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Mészáros B, Sámano-Sánchez H, Alvarado-Valverde J, Čalyševa J, Martínez-Pérez E, Alves R, Shields DC, Kumar M, Rippmann F, Chemes LB, Gibson TJ. Short linear motif candidates in the cell entry system used by SARS-CoV-2 and their potential therapeutic implications. Sci Signal 2021; 14:eabd0334. [PMID: 33436497 PMCID: PMC7928535 DOI: 10.1126/scisignal.abd0334] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Accepted: 12/10/2020] [Indexed: 12/12/2022]
Abstract
The first reported receptor for SARS-CoV-2 on host cells was the angiotensin-converting enzyme 2 (ACE2). However, the viral spike protein also has an RGD motif, suggesting that cell surface integrins may be co-receptors. We examined the sequences of ACE2 and integrins with the Eukaryotic Linear Motif (ELM) resource and identified candidate short linear motifs (SLiMs) in their short, unstructured, cytosolic tails with potential roles in endocytosis, membrane dynamics, autophagy, cytoskeleton, and cell signaling. These SLiM candidates are highly conserved in vertebrates and may interact with the μ2 subunit of the endocytosis-associated AP2 adaptor complex, as well as with various protein domains (namely, I-BAR, LC3, PDZ, PTB, and SH2) found in human signaling and regulatory proteins. Several motifs overlap in the tail sequences, suggesting that they may act as molecular switches, such as in response to tyrosine phosphorylation status. Candidate LC3-interacting region (LIR) motifs are present in the tails of integrin β3 and ACE2, suggesting that these proteins could directly recruit autophagy components. Our findings identify several molecular links and testable hypotheses that could uncover mechanisms of SARS-CoV-2 attachment, entry, and replication against which it may be possible to develop host-directed therapies that dampen viral infection and disease progression. Several of these SLiMs have now been validated to mediate the predicted peptide interactions.
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Affiliation(s)
- Bálint Mészáros
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany.
| | - Hugo Sámano-Sánchez
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany
| | - Jesús Alvarado-Valverde
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany
- Collaboration for joint PhD degree between EMBL and Heidelberg University, Faculty of Biosciences
| | - Jelena Čalyševa
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany
- Collaboration for joint PhD degree between EMBL and Heidelberg University, Faculty of Biosciences
| | - Elizabeth Martínez-Pérez
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany
- Laboratorio de bioinformática estructural, Fundación Instituto Leloir, C1405BWE Buenos Aires, Argentina
| | - Renato Alves
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany
| | - Denis C Shields
- School of Medicine, University College Dublin, Dublin 4, Ireland
| | - Manjeet Kumar
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany.
| | - Friedrich Rippmann
- Computational Chemistry & Biology, Merck KGaA, Frankfurter Str. 250, 64293 Darmstadt, Germany
| | - Lucía B Chemes
- Instituto de Investigaciones Biotecnológicas "Dr. Rodolfo A. Ugalde", IIB-UNSAM, IIBIO-CONICET, Universidad Nacional de San Martín, CP1650 San Martín, Buenos Aires, Argentina.
| | - Toby J Gibson
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany.
