Comment on "SUMO deconjugation is required for arsenic-triggered ubiquitylation of PML".

Fasci et al proposed that a SENP1-mediated switch from SUMO2 to SUMO1 conjugation on Lys(65) in promyelocytic leukemia protein (PML) is required for arsenic-induced PML degradation, the basis for the antileukemic activity of arsenic. We found that PML or PML/RARA (retinoic acid receptor α) mutants that cannot be SUMO-conjugated on this specific site nevertheless underwent immediate arsenic-triggered SUMO modification. Moreover, these mutants were efficiently degraded in cells and even in vivo, demonstrating that SUMOylation of Lys(65) was dispensable for arsenic response. The existence and putative role of a SUMO switch on PML should thus be reassessed.