PD98059 inhibited IFNα-induced growth-stimulation effect and increase of ERK activation in U266 cells. (A) U266 cells were left untreated or treated with IFNα (100 U/ml) or pre-treated with PD98059 (50 μM) before IFNα was added. Then cytoplasmic proteins were extracted and the expressions of phospho-ERK and ERK were determined by immunoblot assay as same as in Fig. 3. (B) U266 cells (2 × 106 /well) were cultured in 96-well tissue culture plates in the absence or presence of IFNα (100 U/ml) alone or IFNα together with PD98059 (50 μM). MTT assay was preformed as described in Fig. 1. The p values were determined by paired t-test. *significantly different (p < 0.01) from the corresponding values in cultures with IFNα alone.