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A human carboxypeptidase E/NF-α1 gene mutation in an Alzheimer's disease patient leads to dementia and depression in mice. Transl Psychiatry 2016; 6:e973. [PMID: 27922637 PMCID: PMC5315563 DOI: 10.1038/tp.2016.237] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 10/16/2016] [Indexed: 12/11/2022] Open
Abstract
Patients with Alzheimer's disease (AD), a common dementia among the aging population, often also suffer from depression. This comorbidity is poorly understood. Although most forms of AD are not genetically inherited, we have identified a new human mutation in the carboxypeptidase E (CPE)/neurotrophic factor-α1 (NF-α1) gene from an AD patient that caused memory deficit and depressive-like behavior in transgenic mice. This mutation consists of three adenosine inserts, introducing nine amino acids, including two glutamines into the mutant protein, herein called CPE-QQ. Expression of CPE-QQ in Neuro2a cells demonstrated that it was not secreted, but accumulated in the endoplasmic reticulum and was subsequently degraded by proteasomes. Expression of CPE-QQ in rat hippocampal neurons resulted in cell death, through increased ER stress and decreased expression of pro-survival protein, BCL-2. Transgenic mice expressing CPE-QQ did not show any difference in the processing enzyme activity of CPE compared with wild-type mice. However, the transgenic mice exhibited poor memory, depressive-like behavior, severely decreased dendrites in the hippocampal CA3 region and medial prefrontal cortex indicative of neurodegeneration, hyperphosphorylation of tau at Ser396, and diminished neurogenesis in the dentate gyrus at 50 weeks old. All these pathologies are associated with AD and the latter with depression and were observed in 50-week-old mice. Interestingly, the younger CPE-QQ mice (11 weeks old) did not show deficits in dendrite outgrowth and neurogenesis. This study has uncovered a human CPE/NF-α1 gene mutation that could lead to comorbidity of dementia and depression, emphasizing the importance of this gene in cognitive function.
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Abstract
The failure of pancreatic β‐cells to supply insulin in quantities sufficient to maintain euglycemia is a hallmark of type 2 diabetes. Perturbation of β‐cell cholesterol homeostasis, culminating in elevated intracellular cholesterol levels, impairs insulin secretion and has therefore been proposed as a mechanism contributing to β‐cell dysfunction. The manner in which this occurs, however, is unclear. Cholesterol is an essential lipid, as well as a major component of membrane rafts, and numerous proteins critical for the regulation of insulin secretion have been reported to associate with these domains. Although this suggests that alterations in membrane rafts could partially account for the reduction in insulin secretion observed when β‐cell cholesterol accumulates, this has not yet been demonstrated. In this review, we provide a brief overview of recent work implicating membrane rafts in some of the basic molecular mechanisms of insulin secretion, and discuss the insight it provides into the β‐cell dysfunction characteristic of type 2 diabetes. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2012.00200.x, 2012)
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Affiliation(s)
- Ronald Dirkx
- Molecular Diabetology, Paul Langerhans Institute Dresden, School of Medicine and University Clinic "Carl Gustav Carus", Dresden University of Technology
| | - Michele Solimena
- Molecular Diabetology, Paul Langerhans Institute Dresden, School of Medicine and University Clinic "Carl Gustav Carus", Dresden University of Technology ; Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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Lou H, Park JJ, Phillips A, Loh YP. γ-Adducin promotes process outgrowth and secretory protein exit from the Golgi apparatus. J Mol Neurosci 2013; 49:1-10. [PMID: 22706708 PMCID: PMC3681813 DOI: 10.1007/s12031-012-9827-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 05/30/2012] [Indexed: 12/19/2022]
Abstract
α, β, and γ adducins mediate F-actin remodeling of plasma membrane structures as heterotetramers. Here, we present two new functions of γ-adducin. (1) Overexpression of γ-adducin promoted formation of neurite-like processes in non-neuronal fibroblast COS7 cells. Conversely, overexpression of the C-terminal 38 amino acids of γ-adducin (γAdd(C38)) acting as a dominant negative inhibited formation of neurites/processes in Neuro2A cells and anterior pituitary AtT20 cells. (2) γ-Adducin appears to facilitate pro-opiomelanocortin (POMC) exit from the trans-Golgi network (TGN) by re-organizing the actin network around the Golgi complex. Filamentous actins (F-actins) which formed puncti around the Golgi complex in control cells were dispersed in AtT20 cells stably transfected with γAdd(C38). Furthermore, γAdd(C38)-transfectants showed significant accumulation of POMC/adrenocorticotropin (ACTH) in the Golgi complex and diminished POMC/ACTH vesicles in the cell processes. The C-terminal 38 amino acids of γ-adducin interacted with F-actins around the Golgi complex, to facilitate F-actin-mediated budding of POMC/ACTH vesicles from the TGN. Thus, we propose that γ-adducin, via its interaction with F-actins, plays a critical role in actin remodeling to facilitate process/neurite outgrowth, as well as budding of POMC/ACTH vesicles from the TGN via its interaction with peri-Golgi F-actins.
