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Šťastný D, Petrisková L, Tahotná D, Bauer J, Pokorná L, Holič R, Valachovič M, Pevala V, Cockcroft S, Griač P. Yeast Sec14-like lipid transfer proteins Pdr16 and Pdr17 bind and transfer the ergosterol precursor lanosterol in addition to phosphatidylinositol. FEBS Lett 2023; 597:504-514. [PMID: 36482167 DOI: 10.1002/1873-3468.14558] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Revised: 11/15/2022] [Accepted: 11/30/2022] [Indexed: 12/13/2022]
Abstract
Yeast Sec14-like phosphatidylinositol transfer proteins (PITPs) contain a hydrophobic cavity capable of accepting a single molecule of phosphatidylinositol (PI) or another molecule in a mutually exclusive manner. We report here that two yeast Sec14 family PITPs, Pdr16p (Sfh3p) and Pdr17p (Sfh4p), possess high-affinity binding and transfer towards lanosterol. To our knowledge, this is the first identification of lanosterol transfer proteins. In addition, a pdr16Δpdr17Δ double mutant had a significantly increased level of cellular lanosterol compared with the corresponding wild-type. Based on the lipid profiles of wild-type and pdr16Δpdr17Δ cells grown in aerobic and anaerobic conditions, we suggest that PI-lanosterol transfer proteins are important predominantly for the optimal functioning of the post-lanosterol part of sterol biosynthesis.
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Affiliation(s)
- Dominik Šťastný
- Centre of Biosciences, Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Lívia Petrisková
- Centre of Biosciences, Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Dana Tahotná
- Centre of Biosciences, Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Jacob Bauer
- Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Lucia Pokorná
- Centre of Biosciences, Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Roman Holič
- Centre of Biosciences, Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Martin Valachovič
- Centre of Biosciences, Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Vladimír Pevala
- Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovakia
| | - Shamshad Cockcroft
- Division of Biosciences, Department of Neuroscience, Physiology and Pharmacology, University College London, UK
| | - Peter Griač
- Centre of Biosciences, Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia
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2
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Kimura AK, Kimura T. Phosphatidylserine biosynthesis pathways in lipid homeostasis: Toward resolution of the pending central issue for decades. FASEB J 2020; 35:e21177. [PMID: 33205488 DOI: 10.1096/fj.202001802r] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 10/17/2020] [Accepted: 10/26/2020] [Indexed: 12/28/2022]
Abstract
Enzymatic control of lipid homeostasis in the cell is a vital element in the complex organization of life. Phosphatidylserine (PS) is an essential anionic phospholipid of cell membranes, and conducts numerous roles for their structural and functional integrity. In mammalian cells, two distinct enzymes phosphatidylserine synthases-1 (PSS1) and -2 (PSS2) in the mitochondria-associated membrane (MAM) in the ER perform de novo synthesis of PS. It is based on base-exchange reactions of the preexisting dominant phospholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE). While PSS2 specifically catalyzes the reaction "PE → PS," whether or not PSS1 is responsible for the same reaction along with the reaction "PC → PS" remains unsettled despite its fundamental impact on the major stoichiometry. We propose here that a key but the only report that appeared to have put scientists on hold for decades in answering to this issue may be viewed consistently with other available research reports; PSS1 utilizes the two dominant phospholipid classes at a similar intrinsic rate. In this review, we discuss the issue in view of the current information for the enzyme machineries, membrane structure and dynamics, intracellular network of lipid transport, and PS synthesis in health and disease. Resolution of the pending issue is thus critical in advancing our understanding of roles of the essential anionic lipid in biology, health, and disease.
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Affiliation(s)
- Atsuko K Kimura
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
| | - Tomohiro Kimura
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
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3
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Pevalová Z, Pevala V, Blunsom NJ, Tahotná D, Kotrasová V, Holič R, Pokorná L, Bauer JA, Kutejová E, Cockcroft S, Griač P. Yeast phosphatidylinositol transfer protein Pdr17 does not require high affinity phosphatidylinositol binding for its cellular function. Biochim Biophys Acta Mol Cell Biol Lipids 2019; 1864:1412-1421. [DOI: 10.1016/j.bbalip.2019.07.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Accepted: 07/09/2019] [Indexed: 11/28/2022]
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4
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Pemberton JG, Balla T. Polyphosphoinositide-Binding Domains: Insights from Peripheral Membrane and Lipid-Transfer Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1111:77-137. [PMID: 30483964 DOI: 10.1007/5584_2018_288] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Within eukaryotic cells, biochemical reactions need to be organized on the surface of membrane compartments that use distinct lipid constituents to dynamically modulate the functions of integral proteins or influence the selective recruitment of peripheral membrane effectors. As a result of these complex interactions, a variety of human pathologies can be traced back to improper communication between proteins and membrane surfaces; either due to mutations that directly alter protein structure or as a result of changes in membrane lipid composition. Among the known structural lipids found in cellular membranes, phosphatidylinositol (PtdIns) is unique in that it also serves as the membrane-anchored precursor of low-abundance regulatory lipids, the polyphosphoinositides (PPIn), which have restricted distributions within specific subcellular compartments. The ability of PPIn lipids to function as signaling platforms relies on both non-specific electrostatic interactions and the selective stereospecific recognition of PPIn headgroups by specialized protein folds. In this chapter, we will attempt to summarize the structural diversity of modular PPIn-interacting domains that facilitate the reversible recruitment and conformational regulation of peripheral membrane proteins. Outside of protein folds capable of capturing PPIn headgroups at the membrane interface, recent studies detailing the selective binding and bilayer extraction of PPIn species by unique functional domains within specific families of lipid-transfer proteins will also be highlighted. Overall, this overview will help to outline the fundamental physiochemical mechanisms that facilitate localized interactions between PPIn lipids and the wide-variety of PPIn-binding proteins that are essential for the coordinate regulation of cellular metabolism and membrane dynamics.
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Affiliation(s)
- Joshua G Pemberton
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Tamas Balla
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
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5
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Lipid transfer proteins and the tuning of compartmental identity in the Golgi apparatus. Chem Phys Lipids 2016; 200:42-61. [DOI: 10.1016/j.chemphyslip.2016.06.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2016] [Revised: 06/21/2016] [Accepted: 06/22/2016] [Indexed: 11/23/2022]
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Yadav S, Garner K, Georgiev P, Li M, Gomez-Espinosa E, Panda A, Mathre S, Okkenhaug H, Cockcroft S, Raghu P. RDGBα, a PtdIns-PtdOH transfer protein, regulates G-protein-coupled PtdIns(4,5)P2 signalling during Drosophila phototransduction. J Cell Sci 2015. [PMID: 26203165 PMCID: PMC4582195 DOI: 10.1242/jcs.173476] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Many membrane receptors activate phospholipase C (PLC) during signalling, triggering changes in the levels of several plasma membrane lipids including phosphatidylinositol (PtdIns), phosphatidic acid (PtdOH) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. It is widely believed that exchange of lipids between the plasma membrane and endoplasmic reticulum (ER) is required to restore lipid homeostasis during PLC signalling, yet the mechanism remains unresolved. RDGBα (hereafter RDGB) is a multi-domain protein with a PtdIns transfer protein (PITP) domain (RDGB-PITPd). We find that, in vitro, the RDGB-PITPd binds and transfers both PtdOH and PtdIns. In Drosophila photoreceptors, which experience high rates of PLC activity, RDGB function is essential for phototransduction. We show that binding of PtdIns to RDGB-PITPd is essential for normal phototransduction; however, this property is insufficient to explain the in vivo function because another Drosophila PITP (encoded by vib) that also binds PtdIns cannot rescue the phenotypes of RDGB deletion. In RDGB mutants, PtdIns(4,5)P2 resynthesis at the plasma membrane following PLC activation is delayed and PtdOH levels elevate. Thus RDGB couples the turnover of both PtdIns and PtdOH, key lipid intermediates during G-protein-coupled PtdIns(4,5)P2 turnover.
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Affiliation(s)
- Shweta Yadav
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore, Karnataka 560065, India
| | - Kathryn Garner
- Department of Neuroscience, Physiology and Pharmacology, University College, London WC1E 6JJ, UK
| | - Plamen Georgiev
- Inositide Laboratory, Babraham Institute, Cambridge CB22 3AT, UK
| | - Michelle Li
- Department of Neuroscience, Physiology and Pharmacology, University College, London WC1E 6JJ, UK
| | - Evelyn Gomez-Espinosa
- Department of Neuroscience, Physiology and Pharmacology, University College, London WC1E 6JJ, UK
| | - Aniruddha Panda
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore, Karnataka 560065, India Manipal University, Madhav Nagar, Manipal, Karnataka 576104, India
| | - Swarna Mathre
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore, Karnataka 560065, India Manipal University, Madhav Nagar, Manipal, Karnataka 576104, India
| | | | - Shamshad Cockcroft
- Department of Neuroscience, Physiology and Pharmacology, University College, London WC1E 6JJ, UK
| | - Padinjat Raghu
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore, Karnataka 560065, India Inositide Laboratory, Babraham Institute, Cambridge CB22 3AT, UK
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Phosphatidylinositol binding of Saccharomyces cerevisiae Pdr16p represents an essential feature of this lipid transfer protein to provide protection against azole antifungals. Biochim Biophys Acta Mol Cell Biol Lipids 2014; 1842:1483-90. [PMID: 25066473 PMCID: PMC4331669 DOI: 10.1016/j.bbalip.2014.07.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Revised: 06/25/2014] [Accepted: 07/18/2014] [Indexed: 12/30/2022]
Abstract
Pdr16p is considered a factor of clinical azole resistance in fungal pathogens. The most distinct phenotype of yeast cells lacking Pdr16p is their increased susceptibility to azole and morpholine antifungals. Pdr16p (also known as Sfh3p) of Saccharomyces cerevisiae belongs to the Sec14 family of phosphatidylinositol transfer proteins. It facilitates transfer of phosphatidylinositol (PI) between membrane compartments in in vitro systems. We generated Pdr16pE235A, K267A mutant defective in PI binding. This PI binding deficient mutant is not able to fulfill the role of Pdr16p in protection against azole and morpholine antifungals, providing evidence that PI binding is critical for Pdr16 function in modulation of sterol metabolism in response to these two types of antifungal drugs. A novel feature of Pdr16p, and especially of Pdr16pE235A, K267A mutant, to bind sterol molecules, is observed. Yeast Pdr16p binds phosphatidylinositol (PI) and cholesterol in lipid binding assay. Pdr16pE235A, K267A is defective in PI binding, it binds sterols instead of PI. Pdr16p defective in PI binding does not fulfill Pdr16p role in azole protection. PI binding of Pdr16p is critical for its function.
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Sakai-Kato K, Un K, Nanjo K, Nishiyama N, Kusuhara H, Kataoka K, Kawanishi T, Goda Y, Okuda H. Elucidating the molecular mechanism for the intracellular trafficking and fate of block copolymer micelles and their components. Biomaterials 2014; 35:1347-58. [DOI: 10.1016/j.biomaterials.2013.11.027] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 11/08/2013] [Indexed: 01/14/2023]
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9
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Un K, Sakai-Kato K, Kawanishi T, Okuda H, Goda Y. Effects of Liposomal Phospholipids and Lipid Transport-Related Protein on the Intracellular Fate of Encapsulated Doxorubicin. Mol Pharm 2014; 11:560-7. [DOI: 10.1021/mp400505a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Keita Un
- Division
of Drugs, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Kumiko Sakai-Kato
- Division
of Drugs, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Toru Kawanishi
- National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Haruhiro Okuda
- National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
| | - Yukihiro Goda
- Division
of Drugs, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
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van Ooij C, Withers-Martinez C, Ringel A, Cockcroft S, Haldar K, Blackman MJ. Identification of a Plasmodium falciparum phospholipid transfer protein. J Biol Chem 2013; 288:31971-83. [PMID: 24043620 PMCID: PMC3814793 DOI: 10.1074/jbc.m113.474189] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Infection of erythrocytes by the human malaria parasite Plasmodium falciparum results in dramatic modifications to the host cell, including changes to its antigenic and transport properties and the de novo formation of membranous compartments within the erythrocyte cytosol. These parasite-induced structures are implicated in the transport of nutrients, metabolic products, and parasite proteins, as well as in parasite virulence. However, very few of the parasite effector proteins that underlie remodeling of the host erythrocyte are functionally characterized. Using bioinformatic examination and modeling, we have found that the exported P. falciparum protein PFA0210c belongs to the START domain family, members of which mediate transfer of phospholipids, ceramide, or fatty acids between membranes. In vitro phospholipid transfer assays using recombinant PFA0210 confirmed that it can transfer phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, and sphingomyelin between phospholipid vesicles. Furthermore, assays using HL60 cells containing radiolabeled phospholipids indicated that orthologs of PFA0210c can also transfer phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine. Biochemical and immunochemical analysis showed that PFA0210c associates with membranes in infected erythrocytes at mature stages of intracellular parasite growth. Localization studies in live parasites revealed that the protein is present in the parasitophorous vacuole during growth and is later recruited to organelles in the parasite. Together these data suggest that PFA0210c plays a role in the formation of the membranous structures and nutrient phospholipid transfer in the malaria-parasitized erythrocyte.
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Affiliation(s)
- Christiaan van Ooij
- From the Division of Parasitology, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom
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11
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Abstract
Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.
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Affiliation(s)
- Tamas Balla
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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12
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Taouji S, Higa A, Delom F, Palcy S, Mahon FX, Pasquet JM, Bossé R, Ségui B, Chevet E. Phosphorylation of serine palmitoyltransferase long chain-1 (SPTLC1) on tyrosine 164 inhibits its activity and promotes cell survival. J Biol Chem 2013; 288:17190-201. [PMID: 23629659 DOI: 10.1074/jbc.m112.409185] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In BCR-ABL-expressing cells, sphingolipid metabolism is altered. Because the first step of sphingolipid biosynthesis occurs in the endoplasmic reticulum (ER), our objective was to identify ABL targets in the ER. A phosphoproteomic analysis of canine pancreatic ER microsomes identified 49 high scoring phosphotyrosine-containing peptides. These were then categorized in silico and validated in vitro. We demonstrated that the ER-resident human protein serine palmitoyltransferase long chain-1 (SPTLC1), which is the first enzyme of sphingolipid biosynthesis, is phosphorylated at Tyr(164) by the tyrosine kinase ABL. Inhibition of BCR-ABL using either imatinib or shRNA-mediated silencing led to the activation of SPTLC1 and to increased apoptosis in both K562 and LAMA-84 cells. Finally, we demonstrated that mutation of Tyr(164) to Phe in SPTLC1 increased serine palmitoyltransferase activity. The Y164F mutation also promoted the remodeling of cellular sphingolipid content, thereby sensitizing K562 cells to apoptosis. Our observations provide a mechanistic explanation for imatinib-mediated cell death and a novel avenue for therapeutic strategies.
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Un K, Sakai-Kato K, Oshima Y, Kawanishi T, Okuda H. Intracellular trafficking mechanism, from intracellular uptake to extracellular efflux, for phospholipid/cholesterol liposomes. Biomaterials 2012; 33:8131-41. [DOI: 10.1016/j.biomaterials.2012.07.030] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Accepted: 07/15/2012] [Indexed: 01/27/2023]
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Garner K, Hunt AN, Koster G, Somerharju P, Groves E, Li M, Raghu P, Holic R, Cockcroft S. Phosphatidylinositol transfer protein, cytoplasmic 1 (PITPNC1) binds and transfers phosphatidic acid. J Biol Chem 2012; 287:32263-76. [PMID: 22822086 DOI: 10.1074/jbc.m112.375840] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Phosphatidylinositol transfer proteins (PITPs) are versatile proteins required for signal transduction and membrane traffic. The best characterized mammalian PITPs are the Class I PITPs, PITPα (PITPNA) and PITPβ (PITPNB), which are single domain proteins with a hydrophobic cavity that binds a phosphatidylinositol (PI) or phosphatidylcholine molecule. In this study, we report the lipid binding properties of an uncharacterized soluble PITP, phosphatidylinositol transfer protein, cytoplasmic 1 (PITPNC1) (alternative name, RdgBβ), of the Class II family. We show that the lipid binding properties of this protein are distinct to Class I PITPs because, besides PI, RdgBβ binds and transfers phosphatidic acid (PA) but hardly binds phosphatidylcholine. RdgBβ when purified from Escherichia coli is preloaded with PA and phosphatidylglycerol. When RdgBβ was incubated with permeabilized HL60 cells, phosphatidylglycerol was released, and PA and PI were now incorporated into RdgBβ. After an increase in PA levels following activation of endogenous phospholipase D or after addition of bacterial phospholipase D, binding of PA to RdgBβ was greater at the expense of PI binding. We propose that RdgBβ, when containing PA, regulates an effector protein or can facilitate lipid transfer between membrane compartments.
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Affiliation(s)
- Kathryn Garner
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6JJ, United Kingdom
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Milhas D, Andrieu-Abadie N, Levade T, Benoist H, Ségui B. The tricyclodecan-9-yl-xanthogenate D609 triggers ceramide increase and enhances FasL-induced caspase-dependent and -independent cell death in T lymphocytes. Int J Mol Sci 2012; 13:8834-8852. [PMID: 22942738 PMCID: PMC3430269 DOI: 10.3390/ijms13078834] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2012] [Revised: 06/30/2012] [Accepted: 07/04/2012] [Indexed: 01/02/2023] Open
Abstract
D609 is known to modulate death receptor-induced ceramide generation and cell death. We show that in Jurkat cells, non-toxic D609 concentrations inhibit sphingomyelin synthase and, to a lesser extent, glucosylceramide synthase, and transiently increase the intracellular ceramide level. D609 significantly enhanced FasL-induced caspase activation and apoptosis. D609 stimulated FasL-induced cell death in caspase-8-deficient Jurkat cells, indicating that D609 acts downstream of caspase-8. At high FasL concentration (500 ng/mL), cell death was significantly, but not completely, inhibited by zVAD-fmk, a broad-spectrum caspase inhibitor, indicating that FasL can activate both caspase-dependent and -independent cell death signaling pathways. FasL-induced caspase activation was abolished by zVAD-fmk, whereas ceramide production was only partially impaired. D609 enhanced caspase-independent ceramide increase and cell death in response to FasL. Also, D609 overcame zVAD-fmk-conferred resistance to a FasL concentration as low as 50 ng/mL and bypassed RIP deficiency. It is likely that mitochondrial events were involved, since Bcl-xL over-expression impaired D609 effects. In PHA-activated human T lymphocytes, D609 enhanced FasL-induced cell death in the presence or absence of zVAD-fmk. Altogether, our data strongly indicate that the inhibition of ceramide conversion to complex sphingolipids by D609 is accompanied by an enhancement of FasL-induced caspase-dependent and -independent cell death in T lymphocytes.
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Affiliation(s)
- Delphine Milhas
- Team 4, Cancer Research Center of Toulouse, INSERM UMR1037, BP84225, 31432 Toulouse Cedex 4, France; E-Mails: (D.M.); (N.A.-A.); (T.L.); (H.B.)
| | - Nathalie Andrieu-Abadie
- Team 4, Cancer Research Center of Toulouse, INSERM UMR1037, BP84225, 31432 Toulouse Cedex 4, France; E-Mails: (D.M.); (N.A.-A.); (T.L.); (H.B.)
| | - Thierry Levade
- Team 4, Cancer Research Center of Toulouse, INSERM UMR1037, BP84225, 31432 Toulouse Cedex 4, France; E-Mails: (D.M.); (N.A.-A.); (T.L.); (H.B.)
| | - Hervé Benoist
- Team 4, Cancer Research Center of Toulouse, INSERM UMR1037, BP84225, 31432 Toulouse Cedex 4, France; E-Mails: (D.M.); (N.A.-A.); (T.L.); (H.B.)
- Department of Cell Biology, Hematology and Immunology, Faculty of Pharmaceutical Sciences, Paul Sabatier University (Toulouse III), 31062 Toulouse, France
| | - Bruno Ségui
- Team 4, Cancer Research Center of Toulouse, INSERM UMR1037, BP84225, 31432 Toulouse Cedex 4, France; E-Mails: (D.M.); (N.A.-A.); (T.L.); (H.B.)
- Department of Cell Biology, Hematology and Immunology, Faculty of Pharmaceutical Sciences, Paul Sabatier University (Toulouse III), 31062 Toulouse, France
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +33-5-61-32-35-31; Fax: +33-5-61-32-20-84
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The phosphatidylinositol transfer protein RdgBβ binds 14-3-3 via its unstructured C-terminus, whereas its lipid-binding domain interacts with the integral membrane protein ATRAP (angiotensin II type I receptor-associated protein). Biochem J 2011; 439:97-111. [DOI: 10.1042/bj20110649] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
PITPs [PI (phosphatidylinositol) transfer proteins] bind and transfer PI between intracellular membranes and participate in many cellular processes including signalling, lipid metabolism and membrane traffic. The largely uncharacterized PITP RdgBβ (PITPNC1; retinal degeneration type B β), contains a long C-terminal disordered region following its defining N-terminal PITP domain. In the present study we report that the C-terminus contains two tandem phosphorylated binding sites (Ser274 and Ser299) for 14-3-3. The C-terminus also contains PEST sequences which are shielded by 14-3-3 binding. Like many proteins containing PEST sequences, the levels of RdgBβ are regulated by proteolysis. RdgBβ is degraded with a half-life of 4 h following ubiquitination via the proteasome. A mutant RdgBβ which is unable to bind 14-3-3 is degraded even faster with a half-life of 2 h. In vitro, RdgBβ is 100-fold less active than PITPα for PI transfer, and RdgBβ proteins (wild-type and a mutant that cannot bind 14-3-3) expressed in COS-7 cells or endogenous proteins from heart cytosol do not exhibit transfer activity. When cells are treated with PMA, the PITP domain of RdgBβ interacts with the integral membrane protein ATRAP (angiotensin II type I receptor-associated protein; also known as AGTRAP) causing membrane recruitment. We suggest that RdgBβ executes its function following recruitment to membranes via its PITP domain and the C-terminal end of the protein could regulate entry to the hydrophobic cavity.
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Cockcroft S, Garner K. Function of the phosphatidylinositol transfer protein gene family: is phosphatidylinositol transfer the mechanism of action? Crit Rev Biochem Mol Biol 2011; 46:89-117. [DOI: 10.3109/10409238.2010.538664] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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Cockcroft S. Measurement of phosphatidylinositol and phosphatidylcholine binding and transfer activity of the lipid transport protein PITP. Methods Mol Biol 2009; 462:363-377. [PMID: 19160681 DOI: 10.1007/978-1-60327-115-8_23] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Mammalian cells have evolved proteins that can extract single lipids from membranes and sequester them in their hydrophobic cavity. These proteins, collectively known as lipid transport proteins, play essential roles in many aspects of lipid metabolism, lipid signaling, and membrane traffic. Phosphatidylinositol transfer proteins (alpha and beta) are lipid transport proteins that specifically bind phosphatidylinositol or phosphatidylcholine in their hydrophobic cavity and facilitate their transfer from one membrane compartment to another. In addition, PITPbeta can facilitate sphingomyelin transfer. This chapter describes methods to monitor the transfer and binding activity of PITPs using a variety of assays, including an assay that uses microsomes as a donor and liposomes as an acceptor of PtdIns. For phosphatidylcholine and sphingomyelin transfer, liposomes are used as a donor compartment and mitochondria as an acceptor compartment. A separate method describes the use of permeabilized cells as a source of donor lipids and liposomes as an acceptor membrane. In addition to lipid transfer, methods to identify the lipids that occupy the hydrophobic cavity of PITPs are discussed.
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Affiliation(s)
- Shamshad Cockcroft
- Department of Physiology, Rockefeller Building, University College London, London, UK.
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20
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Shadan S, Holic R, Carvou N, Ee P, Li M, Murray-Rust J, Cockcroft S. Dynamics of lipid transfer by phosphatidylinositol transfer proteins in cells. Traffic 2008; 9:1743-56. [PMID: 18636990 PMCID: PMC2635478 DOI: 10.1111/j.1600-0854.2008.00794.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Of many lipid transfer proteins identified, all have been implicated in essential cellular processes, but the activity of none has been demonstrated in intact cells. Among these, phosphatidylinositol transfer proteins (PITP) are of particular interest as they can bind to and transfer phosphatidylinositol (PtdIns) – the precursor of important signalling molecules, phosphoinositides – and because they have essential functions in neuronal development (PITPα) and cytokinesis (PITPβ). Structural analysis indicates that, in the cytosol, PITPs are in a ‘closed’ conformation completely shielding the lipid within them. But during lipid exchange at the membrane, they must transiently ‘open’. To study PITP dynamics in intact cells, we chemically targeted their C95 residue that, although non-essential for lipid transfer, is buried within the phospholipid-binding cavity, and so, its chemical modification prevents PtdIns binding because of steric hindrance. This treatment resulted in entrapment of open conformation PITPs at the membrane and inactivation of the cytosolic pool of PITPs within few minutes. PITP isoforms were differentially inactivated with the dynamics of PITPβ faster than PITPα. We identify two tryptophan residues essential for membrane docking of PITPs.
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Affiliation(s)
- Sadaf Shadan
- Department of Cell and Developmental Biology, Lipid Signalling Group, University College London, London, UK
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21
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Haberkant P, Schmitt O, Contreras FX, Thiele C, Hanada K, Sprong H, Reinhard C, Wieland FT, Brügger B. Protein-sphingolipid interactions within cellular membranes. J Lipid Res 2007; 49:251-62. [PMID: 17906222 DOI: 10.1194/jlr.d700023-jlr200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Each intracellular organelle critically depends on maintaining its specific lipid composition that in turn contributes to the biophysical properties of the membrane. With our knowledge increasing about the organization of membranes with defined microdomains of different lipid compositions, questions arise regarding the molecular mechanisms that underlie the targeting to/segregation from microdomains of a given protein. In addition to specific lipid-transmembrane segment interactions as a basis for partitioning, the presence in a given microdomain may alter the conformation of proteins and, thus, the activity and availability for regulatory modifications. However, for most proteins, the specific lipid environment of transmembrane segments as well as its relevance to protein function and overall membrane organization are largely unknown. To help fill this gap, we have synthesized a novel photoactive sphingolipid precursor that, together with a precursor for phosphoglycerolipids and with photo-cholesterol, was investigated in vivo with regard to specific protein transmembrane span-lipid interactions. As a proof of principle, we show specific labeling of the ceramide transporter with the sphingolipid probe and describe specific in vivo interactions of lipids with caveolin-1, phosphatidylinositol transfer protein beta, and the mature form of nicastrin. This novel photolabile sphingolipid probe allows the detection of protein-sphingolipid interactions within the membrane bilayer of living cells.
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Affiliation(s)
- Per Haberkant
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
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22
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Cockcroft S, Carvou N. Biochemical and biological functions of class I phosphatidylinositol transfer proteins. Biochim Biophys Acta Mol Cell Biol Lipids 2007; 1771:677-91. [PMID: 17490911 DOI: 10.1016/j.bbalip.2007.03.009] [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] [Received: 12/06/2006] [Revised: 03/05/2007] [Accepted: 03/27/2007] [Indexed: 12/21/2022]
Abstract
Phosphoinositides function in a diverse array of cellular activities. They include a role as substrate for lipid kinases and phospholipases to generate second messengers, regulators of the cytoskeleton, of enzymes and of ion channels, and docking sites for reversible recruitment of proteins to membranes. Mammalian phosphatidylinositol transfer proteins, PITPalpha and PITPbeta are paralogs that share 77% sequence identity and contain a hydrophobic cavity that can sequester either phosphatidylinositol or phosphatidylcholine. A string of 11 amino acid residues at the C-terminal acts as a "lid" which shields the lipid from the aqueous environment. PITPs in vitro can facilitate inter-membrane lipid transfer and this requires the movement of the "lid" to allow the lipid cargo to be released. Thus PITPs are structurally designed for delivering lipid cargo and could thus participate in cellular events that are dependent on phosphatidylinositol or derivatives of phosphatidylinositol. Phosphatidylinositol, the precursor for all phosphoinositides is synthesised at the endoplasmic reticulum and its distribution to other organelles could be facilitated by PITPs. Here we highlight recent studies that report on the three-dimensional structures of the different PITP forms and suggest how PITPs are likely to dock at the membrane surface for lipid delivery and extraction. Additionally we discuss whether PITPs are important regulators of sphingomyelin metabolism, and finally describe recent studies that link the association of PITPs with diverse functions including membrane traffic at the Golgi, neurite outgrowth, cytokinesis and stem cell growth.
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Affiliation(s)
- Shamshad Cockcroft
- Department of Physiology, 21 University Street, University College London, London WC1E 6JJ, UK.
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23
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Morgan C, Allen-Baume V, Radulovic M, Li M, Skippen A, Cockcroft S. Differential expression of a C-terminal splice variant of phosphatidylinositol transfer protein beta lacking the constitutive-phosphorylated Ser262 that localizes to the Golgi compartment. Biochem J 2006; 398:411-21. [PMID: 16780419 PMCID: PMC1559474 DOI: 10.1042/bj20060420] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Mammalian PITPbeta (phosphatidylinositol transfer protein beta) is a 272-amino-acid polypeptide capable of transferring PtdIns, PtdCho and SM (sphingomyelin) between membrane bilayers. It has been reported that Ser262 present in the C-terminus of PITPbeta is constitutively phosphorylated and determines Golgi localization. We provide evidence for the expression of an sp (splice) variant of PITPbeta (PITPbeta-sp2) where the C-terminal 15 amino acids of PITPbeta-sp1 are replaced by an alternative C-terminus of 16 amino acids. PITPbeta-sp1 is the product of the first 11 exons, whereas PITPbeta-sp2 is a product of the first 10 exons followed by the twelfth exon--exon 11 being 'skipped'. Both splice variants are capable of PtdIns and PtdCho transfer, with PITPbeta-sp2 being unable to transport SM. PITPbeta is ubiquitously expressed, with the highest amounts of PITPbeta found in HL60 cells and in rat liver; HL60 cells express only PITPbeta-sp1, whereas rat liver expresses both sp variants in similar amounts. In both cell types, PITPbeta-sp1 is constitutively phosphorylated and both the PtdIns and PtdCho forms of PITPbeta-sp1 are present. In contrast, PITPbeta-sp2 lacks the constitutively phosphorylated Ser262 (replaced with glutamine). Nonetheless, both PITPbeta variants localize to the Golgi and, moreover, dephosphorylation of Ser262 of PITPbeta-sp1 does not affect its Golgi localization. The presence of PITPbeta sp variants adds an extra level of proteome complexity and, in rat liver, the single gene for PITPbeta gives rise to seven distinct protein species that can be resolved on the basis of their charge differences.
