Arsenic trioxide-induced autophagic degradation of BCR-ABL. (A) K562 cells were transfected with control siRNA or siRNAs specifically targeting beclin 1 (Becn1) or Atg7 or p62/SQSTM1, as indicated. Cells were lysed, and total lysates were resolved by SDS-PAGE and immunoblotted with the indicated antibodies. (B) K562 cells were transfected with control siRNA or siRNAs specifically targeting Becn1 or Atg7 or p62/SQSTM1, as indicated and were subsequently treated for 24 hours with As₂O₃ (2μM). Total lysates were resolved by SDS-PAGE and immunoblotted with the indicated antibodies. (C) K562 cells were pretreated for 60 minutes with pepstatin A (10μM) and E64-d (10μM) as indicated, and were subsequently treated for 24 hours with As₂O₃ (2μM) in the continuous presence or absence of the inhibitors, as indicated. Total cell lysates were resolved by SDS-PAGE and immunoblotted with an anti-ABL or anti-Hsp90 antibodies, as indicated. (D-E) K562 cells were transfected with control-siRNA or Atg7 siRNA or Beclin1 siRNA (D) or p62/SQSMT1 siRNA (E) as indicated and the effects of AS₂O₃ (0.5μM) on leukemic progenitor (CFU-L) colony formation were assessed in clonogenic assays in methylcellulose. Data are expressed as percent control of CFU-L colony numbers for control siRNA-treated cells and represent means ± SE of 4 independent experiments. Paired t test analysis comparing A_S2O₃–treated control siRNA transfected cells versus A_S2O₃–treated Atg7 siRNA transfected cells or versus A_S2O₃–treated Beclin1 siRNA transfected cells or versus A_S2O₃–treated p62/SQSMT1 siRNA transfected cells and the corresponding paired P values are indicated.