scholarly journals Phosphatidylcholine increases the secretion of triacylglycerol-rich lipoproteins by CaCo-2 cells

1996 ◽  
Vol 314 (2) ◽  
pp. 569-575 ◽  
Author(s):  
Satya N. MATHUR ◽  
Ella BORN ◽  
Shubha MURTHY ◽  
F. Jeffrey FIELD
Keyword(s):  
Cholesteryl Ester ◽  
Secretory Pathway ◽  
Cholesterol Acyltransferase ◽  
Lipid Synthesis ◽  
Brefeldin A ◽  
Mrna Levels ◽  
Ester Synthesis ◽  
Acyltransferase Activity ◽  
Apob Mrna ◽  
Triacylglycerol Synthesis

The regulation of lipid synthesis and secretion by phosphatidylcholine was investigated in CaCo-2 cells grown on semipermeable filters. In cells incubated with 1 mM taurocholate and 100–500 μM phosphatidylcholine, cholesteryl ester synthesis was decreased, triacylglycerol synthesis was increased modestly, whereas phospholipid synthesis was unaffected. Acyl-CoA–cholesterol acyltransferase activity was decreased secondary to a decrease in the substrate (cholesterol) supply. The basolateral secretion of newly synthesized triacylglycerol and triacylglycerol mass was significantly increased by phosphatidylcholine, whereas cellular triacylglycerol mass decreased. This effect was not specific for phosphatidylcholine as phosphatidylethanolamine and phosphatidylserine also increased the secretion of newly synthesized triacylglycerols. Dioleoylphosphatidylcholine was as effective as egg phosphatidylcholine in increasing triacylglycerol transport. Dipalmitoylphosphatidylcholine, in contrast, was without effect. Phosphatidylcholine also increased the basolateral secretion of apolipoprotein B (apoB) mass without altering apoB mRNA levels. Disruption of the Golgi apparatus by monensin or brefeldin A prevented the increase in apoB secretion by phosphatidylcholine. Compared with microsomes prepared from control cells, those from cells incubated with phosphatidylcholine contained more newly synthesized apoB. The percentage of new synthesized apoB isolated from the lumen of microsomes (as an estimate of apoB destined for secretion), however, was similar in the two preparations. Thus in CaCo-2 cells incubated with phosphatidylcholine, the transport of apoB and triacylglycerols is increased whereas cholesteryl ester synthesis and secretion are decreased. A normally functioning secretory pathway is required for phosphatidylcholine to increase triacylglycerol-rich lipoprotein secretion.

Lipid synthesis in macrophages derived from the human cell line THP-1: modulation of the effects of native and oxidized chylomicron-remnant-like particles by oestrogen

2001 ◽  
Vol 101 (4) ◽  
pp. 403-413 ◽  
Author(s):  
Mariarosaria NAPOLITANO ◽  
Kelly V. BATT ◽  
Michael AVELLA ◽  
Elena BRAVO ◽  
Kathleen M. BOTHAM
Keyword(s):  
Cholesteryl Ester ◽  
Cell Line ◽  
Lipid Synthesis ◽  
Thiobarbituric Acid ◽  
Human Monocyte ◽  
Cholesterol Esterification ◽  
Chylomicron Remnant ◽  
Triacylglycerol Synthesis ◽  
Ester Formation ◽  
Chylomicron Remnants