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Affiliation(s)
- Clive P. Morgan
- *Lipid Signalling Group, Department of Physiology, University College London, 21 University Street, Rockefeller Building, London WC1E 6JJ, U.K
| | - Victoria Allen-Baume
- *Lipid Signalling Group, Department of Physiology, University College London, 21 University Street, Rockefeller Building, London WC1E 6JJ, U.K
| | - Marko Radulovic
- †Department of Medicine, University College London, WC1E 6JJ, U.K
| | - Michelle Li
- *Lipid Signalling Group, Department of Physiology, University College London, 21 University Street, Rockefeller Building, London WC1E 6JJ, U.K
| | - Alison Skippen
- *Lipid Signalling Group, Department of Physiology, University College London, 21 University Street, Rockefeller Building, London WC1E 6JJ, U.K
| | - Shamshad Cockcroft
- *Lipid Signalling Group, Department of Physiology, University College London, 21 University Street, Rockefeller Building, London WC1E 6JJ, U.K
- To whom correspondence should be addressed (email )
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24
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Denny PW, Shams-Eldin H, Price HP, Smith DF, Schwarz RT. The protozoan inositol phosphorylceramide synthase: a novel drug target that defines a new class of sphingolipid synthase. J Biol Chem 2006; 281:28200-9. [PMID: 16861742 PMCID: PMC1817671 DOI: 10.1074/jbc.m600796200] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sphingolipids are ubiquitous and essential components of eukaryotic membranes, particularly the plasma membrane. The biosynthetic pathway for the formation of these lipid species is conserved up to the formation of sphinganine. However, a divergence is apparent in the synthesis of complex sphingolipids. In animal cells, ceramide is a substrate for sphingomyelin (SM) production via the enzyme SM synthase. In contrast, fungi utilize phytoceramide in the synthesis of inositol phosphorylceramide (IPC) catalyzed by IPC synthase. Because of the absence of a mammalian equivalent, this essential enzyme represents an attractive target for anti-fungal compounds. In common with the fungi, the kinetoplastid protozoa (and higher plants) synthesize IPC rather than SM. However, orthologues of the gene believed to encode the fungal IPC synthase (AUR1) are not readily identified in the complete genome data bases of these species. By utilizing bioinformatic and functional genetic approaches, we have isolated a functional orthologue of AUR1 in the kinetoplastids, causative agents of a range of important human diseases. Expression of this gene in a mammalian cell line led to the synthesis of an IPC-like species, strongly indicating that IPC synthase activity is reconstituted. Furthermore, the gene product can be specifically inhibited by an anti-fungal-targeting IPC synthase. We propose that the kinetoplastid AUR1 functional orthologue encodes an enzyme that defines a new class of protozoan sphingolipid synthase. The identification and characterization of the protozoan IPC synthase, an enzyme with no mammalian equivalent, will raise the possibility of developing anti-protozoal drugs with minimal toxic side affects.
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Affiliation(s)
- Paul W Denny
- Centre for Infectious Diseases, Wolfson Research Institute, Durham University, Queen's Campus, Stockton-on-Tees TS17 6BH, United Kingdom.
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25
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Perry RJ, Ridgway ND. Molecular mechanisms and regulation of ceramide transport. Biochim Biophys Acta Mol Cell Biol Lipids 2005; 1734:220-34. [PMID: 15907394 DOI: 10.1016/j.bbalip.2005.04.001] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2005] [Revised: 04/06/2005] [Accepted: 04/07/2005] [Indexed: 10/25/2022]
Abstract
De novo biosynthesis of sphingolipids begins in the endoplasmic reticulum (ER) and continues in the Golgi apparatus and plasma membrane. A crucial step in sphingolipid biosynthesis is the transport of ceramide by vesicular and non-vesicular mechanisms from its site of synthesis in the ER to the Golgi apparatus. The recent discovery of the ceramide transport protein CERT has revealed a novel pathway for the delivery of ceramide to the Golgi apparatus for sphingomyelin (SM) synthesis. In addition to a ceramide-binding START domain, CERT has FFAT (referring to two phenylalanines [FF] in an acidic tract) and pleckstrin homology (PH) domains that recognize the ER integral membrane protein VAMP-associated protein (VAP) and Golgi-associated PtdIns 4-phosphate, respectively. Mechanisms for vectorial transport involving dual-organellar targeting and sites of deposition of ceramide in the Golgi apparatus are proposed. Similar Golgi-ER targeting motifs are also present in the oxysterol-binding protein (OSBP), which regulates ceramide transport and SM synthesis in an oxysterol-dependent manner. Consequently, this emerges as a potential mechanism for integration of sphingolipid and cholesterol metabolism. The identification of organellar targeting motifs in other related lipid-binding/transport proteins indicate that concepts learned from the study of ceramide transport can be applied to other lipid transport processes.
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Affiliation(s)
- Ryan J Perry
- Atlantic Research Centre, Dalhousie University, 5849 University Avenue, Halifax, N.S., Canada B3H 4H7
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26
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Hunt AN, Skippen AJ, Koster G, Postle AD, Cockcroft S. Acyl chain-based molecular selectivity for HL60 cellular phosphatidylinositol and of phosphatidylcholine by phosphatidylinositol transfer protein α. Biochim Biophys Acta Mol Cell Biol Lipids 2004; 1686:50-60. [PMID: 15522822 DOI: 10.1016/j.bbalip.2004.08.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2004] [Accepted: 08/11/2004] [Indexed: 11/15/2022]
Abstract
Mammalian phosphatidylinositol transfer protein alpha (PITP) is an intracellular lipid transporter with a binding site that can accommodate a single molecule of phosphatidylinositol (PI) or phosphatidylcholine (PC). Phospholipids are a heterogeneous population of molecular species that can be distinguished by their characteristic headgroups as well as their acyl chains at the sn-1 and sn-2 position. In this study, we have defined the acyl chain preference for PITPalpha when presented with a total population of cellular lipids. Recombinant PITPalpha loaded with bacterial lipid, phosphatidylglycerol (PG), was incubated with permeabilised HL60 cells, followed by recovery of PITPalpha by affinity chromatography. Lipids extracted from the PITPalpha were analysed by tandem electrospray ionisation mass spectrometry (ESI-MS) and showed total exchange of acquired bacterial lipids for HL60 cellular PI and PC. Detailed comparison of the molecular species composition of bound phospholipids with those in whole cells permitted the assessment of selectivity of acyl chain binding. For both phospholipid classes, progressive fractional enrichments in bound species possessing shorter acyl chains were apparent with a preference order: 16:1>16:0>18:1>18:0>20:4. A recapitulation of this specificity order was also seen from a dramatically altered range of molecular species present in HL60 cells enriched with arachidonate over many weeks of culture. We speculate that short-chain, saturate-binding preferences under both conditions may reflect properties in vivo. This is consistent with target cell membranes actively remodelling newly delivered phospholipids after transport rather than relying on the transport of the specific molecular species conventionally found in mammalian membranes.
