CircMLLT10 acts as a miRNA sponge and inhibits miR-509-3-5p activity. A, Heat map of the differentially expressed circRNAs among 6 fresh frozen gastric cancer tissues and paired normal gastric tissues. B, Schematic representation of the circMLLT10 production process. C, CircMLLT10 expression in 61 fresh frozen gastric cancer tissues. D, Pearson's correlation among circMLLT10, miR-509-3-5p, and GINS4 mRNA expression in 61 fresh frozen gastric cancer tissues. E, FISH results for circMLLT10 and miR-509-3-5p localization in MGC-803 and AGS cells. F, qRT-PCR results for circMLLT10 knockdown in MGC-803 cells and overexpression in AGS cells. G, The effect of altered circMLLT10 expression on miR-509-3-5p expression. H, The effects of altered circMLLT10 expression on the level of GINS4 protein and the activation of Rac1/CDC4 and their downstream pathways were detected by western blot. I&J, Negative control (NC), wild-type (WT) or mutant (Mutant) of circMLLT10 sequences were respectively cloned into luciferase reporter plasmids. The relative luciferase activity was detected in MGC-803 and AGS cells. K&L, The effects of altered circMLLT10 and miR-509-3-5p expression on GINS4 mRNA and protein expression were detected by qRT-PCR and western blot. All data are presented as the mean ± SEM of three experiments. **P<0.01.