Study of subcellular localization and proteolysis of ataxin-3.
In this work we investigate subcellular localization and proteolytic cleavage of different forms of ataxin-3 (AT-3), the protein responsible for spinocerebellar ataxia type 3. Normal (AT-3Q6 and AT-3Q26) and pathological (AT-3Q72) ataxins-3, as well as two truncated forms lacking poly-Q, were studied. Full-length proteins were also expressed as C14A mutants, in order to assess whether AT-3 autoproteolytic activity was involved in its fragmentation. We found that both normal and pathological proteins localized in the cytoplasm and in the nucleus, as expected, but also in the mitochondria. Microsequencing showed that all ataxins-3 underwent the same proteolytic cleavage, removing the first 27 amino acids. Interestingly, while normal ataxins were further cleaved at a number of caspase sites, pathological AT-3 was proteolyzed to a much lesser extent. This may play a role in the pathogenesis, hampering degradation of aggregation-prone expanded AT-3. In addition, autolytic cleavage was apparently not involved in AT-3 proteolysis.
Pozzi
Chiara
C
Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, P.za della Scienza 2, 20126 Milan, Italy.
Valtorta
Marco
M
Tedeschi
Gabriella
G
Galbusera
Elena
E
Pastori
Valentina
V
Bigi
Alessandra
A
Nonnis
Simona
S
Grassi
Eleonora
E
Fusi
Paola
P
D000818:Animals; D000067699:Ataxin-3; D019556:COS Cells; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D002522:Chlorocebus aethiops; D006801:Humans; D006868:Hydrolysis; D017827:Machado-Joseph Disease / Q000209:etiology / Q000378:metabolism; D051379:Mice; D009419:Nerve Tissue Proteins / Q000032:analysis* / Q000378:metabolism*; D009687:Nuclear Proteins / Q000032:analysis* / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D020033:Protein Isoforms / Q000032:analysis / Q000378:metabolism; D012097:Repressor Proteins / Q000032:analysis* / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism*
D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D020033:Protein Isoforms; D012097:Repressor Proteins; D010447:Peptide Hydrolases; C092341:ATXN3 protein, human; D000067699:Ataxin-3