Sox2 is necessary for maintaining the self-renewal of SP cells. (A) H1650-SPAdh cells were transfected with non-targeting control siRNA, or siRNA against EGFR, Src, or Sox2 and western blot analysis was performed for Sox2, Oct4, EGFR and Src expression. (B) siRNA transfected cells were plated for self-renewal assay and analyzed after 5 days of plating. Average number of spheres generated per well from 1000 cells is plotted (mean ± SD). (C) NSCLC cell lines were transfected with control or Sox2 siRNAs and SP frequency was evaluated. Average fold change in SP-frequency (± SD) is plotted. (D) Decrease in ABCG2 expression in Sox2 siRNA transfected cells was detected by western blotting. The Sox2 expression was evaluated by qRT-PCR and results are presented as bar diagram.