Ubiquitin-proteasome system alterations in a striatal cell model of huntington's disease

Authors

  • Jesse M. Hunter,

    1. Department of Cell Biology, and Department of Psychiatry, The University of Alabama at Birmingham, Birmingham, Alabama
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  • Mathieu Lesort,

    1. Department of Cell Biology, and Department of Psychiatry, The University of Alabama at Birmingham, Birmingham, Alabama
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    • Mathieu Lesort and Gail V.W. Johnson contributed equally to this work.

  • Gail V.W. Johnson

    Corresponding author
    1. Department of Cell Biology, and Department of Psychiatry, The University of Alabama at Birmingham, Birmingham, Alabama
    • Department of Anesthesiology, University of Rochester Medical Center, 601 Elmwood Ave, Box 604, Rochester, NY 14642
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    • Mathieu Lesort and Gail V.W. Johnson contributed equally to this work.


Abstract

Huntington's disease (HD) is a progressive, autosomal dominant neurodegenerative disease caused by an abnormally expanded CAG repeat in the HD gene. Ubiquitylated aggregates containing mutant huntingtin protein in neurons are hallmarks of HD. Misfolded mutant huntingtin monomers, oligomers, or aggregates may be a result of, and cause, ubiquitin- proteasome dysfunction. To investigate the ubiquitin-proteasome system we designed a series of firefly luciferase reporters targeted selectively to different points along this pathway. These reporters were used to monitor ubiquitin-proteasome system function in a striatal cell culture model of HD. Ubiquitylation processes were not reduced in mutant huntingtin cells but recognition or degradation of ubiquitylated substrates was decreased. We also found mutant huntingtin expressing cells had slight but significant decreases in chymotrypsin-like and caspase-like activities, and an unexpected increase in trypsin-like activity of the proteasome core. General proteasome core inhibitors, as well as selective caspase-like activity inhibitors, were less effective in mutant cells. Finally, treatment with 3-nitropropionic acid, a succinate dehydrogenase inhibitor, had opposite effects on the ubiquitin-proteasome system with activation in wild-type and decreased activity in mutant huntingtin expressing cells. The results of these experiments show clearly selective disruption of the ubiquitin-proteasome system in this cell culture model of HD. The high throughput tools that we have designed and optimized will also be useful in identifying compounds that alter ubiquitin-proteasome system function and to investigate other neurodegenerative diseases such Alzheimer's disease and Parkinson's disease. © 2007 Wiley-Liss, Inc.

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