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Affiliation(s)
- Alan N Hunt
- Division of Infection, Inflammation and Repair, School of Medicine, University of Southampton, Southampton SO16 6YD, UK
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27
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Morgan CP, Skippen A, Segui B, Ball A, Allen-Baume V, Larijani B, Murray-Rust J, McDonald N, Sapkota G, Morrice N, Cockcroft S. Phosphorylation of a distinct structural form of phosphatidylinositol transfer protein alpha at Ser166 by protein kinase C disrupts receptor-mediated phospholipase C signaling by inhibiting delivery of phosphatidylinositol to membranes. J Biol Chem 2004; 279:47159-71. [PMID: 15322105 DOI: 10.1074/jbc.m405827200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphatidylinositol transfer protein alpha (PITPalpha) participates in the supply of phosphatidylinositol (PI) required for many cellular events including phospholipase C (PLC) beta and gamma signaling by G-protein-coupled receptors and receptor-tyrosine kinases, respectively. Protein kinase C has been known to modulate PLC signaling by G-protein-coupled receptors and receptor-tyrosine kinases, although the molecular target has not been identified in most instances. In each case phorbol myristate acetate pretreatment of HL60, HeLa, and COS-7 cells abrogated PLC stimulation by the agonists formyl-Met-Leu-Phe, ATP, and epidermal growth factor, respectively. Here we show that phosphorylation of PITPalpha at Ser166 resulted in inhibition of receptor-stimulated PLC activity. Ser166 is localized in a small pocket between the 165-172 loop and the rest of the protein and was not solvent-accessible in either the PI- or phosphatidylcholine-loaded structures of PITPalpha. To allow phosphorylation at Ser166, a distinct structural form is postulated, and mutation of Thr59 to alanine shifted the equilibrium to this form, which could be resolved on native PAGE. The elution profile observed by size exclusion chromatography of phosphorylated PITPalpha from rat brain or in vitro phosphorylated PITPalpha demonstrated that phosphorylated PITPalpha is structurally distinct from the non-phosphorylated form. Phosphorylated PITPalpha was unable to deliver its PI cargo, although it could deliver phosphatidylcholine. We conclude that the PITPalpha structure has to relax to allow access to the Ser166 site, and this may occur at the membrane surface where PI delivery is required for receptor-mediated PLC signaling.
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Affiliation(s)
- Clive P Morgan
- Department of Physiology, University College London, London WC1E 6JJ
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28
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van Tiel CM, Schenning M, Snoek GT, Wirtz KWA. Overexpression of phosphatidylinositol transfer protein β in NIH3T3 cells has a stimulatory effect on sphingomyelin synthesis and apoptosis. Biochim Biophys Acta Mol Cell Biol Lipids 2004; 1636:151-8. [PMID: 15164762 DOI: 10.1016/j.bbalip.2003.08.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2003] [Revised: 08/18/2003] [Accepted: 08/18/2003] [Indexed: 11/17/2022]
Abstract
Phosphatidylinositol transfer proteins (PI-TPs) consist of two isoforms (PI-TPalpha and PI-TPbeta), which differ in phospholipid transfer properties and intracellular localization. Both PI-TP isoforms are substrates for protein kinase C and contain a minor phosphorylation site (Ser166 in PI-TPalpha; Ser165 in PI-TPbeta). Only PI-TPbeta contains a major phosphorylation site at Ser262, which must be phosphorylated for PI-TPbeta to be associated with the Golgi. The PI-TP isoforms are completely conserved between mammals. Although their function is still not clear, their importance follows from knock-out studies, showing that mice lacking PI-TPalpha die soon after birth and that embryonic stems cells lacking PI-TPbeta cannot be generated [Mol. Biol. Cell 13 (2002) 739]. We determined the levels of the PI-TP isoforms in various mouse tissues by immunoblotting. PI-TPalpha is present in all tissues investigated, with highest levels in brain (167 ng/100 microg total protein). The levels of PI-TPbeta are 50-100 times lower than those of PI-TPalpha, with relatively high levels found in liver and brain (1.2 and 1.8 ng/100 microg of total protein, respectively). In contrast to NIH3T3 cells overexpressing PI-TPalpha, cells overexpressing PI-TPbeta (SPIbeta cells) were able to maintain steady-state levels of sphingomyelin in plasma membrane under conditions where this lipid is degraded by exogenous sphingomyelinase. This process of rapid sphingomyelin replenishment is dependent on PI-TPbeta being associated with the Golgi as cells overexpressing a mutant PI-TPbeta in which the major phosphorylation site is replaced (PI-TPbeta(S262A) behave as wild-type NIH3T3 cells. Since the SPIbeta cells display a decreased growth rate (35 h as compared to 21 h for wtNIH3T3 cells), we have investigated the sensitivity of these cells towards UV-induced apoptosis. We have found that the SPIbeta cells, but not the cells overexpressing PI-TPbeta(S262A), are very sensitive. We are currently investigating whether a relationship exists between PI-TPbeta being involved in maintaining plasma membrane sphingomyelin levels and the enhanced sensitivity towards apoptosis.
