Interaction of the polyglutamine protein ataxin-3 with Rad23 regulates toxicity in Drosophila models of Spinocerebellar Ataxia Type 3.
Polyglutamine (polyQ) repeat expansion in the deubiquitinase ataxin-3 causes neurodegeneration in Spinocerebellar Ataxia Type 3 (SCA3), one of nine inherited, incurable diseases caused by similar mutations. Ataxin-3's degradation is inhibited by its binding to the proteasome shuttle Rad23 through ubiquitin-binding site 2 (UbS2). Disrupting this interaction decreases levels of ataxin-3. Since reducing levels of polyQ proteins can decrease their toxicity, we tested whether genetically modulating the ataxin-3-Rad23 interaction regulates its toxicity in Drosophila. We found that exogenous Rad23 increases the toxicity of pathogenic ataxin-3, coincident with increased levels of the disease protein. Conversely, reducing Rad23 levels alleviates toxicity in this SCA3 model. Unexpectedly, pathogenic ataxin-3 with a mutated Rad23-binding site at UbS2, despite being present at markedly lower levels, proved to be more pathogenic than a disease-causing counterpart with intact UbS2. Additional studies established that the increased toxicity upon mutating UbS2 stems from disrupting the autoprotective role that pathogenic ataxin-3 has against itself, which depends on the co-chaperone, DnaJ-1. Our data reveal a previously unrecognized balance between pathogenic and potentially therapeutic properties of the ataxin-3-Rad23 interaction; they highlight this interaction as critical for the toxicity of the SCA3 protein, and emphasize the importance of considering protein context when pursuing suppressive avenues.
Department of Pharmacology, Wayne State University, Detroit MI, USA.
Joanna R
JR
Sutton
Department of Pharmacology, Wayne State University, Detroit MI, USA.
Jessica R
JR
Blount
Department of Pharmacology, Wayne State University, Detroit MI, USA.
Kozeta
K
Libohova
Department of Pharmacology, Wayne State University, Detroit MI, USA.
Wei-Ling
WL
Tsou
Department of Pharmacology, Wayne State University, Detroit MI, USA.
Gnanada S
GS
Joshi
Department of Neurology, University of Michigan, Ann Arbor MI, USA.
Henry L
HL
Paulson
Department of Neurology, University of Michigan, Ann Arbor MI, USA.
Maria do Carmo
MDC
Costa
Department of Biochemistry and the Neuroscience Research Center, Medical College of Wisconsin, Milwaukee WI, USA.
K Matthew
KM
Scaglione
Department of Pharmacology, Wayne State University, Detroit MI, USA.|Department of Neurology, Wayne State University, Detroit MI, USA.
Sokol V
SV
Todi
D000818:Animals; D000067699:Ataxin-3 / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D045643:DNA Repair Enzymes / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004195:Disease Models, Animal; D004331:Drosophila melanogaster / Q000235:genetics; D006801:Humans; D017827:Machado-Joseph Disease / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018832:Molecular Chaperones / Q000235:genetics; D009410:Nerve Degeneration / Q000235:genetics* / Q000473:pathology; D010455:Peptides / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics
D004268:DNA-Binding Proteins; D018832:Molecular Chaperones; D010455:Peptides; D012097:Repressor Proteins; D025801:Ubiquitin; C086985:RAD23A protein, human; C097188:polyglutamine; C092341:ATXN3 protein, human; D000067699:Ataxin-3; D046988:Proteasome Endopeptidase Complex; D045643:DNA Repair Enzymes