Abstract
Insulin stimulates glucose transport into fat and muscle cells by increasing the exocytic trafficking rate of the GLUT4 facilitative glucose transporter from intracellular stores to the plasma membrane. Delivery of GLUT4 to the plasma membrane is mediated by formation of functional SNARE complexes containing syntaxin4, SNAP23, and VAMP2. Here we have used an in situ proximity ligation assay to integrate these two observations by demonstrating for the first time that insulin stimulation causes an increase in syntaxin4-containing SNARE complex formation in adipocytes. Furthermore, we demonstrate that insulin brings about this increase in SNARE complex formation by mobilizing a pool of syntaxin4 held in an inactive state under basal conditions. Finally, we have identified phosphorylation of the regulatory protein Munc18c, a direct target of the insulin receptor, as a molecular switch to coordinate this process. Hence, this report provides molecular detail of how the cell alters membrane traffic in response to an external stimulus, in this case, insulin.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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3T3-L1 Cells
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Adipocytes / metabolism
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Animals
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Cell Membrane / metabolism
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Glucose Transporter Type 4 / metabolism
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Insulin / metabolism*
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Mice
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Multiprotein Complexes / chemistry
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Multiprotein Complexes / genetics
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Multiprotein Complexes / metabolism
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Munc18 Proteins / genetics
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Munc18 Proteins / metabolism
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Phosphorylation
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Protein Transport
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Qa-SNARE Proteins / chemistry*
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Qa-SNARE Proteins / genetics
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Qa-SNARE Proteins / metabolism*
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Qb-SNARE Proteins / genetics
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Qb-SNARE Proteins / metabolism
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Qc-SNARE Proteins / genetics
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Qc-SNARE Proteins / metabolism
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Rats
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Recombinant Fusion Proteins / chemistry
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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SNARE Proteins / chemistry*
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SNARE Proteins / genetics
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SNARE Proteins / metabolism*
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Vesicle-Associated Membrane Protein 2 / genetics
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Vesicle-Associated Membrane Protein 2 / metabolism
Substances
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Glucose Transporter Type 4
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Insulin
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Multiprotein Complexes
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Munc18 Proteins
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Qa-SNARE Proteins
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Qb-SNARE Proteins
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Qc-SNARE Proteins
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Recombinant Fusion Proteins
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SNARE Proteins
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Slc2a4 protein, mouse
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Snap23 protein, mouse
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Vesicle-Associated Membrane Protein 2
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vesicle-associated membrane protein 2, mouse