Fig. 2. FTI blocks the degradation of the EGF receptor in EGF stimulated HeLa cells. Serum-starved HeLa cells incubated without (a), or with (b) FTI were stimulated with 100 ng/ml EGF for the indicated times. Total EGF receptor content at each time point was analyzed by western blot. The positions of the intact EGF receptor and an intermediate degradation product are indicated to the left of the figure, as is the position of a non-specific band (*). Serum starved cells incubated without (c) or with (d) FTI were pulse-labelled with [¹²⁵I]EGF. Following the removal of surface bound ligand, cells were chased with unlabeled EGF and medium was collected at the indicated times. Medium was analyzed for intact and degraded EGF and after 4 hours the cells were lysed and assayed for retained radio-ligand. Error bars represent standard error of the mean (s.e.m.) based on four independent experiments, with three replicates per experiment. Differences between EGF receptor degradation in control and FTI treated cells were found to be significant by two-way ANOVA (P<0.001).