FIG. 4.

Double silencing of ERK1 and ERK2 is equally effective as silencing ERK2 alone in slowing cell proliferation. Cells were transfected with 3 μg of pBabePuro plasmid and 27 μg of control plasmid, 13 μg pSUPER-ERK2 plus 13 μg of control plasmid (sh-ERK2), or 13 μg pSUPER-ERK2 plus 13 μg pSUPER-ERK1 plasmids (sh-ERK1+sh-ERK2). 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 described for Fig. 2. The level of actin was determined as a control for loading. (B) Cells plated on 12-well plates were fixed and counted as described for Fig. 2. Data are representative of at least four independent experiments. Values are as described for Fig. 2.