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Long T, Li D, Vale G, Jiang Y, Schmiege P, Yang ZJ, McDonald JG, Li X. Molecular insights into human phosphatidylserine synthase 1 reveal its inhibition promotes LDL uptake. Cell 2024:S0092-8674(24)00895-X. [PMID: 39208797 DOI: 10.1016/j.cell.2024.08.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Revised: 06/04/2024] [Accepted: 08/05/2024] [Indexed: 09/04/2024]
Abstract
In mammalian cells, two phosphatidylserine (PS) synthases drive PS synthesis. Gain-of-function mutations in the Ptdss1 gene lead to heightened PS production, causing Lenz-Majewski syndrome (LMS). Recently, pharmacological inhibition of PSS1 has been shown to suppress tumorigenesis. Here, we report the cryo-EM structures of wild-type human PSS1 (PSS1WT), the LMS-causing Pro269Ser mutant (PSS1P269S), and PSS1WT in complex with its inhibitor DS55980254. PSS1 contains 10 transmembrane helices (TMs), with TMs 4-8 forming a catalytic core in the luminal leaflet. These structures revealed a working mechanism of PSS1 akin to the postulated mechanisms of the membrane-bound O-acyltransferase family. Additionally, we showed that both PS and DS55980254 can allosterically inhibit PSS1 and that inhibition by DS55980254 activates the SREBP pathways, thus enhancing the expression of LDL receptors and increasing cellular LDL uptake. This work uncovers a mechanism of mammalian PS synthesis and suggests that selective PSS1 inhibitors have the potential to lower blood cholesterol levels.
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Affiliation(s)
- Tao Long
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Dongyu Li
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Goncalo Vale
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Yaoyukun Jiang
- Department of Chemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN 37235, USA
| | - Philip Schmiege
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Zhongyue J Yang
- Department of Chemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN 37235, USA
| | - Jeffrey G McDonald
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Xiaochun Li
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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2
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Niu Y, Pemberton JG, Kim YJ, Balla T. Phosphatidylserine enrichment in the nuclear membrane regulates key enzymes of phosphatidylcholine synthesis. EMBO J 2024; 43:3414-3449. [PMID: 38918635 PMCID: PMC11329639 DOI: 10.1038/s44318-024-00151-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2024] [Revised: 05/07/2024] [Accepted: 06/04/2024] [Indexed: 06/27/2024] Open
Abstract
Phosphatidylserine (PS) is an important anionic phospholipid that is synthesized within the endoplasmic reticulum (ER). While PS shows the highest enrichment and serves important functional roles in the plasma membrane (PM) but its role in the nucleus is poorly explored. Using three orthogonal approaches, we found that PS is also uniquely enriched in the inner nuclear membrane (INM) and the nuclear reticulum (NR). Nuclear PS is critical for supporting the translocation of CCTα and Lipin1α, two key enzymes important for phosphatidylcholine (PC) biosynthesis, from the nuclear matrix to the INM and NR in response to oleic acid treatment. We identified the PS-interacting regions within the M-domain of CCTα and M-Lip domain of Lipin1α, and show that lipid droplet formation is altered by manipulations of nuclear PS availability. Our studies reveal an unrecognized regulatory role of nuclear PS levels in the regulation of key PC synthesizing enzymes within the nucleus.
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Affiliation(s)
- Yang Niu
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA.
| | - 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, 20892, USA
| | - Yeun Ju Kim
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, 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, 20892, USA.
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3
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Abstract
The sorting and trafficking of lipids between organelles gives rise to a dichotomy of bulk membrane properties between organelles of the secretory and endolysosome networks, giving rise to two "membrane territories" based on differences in lipid-packing density, net membrane charge, and bilayer leaflet asymmetries. The cellular organelle membrane dichotomy emerges from ER-to-PM anterograde membrane trafficking and the synthesis of sphingolipids and cholesterol flux at the trans-Golgi network, which constitutes the interface between the two membrane territories. Organelle homeostasis is maintained by vesicle-mediated retrieval of bulk membrane from the distal organelles of each territory to the endoplasmic reticulum or plasma membrane and by soluble lipid transfer proteins that traffic particular lipids. The concept of cellular membrane territories emphasizes the contrasting features of organelle membranes of the secretory and endolysosome networks and the essential roles of lipid-sorting pathways that maintain organelle function.
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Affiliation(s)
- Yeongho Kim
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520, USA
| | - Christopher G Burd
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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4
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Anari M, Montgomery MK. Phospholipid metabolism in the liver - Implications for phosphatidylserine in non-alcoholic fatty liver disease. Biochem Pharmacol 2023; 213:115621. [PMID: 37217141 DOI: 10.1016/j.bcp.2023.115621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 05/13/2023] [Accepted: 05/16/2023] [Indexed: 05/24/2023]
Abstract
Mammalian cells contain more than a thousand different glycerophospholipid species that are essential membrane components and signalling molecules, with phosphatidylserine (PS) giving membranes their negative surface charge. Depending on the tissue, PS is important in apoptosis, blood clotting, cancer pathogenesis, as well as muscle and brain function, processes that are dependent on the asymmetrical distribution of PS on the plasma membrane and/or the capacity of PS to act as anchorage for various signalling proteins. Recent studies have implicated hepatic PS in the progression of non-alcoholic fatty liver disease (NAFLD), either as beneficial in the context of suppressing hepatic steatosis and fibrosis, or on the other hand as a potential contributor to the progression of liver cancer. This review provides an extensive overview of hepatic phospholipid metabolism, including its biosynthetic pathways, intracellular trafficking and roles in health and disease, further taking a deeper dive into PS metabolism, including associate and causative evidence of the role of PS in advanced liver disease.
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Affiliation(s)
- Marziyeh Anari
- Department of Anatomy and Physiology, School of Biomedical Sciences, Faculty of Medicine Dentistry and Health Sciences, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Magdalene K Montgomery
- Department of Anatomy and Physiology, School of Biomedical Sciences, Faculty of Medicine Dentistry and Health Sciences, University of Melbourne, Melbourne, VIC 3010, Australia.
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5
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Morita SY, Ikeda Y. Regulation of membrane phospholipid biosynthesis in mammalian cells. Biochem Pharmacol 2022; 206:115296. [DOI: 10.1016/j.bcp.2022.115296] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 10/05/2022] [Accepted: 10/05/2022] [Indexed: 11/02/2022]
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Ventura R, Martínez-Ruiz I, Hernández-Alvarez MI. Phospholipid Membrane Transport and Associated Diseases. Biomedicines 2022; 10:biomedicines10051201. [PMID: 35625937 PMCID: PMC9138374 DOI: 10.3390/biomedicines10051201] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Revised: 05/19/2022] [Accepted: 05/20/2022] [Indexed: 11/16/2022] Open
Abstract
Phospholipids are the basic structure block of eukaryotic membranes, in both the outer and inner membranes, which delimit cell organelles. Phospholipids can also be damaged by oxidative stress produced by mitochondria, for instance, becoming oxidized phospholipids. These damaged phospholipids have been related to prevalent diseases such as atherosclerosis or non-alcoholic steatohepatitis (NASH) because they alter gene expression and induce cellular stress and apoptosis. One of the main sites of phospholipid synthesis is the endoplasmic reticulum (ER). ER association with other organelles through membrane contact sites (MCS) provides a close apposition for lipid transport. Additionally, an important advance in this small cytosolic gap are lipid transfer proteins (LTPs), which accelerate and modulate the distribution of phospholipids in other organelles. In this regard, LTPs can be established as an essential point within phospholipid circulation, as relevant data show impaired phospholipid transport when LTPs are defected. This review will focus on phospholipid function, metabolism, non-vesicular transport, and associated diseases.
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Affiliation(s)
- Raúl Ventura
- Departament de Bioquímica i Biomedicina Molecular, Facultat de Biologia, Universitat de Barcelona, 08028 Barcelona, Spain; (R.V.); (I.M.-R.)
| | - Inma Martínez-Ruiz
- Departament de Bioquímica i Biomedicina Molecular, Facultat de Biologia, Universitat de Barcelona, 08028 Barcelona, Spain; (R.V.); (I.M.-R.)
| | - María Isabel Hernández-Alvarez
- Departament de Bioquímica i Biomedicina Molecular, Facultat de Biologia, Universitat de Barcelona, 08028 Barcelona, Spain; (R.V.); (I.M.-R.)
