miR-17-92 expression in K562 cells. (A) c-MYC mRNA levels (i) were measured by real-time qRT-PCR 4 days after lentiviral transduction and normalized in comparison to GAPDH expression. c-MYC mRNA expression of control dcH1-ctrl-SR–transduced cells was set to 100% (average of 3 independent experiments). Effects of lentiviral-mediated c-MYC shRNA expression compared with control shRNAs on cell proliferation (ii). Viable cells were counted by trypan blue exclusion. Mean and SD of 2 independent experiments are shown. (B) miR-17-92 expression after treatment with imatinib (black bars), lentivirally expressed anti–c-MYC shRNA (light gray bars), or simultaneous treatment with imatinib and anti–c-MYC shRNA (gray bars) as determined by miR–qRT-PCR. Mean and SD of 2 independent experiments. *No change in miRNA expression. (C) Expression of miR-17-92 pri-miRNA transcripts after treatment with imatinib (dark gray bar), lentivirally expressed anti–c-myc shRNA (light gray bar), or simultaneous treatment with imatinib and c-myc RNAi as determined by real-time RT-PCR. Mean and SD of 2 independent experiments.