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

Abstract

α-Synuclein is an abundant brain protein that binds to lipid membranes and is involved in the recycling of presynaptic vesicles. In Parkinson disease, α-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 α-synuclein, unlike ligases previously implicated in its degradation. Purified Nedd4 recognizes the carboxyl terminus of α-synuclein (residues 120–133) and attaches K63-linked ubiquitin chains. In human cells, Nedd4 overexpression enhances α-synuclein ubiquitination and clearance by a lysosomal process requiring components of the endosomal-sorting complex required for transport. Conversely, Nedd4 down-regulation increases α-synuclein content. In yeast, disruption of the Nedd4 ortholog Rsp5p decreases α-synuclein degradation and enhances inclusion formation and α-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 α-synuclein to the endosomal–lysosomal pathway and, by reducing α-synuclein content, may help protect against the pathogenesis of Parkinson disease and other α-synucleinopathies.

Lys-63-linked Ubiquitination by E3 Ubiquitin Ligase Nedd4-1 Facilitates Endosomal Sequestration of Internalized α-Synuclein

“…4a). This finding is consistent with earlier research showing that Nedd4-1 promotes the endolysosomal sorting of aS for degradation (9). After washing off the medium, we did not detect re-secreted aS within 1 h, but a detectable amount of extracellular aS was observed up to 24 h (Fig.…”

“…2b, upper panel). This finding is contradictory to a report by Tofaris et al (9), which demonstrated that UbcH7 ubiquitinates aS together with Nedd4. This discrepancy could be due to different experimental conditions.…”

“…Nedd4-1 Catalyzes the Lys-63-and Lys-11-linked Polyubiquitination of aS-Several E3 ligases are known to catalyze the Lys-63-linked ubiquitination of aS, leading to its endolysosomal targeting and degradation (9,(17)(18)(19)(20). To elucidate E3 ligase activity for aS, an in vitro aS ubiquitination assay was performed using the following human E3 ligases: SIAH-1, SIAH-2, Parkin, CHIP, Nedd4-1, and Nedd4-2 (Fig.…”

“…Among the E3 ligases that catalyze aS ubiquitination, researchers have focused on Nedd4 (neural precursor cell expressed developmentally down-regulated protein 4) because this E3 ligase is highly expressed in neurons containing LBs and catalyzes the Lys-63-linked ubiquitination of aS (9,10). Mammalian Nedd4 exists in two isoforms, Nedd4-1 and Nedd4-2.…”

Synthetic polyubiquitinated α-Synuclein reveals important insights into the roles of the ubiquitin chain in regulating its pathophysiology

“…Several studies have shown that ubiquitination plays an important role in regulating α-Syn degradation by the proteasome (39)(40)(41)(42)(43)(44). Interestingly, Tofaris et al (45) showed that ubiquitination of α-Syn by Nedd4 targets it for degradation via the endosomal/lysosomal pathway. However, the nature of the ubiquitination signal required for targeting α-Syn for proteasomal or lysosomal degradation remained unexplored.…”