Figure 1.

Stimulation of ERK1, ERK2, and p46 ERK phosphorylation in various cell lines. (a) Stimulation of extracellular signal‐regulated kinases (ERKs) phosphorylation in Rat1 cells. Rat1 cells were stimulated with epidermal growth factor (EGF; 50 ng/ml, upper panel) or tetradecanoyl phorbol acetate (TPA; 250 ng/ml, lower panel) for the indicated times in the absence (left side) or presence of the mitogen‐activated protein kinase/ERK kinase (MEK) inhibitor PD98059 (Biomol, 15 min prestimulation, 30 µM). (b) Extracts (containing cytosolic and nuclear proteins; 60 µg) of rat PC12 cells stimulated with EGF (50 ng/ml) or nerve growth factor (Sigma, 50 ng/ml) for the indicated times. (c) Extracts (50 µg) of human breast cancer‐derived MCF7 cells stimulated with okadaic acid (Sigma, 4 µM, 15 min, left) or left untreated (right). Each of these blots was immunoblotted with antibodies (Abs) to dually phosphorylated ERK (DP) and anti‐C terminus of ERK‐Ab (C16). The position of ERK2, ERK1, and p46 ERK is indicated. Each of these experiments was reproduced at least three times