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Abstract
Lipid droplets (LDs) are dynamic cellular hubs of lipid metabolism. While LDs contact a plethora of organelles, they have the most intimate relationship with the endoplasmic reticulum (ER). Indeed, LDs are initially assembled at specialized ER subdomains, and recent work has unraveled an increasing array of proteins regulating ER-LD contacts. Among these, seipin, a highly conserved lipodystrophy protein critical for LD growth and adipogenesis, deserves special attention. Here, we review recent insights into the role of seipin in LD biogenesis and as a regulator of ER-LD contacts. These studies have also highlighted the evolving concept of ER and LDs as a functional continuum for lipid partitioning and pinpointed a role for seipin at the ER-LD nexus in controlling lipid flux between these compartments.
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Affiliation(s)
- Veijo T. Salo
- Department of Anatomy and Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Maarit Hölttä-Vuori
- Department of Anatomy and Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Elina Ikonen
- Department of Anatomy and Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
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2
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Luukkonen PK, Nick A, Hölttä-Vuori M, Thiele C, Isokuortti E, Lallukka-Brück S, Zhou Y, Hakkarainen A, Lundbom N, Peltonen M, Orho-Melander M, Orešič M, Hyötyläinen T, Hodson L, Ikonen E, Yki-Järvinen H. Human PNPLA3-I148M variant increases hepatic retention of polyunsaturated fatty acids. JCI Insight 2019; 4:127902. [PMID: 31434800 DOI: 10.1172/jci.insight.127902] [Citation(s) in RCA: 83] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 07/16/2019] [Indexed: 12/14/2022] Open
Abstract
The common patatin-like phospholipase domain-containing protein 3 (PNPLA3) variant I148M predisposes to nonalcoholic liver disease but not its metabolic sequelae. We compared the handling of labeled polyunsaturated fatty acids (PUFAs) and saturated fatty acids (SFA) in vivo in humans and in cells harboring different PNPLA3 genotypes. In 148M homozygous individuals, triglycerides (TGs) in very low-density lipoproteins (VLDL) were depleted of PUFAs both under fasting and postprandial conditions compared with 148I homozygotes, and the PUFA/SFA ratio in VLDL-TGs was lower relative to the chylomicron precursor pool. In human PNPLA3-148M and PNPLA3-KO cells, PUFA but not SFA incorporation into TGs was increased at the expense of phosphatidylcholines, and under lipolytic conditions, PUFA-containing diacylglycerols (DAGs) accumulated compared with PNPLA3-148I cells. Polyunsaturated TGs were increased, while phosphatidylcholines (PCs) were decreased in the human liver in 148M homozygous individuals as compared with 148I homozygotes. We conclude that human PNPLA3-I148M is a loss-of-function allele that remodels liver TGs in a polyunsaturated direction by impairing hydrolysis/transacylation of PUFAs from DAGs to feed phosphatidylcholine synthesis.
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Affiliation(s)
- Panu K Luukkonen
- Minerva Foundation Institute for Medical Research, Helsinki, Finland.,Department of Medicine, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | - Auli Nick
- Minerva Foundation Institute for Medical Research, Helsinki, Finland.,Faculty of Medicine, Department of Anatomy, University of Helsinki, Helsinki, Finland
| | - Maarit Hölttä-Vuori
- Minerva Foundation Institute for Medical Research, Helsinki, Finland.,Faculty of Medicine, Department of Anatomy, University of Helsinki, Helsinki, Finland
| | | | - Elina Isokuortti
- Minerva Foundation Institute for Medical Research, Helsinki, Finland.,Department of Medicine, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | - Susanna Lallukka-Brück
- Minerva Foundation Institute for Medical Research, Helsinki, Finland.,Department of Medicine, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
| | - You Zhou
- Minerva Foundation Institute for Medical Research, Helsinki, Finland.,Systems Immunity Research Institute, Cardiff University, Cardiff, United Kingdom.,Division of Infection and Immunity, Cardiff University School of Medicine, Cardiff, United Kingdom
| | - Antti Hakkarainen
- Department of Radiology, HUS Medical Imaging Center, Helsinki University Hospital and University of Helsinki, Helsinki, Finland.,Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
| | - Nina Lundbom
- Department of Radiology, HUS Medical Imaging Center, Helsinki University Hospital and University of Helsinki, Helsinki, Finland
| | - Markku Peltonen
- Department of Public Health Solutions, National Institute for Health and Welfare, Helsinki, Finland
| | | | - Matej Orešič
- Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, Turku, Finland.,School of Medical Sciences and
| | | | - Leanne Hodson
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, United Kingdom
| | - Elina Ikonen
- Minerva Foundation Institute for Medical Research, Helsinki, Finland.,Faculty of Medicine, Department of Anatomy, University of Helsinki, Helsinki, Finland
| | - Hannele Yki-Järvinen
- Minerva Foundation Institute for Medical Research, Helsinki, Finland.,Department of Medicine, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
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3
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Gungor B, Vanharanta L, Hölttä-Vuori M, Pirhonen J, Petersen NHT, Gramolelli S, Ojala PM, Kirkegaard T, Ikonen E. HSP70 induces liver X receptor pathway activation and cholesterol reduction in vitro and in vivo. Mol Metab 2019; 28:135-143. [PMID: 31327756 PMCID: PMC6822257 DOI: 10.1016/j.molmet.2019.07.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 07/03/2019] [Indexed: 12/15/2022] Open
Abstract
Objective Heat Shock Proteins (HSPs) maintain cellular homeostasis under stress. HSP70 represents a major stress-inducible family member and has been identified as a druggable target in inherited cholesterol-sphingolipid storage diseases. We investigated if HSP70 modulates cholesterol accumulation in more common conditions related to atherogenesis. Methods We studied the effects of recombinant HSP70 in cholesterol-laden primary macrophages from human blood donors and pharmacological HSP70 upregulation in high-cholesterol diet fed zebrafish. Results Recombinant HSP70 facilitated cholesterol removal from primary human macrophage foam cells. RNA sequencing revealed that HSP70 induced a robust transcriptional re-programming, including upregulation of key targets of liver X receptors (LXR), master regulators of whole-body cholesterol removal. Mechanistically, HSP70 interacted with the macrophage LXRalpha promoter, increased LXRalpha and its target mRNAs, and led to elevated levels of key proteins facilitating cholesterol efflux, including ATP-binding cassette transporters A1 and G1. Pharmacological augmentation of endogenous HSP70 in high-cholesterol diet fed zebrafish activated LXR and its target mRNAs and reduced cholesterol storage at the whole organism level. Conclusion These data demonstrate that HSP70 exerts a cholesterol lowering effect in primary human cells and animals and uncover a nuclear action of HSP70 in mediating cross-talk between HSP and LXR transcriptional regulation.
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Affiliation(s)
- Burcin Gungor
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Haartmaninkatu 8 00290 Helsinki, Finland; Minerva Foundation Institute for Medical Research, Tukholmankatu 8, 00290 Helsinki, Finland
| | - Lauri Vanharanta
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Haartmaninkatu 8 00290 Helsinki, Finland; Minerva Foundation Institute for Medical Research, Tukholmankatu 8, 00290 Helsinki, Finland
| | - Maarit Hölttä-Vuori
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Haartmaninkatu 8 00290 Helsinki, Finland; Minerva Foundation Institute for Medical Research, Tukholmankatu 8, 00290 Helsinki, Finland
| | - Juho Pirhonen
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Haartmaninkatu 8 00290 Helsinki, Finland; Minerva Foundation Institute for Medical Research, Tukholmankatu 8, 00290 Helsinki, Finland
| | | | - Silvia Gramolelli
- Research Programs Unit, Translational Cancer Biology, University of Helsinki, Haartmaninkatu 8, 00290 Helsinki, Finland
| | - Päivi M Ojala
- Research Programs Unit, Translational Cancer Biology, University of Helsinki, Haartmaninkatu 8, 00290 Helsinki, Finland; Foundation for the Finnish Cancer Institute, Helsinki, Finland
| | | | - Elina Ikonen
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Haartmaninkatu 8 00290 Helsinki, Finland; Minerva Foundation Institute for Medical Research, Tukholmankatu 8, 00290 Helsinki, Finland.
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4
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Salo VT, Li S, Vihinen H, Hölttä-Vuori M, Szkalisity A, Horvath P, Belevich I, Peränen J, Thiele C, Somerharju P, Zhao H, Santinho A, Thiam AR, Jokitalo E, Ikonen E. Seipin Facilitates Triglyceride Flow to Lipid Droplet and Counteracts Droplet Ripening via Endoplasmic Reticulum Contact. Dev Cell 2019; 50:478-493.e9. [PMID: 31178403 DOI: 10.1016/j.devcel.2019.05.016] [Citation(s) in RCA: 113] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 02/27/2019] [Accepted: 05/03/2019] [Indexed: 01/02/2023]
Abstract
Seipin is an oligomeric integral endoplasmic reticulum (ER) protein involved in lipid droplet (LD) biogenesis. To study the role of seipin in LD formation, we relocalized it to the nuclear envelope and found that LDs formed at these new seipin-defined sites. The sites were characterized by uniform seipin-mediated ER-LD necks. At low seipin content, LDs only grew at seipin sites, and tiny, growth-incompetent LDs appeared in a Rab18-dependent manner. When seipin was removed from ER-LD contacts within 1 h, no lipid metabolic defects were observed, but LDs became heterogeneous in size. Studies in seipin-ablated cells and model membranes revealed that this heterogeneity arises via a biophysical ripening process, with triglycerides partitioning from smaller to larger LDs through droplet-bilayer contacts. These results suggest that seipin supports the formation of structurally uniform ER-LD contacts and facilitates the delivery of triglycerides from ER to LDs. This counteracts ripening-induced shrinkage of small LDs.
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Affiliation(s)
- Veijo T Salo
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Shiqian Li
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Helena Vihinen
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Maarit Hölttä-Vuori
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | | | | | - Ilya Belevich
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Johan Peränen
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | | | - Pentti Somerharju
- Department of Biochemistry, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Hongxia Zhao
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Alexandre Santinho
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Universite de Paris, Paris, France
| | - Abdou Rachid Thiam
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Universite de Paris, Paris, France.
| | - Eija Jokitalo
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
| | - Elina Ikonen
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Helsinki, Finland.
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5
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Capasso S, Sticco L, Rizzo R, Pirozzi M, Russo D, Dathan NA, Campelo F, van Galen J, Hölttä-Vuori M, Turacchio G, Hausser A, Malhotra V, Riezman I, Riezman H, Ikonen E, Luberto C, Parashuraman S, Luini A, D'Angelo G. Sphingolipid metabolic flow controls phosphoinositide turnover at the trans-Golgi network. EMBO J 2017; 36:1736-1754. [PMID: 28495678 DOI: 10.15252/embj.201696048] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Revised: 03/31/2017] [Accepted: 04/04/2017] [Indexed: 11/09/2022] Open
Abstract
Sphingolipids are membrane lipids globally required for eukaryotic life. The sphingolipid content varies among endomembranes with pre- and post-Golgi compartments being poor and rich in sphingolipids, respectively. Due to this different sphingolipid content, pre- and post-Golgi membranes serve different cellular functions. The basis for maintaining distinct subcellular sphingolipid levels in the presence of membrane trafficking and metabolic fluxes is only partially understood. Here, we describe a homeostatic regulatory circuit that controls sphingolipid levels at the trans-Golgi network (TGN). Specifically, we show that sphingomyelin production at the TGN triggers a signalling pathway leading to PtdIns(4)P dephosphorylation. Since PtdIns(4)P is required for cholesterol and sphingolipid transport to the trans-Golgi network, PtdIns(4)P consumption interrupts this transport in response to excessive sphingomyelin production. Based on this evidence, we envisage a model where this homeostatic circuit maintains a constant lipid composition in the trans-Golgi network and post-Golgi compartments, thus counteracting fluctuations in the sphingolipid biosynthetic flow.