The effects of native and oxidized chylomicron remnants on the synthesis of cholesteryl ester and triacylglycerol in macrophages, and the way that this is influenced by exposure of the cells to oestrogen, was investigated using the human monocyte cell line THP-1 and chylomicron-remnant-like particles containing human apolipoprotein E (CRLPs). Synthesis of the lipids was measured by the incorporation of [3H]oleate into cholesteryl ester and triacylglycerol. CRLPs (5-40μg of cholesterol/ml) containing either trilinolein or triolein as the triacylglycerol component caused a dose-dependent decrease in cholesteryl ester formation, while triacylglycerol production was unchanged. After oxidation of the CRLPs, the level of thiobarbituric acid-reactive substances was increased by 6.3-fold and 2.2-fold in particles containing trilinolein and triolein respectively. Furthermore, CRLPs containing oxidized trilinolein lost their ability to down-regulate cholesterol esterification, while CRLPs containing oxidized triolein did not. Both types of oxidized CRLPs decreased triacylglycerol synthesis. Treatment of the macrophages with 17β-oestradiol caused increases of approx. 94% and 34% in the synthesis of cholesteryl ester and triacylglycerol respectively in the absence of CRLPs. The differences between control and oestrogen-treated cells were abolished, however, when CRLPs (40μg of cholesterol/ml) were added to the incubations. In addition, in contrast with their lack of effect in control cells, CRLPs containing oxidized trilinolein decreased cholesterol esterification in oestrogen-treated cells by approx. 48%. These findings with CRLPs suggest that chylomicron remnants have significant effects on cholesteryl ester and triacylglycerol synthesis in macrophages, which may be modulated both by the oxidation state of the particles and by oestrogen.

scholarly journals Lysophosphatidylcholine increases the secretion of cholesteryl ester-poor triacylglycerol-rich lipoproteins by CaCo-2 cells

1994 ◽  
Vol 304 (1) ◽  
pp. 35-42 ◽  
Author(s):  
F J Field ◽  
E Born ◽  
H Chen ◽  
S Murthy ◽  
S N Mathur
Keyword(s):  
Cholesteryl Ester ◽  
Cholesterol Esterification ◽  
Ester Synthesis ◽  
Triacylglycerol Synthesis ◽  
Apoprotein B ◽  
Apob Synthesis ◽  
Mass Accumulation

To address the effect of lysophosphatidylcholine on triacylglycerol transport in intestine, CaCo-2 cells, grown on semipermeable supports, were incubated with lysophosphatidylcholine solubilized in 1 mM taurocholate. [14C]Palmitoyllysophosphatidylcholine was readily taken up and incorporated predominantly into cellular phospholipids, particularly phosphatidylcholine. Twenty-five percent of the label was found in triacylglycerols. Compared with labelled cellular phospholipids, labelled triacylglycerols were preferentially secreted. Lysophosphatidylcholine caused a profound decrease in cholesteryl ester synthesis and secretion, whereas cellular triacylglycerol mass and triacylglycerol synthesis and secretion were increased. The effect was more pronounced with oleoyllysophosphatidylcholine than with either palmitoyl- or stearyl-lysophosphatidylcholine. Lysophosphatidylcholine increased the secretion of immunoreactive and newly-synthesized apoprotein B (apoB) without altering the rate of apoB synthesis. Thus, luminal lysophosphatidylcholine and/or its uptake decreases cholesterol esterification and secretion, but increases triacylglycerol synthesis and secretion, triacylglycerol mass accumulation and the secretion of apoB by CaCo-2 cells.

Leptin biosynthetic pathway in white adipocytes

2006 ◽  
Vol 84 (2) ◽  
pp. 207-214 ◽  
Author(s):  
Philippe G Cammisotto ◽  
Ludwik J Bukowiecki ◽  
Yves Deshaies ◽  
Moise Bendayan
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
De Novo ◽  
Brefeldin A ◽  
Mrna Levels ◽  
De Novo Synthesis ◽  
Cellular Content ◽  
Constitutive Secretion

The aim of this study was to determine through morphological and biochemical means the biosynthetic and secretory pathway followed by leptin in adipocytes. Immunocytochemistry revealed the presence of leptin in the rough endoplasmic reticulum, the Golgi apparatus, and in numerous small vesicles along the plasma membrane of white adipo cytes. In vitro, isolated adipocytes under nonstimulated conditions (basal) continuously secreted leptin while their intra cellular content remained unchanged. When adipocytes were stimulated with insulin, leptin cellular content and secretion increased in parallel and were significantly different from basal secretion only after 45 min. L-leucine and L-glutamate also strongly stimulated leptin synthesis and secretion. These stimulating effects were abolished by cycloheximide and brefeldin A. The transcriptional inhibitor actinomycin D did not have any effects in either basal or stimulated conditions. Leptin mRNA levels were not affected by any stimulating or inhibiting agents. Finally, norepinephrine, isoproterenol, CL316243, and palmitate inhibited the effects of insulin, L-leucine, and L-glutamate on leptin synthesis. We thus conclude that (i) adipocytes continuously synthesize and secrete leptin along a rough endoplasmic reticulum–Golgi secretory vesicles pathway, (ii) an increase in leptin secretion requires increased de novo synthesis, and (iii) short-term leptin secretion does not involve changes in mRNA levels.Key words: leptin, vesicles, constitutive secretion, de novo synthesis, transcription.

