miR-17-92 function in K562 cells. (A) Inhibition of miR-17-5p and miR-20a function by antagomirs. K562 cells stably transfected with miR-17-5p (i) and miR-20a sensor (ii) luciferase constructs with normal (dcH1-ctrl-shRNA, left columns) or reduced c-MYC expression (dcH1-MYC-shRNA, right columns) were electroporated alone (mock) or with the following antagomirs, as indicated: scrambled, antagomiR-17-5p, or antagomir-20a. The ratio of normalized sensor to control luciferase activity is shown. Mean and SD of 2 independent experiments. (B) Diagram of miR-17-19b, a variant miR-17-92 cluster, transcribed as a polycistronic transcript from an SFFV promoter (long terminal repeat [LTR] of spleen focus–forming virus) inserted in a lentiviral vector, S-17-19b-IEW. The vector encodes EGFP as a marker gene. (C) miR-17-19b expression in 3 independent lentivirally transduced K562 clones (nos. 1-3) in comparison to K562 transduced with empty vector as determined by miR–qRT-PCR. (D) Cell proliferation of 3 miR-17-19b lentivirally transduced K562 cell clones compared with empty vector controls. K562 cells were lentivirally transduced (transduction efficacy > 95%; data not shown), plated at 10⁴ cells per well 2 days after transduction, and the number of EGFP⁺ cells was counted. Cell proliferation was standardized to the fastest proliferating cells (clone 1), which was set to 100%. Mean and SD of 2 independent experiments. (E) Cell proliferation of 3 miR-17-19b lentivirally transduced K562 cell clones compared with empty vector controls upon reduction of c-MYC expression. The experiments were performed as described in panel D. (F) Imatinib-induced cell death in 3 miR-17-19b lentivirally transduced K562 cell clones compared with empty vector controls. Ratio of PI-positive cells in the presence of increasing concentrations of imatinib are shown. Mean and SD of 2 independent experiments.