Fig. 6. Induction of cell type–specific cell death by miRNA-ON and -OFF switches.

(A) Schematic illustration of the combination of switches that efficiently purify miR-21-5p–active (HeLa) or –inactive (293FT) cells. The translation of miR-21-5p–ON switch encoding Bn and OFF switch encoding Bs increases and decreases, respectively, in HeLa cells due to high miR-21-5p activity, resulting in the activation of Bn and thus the promotion of cell death. In contrast, the translation of Bn and Bs decreases and increases in 293FT cells, respectively, resulting in the survival of 293FT cells. HeLa cells can also be purified using miR-21-5p–Bs-ON and miR-21-5p–Bn-OFF switches. (B) Microscopic images of each cell 2 days after transfection. miR-21-5p–Bn-ON, miR-21-5p–Bs-ON, miR-21-5p–Bn-OFF, and miR-21-5p–Bs-OFF are the same as in Fig. 5B. In the case of the dual switch using miR-21-5p–Bs-ON and miR-21-5p–Bn-OFF (top left), 293FT cells showed an abnormal shape and detached from the bottom of the well. In the case of miR-21-5p–Bs-OFF and miR-21-5p–Bn-ON (bottom left), HeLa cells detached from the well. Both cell types transfected with either single miR-21-5p–Bn-OFF or miR-21-5p–Bn-ON switch showed abnormal morphology. Scale bar, 200 μm. (C) Cell viability by the WST-1 assay was performed 2 days after the transfection. The absorbance values were subtracted by the absorbance of blank wells and normalized by the absorbance of untransfected cells. Error bars represent the means ± SD (n = 3), and data of each biological replicate are shown as a point. *P < 0.05 and ***P < 0.001.