Ubiquitin ligase Nedd4 promotes α-synuclein degradation by the endosomal-lysosomal pathway

alpha-Synuclein is an abundant brain protein that binds to lipid membranes and is involved in the recycling of presynaptic vesicles. In Parkinson disease, alpha-synuclein accumulates in intraneuronal inclusions often containing ubiquitin chains. Here we show that the ubiquitin ligase Nedd4, which functions in the endosomal-lysosomal pathway, robustly ubiquitinates alpha-synuclein, unlike ligases previously implicated in its degradation. Purified Nedd4 recognizes the carboxyl terminus of alpha-synuclein (residues 120-133) and attaches K63-linked ubiquitin chains. In human cells, Nedd4 overexpression enhances alpha-synuclein ubiquitination and clearance by a lysosomal process requiring components of the endosomal-sorting complex required for transport. Conversely, Nedd4 down-regulation increases alpha-synuclein content. In yeast, disruption of the Nedd4 ortholog Rsp5p decreases alpha-synuclein degradation and enhances inclusion formation and alpha-synuclein toxicity. In human brains, Nedd4 is present in pigmented neurons and is expressed especially strongly in neurons containing Lewy bodies. Thus, ubiquitination by Nedd4 targets alpha-synuclein to the endosomal- lysosomal pathway and, by reducing alpha-synuclein content, may help protect against the pathogenesis of Parkinson disease and other alpha-synucleinopathies.