Abstract
The proteasome is a major proteolytic machine that regulates cellular proteostasis through selective degradation of ubiquitylated proteins(1,2). A number of ubiquitin-related molecules have recently been found to be involved in the regulation of biomolecular condensates or membraneless organelles, which arise by liquid-liquid phase separation of specific biomolecules, including stress granules, nuclear speckles and autophagosomes(3-8), but it remains unclear whether the proteasome also participates in such regulation. Here we reveal that proteasome-containing nuclear foci form under acute hyperosmotic stress. These foci are transient structures that contain ubiquitylated proteins, p97 (also known as valosin-containing protein (VCP)) and multiple proteasome-interacting proteins, which collectively constitute a proteolytic centre. The major substrates for degradation by these foci were ribosomal proteins that failed to properly assemble. Notably, the proteasome foci exhibited properties of liquid droplets. RAD23B, a substrate-shuttling factor for the proteasome, and ubiquitylated proteins were necessary for formation of proteasome foci. In mechanistic terms, a liquid-liquid phase separation was triggered by multivalent interactions of two ubiquitin-associated domains of RAD23B and ubiquitin chains consisting of four or more ubiquitin molecules. Collectively, our results suggest that ubiquitin-chain-dependent phase separation induces the formation of a nuclear proteolytic compartment that promotes proteasomal degradation. Hyperosmotic stress leads to a phase separation of the proteasome, triggered by interactions between RAD23B and ubiquitylated proteins, which bring together p97 and proteasome-associated proteins into nuclear proteolytic foci.
Item Type: | Journal article |
---|---|
Faculties: | Chemistry and Pharmacy > Department of Biochemistry |
Research Centers: | Center for Integrated Protein Science Munich (CIPSM) |
Subjects: | 500 Science > 540 Chemistry |
ISSN: | 0028-0836 |
Language: | English |
Item ID: | 89722 |
Date Deposited: | 25. Jan 2022, 09:32 |
Last Modified: | 25. Jan 2022, 09:32 |