1
|
Rosas LE, Doolittle LM, Joseph LM, El-Musa H, Novotny MV, Hickman-Davis JM, Hite RD, Davis IC. Postexposure Liponucleotide Prophylaxis and Treatment Attenuates Acute Respiratory Distress Syndrome in Influenza-infected Mice. Am J Respir Cell Mol Biol 2021; 64:677-686. [PMID: 33606602 DOI: 10.1165/rcmb.2020-0465oc] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
There is an urgent need for new drugs for patients with acute respiratory distress syndrome (ARDS), including those with coronavirus disease (COVID-19). ARDS in influenza-infected mice is associated with reduced concentrations of liponucleotides (essential precursors for de novo phospholipid synthesis) in alveolar type II (ATII) epithelial cells. Because surfactant phospholipid synthesis is a primary function of ATII cells, we hypothesized that disrupting this process could contribute significantly to the pathogenesis of influenza-induced ARDS. The goal of this study was to determine whether parenteral liponucleotide supplementation can attenuate ARDS. C57BL/6 mice inoculated intranasally with 10,000 plaque-forming units/mouse of H1N1 influenza A/WSN/33 virus were treated with CDP (cytidine 5'-diphospho)-choline (100 μg/mouse i.p.) ± CDP -diacylglycerol 16:0/16:0 (10 μg/mouse i.p.) once daily from 1 to 5 days after inoculation (to model postexposure influenza prophylaxis) or as a single dose on Day 5 (to model treatment of patients with ongoing influenza-induced ARDS). Daily postexposure prophylaxis with CDP-choline attenuated influenza-induced hypoxemia, pulmonary edema, alterations in lung mechanics, impairment of alveolar fluid clearance, and pulmonary inflammation without altering viral replication. These effects were not recapitulated by the daily administration of CTP (cytidine triphosphate) and/or choline. Daily coadministration of CDP-diacylglycerol significantly enhanced the beneficial effects of CDP-choline and also modified the ATII cell lipidome, reversing the infection-induced decrease in phosphatidylcholine and increasing concentrations of most other lipid classes in ATII cells. Single-dose treatment with both liponucleotides at 5 days after inoculation also attenuated hypoxemia, altered lung mechanics, and inflammation. Overall, our data show that liponucleotides act rapidly to reduce disease severity in mice with severe influenza-induced ARDS.
Collapse
Affiliation(s)
| | | | | | | | - Michael V Novotny
- Department of Immunology and Inflammation, Cleveland Clinic, Cleveland, Ohio; and
| | - Judy M Hickman-Davis
- Department of Veterinary Preventive Medicine, The Ohio State University, Columbus, Ohio
| | - R Duncan Hite
- Division of Pulmonary, Critical Care, and Sleep Medicine, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio
| | | |
Collapse
|
2
|
Jin N, Jin N, Wang Z, Liu L, Meng L, Li D, Li X, Zhou D, Liu J, Bu W, Sun H, Yang B. Osteopromotive carbon dots promote bone regeneration through the PERK-eIF2α-ATF4 pathway. Biomater Sci 2021; 8:2840-2852. [PMID: 32307492 DOI: 10.1039/d0bm00424c] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Bone defects are still an unsolved clinical issue that must be overcome. Carbon dots have shown very promising effects in biological therapy. In the current study, we explored their effects on osteogenesis. Furthermore, we revealed the mechanisms in order to develop novel therapeutic approaches to manage the bone defect. For this study, ascorbic acid carbon dots (CDs) were created by a one-step microwave-assisted method. Results showed that the CDs effectively enhanced matrix mineralization, promoted osteogenic differentiation in vitro, and promoted new bone regeneration in the skull defect model in vivo. Furthermore, our data demonstrated that the ER stress and PERK-eIF2α-ATF4 pathway were activated by the CD-induced increase in intracellular calcium. Taken together, our findings suggest that the PERK pathway plays a critical role in CD-induced osteogenic differentiation, and the CDs created herein have the potential to be used to repair bone defects in clinical practice.
Collapse
Affiliation(s)
- Nianqiang Jin
- Department of Oral Pathology, School and Hospital of Stomatology, China Medical University, 110001, Shenyang, China.
| | - Nuo Jin
- Department of Oral Pathology, School and Hospital of Stomatology, China Medical University, 110001, Shenyang, China.
| | - Zilin Wang
- Department of Oral Pathology, School and Hospital of Stomatology, Jilin University, 130000, Changchun, China.
| | - Lili Liu
- Department of Oral Pathology, School and Hospital of Stomatology, Jilin University, 130000, Changchun, China.
| | - Lin Meng
- Department of Oral Pathology, School and Hospital of Stomatology, Jilin University, 130000, Changchun, China.
| | - Daowei Li
- Jilin Provincial Key Laboratory of Tooth Development and Bone Remodeling, School of Stomatology, Jilin University, Changchun, 130021, China.
| | - Xing Li
- Department of Oral Pathology, School and Hospital of Stomatology, China Medical University, 110001, Shenyang, China.
| | - Dabo Zhou
- School and Hospital of Stomatology, China Medical University, 117 Nanjing North Street, Shenyang, 110001, China.
| | - Jie Liu
- Department of Head and Neck Tumor Surgery, School of Stomatology, Wuhan University, Wuhan, 430000, China.
| | - Wenhuan Bu
- Department of Dental Materials, School of Stomatology, China Medical University, Shenyang 110001, China. and Department of Center Laboratory, School of Stomatology, China Medical University, Shenyang 110001, China
| | - Hongchen Sun
- Department of Oral Pathology, School and Hospital of Stomatology, China Medical University, 110001, Shenyang, China.
| | - Bai Yang
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, 130012, Changchun, China
| |
Collapse
|
3
|
Izrael R, Marton L, Nagy GN, Pálinkás HL, Kucsma N, Vértessy BG. Identification of a nuclear localization signal in the Plasmodium falciparum CTP: phosphocholine cytidylyltransferase enzyme. Sci Rep 2020; 10:19739. [PMID: 33184408 PMCID: PMC7665022 DOI: 10.1038/s41598-020-76829-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Accepted: 11/02/2020] [Indexed: 12/30/2022] Open
Abstract
The phospholipid biosynthesis of the malaria parasite, Plasmodium falciparum is a key process for its survival and its inhibition is a validated antimalarial therapeutic approach. The second and rate-limiting step of the de novo phosphatidylcholine biosynthesis is catalysed by CTP: phosphocholine cytidylyltransferase (PfCCT), which has a key regulatory function within the pathway. Here, we investigate the functional impact of the key structural differences and their respective role in the structurally unique pseudo-heterodimer PfCCT protein in a heterologous cellular context using the thermosensitive CCT-mutant CHO-MT58 cell line. We found that a Plasmodium-specific lysine-rich insertion within the catalytic domain of PfCCT acts as a nuclear localization signal and its deletion decreases the nuclear propensity of the protein in the model cell line. We further showed that the putative membrane-binding domain also affected the nuclear localization of the protein. Moreover, activation of phosphatidylcholine biosynthesis by phospholipase C treatment induces the partial nuclear-to-cytoplasmic translocation of PfCCT. We additionally investigated the cellular function of several PfCCT truncated constructs in a CHO-MT58 based rescue assay. In absence of the endogenous CCT activity we observed that truncated constructs lacking the lysine-rich insertion, or the membrane-binding domain provided similar cell survival ratio as the full length PfCCT protein.
Collapse
Affiliation(s)
- Richard Izrael
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary.
- Doctoral School of Multidisciplinary Medical Sciences, University of Szeged, 6720, Szeged, Hungary.
- Department of Applied Biotechnology, Budapest University of Technology and Economics, 1111, Budapest, Hungary.
| | - Lívia Marton
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary
| | - Gergely N Nagy
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary
- Department of Applied Biotechnology, Budapest University of Technology and Economics, 1111, Budapest, Hungary
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, OX3 7BN, UK
| | - Hajnalka L Pálinkás
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary
- Doctoral School of Multidisciplinary Medical Sciences, University of Szeged, 6720, Szeged, Hungary
- Department of Applied Biotechnology, Budapest University of Technology and Economics, 1111, Budapest, Hungary
| | - Nóra Kucsma
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary
| | - Beáta G Vértessy
- Institute of Enzymology, Research Centre for Natural Sciences, 1117, Budapest, Hungary.
- Department of Applied Biotechnology, Budapest University of Technology and Economics, 1111, Budapest, Hungary.
| |
Collapse
|
4
|
Cornell RB. Membrane Lipids Assist Catalysis by CTP: Phosphocholine Cytidylyltransferase. J Mol Biol 2020; 432:5023-5042. [PMID: 32234309 DOI: 10.1016/j.jmb.2020.03.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 03/22/2020] [Accepted: 03/25/2020] [Indexed: 02/06/2023]
Abstract
While most of the articles in this issue review the workings of integral membrane enzymes, in this review, we describe the catalytic mechanism of an enzyme that contains a soluble catalytic domain but appears to catalyze its reaction on the membrane surface, anchored and assisted by a separate regulatory amphipathic helical domain and inter-domain linker. Membrane partitioning of CTP: phosphocholine cytidylyltransferase (CCT), a key regulatory enzyme of phosphatidylcholine metabolism, is regulated chiefly by changes in membrane phospholipid composition, and boosts the enzyme's catalytic efficiency >200-fold. Catalytic enhancement by membrane binding involves the displacement of an auto-inhibitory helix from the active site entrance-way and promotion of a new conformational ensemble for the inter-domain, allosteric linker that has an active role in the catalytic cycle. We describe the evidence for close contact between membrane lipid, a compact allosteric linker, and the CCT active site, and discuss potential ways that this interaction enhances catalysis.
Collapse
Affiliation(s)
- Rosemary B Cornell
- Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, Canada V5A-1S6.
| |
Collapse
|
5
|
Yeganeh B, Lee J, Bilodeau C, Lok I, Ermini L, Ackerley C, Caniggia I, Tibboel J, Kroon A, Post M. Acid Sphingomyelinase Inhibition Attenuates Cell Death in Mechanically Ventilated Newborn Rat Lung. Am J Respir Crit Care Med 2020; 199:760-772. [PMID: 30326731 DOI: 10.1164/rccm.201803-0583oc] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
RATIONALE Premature infants subjected to mechanical ventilation (MV) are prone to lung injury that may result in bronchopulmonary dysplasia. MV causes epithelial cell death and halts alveolar development. The exact mechanism of MV-induced epithelial cell death is unknown. OBJECTIVES To determine the contribution of autophagy to MV-induced epithelial cell death in newborn rat lungs. METHODS Newborn rat lungs and fetal rat lung epithelial (FRLE) cells were exposed to MV and cyclic stretch, respectively, and were then analyzed by immunoblotting and mass spectrometry for autophagy, apoptosis, and bioactive sphingolipids. MEASUREMENTS AND MAIN RESULTS Both MV and stretch first induce autophagy (ATG 5-12 [autophagy related 5-12] and LC3B-II [microtubule-associated proteins 1A/1B light chain 3B-II] formation) followed by extrinsic apoptosis (cleaved CASP8/3 [caspase-8/3] and PARP [poly(ADP-ribose) polymerase] formation). Stretch-induced apoptosis was attenuated by inhibiting autophagy. Coimmunoprecipitation revealed that stretch promoted an interaction between LC3B and the FAS (first apoptosis signal) cell death receptor in FRLE cells. Ceramide levels, in particular C16 ceramide, were rapidly elevated in response to ventilation and stretch, and C16 ceramide treatment of FRLE cells induced autophagy and apoptosis in a temporal pattern similar to that seen with MV and stretch. SMPD1 (sphingomyelin phosphodiesterase 1) was activated by ventilation and stretch, and its inhibition prevented ceramide production, LC3B-II formation, LC3B/first apoptosis signal interaction, caspase-3 activation, and, ultimately, FLRE cell death. SMPD1 inhibition also attenuated ventilation-induced autophagy and apoptosis in newborn rats. CONCLUSIONS Ventilation-induced ceramides promote autophagy-mediated cell death, and identifies SMPD1 as a potential therapeutic target for the treatment of ventilation-induced lung injury in newborns.
Collapse
Affiliation(s)
- Behzad Yeganeh
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Joyce Lee
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada.,2 Institute of Medical Science and
| | - Claudia Bilodeau
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada.,3 Department of Laboratory Medicine and Pathobiology, University of Toronto, Ontario, Canada
| | - Irene Lok
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Leonardo Ermini
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Cameron Ackerley
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Isabella Caniggia
- 4 Mount Sinai Hospital, the Lunenfeld-Tanenbaum Research Institute, Toronto, Ontario, Canada; and
| | - Jeroen Tibboel
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada.,5 Department of Pediatrics, Erasmus MC-Sophia, Rotterdam, the Netherlands
| | - Andre Kroon
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada.,5 Department of Pediatrics, Erasmus MC-Sophia, Rotterdam, the Netherlands
| | - Martin Post
- 1 Translational Medicine Program, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Ontario, Canada.,2 Institute of Medical Science and
| |
Collapse
|
6
|
Abstract
Enzyme control by their products facilitates cellular homeostasis, but for phospholipids, feedback mechanisms also arise from changes in membrane physical properties. In this issue of Developmental Cell, Haider et al. (2018) show that in many actively growing cells, an enzyme of phosphatidylcholine synthesis senses lipid packing in the nuclear membrane.
Collapse
Affiliation(s)
- Rosemary Cornell
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC V5A-1S6, Canada.
| | - Bruno Antonny
- Université Côte d'Azur, CNRS, IPMC, 06560 Valbonne, France.
| |
Collapse
|
7
|
Lagace TA. Phosphatidylcholine: Greasing the Cholesterol Transport Machinery. Lipid Insights 2016; 8:65-73. [PMID: 27081313 PMCID: PMC4821435 DOI: 10.4137/lpi.s31746] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Revised: 02/26/2016] [Accepted: 02/23/2016] [Indexed: 01/19/2023] Open
Abstract
Negative feedback regulation of cholesterol metabolism in mammalian cells ensures a proper balance of cholesterol with other membrane lipids, principal among these being the major phospholipid phosphatidylcholine (PC). Processes such as cholesterol biosynthesis and efflux, cholesteryl ester storage in lipid droplets, and uptake of plasma lipoproteins are tuned to the cholesterol/PC ratio. Cholesterol-loaded macrophages in atherosclerotic lesions display increased PC biosynthesis that buffers against elevated cholesterol levels and may also facilitate cholesterol trafficking to enhance cholesterol sensing and efflux. These same mechanisms could play a generic role in homeostatic responses to acute changes in membrane free cholesterol levels. Here, I discuss the established and emerging roles of PC metabolism in promoting intracellular cholesterol trafficking and membrane lipid homeostasis.
Collapse
Affiliation(s)
- Thomas A Lagace
- Department of Pathology and Laboratory Medicine, University of Ottawa Heart Institute, Ottawa, ON, Canada
| |
Collapse
|
8
|
Participation of prostaglandin D2 in the mobilization of the nuclear-localized CTP:phosphocholine cytidylyltransferase alpha in renal epithelial cells. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:513-23. [PMID: 27032756 DOI: 10.1016/j.bbalip.2016.03.025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 03/03/2016] [Accepted: 03/22/2016] [Indexed: 01/24/2023]
Abstract
Phosphatidylcholine (PC) is the main constituent of mammalian cell membranes. Consequently, preservation of membrane PC content and composition - PC homeostasis - is crucial to maintain cellular life. PC biosynthetic pathway is generally controlled by CTP:phosphocholine cytidylyltransferase (CCT), which is considered the rate-limiting enzyme. CCTα is an amphitropic protein, whose enzymatic activity is commonly associated with endoplasmic reticulum redistribution. However, most of the enzyme is located inside the nuclei. Here, we demonstrate that CCTα is the most abundant isoform in renal collecting duct cells, and its redistribution is dependent on endogenous prostaglandins. Previously we have demonstrated that PC synthesis was inhibited by indomethacin (Indo) treatment, and this effect was reverted by exogenous PGD(2). In this work we found that Indo induced CCTα distribution into intranuclear Lamin A/C foci. Exogenous PGD(2) reverted this effect by inducing CCTα redistribution to nuclear envelope, suggesting that PGD(2) maintains PC synthesis by CCTα mobilization. Interestingly, we found that the effect of PGD(2) was dependent on ERK1/2 activation. In conclusion, our previous observations and the present results lead us to suggest that papillary cells possess the ability to maintain their structural integrity through the synthesis of their own survival molecule, PGD(2), by modulating CCTα intracellular location.
Collapse
|
9
|
Membrane lipid compositional sensing by the inducible amphipathic helix of CCT. Biochim Biophys Acta Mol Cell Biol Lipids 2015; 1861:847-861. [PMID: 26747646 DOI: 10.1016/j.bbalip.2015.12.022] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 12/22/2015] [Accepted: 12/29/2015] [Indexed: 11/21/2022]
Abstract
The amphipathic helical (AH) membrane binding motif is recognized as a major device for lipid compositional sensing. We explore the function and mechanism of sensing by the lipid biosynthetic enzyme, CTP:phosphocholine cytidylyltransferase (CCT). As the regulatory enzyme in phosphatidylcholine (PC) synthesis, CCT contributes to membrane PC homeostasis. CCT directly binds and inserts into the surface of bilayers that are deficient in PC and therefore enriched in lipids that enhance surface charge and/or create lipid packing voids. These two membrane physical properties induce the folding of the CCT M domain into a ≥60 residue AH. Membrane binding activates catalysis by a mechanism that has been partially deciphered. We review the evidence for CCT compositional sensing, and the membrane and protein determinants for lipid selective membrane-interactions. We consider the factors that promote the binding of CCT isoforms to the membranes of the ER, nuclear envelope, or lipid droplets, but exclude CCT from other organelles and the plasma membrane. The CCT sensing mechanism is compared with several other proteins that use an AH motif for membrane compositional sensing. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.
Collapse
|
10
|
Cornell RB, Ridgway ND. CTP:phosphocholine cytidylyltransferase: Function, regulation, and structure of an amphitropic enzyme required for membrane biogenesis. Prog Lipid Res 2015; 59:147-71. [PMID: 26165797 DOI: 10.1016/j.plipres.2015.07.001] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Revised: 07/07/2015] [Accepted: 07/07/2015] [Indexed: 12/12/2022]
Abstract
CTP:phosphocholine cytidylyltransferase (CCT) catalyzes a rate-limiting and regulated step in the CDP-choline pathway for the synthesis of phosphatidylcholine (PC) and PC-derived lipids. Control of CCT activity is multi-layered, and includes direct regulation by reversible membrane binding involving a built-in lipid compositional sensor. Thus CCT contributes to phospholipid compositional homeostasis. CCT also modifies the curvature of its target membrane. Knowledge of CCT structure and regulation of its catalytic function are relatively advanced compared to many lipid metabolic enzymes, and are reviewed in detail. Recently the genetic origins of two human developmental and lipogenesis disorders have been traced to mutations in the gene for CCTα.
Collapse
Affiliation(s)
- Rosemary B Cornell
- Department of Molecular Biology and Biochemistry and the Department of Chemistry, Simon Fraser University, Burnaby, B.C. V5A-1S6, Canada.
| | - Neale D Ridgway
- Departments of Pediatrics, and Biochemistry and Molecular Biology, Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia B3H-4H7, Canada
| |
Collapse
|
11
|
Hoover-Fong J, Sobreira N, Jurgens J, Modaff P, Blout C, Moser A, Kim OH, Cho TJ, Cho SY, Kim SJ, Jin DK, Kitoh H, Park WY, Ling H, Hetrick KN, Doheny KF, Valle D, Pauli RM. Mutations in PCYT1A, encoding a key regulator of phosphatidylcholine metabolism, cause spondylometaphyseal dysplasia with cone-rod dystrophy. Am J Hum Genet 2014; 94:105-12. [PMID: 24387990 DOI: 10.1016/j.ajhg.2013.11.018] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 11/22/2013] [Indexed: 12/30/2022] Open
Affiliation(s)
- Julie Hoover-Fong
- McKusick-Nathans Institute of Genetic Medicine, Greenberg Center for Skeletal Dysplasias, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA; Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Nara Sobreira
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Julie Jurgens
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Predoctoral Training Program in Human Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Peggy Modaff
- Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Carrie Blout
- McKusick-Nathans Institute of Genetic Medicine, Greenberg Center for Skeletal Dysplasias, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA
| | - Ann Moser
- Department of Neurogenetics, Kennedy Krieger Institute, Baltimore, MD 21205, USA
| | - Ok-Hwa Kim
- Department of Radiology, Ajou University Hospital, Suwon, Kyunggi 443-721, Korea
| | - Tae-Joon Cho
- Division of Pediatric Orthopaedics, Seoul National University Children's Hospital, Seoul 110-744, Korea
| | - Sung Yoon Cho
- Department of Pediatrics, Hanyang University Guri Hospital, Hanyang University College of Medicine, Guri, Gyeonggi-Do 471-701, Korea
| | - Sang Jin Kim
- Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea
| | - Dong-Kyu Jin
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea
| | - Hiroshi Kitoh
- Department of Orthopaedic Surgery, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550, Japan
| | - Woong-Yang Park
- Samsung Genome Institute, Samsung Medical Center, Seoul 135-710, Korea; Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon 440-746, Korea
| | - Hua Ling
- Center for Inherited Disease Research, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA
| | - Kurt N Hetrick
- Center for Inherited Disease Research, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA
| | - Kimberly F Doheny
- Center for Inherited Disease Research, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA
| | - David Valle
- Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Richard M Pauli
- Department of Pediatrics, University of Wisconsin-Madison, Madison, WI 53705, USA
| |
Collapse
|
12
|
Ridgway ND. The role of phosphatidylcholine and choline metabolites to cell proliferation and survival. Crit Rev Biochem Mol Biol 2013; 48:20-38. [PMID: 23350810 DOI: 10.3109/10409238.2012.735643] [Citation(s) in RCA: 206] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The reorganization of metabolic pathways in cancer facilitates the flux of carbon and reducing equivalents into anabolic pathways at the expense of oxidative phosphorylation. This provides rapidly dividing cells with the necessary precursors for membrane, protein and nucleic acid synthesis. A fundamental metabolic perturbation in cancer is the enhanced synthesis of fatty acids by channeling glucose and/or glutamine into cytosolic acetyl-CoA and upregulation of key biosynthetic genes. This lipogenic phenotype also extends to the production of complex lipids involved in membrane synthesis and lipid-based signaling. Cancer cells display sensitivity to ablation of fatty acid synthesis possibly as a result of diminished capacity to synthesize complex lipids involved in signaling or growth pathways. Evidence has accrued that phosphatidylcholine, the major phospholipid component of eukaryotic membranes, as well as choline metabolites derived from its synthesis and catabolism, contribute to both proliferative growth and programmed cell death. This review will detail our current understanding of how coordinated changes in substrate availability, gene expression and enzyme activity lead to altered phosphatidylcholine synthesis in cancer, and how these changes contribute directly or indirectly to malignant growth. Conversely, apoptosis targets key steps in phosphatidylcholine synthesis and degradation that are linked to disruption of cell cycle regulation, reinforcing the central role that phosphatidylcholine and its metabolites in determining cell fate.
Collapse
Affiliation(s)
- Neale D Ridgway
- Departments of Pediatrics and Biochemistry & Molecular Biology, The Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia Canada.
| |
Collapse
|
13
|
Cardozo Gizzi AM, Caputto BL. Mechanistic insights into the nongenomic regulation of phospholipid synthesizing enzymes. IUBMB Life 2013; 65:584-92. [PMID: 23712998 DOI: 10.1002/iub.1173] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Accepted: 03/21/2013] [Indexed: 11/06/2022]
Abstract
Lipid synthesis is a complex process regulated at multiple levels. Here, we will discuss nongenomic regulatory mechanisms, particularly the activation and/or recruitment of key enzymes to membranes. The phospholipid synthesis enzymes Lipin and CTP:phosphocholine cytidylyltransferase are taken as examples of these mechanisms that are mediated by posttranslational modifications or by an intrinsic property of the enzyme that senses lipid composition. In addition, special emphasis will be put on another relevant non genomic lipid synthesis regulation mechanism that is dependent on c-Fos, a protein that has deserved less attention so far. This latter regulatory mechanism is emerging as an important determinant for processes that require high rates of lipid synthesis such as those of growth and proliferation.
Collapse
Affiliation(s)
- Andrés M Cardozo Gizzi
- Centro de Investigaciones en Química Biológica de Córdoba, CIQUIBIC (UNC-CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, Argentina
| | | |
Collapse
|
14
|
Lagace TA, Ridgway ND. The role of phospholipids in the biological activity and structure of the endoplasmic reticulum. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2499-510. [PMID: 23711956 DOI: 10.1016/j.bbamcr.2013.05.018] [Citation(s) in RCA: 153] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 05/09/2013] [Accepted: 05/15/2013] [Indexed: 01/22/2023]
Abstract
The endoplasmic reticulum (ER) is an interconnected network of tubular and planar membranes that supports the synthesis and export of proteins, carbohydrates and lipids. Phospholipids, in particular phosphatidylcholine (PC), are synthesized in the ER where they have essential functions including provision of membranes required for protein synthesis and export, cholesterol homeostasis, and triacylglycerol storage and secretion. Coordination of these biological processes is essential, as highlighted by findings that link phospholipid metabolism in the ER with perturbations in lipid storage/secretion and stress responses, ultimately contributing to obesity/diabetes, atherosclerosis and neurological disorders. Phospholipid synthesis is not uniformly distributed in the ER but is localized at membrane interfaces or contact zones with other organelles, and in dynamic, proliferating ER membranes. The topology of phospholipid synthesis is an important consideration when establishing the etiology of diseases that arise from ER dysfunction. This review will highlight our current understanding of the contribution of phospholipid synthesis to proper ER function, and how alterations contribute to aberrant stress responses and disease. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.
Collapse
Affiliation(s)
- Thomas A Lagace
- University of Ottawa Heart Institute, Ottawa, Ontario, Canada.
| | | |
Collapse
|
15
|
Ma D, Baruch D, Shu Y, Yuan K, Sun Z, Ma K, Hoang T, Fu W, Min L, Lan ZS, Wang F, Mull L, He WW. Using protein microarray technology to screen anti-ERCC1 monoclonal antibodies for specificity and applications in pathology. BMC Biotechnol 2012; 12:88. [PMID: 23171216 PMCID: PMC3526464 DOI: 10.1186/1472-6750-12-88] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Accepted: 11/10/2012] [Indexed: 12/15/2022] Open
Abstract
Background An antibody with cross-reactivity can create unexpected side effects or false diagnostic reports if used for clinical purposes. ERCC1 is being explored as a predictive diagnostic biomarker for cisplatin-based chemotherapy. High ERCC1 expression is linked to drug resistance on cisplatin-based chemotherapy. 8F1 is one of the most commonly used monoclonal antibodies for evaluating ERCC1 expression levels in lung cancer patient tissues, but it has been noted that this antibody cross-reacts with an unknown protein. Results By using a high density protein microarray chip technology, we discovered that 8F1 not only reacts with its authentic target, ERCC1, but also cross-reacts with an unrelated nuclear membrane protein, PCYT1A. The cross-reactivity is due to a common epitope presented on these two unrelated proteins. Similar to the subcellular localization of ERCC1, IHC tests demonstrated that PCYT1A is localized mainly on nuclear membrane. In this study, we also discovered that the PCYT1A gene expression level is significantly higher than the ERCC1 gene expression level in a certain population of lung cancer patient tissue samples. To develop the best monoclonal antibody for ERCC1 IHC analysis, 18 monoclonal antibodies were generated and 6 of them were screened against our protein microarray chip. Two clones showed high mono-specificity on the protein microarray chip test and both worked for the IHC application. Conclusion In summary, the 8F1 clone is not suitable for ERCC1 IHC assay due to its cross-reactivity with PCYT1A protein. Two newly generated monoclonal antibodies, 4F9 and 2E12, demonstrated ultra-specificity against ERCC1 protein and superior performance for IHC analyses.
Collapse
Affiliation(s)
- Donghui Ma
- OriGene Technologies Inc, 9620 Medical Center Drive, Rockville, MD 20850, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Agassandian M, Mallampalli RK. Surfactant phospholipid metabolism. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1831:612-25. [PMID: 23026158 DOI: 10.1016/j.bbalip.2012.09.010] [Citation(s) in RCA: 153] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Revised: 09/07/2012] [Accepted: 09/16/2012] [Indexed: 12/16/2022]
Abstract
Pulmonary surfactant is essential for life and is composed of a complex lipoprotein-like mixture that lines the inner surface of the lung to prevent alveolar collapse at the end of expiration. The molecular composition of surfactant depends on highly integrated and regulated processes involving its biosynthesis, remodeling, degradation, and intracellular trafficking. Despite its multicomponent composition, the study of surfactant phospholipid metabolism has focused on two predominant components, disaturated phosphatidylcholine that confers surface-tension lowering activities, and phosphatidylglycerol, recently implicated in innate immune defense. Future studies providing a better understanding of the molecular control and physiological relevance of minor surfactant lipid components are needed. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.
Collapse
Affiliation(s)
- Marianna Agassandian
- Department of Medicine, Acute Lung Injury Center of Excellence, the University of Pittsburgh, Pittsburgh, PA 15213, USA
| | | |
Collapse
|
17
|
Huang Y, Kempen MBV, Munck ABD, Swagemakers S, Driegen S, Mahavadi P, Meijer D, van Ijcken W, van der Spek P, Grosveld F, Günther A, Tibboel D, Rottier RJ. Hypoxia-inducible factor 2α plays a critical role in the formation of alveoli and surfactant. Am J Respir Cell Mol Biol 2012; 46:224-32. [PMID: 22298531 DOI: 10.1165/rcmb.2011-0024oc] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Alveolarization of the developing lung is an important step toward the switch from intrauterine life to breathing oxygen-rich air after birth. The distal airways structurally change to minimize the gas exchange path, and Type II pneumocytes increase the production of surfactants, which are required to reduce surface tension at the air-liquid interface in the alveolus. Hypoxia-inducible factor 2α (Hif2α) is an oxygen-regulated transcription factor expressed in endothelial and Type II cells, and its expression increases toward the end of gestation. We investigated the role of Hif2α in Type II cells by conditionally expressing an oxygen-insensitive mutant of Hif2α in airway epithelial cells during development. Newborn mice expressing the mutant Hif2α were born alive but quickly succumbed to respiratory distress. Subsequent analysis of the lungs revealed dilated alveoli covered with enlarged, aberrant Type II cells and a diminished number of Type I cells. The Type II cells accumulated glycogen in part by increased glucose uptake via the up-regulation of the glucose transporter 1. Furthermore, the cells lacked two crucial enzymes involved in the metabolism of glycogen into surfactant lipids, lysophosphatidylcholine acyltransferase and ATP-binding cassette sub-family A member 3. We conclude that Hif2α is a key regulator in alveolar maturation and the production of phospholipids by Type II cells.
Collapse
Affiliation(s)
- Yadi Huang
- Department of Pediatric Surgery, Erasmus MC-Sophia Children's Hospital, Rotterdam, The Netherlands
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Chen BB, Glasser JR, Coon TA, Mallampalli RK. F-box protein FBXL2 exerts human lung tumor suppressor-like activity by ubiquitin-mediated degradation of cyclin D3 resulting in cell cycle arrest. Oncogene 2011; 31:2566-79. [PMID: 22020328 PMCID: PMC3266958 DOI: 10.1038/onc.2011.432] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Dyregulated behavior of cell cycle proteins and their control by ubiquitin E3 ligases is an emerging theme in human lung cancer. Here we identified and characterized the activity of a novel F box protein, termed FBXL2, belonging to the SCF (Skip-Cullin1-F-box protein) E3 ligase family. Ectopically expressed FBXL2 triggered G2/M phase arrest, induced chromosomal anomalies, and increased apoptosis of transformed lung epithelia by mediating polyubiquitination and degradation of the mitotic regulator, cyclin D3. Unlike other F box proteins that target phosphodegrons within substrates, FBXL2 uniquely recognizes a canonical calmodulin-binding motif within cyclin D3 to facilitate its polyubiquitination. Calmodulin bound and protected cyclin D3 from FBXL2 by direct intermolecular competition with the F box protein for access within this motif. The chemotherapeutic agent vinorelbine increased apoptosis of human lung carcinoma cells by inducing FBXL2 expression and cyclin D3 degradation, an effect accentuated by calmodulin knockdown. Depletion of endogenous FBXL2 stabilized cyclin D3 levels, accellerated cancer cell growth, and increased cell viability after vinorelbine treatment. Last, ectopic expression of FBXL2 significantly inhibited the growth and migration of tumorogenic cells and tumor formation in athymic nude mice. These observations implicate SCFFBXL2 as an indispensible regulator of mitosis that serves as a tumor suppressor.
Collapse
Affiliation(s)
- B B Chen
- Department of Medicine, Acute Lung Injury Center of Excellence, The University of Pittsburgh, Pittsburgh, PA, USA
| | | | | | | |
Collapse
|
19
|
Dennis MK, Taneva SG, Cornell RB. The intrinsically disordered nuclear localization signal and phosphorylation segments distinguish the membrane affinity of two cytidylyltransferase isoforms. J Biol Chem 2011; 286:12349-60. [PMID: 21303909 DOI: 10.1074/jbc.m110.201715] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Membrane phosphatidylcholine homeostasis is maintained in part by a sensing device in the key regulatory enzyme, CTP:phosphocholine cytidylyltransferase (CCT). CCT responds to decreases in membrane phosphatidylcholine content by reversible membrane binding and activation. Two prominent isoforms, CCTα and -β2, have nearly identical catalytic domains and very similar membrane binding amphipathic helical (M) domains but have divergent and structurally disordered N-terminal (N) and C-terminal phosphorylation (P) regions. We found that the binding affinity of purified CCTβ2 for anionic membranes was weaker than CCTα by more than an order of magnitude. Using chimeric CCTs, insertion/deletion mutants, and truncated CCTs, we show that the stronger affinity of CCTα can be attributed in large part to the electrostatic membrane binding function of the polybasic nuclear localization signal (NLS) motif, present in the unstructured N-terminal segment of CCTα but lacking in CCTβ2. The membrane partitioning of CCTβ2 in cells enriched with the lipid activator, oleic acid, was also weaker than that of CCTα and was elevated by incorporation of the NLS motif. Thus, the polybasic NLS can function as a secondary membrane binding motif not only in vitro but in the context of cell membranes. A comparison of phosphorylated, dephosphorylated, and region P-truncated forms showed that the in vitro membrane affinity of CCTβ2 is more sensitive than CCTα to phosphorylation status, which antagonizes membrane binding of both isoforms. These data provide a model wherein the primary membrane binding motif, an amphipathic helical domain, works in collaboration with other intrinsically disordered segments that modulate membrane binding strength. The NLS reinforces, whereas the phosphorylated tail antagonizes the attraction of domain M for anionic membranes.
Collapse
Affiliation(s)
- Melissa K Dennis
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
| | | | | |
Collapse
|
20
|
The rate-limiting enzyme in phosphatidylcholine synthesis is associated with nuclear speckles under stress conditions. Biochim Biophys Acta Mol Cell Biol Lipids 2010; 1801:1184-94. [PMID: 20647050 DOI: 10.1016/j.bbalip.2010.07.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2009] [Revised: 07/02/2010] [Accepted: 07/12/2010] [Indexed: 11/20/2022]
Abstract
Phosphatidylcholine (PtdCho) is the most abundant phospholipid in eukaryotic membranes and its biosynthetic pathway is generally controlled by CTP:Phosphocholine Cytidylyltransferase (CCT), which is considered the rate-limiting enzyme. CCT is an amphitropic protein, whose enzymatic activity is commonly associated with endoplasmic reticulum (ER) translocation; however, most of the enzyme is intranuclearly located. Here we demonstrate that CCTα is concentrated in the nucleoplasm of MDCK cells. Confocal immunofluorescence revealed that extracellular hypertonicity shifted the diffuse intranuclear distribution of the enzyme to intranuclear domains in a foci pattern. One population of CCTα foci colocalised and interacted with lamin A/C speckles, which also contained the pre-mRNA processing factor SC-35, and was resistant to detergent and salt extraction. The lamin A/C silencing allowed us to visualise a second more labile population of CCTα foci that consisted of lamin A/C-independent foci non-resistant to extraction. We demonstrated that CCTα translocation is not restricted to its redistribution from the nucleus to the ER and that intranuclear redistribution must thus be considered. We suggest that the intranuclear organelle distribution of CCTα is a novel mechanism for the regulation of enzyme activity.
Collapse
|
21
|
Elena C, Banchio C. Specific interaction between E2F1 and Sp1 regulates the expression of murine CTP:phosphocholine cytidylyltransferase alpha during the S phase. Biochim Biophys Acta Mol Cell Biol Lipids 2010; 1801:537-46. [PMID: 20096375 DOI: 10.1016/j.bbalip.2010.01.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Revised: 01/06/2010] [Accepted: 01/13/2010] [Indexed: 11/16/2022]
Abstract
CTP:phosphocholine cytidylyltransferase alpha (CCTalpha) is a key enzyme for phosphatidylcholine biosynthesis in mammalian cells. This enzyme plays an essential role in all processes that require membrane biosynthesis such as cell proliferation and viability. Thus, CCTalpha activity and expression fluctuate during the cell cycle to achieve PtdCho requirements. We demonstrated, for the first time, that CCTalpha is localized in the nucleus in cells transiting the S phase, whereas it is localized in the cytoplasm of G(0)-arrested cells, suggesting a specific role of nuclear CCTalpha during the S phase. We also investigated how E2F1 influences the regulation of the CCTalpha-promoter during the S phase; we demonstrated that E2F1 is necessary, but not sufficient, to activate CCTalpha expression when this factor is over-expressed. However, when E2F1 and Sp1 were over-expressed, the transcription from the CCTalpha-promoter reporter construct was super-activated. Transient transfection studies demonstrated that E2F1 could super-activate Sp1-dependent transcription in a promoter containing only the Sp1 binding sites "B" or "C", and that Sp1 could activate Sp1-dependent transcription in a promoter containing the E2F site, thus, further demonstrating a functional interaction of these factors. In conclusion, the present results allowed us to portray the clearest picture of the CCTalpha-gene expression in proliferating cells, and understand the mechanism by which cells coordinate cell cycle progression with the requirement for phosphatidylcholine.
Collapse
Affiliation(s)
- Claudia Elena
- IBR (Instituto de Biología Molecular y Celular de Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas, Area Biología, Departamento de Ciencias Biológicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, Rosario, Argentina
| | | |
Collapse
|
22
|
Agassandian M, Chen BB, Schuster CC, Houtman JCD, Mallampalli RK. 14-3-3zeta escorts CCTalpha for calcium-activated nuclear import in lung epithelia. FASEB J 2009; 24:1271-83. [PMID: 20007511 DOI: 10.1096/fj.09-136044] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Integrity of animal biomembranes is critical to preserve normal cellular functions and viability. Phosphatidylcholine, an indispensible membrane component, requires the enzyme CCTalpha for its biosynthesis. Nuclear expression of CCTalpha is needed for expansion of the nuclear membrane network, but mechanisms for CCTalpha nuclear import are unknown. Herein, we show that in epithelia, extracellular Ca(2+) triggers CCTalpha cytoplasmic-nuclear translocation. CCTalpha nuclear import was associated with binding to 14-3-3zeta, a key regulator of protein trafficking. 14-3-3zeta was both sufficient and required for CCTalpha nuclear import. Helix G within the 14-3-3zeta binding groove interacts with a putative molecular signature within the CCTalpha carboxyl-terminal phosphoserine motif (residues 328-343). 14-3-3zeta was critically involved in preserving phosphatidylcholine synthesis and cell viability in a model of Pseudomonas aeruginosa infection where Ca(2+) concentrations increase within epithelia. Thus, 14-3-3zeta controls CCTalpha nuclear import in response to calcium signals, thereby regulating mammalian phospholipid synthesis. Agassandian, M., Chen, B. B., Schuster, C. C., Houtman, J. C. D., Mallampalli, R. K. 14-3-3zeta escorts CCTalpha for calcium-activated nuclear import in lung epithelia.
Collapse
Affiliation(s)
- Marianna Agassandian
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, Iowa City, Iowa, USA
| | | | | | | | | |
Collapse
|
23
|
Ridsdale R, Tseu I, Wang J, Post M. Functions of membrane binding domain of CTP:phosphocholine cytidylyltransferase in alveolar type II cells. Am J Respir Cell Mol Biol 2009; 43:74-87. [PMID: 19684306 DOI: 10.1165/rcmb.2009-0231oc] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCTalpha) plays a key role in the biosynthesis of surfactant phosphatidylcholine. In this study, we investigated the role of its membrane-binding (M) domain in modulating its structure, function, and cellular distribution. Multiple enhanced green fluorescent protein-CCTalpha constructs were generated to evaluate the subcellular distribution in A549 cells. The M domain targeted CCTalpha to the perinuclear (membrane-rich) region. Microinjections with glutathione-S-transferase fusion protein containing the M domain corroborated the perinuclear targeting. Deletion of the M domain or substitutions of the hydrophobic residues with arginine/serine in the VEEKS(267-277) motif of the M domain resulted in a nuclear appearance and indented nuclei. Membrane binding of CCTalpha decreased gradually as the number of positively charged arginine residues increased in the VEEKS motif. To identify whether membrane-protein interactions cause structural alterations in CCTalpha, we visualized the protein in the absence and presence of lipids by transmission electron microscopy. These studies revealed that CCTalpha forms a dimer-like complex that condenses upon binding to lipid vesicles, but not lipid monolayers. The influence of the M domain on CCTalpha activity was assessed in transgenic mice overexpressing the N-terminal catalytic domain (CCTalpha(1-239)), N-terminal catalytic plus M domain (CCTalpha(1-290)), or full-length CCTalpha(1-367) in fetal type II cells by using the surfactant protein C promoter. Only overexpression of CCTalpha(1-367) increased surfactant phosphatidylcholine synthesis. Thus, the M domain influences membrane binding, cellular distribution, and topology of CCTalpha, but the domain alone is not sufficient to confer CCT activity in alveolar type II cells in vivo.
Collapse
Affiliation(s)
- Ross Ridsdale
- Physiology and Experimental Medicine Program, Hospital for Sick Children Research Institute, 555 University Avenue, Toronto, ON, M5G 1X8 Canada
| | | | | | | |
Collapse
|
24
|
Oxysterol activation of phosphatidylcholine synthesis involves CTP:phosphocholine cytidylyltransferase α translocation to the nuclear envelope. Biochem J 2009; 418:209-17. [DOI: 10.1042/bj20081923] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In addition to suppressing cholesterol synthesis and uptake, oxysterols also activate glycerophospholipid and SM (sphingomyelin) synthesis, possibly to buffer cells from excess sterol accumulation. In the present study, we investigated the effects of oxysterols on the CDP-choline pathway for PtdCho (phosphatidylcholine) synthesis using wild-type and sterol-resistant CHO (Chinese-hamster ovary) cells expressing a mutant of SCAP [SREBP (sterol-regulatory-element-binding protein) cleavage-activating protein] (CHO-SCAP D443N). [3H]Choline-labelling experiments showed that 25OH (25-hydroxycholesterol), 22OH (22-hydroxycholesterol) and 27OH (27-hydroxycholesterol) increased PtdCho synthesis in CHO cells as a result of CCTα (CTP:phosphocholine cytidylyltransferase α) translocation and activation at the NE (nuclear envelope). These oxysterols also activate PtdCho synthesis in J774 macrophages. in vitro, CCTα activity was stimulated 2- to 2.5-fold by liposomes containing 5 mol% 25OH, 22OH or 27OH. Inclusion of up to 5 mol% cholesterol did not further activate CCTα. 25OH activated CCTα in CHO-SCAP D443N cells leading to a transient increase in PtdCho synthesis and accumulation of CDP-choline. CCTα translocation to the NE and intranuclear tubules in CHO-SCAP D443N cells was complete after 1 h exposure to 25OH compared with only partial translocation by 4–6 h in CHO-Mock cells. These enhanced responses in CHO-D443N cells were sterol-dependent since depletion with cyclodextrin or lovastatin resulted in reduced sensitivity to 25OH. However, the lack of effect of cholesterol on in vitro CCT activity indicates an indirect relationship or involvement of other sterols or oxysterol. We conclude that translocation and activation of CCTα at nuclear membranes by side-chain hydroxylated sterols are regulated by the cholesterol status of the cell.
Collapse
|
25
|
Gehrig K, Morton CC, Ridgway ND. Nuclear export of the rate-limiting enzyme in phosphatidylcholine synthesis is mediated by its membrane binding domain. J Lipid Res 2008; 50:966-76. [PMID: 19098306 DOI: 10.1194/jlr.m800632-jlr200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase alpha (CCTalpha), the rate-limiting enzyme in the CDP-choline pathway for phosphatidylcholine (PtdCho) synthesis, is activated by translocation to nuclear membranes. However, CCTalpha is cytoplasmic in cells with increased capacity for PtdCho synthesis and following acute activation, suggesting that nuclear export is linked to activation. The objective of this study was to identify which CCTalpha domains were involved in nuclear export in response to the lipid activators farnesol (FOH) and oleate. Imaging of CCT-green fluorescent protein (GFP) mutants expressed in CCTalpha-deficient CHO58 cells showed that FOH-mediated translocation to nuclear membranes and export to the cytoplasm required the membrane binding amphipathic helix (domain M). Nuclear export was reduced by a mutation that mimics constitutive phosphorylation of the CCT phosphorylation (P) domain. However, domain M alone was sufficient to promote translocation to the nuclear envelope and export of a nuclear-localized GFP construct in FOH- or oleate-treated CHO58 cells. In the context of acute activation with lipid mediators, nuclear export of CCT-GFP mutants correlated with in vitro activity but not PtdCho synthesis. This study describes a nuclear export pathway that is dependent on membrane interaction of an amphipathic helix, thus linking lipid-dependent activation to the nuclear/cytoplasmic distribution of CCTalpha.
Collapse
Affiliation(s)
- Karsten Gehrig
- Department of Pediatrics, and Biochemistry & Molecular Biology, Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia, Canada
| | | | | |
Collapse
|
26
|
Fagone P, Jackowski S. Membrane phospholipid synthesis and endoplasmic reticulum function. J Lipid Res 2008; 50 Suppl:S311-6. [PMID: 18952570 DOI: 10.1194/jlr.r800049-jlr200] [Citation(s) in RCA: 307] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
This review presents an overview of mammalian phospholipid synthesis and the cellular locations of the biochemical activities that produce membrane lipid molecular species. The generalized endoplasmic reticulum compartment is a central site for membrane lipid biogenesis, and examples of the emerging relationships between alterations in lipid composition, regulation of membrane lipid biogenesis, and cellular secretory function are discussed.
Collapse
Affiliation(s)
- Paolo Fagone
- Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105-3678, USA
| | | |
Collapse
|
27
|
Taneva S, Dennis MK, Ding Z, Smith JL, Cornell RB. Contribution of each membrane binding domain of the CTP:phosphocholine cytidylyltransferase-alpha dimer to its activation, membrane binding, and membrane cross-bridging. J Biol Chem 2008; 283:28137-48. [PMID: 18694933 DOI: 10.1074/jbc.m802595200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCT), a rate-limiting enzyme in phosphatidylcholine synthesis, is regulated by reversible membrane interactions mediated by an amphipathic helical domain (M) that binds selectively to anionic lipids. CCT is a dimer; thus the functional unit has two M domains. To probe the functional contribution of each domain M we prepared a CCT heterodimer composed of one full-length subunit paired with a CCT subunit truncated before domain M that was also catalytically dead. We compared this heterodimer to the full-length homodimer with respect to activation by anionic vesicles, vesicle binding affinities, and promotion of vesicle aggregation. Surprisingly for all three functions the dimer with just one domain M behaved similarly to the dimer with two M domains. Full activation of the wild-type subunit was not impaired by loss of one domain M in its partner. Membrane binding affinities were the same for dimers with one versus two M domains, suggesting that the two M domains of the dimer do not engage a single bilayer simultaneously. Vesicle cross-bridging was also unhindered by loss of one domain M, suggesting that another motif couples with domain M for cross-bridging anionic membranes. Mutagenesis revealed that the positively charged nuclear localization signal sequence constitutes that second motif for membrane cross-bridging. We propose that the two M domains of the CCT dimer engage a single bilayer via an alternating binding mechanism. The tethering function involves the cooperation of domain M and the nuclear localization signal sequence, each engaging separate membranes. Membrane binding of a single M domain is sufficient to fully activate the enzymatic activity of the CCT dimer while sustaining the low affinity, reversible membrane interaction required for regulation of CCT activity.
Collapse
Affiliation(s)
- Svetla Taneva
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A-1S6, Canada
| | | | | | | | | |
Collapse
|
28
|
Ryan AJ, Chen BB, Vennalaganti PR, Henderson FC, Tephly LA, Carter AB, Mallampalli RK. 15-deoxy-Delta12,14-prostaglandin J2 impairs phosphatidylcholine synthesis and induces nuclear accumulation of thiol-modified cytidylyltransferase. J Biol Chem 2008; 283:24628-40. [PMID: 18614529 DOI: 10.1074/jbc.m801167200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Synthesis of phosphatidylcholine, the major phospholipid of animal cell membranes, requires the key enzyme cytidylyltransferase (CCTalpha). Cysteine sulfhydryls within CCTalpha are needed for full catalytic activity. Here we show that prostaglandin 15-deoxy-Delta12,14-PGJ2 (15d-PGJ2) inactivates CCTalpha by inducing generation of reactive oxidant species and the appearance of a cross-linked CCTalpha dimer in cells. N-Acetyl-l-cysteine reduced oxidative stress, prevented CCTalpha cross-linking, and restored CCT function in 15d-PGJ2-treated cells. 15d-PGJ2 modified critical cysteine residues within CCTalpha as determined by mutagenesis studies and by incorporation of biotin-15d-PGJ2 into CCTalpha. These effects of 15d-PGJ2 were associated with CCTalpha accumulation within the nucleus. The data indicate that bioactive prostanoids significantly impair membrane phospholipid production by promoting cysteine cross-bridging within CCTalpha.
Collapse
Affiliation(s)
- Alan J Ryan
- Department of Internal Medicine, University of Iowa, Iowa City, Iowa 52242, USA
| | | | | | | | | | | | | |
Collapse
|
29
|
Sugimoto H, Banchio C, Vance DE. Transcriptional regulation of phosphatidylcholine biosynthesis. Prog Lipid Res 2008; 47:204-20. [PMID: 18295604 DOI: 10.1016/j.plipres.2008.01.002] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Phosphatidylcholine biosynthesis in animal cells is primarily regulated by the rapid translocation of CTP:phosphocholine cytidylyltransferase alpha between a soluble form that is inactive and a membrane-associated form that is activated. Until less than 10 years ago there was no information on the transcriptional regulation of phosphatidylcholine biosynthesis. Research has identified the transcription factors Sp1, Rb, TEF4, Ets-1 and E2F as enhancing the expression of the cytidylyltransferase and Net as a factor that represses cytidylyltransferase expression. Key transcription factors involved in cholesterol or fatty acid metabolism (SREBPs, LXRs, PPARs) do not have a major role in transcriptional regulation of the cytidylyltransferase. Rather than being linked to cholesterol or energy metabolism, regulation of the cytidylyltransferase is linked to the cell cycle, cell growth and differentiation. Transcriptional regulation of phospholipid biosynthesis is more elegantly understood in yeast and involves responses to inositol, choline and zinc in the culture medium.
Collapse
Affiliation(s)
- Hiroyuki Sugimoto
- Department of Biochemistry, Dokkyo Medical University School of Medicine, Mibu 321-0293, Japan.
| | | | | |
Collapse
|
30
|
Genetic Abnormalities of Surfactant Metabolism. MOLECULAR PATHOLOGY LIBRARY 2008. [PMCID: PMC7147445 DOI: 10.1007/978-0-387-72430-0_54] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Pulmonary surfactant is the complex mixture of lipids and proteins needed to reduce alveolar surface tension at the air-liquid interface and prevent alveolar collapse at the end of expiration. It has been recognized for almost 50 years that a deficiency in surfactant production due to pulmonary immaturity is the principal cause of the respiratory distress syndrome (RDS) observed in prematurely born infants.1 Secondary surfactant deficiency due to injury to the cells involved in its production and functional inactivation of surfactant is also important in the pathophysiology of acute respiratory distress syndrome (ARDS) observed in older children and adults.2,3 In the past 15 years, it has been recognized that surfactant deficiency may result from genetic mechanisms involving mutations in genes encoding critical components of the surfactant system or proteins involved in surfactant metabolism.4,5 Although rare, these single gene disorders provide important insights into normal surfactant metabolism and into the genes in which frequently occurring allelic variants may be important in more common pulmonary diseases.
Collapse
|
31
|
Carter JM, Demizieux L, Campenot RB, Vance DE, Vance JE. Phosphatidylcholine biosynthesis via CTP:phosphocholine cytidylyltransferase 2 facilitates neurite outgrowth and branching. J Biol Chem 2007; 283:202-212. [PMID: 17981805 DOI: 10.1074/jbc.m706531200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Hallmarks of neuronal differentiation are neurite sprouting, extension, and branching. We previously showed that increased expression of CTP:phosphocholine cytidylyltransferase beta2 (CTbeta2), an isoform of a key phosphatidylcholine (PC) biosynthetic enzyme, accompanies neurite outgrowth (Carter, J. M., Waite, K. A., Campenot, R. B., Vance, J. E., and Vance, D. E. (2003) J. Biol. Chem. 278, 44988-44994). CTbeta2 mRNA is highly expressed in the brain. We show that CTbeta2 is abundant in axons of rat sympathetic neurons and retinal ganglion cells. We used RNA silencing to decrease CTbeta2 expression in PC12 cells differentiated by nerve growth factor. In CTbeta2-silenced cells, numbers of primary and secondary neurites were markedly reduced, suggesting that CTbeta2 facilitates neurite outgrowth and branching. However, the length of individual neurites was significantly increased, and the total amount of neuronal membrane was unchanged. Neurite branching of PC12 cells is known to be inhibited by activation of Akt and promoted by the Akt inhibitor LY294002. Our experiments showed that LY294002 increases neurite sprouting and branching in control PC12 cells but not in CTbeta2-deficient cells. CTbeta2 was not phosphorylated in vitro by Akt. However, inhibition of Cdk5 by roscovitine blocked CTbeta2 phosphorylation and reduced neurite outgrowth and branching. These results highlight the importance of CTbeta2 in neurons for promoting neurite outgrowth and branching and represent the first identification of a lipid biosynthetic enzyme that facilitates these functions.
Collapse
Affiliation(s)
- Jodi M Carter
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids, Edmonton, Alberta T6G 2S2, Canada; Department of Biochemistry, Edmonton, Alberta T6G 2S2, Canada
| | - Laurent Demizieux
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids, Edmonton, Alberta T6G 2S2, Canada; Department of Medicine, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
| | | | - Dennis E Vance
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids, Edmonton, Alberta T6G 2S2, Canada; Department of Biochemistry, Edmonton, Alberta T6G 2S2, Canada
| | - Jean E Vance
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids, Edmonton, Alberta T6G 2S2, Canada; Department of Medicine, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
| |
Collapse
|
32
|
Gehrig K, Cornell RB, Ridgway ND. Expansion of the nucleoplasmic reticulum requires the coordinated activity of lamins and CTP:phosphocholine cytidylyltransferase alpha. Mol Biol Cell 2007; 19:237-47. [PMID: 17959832 DOI: 10.1091/mbc.e07-02-0179] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The nucleoplasmic reticulum (NR), a nuclear membrane network implicated in signaling and transport, is formed by the biosynthetic and membrane curvature-inducing properties of the rate-limiting enzyme in phosphatidylcholine synthesis, CTP:phosphocholine cytidylyltransferase (CCT) alpha. The NR is formed by invagination of the nuclear envelope and has an underlying lamina that may contribute to membrane tubule formation or stability. In this study we investigated the role of lamins A and B in NR formation in response to expression and activation of endogenous and fluorescent protein-tagged CCTalpha. Similarly to endogenous CCTalpha, CCT-green fluorescent protein (GFP) reversibly translocated to nuclear tubules projecting from the NE in response to oleate, a lipid promoter of CCT membrane binding. Coexpression and RNA interference experiments revealed that both CCTalpha and lamin A and B were necessary for NR proliferation. Expression of CCT-GFP mutants with compromised membrane-binding affinity produced fewer nuclear tubules, indicating that the membrane-binding function of CCTalpha promotes the expansion of the NR. Proliferation of atypical bundles of nuclear membrane tubules by a CCTalpha mutant that constitutively associated with membranes revealed that expansion of the double-bilayer NR requires the coordinated assembly of an underlying lamin scaffold and induction of membrane curvature by CCTalpha.
Collapse
Affiliation(s)
- Karsten Gehrig
- *Departments of Pediatrics, and Biochemistry and Molecular Biology, Atlantic Research Centre, Dalhousie University, Halifax, NS, Canada B3H 4H7
| | | | | |
Collapse
|
33
|
Chen BB, Mallampalli RK. Calmodulin binds and stabilizes the regulatory enzyme, CTP: phosphocholine cytidylyltransferase. J Biol Chem 2007; 282:33494-33506. [PMID: 17804406 DOI: 10.1074/jbc.m706472200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCTalpha) is a proteolytically sensitive enzyme essential for production of phosphatidylcholine, the major phospholipid of animal cell membranes. The molecular signals that govern CCTalpha protein stability are unknown. An NH(2)-terminal PEST sequence within CCTalpha did not serve as a degradation signal for the proteinase, calpain. Calmodulin (CaM) stabilized CCTalpha from calpain proteolysis. Adenoviral gene transfer of CaM in cells protected CCTalpha, whereas CaM small interfering RNA accentuated CCTalpha degradation by calpains. CaM bound CCTalpha as revealed by fluorescence resonance energy transfer and two-hybrid analysis. Mapping and site-directed mutagenesis of CCTalpha uncovered a motif (LQERVDKVK) harboring a vital recognition site, Gln(243), whereby CaM directly binds to the enzyme. Mutagenesis of CCTalpha Gln(243) not only resulted in loss of CaM binding but also led to complete calpain resistance in vitro and in vivo. Thus, calpains and CaM both access CCTalpha using a structurally similar molecular signature that profoundly affects CCTalpha levels. These data suggest that CaM, by antagonizing calpain, serves as a novel binding partner for CCTalpha that stabilizes the enzyme under proinflammatory stress.
Collapse
Affiliation(s)
- Bill B Chen
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, 52242
| | - Rama K Mallampalli
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, 52242; Department of Internal Medicine, University of Iowa, Iowa City, Iowa, 52242; Department of Veterans Affairs Medical Center and the Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242.
| |
Collapse
|
34
|
Fagone P, Sriburi R, Ward-Chapman C, Frank M, Wang J, Gunter C, Brewer JW, Jackowski S. Phospholipid Biosynthesis Program Underlying Membrane Expansion during B-lymphocyte Differentiation. J Biol Chem 2007; 282:7591-605. [PMID: 17213195 DOI: 10.1074/jbc.m608175200] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Stimulated B-lymphocytes differentiate into plasma cells committed to antibody production. Expansion of the endoplasmic reticulum and Golgi compartments is a prerequisite for high rate synthesis, assembly, and secretion of immunoglobulins. The bacterial cell wall component lipopolysaccharide (LPS) stimulates murine B-cells to proliferate and differentiate into antibody-secreting cells that morphologically resemble plasma cells. LPS activation of CH12 B-cells augmented phospholipid production and initiated a genetic program, including elevated expression of the genes for the synthesis, elongation, and desaturation of fatty acids that supply the phospholipid acyl moieties. Likewise, many of the genes in phospholipid biosynthesis were up-regulated, most notably those encoding Lipin1 and choline phosphotransferase. In contrast, CTP:phosphocholine cytidylyltransferase alpha (CCTalpha) protein, a key control point in phosphatidylcholine biosynthesis, increased because of stabilization of protein turnover rather than transcriptional activation. Furthermore, an elevation in cellular diacylglycerol and fatty acid correlated with enhanced allosteric activation of CCTalpha by the membrane lipids. This work defines a genetic and biochemical program for membrane phospholipid biogenesis that correlates with an increase in the phospholipid components of the endoplasmic reticulum and Golgi compartments in LPS-stimulated B-cells.
Collapse
Affiliation(s)
- Paolo Fagone
- Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105-2794, USA
| | | | | | | | | | | | | | | |
Collapse
|
35
|
Tian Y, Zhou R, Rehg JE, Jackowski S. Role of phosphocholine cytidylyltransferase alpha in lung development. Mol Cell Biol 2006; 27:975-82. [PMID: 17130238 PMCID: PMC1800673 DOI: 10.1128/mcb.01512-06] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lung development depends upon the differentiation and expansion of a variety of specialized epithelial cell types, including distal type I and type II pneumocytes in the late term. Previous studies have shown a strict dependence on the choline cytidylyltransferase alpha isoform (CCTalpha) to mediate membrane phospholipid formation in cultured cells and during preimplantation embryogenesis. CCTalpha expression is highest in lung, and there has long been speculation about its precise role, due to the dual requirement for phospholipid in proliferating cell membranes and for lung surfactant production from alveolar type II cells. We investigated the function of CCTalpha in lung development, using an inducible, epithelial cell-specific CCTalpha knockout mouse line. Deletion of CCTalpha beginning at embryonic day 7.5 did not restrict lung development but resulted in severe respiratory failure at birth. Alveolar lavage and lung lipid analyses showed significant decreases in the major surfactant phospholipid, dipalmitoyl-phosphatidylcholine. The fatty acids destined for the surfactant phospholipid were redirected to an expanded triglyceride pool. Transcripts encoding type II cell-specific markers were expressed in the knockout mice, indicating the expected progression of differentiation in lung epithelia. However, surfactant protein levels were reduced, with the exception of that for surfactant protein B, which was elevated. Ultrastructural analysis of the type II cells showed Golgi complex abnormalities and aberrant lamellar bodies, which deliver surfactant lipid and protein to the alveolar lumen. Thus, CCTalpha was not required for the proliferation or differentiation of lung epithelia but was essential for the secretory component of phospholipid synthesis and critical for the proper formation of lamellar bodies and surfactant protein homeostasis.
Collapse
Affiliation(s)
- Yong Tian
- Department of Infectious Diseases, St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105-2794, USA
| | | | | | | |
Collapse
|
36
|
Lin W, Arthur G. Phospholipids are synthesized in the G2/M phase of the cell cycle. Int J Biochem Cell Biol 2006; 39:597-605. [PMID: 17113814 DOI: 10.1016/j.biocel.2006.10.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2006] [Revised: 09/19/2006] [Accepted: 10/11/2006] [Indexed: 11/29/2022]
Abstract
Very little is known about the metabolism of phospholipids in the G2 and M phases of the cell cycle, but limited studies have led to the postulation that phospholipid synthesis ceases during this period. To investigate whether phospholipids are synthesized in the G2/M phase of the cell cycle, protocols were developed to produce synchronized MCF-7 cell populations with greater than 80% of the cells in G1/S or G2/M phases that moved in synchrony following removal of the blocking agent. Analysis of the activities of key phosphatidylcholine and phosphatidylethanolamine biosynthetic enzymes in subcellular fractions obtained from MCF-7 cells at different cell cycle phases revealed that there was robust activity of key enzymes in the fractions prepared from MCF-7 cells in G2/M phase. Radiolabeled choline and ethanolamine were rapidly incorporated into cells maintained at G2/M phase with nocodazole, and the rates of incorporation were similar to those obtained in cells allowed to progress into the G1 phase. Furthermore, radiolabeled glycerol was incorporated into phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine and phosphatidic acid in MCF-7 cells maintained at G2/M phase with nocodazole. Similar results were obtained in CHO cells. These results demonstrate that glycerophospholipid synthesis is very active in the G2/M phase of these cells. Therefore, the postulated cessation of phospholipid synthesis in G2/M phases is not applicable to all cell types.
Collapse
Affiliation(s)
- Weiyang Lin
- Department of Biochemistry and Medical Genetics, University of Manitoba, 770 Bannatyne Avenue, Winnipeg, Manitoba, Canada R3E 0W3
| | | |
Collapse
|
37
|
Henderson FC, Miakotina OL, Mallampalli RK. Proapoptotic effects of P. aeruginosa involve inhibition of surfactant phosphatidylcholine synthesis. J Lipid Res 2006; 47:2314-24. [PMID: 16868337 DOI: 10.1194/jlr.m600284-jlr200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Pseudomonas aeruginosa causes sepsis-induced acute lung injury, a disorder associated with deficiency of surfactant phosphatidylcholine (PtdCho). P. aeruginosa (PA103) utilizes a type III secretion system (TTSS) to induce programmed cell death. Herein, we observed that PA103 reduced alveolar PtdCho levels, resulting in impaired lung biophysical activity, an effect partly attributed to caspase-dependent cleavage of the key PtdCho biosynthetic enzyme, CTP:phosphocholine cytidylyltransferase-alpha (CCTalpha). Expression of recombinant CCTalpha variants harboring point mutations at putative caspase cleavage sites in murine lung epithelia resulted in partial proteolytic resistance of CCTalpha to PA103. Further, caspase-directed CCTalpha degradation, decreased PtdCho levels, and cell death in murine lung epithelia were lessened after exposure of cells to bacterial strains lacking the TTSS gene product, exotoxin U (ExoU), but not ExoT. These observations suggest that during the proapoptotic program driven by P. aeruginosa, deleterious effects on phospholipid metabolism are mediated by a TTSS in concert with caspase activation, resulting in proteolysis of a key surfactant biosynthetic enzyme.
Collapse
Affiliation(s)
- Florita C Henderson
- Department of Internal Medicine, The University of Iowa, Iowa City, IA 52242, USA
| | | | | |
Collapse
|
38
|
Nieto-Miguel T, Gajate C, Mollinedo F. Differential Targets and Subcellular Localization of Antitumor Alkyl-lysophospholipid in Leukemic Versus Solid Tumor Cells. J Biol Chem 2006; 281:14833-40. [PMID: 16540473 DOI: 10.1074/jbc.m511251200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Synthetic alkyl-lysophospholipids represent a family of promising anticancer drugs that induce apoptosis in a variety of tumor cells. Here we have found a differential subcellular distribution of the alkyl-lysophospholipid edelfosine in leukemic and solid tumor cells that leads to distinct anticancer responses. Edelfosine induced rapid apoptosis in human leukemic cells, including acute T-cell leukemia Jurkat and Peer cells, but promoted a late apoptotic response, preceded by G(2)/M arrest, in human solid tumor cells such as cervix epitheloid carcinoma HeLa cells and lung carcinoma A549 cells. c-Jun amino-terminal kinase (JNK) and caspase-3 were accordingly activated at earlier times in edelfosine-treated Jurkat cells as compared with drug-treated HeLa cells. Both leukemic and solid tumor cells took up this alkyl-lysophospholipid and expressed the two putative edelfosine targets, namely cell surface Fas death receptor (also known as APO-1 or CD95) and endoplasmic reticulum CTP: phosphocholine cytidylyltransferase. However, edelfosine was mainly located to plasma membrane lipid rafts in Jurkat and Peer leukemic cells and to endoplasmic reticulum in solid tumor HeLa and A549 cells. Edelfosine induced translocation of Fas, Fas-associated death domain-containing protein, and JNK into membrane rafts in Jurkat cells, but not in HeLa cells. In contrast, edelfosine inhibited phosphatidylcholine biosynthesis in both HeLa and A549 cells, but not in Jurkat or Peer leukemic cells, before the triggering of apoptosis. These data indicate that edelfosine targets two different subcellular structures in a cell type-dependent manner, namely cell surface lipid rafts in leukemic cells and endoplasmic reticulum in solid tumor cells.
Collapse
Affiliation(s)
- Teresa Nieto-Miguel
- Centro de Investigación del Cáncer, Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior de Investigaciones Científicas-Universidad de Salamanca, Campus Miguel de Unamuno, E-37007 Salamanca, Spain
| | | | | |
Collapse
|
39
|
Lagace T, Ridgway N. Induction of apoptosis by lipophilic activators of CTP:phosphocholine cytidylyltransferase alpha (CCTalpha). Biochem J 2006; 392:449-56. [PMID: 16097951 PMCID: PMC1316283 DOI: 10.1042/bj20051021] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
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, CCTalpha (CTP:phosphocholine cytidylyltransferase alpha), 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 CCTalpha 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 CCTalpha, which was prevented by treatment with oleate or DiC8 (dioctanoylglycerol). Protection from FOH-induced apoptosis required CCTalpha 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 CCTalpha and increased PtdCho synthesis in CCTalpha-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 CCTalpha and PtdCho syntheses were sustained.
Collapse
Affiliation(s)
- Thomas A. Lagace
- Atlantic Research Centre, Departments of Pediatrics and Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada B3H 4H7
| | - Neale D. Ridgway
- Atlantic Research Centre, Departments of Pediatrics and Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada B3H 4H7
- To whom correspondence should be addressed, at Rm C306, CRC Bldg, Dalhousie University, 5849 University Avenue, Halifax, NS, Canada B3H 4H7 (email )
| |
Collapse
|
40
|
Ryan AJ, Andrews M, Zhou J, Mallampalli RK. c-Jun N-terminal kinase regulates CTP:phosphocholine cytidylyltransferase. Arch Biochem Biophys 2006; 447:23-33. [PMID: 16466687 DOI: 10.1016/j.abb.2006.01.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2005] [Revised: 01/09/2006] [Accepted: 01/11/2006] [Indexed: 11/19/2022]
Abstract
CTP:phosphocholine cytidylyltransferase (CCTalpha) is a rate-regulatory enzyme required for phosphatidylcholine (PtdCho) synthesis. CCTalpha is also a phosphoenzyme, but the physiologic role of kinases on enzyme function remains unclear. We report high-level expression of two major isoforms of the c-Jun N-terminal kinase family (JNK1 and JNK2) in murine lung epithelia. Further, JNK1 and JNK2 phosphorylated purified CCTalpha in vitro, and this was associated with a dose-dependent decrease (approximately 40%) in CCT activity. To evaluate JNK in vivo, lung epithelial cells were infected with a replication defective adenoviral vector encoding murine JNK2 (Adv-JNK2) or an empty vector. Adv-JNK2 infection, unlike the empty vector, markedly increased JNK2 expression concomitant with increased incorporation of [32P]orthophosphate into endogenous CCTalpha. Although Adv-JNK2 infection only modestly reduced CCT activity, it reduced PtdCho synthesis by approximately 30% in cells. These observations suggest a role for JNK kinases as negative regulators of phospholipid synthesis in murine lung epithelia.
Collapse
Affiliation(s)
- Alan J Ryan
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
| | | | | | | |
Collapse
|
41
|
Abstract
Once nuclear envelope membranes have been removed from isolated nuclei, around 6% of mammalian cell phospholipid is retained within the nuclear matrix, which calculations suggest may occupy 10% of the volume of this subcellular compartment. It is now acknowledged that endonuclear phospholipid, largely ignored for the past 40 years, provides substrate for lipid-mediated signaling events. However, given its abundance, it likely also has other as yet incompletely defined roles. Endonuclear phosphatidylcholine is the predominant phospholipid comprising distinct and highly saturated molecular species compared with that of the whole cell. Moreover, this unusual composition is subject to tight homeostatic maintenance even under conditions of extreme dietary manipulation, presumably reflecting a functional requirement for highly saturated endonuclear phosphatidylcholine. Recent application of new lipidomic technologies exploiting tandem electrospray ionization mass spectrometry in conjunction with deuterium stable isotope labeling have permitted us to probe not just molecular species compositions but endonuclear phospholipid acquisition and turnover with unparalleled sensitivity and specificity. What emerges is a picture of a dynamic pool of endonuclear phospholipid subject to autonomous regulation with respect to bulk cellular phospholipid metabolism. Compartmental biosynthesis de novo of endonuclear phosphatidylcholine contrasts with import of phosphatidylinositol synthesized elsewhere. However, irrespective of the precise temporal-spatial-dynamic relationships underpinning phospholipid acquisition, derangement of endonuclear lipid-mediated signaling from these parental phospholipids halts cell growth and division indicating a pivotal control point. This in turn defines the manipulation of compartmentalized endonuclear phospholipid acquisition and metabolism as intriguing potential targets for the development of future antiproliferative strategies.
Collapse
Affiliation(s)
- Alan N Hunt
- Allergy and Inflammation Research, Division of Infection, Inflammation & Repair, School of Medicine, University of Southampton, Southampton SO16 6YD, United Kingdom.
| |
Collapse
|
42
|
Joly E, Bendayan M, Roduit R, Saha AK, Ruderman NB, Prentki M. Malonyl-CoA decarboxylase is present in the cytosolic, mitochondrial and peroxisomal compartments of rat hepatocytes. FEBS Lett 2005; 579:6581-6. [PMID: 16298369 DOI: 10.1016/j.febslet.2005.10.050] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2005] [Accepted: 10/25/2005] [Indexed: 10/25/2022]
Abstract
A role for cytosolic malonyl-CoA decarboxylase (MCD) as a regulator of fatty acid oxidation has been postulated. However, there is no direct evidence that MCD is present in the cytosol. To address this issue, we performed cell fractionation and electron microscopic colloidal gold studies of rat liver to determine the location and activity of MCD. By both methods, substantial amounts of MCD protein and activity were found in the cytosol, mitochondria and peroxisomes, the latter with the highest specific activity. MCD species with different electrophoretic mobility were observed in the three fractions. The data demonstrate that active MCD is present in the cytosol, mitochondria and peroxisomes of rat liver, consistent with the view that MCD participates in the regulation of cytosolic malonyl-CoA levels and of hepatic fatty acid oxidation.
Collapse
Affiliation(s)
- Erik Joly
- Molecular Nutrition Unit and the Montreal Diabetes Research Center, Centre de recherche du CHUM, Pavillon de Sève, Y-4603, 1560 Sherbrooke Est, and the Department of Nutrition and Biochemistry, Université de Montréal, Montréal PQ, Canada, H3T 1C5
| | | | | | | | | | | |
Collapse
|
43
|
Agassandian M, Zhou J, Tephly LA, Ryan AJ, Carter AB, Mallampalli RK. Oxysterols inhibit phosphatidylcholine synthesis via ERK docking and phosphorylation of CTP:phosphocholine cytidylyltransferase. J Biol Chem 2005; 280:21577-87. [PMID: 15788406 DOI: 10.1074/jbc.m412409200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Surfactant deficiency contributes to acute lung injury and may result from the elaboration of bioactive lipids such as oxysterols. We observed that the oxysterol 22-hydroxycholesterol (22-HC) in combination with its obligate partner, 9-cis-retinoic acid (9-cis-RA), decreased surfactant phosphatidylcholine (PtdCho) synthesis by increasing phosphorylation of the regulatory enzyme CTP:phosphocholine cytidylyltransferase-alpha (CCTalpha). Phosphorylation of CCTalpha decreased its activity. 22-HC/9-cis-RA inhibition of PtdCho synthesis was blocked by PD98059 or dominant-negative ERK (p42 kinase). Overexpression of constitutively active MEK1, the kinase upstream of p42 kinase, increased CCTalpha phosphorylation. Expression of truncated CCTalpha mutants lacking proline-directed sites within the C-terminal phosphorylation domain partially blocked oxysterol-mediated inhibition of PtdCho synthesis. Mutagenesis of Ser315 within CCTalpha was both required and sufficient to confer significant resistance to 22-HC/9-cis-RA inhibition of PtdCho synthesis. A novel putative ERK-docking domain N-terminal to this phosphoacceptor site was mapped within the CCTalpha membrane-binding domain (residues 287-300). The results are the first demonstration of a physiologically relevant phosphorylation site and docking domain within CCTalpha that serve as targets for ERKs, resulting in inhibition of surfactant synthesis.
