Knockdown of EGFR-HER2 exerts a pro-apoptotic effect in NCI-H3122 R cells. (A) NCI-H3122 R cells were transfected with siEGFR and/or siHER2 and were incubated for 24 h. Cells were harvested and the expression of EGFR and HER2 was evaluated with Western blotting. β-Actin served as the loading control. (B) Apoptosis was evaluated using flow cytometry of Annexin V-PI double-stained NCI-H3122 R cells after transfection with siEGFR and/or siHER2 for 24 h. The Y-axis represents the PI-labeled population, whereas the X-axis represents the Annexin V positive cells. The left lower gating (Annexin V-, PI-) indicates normal cells, whereas the right lower gating (Annexin V+, PI-) and the right upper gating (Annexin V+, PI+) are the early and late apoptotic cells, respectively. (C) Data are presented as histograms. Means with different letters (a and b) indicate statistically significant differences (p < 0.05; N.S., not significant). (D) Caspase 3/7 activity was quantified 24 h after transfection with siEGFR and/or siHER2 in NCI-H3122 R cells. Means with different letters (a and b) indicate statistically significant differences (p < 0.05; N.S., not significant).