ERK1/2 activation is mediated by KRAS in GHM cells. (A) Fold change of NRAS, HRAS and KRAS mRNA after silencing with specific siRNAs in HoMel-A1 and HoMel-L1 cells in comparison to scrambled control siRNA (siNeg). Fold changes are expressed as in Figure 4A. (B, D) Combined (left panels) and individual (right panels) contribution of RAS kinases to ERK1/2 activation in HoMel-A1 and HoMel-L1 cells as assessed by Western blot analysis. Representative images of one of two independent experiments made in biological triplicates are shown. (C, E) Quantification of total ERK1/2-normalized NRAS, HRAS, KRAS and P-ERK1/2 protein levels in individual silencings. Shown are the mean ± s.e. of the two independent experiments.