SUMO5, a Novel Poly-SUMO Isoform, Regulates PML Nuclear Bodies

Abstract

Promyelocytic leukemia nuclear bodies (PML-NBs) are PML-based nuclear structures that regulate various cellular processes. SUMOylation, the process of covalently conjugating small ubiquitin-like modifiers (SUMOs), is required for both the formation and the disruption of PML-NBs. However, detailed mechanisms of how SUMOylation regulates these processes remain unknown. Here we report that SUMO5, a novel SUMO variant, mediates the growth and disruption of PML-NBs. PolySUMO5 conjugation of PML at lysine 160 facilitates recruitment of PML-NB components, which enlarges PMLNBs. SUMO5 also increases polySUMO2/3 conjugation of PML, resulting in RNF4-mediated disruption of PML-NBs. The acute promyelocytic leukemia oncoprotein PML-RARα blocks SUMO5 conjugation of PML, causing cytoplasmic displacement of PML and disruption of PML-NBs. Our work not only identifies a new member of the SUMO family but also reveals the mechanistic basis of the PML-NB life cycle in human cells.Promyelocytic leukemia nuclear bodies (PML-NBs) are non-membrane-bound domains in the cell nucleus that regulate transcription, antiviral response, DNA repair, apoptosis, senescence, and tumor suppression 1 . PML-NBs require PML to form 2 . Mature PML-NBs also contain other components such as SP100, HIPK2 and Daxx, which depends on the cellular environment 2-4 and results in heterogeneity in PML-NBs. Proper generation of PML-NBs is critical to the individual as an absence or delocalization of PML-NBs results in several pathological conditions, including polyglutamine repeat neurodegenerative diseases 5 and acute promyelocytic leukemia (APL) 6 . Arsenic trioxide (ATO) induces the formation of PML-NBs through a two-step process: first, oxidized PML dimerizes using the BRCC domain 7,8 to form a ring-like structure of PML shells. This step has been referred to as nucleation of PML-NBs 9 . PML shells then start to mature by recruiting additional PML-NB components 1 . In cells without oxidative stress, PML-NBs become prominent when cells enter G1 phase. During mitosis, PML-NBs fall apart and PML forms aggregates. PML-NB components start to enter the bodies to colocalize with PML after mitotic exit 10,11 , suggesting that the initiation of PML-NB formation happens at the end of mitosis. Taken together, current evidence suggests that the biogenesis of PML-NBs, which finishes in G1, needs at least two steps: nucleation through PML dimerization and the recruitment of PML-NB components.The recruitment of PML-NB components depends on SUMOylation 2,12 as loss of UBC9, an E2 ligase for SUMOylation, blocks the formation of PML-NBs 13 . PML can be conjugated by SUMO1 on three lysines: K65, K160, and K490 12,14-17 . PML also contains a SUMO interaction domain (SIM), which mediates interaction with SUMOs. As PML-NB components are also SUMO1-conjugated or SIM-containing proteins 18 , it was proposed that PML-NBs mature through SUMO-SIM interaction networks that recruit PML-NB components, causing PML shells to enlarge 19 . However, a recent report showing that loss of SUMO1...

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