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Instituto de Salud Carlos III, 28029 Madrid, Spain
- IBUB Universitat de Barcelona—Institut de Biomedicina de la Universitat de Barcelona, 08028 Barcelona, Spain
- Correspondence:
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Gracie S, Sengupta N, Ferreira C, Pemberton J, Anderson I, Wang X, Rhodes L, Brown K, Balla T, Larson A. De novo loss-of-function variant in PTDSS1 is associated with developmental delay. Am J Med Genet A 2022; 188:1739-1745. [PMID: 35224839 DOI: 10.1002/ajmg.a.62695] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 01/24/2022] [Accepted: 01/27/2022] [Indexed: 11/07/2022]
Abstract
Heterozygous de novo missense pathogenic variants in PTDSS1 that result in gain-of-function of phosphatidylserine synthase 1 are associated with Lenz-Majewski hyperostotic dwarfism (LMHD). We identified the novel heterozygous de novo variant p.(Leu137Phe) in PTDSS1 in a child with mild-to-moderate developmental delay. Skeletal survey revealed no evidence of LMHD in this patient. Functional assessment of the p.Leu137Phe variant was performed by overexpressing the mutant protein into HEK293 cells. Following C14 -serine labeling and TLC analysis of lipids, we observed that the p.(Leu137Phe) variant displayed no catalytic activity compared to the wild-type enzyme. We conclude that p.(Leu137Phe) variant has decreased enzymatic activity and that is likely to be the etiology of the patient's symptoms given the gene's constraint in the population. This is the first report of the clinical phenotype seen in an individual with a heterozygous loss-of-function variant in PTDSS1. This phenotype is distinct from LMHD, which results from gain-of-function pathogenic variants in the same gene. Evaluation of the neurodevelopmental phenotype of additional individuals with loss-of-function variants in PTDSS1 is indicated to determine the spectrum of associated phenotypes.
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Affiliation(s)
- Sara Gracie
- Department of Pediatrics, Section of Genetics and Children's Hospital Colorado, University of Colorado School of Medicine, Aurora, Colorado, USA
| | - Nivedita Sengupta
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Carlos Ferreira
- Medical Genomics and Metabolic Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Joshua Pemberton
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Ilse Anderson
- University of Tennessee Graduate School of Medicine, Knoxville, Tennessee, USA
| | - Xin Wang
- GeneDx, Gaithersburg, Maryland, USA
| | | | - Kathleen Brown
- Department of Pediatrics, Section of Genetics and Children's Hospital Colorado, University of Colorado School of Medicine, Aurora, Colorado, USA
| | - Tamas Balla
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Austin Larson
- Department of Pediatrics, Section of Genetics and Children's Hospital Colorado, University of Colorado School of Medicine, Aurora, Colorado, USA
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8
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Miyata N, Kuge O. Topology of phosphatidylserine synthase 1 in the endoplasmic reticulum membrane. Protein Sci 2021; 30:2346-2353. [PMID: 34516042 DOI: 10.1002/pro.4182] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 09/02/2021] [Accepted: 09/07/2021] [Indexed: 12/28/2022]
Abstract
Phosphatidylserine (PS) synthase 1 (PSS1) of mammalian cells is a multiple membrane-spanning protein of the endoplasmic reticulum (ER) and regulated by inhibition with the product PS. Alanine-scanning mutagenesis of PSS1 has revealed eight amino acid residues as those crucial for its activity and six as those important for its regulation. Furthermore, three missense mutations in the human PSS1 gene, which lead to regulatory dysfunctions of PSS1 and are causative of Lenz-Majewski syndrome, have been identified. In this study, we investigated the membrane topology of PSS1 by means of epitope insertion and immunofluorescence. According to a 10-transmembrane segment model supported by topology analysis of PSS1, all the 8 amino acid residues crucial for the enzyme activity were localized to the luminal side of the lipid bilayer or the lumen of the ER, whereas all the 9 amino acid residues involved in the enzyme regulation were localized to the cytosol or the cytoplasmic side of the lipid bilayer of the ER. This localization of the functional amino acid residues suggests that PSS1 is regulated by inhibition with PS in the cytoplasmic leaflet of the ER membrane and synthesizes PS at the luminal leaflet.
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Affiliation(s)
- Non Miyata
- Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Japan
| | - Osamu Kuge
- Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Japan
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