FIGURE 5.

Binning HeLa cells according to ERK2 expression level reveals a time-dependent switch from a bell-shaped to a monotonic ERK2-ppERK2 relationship. Cells were transfected with siRNA targeting endogenous ERK1 and ERK2 and transduced with Ad ERK2-GFP before treatment for 5 or 15 min with 10 nm EGF (panels A and B, filled circles) or 1 μm PDBu (panels C and D, filled triangles) or without stimulus (Ctrl., open circles). Individual cells were binned according to ERK2-GFP expression, and mean ppERK2 level was calculated for each bin. The figures show ppERK2 levels plotted against bin center and are pooled from three experiments (mean ± S.E., n = 3).