Stimulation of the LDL receptor activity in the human hepatoma cell line Hep G2 by high-density serum fractions

Havekes, Louis M.; Schouten, Donald; Wit, E.C.M. de; Cohen, Louis; Griffioen, Marieke; Hinsbergh, Victor W.M. van; Princen, H.M.G.

doi:10.1016/0005-2760(86)90173-6

Cited by 55 publications

(33 citation statements)

References 43 publications

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“…HepG2 cells also have higher absolute levels of LDL receptor mRNA than fibroblasts, but both cell lines show a similar degree of upregulation in response to LPDS (47). However, in HepG2 cells the receptor number is differentially increased relative to the receptor number in fibroblasts in response to several stimuli such as taurine, estrogen, and high density lipoproteins, all of which are believed to increase LDL receptor synthesis by depleting the cells of cholesterol (46,48,49). HepG2 cells also respond to a plasma component that stimulates receptor synthesis without a corresponding cellular cholesterol depletion whereas fibroblasts are unresponsive (50).…”

Section: Discussionmentioning

confidence: 99%

Plasma triglycerides determine low density lipoprotein composition, physical properties, and cell-specific binding in cultured cells.

McKeone¹,

Patsch²,

Pownall³

1993

J. Clin. Invest.

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The relationship between the plasma triglycerides and the LDL triglycerides of 30 normal and 48 hypertriglyceridemic subjects has been quantified; the data fit a simple adsorption isotherm, LDL triglyceride/(LDL triglyceride + LDL cholesterol ester) = 0.65 plasma triglyceride/(464 + plasma triglyceride). In vitro transfer of triglyceride from concentrated VLDL to VLDL-depleted plasma produced triglyceride-rich LDL that had similar properties. LDL uptake by HepG2 cells increased with LDL triglyceride content whereas the reverse was found with skin fibroblasts. At 370C, the cores of both normal and hypertriglyceridemic LDL were isotropic liquids. Circular dichroic spectra revealed no difference in the secondary structure of normal and triglyceride-rich LDL. The affinity of monoclonal antibody MB47, which binds to the receptor ligand of apo B-100 was independent of LDL triglyceride content. MB3, which binds near residue 1022 ofapo B-100, showed a triglyceride-dependent decrease in affinity for LDL from hypertriglyceridemic subjects and from in vitro incubations. LDL with an elevated triglyceride content formed in vitro had reduced proteolytic cleavage of apo B-100 by Staphylococcus aureus V8 protease. From these data, we infer that (a) LDL triglyceride is a predictable function of plasma triglyceride, (b) triglyceride induces subtle changes in apo B-100 structure at a site that is remote from the putative receptor binding ligand, and (c) the triglyceride-dependent receptor-binding determinants of apo B-100 are recognized differently by fibroblasts and HepG2

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Section: Discussionmentioning

confidence: 99%

Plasma triglycerides determine low density lipoprotein composition, physical properties, and cell-specific binding in cultured cells.

McKeone¹,

Patsch²,

Pownall³

1993

J. Clin. Invest.

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“…Based upon studies with HepG2 cells [38], it was suggested that in liver the less efficient down-regulation, compared to extrahepatic cells, of LDL receptors by LDL, might be related to the intracellular processing of cholesterol. The more effective down-regulation observed by feeding 2% cholesterol [lo, 391, might then be explained by the more rapid processing system coupled to p-VLDL uptake.…”

Section: Fig 9 Accumulation Of 3h Radioactivity In Control and Chlomentioning

confidence: 99%

Hepatic processing and biliary secretion of the cholesteryl esters from β very‐low‐density lipoproteins in the rat

Water

Hessels

Bakkeren

et al. 1990

European Journal of Biochemistry

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P-Migrating very-low-density lipoproteins (P-VLDL) are cholesteryl-ester-enriched lipoproteins which accumulate in the serum of cholesterol-fed animals or patients with type 111 hyperlipoproteinemia. In the rat, P-VLDL are rapidly cleared by the liver and parenchymal liver cells form the major site for uptake. In this investigation, P-VLDL were labeled with [3H]cholesteryl esters and the hepatic intracellular transport of these esters was followed. 2 min after injection, the major part of the [3H]cholesteryl esters is already associated with the liver and a significant proportion is recovered in endosomes. Up to 25 rnin after injection, an increase in radioactivity in the lysosomal compartment is noticed. This radioactivity initially represents cholesteryl esters, while from 25 min onward, radioactivity is mainly present in unesterified cholesterol. Between 45 rnin and 90 min after P-VLDL injection, specific transfer of unesterified [3H]cholesterol to the endoplasmic reticulum is observed, while by 3 h the majority is located in this fraction. The appearance of radioactivity in the bile was rather slow as compared to the rapid initial uptake and processing, and up to 5 h after injection only 10% of the injected dose had reached the bile (mainly as bile acids). 72 h after injection, the amount of the injected radioactivity recovered in the bile had increased to 50%. Chloroquine treatment of the rats inhibited the hydrolysis of the cholesteryl esters and the appearance of radioactivity in the bile was retarded.It is concluded that P-VLDL are rapidly processed by parenchymal liver cells and that the cholesteryl esters from P-VLDL are hydrolyzed in the lysosomal compartment. Unesterified cholesterol remains associated with the endoplasmic reticulum for a prolonged time, although ultimately the majority will be secreted into the bile as bile acids. The effective operation of this pathway will prevent extrahepatic accumulation of cholesteryl esters from P-VLDL, while the prolonged residence time of unesterified cholesterol in the endoplasmic reticulum might be important for regulation of low-density lipoprotein (LDL) receptors in liver and thus for LDL levels in the blood.An abnormal form of very-low-density lipoproteins (VLDL) can be recognized in laboratory animals fed a diet high in fat and cholesterol, and in humans with the genetic disorder type I11 hypercholesterolemia [l -41. In comparison to normal VLDL, the so-called j-VLDL are enriched in cholesteryl esters and on electrophoresis it show p mobility [5].The presence of P-VLDL in the blood is associated with an increased risk of atherosclerosis [6] and in vitro this lipoprotein can provoke intracellular cholesterol(ester) accumulation in monocytes and macrophages whereby these cells are converted to foam cells which have a similar appearance to cells found in the atherosclerotic plaque [3, 7-91, In cholesterolfed animals, P-VLDL accumulation may be induced by a saturation of the hepatic clearance system [lo] or as consequence of an increased synthesis of the p...

