# The ubiquitin ligase Nedd4-2 promotes localization of DNMBP/Tuba to P-bodies under hyperosmotic stress

## TL;DR

This study shows that the ubiquitin ligase Nedd4-2 helps position a protein called DNMBP in P-bodies during high osmolarity, which is important for activating a key signaling pathway.

## Contribution

The paper identifies DNMBP as a novel substrate of Nedd4-2 and reveals their role in P-body localization and Cdc42 activation under hyperosmotic stress.

## Key findings

- Nedd4-2 interacts with and ubiquitinates DNMBP under hyperosmotic conditions.
- DNMBP promotes P-body formation and is targeted to P-bodies by Nedd4-2.
- Nedd4-2 and DNMBP are required for Cdc42 and p38-MAPK activation under stress.

## Abstract

The ubiquitin ligase Nedd4-2/NEDD4L, comprised of C2-WW(x4)-HECT domains, is known to regulate several ion transporters and channels. We recently showed that elevated intracellular [Na+] and osmolarity enhances Nedd4-2 enzymatic activity. To globally identify its interactome and substrates in cells under hyperosmotic stress, we performed a BioID screen using miniTurbo with Nedd4-2 as a bait under hyperosmotic (vs. isosmotic) conditions. One of the top hits identified that preferentially binds Nedd4-2 under hyperosmolarity was Dynamin Binding Protein (DNMBP)/Tuba, a known GEF for Cdc42. We then showed that DNMBP is a substrate for Nedd4-2, and that active Nedd4-2 targets DNMBP to P-body condensates under hyperosmotic stress. Moreover, DNMBP itself promotes P-body formation under hyperosmolarity. Both Nedd4-2 and DNMBP are required for the activation of Cdc42 following hyperosmotic treatment, and accordingly, knockout of DNMBP results in suppression of Cdc42 and its downstream effector p38-MAPK. We thus propose that Nedd4-2–mediated targeting of DNMBP to P-bodies under hyperosmotic stress facilitates the activation of Cdc42 by this GEF.