Collapse
Affiliation(s)
- Marianna Agassandian
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City 52242, USA
| | | | | | | | | | | |
Collapse
|
44
|
Kent C. Regulatory enzymes of phosphatidylcholine biosynthesis: a personal perspective. Biochim Biophys Acta Mol Cell Biol Lipids 2005; 1733:53-66. [PMID: 15749057 DOI: 10.1016/j.bbalip.2004.12.008] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2004] [Revised: 12/14/2004] [Accepted: 12/17/2004] [Indexed: 12/22/2022]
Abstract
Phosphatidylcholine is a prominent constituent of eukaryotic and some prokaryotic membranes. This Perspective focuses on the two enzymes that regulate its biosynthesis, choline kinase and CTP:phosphocholine cytidylyltransferase. These enzymes are discussed with respect to their molecular properties, isoforms, enzymatic activities, and structures, and the possible molecular mechanisms by which they participate in regulation of phosphatidylcholine levels in the cell.
Collapse
|
45
|
Ridsdale R, Tseu I, Roth-Kleiner M, Wang J, Post M. Increased Phosphatidylcholine Production but Disrupted Glycogen Metabolism in Fetal Type II Cells of Mice That Overexpress CTP:Phosphocholine Cytidylyltransferase. J Biol Chem 2004; 279:55946-57. [PMID: 15498769 DOI: 10.1074/jbc.m407670200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCT) is a rate-determining enzyme in the de novo synthesis of phosphatidylcholine (PtdCho). Alveolar type II cells synthesize large quantities of disaturated PtdCho, the surface-active agent of pulmonary surfactant, particularly at late gestation when the lung prepares itself for postnatal air breathing. To clarify the role of CCTalpha in lung surfactant maturation, we overexpressed CCTalpha(1-367) using the surfactant protein-C promoter. Lungs of transgenic mice were analyzed at day 18 of gestation (term = 19 days). Overexpression of CCTalpha(1-367) increased the synthesis and content of PtdCho in fetal type II cells isolated from the transgenic mice. Also, PtdCho content of fetal lung fluid was increased. No changes in surfactant protein content were detected. Interestingly, fetal type II cells of transgenic mice contained more glycogen than control cells. Incorporation studies with [U-(14)C]glucose demonstrated that overexpression of CCTalpha(1-367) in fetal type II cells increased glycogen synthesis without affecting glycogen breakdown. To determine which domain contributes to this glycogen phenotype, two additional transgenes were created overexpressing either CCTalpha(1-239) or CCTalpha(239-367). Glycogen synthesis and content were increased in fetal type II cells expressing CCTalpha(239-367) but not CCTalpha(1-239)(.) We conclude that overexpression of CCTalpha increases surfactant PtdCho synthesis without affecting surfactant protein levels but that it disrupts glycogen metabolism in differentiating type II cells via its regulatory domain.
Collapse
Affiliation(s)
- Ross Ridsdale
- Canadian Institutes of Health Research Group in Lung Development, Hospital for Sick Children Research Institute and Institute of Medical Sciences, University of Toronto, 555 University Avenue, Toronto M5G 1X8, Canada
| | | | | | | | | |
Collapse
|
46
|
Jackowski S, Fagone P. CTP: Phosphocholine cytidylyltransferase: paving the way from gene to membrane. J Biol Chem 2004; 280:853-6. [PMID: 15536089 DOI: 10.1074/jbc.r400031200] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- Suzanne Jackowski
- Protein Science Division, Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
| | | |
Collapse
|
47
|
Abstract
Identification of the genes and gene products involved in the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine has lagged behind that in many other fields because of difficulties encountered in purifying the respective proteins. Nevertheless, most of these genes have now been identified. In this review article, we have highlighted important new findings on the individual enzymes and the corresponding genes of phosphatidylcholine synthesis via its two major biosynthetic pathways: the CDP-choline pathway and the methylation pathway. We also review recent studies on phosphatidylethanolamine biosynthesis by two pathways: the CDP-ethanolamine pathway, which is active in the endoplasmic reticulum, and the phosphatidylserine decarboxylase pathway, which operates in mitochondria. Finally, the two base-exchange enzymes, phosphatidylserine synthase-1 and phosphatidylserine synthase-2, that synthesize phosphatidylserine in mammalian cells are also discussed.
Collapse
Affiliation(s)
- Jean E Vance
- Department of Medicine and CIHR Group on the Molecualr and Cell Biology of Lipids, University of Alberta, Edmonton, Canada.
| | | |
Collapse
|
48
|
Zhou J, You Y, Ryan AJ, Mallampalli RK. Upregulation of surfactant synthesis triggers ABCA1-mediated basolateral phospholipid efflux. J Lipid Res 2004; 45:1758-67. [PMID: 15210848 DOI: 10.1194/jlr.m400179-jlr200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Alveolar type II lung epithelia produce surfactant, an essential surface-active material highly enriched with disaturated phosphatidylcholine (DSPC), which requires a key regulatory enzyme, CTP:phosphocholine cytidylyltransferase alpha (CCTalpha), for its synthesis before its export apically into the alveolus. In this study, we examined whether surfactant phosphatidylcholine (PC) synthesis and export are physiologically linked. Stable overexpression of CCTalpha in lung epithelial cell lines increased rates of PC synthesis and cellular DSPC mass without altering total cellular PC content. Overexpression of CCTalpha was associated with i) increased basolateral, rather than apical, PC export catalyzed by ABCA1; ii) basolateral export of significant levels of unsaturated (nonsurfactant) PC; and iii) transcriptional activation of the ABCA1 gene via a liver X receptor/retinoic acid receptor-independent pathway. Cells exposed to PC vesicles exhibited a dose-dependent increase in ABCA1 transcriptional activity. These data provide the first evidence that surfactant PC synthesis is linked to its export via a basolateral lipid efflux pathway. This pathway is mediated, in part, by a phospholipid sensor, ABCA1, that appears to partake in the autoregulation of both cellular content and composition of PC, thereby providing a potentially novel exit route for a newly synthesized pool of PC distinct from surfactant.
Collapse
Affiliation(s)
- Jiming Zhou
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | | | | | | |
Collapse
|
49
|
Jackowski S, Rehg JE, Zhang YM, Wang J, Miller K, Jackson P, Karim MA. Disruption of CCTbeta2 expression leads to gonadal dysfunction. Mol Cell Biol 2004; 24:4720-33. [PMID: 15143167 PMCID: PMC416414 DOI: 10.1128/mcb.24.11.4720-4733.2004] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
There are two mammalian genes that encode isoforms of CTP:phosphocholine cytidylyltransferase (CCT), a key rate-controlling step in membrane phospholipid biogenesis. Quantitative determination of the CCT transcripts reveals that CCTalpha is ubiquitously expressed and is found at the highest levels in the testis and lung, with lower levels in the liver and ovary. CCTbeta2 is a very minor isoform in most tissues but is significantly expressed in the brain, lung, and gonads. CCTbeta3 is the third isoform recently discovered in mice and is expressed in the same tissues as CCTbeta2, with its highest level in testes. We investigated the role(s) of CCTbeta2 by generating knockout mice. The brains and lungs of mice lacking CCTbeta2 expression did not exhibit any overt defects. On the other hand, a large percentage of the CCTbeta2(-/-) females were sterile and their ovaries exhibited defective ovarian follicle development. The proportion of female CCTbeta2(-/-) mice with defective ovaries increased as the animals aged. The rare litters born from CCTbeta2(-/-) x CCTbeta2(-/0) matings had the normal number of pups. The abnormal ovarian histopathology was characterized by disorganization of the tissue in young adult mice and absence of follicles and ova in older mice, along with interstitial stromal cell hyperplasia which culminated in the emergence of tubulostromal ovarian tumors by 16 months of age. Grossly defective CCTbeta2(-/-) ovaries were associated with high follicle-stimulating (FSH) and luteinizing (LH) hormone levels. Male CCTbeta2(-/0) mice exhibited progressive multifocal testicular degeneration and reduced fertility but had normal FSH and LH levels. Thus, the most notable phenotype of CCTbeta2 knockout mice was gonad degeneration and reproductive deficiency. The results indicate that although CCTbeta2 is expressed at very low levels compared to the alpha-isoform, loss of CCTbeta2 expression causes a breakdown in the gonadal response to hormonal stimulation.
Collapse
Affiliation(s)
- Suzanne Jackowski
- Protein Science Division, Department of Infectious Diseases, St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105-2794, USA.
| | | | | | | | | | | | | |
Collapse
|
50
|
Ridsdale R, Post M. Surfactant lipid synthesis and lamellar body formation in glycogen-laden type II cells. Am J Physiol Lung Cell Mol Physiol 2004; 287:L743-51. [PMID: 15169678 DOI: 10.1152/ajplung.00146.2004] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Pulmonary surfactant is a lipoprotein complex that functions to reduce surface tension at the air liquid interface in the alveolus of the mature lung. In late gestation glycogen-laden type II cells shift their metabolic program toward the synthesis of surfactant, of which phosphatidylcholine (PC) is by far the most abundant lipid. To investigate the cellular site of surfactant PC synthesis in these cells we determined the subcellular localization of two key enzymes for PC biosynthesis, fatty acid synthase (FAS) and CTP:phosphocholine cytidylyltransferase-alpha (CCT-alpha), and compared their localization with that of surfactant storage organelles, the lamellar bodies (LBs), and surfactant proteins (SPs) in fetal mouse lung. Ultrastructural analysis showed that immature and mature LBs were present within the glycogen pools of fetal type II cells. Multivesicular bodies were noted only in the cytoplasm. Immunogold electron microscopy (EM) revealed that the glycogen pools were the prominent cellular sites for FAS and CCT-alpha. Energy-filtering EM demonstrated that CCT-alpha bound to phosphorus-rich (phospholipid) structures in the glycogen. SP-B and SP-C, but not SP-A, localized predominantly to the glycogen stores. Collectively, these data suggest that the glycogen stores in fetal type II cells are a cellular site for surfactant PC synthesis and LB formation/maturation consistent with the idea that the glycogen is a unique substrate for surfactant lipids.
Collapse
Affiliation(s)
- Ross Ridsdale
- Canadian Institutes of Health Research Group in Lung Development, Hospital for Sick Children Research Institute, and Institute of Medical Sciences, University of Toronto, Toronto, Ontario, M5G 1X8, Canada
| | | |
Collapse
|