Proteasomal Inhibition by α-Synuclein Filaments and Oligomers

Evo Lindersson,Rasmus Beedholm,Peter Højrup,Torben Moos,Weiping Gai,Klavs B Hendil,Poul H Jensen

doi:10.1074/jbc.m306390200

Abstract

A unifying feature of many neurodegenerative disorders is the accumulation of polyubiquitinated protein inclusions in dystrophic neurons, e.g. containing alpha-synuclein, which is suggestive of an insufficient proteasomal activity. We demonstrate that alpha-synuclein and 20 S proteasome components co-localize in Lewy bodies and show that subunits from 20 S proteasome particles, in contrast to subunits of the 19 S regulatory complex, bind efficiently to aggregated filamentous but not monomeric alpha-synuclein. Proteasome binding to insoluble alpha-synuclein filaments and soluble alpha-synuclein oligomers results in marked inhibition of its chymotrypsin-like hydrolytic activity through a non-competitive mechanism that is mimicked by model amyloid-Abeta peptide aggregates. Endogenous ligands of aggregated alpha-synuclein like heat shock protein 70 and glyceraldehyde-6-phosphate dehydrogenase bind filaments and inhibit their anti-proteasomal activity. The inhibitory effect of amyloid aggregates may thus be amenable to modulation by endogenous chaperones and possibly accessible for therapeutic intervention.

Highlights

A unifying feature of many neurodegenerative disorders is the accumulation of polyubiquitinated protein inclusions in dystrophic neurons, e.g. containing ␣-synuclein, which is suggestive of an insufficient proteasomal activity
20 S proteasomes were observed in the cytoplasm of both control and brain disease cases, and the ␣6 subunit-specific antibody MCP20 labeled Lewy bodies of both Parkinson’s disease (PD) and dementia with Lewy bodies (DLB) cases (Fig. 1C)
This report describes a mechanistic link between two hallmarks of the neurodegenerative disorders PD, DLB, Lewy body variant of PD, and multiple system atrophy, namely the presence of aggregated Aggregates of misfolded ␣-synuclein (AS) and the accumulation of polyubiquitinated proteins

Summary

Introduction

A unifying feature of many neurodegenerative disorders is the accumulation of polyubiquitinated protein inclusions in dystrophic neurons, e.g. containing ␣-synuclein, which is suggestive of an insufficient proteasomal activity. We demonstrate that ␣-synuclein and 20 S proteasome components co-localize in Lewy bodies and show that subunits from 20 S proteasome particles, in contrast to subunits of the 19 S regulatory complex, bind efficiently to aggregated filamentous but not monomeric ␣-synuclein. Most important, aggregated AS displayed a strongly increased inhibitory activity toward the proteasome in vitro as compared with monomeric AS [24] Such a proteasomal inhibition may have an impact on the dopaminergic neurons that seem to be vulnerable to the stress of unfolded proteins [23]. The proteasome binding results in an efficient and selective non-competitive inhibition of the chymotrypsin-like proteasomal activity of the 20 S

Methods

Results

Conclusion