miRNA signature of TPA-treated K562 cells differentiated into megakaryocytes. (A) miRNAs up-regulated at least 6-fold 4 days after TPA treatment by microarray. Background counts were ≤ 500 and the assay saturated at 65 232 counts. Reproducibility of the miRNA microarray in 2 TPA-treated K562 samples is shown in supplemental Figure 1B. (Supplemental Table 1 shows data for all miRNAs analyzed.) (B-C) Change in miRNA expression after TPA or hemin treatment analyzed by Northern blot. U6 snRNA is a loading control. The miRNAs most induced by TPA were not induced by hemin (supplemental Figure 1C). MK differentiation by TPA and erythroid differentiation by hemin were verified (supplemental Figure 1A). miR-24 expression increased after either TPA or hemin treatment.