scholarly journals Triacylglycerol and phytyl ester synthesis inSynechocystissp. PCC6803

2020 ◽  
Vol 117 (11) ◽  
pp. 6216-6222 ◽  
Author(s):  
Mohammed Aizouq ◽  
Helga Peisker ◽  
Katharina Gutbrod ◽  
Michael Melzer ◽  
Georg Hölzl ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Acyl Carrier Protein ◽  
Sequence Similarity ◽  
Wax Esters ◽  
Oxygenic Photosynthesis ◽  
Wax Ester ◽  
Ester Synthesis ◽  
Acyltransferase Activity ◽  
Storage Lipids ◽  
Triacylglycerol Synthesis

Cyanobacteria are unicellular prokaryotic algae that perform oxygenic photosynthesis, similar to plants. The cells harbor thylakoid membranes composed of lipids related to those of chloroplasts in plants to accommodate the complexes of photosynthesis. The occurrence of storage lipids, including triacylglycerol or wax esters, which are found in plants, animals, and some bacteria, nevertheless remained unclear in cyanobacteria. We show here that the cyanobacteriumSynechocystissp. PCC6803 accumulates both triacylglycerol and wax esters (fatty acid phytyl esters). Phytyl esters accumulate in higher levels under abiotic stress conditions. The analysis of an insertional mutant revealed that the acyltransferase slr2103, with sequence similarity to plant esterase/lipase/thioesterase (ELT) proteins, is essential for triacylglycerol and phytyl ester synthesis inSynechocystis. The recombinant slr2103 enzyme showed acyltransferase activity with phytol and diacylglycerol, thus producing phytyl esters and triacylglycerol. Acyl-CoA thioesters were the preferred acyl donors, while acyl-ACP (acyl carrier protein), free fatty acids, or galactolipid-bound fatty acids were poor substrates. The slr2103 protein sequence is unrelated to acyltransferases from bacteria (AtfA) or plants (DGAT1, DGAT2, PDAT), and therefore establishes an independent group of bacterial acyltransferases involved in triacylglycerol and wax ester synthesis. The identification of the geneslr2103responsible for triacylglycerol synthesis in cyanobacteria opens the possibility of using prokaryotic photosynthetic cells in biotechnological applications.

scholarly journals The unfolded protein response coordinates the production of endoplasmic reticulum protein and endoplasmic reticulum membrane.

1997 ◽  
Vol 8 (9) ◽  
pp. 1805-1814 ◽  
Author(s):  
J S Cox ◽  
R E Chapman ◽  
P Walter
Keyword(s):  
Endoplasmic Reticulum ◽  
Unfolded Protein Response ◽  
Secretory Pathway ◽  
Lipid Synthesis ◽  
Secretory Proteins ◽  
Endoplasmic Reticulum Membrane ◽  
Yeast Saccharomyces Cerevisiae ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response

The endoplasmic reticulum (ER) is a multifunctional organelle responsible for production of both lumenal and membrane components of secretory pathway compartments. Secretory proteins are folded, processed, and sorted in the ER lumen and lipid synthesis occurs on the ER membrane itself. In the yeast Saccharomyces cerevisiae, synthesis of ER components is highly regulated: the ER-resident proteins by the unfolded protein response and membrane lipid synthesis by the inositol response. We demonstrate that these two responses are intimately linked, forming different branches of the same pathway. Furthermore, we present evidence indicating that this coordinate regulation plays a role in ER biogenesis.

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