CTP:phosphocholine cytidylyltransferase

Kent, Claudia

doi:10.1016/s0005-2760(97)00112-4

Cited by 203 publications

(195 citation statements)

References 104 publications

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“…This suggests that the reaction catalysed by EPT, the enzyme transferring the phosphoethanolamine moiety from CDPethanolamine to DAG to form PtdEtn, could not keep pace with the reaction catalysed by ECT. Although the last enzymes in the Kennedy pathways for PtdCho and PtdEtn synthesis do not normally determine the rate of phospholipid synthesis, earlier studies have shown that regulation at these steps can contribute to overall PtdCho and PtdEtn synthesis [3,17,42,43]. Two mammalian choline-/ ethanolaminephosphotransferases, encoding cDNAs CPT1 and CEPT1, have been cloned [44,45].…”

Section: Discussionmentioning

confidence: 99%

“…Enzyme-release measurements from digitonin-permeabilized hepatocytes [15] and differential centrifugation studies [15,16] have revealed that ECT is a cytosolic enzyme. These findings make it unlikely that a reversible translocation mechanism similar to that proposed for CCT (CTP:phosphocholine cytidylyltransferase), the rate-limiting enzyme in the CDPcholine pathway [1,17,18], is involved in controlling ECT activity. However, van Hellemond et al [19] did observe a bimodal distribution of ECT between the rough ER (endoplasmic reticulum) and the cytosol.…”

Section: Introductionmentioning

confidence: 96%

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Control of the CDPethanolamine pathway in mammalian cells: effect of CTP:phosphoethanolamine cytidylyltransferase overexpression and the amount of intracellular diacylglycerol

Bleijerveld

Klein

Vaandrager

et al. 2004

Biochemical Journal

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For an insight regarding the control of PtdEtn (phosphatidylethanolamine) synthesis via the CDPethanolamine pathway, rat liver cDNA encoding ECT (CTP:phosphoethanolamine cytidylyltransferase) was transiently or stably transfected in Chinesehamster ovary cells and a rat liver-derived cell line (McA-RH7777), resulting in a maximum of 26-and 4-fold increase in specific activity of ECT respectively. However, no effect of ECT overexpression on the rate of [ 3 H]ethanolamine incorporation into PtdEtn was detected in both cell lines. This was explored further in cells overexpressing four times ECT activity (McA-ECT1). The rate of PtdEtn breakdown and PtdEtn mass were not changed in McA-ECT1 cells in comparison with controltransfected cells. Instead, an accumulation of CDPethanolamine (label and mass) was observed, suggesting that in McA-ECT1 cells the ethanolaminephosphotransferase-catalysed reaction became rate-limiting. However, overexpression of the human choline/ethanolaminephosphotransferase in McA-ECT1 and control-transfected cells had no effect on PtdEtn synthesis. To investigate whether the availability of DAG (diacylglycerol) limited PtdEtn synthesis in these cells, intracellular DAG levels were increased using PMA or phospholipase C. Exposure of cells to PMA or phospholipase C stimulated PtdEtn synthesis and this effect was much more pronounced in McA-ECT1 than in controltransfected cells. In line with this, the DAG produced after PMA exposure was consumed more rapidly in McA-ECT1 cells and the CDPethanolamine level decreased accordingly. In conclusion, our results suggest that the supply of CDPethanolamine, via the expression level of ECT, is an important factor governing the rate of PtdEtn biosynthesis in mammalian cells, under the condition that the amount of DAG is not limiting.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Control of the CDPethanolamine pathway in mammalian cells: effect of CTP:phosphoethanolamine cytidylyltransferase overexpression and the amount of intracellular diacylglycerol

Bleijerveld

Klein

Vaandrager

et al. 2004

Biochemical Journal

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“…PC 1 is the most abundant phospholipid in the membranes of eukaryotic cells (1)(2)(3)(4). It serves as a structural component of the membrane and as a source of bioactive lipids (e.g.…”

mentioning

confidence: 99%

Regulation of Phospholipid Synthesis in the Yeast cki1Δ eki1Δ Mutant Defective in the Kennedy Pathway

