Search PubMed⌕ Search
Home/Archive/PubMed

PubMed · 9469590

Interleukin-1beta and interleukin-6 increase levels of apolipoprotein B mRNA and decrease accumulation of its protein in culture medium of HepG2 cells.

K Yokoyama·T Ishibashi·L Yi-qiang·A Nagayoshi·T Teramoto·Y Maruyama
View original source ↗Export metadata ↓

Abstract

The purpose of the present study was to examine the regulation of levels of apolipoprotein B (apoB) mRNA and its protein by cytokines in HepG2 cells. A dose-dependent increase in apoB mRNA levels was observed in the presence of either interleukin-1beta (IL-1beta) or IL-6 alone. This increase occurred as early as 1 h after IL-1beta or IL-6 stimulation. Exogenous addition of IL-1beta (5 ng/ml) and IL-6 (50 ng/ml) induced 2.8- and 2.1-fold increases as a result of 18 h of culture, respectively. Co-stimulation with IL-1beta and IL-6 significantly enhanced the increase in apoB mRNA levels stimulated with either cytokine alone. Treatment with cycloheximide prevented the induction of apoB mRNA by IL-1beta, but not by IL-6. These findings suggest that enhancement of apoB mRNA levels by these cytokines is mediated through different pathways. Conversely, IL-1beta and IL-6 lowered the accumulation of apoB protein levels in the culture medium. The pulse-chase study showed that addition of N-acetyl leucyl leucyl norleucinal to the medium induced a decrease in newly synthesized apoB in the cell lysate in response to IL-1beta (P < 0.05) or IL-6 (not to a significant extent) compared with control. These findings demonstrated that the lower level of apoB in the medium was caused by the enhanced intracellular degradation. In addition, IL-1beta increased LDL receptor mRNA levels as well as protein activity, although IL-6 did not, suggesting that the more marked decrease in apoB accumulation in the medium induced by IL-1beta compared with that induced by IL-6 may reflect an increased uptake of apoB from the medium by IL-1beta. The present study demonstrates that a cytokine network may be involved in the metabolism of apoB under certain conditions such as inflammation.

Explore related subjects

Apolipoproteins BCulture Media, ConditionedCycloheximideHepatoblastomaHumansInterleukin-1Interleukin-6Iodine RadioisotopesLipoproteins, LDLLiver NeoplasmsProtein Synthesis InhibitorsRNA, MessengerReceptors, LDLTumor Cells, CulturedJournal ArticleResearch Support, Non-U.S. Gov't

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

K Yokoyama, T Ishibashi, L Yi-qiang, A Nagayoshi, T Teramoto, Y Maruyama. 1998. Interleukin-1beta and interleukin-6 increase levels of apolipoprotein B mRNA and decrease accumulation of its protein in culture medium of HepG2 cells.. https://pubmed.ncbi.nlm.nih.gov/9469590/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2006

Genetic defects causing familial hypercholesterolaemia: identification of deletions and duplications in the LDL-receptor gene and summary of all mutations found in patients attending the Hammersmith Hospital Lipid Clinic.

Familial hypercholesterolaemia (FH) results from defective catabolism of low density lipoproteins (LDL), leading to premature atherosclerosis and early coronary heart disease. It is commonly caused by mutations in LDLR, encoding the LDL receptor that mediates hepatic uptake of LDL, or in APOB, encoding its major ligand. More rarely, dominant mutations in PCSK9 or recessive mutations in LDLRAP1 (ARH) cause FH, gene defects that also affect the LDL-receptor pathway. We have used multiplex ligation-dependent probe amplification (MLPA) to identify deletions and rearrangements in LDLR, some not detectable by Southern blotting, thus completing our screening for mutations causing FH in a group of FH patients referred to a Lipid Clinic in London. To summarise, mutations in LDLR were found in 153 unrelated heterozygous FH patients and 24 homozygotes/compound heterozygotes, and in over 200 relatives of 80 index patients. LDLR mutations included 85 different point mutations (7 not previously described) and 13 different large rearrangements. The APOB R3500Q mutation was present in 14 heterozygous patients and a mutation in PCSK9 in another 4; LDLRAP1 mutations were found in 4 "homozygous" FH patients. Our data confirm that DNA-based diagnosis provides information that is important for management of FH in a considerable number of families.

Apolipoproteins B↗
PubMed2006

Proteasomal and autophagic pathways converge on lipid droplets.

Apolipoprotein B (apoB) is the primary protein of very low-density lipoproteins (VLDL). We found that apoB accumulated on the surface of cytoplasmic lipid droplets (LDs) of hepatocytes when the proteasomal or autophagic processes were suppressed. ApoB associated with LDs was poly-ubiquitinated and surrounded by autophagic vacuoles. Moreover, proteasomal subunits were concentrated around LDs. Our data suggest that apoB that is destined to be degraded remains adhered to LDs until it is broken down by the proteasomal and autophagic pathways. We speculate that the LD surface serves as a platform to prevent hydrophobic apoB from forming aggregates, and that LDs may play a similar role for other aggregation-prone hydrophobic proteins.

Apolipoproteins B↗
PubMed2006

Defining lipid-interacting domains in the N-terminal region of apolipoprotein B.

Apolipoprotein B (apoB) is a nonexchangeable apolipoprotein that dictates the synthesis of chylomicrons and very low density lipoproteins. ApoB is the major protein in low density lipoprotein, also known as the "bad cholesterol" that is directly implicated in atherosclerosis. It has been suggested that the N-terminal domain of apoB plays a critical role in the formation of apoB-containing lipoproteins through the initial recruitment of phospholipids in the endoplasmic reticulum. However, very little is known about the mechanism of lipoprotein nucleation by apoB. Here we demonstrate that a strong phospholipid remodeling function is associated with the predicted alpha-helical and C-sheet domains in the N-terminal 17% of apoB (B17). Using dimyristoylphosphatidylcholine (DMPC) as a model lipid, these domains can convert multilamellar DMPC vesicles into discoidal-shaped particles. The nascent particles reconstituted from different apoB domains are distinctive and compositionally homogeneous. This phospholipid remodeling activity is also observed with egg phosphatidylcholine (egg PC) and is therefore not DMPC-dependent. Using kinetic analysis of the DMPC clearance assay, we show that the identified phospholipid binding sequences all map to the surface of the lipid binding pocket in the B17 model based on the homologous protein, lipovitellin. Since both B17 and microsomal triglyceride transfer protein (MTP), a critical chaperone during lipoprotein assembly, are homologous with lipovitellin, the identification of these phospholipid remodeling sequences in B17 provides important insights into the potential mechanism that initiates the assembly of apoB-containing lipoproteins.

Apolipoproteins B↗