期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2003
卷号：100
期号：19
页码：10647-10652
DOI：10.1073/pnas.1534833100
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Sterols mediate feedback inhibition of the sterol regulatory element-binding protein (SREBP) pathway by preventing movement of the SREBP cleavage-activating protein (SCAP)/SREBP complex from endoplasmic reticulum (ER) to Golgi, where proteolytic cleavage of SREBPs releases the transcription factor domain that activates genes for lipid biosynthesis. Our laboratory previously used a trypsin cleavage assay to show that the conformation of SCAP is altered in vitro by addition of cholesterol to ER membranes. More recently, Insig-1 and Insig-2 were identified as ER resident proteins that bind the SCAP/SREBP complex and promote its ER retention when cells are treated with sterols. Here, we use the trypsin assay to show that Insig proteins reduce the concentration of cholesterol needed in vitro to produce the conformational change in SCAP. Insig-1 and Insig-2 also enhance the conformational change in SCAP that occurs upon addition of certain cationic amphiphiles, such as chlorpromazine, trifluoperazine, and imipramine, which mimic the effect of cholesterol. The effects of cationic amphiphiles raise the possibility that SCAP may monitor specifically the composition of the cytoplasmic leaflet of the ER membrane.
