Network protein vulnerability in EGFR TKI‐resistant cells and specific for EGFR‐mutated cells. Network protein vulnerability in EGFR TKI‐resistant cells and specific for EGFR‐mutated cells. (A) Core network protein perturbations track with EGFR TKI resistance mechanisms. For each pair of erlotinib‐sensitive and ‐resistant cells, the protein name and number of significant effects from siRNA transfection in either parent cell line alone or overlapping with EGFR TKI‐resistant cell line are shown in Venn diagram. The criteria for defined sensitivity to siRNA across all three pair cell lines required (i) the knockdown inhibited cell viability by >50% and (ii) had statistical significance (P<0.05) from three data points. (B) Lung cancer cell lines with EGFR‐mutant (n=5) and wild‐type EGFR (n=12) were transfected with pooled siRNA targeting 15 genes as described in Materials and methods. Cell viability was performed by CellTiter Glo 5 days after transfection. Heat map of the average values of cell survival from three technical replicates was plotted by the heatmap function in R ( http://www.r‐project.org/). The range and histogram of the average values are also shown at bottom right. The blue color indicates lower number of viable cells while red color indicates higher number of viable cells. P‐values listed on the right side of the heat map were based on the Wilcoxon rank‐sum test. The significant hits (‘##’: P<0.01; ‘#’: P<0.05) are listed above the red line on the left side of the heat map. The cell lines labeled with ‘*’ are EGFR mutant and resistant to EGFR TKI. (C) PC9 cells were exposed to 100 nM erlotinib for 1 h and DMSO as a negative control. Protein lysates were immunoprecipitated with anti‐ARHG5 antibody and rabbit lgG as a control, then immunoblotted with indicated antibodies. (D) PC9 and PC9GR cells were infected with lentivirus expressing two distinct shRNAs against ARHG5 or lentivirus expressing non‐targeting scrambled shRNA as a control. ARHG5 knockdown was detected by qPCR following 72‐h infection (left panel). Cell viability assay was performed by CellTiter‐Glo following 5‐day infection (right panel). (E) PARP cleavage was evaluated by western blotting after 72‐h infection and equal protein loading was confirmed by β‐actin antibodies. Jiannong Li et al. Mol Syst Biol 2013;9:705 © as stated in the article, figure or figure legend