Abstract
Myosin phosphatase target subunit 1 (MYPT1), together with catalytic subunit of type1 delta isoform (PP1cdelta) and a small 20-kDa regulatory unit (M20), form a heterotrimeric holoenzyme, myosin phosphatase (MP), which is responsible for regulating the extent of myosin light chain phosphorylation. Here we report the identification and characterization of a molecular interaction between Seven in absentia homolog 2 (SIAH2) and MYPT1 that resulted in the proteasomal degradation of the latter in mammalian cells, including neurons and glia. The interaction involved the substrate binding domain of SIAH2 (aa 116-324) and a central region of MYPT1 (aa 445-632) containing a degenerate consensus Siah-binding motif RLAYVAP (aa 493-499) evolutionally conserved from fish to humans. These findings suggest a novel mechanism whereby the ability of MP to modulate myosin light chain might be regulated by the degradation of its targeting subunit MYPT1 through the SIAH2-ubiquitin-proteasomal pathway. In this manner, the turnover of MYPT1 would serve to limit the duration and/or magnitude of MP activity required to achieve a desired physiological effect.
MeSH terms
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Amino Acid Sequence
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Animals
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Astrocytes / metabolism
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Binding Sites / physiology
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Cell Line
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Cell Line, Tumor
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Cells, Cultured
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Consensus Sequence / physiology
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Cysteine Proteinase Inhibitors / pharmacology
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Cytoplasm / metabolism
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Gene Expression / genetics
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Humans
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Mice
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Mice, Inbred Strains
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Molecular Sequence Data
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Mutation / physiology
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Myosin-Light-Chain Phosphatase / genetics
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Myosin-Light-Chain Phosphatase / metabolism*
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Neurons / metabolism
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Peptide Fragments / genetics
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Peptide Fragments / metabolism
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Proteasome Endopeptidase Complex / metabolism
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Proteasome Inhibitors
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Protein Binding / physiology
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Protein Interaction Domains and Motifs / physiology
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Protein Isoforms / genetics
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Protein Isoforms / metabolism
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Sequence Homology, Amino Acid
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Transfection
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Two-Hybrid System Techniques
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Ubiquitin-Protein Ligases / genetics
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Ubiquitin-Protein Ligases / metabolism*
Substances
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Cysteine Proteinase Inhibitors
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Nuclear Proteins
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Peptide Fragments
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Proteasome Inhibitors
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Protein Isoforms
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Recombinant Fusion Proteins
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Ubiquitin-Protein Ligases
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seven in absentia proteins
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Myosin-Light-Chain Phosphatase
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PPP1R12A protein, human
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Proteasome Endopeptidase Complex