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Hiser C, Montgomery BL, Ferguson-Miller S. TSPO protein binding partners in bacteria, animals, and plants. J Bioenerg Biomembr 2021; 53:463-487. [PMID: 34191248 PMCID: PMC8243069 DOI: 10.1007/s10863-021-09905-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 06/12/2021] [Indexed: 12/11/2022]
Abstract
The ancient membrane protein TSPO is phylogenetically widespread from archaea and bacteria to insects, vertebrates, plants, and fungi. TSPO’s primary amino acid sequence is only modestly conserved between diverse species, although its five transmembrane helical structure appears mainly conserved. Its cellular location and orientation in membranes have been reported to vary between species and tissues, with implications for potential diverse binding partners and function. Most TSPO functions relate to stress-induced changes in metabolism, but in many cases it is unclear how TSPO itself functions—whether as a receptor, a sensor, a transporter, or a translocator. Much evidence suggests that TSPO acts indirectly by association with various protein binding partners or with endogenous or exogenous ligands. In this review, we focus on proteins that have most commonly been invoked as TSPO binding partners. We suggest that TSPO was originally a bacterial receptor/stress sensor associated with porphyrin binding as its most ancestral function and that it later developed additional stress-related roles in eukaryotes as its ability to bind new partners evolved.
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Affiliation(s)
- Carrie Hiser
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA. .,Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.
| | - Beronda L Montgomery
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA.,Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.,Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, 48824, USA
| | - Shelagh Ferguson-Miller
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA
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2
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Loth MK, Guariglia SR, Re DB, Perez J, de Paiva VN, Dziedzic JL, Chambers JW, Azzam DJ, Guilarte TR. A Novel Interaction of Translocator Protein 18 kDa (TSPO) with NADPH Oxidase in Microglia. Mol Neurobiol 2020; 57:4467-4487. [PMID: 32743737 PMCID: PMC7515859 DOI: 10.1007/s12035-020-02042-w] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Accepted: 07/24/2020] [Indexed: 12/12/2022]
Abstract
In the brain neuropil, translocator protein 18 kDa (TSPO) is a stress response protein that is upregulated in microglia and astrocytes in diverse central nervous system pathologies. TSPO is widely used as a biomarker of neuroinflammation in preclinical and clinical neuroimaging studies. However, there is a paucity of knowledge on the function(s) of TSPO in glial cells. In this study, we explored a putative interaction between TSPO and NADPH oxidase 2 (NOX2) in microglia. We found that TSPO associates with gp91phox and p22phox, the principal subunits of NOX2 in primary murine microglia. The association of TSPO with gp91phox and p22phox was observed using co-immunoprecipitation, confocal immunofluorescence imaging, and proximity ligation assay. We found that besides gp91phox and p22phox, voltage-dependent anion channel (VDAC) also co-immunoprecipitated with TSPO consistent with previous reports. When we compared lipopolysaccharide (LPS) stimulated microglia to vehicle control, we found that a lower amount of gp91phox and p22phox protein co-immunoprecipitated with TSPO suggesting a disruption of the TSPO-NOX2 subunits association. TSPO immuno-gold electron microscopy confirmed that TSPO is present in the outer mitochondrial membrane but it is also found in the endoplasmic reticulum (ER), mitochondria-associated ER membrane (MAM), and in the plasma membrane. TSPO localization at the MAM may represent a subcellular site where TSPO interacts with gp91phox and p22phox since the MAM is a point of communication between outer mitochondria membrane proteins (TSPO) and ER proteins (gp91phox and p22phox) where they mature and form the cytochrome b558 (Cytb558) heterodimer. We also found that an acute burst of reactive oxygen species (ROS) increased TSPO levels on the surface of microglia and this effect was abrogated by a ROS scavenger. These results suggest that ROS production may alter the subcellular distribution of TSPO. Collectively, our findings suggest that in microglia, TSPO is associated with the major NOX2 subunits gp91phox and p22phox. We hypothesize that this interaction may regulate Cytb558 formation and modulate NOX2 levels, ROS production, and redox homeostasis in microglia.
