miR-34a enhances megakaryocytic differentiation and inhibits proliferation in K562 cells. (A) Overexpression of miR-34a or miR-181a in K562 cells induces the MK integrin CD41. K562 cells were transfected with the indicated miRNA mimic and 24 hours later stimulated with a suboptimal amount of TPA (0.1 nM). Efficient uptake of dsRNA oligonucleotides into transfected K562 cells is shown in supplemental Figure 1D. CD41 expression was analyzed by flow cytometry 72 hours after TPA stimulation. As positive control, K562 cells were treated with 1 nM TPA. Levels of expression of the transfected miRNAs at the time of analysis are shown in supplemental Figure 2B. (B) miR-34a and miR-134 inhibit K562 cell proliferation, assessed by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell proliferation assay. Cells were transfected with the indicated miRNA and then treated with a suboptimal amount of TPA as indicated. Values are mean ± SD.