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Affiliation(s)
- Hong Lou
- Section on Cellular Neurobiology, Program on Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bldg 49, Rm 5A22, 49 Convent Drive, Bethesda, MD 20892, USA
| | - Joshua J. Park
- Section on Cellular Neurobiology, Program on Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bldg 49, Rm 5A22, 49 Convent Drive, Bethesda, MD 20892, USA
- Department of Neurosciences, University of Toledo, College of Medicine, Toledo, OH 43614, USA
| | - Andre Phillips
- Section on Cellular Neurobiology, Program on Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bldg 49, Rm 5A22, 49 Convent Drive, Bethesda, MD 20892, USA
| | - Y. Peng Loh
- Section on Cellular Neurobiology, Program on Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bldg 49, Rm 5A22, 49 Convent Drive, Bethesda, MD 20892, USA
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Cawley NX, Sridhar M, Hong H, Loh P. Exploring the membrane topology of prohormone convertase 1 in AtT20 Cells: in situ analysis by immunofluorescence microscopy. F1000Res 2012; 1:9. [PMID: 24163733 PMCID: PMC3799554 DOI: 10.12688/f1000research.1-9.v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 08/03/2012] [Indexed: 11/20/2022] Open
Abstract
Prohormone convertase 1 (PC1) was previously characterized as a partially transmembrane protein in purified chromaffin granules of bovine adrenal medulla1. This was challenged with experiments on transfected PC1 in COS1 cells, a non-endocrine cell line2. To address this issue, we undertook to analyze its extraction properties in vitro and its immunocytochemical localization in situ in AtT20 cells, an endocrine cell line that expresses PC1. Most of the 87 kDa form of PC1 was resistant to carbonate extraction suggesting that it had properties of a transmembrane protein. Under semi-permeabilized conditions whereby only the plasma membrane was permeabilized, the carboxy-terminus of PC1 was specifically immunostained whereas the amino-terminus was not. These results indicate that the amino-terminus of PC1 was within the lumen of the Golgi and granules, and some of the C-terminus was exposed to the cytosol. Thus, endogenous PC1 can assume a transmembrane orientation in situ in AtT20 cells.
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Affiliation(s)
- Niamh X Cawley
- Section on Cellular Neurobiology, Program in Developmental Neuroscience, Eunice Shriver Kennedy National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA ; National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA
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Cellular Mechanisms for the Biogenesis and Transport of Synaptic and Dense-Core Vesicles. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2012; 299:27-115. [DOI: 10.1016/b978-0-12-394310-1.00002-3] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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Vázquez-Martínez R, Díaz-Ruiz A, Almabouada F, Rabanal-Ruiz Y, Gracia-Navarro F, Malagón MM. Revisiting the regulated secretory pathway: from frogs to human. Gen Comp Endocrinol 2012; 175:1-9. [PMID: 21907200 DOI: 10.1016/j.ygcen.2011.08.017] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Revised: 08/16/2011] [Accepted: 08/20/2011] [Indexed: 01/01/2023]
Abstract
The regulated secretory pathway is a hallmark of endocrine and neuroendocrine cells. This process comprises different sequential steps, including ER-associated protein synthesis, ER-to-Golgi protein transport, Golgi-associated posttranslational modification, sorting and packing of secretory proteins into carrier granules, cytoskeleton-based granule transport towards the plasma membrane and tethering, docking and fusion of granules with specialized releasing zones in the plasma membrane. Each one of these steps is tightly regulated by a large number of factors that function in a spatially and temporarily coordinated fashion. During the past three decades, much effort has been devoted to characterize the precise role of the yet-known proteins participating in the different steps of this process and to identify new regulatory factors in order to obtain a unifying picture of the secretory pathway. In spite of this and given the enormous complexity of the process, certain steps are not fully understood yet and many players remain to be identified. In this review, we offer a summary of the current knowledge on the main molecular mechanisms that govern and ensure the correct release of secretory proteins. In addition, we have integrated the advance on the field made possible by studies carried out in non-mammalian vertebrates, which, although not very numerous, have substantially contributed to acquire a mechanistic understanding of the regulated secretory pathway.
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Affiliation(s)
- Rafael Vázquez-Martínez
- Department of Cell Biology, Physiology and Immunology, Instituto Maimónides de Investigación Biomédica, University of Córdoba, 14014-Córdoba, Spain.
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Lou H, Park JJ, Cawley NX, Sarcon A, Sun L, Adams T, Loh YP. Carboxypeptidase E cytoplasmic tail mediates localization of synaptic vesicles to the pre-active zone in hypothalamic pre-synaptic terminals. J Neurochem 2010; 114:886-96. [PMID: 20492353 DOI: 10.1111/j.1471-4159.2010.06820.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
How synaptic vesicles (SVs) are localized to the pre-active zone (5-200 nm beneath the active zone) in the nerve terminal, which may represent the slow response SV pool, is not fully understood. Electron microscopy revealed the number of SVs located in the pre-active zone, was significantly decreased in hypothalamic neurons of carboxypeptidase E knockout (CPE-KO) mice compared with wild-type mice. Additionally, we found K(+)-stimulated glutamate secretion from hypothalamic embryonic neurons was impaired in CPE-KO mice. Biochemical studies indicate that SVs from the hypothalamus of wild-type mice and synaptic-like microvesicles from PC12 cells contain a transmembrane form of CPE, with a cytoplasmic tail (CPE(C10)), maybe involved in synaptic function. Yeast two-hybrid and pull-down experiments showed that the CPE cytoplasmic tail interacted with gamma-adducin, which binds actin enriched at the nerve terminal. Total internal reflective fluorescence (TIRF) microscopy using PC12 cells as a model showed that expression of GFP-CPE(C15) reduced the steady-state level of synaptophysin-mRFP containing synaptic-like microvesicles accumulated in the area within 200 nm from the sub-plasma membrane (TIRF zone). Our findings identify the CPE cytoplasmic tail, as a new mediator for the localization of SVs in the actin-rich pre-active zone in hypothalamic neurons and the TIRF zone of PC12 cells.
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Affiliation(s)
- Hong Lou
- Section on Cellular Neurobiology, Program on Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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Functional and structural characterization of a dense core secretory granule sorting domain from the PC1/3 protease. Proc Natl Acad Sci U S A 2009; 106:7408-13. [PMID: 19376969 DOI: 10.1073/pnas.0809576106] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Several peptide hormones are initially synthesized as inactive precursors. It is only on entry of these prohormones and their processing proteases into dense core secretory granules (DCSGs) that the precursors are cleaved to generate their active forms. Prohormone convertase (PC)1/3 is a processing protease that is targeted to DCSGs. The signal for targeting PC1/3 to DCSGs resides in its carboxy-terminal tail (PC1/3(617-753)), where 3 regions (PC1/3(617-625), PC1/3(665-682), and PC1/3(711-753)) are known to aid in sorting and membrane association. In this article, we have determined a high-resolution structure of the extreme carboxy-terminal sorting domain, PC1/3(711-753) in micelles by NMR spectroscopy. PC1/3(711-753) contains 2 alpha helices located between residues 722-728 and 738-750. Functional assays demonstrate that the second helix (PC1/3(738-750)) is necessary and sufficient to target a constitutively secreted protein to granules, and that L(745) anchors a hydrophobic patch that is critical for sorting. Also, we demonstrate that calcium binding by the second helix of PC1/3(711-753) promotes aggregation of the domain via the hydrophobic patch centered on L(745). These results provide a structure-function analysis of a DCSG-sorting domain, and reveal the importance of a hydrophobic patch and calcium binding in controlling the sorting of proteins containing alpha helices to DCSGs.