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Affiliation(s)
- Claudia M van Tiel
- Center for Biomembranes and Lipid Enzymology, Department of Lipid Biochemistry, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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29
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Tilley SJ, Skippen A, Murray-Rust J, Swigart PM, Stewart A, Morgan CP, Cockcroft S, McDonald NQ. Structure-Function Analysis of Phosphatidylinositol Transfer Protein Alpha Bound to Human Phosphatidylinositol. Structure 2004; 12:317-26. [PMID: 14962392 DOI: 10.1016/j.str.2004.01.013] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2003] [Revised: 10/31/2003] [Accepted: 11/04/2003] [Indexed: 10/22/2022]
Abstract
Phosphatidylinositol transfer protein alpha (PITPalpha) selectively transports and promotes exchange of phosphatidylinositol (PI) and phosphatidylcholine (PC) between lipid bilayers. In higher eukaryotes PITPalpha is required for cellular functions such as phospholipase C-mediated signaling, regulated exocytosis, and secretory vesicle formation. We have determined the crystal structure of human PITPalpha bound to its physiological ligand, PI, at 2.95 A resolution. The structure identifies the critical side chains within the lipid-headgroup binding pocket that define the exquisite specificity for PI. Mutational analysis of the PI binding pocket is in good agreement with the structural data and allows manipulation of functional properties of PITPalpha. Surprisingly, there are no major conformational differences between PI- and PC-loaded PITPalpha, despite previous predictions. In the crystal, PITPalpha-PI is dimeric, with two identical dimers in the asymmetric unit. The dimer interface masks precisely the sequence we identify as contributing to PITPalpha membrane interaction. Our structure represents a soluble, transport-competent form of PI-loaded PITPalpha.
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Affiliation(s)
- Sarah J Tilley
- School of Crystallography, Birkbeck, University of London, Malet Street, London WC1E 7HX, UK
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30
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Miller EC, Helmkamp GM. Exposure of Phosphatidylinositol Transfer Proteins to Sphingomyelin−Cholesterol Membranes Suggests Transient but Productive Interactions with Raft-Like, Liquid-Ordered Domains. Biochemistry 2003; 42:13250-9. [PMID: 14609336 DOI: 10.1021/bi034616n] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Both isoforms of rat phosphatidylinositol transfer protein (PITP) mediate the intermembrane transfer of sphingomyelin (CerPCho). In the plasma membrane, CerPCho often segregates with cholesterol into microdomains such as lipid rafts and caveolae. To test the hypothesis that PITP exhibits a preference for CerPCho- and cholesterol-rich membranes, we prepared unilamellar vesicles containing variable amounts of these two lipids. We also used CerPCho species with different acyl composition and treated vesicles with agents known to sequester and remove cholesterol. We observed that the beta isoform of rat PITP was more sensitive to membrane cholesterol than was the alpha isoform, as shown by increases in specific activities of lipid transfer of 2-6-fold. A relatively high membrane content of cholesterol (mole fraction > 0.4) was required to elicit such enhancements. Treatment of cholesterol-rich membranes with a series of beta cyclodextrins demonstrated that, upon depletion of cholesterol from participating membranes, the PITPbeta activity changes were fully reversible. We finally noted that the mechanism by which cholesterol enhances the activity of PITPbeta appeared to involve a decreased affinity of the protein for the membrane surface, in a manner that was independent of vesicle size and membrane microviscosity. We conclude that PITPbeta interacts transiently but productively with the liquid-ordered phase formed by CerPCho and cholesterol and discuss the possibility of PITP interactions in vivo with sphingolipid- and cholesterol-rich membrane microdomains.
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Affiliation(s)
- Elizabeth C Miller
- Department of Biochemistry and Molecular Biology, Mail Stop 3030, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, Kansas 66160-7421, USA
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31
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Larijani B, Allen-Baume V, Morgan CP, Li M, Cockcroft S. EGF regulation of PITP dynamics is blocked by inhibitors of phospholipase C and of the Ras-MAP kinase pathway. Curr Biol 2003; 13:78-84. [PMID: 12526750 DOI: 10.1016/s0960-9822(02)01395-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Phosphatidylinositol transfer proteins (PITP) function in signal transduction and in membrane traffic. Studies aimed at elucidating the mechanism of action of PITP have yielded a singular theme; the activity of PITP stems from its ability to transfer phosphatidylinositol (PI) from its site of synthesis to sites of cellular activity and to stimulate the local synthesis of phosphorylated forms of PI. The participation of various phosphoinositides in EGF signal transduction and in the trafficking of the EGF receptors is well documented. Using fluorescence lifetime imaging microscopy (FLIM) to measure fluorescence resonance energy transfer (FRET) between EGFP-PITP proteins and fluorescently labeled phospholipids, we report that PITPalpha and PITPbeta can dynamically interact with PI or PC at the plasma membrane when stimulated with EGF. Additionally, PITPbeta is localized at the Golgi, and EGF stimulation resulted in enhanced FRET. Inhibitors of the PLC and the Ras/MAP kinase pathway were both able to inhibit the EGF-stimulated interaction of PITPalpha with PI at the plasma membrane. The mobility of PITP proteins was determined by using fluorescence recovery after photobleaching (FRAP), and EGF stimulation reduced the mobility at the plasma membrane. We conclude that the dynamic behavior of PITPalpha and PITPbeta in vivo is a regulated process involving multiple mechanisms.
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Affiliation(s)
- Banafshé Larijani
- Cell Biophysics Laboratory, London Research Institute, Cancer Research UK, Lincoln's Inn Fields Laboratory, 44 Lincoln's Inn Fields, WC2A 3PX, London, United Kingdom
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32
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Allen-Baume V, Ségui B, Cockcroft S. Current thoughts on the phosphatidylinositol transfer protein family. FEBS Lett 2002; 531:74-80. [PMID: 12401207 DOI: 10.1016/s0014-5793(02)03412-9] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Monomeric transport of lipids is carried out by a class of proteins that can shield a lipid from the aqueous environment by binding the lipid in a hydrophobic cavity. One such group of proteins is the phosphatidylinositol transfer proteins (PITP) that can bind phosphatidylinositol and phosphatidylcholine and transfer them from one membrane compartment to another. PITPs are found in both unicellular and multicellular organisms but not bacteria. In mice and humans, the PITP domain responsible for lipid transfer is found in five proteins, which can be classified into two classes based on sequence. Class I PITPs comprises two family members, alpha and beta, small 35 kDa proteins with a single PITP domain which are ubiquitously expressed. Class IIA PITPs (RdgBalphaI and II) are larger proteins possessing additional domains that target the protein to membranes and are only able to bind lipids but not mediate transfer. Finally, Class IIB PITP (RdgBbeta) is similar to Class I in size (38 kDa) and is also ubiquitously expressed. Class III PITPs, exemplified by the Sec14p family, are found in yeast and plants but are unrelated in sequence and structure to Class I and Class II PITPs. In this review we discuss whether PITP proteins are passive transporters or are regulated proteins that are able to couple their transport and binding properties to specific biological functions including inositol lipid signalling and membrane turnover.
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