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Synphilin‐1 degradation by the ubiquitin‐proteasome pathway and effects on cell survival
Author(s) -
Lee Gwang,
Junn Eunsung,
Tanaka Mikiei,
Kim Yong Man,
Lee Sang Seop,
Mouradian M. Maral
Publication year - 2002
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2002.01136.x
Subject(s) - proteasome , ubiquitin , protein degradation , immunoprecipitation , microbiology and biotechnology , alpha synuclein , cytoplasm , viability assay , cytoplasmic inclusion , proteasome inhibitor , lactacystin , chemistry , biology , biochemistry , cell , parkinson's disease , medicine , disease , gene
Parkinson's disease is characterized by loss of nigral dopaminergic neurons and the presence of cytoplasmic inclusions known as Lewy bodies. α‐Synuclein and its interacting partner synphilin‐1 are among constituent proteins in these aggregates. The presence of ubiquitin and proteasome subunits in these inclusions supports a role for this protein degradation pathway in the processing of proteins involved in this disease. To begin elucidating the kinetics of synphilin‐1 in cells, we studied its degradation pathway in HEK293 cells that had been engineered to stably express FLAG‐tagged synphilin‐1. Pulse‐chase experiments revealed that this protein is relatively stable with a half‐life of about 16 h. Treatment with proteasome inhibitors resulted in attenuation of degradation and the accumulation of high molecular weight ubiquitinated synphilin‐1 in immunoprecipitation/immunoblot experiments. Additionally, proteasome inhibitors stimulated the formation of peri‐nuclear inclusions which were immunoreactive for synphilin‐1, ubiquitin and α‐synuclein. Cell viability studies revealed increased susceptibility of synphilin‐1 over‐expressing cells to proteasomal dysfunction. These observations indicate that synphilin‐1 is ubiquitinated and degraded by the proteasome. Accumulation of ubiquitinated synphilin‐1 due to impaired clearance results in its aggregation as peri‐nuclear inclusions and in poor cell survival.