Novel covalent modifications of α-synuclein during the recovery from proteasomal dysfunction

Proteasomal dysfunction and α-synuclein (α-syn) have both been implicated in the pathogenesis of Parkinson’s disease (PD). However, the functional relationship between these two remains elusive. Here we show that in human neuroblastoma cells, novel variants of α-syn with molecular weights of 22–25 kDa were induced after washout of the reversible proteasome inhibitors. Induction of these variants seemed to be a specific response to proteasome dysfunction, because the treatment and washout of other protease inhibitor or mitochondrial inhibitor did not induce these variants. Importantly, PD-linked α-syn mutations have effects on the formation of these variants. Recently, O-linked glycosylation and monoubiquitylation of α-syn have been reported. Despite the similarity in molecular weights, biochemical properties of our variants suggest that they are unrelated with such modifications. Taken together, these results suggest that α-syn is regulated by the specific functional state of the proteasomes, and PD-linked mutations may affect this regulation.