Figure 4: Expression level of ABCG2 correlated with cell proliferation and chemoresistance. (a), (b) Freshly sorted ABCG2+ cells were transfected with ABCG2-specific siRNA. ABCG2− cells were transfected with ABCG2-overexpression plasmid. The proliferation of cells after transfection was compared with untransfected cells and negative control (scrambled siRNA or empty plasmid) using MTT assay after indicated time. (c), (d) The expression level of ABCG2 was manipulated as described above. Survival rates after exposure to indicated dose of doxorubicin for 24 h were determined by MTT assay. (e), (f) IC50 value to doxorubicin was calculated for different groups. **.