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Affiliation(s)
- Serena Capasso
- Istituto di Ricovero e Cura a Carattere Scientifico-SDN, Naples, Italy
| | - Lucia Sticco
- Institute of Protein Biochemistry-National Research Council, Naples, Italy
| | - Riccardo Rizzo
- Institute of Protein Biochemistry-National Research Council, Naples, Italy
| | - Marinella Pirozzi
- Institute of Protein Biochemistry-National Research Council, Naples, Italy
| | - Domenico Russo
- Institute of Protein Biochemistry-National Research Council, Naples, Italy
| | - Nina A Dathan
- Institute of Protein Biochemistry-National Research Council, Naples, Italy
| | - Felix Campelo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Barcelona, Spain.,Centre for Genomic Regulation, The Barcelona Institute of Science and Technology, Barcelona, Spain.,Universitat Pompeu Fabra, Barcelona, Spain
| | - Josse van Galen
- Centre for Genomic Regulation, The Barcelona Institute of Science and Technology, Barcelona, Spain.,Universitat Pompeu Fabra, Barcelona, Spain
| | - Maarit Hölttä-Vuori
- Department of Anatomy, Faculty of Medicine, Minerva Research Institute for Medical Research, University of Helsinki, Helsinki, Finland
| | - Gabriele Turacchio
- Institute of Protein Biochemistry-National Research Council, Naples, Italy
| | - Angelika Hausser
- Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany
| | - Vivek Malhotra
- Centre for Genomic Regulation, The Barcelona Institute of Science and Technology, Barcelona, Spain.,Universitat Pompeu Fabra, Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain
| | - Isabelle Riezman
- Department of Biochemistry, NCCR Chemical Biology, University of Geneva, Geneva, Switzerland
| | - Howard Riezman
- Department of Biochemistry, NCCR Chemical Biology, University of Geneva, Geneva, Switzerland
| | - Elina Ikonen
- Department of Anatomy, Faculty of Medicine, Minerva Research Institute for Medical Research, University of Helsinki, Helsinki, Finland
| | - Chiara Luberto
- Stony Brook Cancer Center, Health Science Center, Stony Brook University, Stony Brook, NY, USA
| | | | - Alberto Luini
- Istituto di Ricovero e Cura a Carattere Scientifico-SDN, Naples, Italy.,Institute of Protein Biochemistry-National Research Council, Naples, Italy
| | - Giovanni D'Angelo
- Istituto di Ricovero e Cura a Carattere Scientifico-SDN, Naples, Italy .,Institute of Protein Biochemistry-National Research Council, Naples, Italy
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6
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Salo VT, Belevich I, Li S, Karhinen L, Vihinen H, Vigouroux C, Magré J, Thiele C, Hölttä-Vuori M, Jokitalo E, Ikonen E. Seipin regulates ER-lipid droplet contacts and cargo delivery. EMBO J 2016; 35:2699-2716. [PMID: 27879284 PMCID: PMC5167346 DOI: 10.15252/embj.201695170] [Citation(s) in RCA: 202] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Revised: 10/22/2016] [Accepted: 10/24/2016] [Indexed: 11/10/2022] Open
Abstract
Seipin is an endoplasmic reticulum (ER) membrane protein implicated in lipid droplet (LD) biogenesis and mutated in severe congenital lipodystrophy (BSCL2). Here, we show that seipin is stably associated with nascent ER–LD contacts in human cells, typically via one mobile focal point per LD. Seipin appears critical for such contacts since ER–LD contacts were completely missing or morphologically aberrant in seipin knockout and BSCL2 patient cells. In parallel, LD mobility was increased and protein delivery from the ER to LDs to promote LD growth was decreased. Moreover, while growing LDs normally acquire lipid and protein constituents from the ER, this process was compromised in seipin‐deficient cells. In the absence of seipin, the initial synthesis of neutral lipids from exogenous fatty acid was normal, but fatty acid incorporation into neutral lipids in cells with pre‐existing LDs was impaired. Together, our data suggest that seipin helps to connect newly formed LDs to the ER and that by stabilizing ER–LD contacts seipin facilitates the incorporation of protein and lipid cargo into growing LDs in human cells.
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Affiliation(s)
- Veijo T Salo
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland.,Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Ilya Belevich
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Shiqian Li
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland.,Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Leena Karhinen
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Helena Vihinen
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Corinne Vigouroux
- Sorbonne Universités, UPMC Univ Paris 6, Inserm UMR_S938, Saint-Antoine Research Center, Institute of Cardiometabolism And Nutrition, AP-HP, Saint-Antoine Hospital Department of Molecular Biology and Genetics, Paris, France
| | - Jocelyne Magré
- l'Institut du Thorax, INSERM CNRS UNIV Nantes, Nantes, France
| | | | - Maarit Hölttä-Vuori
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland.,Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Eija Jokitalo
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
| | - Elina Ikonen
- Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland .,Minerva Foundation Institute for Medical Research, Helsinki, Finland
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7
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Kettunen KM, Karikoski R, Hämäläinen RH, Toivonen TT, Antonenkov VD, Kulesskaya N, Voikar V, Hölttä-Vuori M, Ikonen E, Sainio K, Jalanko A, Karlberg S, Karlberg N, Lipsanen-Nyman M, Toppari J, Jauhiainen M, Hiltunen JK, Jalanko H, Lehesjoki AE. Trim37-deficient mice recapitulate several features of the multi-organ disorder Mulibrey nanism. Biol Open 2016; 5:584-95. [PMID: 27044324 PMCID: PMC4874348 DOI: 10.1242/bio.016246] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Mulibrey nanism (MUL) is a rare autosomal recessive multi-organ disorder characterized by severe prenatal-onset growth failure, infertility, cardiopathy, risk for tumors, fatty liver, and type 2 diabetes. MUL is caused by loss-of-function mutations in TRIM37, which encodes an E3 ubiquitin ligase belonging to the tripartite motif (TRIM) protein family and having both peroxisomal and nuclear localization. We describe a congenic Trim37 knock-out mouse (Trim37−/−) model for MUL. Trim37−/− mice were viable and had normal weight development until approximately 12 months of age, after which they started to manifest increasing problems in wellbeing and weight loss. Assessment of skeletal parameters with computer tomography revealed significantly smaller skull size, but no difference in the lengths of long bones in Trim37−/− mice as compared with wild-type. Both male and female Trim37−/− mice were infertile, the gonads showing germ cell aplasia, hilus and Leydig cell hyperplasia and accumulation of lipids in and around Leydig cells. Male Trim37−/− mice had elevated levels of follicle-stimulating and luteinizing hormones, but maintained normal levels of testosterone. Six-month-old Trim37−/− mice had elevated fasting blood glucose and low fasting serum insulin levels. At 1.5 years Trim37−/− mice showed non-compaction cardiomyopathy, hepatomegaly, fatty liver and various tumors. The amount and morphology of liver peroxisomes seemed normal in Trim37−/− mice. The most consistently seen phenotypes in Trim37−/− mice were infertility and the associated hormonal findings, whereas there was more variability in the other phenotypes observed. Trim37−/− mice recapitulate several features of the human MUL disease and thus provide a good model to study disease pathogenesis related to TRIM37 deficiency, including infertility, non-alcoholic fatty liver disease, cardiomyopathy and tumorigenesis. Summary: A congenic Trim37-deficient mouse model recapitulates several features of the human disorder Mulibrey nanism, and thus provides a good model to study disease pathogenesis related to TRIM37 deficiency.
