Trivalent antimonials trigger the degradation of PML-RAR in RA-sensitive and -resistant APL cells. Cellular extracts from NB4 cells (lanes 1 through 5) and from the RA-resistant NB4R4 cells (lanes 6 through 10) were prepared in SDS sample buffer. Cells were untreated (lanes 1 and 6), treated with either 1 μmol/L RA for 36 hours (lanes 2 and 7) or 1 μmol/L As₂O₃(lane 3 and 8), or 1 μmol/L Sb₂O₃ (lanes 4 and 9) or 1 μmol/L Bi₂O₃ (lanes 5 and 10) for 12 hours. Proteins were separated on a 7.5% SDS-PAGE gel, transferred to a nitrocellulose membrane, and probed with an anti-RAR polyclonal antibody. The 120-kD PML-RAR and the 50-kD RAR proteins are indicated by arrowheads. The SUMO-1–PML-RAR conjugates are indicated by open triangles and the 80-kD PML-RAR cleavage product observed after RA treatment is indicated by an asteriks.