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“…LDL, low-density lipoprotein ; a-VLDL, cholesteryl ester-rich P-migrating very-low-density lipoprotein; PMA, 4p-phorbol 12-myristate 13-acetate; PKC, protein kinase C ; ACAT, acyl-CoA :cholesterol acyltransferase ; DMEM, Dulbecco's modified eagle medium. specific metabolic functions including LDL receptors [7, 81, a similar regulatory phenomenon is reported for the regulation of the LDL-receptor activity, as with human liver cells [9]. It was speculated that the inability of LDL to block LDLreceptor synthesis completely, would allow the liver to take up LDL even at high blood-LDL levels [6].…”

mentioning

confidence: 91%

Regulation of low‐density‐lipoprotein receptors in the human hepatoma cell line Hep G2

Kamps

Berkel

1993

European Journal of Biochemistry

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The regulation of low-density-lipoprotein(LDL)-receptor activity by 4P-phorbol 12-myristate 13-acetate (PMA) and LDL was investigated in the human hepatoma cell line Hep G2. Treatment of Hep G2 cells for 22 h with PMA results in an 18.6-fold increase in the amount of LDL-binding sites on the cell surface. The rate of turnover of LDL receptors was not significantly altered upon PMA treatment. Treatment of cultured rat parenchymal cells and human parenchymal cells with PMA did not lead to increased binding of LDL to these cells, suggesting that protein-kinase-cmediated regulation of LDL-receptor activity is specific for Hep G2 cells and that in this aspect of regulation of LDL receptors, Hep G2 cells do not reflect human hepatocytes. The down-regulation of LDL receptors by a 22-h prior incubation with LDL in PMA-treated Hep G2 cells, in which LDL receptors are upregulated, is more effective than in non-treated cells. Prior incubation of control Hep G2 cells with an excess of LDL caused a partial down-regulation to 33% of the initial level of receptor binding. In PMA-treated Hep G2 cells an excess of non-labeled LDL, led to a downregulation to 13% of the PMA-induced level. Prior incubation of Hep G2 cells with LDL in the presence of PMA led to a 2.3-fold increase of intracellular cholesteryl esters and a 9.1-fold increase in acyl-CoA :cholesterol-acyltransferase (ACAT) activity. In control cells, LDL prior incubation led to a 1.6-fold increase in intracellular cholesteryl esters and a 1.8-fold increase of ACAT activity. It is concluded that in Hep G2 cells LDL itself can be an effective suppressor of the expression of LDL receptors, provided that the initial amount of receptor allows an adequate intracellular delivery of cholesterol to its sterol-regulatory site.The liver is the major site of expression of low-density lipoprotein (LDL) receptors and it is the only organ in which cholesterol can be removed from the circulation and degraded to bile acids. Therefore the amount of LDL receptor in the liver plays a decisive role in the regulation of blood-LDL cholesterol levels [l].Extensive studies with fibroblasts have demonstrated that the LDL-receptor activity is efficiently regulated by cellular cholesterol levels [ 1, 21. LDL receptor-activity in fibroblasts is down-regulated almost completely after prior incubation of the cells with an excess of LDL, while only partial downregulation of LDL-receptor activity is observed when cultured human liver parenchymal cells are incubated with a similar excess of LDL [3-61. With the human hepatoma cell line Hep G2, a cell line which expresses a variety of liverCorrespondence to Th. J. C. van Berkel, Division of Biopharmaceutics, Center for Bio-Pharmaceutical Sciences, Sylvius Laboratory, University of Leiden, P. 0. Box 9503, NL-2300 RA Leiden, The Netherlands Fax: +31 71 216292. Abbreviation. LDL, low-density lipoprotein ; a-VLDL, cholesteryl ester-rich P-migrating very-low-density lipoprotein; PMA, 4p-phorbol 12-myristate 13-acetate; PKC, protein kinase C ; ACAT, acyl-CoA :...

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Stimulation of the LDL receptor activity in the human hepatoma cell line Hep G2 by high-density serum fractions

Cited by 55 publications

References 43 publications

Plasma triglycerides determine low density lipoprotein composition, physical properties, and cell-specific binding in cultured cells.

Plasma triglycerides determine low density lipoprotein composition, physical properties, and cell-specific binding in cultured cells.

Hepatic processing and biliary secretion of the cholesteryl esters from β very‐low‐density lipoproteins in the rat

Regulation of low‐density‐lipoprotein receptors in the human hepatoma cell line Hep G2

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