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Affiliation(s)
- Meredith K Loth
- Department of Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, NY, USA
| | - Sara R Guariglia
- Department of Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, NY, USA
| | - Diane B Re
- Department of Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, NY, USA
| | - Juan Perez
- Department of Environmental Health Sciences, Robert Stempel College of Public Health & Social Work, Florida International University, Miami, FL, 33199, USA
| | - Vanessa Nunes de Paiva
- Department of Environmental Health Sciences, Robert Stempel College of Public Health & Social Work, Florida International University, Miami, FL, 33199, USA
| | - Jennifer L Dziedzic
- Department of Environmental Health Sciences, Robert Stempel College of Public Health & Social Work, Florida International University, Miami, FL, 33199, USA
| | - Jeremy W Chambers
- Department of Environmental Health Sciences, Robert Stempel College of Public Health & Social Work, Florida International University, Miami, FL, 33199, USA
| | - Diana J Azzam
- Department of Environmental Health Sciences, Robert Stempel College of Public Health & Social Work, Florida International University, Miami, FL, 33199, USA
| | - Tomás R Guilarte
- Department of Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, NY, USA.
- Department of Environmental Health Sciences, Robert Stempel College of Public Health & Social Work, Florida International University, Miami, FL, 33199, USA.
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3
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Marginedas-Freixa I, Alvarez CL, Moras M, Hattab C, Bouyer G, Chene A, Lefevre SD, Le Van Kim C, Bihel F, Schwarzbaum PJ, Ostuni MA. Induction of ATP Release, PPIX Transport, and Cholesterol Uptake by Human Red Blood Cells Using a New Family of TSPO Ligands. Int J Mol Sci 2018; 19:ijms19103098. [PMID: 30308949 PMCID: PMC6213633 DOI: 10.3390/ijms19103098] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Revised: 10/05/2018] [Accepted: 10/07/2018] [Indexed: 02/07/2023] Open
Abstract
Two main isoforms of the Translocator Protein (TSPO) have been identified. TSPO1 is ubiquitous and is mainly present at the outer mitochondrial membrane of most eukaryotic cells, whereas, TSPO2 is specific to the erythroid lineage, located at the plasma membrane, the nucleus, and the endoplasmic reticulum. The design of specific tools is necessary to determine the molecular associations and functions of TSPO, which remain controversial nowadays. We recently demonstrated that TSPO2 is involved in a supramolecular complex of the erythrocyte membrane, where micromolar doses of the classical TSPO ligands induce ATP release and zinc protoporphyrin (ZnPPIX) transport. In this work, three newly-designed ligands (NCS1016, NCS1018, and NCS1026) were assessed for their ability to modulate the functions of various erythrocyte's and compare them to the TSPO classical ligands. The three new ligands were effective in reducing intraerythrocytic Plasmodium growth, without compromising erythrocyte survival. While NCS1016 and NCS1018 were the most effective ligands in delaying sorbitol-induced hemolysis, NCS1016 induced the highest uptake of ZnPPIX and NCS1026 was the only ligand inhibiting the cholesterol uptake. Differential effects of ligands are probably due, not only, to ligand features, but also to the dynamic interaction of TSPO with various partners at the cell membrane. Further studies are necessary to fully understand the mechanisms of the TSPO's complex activation.
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Affiliation(s)
- Irene Marginedas-Freixa
- UMR-S1134, Integrated Biology of Red Blood Cells, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Université de la Réunion, Université des Antilles, F-75015 Paris, France.
- Institut National de la Transfusion Sanguine, Laboratoire d'Excellence GR-Ex, F-75015 Paris, France.
| | - Cora L Alvarez
- Instituto de Química y Fisico-Química Biológicas "Prof. Alejandro C. Paladini", UBA, CONICET, Facultad de Farmacia y Bioquímica, Junín 956, C1113AAD Buenos Aires, Argentina.
- Departamento de Biodiversidad y Biología Experimental, Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1113AAD Buenos Aires, Argentina.
| | - Martina Moras
- UMR-S1134, Integrated Biology of Red Blood Cells, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Université de la Réunion, Université des Antilles, F-75015 Paris, France.
- Institut National de la Transfusion Sanguine, Laboratoire d'Excellence GR-Ex, F-75015 Paris, France.
| | - Claude Hattab
- UMR-S1134, Integrated Biology of Red Blood Cells, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Université de la Réunion, Université des Antilles, F-75015 Paris, France.
- Institut National de la Transfusion Sanguine, Laboratoire d'Excellence GR-Ex, F-75015 Paris, France.
| | - Guillaume Bouyer
- UMR 8227 LBI2M, Comparative Erythrocyte's Physiology, CNRS, Sorbonne Université, Laboratoire d'Excellence GR-Ex, F-29680 Roscoff, France.
| | - Arnaud Chene
- UMR-S1134, Integrated Biology of Red Blood Cells, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Université de la Réunion, Université des Antilles, F-75015 Paris, France.
- Institut National de la Transfusion Sanguine, Laboratoire d'Excellence GR-Ex, F-75015 Paris, France.
| | - Sophie D Lefevre
- UMR-S1134, Integrated Biology of Red Blood Cells, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Université de la Réunion, Université des Antilles, F-75015 Paris, France.
- Institut National de la Transfusion Sanguine, Laboratoire d'Excellence GR-Ex, F-75015 Paris, France.
| | - Caroline Le Van Kim
- UMR-S1134, Integrated Biology of Red Blood Cells, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Université de la Réunion, Université des Antilles, F-75015 Paris, France.
- Institut National de la Transfusion Sanguine, Laboratoire d'Excellence GR-Ex, F-75015 Paris, France.
| | - Frederic Bihel
- UMR7200, Laboratoire d'Innovation Thérapeutique, Faculty of Pharmacy, University of Strasbourg, CNRS, F-67400 Illkirch Graffenstaden, France.
| | - Pablo J Schwarzbaum
- Instituto de Química y Fisico-Química Biológicas "Prof. Alejandro C. Paladini", UBA, CONICET, Facultad de Farmacia y Bioquímica, Junín 956, C1113AAD Buenos Aires, Argentina.
- Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, C1113AAD Buenos Aires, Argentina.
| | - Mariano A Ostuni
- UMR-S1134, Integrated Biology of Red Blood Cells, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Université de la Réunion, Université des Antilles, F-75015 Paris, France.
- Institut National de la Transfusion Sanguine, Laboratoire d'Excellence GR-Ex, F-75015 Paris, France.
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Selvaraj V, Tu LN. Current status and future perspectives: TSPO in steroid neuroendocrinology. J Endocrinol 2016; 231:R1-R30. [PMID: 27422254 DOI: 10.1530/joe-16-0241] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 07/15/2016] [Indexed: 12/21/2022]
Abstract
The mitochondrial translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), has received significant attention both as a diagnostic biomarker and as a therapeutic target for different neuronal disease pathologies. Recently, its functional basis believed to be mediating mitochondrial cholesterol import for steroid hormone production has been refuted by studies examining both in vivo and in vitro genetic Tspo-deficient models. As a result, there now exists a fundamental gap in the understanding of TSPO function in the nervous system, and its putative pharmacology in neurosteroid production. In this review, we discuss several recent findings in steroidogenic cells that are in direct contradiction to previous studies, and necessitate a re-examination of the purported role for TSPO in de novo neurosteroid biosynthesis. We critically examine the pharmacological effects of different TSPO-binding drugs with particular focus on studies that measure neurosteroid levels. We highlight the basis of key misconceptions regarding TSPO that continue to pervade the literature, and the need for interpretation with caution to avoid negative impacts. We also summarize the emerging perspectives that point to new directions that need to be investigated for understanding the molecular function of TSPO, only after which the true potential of this therapeutic target in medicine may be realized.
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Affiliation(s)
- Vimal Selvaraj
- Department of Animal ScienceCornell University, Ithaca, New York, USA
| | - Lan N Tu
- Department of Animal ScienceCornell University, Ithaca, New York, USA
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5
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TSPO ligands stimulate ZnPPIX transport and ROS accumulation leading to the inhibition of P. falciparum growth in human blood. Sci Rep 2016; 6:33516. [PMID: 27641616 PMCID: PMC5027585 DOI: 10.1038/srep33516] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 08/30/2016] [Indexed: 11/08/2022] Open
Abstract
After invading red blood cells (RBCs), Plasmodium falciparum (Pf) can export its own proteins to the host membrane and activate endogenous channels that are present in the membrane of RBCs. This transport pathway involves the Voltage Dependent Anion Channel (VDAC). Moreover, ligands of the VDAC partner TranSlocator PrOtein (TSPO) were demonstrated to inhibit the growth of the parasite. We studied the expression of TSPO and VDAC isoforms in late erythroid precursors, examined the presence of these proteins in membranes of non-infected and infected human RBCs, and evaluated the efficiency of TSPO ligands in inhibiting plasmodium growth, transporting the haem analogue Zn-protoporphyrin-IX (ZnPPIX) and enhancing the accumulation of reactive oxygen species (ROS). TSPO and VDAC isoforms are differentially expressed on erythroid cells in late differentiation states. TSPO2 and VDAC are present in the membranes of mature RBCs in a unique protein complex that changes the affinity of TSPO ligands after Pf infection. TSPO ligands dose-dependently inhibited parasite growth, and this inhibition was correlated to ZnPPIX uptake and ROS accumulation in the infected RBCs. Our results demonstrate that TSPO ligands can induce Pf death by increasing the uptake of porphyrins through a TSPO2-VDAC complex, which leads to an accumulation of ROS.