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Affiliation(s)
- Kaisa M Kettunen
- Folkhälsan Institute of Genetics, FI-00290 Helsinki, Finland Research Programs Unit, Molecular Neurology, University of Helsinki, FI-00290 Helsinki, Finland Neuroscience Center, University of Helsinki, FI-00790 Helsinki, Finland Institute for Molecular Medicine Finland FIMM, University of Helsinki, FI-00290 Helsinki, Finland
| | - Riitta Karikoski
- Department of Pathology, Central Hospital of Tavastia, FI-13530 Hämeenlinna, Finland
| | - Riikka H Hämäläinen
- Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio FI-70211, Finland
| | | | - Vasily D Antonenkov
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, FI-90220 Oulu, Finland
| | | | - Vootele Voikar
- Neuroscience Center, University of Helsinki, FI-00790 Helsinki, Finland
| | - Maarit Hölttä-Vuori
- Department of Anatomy, Faculty of Medicine, University of Helsinki, FI-00290 Helsinki, Finland Minerva Foundation Institute for Medical Research, FI-00290 Helsinki, Finland
| | - Elina Ikonen
- Department of Anatomy, Faculty of Medicine, University of Helsinki, FI-00290 Helsinki, Finland Minerva Foundation Institute for Medical Research, FI-00290 Helsinki, Finland
| | - Kirsi Sainio
- Biochemistry and Developmental Biology, Institute of Biomedicine, University of Helsinki, FI-00290 Helsinki, Finland
| | - Anu Jalanko
- Genomics and Biomarkers Unit, National Institute for Health and Welfare, Biomedicum, FI-00290 Helsinki, Finland
| | - Susann Karlberg
- Department of Endocrinology, Children's Hospital, University of Helsinki and Helsinki University Hospital, FI-00290 Helsinki, Finland
| | - Niklas Karlberg
- Department of Endocrinology, Children's Hospital, University of Helsinki and Helsinki University Hospital, FI-00290 Helsinki, Finland
| | - Marita Lipsanen-Nyman
- Department of Endocrinology, Children's Hospital, University of Helsinki and Helsinki University Hospital, FI-00290 Helsinki, Finland
| | - Jorma Toppari
- Departments of Physiology and Pediatrics, University of Turku, FI-20520 Turku, Finland
| | - Matti Jauhiainen
- Genomics and Biomarkers Unit, National Institute for Health and Welfare, Biomedicum, FI-00290 Helsinki, Finland
| | - J Kalervo Hiltunen
- Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, FI-90220 Oulu, Finland
| | - Hannu Jalanko
- Department of Nephrology and Transplantation, Children's Hospital, University of Helsinki and Helsinki University Hospital, FI-00290 Helsinki, Finland
| | - Anna-Elina Lehesjoki
- Folkhälsan Institute of Genetics, FI-00290 Helsinki, Finland Research Programs Unit, Molecular Neurology, University of Helsinki, FI-00290 Helsinki, Finland Neuroscience Center, University of Helsinki, FI-00790 Helsinki, Finland
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8
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Vassilev B, Sihto H, Li S, Hölttä-Vuori M, Ilola J, Lundin J, Isola J, Kellokumpu-Lehtinen PL, Joensuu H, Ikonen E. Elevated levels of StAR-related lipid transfer protein 3 alter cholesterol balance and adhesiveness of breast cancer cells: potential mechanisms contributing to progression of HER2-positive breast cancers. Am J Pathol 2015; 185:987-1000. [PMID: 25681734 DOI: 10.1016/j.ajpath.2014.12.018] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 11/07/2014] [Accepted: 12/09/2014] [Indexed: 10/24/2022]
Abstract
The STARD3 gene belongs to the minimal amplicon in HER2-positive breast cancers and encodes a cholesterol-binding membrane protein. To study how elevated StAR-related lipid transfer protein 3 (StARD3) expression affects breast cancer cells, we generated MCF-7 cells stably overexpressing StARD3-green fluorescent protein. We found that StARD3-overexpressing cells exhibited nonadherent morphological features, had increased Src levels, and had altered cholesterol balance, as evidenced by elevated mRNA levels of the cholesterol biosynthesis rate-limiting enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and increased plasma membrane cholesterol content. On removal of serum and insulin from the culture medium, the morphological characteristics of the StARD3-overexpressing cells changed, the cells became adherent, and they developed enlarged focal adhesions. Under these conditions, the StARD3-overexpressing cells maintained elevated Src and plasma membrane cholesterol content and showed increased phosphorylation of focal adhesion kinase. In two Finnish nationwide patient cohorts, approximately 10% (212/2220) breast cancers exhibited high StARD3 protein levels, which was strongly associated with HER2 amplification; several factors related to poor disease outcome and poor breast cancer-specific survival. In addition, high StARD3 levels in breast cancers were associated with elevated 3-hydroxy-3-methylglutaryl-coenzyme A reductase mRNA levels and anti-Src-Tyr416 immunoreactivity. These results provide evidence that StARD3 overexpression results in increased cholesterol biosynthesis and Src kinase activity in breast cancer cells and suggest that elevated StARD3 expression may contribute to breast cancer aggressiveness by increasing membrane cholesterol and enhancing oncogenic signaling.
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Affiliation(s)
- Boris Vassilev
- Faculty of Medicine, Department of Anatomy, University of Helsinki, Helsinki, Finland
| | - Harri Sihto
- Laboratory of Molecular Oncology, Translational Cancer Biology Program, University of Helsinki, Helsinki, Finland
| | - Shiqian Li
- Faculty of Medicine, Department of Anatomy, University of Helsinki, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland
| | - Maarit Hölttä-Vuori
- Faculty of Medicine, Department of Anatomy, University of Helsinki, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland
| | - Jaakko Ilola
- Faculty of Medicine, Department of Anatomy, University of Helsinki, Helsinki, Finland
| | - Johan Lundin
- Institute for Molecular Medicine Finland, University of Helsinki, Biomedicum Helsinki 2U, Helsinki, Finland
| | - Jorma Isola
- Institute of Medical Technology, University of Tampere and Tampere University Central Hospital, Tampere, Finland
| | | | - Heikki Joensuu
- Department of Oncology, Helsinki University Central Hospital, Helsinki, Finland
| | - Elina Ikonen
- Faculty of Medicine, Department of Anatomy, University of Helsinki, Helsinki, Finland; Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland.