Choi

Sreenivas

Han

et al. 2004

Journal of Biological Chemistry

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In the yeast Saccharomyces cerevisiae, the most abundant phospholipid phosphatidylcholine is synthesized by the complementary CDP-diacylglycerol and Kennedy pathways. Using a cki1⌬ eki1⌬ mutant defective in choline kinase and ethanolamine kinase, we examined the consequences of a block in the Kennedy pathway on the regulation of phosphatidylcholine synthesis by the CDP-diacylglycerol pathway. The cki1⌬ eki1⌬ mutant exhibited increases in the synthesis of phosphatidylserine, phosphatidylethanolamine, and phosphatidylcholine via the CDP-diacylglycerol pathway. The increase in phospholipid synthesis correlated with increased activity levels of the CDPdiacylglycerol pathway enzymes phosphatidylserine synthase, phosphatidylserine decarboxylase, phosphatidylethanolamine methyltransferase, and phospholipid methyltransferase. However, other enzyme activities, including phosphatidylinositol synthase and phosphatidate phosphatase, were not affected in the cki1⌬ eki1⌬ mutant. For phosphatidylserine synthase, the enzyme catalyzing the committed step in the pathway, activity was regulated by increases in the levels of mRNA and protein. Decay analysis of CHO1 mRNA indicated that a dramatic increase in transcript stability was a major component responsible for the elevated level of phosphatidylserine synthase. These results revealed a novel mechanism that controls phospholipid synthesis in yeast.PC 1 is the most abundant phospholipid in the membranes of eukaryotic cells (1-4). It serves as a structural component of the membrane and as a source of bioactive lipids (e.g. lyso-PC, PA, DAG) (1-5). The importance of PC is underscored by the fact that alterations in its metabolism are linked to apoptosis (6 -9) and oncogenic transformation (10 -12). In the model eukaryote Saccharomyces cerevisiae, PC is synthesized by complementary pathways that are common to those found in mammalian cells 2 ( Fig. 1) (1,4,(13)(14)(15)(16)(17). In the CDP-DAG pathway, PC is synthesized from CDP-DAG via the reactions catalyzed by PS synthase (18 -20), PS decarboxylase (21-23), PE methyltransferase (24, 25), and phospholipid methyltransferase (24,26). In the CDP-choline branch of the Kennedy pathway, PC is synthesized from choline via the reactions catalyzed by choline kinase (27), phosphocholine cytidylyltransferase (28), and choline phosphotransferase (29,30). Analyses of mutations in S. cerevisiae (4, 31, 32), as well as in mammalian cells (33,34) indicate that the physiological role(s) of PC synthesized by the two pathways are different.The contribution of the CDP-DAG and Kennedy pathways for PC synthesis in wild type S. cerevisiae is dependent on the exogenous supply of choline (35). When grown in the presence of choline, yeast primarily synthesizes PC via the Kennedy pathway (35). On the other hand, when cells are grown in the absence of choline, PC is primarily synthesized via the CDP-DAG pathway (35). Yet, even under this growth condition, the Kennedy pathway still contributes to the synthesis of PC (36 -41). The choline required for the Kenne...

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“…All eukaryotic cells synthesize phosphatidylcholine (PC) 1 , which has an integral role in membrane ultrastructure and intracellular signaling (1,2). In hepatocytes, an additional and substantial demand is imposed on the PC pool by the liverspecific functions of bile and very low density lipoprotein (VLDL) particle production and secretion (3,4).…”

mentioning

confidence: 99%

“…The phosphatidylethanolamine N-methyltransferase (PEMT) and CDP-choline biosynthetic pathways mediate continual replenishment of the hepatic PC pools (5). The liver is the primary site of PEMT activity whereas the enzymes of the CDP-choline pathway are active in all nucleated cells (2,6).…”

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confidence: 99%

Membrane Topography of Human Phosphatidylethanolamine N-Methyltransferase

Shields¹,

Lehner²,

Agellon³

et al. 2003

Journal of Biological Chemistry

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In liver, phosphatidylethanolamine is converted to phosphatidylcholine through a series of three sequential methylation reactions. Phosphatidylethanolamine N-methyltransferase (PEMT) catalyzes each transmethylation reaction, and S-adenosylmethionine is the methyl group donor. Biochemical analysis of human liver revealed that the methyltransferase activity is primarily localized to the endoplasmic reticulum and mitochondria-associated membranes. Bioinformatic analysis of the predicted amino acid sequence suggested that the enzyme adopts a polytopic conformation in those membranes. To elucidate the precise membrane topography of PEMT and thereby provide the basis for in-depth functional characterization of the enzyme, we performed endoproteinase-protection analysis of epitopetagged, recombinant protein. Our data suggest a topographical model of PEMT in which four transmembrane regions span the membrane such that both the N and C termini of the enzyme are localized external to the ER. Two hydrophilic connecting loops protrude into the luminal space of the microsomes whereas a corresponding loop on the cytosolic side remains proximate to the membrane. Further support for this model was obtained following endoproteinase-protection analysis of mutant recombinant PEMT derivatives in which specific protease cleavage sites had been genetically engineered or ablated.

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CTP:phosphocholine cytidylyltransferase

Cited by 203 publications

References 104 publications

Control of the CDPethanolamine pathway in mammalian cells: effect of CTP:phosphoethanolamine cytidylyltransferase overexpression and the amount of intracellular diacylglycerol

Control of the CDPethanolamine pathway in mammalian cells: effect of CTP:phosphoethanolamine cytidylyltransferase overexpression and the amount of intracellular diacylglycerol

Regulation of Phospholipid Synthesis in the Yeast cki1Δ eki1Δ Mutant Defective in the Kennedy Pathway

Membrane Topography of Human Phosphatidylethanolamine N-Methyltransferase

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