Proteasome function is inhibited by polyglutamine-expanded ataxin-1, the SCA1 gene product.
Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder caused by expansion of the polyglutamine tract in the SCA1 gene product, ataxin-1. Using d2EGFP, a short-lived enhanced green fluorescent protein, we investigated whether polyglutamine-expanded ataxin-1 affects the function of the proteasome, a cellular multicatalytic protease that degrades most misfolded proteins and regulatory proteins. In Western blot analysis and immunofluorescence experiments, d2EGFP was less degraded in HEK 293T cells transfected with ataxin-1(82Q) than in cells transfected with lacZ or empty vector controls. To test whether the stability of the d2EGFP protein was due to aggregation of ataxin-1, we constructed a plasmid carrying ataxin-1-Delta114, lacking the self-association region (SAR), and examined degradation of the d2EGFP. Both the level of ataxin-1-Delta114 aggregates and the amount of d2EGFP were drastically reduced in cells containing ataxin-1-Delta114. Furthermore, d2EGFP localization experiments showed that polyglutamine-expanded ataxin-1 inhibited the general function of the proteasome activity. Taken together, these results demonstrate that polyglutamine-expanded ataxin-1 decreases the activity of the proteasome, implying that a disturbance in the ubiquitin-proteasome pathway is directly involved in the development of spinocerebellar ataxia type1.
Park
Yongjae
Y
Graduate School of Biotechnology, Korea University, Seoul 136-701, Korea.
Hong
Sunghoi
S
Kim
Sung-Jo
SJ
Kang
Seongman
S
D000067696:Ataxin-1; D000067528:Ataxins; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000196:embryology; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000502:physiology*; D020836:Protein Structure, Quaternary; D020754:Spinocerebellar Ataxias / Q000503:physiopathology*; D014162:Transfection
C000593749:ATXN1 protein, human; D000067696:Ataxin-1; D000067528:Ataxins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex