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Gunn PJ, Pramfalk C, Millar V, Cornfield T, Hutchinson M, Johnson EM, Nagarajan SR, Troncoso‐Rey P, Mithen RF, Pinnick KE, Traka MH, Green CJ, Hodson L. Modifying nutritional substrates induces macrovesicular lipid droplet accumulation and metabolic alterations in a cellular model of hepatic steatosis. Physiol Rep 2020; 8:e14482. [PMID: 32643289 PMCID: PMC7343665 DOI: 10.14814/phy2.14482] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2020] [Revised: 05/02/2020] [Accepted: 05/18/2020] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND AND AIMS Nonalcoholic fatty liver disease (NAFLD) begins with steatosis, where a mixed macrovesicular pattern of large and small lipid droplets (LDs) develops. Since in vitro models recapitulating this are limited, the aims of this study were to develop mixed macrovesicular steatosis in immortalized hepatocytes and investigate effects on intracellular metabolism by altering nutritional substrates. METHODS Huh7 cells were cultured in 11 mM glucose and 2% human serum (HS) for 7 days before additional sugars and fatty acids (FAs), either with 200 µM FAs (low fat low sugar; LFLS), 5.5 mM fructose + 200 µM FAs (low fat high sugar; LFHS), or 5.5 mM fructose + 800 µM FAs (high fat high sugar; HFHS), were added for 7 days. FA metabolism, lipid droplet characteristics, and transcriptomic signatures were investigated. RESULTS Between the LFLS and LFHS conditions, there were few notable differences. In the HFHS condition, intracellular triacylglycerol (TAG) was increased and the LD pattern and distribution was similar to that found in primary steatotic hepatocytes. HFHS-treated cells had lower levels of de novo-derived FAs and secreted larger, TAG-rich lipoprotein particles. RNA sequencing and gene set enrichment analysis showed changes in several pathways including those involved in metabolism and cell cycle. CONCLUSIONS Repeated doses of HFHS treatment resulted in a cellular model of NAFLD with a mixed macrovesicular LD pattern and metabolic dysfunction. Since these nutrients have been implicated in the development of NAFLD in humans, the model provides a good physiological basis for studying NAFLD development or regression in vitro.
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Affiliation(s)
- Pippa J. Gunn
- Oxford Centre for Diabetes, Endocrinology and MetabolismRadcliffe Department of MedicineUniversity of OxfordOxfordUK
| | - Camilla Pramfalk
- Division of Clinical ChemistryDepartment of Laboratory MedicineKarolinska Institutet at Karolinska University Hospital HuddingeStockholmSweden
| | - Val Millar
- Target Discovery InstituteNuffield Department of MedicineUniversity of OxfordOxfordUK
| | - Thomas Cornfield
- Oxford Centre for Diabetes, Endocrinology and MetabolismRadcliffe Department of MedicineUniversity of OxfordOxfordUK
| | - Matthew Hutchinson
- Oxford Centre for Diabetes, Endocrinology and MetabolismRadcliffe Department of MedicineUniversity of OxfordOxfordUK
| | - Elspeth M. Johnson
- Oxford Centre for Diabetes, Endocrinology and MetabolismRadcliffe Department of MedicineUniversity of OxfordOxfordUK
| | - Shilpa R. Nagarajan
- Oxford Centre for Diabetes, Endocrinology and MetabolismRadcliffe Department of MedicineUniversity of OxfordOxfordUK
| | | | | | - Katherine E. Pinnick
- Oxford Centre for Diabetes, Endocrinology and MetabolismRadcliffe Department of MedicineUniversity of OxfordOxfordUK
| | | | - Charlotte J. Green
- Oxford Centre for Diabetes, Endocrinology and MetabolismRadcliffe Department of MedicineUniversity of OxfordOxfordUK
| | - Leanne Hodson
- Oxford Centre for Diabetes, Endocrinology and MetabolismRadcliffe Department of MedicineUniversity of OxfordOxfordUK
- National Institute for Health Research Oxford Biomedical Research CentreOxford University Hospital TrustsOxfordUK
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Sacks FM, Brewer HB. Petar Alaupovic: The father of lipoprotein classification based on apolipoprotein composition. Arterioscler Thromb Vasc Biol 2014; 34:1111-3. [PMID: 24945028 DOI: 10.1161/atvbaha.114.303500] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Frischmann ME, Ikewaki K, Trenkwalder E, Lamina C, Dieplinger B, Soufi M, Schweer H, Schaefer JR, König P, Kronenberg F, Dieplinger H. In vivo stable-isotope kinetic study suggests intracellular assembly of lipoprotein(a). Atherosclerosis 2012; 225:322-7. [PMID: 23099120 DOI: 10.1016/j.atherosclerosis.2012.09.031] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Revised: 08/17/2012] [Accepted: 09/26/2012] [Indexed: 11/29/2022]
Abstract
OBJECTIVE Lipoprotein(a) [Lp(a)] consists of apolipoprotein B-100 (apoB-100) as part of an LDL-like particle and the covalently linked glycoprotein apolipoprotein(a) [apo(a)]. Detailed mechanisms of its biosynthesis, assembly, secretion and catabolism are still poorly understood. To address the Lp(a) assembly mechanism, we studied the in vivo kinetics of apo(a) and apoB-100 from Lp(a) and LDL apoB-100 in nine healthy probands using stable-isotope methodology. METHODS The level of isotope enrichment was used to calculate the fractional synthesis rate (FSR), production rate (PR) and retention time (RT) using SAAMII software and multicompartmental modeling. RESULTS We observed a similar mean PR for apo(a) (1.15 nmol/kg/d) and apoB-100 (1.31 nmol/kg/d) from Lp(a), which differed significantly from the PR for apoB-100 from LDL (32.6 nmol/kg/d). Accordingly, mean FSR and RT values for Lp(a)-apo(a) were similar to those of Lp(a)-apoB and different from those for LDL-apoB. CONCLUSION Two different kinetic apoB pools within Lp(a) and LDL suggest intracellular Lp(a) assembly from apo(a) and newly synthesized LDL.
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Affiliation(s)
- Michael E Frischmann
- Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Austria
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PARK YEONHWA, ALBRIGHT KARENJ, STORKSON JAYNEM, LIU WEI, PARK YOOHEON, PARIZA MICHAELW. INFLUENCE OF STEARIDONIC ACID ON LIPOPROTEIN SECRETION AND FATTY ACID COMPOSITION IN HEPG2 CELLS. ACTA ACUST UNITED AC 2007. [DOI: 10.1111/j.1745-4522.2007.00092.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Alaupovic P, Attman PO, Knight-Gibson C, Mulec H, Weiss L, Samuelsson O. Effect of fluvastatin on apolipoprotein-defined lipoprotein subclasses in patients with chronic renal insufficiency. Kidney Int 2006; 69:1865-71. [PMID: 16572113 DOI: 10.1038/sj.ki.5000327] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
According to the concept of apolipoprotein (apo)-defined lipoproteins, apoA-I-containing lipoproteins consist of two subclasses referred to as lipoprotein A-I (LpA-I) and lipoprotein A-I:A-II (LpA-I:A-II), and apoB-containing lipoproteins of five subclasses, namely lipoprotein B (LpB), lipoprotein B:C (LpB:C), lipoprotein B:E (LpB:E), lipoprotein B:C:E (LpB:C:E), and lipoprotein A-II:B:C:D:E (LpA-II:B:C:D:E). The purpose of this study was to determine the levels of apoA-I- and apoB-containing lipoprotein subclasses before and after fluvastatin treatment of patients with chronic renal insufficiency. ApoA-I- and apoB-containing lipoprotein subclasses were measured in 15 patients with chronic renal failure and 15 asymptomatic subjects. The effect of fluvastatin on lipoprotein subclasses was determined in a randomized, double-blind, placebo-controlled, two-way, treatment period crossover study. Patients were administered fluvastatin 40 mg/day or placebo during 8 weeks in a randomized order. Patients were characterized by significantly higher levels of LpB (P < 0.001), LpB:C (P < 0.001), and LpB:E (P < 0.05), and slightly higher levels of LpB:C:E and LpA-II:B:C:D:E than controls. The levels of LpA-I:A-II were significantly lower (P < 0.01) in patients than controls. Fluvastatin treatment reduced all apoB-containing subclasses, but only the reduced level of LpB subclass was statistically significant (P < 0.02). The levels of LpA-I and LpA-I:A-II were not affected. Fluvastatin treatment reduced and normalized LpB and LpB:E subclasses. Although slightly reduced, the levels of markedly atherogenic LpB:C subclass were not normalized. The potential role of LpB:C on the progression of coronary artery disease in chronic renal insufficiency remains to be determined in future studies.
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Affiliation(s)
- P Alaupovic
- Lipid and Lipoprotein Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, 73104, USA.
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Effects of trans-10,cis-12 conjugated linoleic acid and cognates on apolipoprotein B secretion in HepG2 cells. Nutr Res 2005. [DOI: 10.1016/j.nutres.2004.12.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Manchekar M, Richardson PE, Forte TM, Datta G, Segrest JP, Dashti N. Apolipoprotein B-containing lipoprotein particle assembly: lipid capacity of the nascent lipoprotein particle. J Biol Chem 2004; 279:39757-66. [PMID: 15254032 DOI: 10.1074/jbc.m406302200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We previously proposed that the N-terminal 1000-residue betaalpha(1) domain of apolipoprotein B (apoB) forms a bulk lipid pocket homologous to that of lamprey lipovitellin. In support of this "lipid pocket" hypothesis, we demonstrated that apoB:1000 (residues 1-1000) is secreted by a stable transformant of McA-RH7777 cells as a monodisperse particle with high density lipoprotein 3 (HDL(3)) density. In contrast, apoB:931 (residues 1-931), missing only 69 residues of the sequence homologous to lipovitellin, was secreted as a particle considerably more dense than HDL(3). In the present study we have determined the stoichiometry of the lipid component of the apoB:931 and apoB:1000 particles. The secreted [(3)H]glycerol-labeled apoB:1000 particles, isolated by nondenaturing gradient gel electrophoresis, contained 50 phospholipid (PL) and 11 triacylglycerol (TAG) molecules/particle. In contrast, apoB:931 particles contained only a few molecules of PL and were devoid of TAG. The unlabeled apoB:1000 particles, isolated by immunoaffinity chromatography, contained 56 PL, 8 TAG, and 7 cholesteryl ester molecules/particle. The surface to core lipid ratio of apoB:1000-containing particles was approximately 4:1 and was not affected by oleate supplementation. Although very small amounts of microsomal triglyceride transfer protein (MTP) were associated with apoB:1000 particles, it never approached a 1:1 molar ratio of MTP to apoB. These results support a model in which (i) the first 1000 amino acid residues of apoB are competent to complete the lipid pocket without a structural requirement for MTP; (ii) a portion, or perhaps all, of the amino acid residues between 931 and 1000 of apoB-100 are critical for the formation of a stable, bulk lipid-containing nascent lipoprotein particle, and (iii) the lipid pocket created by the first 1000 residues of apoB-100 is PL-rich, suggesting a small bilayer type organization and has a maximum capacity on the order of 50 molecules of phospholipid.
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Affiliation(s)
- Medha Manchekar
- Department of Medicine, Atherosclerosis Research Unit, University of Alabama at Birmingham Medical Center, Birmingham, Alabama 35294, USA
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Alaupovic P. The concept of apolipoprotein-defined lipoprotein families and its clinical significance. Curr Atheroscler Rep 2003; 5:459-67. [PMID: 14525679 DOI: 10.1007/s11883-003-0036-8] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Classification of plasma lipoproteins on the basis of apolipoprotein (apo) composition recognizes two lipoprotein (Lp) classes, one of which is characterized by apoA-I and the other by apoB as major protein constituents. The former lipoprotein class consists of three major subclasses referred to (according to their apolipoprotein constituents) as Lp-A-I, Lp-A-I:A-II, and Lp-A-II, and the latter one of five subclasses called Lp-B, Lp-B:E, Lp-B:C, Lp-B:C:E, and Lp-A-II:B:C:D:E. As polydisperse systems of particles, the apoA-I-containing lipoproteins overlap in high-density segments and apoB- containing lipoproteins in low-density segments of the density gradient. Each subclass is characterized by a specific chemical composition and metabolic property. Normolipidemia and dyslipoproteinemias are characterized by quantitative rather than qualitative differences in the levels of apoA- and apoB-containing subclasses. Furthermore, apoA-containing subclasses seem to differ with respect to their relative antiatherogenic capacities, and apoB-containing subclasses regarding their relative atherogenic potentials. Whereas Lp-A-I may have a greater antiatherogenic capacity than other apoA-containing subclasses, the cholesterol-enriched Lp-B:C appears to be the most atherogenic subclass among apoB-containing lipoprotein families. The use of pharmacologic and/or dietary interventions to treat dyslipoproteinemias has already shown that these therapeutic modalities may affect selectively individual apolipoprotein-defined lipoproteins, and thus allow the selection of individualized treatments targeted at decreasing harmful and/or increasing beneficial lipoprotein subclasses.
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Affiliation(s)
- Petar Alaupovic
- Lipid and Lipoprotein Laboratory, Oklahoma Medical Research Foundation, 800 Research Parkway, Suite 340, Oklahoma City, OK 73104, USA
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Lee DM, Knight-Gibson C, Samuelsson O, Attman PO, Wang CS, Alaupovic P. Lipoprotein particle abnormalities and the impaired lipolysis in renal insufficiency. Kidney Int 2002; 61:209-18. [PMID: 11786103 DOI: 10.1046/j.1523-1755.2002.00116.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Increased concentrations of very low- (VLDL) and intermediate-density (IDL) lipoproteins in chronic renal failure (CRF) are thought to result from a defect(s) in degradation of plasma triglyceride (TG)-rich lipoproteins. The purpose of this study was to identify lipoprotein abnormalities associated with the reduced lipolytic rate constant, k1, of combined VLDL and IDL substrate from renal patients and asymptomatic controls. METHODS The VLDL + IDL were isolated from 18 predialytic patients (CRF-I), 8 patients on hemodialysis (CRF-II) and 10 asymptomatic controls. The lipolytic rate constant (k1) of VLDL + IDL was measured by an assay using bovine milk lipoprotein lipase and determination of TG before and after incubation by gas chromatography (GC). Neutral lipids were measured by GC and apolipoproteins by electroimmunoassays; the apolipoprotein-defined TG-rich lipoproteins including Lp-B:C, Lp-B:C:E and Lp-A-II:B:C:D:E were determined by immunoaffinity chromatography. RESULTS The k1 values of VLDL + IDL were significantly (P < 0.001) lower in CRF-I and CRF-II patients (0.0341 and 0.0352 min-1, respectively) than controls (0.0515 min-1). The levels of apolipoproteins B, C-III and E, and TG-rich Lp-B:C, Lp-B:C:E and Lp-A-II:B:C:D:E particles normalized to 100 mg TG per VLDL + IDL were significantly higher in both groups of CRF patients than in controls. All three TG-rich lipoproteins were characterized by significantly increased percent contents of free (FC) and esterified (CE) cholesterol and a decreased percentage of TG. The k1 values of the combined CRF-I and CRF-II patient groups showed significant negative correlations (P < 0.001) with FC (r=-0.81) and CE (r=-0.63) and a positive correlation with TG (r=0.72). Among lipoprotein particles, only Lp-A-II:B:C:D:E levels showed a significant negative correlation with k1 values (r=-0.47, P < 0.03). CONCLUSIONS This study shows that the abnormal neutral lipid composition of all three TG-rich lipoprotein particles and increased concentrations of Lp-A-II:B:C:D:E particles represent the main factors affecting the in vitro lipolytic rates of VLDL + IDL substrate in both the CRF patients before dialysis and patients on hemodialysis.
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Affiliation(s)
- Diana M Lee
- Department of Obstetrics & Gynecology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
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Abstract
Our understanding of the genetics, metabolism and pathophysiology of the atherogenic plasma lipoprotein Lp(a) has considerably increased over past years. Nevertheless, the precise mechanisms regulating the biosynthesis and assembly of Lp(a) are poorly understood and controversially discussed. Lp(a) plasma concentrations are determined by synthesis and not by degradation. Transcriptional and post-translational mechanisms have been identified as regulating Lp(a) production in primary hepatocytes and transfected cell lines. Assembly of Lp(a) occurs extracellularly from newly synthesized apolipoprotein(a) and circulating LDL. This view has recently been challenged by in-vivo kinetic studies in humans which are compatible with an intracellular assembly event. Lp(a) assembly is a complex two-step process of multiple non-covalent interactions between apolipoprotein(a) and apolipoprotein B-100 of LDL followed by covalent disulfide linkage of two free cysteine residues on both proteins.
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Affiliation(s)
- H Dieplinger
- Institute of Medical Biology and Human Genetics, University of Innsbruck, Austria
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Yotsumoto H, Hara E, Naka S, Adlof R, Emken E, Yanagita T. 10trans, 12cis-Linoleic acid reduces apolipoprotein B secretion in HepG2 cells. Food Res Int 1998. [DOI: 10.1016/s0963-9969(98)00103-3] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Estrogen dependence of synthesis and secretion of apolipoprotein B-containing lipoproteins in the chicken hepatoma cell line, LMH-2A. J Lipid Res 1997. [DOI: 10.1016/s0022-2275(20)37415-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Dashti N, Franklin FA, Abrahamson DR. Effect of ethanol on the synthesis and secretion of apoA-I- and apoB-containing lipoproteins in HepG2 cells. J Lipid Res 1996. [DOI: 10.1016/s0022-2275(20)37579-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Alaupovic P. Significance of apolipoproteins for structure, function, and classification of plasma lipoproteins. Methods Enzymol 1996; 263:32-60. [PMID: 8748999 DOI: 10.1016/s0076-6879(96)63004-3] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- P Alaupovic
- Lipid and Lipoprotein Laboratory, Oklahoma Medical Research Foundation, Oklahoma City 73104, USA
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Benoist F, Grand-Perret T. A sensitive method to analyze in vitro secretion of lipoproteins: distribution of apolipoproteins is modulated by oleic acid in HepG2 cells. J Lipid Res 1996. [DOI: 10.1016/s0022-2275(20)39208-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Inhibition of acyl-CoA: cholesterol acyltransferase decreases apolipoprotein B-100-containing lipoprotein secretion from HepG2 cells. J Lipid Res 1996. [DOI: 10.1016/s0022-2275(20)37630-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Brunner C, Kraft HG, Utermann G, Müller HJ. Cys4057 of apolipoprotein(a) is essential for lipoprotein(a) assembly. Proc Natl Acad Sci U S A 1993; 90:11643-7. [PMID: 7505444 PMCID: PMC48040 DOI: 10.1073/pnas.90.24.11643] [Citation(s) in RCA: 115] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Lipoprotein(a) contains one copy each of apolipoprotein B-100 and apolipoprotein(a). It has been hypothesized that a disulfide bond might exist between Cys4057 of apolipoprotein(a) and Cys3734 in apolipoprotein B-100. To investigate the role of Cys4057 for lipoprotein(a) assembly, wild-type and in vitro mutagenized apolipoprotein(a) cDNA plasmids were expressed in the human hepatocarcinoma line HepG2. The mutant plasmids encoded apolipoprotein(a) species with Cys4057 exchanged to either serine or glycine. Untransfected HepG2 cells, although able to secrete apolipoprotein B-100-containing lipoproteins, do not synthesize detectable amounts of apolipoprotein(a). After transfection of wild-type plasmid, almost all apolipoprotein(a) in the culture supernatant was present in lipoprotein(a)-like particles as demonstrated by immunoblotting, density-gradient centrifugation, and ELISA. The same analysis performed with supernatants of cells transfected with plasmids mutated in codon 4057 revealed free apolipoprotein(a) glycoprotein without detectable amounts of lipoprotein-associated apolipoprotein(a). Our results strongly suggest the existence of a disulfide bridge between Cys4057 of apolipoprotein(a) and apolipoprotein B-100 within recombinant lipoprotein(a) particles. Furthermore, they indicate that disulfide bridge formation is essential for assembly of the lipoprotein(a)-like complex produced by HepG2 cells and suggest a similar role of Cys4057 during lipoprotein(a) assembly in vivo.
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Affiliation(s)
- C Brunner
- Department of Molecular Pharmacology, Boehringer Mannheim GmbH, Mannheim, Germany
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Kamps JA, van Berkel TJ. Regulation of low-density-lipoprotein receptors in the human hepatoma cell line Hep G2. Effect of phorbol 12-myristate 13-acetate and low-density lipoprotein. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 213:989-94. [PMID: 8389299 DOI: 10.1111/j.1432-1033.1993.tb17845.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The regulation of low-density-lipoprotein(LDL)-receptor activity by 4 beta-phorbol 12-myristate 13-acetate (PMA) and LDL was investigated in the human hepatoma cell line Hep G2. Treatment of Hep G2 cells for 22h 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-C-mediated 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 down-regulation 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.
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Affiliation(s)
- J A Kamps
- Division of Biopharmaceutics, Sylvius Laboratory, University of Leiden, The Netherlands
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Zannis VI, Kardassis D, Zanni EE. Genetic mutations affecting human lipoproteins, their receptors, and their enzymes. ADVANCES IN HUMAN GENETICS 1993; 21:145-319. [PMID: 8391199 DOI: 10.1007/978-1-4615-3010-7_3] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- V I Zannis
- Department of Medicine, Housman Medical Research Center, Boston University Medical Center, Massachusetts 02118
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Koren E, Reichlin MW, Koscec M, Fugate RD, Reichlin M. Autoantibodies to the ribosomal P proteins react with a plasma membrane-related target on human cells. J Clin Invest 1992; 89:1236-41. [PMID: 1313450 PMCID: PMC442983 DOI: 10.1172/jci115707] [Citation(s) in RCA: 147] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Autoantibodies to ribosomal P-proteins are present in 12-16% of patients with systemic lupus erythematosus and are associated with neuropsychiatric disease. As the ribosomal P proteins are located in the cytoplasm, the pathogenic effects of their cognate autoantibodies are unclear. In this study affinity-purified anti-P autoantibodies were used to explore the cell surface of several types of human and animal cells. Immunofluorescence as well as EM immunogold analysis demonstrated, on the surface of human hepatoma cells, the presence of an epitope that is antigenically related to the immunodominant carboxy terminus of P-proteins. The presence of this epitope was also demonstrated on the surface of human neuroblastoma cells and, to a lesser extent, on human fibroblasts. Furthermore, the Western blot technique revealed in purified human and animal plasma membranes a 38-kD protein that is closely related or identical with ribosomal P0 protein. The availability of reactive P peptide on the surface of cells makes possible the direct effect of autoantibodies on the function and viability of cells that express this antigenic target. This delineates one of the possible impacts of anti-P antibodies in disease expression.
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Affiliation(s)
- E Koren
- Arthritis and Immunology Research Program, Oklahoma Medical Research Foundation, Oklahoma City 73104
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The effect of low density lipoproteins, cholesterol, and 25-hydroxycholesterol on apolipoprotein B gene expression in HepG2 cells. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)50552-x] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Hahn SE, Parkes JG, Goldberg DM. Enzyme-linked immunosorbent assay to measure apolipoproteins AI and B secreted by a human hepatic carcinoma cell line (Hep G2). J Clin Lab Anal 1992; 6:182-9. [PMID: 1403337 DOI: 10.1002/jcla.1860060404] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We describe an enzyme-linked immunosorbent assay (ELISA) to measure apolipoproteins AI and B secreted by Hep G2 cells and in cell homogenates. These assays utilize commercially available polyclonal antibodies, affinity-purified to improve their specificity, thereby achieving a dramatic increase in the sensitivity of the assay. These affinity-purified antibodies were also more sensitive than a series of monoclonal antibodies tested. We achieved a sensitivity of 0.4 ng in the apo AI assay, and a sensitivity of 5 ng in the apo B assay. By these methods, we measured secretion rates by Hep G2 cells of 358 +/- 41 ng/mg cell protein/hr for apo B and 137 +/- 8 ng/mg cell protein/hr for apo AI. These assays also allowed the measurement of intracellular apolipoproteins and thus can be used to facilitate investigations of human lipoprotein metabolism in cell culture systems.
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Affiliation(s)
- S E Hahn
- Department of Clinical Biochemistry, University of Toronto, Ontario, Canada
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24
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Fuki IV, Menschikov GB, Menschikowski M, Adamova IYu, Repin VS. Interaction of apolipoprotein B-containing lipoprotein secreted by Hep G2 cells with receptors for low-density lipoprotein. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1086:237-40. [PMID: 1657183 DOI: 10.1016/0005-2760(91)90013-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Radioligand and immunoenzymatic techniques were used to characterize the receptor binding properties of apolipoprotein B-containing lipoprotein produced by HepG2 cell line (H-LpB). It was found that compared to plasma low-density lipoprotein (LDL), the interaction of H-LpB nonseparated from conditioned medium with normal fibroblasts was 6-8-times lower and only slightly exceeded the nonspecific binding of LDL modified by malondialdehyde, while the uptake of the indicated lipoproteins by LDL receptor-negative strain of fibroblasts were identical. The uptake of H-LpB by normal fibroblasts increased 1.5-2-times after isolation from the culture medium by immunoaffinity chromatography. The effect of isolation could be explained by the finding that apolipoprotein E-containing lipoprotein secreted by HepG2 cells effectively competed for the binding with LDL-receptors. The obtained results suggest that H-LpB produced by HepG2 cells is poorly recognized by the LDL-receptors.
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Affiliation(s)
- I V Fuki
- Institute of Experimental Cardiology, USSR Cardiology Research Center, Moscow
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25
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Weinhold PA, Charles L, Rounsifer ME, Feldman DA. Control of phosphatidylcholine synthesis in Hep G2 cells. Effect of fatty acids on the activity and immunoreactive content of choline phosphate cytidylyltransferase. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)38088-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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26
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Hussain MM, Roghani A, Cladaras C, Zanni EE, Zannis VI. Secretion of lipid-poor nascent human apolipoprotein apoAI, apoCIII, and apoE by cell clones expressing the corresponding genes. Electrophoresis 1991; 12:273-83. [PMID: 1906400 DOI: 10.1002/elps.1150120408] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The human apolipoprotein apoAI, apoCIII, and apoE genes were placed under the control of the mouse metallothionein 1 promoter in a bovine papilloma virus vector that also contained the human metallothionein 1A gene. Following transfection of mouse C127 cells with the expression vector, cell clones resistant to Cd2+ were selected and found to express in high abundance specific apolipoprotein genes. Individual cell clones expressing apoAI, apoCIII, or apoE genes were used further to study the isoprotein composition and the flotation properties of the corresponding nascent apolipoproteins. It was found that the lipoproteins secreted by cell clones expressing the apoAI, apoCIII, and apoE genes consisted of the proapoAI disialylated form of apoCIII (apoCIIIS2) and mainly sialylated forms of apoE. Separation of the secreted apolipoproteins by density gradient ultracentrifugation resulted in limited flotation of nascent apoAI, apoE and apoCIII in the high density lipoprotein (HDL) fraction. Similar analysis in the presence of human serum increased the flotation of apoAI, apoE, and apoCIII to 6.5-, 4.5-, and 5.5-fold, respectively, and resulted in their redistribution to various lipoprotein fractions. HDL increased the flotation of apoAI to 12-fold and very low density lipoprotein (VLDL) increased the flotation of apoCIII and apoE to 6.5- and 5.5-fold, respectively. These findings suggest that in the cell system used, the majority of nascent apoAI, apoCIII and apoE is secreted in the lipid-poor form, which then associates extracellularly with preexisting lipoproteins.
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Affiliation(s)
- M M Hussain
- Section of Molecular Genetics, Cardiovascular Institute, Boston University Medical Center, MA 02118
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27
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Bard JM, Candelier L, Agnani G, Clavey V, Torpier G, Steinmetz A, Fruchart JC. Isolation and characterization of human Lp-B lipoprotein containing apolipoprotein B as the sole apolipoprotein. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1082:170-6. [PMID: 2007180 DOI: 10.1016/0005-2760(91)90191-j] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A sequential immunoaffinity chromatography procedure was developed to isolate from whole normolipidemic human plasma a subpopulation of apoB containing particles (Lp-B) which is virtually free of non apoB protein. The absence of non apoB protein in Lp-B was assessed by enzyme immunoassay against apolipoproteins A-I, A-II, A-IV, E, C-III and (a). Electron microscopy and fractionation of the isolated particles by gel filtration demonstrated that these particles were heterogeneous in size. However, most of them had diameters between 18 and 26 nm. These particles were found to be rich in cholesterol (molar ratio cholesterol/apoB = 2246 +/- 995) poor in triacylglycerol (molar ratio triacylglycerol/apoB = 555 +/- 518) and had a phospholipids/apoB molar ratio of 713 +/- 348. Most of the cholesterol was esterified (66% +/- 5%). Lp-B particles bound to the apoB, E receptor of HeLa cells with a lower affinity than LDL prepared by ultracentrifugation (1.030 kg/l less than d less than 1.053 kg/l). (KD = 18.9 vs 10.5 nmol/l).
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Affiliation(s)
- J M Bard
- Serlia, INSERM U. 325, Institut Pasteur, Lille, France
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28
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Abstract
The effect of insulin on apolipoprotein (apo) B secretion was investigated in human hepatocytes. Freshly isolated hepatocytes, prepared by collagenase dispersion of liver specimens, were incubated in serum-free media in the absence and presence of 100 nmol/L insulin for 2 hours. The media was then assayed for apo B content by radioimmunoassay. In hepatocytes incubated without insulin, the secretion of apo B (relative to human low-density lipoprotein [LDL]) was 125 +/- 37 ng/10(6) cells/2 hours. In the presence of insulin, apo B secretion was reduced to 83 +/- 29 ng/10(6) cells/2 hours (34% inhibition, P less than .05). These results using human hepatocytes are consistent with previous data from our laboratory describing insulin-dependent inhibition of apo B secretion in primary cultures of rat hepatocytes and studies by others employing the human-derived hepatoma cell line, Hep G2. We conclude that human hepatic apo B secretion is under insulin control. The role of more chronic insulin exposure requires further investigation.
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Affiliation(s)
- A I Salhanick
- Department of Medicine, University of Rochester School of Medicine and Dentistry, NY 14642
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29
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Isolation and characterization of an apoA-II-containing lipoprotein (LP-A-II:B complex) from plasma very low density lipoproteins of patients with Tangier disease and type V hyperlipoproteinemia. J Lipid Res 1991. [DOI: 10.1016/s0022-2275(20)42239-4] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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30
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Adeli K, Sinkevitch C. Secretion of apolipoprotein B in serum-free cultures of human hepatoma cell line, HepG2. FEBS Lett 1990; 263:345-8. [PMID: 2185956 DOI: 10.1016/0014-5793(90)81410-p] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We have developed a defined medium which can maintain efficient growth of HepG2 cells sustaining the synthesis of a variety of plasma proteins including apolipoprotein B. This defined system was used to investigate long-term effects of insulin, estrogen, triiodothyronine, cholesterol, and oleate on the growth pattern of HepG2 cells and secretion rate of apolipoprotein B. Oleate and triiodothyronine caused significant increases in secretion of apolipoprotein B. The stimulatory effect of triiodothyronine was only observed after long (6 days) exposure of cells to the hormone. In contrast, insulin caused up to a 4-fold decrease in the secretion rate of apolipoprotein B during the early growth periods. This inhibitory effect appeared to be partially abolished after 6 days. Our data suggest that some important questions on regulation of apolipoprotein B expression can be addressed by the long-term culture of HepG2 cells in defined medium.
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Affiliation(s)
- K Adeli
- Department of Chemistry and Biochemistry, University of Windsor, Ontario, Canada
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31
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Lovastatin therapy reduces low density lipoprotein apoB levels in subjects with combined hyperlipidemia by reducing the production of apoB-containing lipoproteins: implications for the pathophysiology of apoB production. J Lipid Res 1990. [DOI: 10.1016/s0022-2275(20)42825-1] [Citation(s) in RCA: 162] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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32
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Alaupovic P, Blackenhorn DH, Knight-Gibson C, Tavella M, Bard JM, Shafer D, Lee ET, Brasuell J. apoB-containing lipoprotein particles as risk factors for coronary artery disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1990; 285:299-309. [PMID: 1858560 DOI: 10.1007/978-1-4684-5904-3_36] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- P Alaupovic
- Lipoprotein and Atherosclerosis Research Program, Oklahoma Medical Research Foundation, Oklahoma City
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33
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Dashti N, Smith EA, Alaupovic P. Increased production of apolipoprotein B and its lipoproteins by oleic acid in Caco-2 cells. J Lipid Res 1990. [DOI: 10.1016/s0022-2275(20)42765-8] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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34
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Effects of khellin and timefurone on secretion and catabolism of lipoproteins by cultured rabbit and human hepatocytes. Int J Pharm 1989. [DOI: 10.1016/0378-5173(89)90211-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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35
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Cheung MC, Lum KD, Brouillette CG, Bisgaier CL. Characterization of apoA-I-containing lipoprotein subpopulations secreted by HepG2 cells. J Lipid Res 1989. [DOI: 10.1016/s0022-2275(20)38257-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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36
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Dashti N, Koren E, Alaupovic P. Identification and partial characterization of discrete apolipoprotein A-containing lipoprotein particles secreted by human hepatoma cell line HepG2. Biochem Biophys Res Commun 1989; 163:574-80. [PMID: 2549999 DOI: 10.1016/0006-291x(89)92176-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The purpose of this study was to identify the apolipoprotein A-containing lipoprotein particles produced by HepG2 cells. The apolipoprotein A-containing lipoproteins separated from apolipoprotein B-containing lipoproteins by affinity chromatography of culture medium on concanavalin A were fractionated on an immunosorber with monoclonal antibodies to apolipoprotein A-II. The retained fraction contained apolipoproteins A-I, A-II and E, while the unretained fraction contained apolipoproteins A-I and E. Both fractions were characterized by free cholesterol as the major and triglycerides and cholesterol esters as the minor neutral lipids. Further chromatography of both fractions on an immunosorber with monoclonal antibodies to apolipoprotein A-I showed that 1) apolipoprotein A-II only occurs in association with apolipoprotein A-I, 2) apolipoprotein A-IV is only present as part of a separate lipoprotein family (lipoprotein A-IV), and 3) apolipoprotein E-enriched lipoprotein A-I:A-II and lipoprotein A-I are the main apolipoprotein A-containing lipoproteins secreted by HepG2 cells.
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Affiliation(s)
- N Dashti
- Lipoprotein and Atherosclerosis Research Program, Oklahoma Medical Research Foundation, Oklahoma City 73104
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37
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Rinninger F, Pittman RC. Mechanism of the Cholesteryl Ester Transfer Protein-mediated Uptake of High Density Lipoprotein Cholesteryl Esters by Hep G2 Cells. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)83320-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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38
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39
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Rinninger F, Pittman RC. Regulation of the selective uptake of high density lipoprotein-associated cholesteryl esters by human fibroblasts and Hep G2 hepatoma cells. J Lipid Res 1988. [DOI: 10.1016/s0022-2275(20)38450-9] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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40
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Craig WY, Nutik R, Cooper AD. Regulation of apoprotein synthesis and secretion in the human hepatoma Hep G2. The effect of exogenous lipoprotein. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68326-7] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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41
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42
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Alaupovic P, Tavella M, Bard JM, Wang CS, Attman PO, Koren E, Corder C, Knight-Gibson C, Downs D. Lipoprotein particles in hypertriglyceridemic states. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1988; 243:289-97. [PMID: 3223422 DOI: 10.1007/978-1-4613-0733-4_37] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- P Alaupovic
- Lipoprotein and Atherosclerosis Research Program, Oklahoma Medical Research Foundation, Oklahoma City 73104
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