Biopolym. Cell. 2019; 35(3):242-243.
Chronicle and Information
ROS-induced PML nuclear bodies biogenesis
- College de France U1050
Promyelocytic leukemia nuclear bodies (PML-NBs) are stress-sensitive membrane-less organelles organized by PML, a tumor suppressor protein. PML-NBs are involved in a wide array of biological processes, such as apoptosis, senescence, DNA repair, epigenetic control, control of oncogenesis. The two-step PML-NBs assembly consists first in PML scaffold polymerization in shell-like bodies, then interaction with huge diversity of unrelated proteins recruited in the inner-core. PML-NBs are considered as privileged sites for post-translational modifications (PTM), especially sumoylation. The oxidative stress like that induced by arsenic promotes PML intermolecular disulfide bonds formation and sumoylation, but the mechanism of PML-NBs assembly and dynamics upon stress or at basal level is still poorly understood. Our aim is to unravel the mechanism of PML-NBs biogenesis, assembly and function through the interdisciplinary approach combing molecular and cell biology perspective, and biophysical insight of PML dynamics in living cells to shed light on the way in which PML biological activity modulates the NBs organization. In living cells, we observed PML NBs fusion and fission events. Quantitative analyses of PML dynamics show that PML behaves as a viscous fluid. As2O3 treatment dramatically decreases the diffused PML in nucleus with time, and the dynamic turnover of PML at NBs (FRAP) is abolished. These data revealed that PML has properties at the frontier of liquid and gel, which is strongly modulated by oxidative stress. Upon oxidative stress, PML is covalently bound through intermolecular disulfide bonds, which are formed by the oxidation of cysteines in PML. We show that cysteine mutants in the conserved RBCC domain of PML B2 box are not able to form normal PML-NBs and further sumoylation. These mutants have more diffused PML distributed in the nucleus, but no difference can be observed after As2O3 treatment, suggesting oxidative stress-induced di-sulfide bonds are also impaired in these mutants. We conclude that the oxidation of B2 box in PML plays a key role in PML-NBs assembly and sumoylation. We also identified a specific C-terminal cysteine in PML that participates in the formation of intermolecular disulfide bonds, yet not essential for PML-NBs assembly. This oxidized PML might contribute to maintain a specific redox environment in cells.