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6
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Zhao AH, Tu LN, Mukai C, Sirivelu MP, Pillai VV, Morohaku K, Cohen R, Selvaraj V. Mitochondrial Translocator Protein (TSPO) Function Is Not Essential for Heme Biosynthesis. J Biol Chem 2015; 291:1591-1603. [PMID: 26627829 DOI: 10.1074/jbc.m115.686360] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Indexed: 01/08/2023] Open
Abstract
Function of the mammalian translocator protein (TSPO; previously known as the peripheral benzodiazepine receptor) remains unclear because its presumed role in steroidogenesis and mitochondrial permeability transition established using pharmacological methods has been refuted in recent genetic studies. Protoporphyrin IX (PPIX) is considered a conserved endogenous ligand for TSPO. In bacteria, TSPO was identified to regulate tetrapyrrole metabolism and chemical catalysis of PPIX in the presence of light, and in vertebrates, TSPO function has been linked to porphyrin transport and heme biosynthesis. Positive correlation between high TSPO expression in cancer cells and susceptibility to photodynamic therapy based on their increased ability to convert the precursor 5-aminolevulinic acid (ALA) to PPIX appeared to reinforce this mechanism. In this study, we used TSPO knock-out (Tspo(-/-)) mice, primary cells, and different tumor cell lines to examine the role of TSPO in erythropoiesis, heme levels, PPIX biosynthesis, phototoxic cell death, and mitochondrial bioenergetic homeostasis. In contrast to expectations, our results demonstrate that TSPO deficiency does not adversely affect erythropoiesis, heme biosynthesis, bioconversion of ALA to PPIX, and porphyrin-mediated phototoxic cell death. TSPO expression levels in cancer cells do not correlate with their ability to convert ALA to PPIX. In fibroblasts, we observed that TSPO deficiency decreased the oxygen consumption rate and mitochondrial membrane potential (ΔΨm) indicative of a cellular metabolic shift, without a negative impact on porphyrin biosynthetic capability. Based on these findings, we conclude that mammalian TSPO does not have a critical physiological function related to PPIX and heme biosynthesis.
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Affiliation(s)
- Amy H Zhao
- From the Department of Animal Science, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853
| | - Lan N Tu
- From the Department of Animal Science, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853
| | - Chinatsu Mukai
- the Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, and
| | - Madhu P Sirivelu
- the Department of Clinical Pathology, College of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Viju V Pillai
- From the Department of Animal Science, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853
| | - Kanako Morohaku
- From the Department of Animal Science, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853
| | - Roy Cohen
- the Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, and
| | - Vimal Selvaraj
- From the Department of Animal Science, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853,.
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7
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Enigmatic Translocator protein (TSPO) and cellular stress regulation. Trends Biochem Sci 2015; 40:497-503. [PMID: 26228316 DOI: 10.1016/j.tibs.2015.07.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Revised: 06/25/2015] [Accepted: 07/06/2015] [Indexed: 11/23/2022]
Abstract
Translocator proteins (TSPOs) are conserved, ubiquitous membrane proteins identified initially as benzodiazepine-binding proteins in mammalian cells. Recent genetic and biochemical studies have challenged the accepted model that TSPOs are essential and required for steroidogenesis in animal cells. Instead, evidence from different kingdoms of life suggests that TSPOs are encoded by nonessential genes that are temporally upregulated in cells encountering conditions of oxidative stress, including inflammation and tissue injury. Here we discuss how TSPOs may be involved in complex homeostasis signaling mechanisms. We suggest that the main physiological role of TSPOs may be to modulate oxidative stress, irrespective of the cell type or subcellular localization, in part through the subtle regulation of tetrapyrrole metabolism.
