FIGURE 8.

Effect of exosite mutations on LF activity in melanoma cells. A, A375 cells were treated with 0.5 μg/ml PA and the indicated concentrations of WT or mutant LF for 72 h, and cell viability was measured by resazurin assay. Measurements from three independent experiments are plotted as percentages of cell number in the untreated control group. The error bars indicate S.E. B, IC₅₀ values calculated from A375 cell growth assays. The means and S.E. are shown (n = 3). C–E. A375 cells were treated with 0.5 μg/ml PA and 0.2 ng/ml LF or LF mutant for 16 h, and cells were harvested. Cell lysates were prepared and immunoblotted to detect phospho-ERK1/2 (C), phospho-p38 (D), and MKK3 (E). Representative immunoblots are shown at left, and mean quantified signals relative to the untreated control are shown at right. The error bars indicate standard errors (n = 3). Statistical significance was calculated as for Fig. 3. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001.