An isoform of ataxin-3 accumulates in the nucleus of neuronal cells in affected brain regions of SCA3 patients.
Autosomal dominant spinocerebellar ataxias (SCA) form a group of clinically and genetically heterogeneous neurodegenerative disorders. The defect responsible for SCA3/Machado-Joseph disease (MJD) has been identified as an unstable and expanded (CAG)n trinucleotide repeat in the coding region of a novel gene of unknown function. The MJD1 gene product, ataxin-3, exists in several isoforms. We generated polyclonal antisera against an alternate carboxy terminus of ataxin-3. This isoform, ataxin-3c, is expressed as a protein of approximately 42 kDa in normal individuals but is significantly enlarged in affected patients confirming that the CAG repeat is part of the ataxin-3c isoform and is translated into a polyglutamine stretch, a feature common to all known CAG repeat disorders. Ataxin-3 like immunoreactivity was observed in all human brain regions and peripheral organs studied. In neuronal cells of control individuals, ataxin-3c was expressed cytoplasmatically and had a somatodendritic and axonal distribution. In SCA3 patients, however, C-terminal ataxin-3c antibodies as well as anti-ataxin-3 monoclonal antibodies (1 H9) and anti-ubiquitin antibodies detected intranuclear inclusions (NIs) in neuronal cells of affected brain regions. A monoclonal antibody, 2B6, directed against an internal part of the protein, barely detected these NIs implying proteolytic cleavage of ataxin-3 prior to its transport into the nucleus. These findings provide evidence that the alternate isoform of ataxin-3 is involved in the pathogenesis of SCA3/MJD. Intranuclear protein aggregates appear as a common feature of neurodegenerative polyglutamine disorders.
Schmidt
T
T
Molecular Human Genetics, Ruhr-University, Bochum, Germany.
Landwehrmeyer
G B
GB
Schmitt
I
I
Trottier
Y
Y
Auburger
G
G
Laccone
F
F
Klockgether
T
T
Völpel
M
M
Epplen
J T
JT
Schöls
L
L
Riess
O
O
D000595:Amino Acid Sequence; D000818:Animals; D000067699:Ataxin-3; D015153:Blotting, Western; D001921:Brain / Q000473:pathology*; D001923:Brain Chemistry / Q000502:physiology*; D001932:Brain Neoplasms / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D004247:DNA / Q000032:analysis / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D006801:Humans; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009447:Neuroblastoma / Q000378:metabolism; D009474:Neurons / Q000378:metabolism* / Q000473:pathology* / Q000648:ultrastructure; D009687:Nuclear Proteins; D051381:Rats; D012097:Repressor Proteins; D013132:Spinocerebellar Degenerations / Q000378:metabolism* / Q000473:pathology*
D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D004247:DNA; C092341:ATXN3 protein, human; D000067699:Ataxin-3; C511593:Atxn3 protein, rat