Abstract
Using coimmunoprecipitation and tandem mass spectrometry, we identify INSIG-1 as an ER protein that binds the sterol-sensing domain of SREBP cleavage-activating protein (SCAP) and facilitates retention of the SCAP/SREBP complex in the ER. In sterol-depleted cells, SCAP escorts SREBPs from ER to Golgi for proteolytic processing, thereby allowing SREBPs to stimulate cholesterol synthesis. Sterols induce binding of SCAP to INSIG-1, as determined by blue native-PAGE, and this is correlated with the inhibition of SCAP exit from the ER. Overexpression of INSIG-1 increases the sensitivity of cells to sterol-mediated inhibition of SREBP processing. Mutant SCAP(Y298C) fails to bind INSIG-1 and is resistant to sterol-mediated inhibition of ER exit. By facilitating sterol-dependent ER retention of SCAP, INSIG-1 plays a central role in cholesterol homeostasis.
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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CCAAT-Enhancer-Binding Proteins / metabolism*
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Cell Membrane / metabolism*
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Cell Membrane / ultrastructure
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Cells, Cultured
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Cholesterol / biosynthesis*
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DNA-Binding Proteins / metabolism*
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Endoplasmic Reticulum / metabolism*
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Endoplasmic Reticulum / ultrastructure
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Eukaryotic Cells / cytology
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Eukaryotic Cells / metabolism
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Gene Expression Regulation / physiology
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Genetic Vectors / physiology
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Golgi Apparatus / metabolism
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Golgi Apparatus / ultrastructure
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Homeostasis / genetics*
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Humans
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Intracellular Signaling Peptides and Proteins
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Membrane Proteins / genetics
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Membrane Proteins / metabolism*
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Mutation / genetics
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Peptide Hydrolases / metabolism
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Protein Binding / physiology
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Protein Structure, Tertiary / physiology
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Protein Transport / physiology
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Proteins / genetics
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Proteins / metabolism*
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Sterol Regulatory Element Binding Protein 1
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Sterols / metabolism
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Transcription Factors*
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Transfection
Substances
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CCAAT-Enhancer-Binding Proteins
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DNA-Binding Proteins
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INSIG1 protein, human
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Intracellular Signaling Peptides and Proteins
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Membrane Proteins
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Proteins
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SREBF1 protein, human
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SREBP cleavage-activating protein
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Sterol Regulatory Element Binding Protein 1
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Sterols
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Transcription Factors
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Cholesterol
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Peptide Hydrolases