Nuclear aggregation of polyglutamine-expanded ataxin-3: fragments escape the cytoplasmic quality control.
Expansion of a polymorphic polyglutamine segment is the common denominator of neurodegenerative polyglutamine diseases. The expanded proteins typically accumulate in large intranuclear inclusions and induce neurodegeneration. However, the mechanisms that determine the subcellular site and rate of inclusion formation are largely unknown. We found that the conserved putative nuclear localization sequence Arg-Lys-Arg-Arg, which is retained in a highly aggregation-prone fragment of ataxin-3, did not affect the site and degree of inclusion formation in a cell culture model of spinocerebellar ataxia type 3. Addition of synthetic nuclear export or import signals led to the expected localization of ataxin-3 and determined the subcellular site of aggregate formation. Triggering a cellular stress response by heat shock transcription factor DeltaHSF1 coexpression abrogated aggregation in the cytoplasm but not in the nucleus. These findings indicate that native aggregation-prone fragments derived from expanded ataxin-3 may eventually escape the cytoplasmic quality control, resulting in aggregation in the nuclear compartment.
Breuer
Peter
P
Department of Neurology, University of Bonn, 53105 Bonn, Germany. peter.breuer@ukb.uni-bonn.de
Haacke
Annette
A
Evert
Bernd O
BO
Wüllner
Ullrich
U
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D000067699:Ataxin-3; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm; D018869:Heat-Shock Response; D006801:Humans; D002479:Inclusion Bodies; D017827:Machado-Joseph Disease; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D019636:Neurodegenerative Diseases; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D010455:Peptides; D055503:Protein Multimerization; D051381:Rats; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D009419:Nerve Tissue Proteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D010446:Peptide Fragments; D010455:Peptides; D012097:Repressor Proteins; D014157:Transcription Factors; C097188:polyglutamine; C092341:ATXN3 protein, human; D000067699:Ataxin-3; C511594:Atxn3 protein, mouse