Fig. 6

Let-7b directly targets PBX3 3′-UTR and forms a positive feedback loop. a Predicted binding sites of wild-type (WT) and mutant sequences of let-7b in the 3′-UTR of PBX3 mRNA. b Luciferase reporter assays were performed in U87 and U251 cells with co-transfection of indicated WT or mutant 3′-UTR constructs and pre-let-7b mimic or miR-NC mimic. **p < 0.01. c Western blot analysis of PBX3, p-MEK, MEK, p-ERK1/2, ERK1/2, c-myc, and LIN28 protein levels in let-7b overexpressing- or depleting-cells. d Western blot analysis of HMGA2, p-STAT3, and STAT3 protein levels in let-7b overexpressing- or depleting-cells and ELISA analysis of IL-6 protein levels in the supernatants of let-7b overexpressing- or depleting-cells. **p < 0.01. e qRT-PCR analysis of HMGA2 and IL-6 mRNA levels and western blot analysis of p-STAT3 and STAT3 protein levels in U87 and U251 cells transfected with LV-siRNA-NC or LV-siRNA-PBX3. f Pearson’s correlation analyses indicated that let-7b expression was negatively associated with PBX3, HMGA2 and IL-6 mRNA levels in GBM tissues. g Schematic diagram of the positive feedback loop involves PBX3, MEK/ERK1/2, c-myc and LIN28/let-7b