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Abstract
Pax6 is important in the development of the pancreas and was previously shown to regulate pancreatic endocrine differentiation, as well as the insulin, glucagon, and somatostatin genes. Prohormone convertase 2 (PC2) is the main processing enzyme in pancreatic alpha cells, where it processes proglucagon to produce glucagon under the spatial and temporal control of 7B2, which functions as a molecular chaperone. To investigate the role of Pax6 in glucagon biosynthesis, we studied potential target genes in InR1G9 alpha cells transfected with Pax6 small interfering RNA and in InR1G9 clones expressing a dominant-negative form of Pax6. We now report that Pax6 controls the expression of the PC2 and 7B2 genes. By binding and transactivation studies, we found that Pax6 indirectly regulates PC2 gene transcription through cMaf and Beta2/NeuroD1 while it activates the 7B2 gene both directly and indirectly through the same transcription factors, cMaf and Beta2/NeuroD1. We conclude that Pax6 is critical for glucagon biosynthesis and processing by directly and indirectly activating the glucagon gene through cMaf and Beta2/NeuroD1, as well as the PC2 and 7B2 genes.
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Abstract
Exocrine, endocrine, and neuroendocrine cells store hormones and neuropeptides in secretory granules (SGs), which undergo regulated exocytosis in response to an appropriate stimulus. These cargo proteins are sorted at the trans-Golgi network into forming immature secretory granules (ISGs). ISGs undergo maturation while they are transported to and within the F-actin-rich cortex. This process includes homotypic fusion of ISGs, acidification of their lumen, processing, and aggregation of cargo proteins as well as removal of excess membrane and missorted cargo. The resulting mature secretory granules (MSGs) are stored in the F-actin-rich cell cortex, perhaps as segregated pools exhibiting specific responses to stimuli for regulated exocytosis. During the last decade our understanding of the maturation of ISGs advanced substantially. The use of biochemical approaches led to the identification of membrane molecules mechanistically involved in this process. Furthermore, live cell imaging in combination with fluorescently tagged marker proteins of SGs provided insights into the dynamics of maturing ISGs, and the functional implications of cytoskeletal elements and motor proteins.
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Samuni Y, Cawley NX, Zheng C, Cotrim AP, Loh YP, Baum BJ. Sorting behavior of a transgenic erythropoietin-growth hormone fusion protein in murine salivary glands. Hum Gene Ther 2008; 19:279-86. [PMID: 18303958 DOI: 10.1089/hum.2007.0136] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Salivary glands are useful gene transfer target sites for the production of therapeutic proteins, and can secrete proteins into both saliva and the bloodstream. The mechanisms involved in this differential protein sorting are not well understood, although it is believed, at least in part, to be based on the amino acid sequence of the encoded protein. We hypothesized that a transgenic protein, human erythropoietin (hEpo), normally sorted from murine salivary glands into the bloodstream, could be redirected into saliva by fusing it with human growth hormone (hGH). After transfection, the hEpo-hGH fusion protein was expressed and glycosylated in both HEK 293 and A5 cells. When packaged in an adenovirus serotype 5 vector and delivered to murine submandibular cells in vivo via retroductal cannulation, the hEpo-hGH fusion protein was also expressed, albeit at approximately 26% of the levels of hEpo expression. Importantly, in multiple experiments with different cohorts of mice, the hEpo-hGH fusion protein was sorted more frequently into saliva, versus the bloodstream, than was the hEpo protein (p < 0.001). These studies show it is possible to redirect the secretion of a transgenic constitutive pathway protein from salivary gland cells after gene transfer in vivo, a finding that may facilitate developing novel treatments for certain upper gastrointestinal tract disorders.
