RAB21, RAB23, RAB18 and RAB3B is a direct target of miR-200b. (A) miR-200b binds to the 3′UTRs of RAB21, RAB23, RAB18, RAB3B, RAB37, RAB8B, RAB7A, RAP1B and RAP2C. Predicted binding between miR-200b and the seeds match in the nine predicted genes’ 3′UTRs. (B) Luciferase reporter assays 48 h after transfection with indicated pMIR-Report plasmids and a renilla transfection control plasmid, co-transfected with miR-200b mimics, or relevant scramble controls. Luciferase activities were significantly inhibited on co-transfection of miR-200b mimics and pMIR-Report plasmids of RAB21, RAB23, RAB18 and RAB3B. Mutation in the corresponding binding sites abolished this inhibition. Data shown were the mean ± s.d. of six replicates and were representative of three independent experiments. *P < 0.05 (C) miR-200b regulated the expression of RAB21, RAB23, RAB18 and RAB3B. Western blot analyzed their expression 48 h after transfection with miR-200b mimics or scramble control in MDA-MB-231 and 4 T1 cells.