Abstract
We report the cloning and functional characterization of myopodin, the second member of the synaptopodin gene family. Myopodin shows no significant homology to any known protein except synaptopodin. Northern blot analysis resulted in a 3.6-kb transcript for mouse skeletal and heart muscle. Western blots showed an 80-kD signal for skeletal and a 95-kD signal for heart muscle. Myopodin contains one PPXY motif and multiple PXXP motifs. Myopodin colocalizes with alpha-actinin and is found at the Z-disc as shown by immunogold electron microscopy. In myoblasts, myopodin shows preferential nuclear localization. During myotube differentiation, myopodin binds to stress fibers in a punctuated pattern before incorporation into the Z-disc. Myopodin can directly bind to actin and contains a novel actin binding site in the center of the protein. Myopodin has actin-bundling activity as shown by formation of latrunculin-A-sensitive cytosolic actin bundles and nuclear actin loops in transfected cells expressing green fluorescent protein-myopodin. Under stress conditions, myopodin accumulates in the nucleus and is depleted from the cytoplasm. Nuclear export of myopodin is sensitive to leptomycin B, despite the absence of a classical nuclear export sequence. We propose a dual role for myopodin as a structural protein also participating in signaling pathways between the Z-disc and the nucleus.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Actins / metabolism
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Amino Acid Sequence
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Animals
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Binding Sites
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Bridged Bicyclo Compounds, Heterocyclic / pharmacology
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Cell Differentiation
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Cell Line
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Cell Nucleus / metabolism*
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Cytoplasm / metabolism*
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Gene Expression
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Green Fluorescent Proteins
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Heat-Shock Response
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Heating
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Humans
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Luminescent Proteins / genetics
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Mice
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Microfilament Proteins / classification
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Microfilament Proteins / genetics
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Microfilament Proteins / metabolism*
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Microfilament Proteins / physiology
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Molecular Sequence Data
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Muscle Proteins / classification
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Muscle Proteins / genetics
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Muscle Proteins / metabolism*
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Muscle Proteins / physiology
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Muscle, Skeletal / cytology
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Muscle, Skeletal / metabolism
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Muscle, Smooth / cytology
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Muscle, Smooth / metabolism
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Mutagenesis
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Myocardium / metabolism
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Nuclear Localization Signals / genetics
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Nuclear Localization Signals / metabolism
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Protein Transport
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RNA, Messenger
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Recombinant Fusion Proteins / genetics
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Sequence Homology, Amino Acid
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Stress, Physiological
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Thiazoles / pharmacology
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Thiazolidines
Substances
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Actins
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Bridged Bicyclo Compounds, Heterocyclic
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Luminescent Proteins
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Microfilament Proteins
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Muscle Proteins
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Nuclear Localization Signals
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RNA, Messenger
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Recombinant Fusion Proteins
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SYNPO protein, human
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SYNPO2 protein, human
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Synpo protein, mouse
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Synpo2 protein, mouse
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Thiazoles
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Thiazolidines
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Green Fluorescent Proteins
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latrunculin A