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9
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Ruhanen H, Perttilä J, Hölttä-Vuori M, Zhou Y, Yki-Järvinen H, Ikonen E, Käkelä R, Olkkonen VM. PNPLA3 mediates hepatocyte triacylglycerol remodeling. J Lipid Res 2014; 55:739-46. [PMID: 24511104 DOI: 10.1194/jlr.m046607] [Citation(s) in RCA: 90] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The I148M substitution in patatin-like phospholipase domain containing 3 (PNPLA3(I148M)) determines a genetic form of nonalcoholic fatty liver disease. To elucidate the mode of PNPLA3 action in human hepatocytes, we studied effects of WT PNPLA3 (PNPLA3(WT)) and PNPLA3(I148M) on HuH7 cell lipidome after [(13)C]glycerol labeling, cellular turnover of oleic acid labeled with 17 deuterium atoms ([D17]oleic acid) in triacylglycerols (TAGs), and subcellular distribution of the protein variants. PNPLA3(I148M) induced a net accumulation of unlabeled TAGs, but not newly synthesized total [(13)C]TAGs. Principal component analysis (PCA) revealed that both PNPLA3(WT) and PNPLA3(I148M) induced a relative enrichment of TAGs with saturated FAs or MUFAs, with concurrent enrichment of polyunsaturated phosphatidylcholines. PNPLA3(WT) associated in PCA with newly synthesized [(13)C]TAGs, particularly 52:1 and 50:1, while PNPLA3(I148M) associated with similar preexisting TAGs. PNPLA3(WT) overexpression resulted in increased [D17]oleic acid labeling of TAGs during 24 h, and after longer incubations their turnover was accelerated, effects not detected with PNPLA3(I148M). PNPLA3(I148M) localized more extensively to lipid droplets (LDs) than PNPLA3(WT), suggesting that the substitution alters distribution of PNPLA3 between LDs and endoplasmic reticulum/cytosol. This study reveals a function of PNPLA3 in FA-selective TAG remodeling, resulting in increased TAG saturation. A defect in TAG remodeling activity likely contributes to the TAG accumulation observed in cells expressing PNPLA3(I148M).
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Affiliation(s)
- Hanna Ruhanen
- Minerva Foundation Institute for Medical Research, Biomedicum 2U, FI-00290 Helsinki, Finland
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10
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Hölttä-Vuori M, Salo VT, Ohsaki Y, Suster ML, Ikonen E. Alleviation of seipinopathy-related ER stress by triglyceride storage. Hum Mol Genet 2012; 22:1157-66. [PMID: 23250914 DOI: 10.1093/hmg/dds523] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Mutations affecting the N-glycosylation site in Berardinelli-Seip lipodystrophy (BSCL)-associated gene BSCL2/seipin lead to a dominantly inherited spastic paraplegia termed seipinopathy. While the loss of function of seipin leads to severe congenital lipodystrophy, the effects of seipin N-glycosylation mutations on lipid balance in the nervous system are unknown. In this study, we show that expression of seipin N-glycosylation mutant N88S led to decreased triglyceride (TG) content in astrocytoma and motor neuron cell lines. This was corrected by supplementation with exogenous oleic acid. Upon oleic acid loading, seipin N88S protein was relocated from the endoplasmic reticulum (ER) to the surface of lipid droplets and this was paralleled by alleviation of ER stress induced by the mutant protein. This effect was not limited to seipin N88S, as oleic acid loading also reduced tunicamycin-induced ER stress in motor neuron cells. Furthermore, both seipin N88S and tunicamycin-induced ER stress were decreased by inhibiting lipolysis, suggesting that lipid droplets protected neuronal cells from ER stress. In developing zebrafish larvae, seipin N88S expression led to TG imbalance and reduced spontaneous free swimming. Importantly, supplementation with exogenous oleic acid reduced ER stress in the zebrafish head and increased fish motility. We propose that the decreased TG content contributes to the pathology induced by seipin N88S, and that rescuing TG levels may provide a novel therapeutic strategy in seipinopathy.
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Affiliation(s)
- Maarit Hölttä-Vuori
- Institute of Biomedicine, Anatomy, University of Helsinki, 00014 Helsinki, Finland
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11
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Hölttä-Vuori M, Vainio S, Kauppi M, Van Eck M, Jokitalo E, Ikonen E. Endosomal actin remodeling by coronin-1A controls lipoprotein uptake and degradation in macrophages. Circ Res 2012; 110:450-5. [PMID: 22223354 DOI: 10.1161/circresaha.111.256842] [Citation(s) in RCA: 182] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE The actin cytoskeleton has been implicated in the processing of atherogenic lipoproteins in macrophages. However, the functional role of actin and the regulatory proteins involved are unknown. OBJECTIVE Coronin-1A (Coro1A) was identified as a differentially expressed transcript in wild-type versus Niemann-Pick type C1 deficient macrophages exposed to acetylated low-density lipoproteins (AcLDL). We investigated whether Coro1A plays a role in the uptake or processing of modified lipoproteins in macrophages and if this is related to its actin regulatory functions. METHODS AND RESULTS In wild-type primary macrophages, filamentous actin transiently decorated AcLDL containing endosomes that also recruited Coro1A. This dynamic association of F-actin with endosomes was disturbed in Coro1A deficient macrophages. In Coro1A knockout macrophages the uptake of AcLDL was increased, rate of AcLDL delivery to lysosomes enhanced, and lipoprotein-derived cholesteryl ester hydrolysis accelerated. Overexpression of wild-type Coro1A normalized AcLDL uptake in Coro1A knockout macrophages while a Coro1A actin binding mutant did not. Furthermore, the effects of macrophage Coro1A silencing on endosomal actin association and AcLDL delivery to lysosomes resembled those of cofilin silencing. CONCLUSIONS Coro1A controls actin association with endocytic organelles, thereby negatively regulating endo-lysosomal delivery, degradation of modified lipoproteins and cholesterol deposition in macrophages.