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8
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Weng W, Sheng G. Five transcription factors and FGF pathway inhibition efficiently induce erythroid differentiation in the epiblast. Stem Cell Reports 2014; 2:262-70. [PMID: 24672750 PMCID: PMC3964278 DOI: 10.1016/j.stemcr.2014.01.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Revised: 01/27/2014] [Accepted: 01/29/2014] [Indexed: 02/04/2023] Open
Abstract
Primitive erythropoiesis follows a stereotypic developmental program of mesoderm ventralization and internalization, hemangioblast formation and migration, and erythroid lineage specification. Induction of erythropoiesis is inefficient in either ES/iPS cells in vitro or nonhemangioblast cell populations in vivo. Using the chick model, we report that epiblast cells can be directly and efficiently differentiated into the erythroid lineage by expressing five hematopoietic transcription regulators (SCL+LMO2+GATA2+LDB1+E2A) and inhibiting the FGF pathway. We show that these five genes are expressed with temporal specificity during normal erythropoiesis. Initiation of SCL and LMO2 expression requires FGF activity, whereas erythroid differentiation is enhanced by FGF inhibition. The lag between hematopoiesis and erythropoiesis is attributed to sequential coregulator expression and hemangioblast migration. Globin gene transcription can be ectopically and prematurely induced by manipulating the availability of these factors and the FGF pathway activity. We propose that similar approaches can be taken for efficient erythroid differentiation in vitro.
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Affiliation(s)
- Wei Weng
- Laboratory for Early Embryogenesis, RIKEN Center for Developmental Biology, Kobe, Hyogo 650-0047, Japan
| | - Guojun Sheng
- Laboratory for Early Embryogenesis, RIKEN Center for Developmental Biology, Kobe, Hyogo 650-0047, Japan
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Nakazawa F, Alev C, Jakt LM, Sheng G. Yolk sac endoderm is the major source of serum proteins and lipids and is involved in the regulation of vascular integrity in early chick development. Dev Dyn 2011; 240:2002-10. [PMID: 21761483 DOI: 10.1002/dvdy.22690] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
An important function of the vascular system is nutrient delivery. In adult animals, this is mediated through a close contact of the mesoderm-derived vasculature with the endoderm-derived enterocytes and hepatocytes. During embryonic development, the yolk sac (YS) endoderm has been suggested to play a similar role. Physiological and molecular nature of the contact between the YS endoderm and the vasculature is not well-understood. To understand roles of the YS endoderm in early development, we used the avian model and carried out a gene expression profiling analysis of isolated area vasculosa YS endoderm tissues from embryonic day 2-4 chick embryos, covering the first 48 hr of postcirculation development. Genes involved in lipid metabolism are highly enriched, indicating an active modification of lipid components during their transfer from the yolk to the circulatory system. We also uncovered genes encoding major serum proteins and key regulators of vascular integrity. In particular, PTGDS, an enzyme controlling the last step of prostaglandin D2 production, shows high expression in the YS endoderm. Experimental introduction of prostaglandin D2 into embryonic circulation led to intraembryonic vessel rupture. These data suggest that the YS endoderm is the major, if not exclusive, source of lipid and protein constituents of the early embryonic serum and plays an important role in the regulation of vascular integrity in developing embryo.
