Biological differences in promyelocytic leukemia (PML) proteins between PML-nuclear bodies (PML-NBs) and extranuclear PML bodies (EnPBs) in arsenite-exposed cells

Abstract Promyelocytic leukemia (PML) proteins are known to form phase-separated nuclear punctate structures called PML-nuclear bodies (PML-NBs). The integrity disruption of PML-NBs is linked with the pathogenesis of acute promyelocytic leukemia (APL), and trivalent arsenic (As 3+ ) has been used for the clinical treatment of APL to restore normal PML-NBs. As 3+ is considered to bind to cysteine residues and enhances modification of PML with small-ubiquitin-like protein (SUMO). We exposed U-2OS and CHO-K1 cells stably overexpressing PML-VI to As 3+ and found that the solubility of PML decreased and SUMOylation of PML increased after 2 h-exposure to 3 μM As 3+ . Contrary to As 3+ -induced remarkable biochemical changes including the solubility change and SUMOylation of PML, microscopic observation of PML-NBs was not changed clearly after a short-term exposure to As 3+ . The number of PML-NBs decreased and extranuclear PML bodies (EnPBs), which are remniscences of PML-NBs after nuclear membrane breakdown at mitosis, increased after exposure to As 3+ for 24 - 72 h. The amount of SUMOylated PML decreased after prolonged exposure to As 3+ while the solubility of PML was kept low, suggesting that As 3+ stabilized EnPB without SUMOylation. The effects of As 3+ on EnPBs were clearly observed at as low as 0.3 μM As 3+ which corresponds to inorganic arsenic level in drinking water worldwide.