Chaperone suppression of aggregation and altered subcellular proteasome localization imply protein misfolding in SCA1.
Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder caused by expansion of a polyglutamine tract in ataxin-1. In affected neurons of SCA1 patients and transgenic mice, mutant ataxin-1 accumulates in a single, ubiquitin-positive nuclear inclusion. In this study, we show that these inclusions stain positively for the 20S proteasome and the molecular chaperone HDJ-2/HSDJ. Similarly, HeLa cells transfected with mutant ataxin-1 develop nuclear aggregates which colocalize with the 20S proteasome and endogenous HDJ-2/HSDJ. Overexpression of wild-type HDJ-2/HSDJ in HeLa cells decreases the frequency of ataxin-1 aggregation. These data suggest that protein misfolding is responsible for the nuclear aggregates seen in SCA1, and that overexpression of a DnaJ chaperone promotes the recognition of a misfolded polyglutamine repeat protein, allowing its refolding and/or ubiquitin-dependent degradation.
Cummings
C J
CJ
Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA.
Mancini
M A
MA
Antalffy
B
B
DeFranco
D B
DB
Orr
H T
HT
Zoghbi
H Y
HY
D000818:Animals; D000067696:Ataxin-1; D000067528:Ataxins; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D018832:Molecular Chaperones / Q000502:physiology*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D017510:Protein Folding; D011689:Purkinje Cells / Q000378:metabolism / Q000473:pathology; D013132:Spinocerebellar Degenerations / Q000235:genetics / Q000473:pathology*; D014162:Transfection
C000593749:ATXN1 protein, human; D000067696:Ataxin-1; D000067528:Ataxins; C000593750:Atxn1 protein, mouse; D002352:Carrier Proteins; C107481:DNAJA1 protein, human; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; D006360:Heat-Shock Proteins; C494372:Hspa8 protein, mouse; D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex