Lipoprotein assembly. Apolipoprotein B size determines lipoprotein core circumference.

Spring, Denise J.; Chen-Liu, L W; Chatterton, Jon E.; Elovson, John; Schumaker, Verne N.

doi:10.1016/s0021-9258(18)42116-3

Cited by 123 publications

(25 citation statements)

References 34 publications

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“…ApoB-containing lipoprotein assembly then occurs in a complex process with two major steps. A nascent lipoprotein particle is first formed in the rough ER (Borén et al 1992;Spring et al 1992) and then there is expansion and maturation of the lipid core of the particle in the smooth ER (Alexander et al 1976) or possibly the Golgi (Higgins 1988;Bamberger and Lane 1990). Regulation of the secretion of apoB in liver is primarily post-translational (Borchardt and Davis 1987;Dixon and Ginsberg 1993;Davis 1999).…”

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Apolipoprotein B Is Synthesized in Selected Human Non-hepatic Cell Lines But Not Processed into Mature Lipoprotein

Dixon

Biddle

et al. 2002

J Histochem Cytochem.

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We studied apolipoprotein B100 (apoB) metabolism in a series of non-hepatic cell lines (HT29 colon adenocarcinoma, HeLa cervical epithelioid carcinoma, and 1321N1J astrocytoma human cell lines) and in the human hepatoma cell line HepG2. ApoB mRNA was detected by reverse transcription polymerase chain reaction in each non-hepatic cell line. ApoB was detected in HepG2 cells by immunoprecipitation, Western blotting, and immunocytochemistry using a polyclonal anti-human low-density lipoprotein (LDL) antibody, an anti-human apoB peptide antibody, and several monoclonal anti-apoB antibodies. ApoB was identified in the three non-hepatic cell lines by each method using the anti-apoB peptide and monoclonal antibodies, but not with the anti-LDL antibody. Immunocytochemistry indicated that epitopes of apoB were evident throughout the endoplasmic reticulum, and gel mobility of newly labeled apoB and immunoblot with anti-ubiquitin showed that apoB was highly ubiquinated in non-hepatic cells. The observations that apoB is synthesized in non-hepatic cell lines but never recognized by the anti-LDL antibody suggests that apoB is not processed into a nascent lipoprotein in these cells. Immunocytochemical localization of apoB epitopes at many locations throughout non-hepatic cells raises the exciting possibility that apoB can be used for other purposes in these cells.

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confidence: 99%

Apolipoprotein B Is Synthesized in Selected Human Non-hepatic Cell Lines But Not Processed into Mature Lipoprotein

Dixon

Biddle

et al. 2002

J Histochem Cytochem.

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“…[ 35 S]methionine-labeled peptides were visualized and quantitated on the Phospho-Imager using the Image-QuaNT software (Molecular Dynamics, Sunnyvale, CA). Unlabeled apoB peptides were analyzed by immunoblotting as described ( 29), using monoclonal antibodies 1D1 or B sol 16 to detect N-or C-terminal epitopes, respectively. Triglyceride-rich lipoproteins from a normolipemic donor were obtained by centrifugation of plasma at 45,000 rpm at 20ЊC for 24 h, after which the top 2 ml was removed from each tube.…”

Section: Kinetic Gradient Ultracentrifugation Of Lipoproteins Secreted By Mca-rh7777 Cellsmentioning

confidence: 99%

“…The density of the primary particles secreted by the transfected cells was determined by isopycnic density centrifugation as previously described (16).…”

Section: Kinetic Gradient Ultracentrifugation Of Lipoproteins Secreted By Mca-rh7777 Cellsmentioning

confidence: 99%

“…VLDL assembly has been under active investigation recently, and kinetic data obtained from cell culture and rat liver studies has suggested that the assembly of apoB-100containing particles and apoB-48-containing particles follow broadly similar pathways, with at least the latter proceeding in two discrete steps (5)(6)(7)(8)(9)(10)(11)(12). The first step involves the co-translational association of elongating nascent apoB peptides with increasing amount of triglyceride, so that upon completion of translation the size of the nascent primary particle is directly proportional to the length of the resident apoB (13)(14)(15)(16)(17)(18). Actually, data from studies in HepG2 cells have shown that the length of the apoB protein Abbreviations: VLDL, very low density lipoproteins; LDL, low density lipoproteins; HDL, high density lipoproteins; IDL, intermediate density lipoproteins; MTP, microsomal triglyceride transfer protein; apoB, apolipoprotein B; ALLN, N-acetyl-leucyl-leucyl-norleucinal; DMEM, Dulbecco's modified Eagle's medium; SDS-PAGE, 5%-polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate; PMSF, phenylmethylsulfonyl sulfide; CMV, cytomegalovirus.…”

mentioning

confidence: 99%

“…equals the circumference of the core of the primary particle (16), suggesting that apoB wraps once about the core. Microsomal triglyceride transfer protein (MTP) clearly is required for normal VLDL assembly (11, 17 -20).…”

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confidence: 99%

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Rat McA-RH7777 cells efficiently assemble rat apolipoprotein B-48 or larger fragments into VLDL but not human apolipoprotein B of any size

Xiao

Elovson

Schumaker

2000

Journal of Lipid Research

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Studies of truncated apoB peptides in human subjects with familial hypobetalipoproteinemia, as well as of puromycin-generated spectra of nascent apoB peptides in rat and hamster liver, suggest that a minimum size is required for N-terminal fragments of apoB to be efficiently assembled into full-sized VLDL. We report here results of experiments undertaken to examine this phenomenon in greater detail by expressing individual carboxyl-truncated human apoB constructs in McArdle cells. Thus, apoB-29, -32, -37, -42, -47, -53, -70 and full length apoB-100 were transiently expressed in rat McA-RH7777 hepatoma cells, or human apoB-31 and apoB-53 were stably expressed in the same cells, and the secreted VLDL particles were characterized by kinetic gradient ultracentrifugal flotation. Calibration with rat plasma VLDL subfractions showed that about 90 and 50%, respectively, of lipoprotein particles containing endogenous rat B-100 and B-48 floated between fractions 2-8 of the 11-fraction gradient. This corresponds to the normal VLDL diameter range of about 47 to 28 nm, with the remaining half of rat B-48 recovered as HDL particles in the 1.1 g/ml range. In contrast, regardless of their size, only 2-5% of any of the truncated human apoB peptides expressed in these cells was recovered in the VLDL region of the gradient. The remaining 95 ؉ % of the lipoproteins were found as high density particles; as previously found in other systems the densities of the latter were inversely related to their peptide chain-length. Furthermore, transiently expressed full-length human apoB-100 was inefficiently secreted as VLDL by these cells, with the remainder appearing as LDL-sized particles. Thus, although we showed that McA-RH7777 cells secreted endogenous rat apoB as normal-sized VLDL, we found them unsuitable for our original purpose of using human apoB fragments to further define effects of apoB size on VLDL assembly. These cells appeared unable to efficiently use any size of human apoB for that process. Pulse-labeled untransfected McA-RH7777 cells chased in the presence of puromycin did, however, show a sharp decline in VLDL assembly efficiency for endogenous nascent rat apoB peptides shorter than B-48, similar to that originally found in normal rat liver. -Xiao, Q., J. Elovson, and V. N. Schumaker. Rat McA-RH7777 cells efficiently assemble rat apolipoprotein B-48 or larger fragments into VLDL but not human apolipoprotein B of any size.

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Metabolic pre‐conditioning of cultured cells in physiological levels of insulin: Generating resistance to the lipid‐accumulating effects of plasma in hepatocytes

Chan

Berthiaume

Washizu

et al. 2002

Biotech & Bioengineering

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Understanding the regulation of hepatocyte lipid metabolism is important for several biotechnological applications involving liver cells. During exposure of hepatocytes to plasma, as is the case in extracorporeal bioartificial liver assist devices, it has been reported that hepatic-specific functions, e.g., albumin and urea synthesis and diazepam removal, are dramatically compromised and hepatocytes progressively accumulate cytoplasmic lipid droplets. We hypothesized that the composition of hepatocyte culture medium significantly affects lipid metabolism during subsequent plasma exposure. Rat hepatocytes were cultured in medium containing either physiological (50 microU/mL) or supra-physiological (500 mU/mL) insulin levels for 1 week and then exposed to human plasma supplemented with or without amino acids. We found that insulin's anabolic effects, such as stimulation of triglyceride storage, were carried over from the pre-conditioning to the plasma exposure period. While hepatocytes cultured in high insulin medium accumulated large quantities of triglycerides during subsequent plasma exposure, culture in low insulin medium largely prevented lipid accumulation. Urea and albumin secretion, as well as the ammonia removal rate, were largely unaffected by insulin but increased with amino acid supplementation. Thus, hepatocyte metabolism during plasma exposure can be modulated by medium pre-conditioning and supplements added to plasma.

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Lipoprotein assembly. Apolipoprotein B size determines lipoprotein core circumference.

Cited by 123 publications

References 34 publications

Apolipoprotein B Is Synthesized in Selected Human Non-hepatic Cell Lines But Not Processed into Mature Lipoprotein

Apolipoprotein B Is Synthesized in Selected Human Non-hepatic Cell Lines But Not Processed into Mature Lipoprotein

Rat McA-RH7777 cells efficiently assemble rat apolipoprotein B-48 or larger fragments into VLDL but not human apolipoprotein B of any size

Metabolic pre‐conditioning of cultured cells in physiological levels of insulin: Generating resistance to the lipid‐accumulating effects of plasma in hepatocytes

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