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12
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Schneede A, Schmidt CK, Hölttä-Vuori M, Heeren J, Willenborg M, Blanz J, Domanskyy M, Breiden B, Brodesser S, Landgrebe J, Sandhoff K, Ikonen E, Saftig P, Eskelinen EL. Role for LAMP-2 in endosomal cholesterol transport. J Cell Mol Med 2011; 15:280-95. [PMID: 19929948 PMCID: PMC3822795 DOI: 10.1111/j.1582-4934.2009.00973.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Accepted: 11/09/2009] [Indexed: 01/24/2023] Open
Abstract
The mechanisms of endosomal and lysosomal cholesterol traffic are still poorly understood. We showed previously that unesterified cholesterol accumulates in the late endosomes and lysosomes of fibroblasts deficient in both lysosome associated membrane protein-2 (LAMP-2) and LAMP-1, two abundant membrane proteins of late endosomes and lysosomes. In this study we show that in cells deficient in both LAMP-1 and LAMP-2 (LAMP(-/-)), low-density lipoprotein (LDL) receptor levels and LDL uptake are increased as compared to wild-type cells. However, there is a defect in esterification of both endogenous and LDL cholesterol. These results suggest that LAMP(-/-) cells have a defect in cholesterol transport to the site of esterification in the endoplasmic reticulum, likely due to defective export of cholesterol out of late endosomes or lysosomes. We also show that cholesterol accumulates in LAMP-2 deficient liver and that overexpression of LAMP-2 retards the lysosomal cholesterol accumulation induced by U18666A. These results point to a critical role for LAMP-2 in endosomal/lysosomal cholesterol export. Moreover, the late endosomal/lysosomal cholesterol accumulation in LAMP(-/-) cells was diminished by overexpression of any of the three isoforms of LAMP-2, but not by LAMP-1. The LAMP-2 luminal domain, the membrane-proximal half in particular, was necessary and sufficient for the rescue effect. Taken together, our results suggest that LAMP-2, its luminal domain in particular, plays a critical role in endosomal cholesterol transport and that this is distinct from the chaperone-mediated autophagy function of LAMP-2.
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Affiliation(s)
| | | | | | - Jörg Heeren
- Department of Biochemistry and Molecular Biology II: Molecular Cell Biology, University Medical Center Hamburg-EppendorfHamburg, Germany
| | | | - Judith Blanz
- Institute of Biochemistry, University of KielKiel, Germany
| | - Mykola Domanskyy
- Department of Biological and Environmental Sciences, Division of Biochemistry, University of HelsinkiHelsinki, Finland
| | - Bernadette Breiden
- LIMES, Membrane Biology and Lipid Biochemistry Unit, c/o Kekulé-Institute for Organic Chemistry and BiochemistryBonn, Germany
| | - Susanne Brodesser
- LIMES, Membrane Biology and Lipid Biochemistry Unit, c/o Kekulé-Institute for Organic Chemistry and BiochemistryBonn, Germany
| | - Jobst Landgrebe
- Georg-August University Göttingen, Department of BiochemistryGöttingen, Germany
| | - Konrad Sandhoff
- LIMES, Membrane Biology and Lipid Biochemistry Unit, c/o Kekulé-Institute for Organic Chemistry and BiochemistryBonn, Germany
| | - Elina Ikonen
- Institute of Biomedicine/Anatomy, University of HelsinkiHelsinki, Finland
| | - Paul Saftig
- Institute of Biochemistry, University of KielKiel, Germany
| | - Eeva-Liisa Eskelinen
- Department of Biological and Environmental Sciences, Division of Biochemistry, University of HelsinkiHelsinki, Finland
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13
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Hölttä-Vuori M, Uronen RL, Repakova J, Salonen E, Vattulainen I, Panula P, Li Z, Bittman R, Ikonen E. BODIPY-cholesterol: a new tool to visualize sterol trafficking in living cells and organisms. Traffic 2008; 9:1839-49. [PMID: 18647169 DOI: 10.1111/j.1600-0854.2008.00801.x] [Citation(s) in RCA: 192] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Analysis of sterol distribution and transport in living cells has been hampered by the lack of bright, photostable fluorescent sterol derivatives that closely resemble cholesterol. In this study, we employed atomistic simulations and experiments to characterize a cholesterol compound with fluorescent boron dipyrromethene difluoride linked to sterol carbon-24 (BODIPY-cholesterol). This probe packed in the membrane and behaved similarly to cholesterol both in normal and in cholesterol-storage disease cells and with trace amounts allowed the visualization of sterol movement in living systems. Upon injection into the yolk sac, BODIPY-cholesterol did not disturb zebrafish development and was targeted to sterol-enriched brain regions in live fish. We conclude that this new probe closely mimics the membrane partitioning and trafficking of cholesterol and, because of its excellent fluorescent properties, enables the direct monitoring of sterol movement by time-lapse imaging using trace amounts of the probe. This is, to our knowledge, the first cholesterol probe that fulfills these prerequisites.
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Affiliation(s)
- Maarit Hölttä-Vuori
- Institute of Biomedicine/Anatomy, Haartmaninkatu 8, University of Helsinki, Helsinki 00014, Finland
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14
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Tiala I, Suomela S, Huuhtanen J, Wakkinen J, Hölttä-Vuori M, Kainu K, Ranta S, Turpeinen U, Hämäläinen E, Jiao H, Karvonen SL, Ikonen E, Kere J, Saarialho-Kere U, Elomaa O. The CCHCR1 (HCR) gene is relevant for skin steroidogenesis and downregulated in cultured psoriatic keratinocytes. J Mol Med (Berl) 2007; 85:589-601. [PMID: 17221218 DOI: 10.1007/s00109-006-0155-0] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2006] [Revised: 12/05/2006] [Accepted: 12/13/2006] [Indexed: 11/24/2022]
Abstract
The HCR gene, officially called Coiled-Coil alpha-Helical Rod protein 1 (CCHCR1), located within the major psoriasis susceptibility locus PSORS1, is a plausible candidate gene for the risk effect. Recently, CCHCR1 was shown to promote steroidogenesis by interacting with the steroidogenic acute regulator protein (StAR). Here, we examined the role of CCHCR1 in psoriasis and cutaneous steroid metabolism. We found that CCHCR1 and StAR are expressed in basal keratinocytes in overlapping areas of the human skin, and CCHCR1 stimulated pregnenolone production in steroidogenesis assay. Overexpression of either the CCHCR1*WWCC risk allele or the non-risk allele enhanced steroid synthesis in vitro. Furthermore, the cytochrome P450scc enzyme was expressed in human keratinocytes and was induced by forskolin, a known activator of steroidogenesis, and forskolin also upregulated CCHCR1. CCHCR1 has an altered expression pattern in lesional psoriatic skin compared to normal healthy skin, suggesting its dysregulation in psoriasis. We found that the expression of CCHCR1 is downregulated twofold at the mRNA level in cultured non-lesional psoriatic keratinocytes when compared to non-psoriatic healthy cells. Our results also suggest a connection between CCHCR1 and vitamin D metabolism in keratinocytes. The expression of the vitamin D receptor (VDR) gene was lower in non-lesional psoriatic keratinocytes than in healthy cells. Furthermore, Vdr expression was downregulated in the keratinocytes of mice overexpressing the CCHCR1*WWCC risk allele when compared to keratinocytes from mice with the non-risk allele of CCHCR1. Finally, we demonstrate that other agents relevant for psoriasis and/or the regulation of steroidogenesis influence CCHCR1 expression in keratinocytes, including insulin, EGF, cholesterol, estrogen, and cyclosporin A. Taken the role of steroid hormones, including vitamin D and estrogen, in cell proliferation, epidermal barrier homeostasis, differentiation, and immune response, our results suggest a role for CCHCR1 in the pathogenesis of psoriasis via the regulation of skin steroid metabolism.
