The effect of N-terminal TOP2B mutants on DRZ-induced TOP2B depletion. (A) siRNA oligonucleotides against rat Top2b or GFP (control) were transfected into H9C2 cells and Western blot was performed to detect Top2a/b protein level 48 h after transfection. (B) Western blot of γ-H2AX in mock-, GFP-siRNA- or TOP2B-siRNA-transfected H9C2 cells incubated with 0.1 or 1 μM DOX for 24 h. siRNA were transfected 24 h before DOX addition. (C) HTETOP cells were transiently transfected with plasmids expressing YFP-tagged wild type (WT) or mutated TOP2B carrying single amino acid mutation. DRZ (100 μM) was added 24 h later and Western blot was conducted using antibody specific for YFP (upper panel) or human TOP2B (lower panel) after another 24 h.