The role of protein composition in specifying nuclear inclusion formation in polyglutamine disease.
Intracellular inclusions are a unifying feature of polyglutamine (polyQ) neurodegenerative diseases, yet each polyQ disease displays a unique pattern of neuronal degeneration. This implies that the protein context of expanded polyQ plays an important role in establishing selective neurotoxicity. Here, in studies of the spinocerebellar ataxia type 3 disease protein ataxin-3, we demonstrate that the protein sequence surrounding polyQ specifies the constituents of nuclear inclusions (NI) formed by the disease protein. The nuclear proteins cAMP response element-binding protein-binding protein (CBP) and Mastermind-like-1 strongly colocalize only to NI formed by full-length ataxin-3, whereas the splicing factor SC35 colocalizes only to NI formed by a polyQ-containing, carboxyl-terminal fragment of ataxin-3. These differences in NI formation reflect specific protein interactions normally undertaken by ataxin-3, as both normal and mutant full-length ataxin-3 co-immunoprecipitate with CBP and sediment on density gradients as macromolecular complexes. Moreover, normal ataxin-3 represses cAMP response element-binding protein-mediated transcription, indicating a functional consequence of ataxin-3 interactions with CBP. Finally, we show that mutant ataxin-3 forms insoluble intranuclear complexes, or microaggregates, before NI can be detected, implying a precursor-product relationship. These results suggest that protein context-dependent recruitment of nuclear proteins to intranuclear microaggregates, and subsequently to NI, may contribute to selective neurotoxicity in polyQ diseases.
Chai
Y
Y
Department of Neurology, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
Wu
L
L
Griffin
J D
JD
Paulson
H L
HL
D000067699:Ataxin-3; D002467:Cell Nucleus / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism; D019636:Neurodegenerative Diseases / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D010455:Peptides / Q000235:genetics* / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins; D013347:Subcellular Fractions; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection
D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D012097:Repressor Proteins; D015534:Trans-Activators; C097188:polyglutamine; C092341:ATXN3 protein, human; D000067699:Ataxin-3