factor α in siRNA-transfected SGC-7901 cells were determined by enzyme-linked immunosorbent assay. 
Results: MiRNA-21-5p was consistently upregulated in gastric cancer tissues and SGC-7901 cells compared to normal tissues or cells. The knockdown of miRNA-21-5p with antisense oligonucleotides suppressed cell proliferation, migration, and invasion as well as inflammatory response, and promoted cell apoptosis and SMAD7 expression. 
Conclusion: These results indicate SMAD7 may mediate the oncogenic properties of miRNA-21-5p in gastric cancer, and miRNA-21-5p would be a promising strategy for the treatment of gastric cancer.
Keywords: miRNA-21-5p, gastric cancer, SMAD7, SGC-7901, migration, invasion