TY - JOUR
T1 - Cholesterol and 25-hydroxycholesterol inhibit activation of SREBPs by different mechanisms, both involving SCAP and insigs
AU - Adams, Christopher M.
AU - Reitz, Julian
AU - De Brabander, Jef K.
AU - Feramisco, Jamison D.
AU - Li, Lu
AU - Brown, Michael S.
AU - Goldstein, Joseph L.
PY - 2004/12/10
Y1 - 2004/12/10
N2 - The current paper demonstrates that cholesterol and its hydroxylated derivative, 25-hydroxycholesterol (25-HC), inhibit cholesterol synthesis by two different mechanisms, both involving the proteins that control sterol regulatory element-binding proteins (SREBPs), membrane-bound transcription factors that activate genes encoding enzymes of lipid synthesis. Using methyl-β- cyclodextrin as a delivery vehicle, we show that cholesterol enters cultured Chinese hamster ovary cells and elicits a conformational change in SREBP cleavage-activating protein (SCAP), as revealed by the appearance of a new fragment in tryptic digests. This change causes SCAP to bind to Insigs, which are endoplasmic reticulum retention proteins that abrogate movement of the SCAP-SREBP complex to the Golgi apparatus where SBEBPs are normally processed to their active forms. Direct binding of cholesterol to SCAP in intact cells was demonstrated by showing that a photoactivated derivative of cholesterol cross-links to the membrane domain of SCAP. The inhibitory actions of cholesterol do not require the isooctyl side chain or the Δ5-double bond of cholesterol, but they do require the 30-hydroxyl group. 25-HC is more potent than cholesterol in eliciting SCAP binding to Insigs, but 25-HC does not cause a detectable conformational change in SCAP. Moreover, a photoactivated derivative of 25-HC does not cross-link to SCAP. These data imply that cholesterol interacts with SCAP directly by inducing it to bind to Insigs, whereas 25-HC works indirectly through a putative 25-HC sensor protein that elicits SCAP-Insig binding.
AB - The current paper demonstrates that cholesterol and its hydroxylated derivative, 25-hydroxycholesterol (25-HC), inhibit cholesterol synthesis by two different mechanisms, both involving the proteins that control sterol regulatory element-binding proteins (SREBPs), membrane-bound transcription factors that activate genes encoding enzymes of lipid synthesis. Using methyl-β- cyclodextrin as a delivery vehicle, we show that cholesterol enters cultured Chinese hamster ovary cells and elicits a conformational change in SREBP cleavage-activating protein (SCAP), as revealed by the appearance of a new fragment in tryptic digests. This change causes SCAP to bind to Insigs, which are endoplasmic reticulum retention proteins that abrogate movement of the SCAP-SREBP complex to the Golgi apparatus where SBEBPs are normally processed to their active forms. Direct binding of cholesterol to SCAP in intact cells was demonstrated by showing that a photoactivated derivative of cholesterol cross-links to the membrane domain of SCAP. The inhibitory actions of cholesterol do not require the isooctyl side chain or the Δ5-double bond of cholesterol, but they do require the 30-hydroxyl group. 25-HC is more potent than cholesterol in eliciting SCAP binding to Insigs, but 25-HC does not cause a detectable conformational change in SCAP. Moreover, a photoactivated derivative of 25-HC does not cross-link to SCAP. These data imply that cholesterol interacts with SCAP directly by inducing it to bind to Insigs, whereas 25-HC works indirectly through a putative 25-HC sensor protein that elicits SCAP-Insig binding.
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U2 - 10.1074/jbc.M410302200
DO - 10.1074/jbc.M410302200
M3 - Article
C2 - 15452130
AN - SCOPUS:10644239801
SN - 0021-9258
VL - 279
SP - 52772
EP - 52780
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 50
ER -