Machado-Joseph disease also called spinocerebellar ataxia type 3 (MJD/SCA3) is a hereditary and neurodegenerative movement disorder caused by ataxin-3 with a polyglutamine expansion (mutant ataxin-3). Neuronal loss in MJD/SCA3 is associated with a mutant ataxin-3 toxic fragment. Defining mutant ataxin-3 proteolytic site(s) could facilitate the identification of the corresponding enzyme(s). Previously, we reported a mutant ataxin-3 mjd1a fragment in the brain of transgenic mice (Q71) that contained epitopes C-terminal to amino acid 220. In this study, we generated and characterized neuroblastoma cells and transgenic mice expressing mutant ataxin-3 mjd1a lacking amino acids 190-220 (deltaQ71). Less deltaQ71 than Q71 fragments were detected in the cell but not mouse model. The transgenic mice developed an MJD/SCA3-like phenotype and their brain homogenates had a fragment containing epitopes C-terminal to amino acid 220. Our results support the toxic fragment hypothesis and narrow the mutant ataxin-3 cleavage site to the N-terminus of amino acid 190.
Bibliographical noteFunding Information:
We especially thank: (a) Debbie Swing for performing the zygote injections; (b) Mrs. Mary Keyser and Suzanne Fowble for budget administration; and (c) Dr. Pamela Talalay for critical editing of the manuscript. This work was supported by: (a) Donation from JCG (VCG); (b) NIH grant NS42731-01 (VCG); (c) AHA grant EIG 0140166N (VCG); and in part by (d) NIH Intramural Research Program, National Cancer Institute, Center for Cancer Research (NAJ, NGC).
Copyright 2008 Elsevier B.V., All rights reserved.
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