Activation of both p38 and JNKs is essential for Epo-induced differentiation. Various concentrations (0 to 30 μmol/L) of scrambled S-oligo (A), antisense S-oligo (•), or sense S-oligo (○) of p38 (B), JNK1 (C), JNK2 (D), a mixture of JNK1 and JNK2 (E), or ERKs (F) were mixed with SKT6 cells in the presence of Epo, and the hemoglobinized cells were stained with DAF after 4.5 days of culture. The percentage of DAF-positive cells in the presence of Epo is defined as 100%, and the inhibition of erythroid differentiation is shown as a relative value. Each point represents the mean of five replicates. (G) Antisense S-oligos specifically inhibit the expression of each corresponding kinase. The lysates of the cells treated (+) or untreated (−) with antisense S-oligos (30 μmol/L) indicated above were probed with specific antibody against each corresponding kinase shown left.