Mechanisms of dysregulation of low-density lipoprotein receptor expression in HepG2 cells induced by inflammatory cytokines
- Author:
- No author available
- Journal Title:
- CHINESE MEDICAL JOURNAL
- Issue:
- 24
- DOI:
- No doi available
- Key Word:
- low-density lipoprotein receptor;cytokines;sterol regulatory element binding protein-2;SREBP cleavage-activating protein;cholesterol
Abstract： Background Low-density lipoprotein(LDL)receptor is normally regulated via a feedback system that is dependent on intracellular cholesterol levels.We have demonstrated that cytokines disrupt cholesterol-mediated LDL receptor feedback regulation causing intracellular accumulation of unmodified LDL in peripheral cells.Liver is the centraI organ for lipid homeostasis.The aim of this study was to investigate the regulation of cholesterol exogenous uptake via LDL receptor and its underlying mechanisms in human hepatic cell line(HepG2)cells under physiological and inflammatory conditions.Methods Intracellular total cholesterol(TC),free cholesterol(FC)and cholesterol ester(CE)were measured by an enzymic assay.Oil Red O staining was used to visualize lipid droplet accumulation in cells.Total cellular RNA was isolated from cells for detecting LDL receptor,sterol regulatory element binding protein (SREBP)-2 and SREBP cleavage-activating protein(SCAP)mRNA levels using real-time quantitative PCR.LDL receptor and SREBP-2 protein expression were examined by Western blotting.Confocal microscopy was used to investigate the translocation of SCAP-SREBP complex from the endoplasmic reticulum(ER)to the Golgi by dual staining with anti-human SCAP and anti-Golgin antibodies.Results LDL loading increased intracellular cholesterol level,thereby reduced LDL receptor mRNA and protein expression in HepG2 cells under physiological conditions.However,interleukin 1β(IL-1β)further increased intracellular cholesterol level in the presence of LDL by increasing both LDL receptor mRNA and protein expression in HepG2.LDL also reduced the SREBP and SCAP mRNA level under physiological conditions.Exposure to IL-1β caused Over-expression of SREBP-2 and also disrupted normal distribution of SCAP-SREBP complex in HepG2 by enhancing translocation of SCAP-SREBP from the ER to the Golgi despite a high concentration of LDL in the culture medium.Conclusions IL-1β disrupts cholesterol-mediated LDL receptor feedback regulation by enhancing SCAP-SREBP complex translocation from the ER to the Golgi,thereby increasing SREBP-2 mediated LDL receptor expression even in the presence of high concentration of LDL.This results in LDL cholesterol accumulation in hepatic cells via LDL receptor pathway under inflammatory stress.
- [1]Sakai J,Rawson RB.The sterol regulatory element-binding protein pathway: control of lipid homeostasis through regulated intracellular transport.[J].2001,12(3).
- [2]M J, Rudling,E, Reihnér,K, Einarsson,etc.Low density lipoprotein receptor-binding activity in human tissues: quantitative importance of hepatic receptors and evidence for regulation of their expression in vivo.[J].1990,87.
- [3]Brown MS,Goldstein JL.A proteolytic pathway that controls the cholesterol content of membranes, cells, and blood.[J].1999,96(20).
- [4]Chieko Yokoyama,Xiadong Wang,Michael R. Briggs,etc.SREBP-1, a basic-helix-loop-helix-leucine zipper protein that controls transcription of the low density lipoprotein receptor gene[J].1993,75(1).
- [5]X, Wang,M R, Briggs,X, Hua,etc.Nuclear protein that binds sterol regulatory element of low density lipoprotein receptor promoter. II. Purification and characterization.[J].1993,268.
- [6]M S, Brown,J L, Goldstein.A receptor-mediated pathway for cholesterol homeostasis.[J].1986,232.
- [7]J R, Smith,T F, Osborne,J L, Goldstein,etc.Identification of nucleotides responsible for enhancer activity of sterol regulatory element in low density lipoprotein receptor gene.[J].1990,265.
- [8]Sanchez HB,Osborne TF,Yieh L.Cooperation by sterol regulatory element-binding protein and Sp1 in sterol regulation of low density lipoprotein receptor gene.[J].1995,270(3).
- [9]B, Angelin.Regulation of hepatic cholesterol metabolism in man.[J].1991,23.
- [10]Hermus A. R.,Sweep C. G.,Demacker P. N.,etc.Continuous infusion of interleukin-1 beta in rats induces a profound fall in plasma levels of cholesterol and triglycerides[J].1992.
- [11]Xiaodong Wang,Ryuichiro Sato,Michael S. Brown,etc.SREBP-1, a membrane-bound transcription factor released by sterol-regulated proteolysis[J].1994,77(1).
- [12]A T, Stopeck,A C, Nicholson,F P, Mancini,etc.Cytokine regulation of low density lipoprotein receptor gene transcription in HepG2 cells.[J].1993,268.
- [13]BROWN M. S.,GOLDSTEIN J. L..The LDL Receptor and the Regulation of Cellular Cholesterol Metabolism[J].1985.
- [14]Brown MS.,Goldstein JL.,Rawson RB..Mutant mammalian cells as tools to delineate the sterol regulatory element-binding protein pathway for feedback regulation of lipid synthesis [Review][J].2002,397(2).
- [15]Svistounov DN,Zykova SN,Iversen H,etc.Release of TNF-alpha From In Vitro-Stimulated Monocytes is Negatively Associated with Serum Levels of Apolipoprotein B in Patients with Type 2 Diabetes.[J].2004,60(5).
- [16]Ruan XZ,Varghese Z,Powis SH,etc.Dysregulation of LDL receptor under the influence of inflammatory cytokines: a new pathway for foam cell formation.[J].2001,60(5).
- [17]Scheek S,Nohturfft A,Goldstein JL,etc.Sterols regulate cycling of SREBP cleavage-activating protein (SCAP) between endoplasmic reticulum and Golgi.[J].1999,96(20).
- [18]Yang T.,Goldstein J. L.,Brown M. S..Overexpression of Membrane Domain of SCAP Prevents Sterols from Inhibiting SCAP{middle dot}SREBP Exit from Endoplasmic Reticulum[J].2000.
- [19]E, Levy,C, Gurbindo,F, Lacaille,etc.Circulating tumor necrosis factor-alpha levels and lipid abnormalities in patients with cystic fibrosis.[J].1993,34.