The feedback circuits between miR-21 and miR-145. (A) Schematic representation of circuits between miR-21 and miR-145, and themselves in cancer stem cells. Herein, it is suggested that miR-21 represses miR-145 transcription by stimulating Ras activity that causes RREB1 to repress miR-145 transcription, and that miR-145 inhibits miR-21 transcription through knockdown target Ras (K-RAS) and decreased AP1, the main transcription factor of miR-21. In the miR-21 positive feedback loop, miR-21 is auto-upregulated via indirect upregulation of AP1. In the miR-145 positive feedback loop, miR145 increases its transcription via knock-down Ras and RREB1, the transcription repressor of miR-145. Pleuripotency factors Sox2, Nanog and Oct4 are the direct targets of miR-145. (B) Real-time qRT-PCR and Western blot analysis showing down-regulation of k-Ras following transfection with k-Ras siRNA for 48 h, compared to the corresponding scrambled siRNA transfected control cells. β-actin was used as a loading control. (C) qRT-PCR showing down-regulation of k-Ras in CR HT-29 cells produces reduction in miR-21 and increases in miR-145 expression, when compared with the corresponding controls (D) qRT-PCR showing relative expression of miR-21 and miR-145 in k-ras-downregulated CR HT-29 cells at 48 h following transfection of mature miR-145 or miR-21. All the qRT-PCR data represent means ± SD of three independent experiments; *P < 0.001, compared to the control.