Trivalent antimonials induce poly–SUMO-1 modification of wild-type PML. Cellular extracts from HeLa cells stably overexpressing PML(F) were prepared in SDS sample buffer. Cells were either untreated (lane 1) or treated with 1 μmol/L RA (lane 2), 1 μmol/L As₂O₃ (lane 3), 1 μmol/L Sb₂O₃ (lane 4), 1 μmol/L PAT (lane 5), 1 μmol/L meglumine antimonate (lane 6), or 1 μmol/L Bi₂O₃ (lane 7). Proteins were run on a 7.5% SDS-PAGE gel, transferred to a nitrocellulose membrane, and the blot was immunostained with a monoclonal antibody directed against the F tag. The unmodified 100-kD PML form is indicated by an open triangle. The oligo–SUMO-1–modified PML forms migrating between 120 and 160 kD are indicated by arrowheads and the high molecular poly–SUMO-1–modified PML species forming a smear toward the top of the gel by a square bracket. The ∼68-kD band represents a protein cross-reacting with the anti-F antibody that has been described previously.39