The E3 Ubiquitin Ligase TRAF6 Interacts with the Cellular Prion Protein and Modulates Its Solubility and Recruitment to Cytoplasmic p62/SQSTM1-Positive Aggresome-Like Structures

The cellular prion protein (PrP C ) is a ubiquitous glycoprotein highly expressed in the brain where it is involved in neurite outgrowth, copper homeostasis, NMDA receptor regulation, cell adhesion, and cell signaling. Conformational conversion of PrP C into its insoluble and aggregation-prone scrapie form (PrP Sc ) is the trigger for several rare devastating neurodegenerative disorders, collectively referred to as prion diseases. Recent work indicates that the ubiquitin–proteasome system is involved in quality control of PrP C . To better dissect the role of ubiquitination in PrP C physiology, we focused on the E3 RING ubiquitin ligase tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6). Here, we report that PrP C interacts with TRAF6 both in vitro, in cells, and in vivo, in the mouse brain. Transient overexpression of TRAF6 indirectly modulates PrP C ubiquitination and triggers redistribution of PrP C into the insoluble fraction. Importantly, in the presence of wild-type TRAF6, but not a mutant lacking E3 ligase activity, PrP C accumulates into cytoplasmic aggresome-like inclusions containing TRAF6 and p62/SQSTM1. Our results suggest that TRAF6 ligase activity could exert a role in the regulation of PrP C redistribution in cells under physiological conditions. This novel interaction may uncover possible mechanisms of cell clearance/reorganization in prion diseases.