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Affiliation(s)
- Inkeri Tiala
- Department of Medical Genetics, University of Helsinki, Helsinki, Finland
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15
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Linder MD, Uronen RL, Hölttä-Vuori M, van der Sluijs P, Peränen J, Ikonen E. Rab8-dependent recycling promotes endosomal cholesterol removal in normal and sphingolipidosis cells. Mol Biol Cell 2006; 18:47-56. [PMID: 17050734 PMCID: PMC1751315 DOI: 10.1091/mbc.e06-07-0575] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The mechanisms by which low-density lipoprotein (LDL)-cholesterol exits the endocytic circuits are not well understood. The process is defective in Niemann-Pick type C (NPC) disease in which cholesterol and sphingolipids accumulate in late endosomal compartments. This is accompanied by defective cholesterol esterification in the endoplasmic reticulum and impaired ATP-binding cassette transporter A1 (ABCA1)-dependent cholesterol efflux. We show here that overexpression of the recycling/exocytic Rab GTPase Rab8 rescued the late endosomal cholesterol deposition and sphingolipid mistrafficking in NPC fibroblasts. Rab8 redistributed cholesterol from late endosomes to the cell periphery and stimulated cholesterol efflux to the ABCA1-ligand apolipoprotein A-I (apoA-I) without increasing cholesterol esterification. Depletion of Rab8 from wild-type fibroblasts resulted in cholesterol deposition within late endosomal compartments. This cholesterol accumulation was accompanied by impaired clearance of LDL-cholesterol from endocytic circuits to apoA-I and could not be bypassed by liver X receptor activation. Our findings establish Rab8 as a key component of the regulatory machinery that leads to ABCA1-dependent removal of cholesterol from endocytic circuits.
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Affiliation(s)
| | | | | | - Peter van der Sluijs
- Department of Cell Biology, University Medical Center Utrecht, 3584 CX Utrecht, The Netherlands
| | - Johan Peränen
- Institute of Biotechnology, University of Helsinki, FI-00014 Helsinki, Finland; and
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16
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Abstract
The endoplasmic reticulum is traditionally perceived as the key compartment for regulating intracellular cholesterol metabolism. Increasing evidence suggests that the endocytic pathway provides an additional regulatory level governing intracellular cholesterol trafficking and homoeostasis. Sterols can enter, and apparently also exit, endosomal compartments via both vesicular and non-vesicular mechanisms. A number of studies have focused on endosomal sterol removal as its defects lead to cholesterol storage diseases. So far, the bulk of evidence on endosomal sterol egress describes the involvement of membrane trafficking machineries. Interestingly, two late endosomal sterol-binding proteins were recently shown to regulate the movement of late endosomes along cytoskeletal tracks. These studies provide the first indications of how non-vesicular and vesicular mechanisms may co-operate in endosomal sterol trafficking.
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Affiliation(s)
- M Hölttä-Vuori
- Institute of Biomedicine/Anatomy, University of Helsinki, Finland
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17
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Hölttä-Vuori M, Alpy F, Tanhuanpää K, Jokitalo E, Mutka AL, Ikonen E. MLN64 is involved in actin-mediated dynamics of late endocytic organelles. Mol Biol Cell 2005; 16:3873-86. [PMID: 15930133 PMCID: PMC1182323 DOI: 10.1091/mbc.e04-12-1105] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
MLN64 is a late endosomal cholesterol-binding membrane protein of an unknown function. Here, we show that MLN64 depletion results in the dispersion of late endocytic organelles to the cell periphery similarly as upon pharmacological actin disruption. The dispersed organelles in MLN64 knockdown cells exhibited decreased association with actin and the Arp2/3 complex subunit p34-Arc. MLN64 depletion was accompanied by impaired fusion of late endocytic organelles and delayed cargo degradation. MLN64 overexpression increased the number of actin and p34-Arc-positive patches on late endosomes, enhanced the fusion of late endocytic organelles in an actin-dependent manner, and stimulated the deposition of sterol in late endosomes harboring the protein. Overexpression of wild-type MLN64 was capable of rescuing the endosome dispersion in MLN64-depleted cells, whereas mutants of MLN64 defective in cholesterol binding were not, suggesting a functional connection between MLN64-mediated sterol transfer and actin-dependent late endosome dynamics. We propose that local sterol enrichment by MLN64 in the late endosomal membranes facilitates their association with actin, thereby governing actin-dependent fusion and degradative activity of late endocytic organelles.
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18
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Lännenpää M, Hassinen M, Ranki A, Hölttä-Vuori M, Lemmetyinen J, Keinonen K, Sopanen T. Prevention of flower development in birch and other plants using a BpFULL1::BARNASE construct. Plant Cell Rep 2005; 24:69-78. [PMID: 15690161 DOI: 10.1007/s00299-004-0903-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2004] [Revised: 11/09/2004] [Accepted: 11/09/2004] [Indexed: 05/20/2023]
Abstract
The prevention of flower formation is important for avoiding the spread of transgenes from genetically modified plants into wild populations. Moreover, the resources not expended for the generation of flowers and fruits might be allocated to increased vegetative growth. We have been developing methods for preventing flower formation in silver birch (Betula pendula), a tree species of considerable economical importance in the boreal region. Here we study the suitability of the promoter of BpFRUITFULL-LIKE1 (BpFULL1, formerly BpMADS5) for tissue-specific ablation of inflorescences in Arabidopsis, tobacco and birch. With all these species, the development of inflorescences was successfully prevented. The results show that the BpFULL1::BARNASE construct has potential biotechnological applications in different plant species.
