MEK-specific inhibitor PD98059 has no effect on Epo-induced erythroid differentiation of SKT6 cells. (A) SKT6 cells were cultured in the presence (+) or absence (−) of Epo and MEK-specific inhibitor PD98059 (50 μmol/L) dissolved in 0.1% ethanol, and the hemoglobinized cells were stained with DAF. (B) Dose-dependency of PD98059 in SKT6 cell differentiation in the presence (•) or absence (○) of Epo. The percentage of hemoglobinized cells in the presence of Epo is defined as 100% as a control. Values shown are the means of five experiments. (C) Dose-dependency of PD98059 on SKT6 cell growth. Cell proliferation was measured by MTT assay. (D) Activity of ERKs was blocked by PD98059. The ERK activity was assayed in the presence (+) or absence (−) of PD98059 (50 μmol/L) 5 minutes after Epo stimulation.