Objective      To investigate the target microRNA and its effect on the down-regulation of transcriptional coactivator p300

and then on the proliferation of human umbilical cord derived mesenchymal stem cells (hUC-MSCs).       Methods      Dual luciferase gene reporter system (Firefly/Renilla Luciferase) was used to screen the effective microRNA targets which interacted with p300 3′ UTR. Then the hUC-MSCs were transfected with microRNA mimics

and the expression of p300 3′ UTR at miRNA and protein levels was detected by RT-qPCR and Western blotting respectively. The levels of pluripotency transcription factors including Nanog

Oct4 and Sox2 were measured by RT-qPCR and Western blotting too. MTT assay was employed to detect the proliferation and colony formation in hUC-MSCs before and after the transfection of microRNA mimics.       Results      It was found that mir 26b-5p binding to p300 3′ UTR with imperfectly matched sequence. The Firefly/Renilla’s relative activity of mir 26b-5p/pmirGLO-p300 3′ UTR co-transfected group was decreased significantly (P0.05). The protein expression level of p300 was significantly reduced after mir 26b-5p transfection compared with NC-mimic transfection  (P0.05)

and the mRNA and protein expression levels of Nanog were significantly down-regulated after the transfection (P0.05). The mir 26b-5p transfection also reduced the proliferation and colony formation of UC-MSCs (P0.05).       Conclusion      mir 26b-5p suppresses the protein expression levels of p300 and Nanog

a pluripotency transcription factor in UC-MSCs

and also inhibits the cell proliferation and colony formation capability.