FIG. 2.

ERK1 ablation has no impact on cell proliferation. NIH 3T3 cells were transfected with 3 μg of pBabePuro plasmid and 27 μg of control plasmid or 27 μg pSUPER-ERK1 (sh-ERK1). After selection, cells were plated under conditions of exponential growth. (A) The levels of ERKs and phosphorylated ERKs were evaluated by immunoblotting at 2.5 days postplating as for Fig. 1. The level of actin analyzed by immunoblotting is given for loading normalization. (B) Cells plated on 12-well plates were fixed at 6 h postplating (day 0) and daily up to 4 days postplating. Proliferation was calculated as described for Fig. 1. Data are representative of at least seven independent experiments. Values are the averages and standard deviations of cell counts obtained when cells were plated at 20, 30, and 40 cells per mm².