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Affiliation(s)
- Yuval Samuni
- Gene Therapy and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA
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Samuni Y, Zheng C, Cawley NX, Cotrim AP, Loh YP, Baum BJ. Sorting of growth hormone-erythropoietin fusion proteins in rat salivary glands. Biochem Biophys Res Commun 2008; 373:136-9. [PMID: 18544341 DOI: 10.1016/j.bbrc.2008.05.177] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2008] [Accepted: 05/30/2008] [Indexed: 10/22/2022]
Abstract
Neuroendocrine and exocrine cells secrete proteins in either a constitutive manner or via the regulated secretory pathway (RSP), but the specific sorting mechanisms involved are not fully understood. After gene transfer to rat salivary glands, the transgenic model proteins human growth hormone (hGH) and erythropoietin (hEpo) are secreted primarily into saliva (RSP; exocrine) and serum (constitutive; endocrine), respectively. We hypothesized that fusion of hGH at either the C-terminus or the N-terminus of hEpo would re-direct hEpo from the bloodstream into saliva. We constructed and expressed two fusion proteins, hEpo-hGH and hGH-hEpo, using serotype 5-adenoviral vectors, and delivered them to rat submandibular glands in vivo via retroductal cannulation. Both the hEpo-hGH and hGH-hEpo fusion proteins, but not hEpo alone, were secreted primarily into saliva (p<0.0001 and p=0.0083, respectively). These in vivo studies demonstrate for the first time that hGH, in an N- as well as C-terminal position, influences the secretion of a constitutive pathway protein.
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Affiliation(s)
- Yuval Samuni
- Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, USA.
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Origins of the regulated secretory pathway. THE GOLGI APPARATUS 2008. [PMCID: PMC7121582 DOI: 10.1007/978-3-211-76310-0_30] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Modes of transport of soluble (or luminal) secretory proteins synthesized in the endoplasmic reticulum (ER) could be divided into two groups. The socalled constitutive secretory pathway (CSP) is common to all eukaryotic cells, constantly delivering constitutive soluble secretory proteins (CSSPs) linked to the rate of protein synthesis but largely independent of external stimuli. In regulated secretion, protein is sorted from the Golgi into storage/secretory granules (SGs) whose contents are released when stimuli trigger their final fusion with the plasma membrane (Hannah et al. 1999).
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Prohormone convertases 1/3, 2, furin and protein 7B2 (Secretogranin V) in endocrine cells of the human pancreas. ACTA ACUST UNITED AC 2007; 146:117-24. [PMID: 17959263 DOI: 10.1016/j.regpep.2007.09.019] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2007] [Revised: 07/12/2007] [Accepted: 09/02/2007] [Indexed: 11/24/2022]
Abstract
Prohormone convertases (PCs) are proteinases that cleave inactive prohormones to biologically active peptides. Seven PCs have been identified; two of them, PC1/3 and PC2, have only been localized in neuroendocrine (NE) tissues; a third, furin, in both endocrine and exocrine tissues. We have studied the immunoreactivity of PC1/3, PC2 and furin in the four major NE cell types of the human pancreas by using double immunofluorescence techniques. The study also included the expression of NE secretory protein 7B2 (secretogranin V), a member of the granin family, which influences the function of PC2. The results showed that the three PCs and 7B2 were expressed only in endocrine pancreas, furin also in exocrine cells. Insulin (B) cells harboured PC1/3 and PC2, but not furin. Glucagon (A) cells were immunoreactive to all three PCs; all glucagon cells expressed PC2, but one subpopulation showed PC1/3 immunoreactivity and another furin. Only a few somatostatin (D) cells contained PC2, but no other proconvertase. Pancreatic polypeptide (PP) cells were non-reactive to all three PCs. 7B2 occurred only in insulin and glucagon cells. A varying co-localization pattern was observed between PCs and between PCs and 7B2, with the exception of PC1/3 and furin which were not co-localized. In conclusion, our study shows that PCs are localized in insulin and glucagon cells and do seem to be important in these cell types for processing of hormone and other protein precursors, especially chromogranins, but for the two other major cell types probably other enzymes are of importance.
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