Specificity of inhibition of ERK and p38 MAP kinase by PD98059 and SB203580, respectively.

(A) Starved G1E-ER2 cells were left untreated (lane 1) or stimulated with SCF (lane 2) or pretreated with the ERK inhibitor PD98059 for an hour and then stimulated with SCF (lane 3). Arrow in the top panel indicates phosphorylated p38. Bottom panel shows total p38 in each lane. (B) Starved cells were left untreated (lane 1) or stimulated with SCF (lane 2) or pretreated with the p38 inhibitor SB203580 for an hour and then stimulated with SCF (lane 3). Arrow in the top panel indicates phosphorylated ERK1/2. Bottom panel shows total ERK1/2 protein in each lane.