A role for smooth endoplasmic reticulum membrane cholesterol ester in determining the intracellular location and regulation of sterol-regulatory-element-binding protein-2.
Cellular cholesterol homoeostasis is regulated through proteolysis of the membrane-bound precursor sterol-regulatory-element-binding protein (SREBP) that releases the mature transcription factor form, which regulates gene expression. Our aim was to identify the nature and intracellular site of the putative sterol-regulatory pool which regulates SREBP proteolysis in hamster liver. Cholesterol metabolism was modulated by feeding hamsters control chow, or a cholesterol-enriched diet, or by treatment with simvastatin or with the oral acyl-CoA:cholesterol acyltransferase inhibitor C1-1011 plus cholesterol. The effects of the different treatments on SREBP activation were confirmed by determination of the mRNAs for the low-density lipoprotein receptor and hydroxymethylglutaryl-CoA (HMG-CoA) reductase and by measurement of HMG-CoA reductase activity. The endoplasmic reticulum was isolated from livers and separated into subfractions by centrifugation in self-generating iodixanol gradients. Immunodetectable SREBP-2 accumulated in the smooth endoplasmic reticulum of cholesterol-fed animals. Cholesterol ester levels of the smooth endoplasmic reticulum membrane (but not the cholesterol levels) increased after cholesterol feeding and fell after treatment with simvastatin or C1-1011. The results suggest that an increased cellular cholesterol load causes accumulation of SREBP-2 in the smooth endoplasmic reticulum and, therefore, that membrane cholesterol ester may be one signal allowing exit of the SREBP-2/SREBP-cleavage-regulating protein complex to the Golgi.
Iddon
C R
CR
Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
Wilkinson
J
J
Bennett
A J
AJ
Bennett
J
J
Salter
A M
AM
Higgins
J A
JA
D000081:Acetamides; D000085:Acetates; D000818:Animals; D002784:Cholesterol / Q000032:analysis; D002788:Cholesterol Esters / Q000378:metabolism*; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004036:Diet, Atherogenic; D018871:Endoplasmic Reticulum, Smooth / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006903:Hydroxymethylglutaryl CoA Reductases / Q000235:genetics / Q000378:metabolism; D007425:Intracellular Membranes / Q000737:chemistry; D008099:Liver / Q000378:metabolism; D008647:Mesocricetus; D012333:RNA, Messenger / Q000096:biosynthesis; D011973:Receptors, LDL / Q000096:biosynthesis / Q000235:genetics; D019821:Simvastatin / Q000494:pharmacology; D002785:Sterol O-Acyltransferase / Q000037:antagonists & inhibitors; D051782:Sterol Regulatory Element Binding Protein 2; D013449:Sulfonamides; D013451:Sulfonic Acids / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014280:Triglycerides / Q000032:analysis
D000081:Acetamides; D000085:Acetates; D002788:Cholesterol Esters; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D011973:Receptors, LDL; D051782:Sterol Regulatory Element Binding Protein 2; D013449:Sulfonamides; D013451:Sulfonic Acids; D014157:Transcription Factors; D014280:Triglycerides; C423185:avasimibe; D002784:Cholesterol; D019821:Simvastatin; D006903:Hydroxymethylglutaryl CoA Reductases; D002785:Sterol O-Acyltransferase