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 (As3+) has been used for the clinical treatment of APL to restore normal PML-NBs. As3+ 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 As3+ and found that the solubility of PML decreased and SUMOylation of PML increased after 2 h-exposure to 3 μM As3+. Contrary to As3+-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 As3+. 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 As3+ for 24 - 72 h. The amount of SUMOylated PML decreased after prolonged exposure to As3+ while the solubility of PML was kept low, suggesting that As3+ stabilized EnPB without SUMOylation. The effects of As3+ on EnPBs were clearly observed at as low as 0.3 μM As3+ which corresponds to inorganic arsenic level in drinking water worldwide.
Keywords: arsenic, small ubiquitin-like modifier (SUMO), solubility, phase separation, promyelocytic leukemia-nuclear body (PML-NB), extranuclear PML body (EnPB)