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Affiliation(s)
- Fumie Nakazawa
- Laboratory for Early Embryogenesis, RIKEN Center for Developmental Biology, Kobe, Hyogo, Japan
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10
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Vanhee C, Zapotoczny G, Masquelier D, Ghislain M, Batoko H. The Arabidopsis multistress regulator TSPO is a heme binding membrane protein and a potential scavenger of porphyrins via an autophagy-dependent degradation mechanism. THE PLANT CELL 2011; 23:785-805. [PMID: 21317376 PMCID: PMC3077796 DOI: 10.1105/tpc.110.081570] [Citation(s) in RCA: 151] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Revised: 12/22/2010] [Accepted: 01/05/2011] [Indexed: 05/18/2023]
Abstract
TSPO, a stress-induced, posttranslationally regulated, early secretory pathway-localized plant cell membrane protein, belongs to the TspO/MBR family of regulatory proteins, which can bind porphyrins. This work finds that boosting tetrapyrrole biosynthesis enhanced TSPO degradation in Arabidopsis thaliana and that TSPO could bind heme in vitro and in vivo. This binding required the His residue at position 91 (H91), but not that at position 115 (H115). The H91A and double H91A/H115A substitutions stabilized TSPO and rendered the protein insensitive to heme-regulated degradation, suggesting that heme binding regulates At-TSPO degradation. TSPO degradation was inhibited in the autophagy-defective atg5 mutant and was sensitive to inhibitors of type III phosphoinositide 3-kinases, which regulate autophagy in eukaryotic cells. Mutation of the two Tyr residues in a putative ubiquitin-like ATG8 interacting motif of At-TSPO did not affect heme binding in vitro but stabilized the protein in vivo, suggesting that downregulation of At-TSPO requires an active autophagy pathway, in addition to heme. Abscisic acid-dependent TSPO induction was accompanied by an increase in unbound heme levels, and downregulation of TSPO coincided with the return to steady state levels of unbound heme, suggesting that a physiological consequence of active TSPO downregulation may be heme scavenging. In addition, overexpression of TSPO attenuated aminolevulinic acid-induced porphyria in plant cells. Taken together, these data support a role for TSPO in porphyrin binding and scavenging during stress in plants.
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Affiliation(s)
| | | | | | | | - Henri Batoko
- Institute of Life Sciences, Molecular Physiology Group, Université Catholique de Louvain, Croix du Sud 4-15, 1348 Louvain-la-Neuve, Belgium
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11
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Fan J, Rone MB, Papadopoulos V. Translocator protein 2 is involved in cholesterol redistribution during erythropoiesis. J Biol Chem 2009; 284:30484-97. [PMID: 19729679 PMCID: PMC2781603 DOI: 10.1074/jbc.m109.029876] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Revised: 08/17/2009] [Indexed: 12/11/2022] Open
Abstract
Translocator protein (TSPO) is an 18-kDa cholesterol- and drug-binding protein conserved from bacteria to humans. While surveying for Tspo-like genes, we identified its paralogous gene, Tspo2, encoding an evolutionarily conserved family of proteins that arose by gene duplications before the divergence of avians and mammals. Comparative analysis of Tspo1 and Tspo2 functions suggested that Tspo2 has become subfunctionalized, typical of duplicated genes, characterized by the loss of diagnostic drug ligand-binding but retention of cholesterol-binding properties, hematopoietic tissue- and erythroid cell-specific distribution, and subcellular endoplasmic reticulum and nuclear membrane localization. Expression of Tspo2 in erythroblasts is strongly correlated with the down-regulation of the enzymes involved in cholesterol biosynthesis. Overexpression of TSPO2 in erythroid cells resulted in the redistribution of intracellular free cholesterol, an essential step in nucleus expulsion during erythrocyte maturation. Taken together, these data identify the TSPO2 family of proteins as mediators of cholesterol redistribution-dependent erythroblast maturation during mammalian erythropoiesis.
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Affiliation(s)
- Jinjiang Fan
- From the Research Institute of the McGill University Health Center and the Departments of Medicine, Biochemistry, and Pharmacology and Therapeutics, McGill University, Montréal, Québec H3A 1A4, Canada
| | - Malena B. Rone
- From the Research Institute of the McGill University Health Center and the Departments of Medicine, Biochemistry, and Pharmacology and Therapeutics, McGill University, Montréal, Québec H3A 1A4, Canada
| | - Vassilios Papadopoulos
- From the Research Institute of the McGill University Health Center and the Departments of Medicine, Biochemistry, and Pharmacology and Therapeutics, McGill University, Montréal, Québec H3A 1A4, Canada
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12
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Alev C, Shinmyozu K, McIntyre BAS, Sheng G. Genomic organization of zebra finch alpha and beta globin genes and their expression in primitive and definitive blood in comparison with globins in chicken. Dev Genes Evol 2009; 219:353-60. [DOI: 10.1007/s00427-009-0294-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Revised: 06/15/2009] [Accepted: 06/16/2009] [Indexed: 10/20/2022]
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