TOP1 is the direct target of miR-23a. A shows that the possible target of TOP1 3′UTR interaction with miR-23a predicted by TargetScan software. B shows that TOP1 protein expression was inhibited by miR-23a. The cells were transiently transfected with either vector of miR-23a-expressing plasmids. Significant suppression of TOP1 protein level could be observed in miR-23a-overexpressing cells; C shows that TOP1 mRNA transcript was inhibited after long exposure to miR-23a. The cells were transiently transfected with either vector of miR-23a-expressing plasmids. Potent inhibition of TOP1 mRNA transcripts could be observed in cells with exposure to miR-23a. D shows that the luciferase activity of vector expressing TOP1 3′UTR could be suppressed in the presence of miR-23a. HEK293T cells were co-transfected with luciferase-containing plasmid expressing TOP1 3′UTR and the plasmid expressing miR-23a. The luciferase activity was detected by dual luciferease reporting assay. Activity of Renilla Luciferase was expressed as control.