Abstract
N-terminal mutant huntingtin (N-mhtt) fragments form inclusions and cause cell death in vitro. Mutant htt expression stimulates autophagy and increases levels of lysosomal proteases. Here, we show that lysosomal proteases, cathepsins D, B and L, affected mhtt processing and levels of cleavage products (cp) known as A and B, which form inclusions. Adding inhibitors of cathepsin D, B and L to clonal striatal cells reduced mhtt, especially mhtt fragment cp A. Mutant htt fully degraded in cathepsin-L-treated lysates but formed stable N-mhtt fragments upon exposure to cathepsin D. Mutagenesis analysis of htt cDNA suggested that cathepsin D and the protease for cp A may cleave htt in the same region. Brain lysates from HD knock-in mice expressed N-mhtt fragments that accumulated with cathepsin D treatment and declined with aspartyl protease inhibition. Findings implicate lysosomal proteases in formation of N-mhtt fragments and clearance of mhtt.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Aspartic Acid Endopeptidases / antagonists & inhibitors
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Aspartic Acid Endopeptidases / metabolism
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Binding Sites / physiology
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Cathepsin D / antagonists & inhibitors
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Cathepsin D / metabolism
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Cathepsins / antagonists & inhibitors
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Cathepsins / metabolism*
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Cell Line, Transformed
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Corpus Striatum / enzymology
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Corpus Striatum / pathology
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Corpus Striatum / physiopathology
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Enzyme Inhibitors / pharmacology
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Huntingtin Protein
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Huntington Disease / enzymology*
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Huntington Disease / genetics
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Huntington Disease / physiopathology
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Lysosomes / enzymology*
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Mice
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Mice, Inbred C57BL
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Mice, Neurologic Mutants
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Mice, Transgenic
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Mutation / genetics
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Nerve Tissue Proteins / chemistry
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Nerve Tissue Proteins / genetics
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Nerve Tissue Proteins / metabolism*
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Neurons / enzymology
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Neurons / pathology
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Nuclear Proteins / chemistry
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Peptide Fragments / metabolism*
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Peptide Hydrolases / drug effects
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Peptide Hydrolases / metabolism*
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Protein Structure, Tertiary / physiology
Substances
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Enzyme Inhibitors
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Htt protein, mouse
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Huntingtin Protein
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Nerve Tissue Proteins
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Nuclear Proteins
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Peptide Fragments
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Cathepsins
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Peptide Hydrolases
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Aspartic Acid Endopeptidases
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Cathepsin D