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Affiliation(s)
- M Lännenpää
- Department of Biology, University of Joensuu, P.O. Box 111, 80101 Joensuu, Finland.
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19
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Abstract
Niemann-Pick type C (NPC) is a lysosomal storage disorder that results in the accumulation of cholesterol and sphingolipids. Mutations in the NPC1 or NPC2 gene are responsible for the disease but the precise functions of the encoded proteins remain unresolved. Recent observations have challenged the traditional concept of NPC as a primary cholesterol transport defect. This review updates the recent NPC literature, summarizing the increasing insight into the cholesterol trafficking circuits and also addressing the contribution of other lipids in the cellular pathogenesis. The importance of NPC as a model for subcellular lipid imbalance in studying more common diseases, such as Alzheimer's and cardiovascular diseases, is discussed.
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Affiliation(s)
- Elina Ikonen
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
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20
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Lännenpää M, Jänönen I, Hölttä-Vuori M, Gardemeister M, Porali I, Sopanen T. A new SBP-box gene BpSPL1 in silver birch (Betula pendula). Physiol Plant 2004; 120:491-500. [PMID: 15032847 DOI: 10.1111/j.0031-9317.2004.00254.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The SBP-box gene family represents a group of plant-specific genes encoding putative transcription factors. Thus far, SBP-domain protein binding sites have been found in the promoters of Arabidopsis APETALA1 and Antirrhinum SQUAMOSA. A putative SBP-domain binding element has been observed in the promoter of BpMADS5, a close homologue of Arabidopsis FRUITFULL in silver birch (Betula pendula). A novel SBP-box gene from birch named BpSPL1 has been cloned and characterized. The nucleotide sequence of BpSPL1 is similar to Antirrhinum SBP2 and Arabidopsis SPL3, apart from the unique finding that BpSPL1 does not contain an intron typical to all other known SBP-box genes studied thus far. According to Northern blot analysis, BpSPL1 is expressed in birch inflorescences as well as in shoots and leaves. Studies using electrophoretic mobility shift assay demonstrate that there are nuclear proteins in birch inflorescences which specifically bind to the SBP binding element of the promoter of BpMADS5. BpSPL1 expressed in Escherichia coli also specifically binds to this element. According to Southern blot analysis, there are at least two SBP-box genes in birch. The results suggest that SBP-box genes are involved in the regulation of flower development in birch.
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Affiliation(s)
- Mika Lännenpää
- Department of Biology, University of Joensuu. P.O.Box 111, FIN-80101 Joensuu, Finland
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21
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Abstract
To analyze the contribution of vesicular trafficking pathways in cellular cholesterol transport we examined the effects of selected endosomal Rab proteins on cholesterol distribution by filipin staining. Transient overexpression of Rab11 resulted in prominent accumulation of free cholesterol in Rab11-positive organelles that sequestered transferrin receptors and internalized transferrin. Sphingolipids were selectively redistributed as pyrene-sphingomyelin and sulfatide cosequestered with Rab11-positive endosomes, whereas globotriaosyl ceramide and GM2 ganglioside did not. Rab11 overexpression did not perturb the transport of 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine-perchlorate-labeled low-density lipoprotein (LDL) to late endosomes or the Niemann-Pick type C1 (NPC1)-induced late endosomal cholesterol clearance in NPC patient cells. However, Rab11 overexpression inhibited cellular cholesterol esterification in an LDL-independent manner. This effect could be overcome by introducing cholesterol to the plasma membrane by using cyclodextrin as a carrier. These results suggest that in Rab11-overexpressing cells, deposition of cholesterol in recycling endosomes results in its impaired esterification, presumably due to defective recycling of cholesterol to the plasma membrane. The findings point to the importance of the recycling endosomes in regulating cholesterol and sphingolipid trafficking and cellular cholesterol homeostasis.
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Affiliation(s)
- Maarit Hölttä-Vuori
- Department of Molecular Medicine, National Public Health Institute, Biomedicum Helsinki, Finland
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Hölttä-Vuori M, Määttä J, Ullrich O, Kuismanen E, Ikonen E. Mobilization of late-endosomal cholesterol is inhibited by Rab guanine nucleotide dissociation inhibitor. Curr Biol 2000; 10:95-8. [PMID: 10662671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Cholesterol entering cells in low-density lipoproteins (LDL) via receptor-mediated endocytosis is transported to organelles of the late endocytic pathway for degradation of the lipoprotein particles. The fate of the free cholesterol released remains poorly understood, however. Recent observations suggest that late-endosomal cholesterol sequestration is regulated by the dynamics of lysobisphosphatidic acid (LBPA)-rich membranes [1]. Genetic studies have pinpointed a protein, Niemann-Pick C-1 (NPC-1), that is required for the mobilization of late-endosomal/lysosomal cholesterol by an unknown mechanism [2]. Here, we report the removal of accumulated cholesterol by overexpression of the NPC-1 protein in NPC-1-deficient fibroblasts from patients with Niemann-Pick disease, and in normal fibroblasts upon release of a progesterone-induced block of cholesterol transport. We show that late-endosomal/lysosomal cholesterol mobilization is specifically inhibited by microinjection of Rab GDP-dissociation inhibitor (Rab-GDI). Moreover, clearance of the cholesterol deposits by NPC-1 in patients' fibroblasts is accompanied by the redistribution of LBPA and of a lysosomal hydrolase that utilizes the mannose-6-phosphate receptor. Our results reveal, for the first time, the involvement of a specific molecular component of the membrane-trafficking machinery in cholesterol transport and the coupling of late-endosomal cholesterol egress to the trafficking of other lipid and protein cargo.
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Affiliation(s)
- M Hölttä-Vuori
- Department of Biochemistry, National Public Health Institute, Helsinki, 00300, Finland
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Hölttä-Vuori M, Määttä J, Ullrich O, Kuismanen E, Ikonen E. Mobilization of late-endosomal cholesterol is inhibited by Rab guanine nucleotide dissociation inhibitor. Curr Biol 2000. [DOI: 10.1016/s0960-9822(00)00289-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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