Autophagy regulates ATRA-induced degradation of PML-RARα. (A) NB4 cells were treated with ATRA (1 µM, 24 h) with or without protease inhibitor cocktails (0.01 mg/ml), caspase inhibitor (z-VAD, 20 µM), 3-methyladenine (“3-MA”, 10 mM) or rapamycin (“Rapa”, 100 nM), and PML-RARα was assayed by western blot using RARα antibody (n = 3, *p = 0.007, column 3 versus column 2; p = 0.017, column 4 versus column 2; p < 0.001, column 6 versus column 2; p < 0.001, column 6 versus column 2; p = 0.036, column 7 versus column 2). (B) NB4 cells were treated with ATRA as indicated (1 µM, 24 h), and PML-RARα was assayed by western blot using RARα antibody (n = 3, *p = 0.021, ATG5 shRNA group versus control shRNA group). Relative PML-RARα levels are shown in the top part, “AU”: arbitrary unit. (C) NB4 cells were treated with ATRA (1 µM) for 36 h and then assayed for colocalization as indicated, by confocal microscopy. Bar = 20 µm.