Crucial step in cholesterol homeostasis: sterols promote binding of SCAP to INSIG-1, a membrane protein that facilitates retention of SREBPs in ER.
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.
Yang
Tong
T
Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75390, USA.
Espenshade
Peter J
PJ
Wright
Michael E
ME
Yabe
Daisuke
D
Gong
Yi
Y
Aebersold
Ruedi
R
Goldstein
Joseph L
JL
Brown
Michael S
MS
D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D002784:Cholesterol / Q000096:biosynthesis*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D005057:Eukaryotic Cells / Q000166:cytology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D005822:Genetic Vectors / Q000502:physiology; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D006706:Homeostasis / Q000235:genetics*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010447:Peptide Hydrolases / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D051780:Sterol Regulatory Element Binding Protein 1; D013261:Sterols / Q000378:metabolism; D014157:Transcription Factors; D014162:Transfection
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C108626:INSIG1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011506:Proteins; C497387:SREBF1 protein, human; C102196:SREBP cleavage-activating protein; D051780:Sterol Regulatory Element Binding Protein 1; D013261:Sterols; D014157:Transcription Factors; D002784:Cholesterol; D010447:Peptide Hydrolases