scholarly journals Differential dephosphorylation of CTP:phosphocholine cytidylyltransferase upon translocation to nuclear membranes and lipid droplets

2020 ◽  
Vol 31 (10) ◽  
pp. 1047-1059 ◽  
Author(s):  
Lambert Yue ◽  
Michael J. McPhee ◽  
Kevin Gonzalez ◽  
Mark Charman ◽  
Jonghwa Lee ◽  
...  
Keyword(s):  
Lipid Droplets ◽  
Nuclear Membranes ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
P Domain ◽  
Rate Limiting ◽  
Phosphatidylcholine Synthesis ◽  
Sustained Phosphorylation

The translocation of CCTα, the rate-limiting enzyme for phosphatidylcholine synthesis, to nuclear membranes and nuclear lipid droplets results in reversible dephosphorylation of S319 and sustained phosphorylation of Y359+S362. Independent regulation of these phosphosites in the P-domain of CCTα is required for activation on nuclear membranes.

scholarly journals Induction of apoptosis by lipophilic activators of CTP:phosphocholine cytidylyltransferase α (CCTα)

2005 ◽  
Vol 392 (3) ◽  
pp. 449-456 ◽  
Author(s):  
Thomas A. Lagace ◽  
Neale D. Ridgway
Keyword(s):  
Nuclear Export ◽  
Oleyl Alcohol ◽  
Caspase Cleavage ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Transient Activation ◽  
Initial Effect ◽  
Induction Of Apoptosis ◽  
Induced Apoptosis ◽  
Rate Limiting ◽  
Phosphatidylcholine Synthesis

Farnesol (FOH) inhibits the CDP-choline pathway for PtdCho (phosphatidylcholine) synthesis, an activity that is involved in subsequent induction of apoptosis. Interestingly, the rate-limiting enzyme in this pathway, CCTα (CTP:phosphocholine cytidylyltransferase α), is rapidly activated, cleaved by caspases and exported from the nucleus during FOH-induced apoptosis. The purpose of the present study was to determine how CCTα activity and PtdCho synthesis contributed to induction of apoptosis by FOH and oleyl alcohol. Contrary to previous reports, we show that the initial effect of FOH and oleyl alcohol was a rapid (10–30 min) and transient activation of PtdCho synthesis. During this period, the mass of DAG (diacylglycerol) decreased by 40%, indicating that subsequent CDP-choline accumulation and inhibition of PtdCho synthesis could be due to substrate depletion. At later time points (>1 h), FOH and oleyl alcohol promoted caspase cleavage and nuclear export of CCTα, which was prevented by treatment with oleate or DiC8 (dioctanoylglycerol). Protection from FOH-induced apoptosis required CCTα activity and PtdCho synthesis since (i) DiC8 and oleate restored PtdCho synthesis, but not endogenous DAG levels, and (ii) partial resistance was conferred by stable overexpression of CCTα and increased PtdCho synthesis in CCTα-deficient MT58 cells. These results show that DAG depletion by FOH or oleyl alcohol could be involved in inhibition of PtdCho synthesis. However, decreased DAG was not sufficient to induce apoptosis provided nuclear CCTα and PtdCho syntheses were sustained.

scholarly journals Long-term autophagy is sustained by activation of CCTβ3 on lipid droplets

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Yuta Ogasawara ◽  
Jinglei Cheng ◽  
Tsuyako Tatematsu ◽  
Misaki Uchida ◽  
Omi Murase ◽  
...  
Keyword(s):  
Cell Survival ◽  
Lipid Droplets ◽  
Degradation Products ◽  
Osteosarcoma Cell ◽  
Prolonged Starvation ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Kennedy Pathway ◽  
Autophagic Degradation ◽  
Rate Limiting

Abstract Macroautophagy initiates by formation of isolation membranes, but the source of phospholipids for the membrane biogenesis remains elusive. Here, we show that autophagic membranes incorporate newly synthesized phosphatidylcholine, and that CTP:phosphocholine cytidylyltransferase β3 (CCTβ3), an isoform of the rate-limiting enzyme in the Kennedy pathway, plays an essential role. In starved mouse embryo fibroblasts, CCTβ3 is initially recruited to autophagic membranes, but upon prolonged starvation, it concentrates on lipid droplets that are generated from autophagic degradation products. Omegasomes and isolation membranes emanate from around those lipid droplets. Autophagy in prolonged starvation is suppressed by knockdown of CCTβ3 and is enhanced by its overexpression. This CCTβ3-dependent mechanism is also present in U2OS, an osteosarcoma cell line, and autophagy and cell survival in starvation are decreased by CCTβ3 depletion. The results demonstrate that phosphatidylcholine synthesis through CCTβ3 activation on lipid droplets is crucial for sustaining autophagy and long-term cell survival.

scholarly journals Nuclear-localized CTP:phosphocholine cytidylyltransferase α regulates phosphatidylcholine synthesis required for lipid droplet biogenesis

2015 ◽  
Vol 26 (16) ◽  
pp. 2927-2938 ◽  
Author(s):  
Adam J. Aitchison ◽  
Daniel J. Arsenault ◽  
Neale D. Ridgway
Keyword(s):  
Nuclear Envelope ◽  
Mammalian Cells ◽  
Lipid Droplets ◽  
Intestinal Epithelial ◽  
Preadipocyte Differentiation ◽  
Human Adipocyte ◽  
Rnai Silencing ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Kennedy Pathway ◽  
Phosphatidylcholine Synthesis

The reversible association of CTP:phosphocholine cytidylyltransferase α (CCTα) with membranes regulates the synthesis of phosphatidylcholine (PC) by the CDP-choline (Kennedy) pathway. Based on results with insect CCT homologues, translocation of nuclear CCTα onto cytoplasmic lipid droplets (LDs) is proposed to stimulate the synthesis of PC that is required for LD biogenesis and triacylglycerol (TAG) storage. We examined whether this regulatory mechanism applied to LD biogenesis in mammalian cells. During 3T3-L1 and human preadipocyte differentiation, CCTα expression and PC synthesis was induced. In 3T3-L1 cells, CCTα translocated from the nucleoplasm to the nuclear envelope and cytosol but did not associate with LDs. The enzyme also remained in the nucleus during human adipocyte differentiation. RNAi silencing in 3T3-L1 cells showed that CCTα regulated LD size but did not affect TAG storage or adipogenesis. LD biogenesis in nonadipocyte cell lines treated with oleate also promoted CCTα translocation to the nuclear envelope and/or cytoplasm but not LDs. In rat intestinal epithelial cells, CCTα silencing increased LD size, but LD number and TAG deposition were decreased due to oleate-induced cytotoxicity. We conclude that CCTα increases PC synthesis for LD biogenesis by translocation to the nuclear envelope and not cytoplasmic LDs.

scholarly journals The Rate-limiting Enzyme in Phosphatidylcholine Synthesis Regulates Proliferation of the Nucleoplasmic Reticulum

2005 ◽  
Vol 16 (3) ◽  
pp. 1120-1130 ◽  
Author(s):  
Thomas A. Lagace ◽  
Neale D. Ridgway
Keyword(s):  
Membrane Binding ◽  
Chinese Hamster ◽  
Lipid Synthesis ◽  
Temperature Sensitive ◽  
Direct Role ◽  
Tubule Formation ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Nucleoplasmic Reticulum ◽  
Rate Limiting

The nucleus contains a network of tubular invaginations of the nuclear envelope (NE), termed the nucleoplasmic reticulum (NR), implicated in transport, gene expression, and calcium homeostasis. Here, we show that proliferation of the NR, measured by the frequency of NE invaginations and tubules, is regulated by CTP:phosphocholine cytidylyltransferase-α (CCTα), the nuclear and rate-limiting enzyme in the CDP–choline pathway for phosphatidylcholine (PtdCho) synthesis. In Chinese hamster ovary (CHO)-K1 cells, fatty acids triggered activation and translocation of CCTα onto intranuclear tubules characteristic of the NR. This was accompanied by a twofold increase in NR tubules quantified by immunostaining for lamin A/C or the NE. CHO MT58 cells expressing a temperature-sensitive CCTα allele displayed reduced PtdCho synthesis and CCTα expression and minimal proliferation of the NR in response to oleate compared with CHO MT58 cells stably expressing CCTα. Expression of CCTα mutants in CHO58 cells revealed that both enzyme activity and membrane binding promoted NR proliferation. In support of a direct role for membrane binding in NR tubule formation, recombinant CCTα caused the deformation of liposomes into tubules in vitro. This demonstrates that a key nuclear enzyme in PtdCho synthesis coordinates lipid synthesis and membrane deformation to promote formation of a dynamic nuclear-cytoplasmic interface.

Choline glycerophospholipid biosynthesis in the guinea pig heart

1987 ◽  
Vol 65 (10) ◽  
pp. 860-868 ◽  
Author(s):  
Monika Wientzek ◽  
Ricky Y. K. Man ◽  
Patrick C. Choy
Keyword(s):  
Guinea Pig ◽  
Choline Kinase ◽  
Major Pathway ◽  
Guinea Pig Heart ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Choline Glycerophospholipids ◽  
Mammalian Liver ◽  
Rate Limiting

The aims of this study were to (i) elucidate the biosynthetic pathways for the formation of plasmenylcholine in the mammalian heart and (ii) investigate whether the control of choline glycerophospholipid production is different in hearts with high plasmenylcholine content. Guinea pig hearts were used throughout this study, since 34% of the cardiac choline glycerophospholipids in this species is present in the plasmenylcholine form. By perfusion of the guinea pig heart in the Langendorff mode with labeled choline, we demonstrated that the majority of plasmenylcholine in the heart was synthesized via the CDP-choline pathway. The ability of the heart to form plasmenylcholine from CDP-choline and 1-alkenyl-2-acylglycerol was also shown. We postulate that 1-alkenyl-2-acylglycerol in the guinea pig heart might originate from the hydrolysis of plasmenylethanolamine. In mammalian liver and other tissues, the CDP-choline pathway is the major pathway for phosphatidylcholine biosynthesis and the rate-limiting step is catalyzed by CTP:phosphocholine cytidylyltransferase. The results obtained from the present study support this supposition. In addition, evidence was obtained indicating that phosphorylation of choline by choline kinase in the CDP-choline pathway may also be rate limiting. Although the involvement of choline kinase as a rate-limiting enzyme in the CDP-choline pathway has been shown in a number of cell cultures, the rate-limiting role of this enzyme in intact mammalian organs has not been previously reported. The rationale for the presence of more than one rate-limiting step in the CDP-choline pathway in the guinea pig heart remains undefined.

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