Impairment of the chaperone and ubiquitin-proteasome system can lead to the aggregation of unfolded proteins and cause neurodegenerative diseases. A strategy that cells employ to avoid toxic aggregates is compartmentalising ubiquitylated misfolded proteins into membraneless structures called aggresomes. p97 is an AAA-ATPase known to localise to these structures, but how it regulates aggresome formation is unclear. Now, Malavika Raman and colleagues (Mukkavalli et al., 2021) identify a role for the p97 adaptor UBXN1 in this process. First, upon inducing aggresome formation by treating cells with a proteasome inhibitor, they find that acute inhibition of p97 leads to a decreased number of cells with aggresomes. The authors then screen for potential p97 adaptors and reveal that the protein UBXN1 robustly localises to aggresomes. Importantly, UBXN1 knockout results in aggresome loss and an increase in aggregates throughout the cytosol. Furthermore, mutating conserved residues in the N- and C-terminal domains of UBXN1 confirmed that the association of UBXN1 with ubiquitin and p97 is required for aggresome formation. Finally, mutation of their orthologue genes in a Caenorhabditis elegans model of Huntington's disease resulted in a twofold increase in polyQ aggregates. Collectively, these findings suggest that the p97-UBXN1 complex has an evolutionarily conserved role in the recognition, formation and subsequent clearance of ubiquitylated protein aggregates.
