1
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Aldworth H, Hooper NM. Post-translational regulation of the low-density lipoprotein receptor provides new targets for cholesterol regulation. Biochem Soc Trans 2024; 52:431-440. [PMID: 38329179 PMCID: PMC10903450 DOI: 10.1042/bst20230918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 01/16/2024] [Accepted: 01/17/2024] [Indexed: 02/09/2024]
Abstract
The amount of the low-density lipoprotein receptor (LDLR) on the surface of hepatocytes is the primary determinant of plasma low-density lipoprotein (LDL)-cholesterol level. Although the synthesis and cellular trafficking of the LDLR have been well-documented, there is growing evidence of additional post-translational mechanisms that regulate or fine tune the surface availability of the LDLR, thus modulating its ability to bind and internalise LDL-cholesterol. Proprotein convertase subtilisin/kexin type 9 and the asialoglycoprotein receptor 1 both independently interact with the LDLR and direct it towards the lysosome for degradation. While ubiquitination by the E3 ligase inducible degrader of the LDLR also targets the receptor for lysosomal degradation, ubiquitination of the LDLR by a different E3 ligase, RNF130, redistributes the receptor away from the plasma membrane. The activity of the LDLR is also regulated by proteolysis. Proteolytic cleavage of the transmembrane region of the LDLR by γ-secretase destabilises the receptor, directing it to the lysosome for degradation. Shedding of the extracellular domain of the receptor by membrane-type 1 matrix metalloprotease and cleavage of the receptor in its LDL-binding domain by bone morphogenetic protein-1 reduces the ability of the LDLR to bind and internalise LDL-cholesterol at the cell surface. A better understanding of how the activity of the LDLR is regulated will not only unravel the complex biological mechanisms controlling LDL-cholesterol metabolism but also could help inform the development of alternative pharmacological intervention strategies for the treatment of hypercholesterolaemia.
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Affiliation(s)
- Harry Aldworth
- Division of Neuroscience, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, U.K
| | - Nigel M Hooper
- Division of Neuroscience, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, U.K
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2
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Tidy A, Abu Bakar N, Carrier D, Kerr ID, Hodgman C, Bennett MJ, Swarup R. Mechanistic insight into the role of AUXIN RESISTANCE4 in trafficking of AUXIN1 and LIKE AUX1-2. PLANT PHYSIOLOGY 2023; 194:422-433. [PMID: 37776522 PMCID: PMC10756756 DOI: 10.1093/plphys/kiad506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 08/10/2023] [Accepted: 08/22/2023] [Indexed: 10/02/2023]
Abstract
AUXIN RESISTANCE4 (AXR4) regulates the trafficking of auxin influx carrier AUXIN1 (AUX1), a plasma-membrane protein that predominantly localizes to the endoplasmic reticulum (ER) in the absence of AXR4. In Arabidopsis (Arabidopsis thaliana), AUX1 is a member of a small multigene family comprising 4 highly conserved genes-AUX1, LIKE-AUX1 (LAX1), LAX2, and LAX3. We report here that LAX2 also requires AXR4 for correct localization to the plasma membrane. AXR4 is a plant-specific protein and contains a weakly conserved α/β hydrolase fold domain that is found in several classes of lipid hydrolases and transferases. We have previously proposed that AXR4 may either act as (i) a post-translational modifying enzyme through its α/β hydrolase fold domain or (ii) an ER accessory protein, which is a special class of ER protein that regulates targeting of their cognate partner proteins. Here, we show that AXR4 is unlikely to act as a post-translational modifying enzyme as mutations in several highly conserved amino acids in the α/β hydrolase fold domain can be tolerated and active site residues are missing. We also show that AUX1 and AXR4 physically interact with each other and that AXR4 reduces aggregation of AUX1 in a dose-dependent fashion. Our results suggest that AXR4 acts as an ER accessory protein. A better understanding of AXR4-mediated trafficking of auxin transporters in crop plants will be crucial for improving root traits (designer roots) for better acquisition of water and nutrients for sustainable and resilient agriculture.
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Affiliation(s)
- Alison Tidy
- Division of Plant and Crop Science, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - Norliza Abu Bakar
- Division of Plant and Crop Science, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
| | - David Carrier
- School of Life Sciences, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK
| | - Ian D Kerr
- School of Life Sciences, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK
| | - Charlie Hodgman
- Division of Plant and Crop Science, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
| | - Malcolm J Bennett
- Division of Plant and Crop Science, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
| | - Ranjan Swarup
- Division of Plant and Crop Science, School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK
- Centre for Plant Integrative Biology, University of Nottingham, Nottingham LE12 5RD, UK
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3
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Reid KM, Brown GC. LRPAP1 is released from activated microglia and inhibits microglial phagocytosis and amyloid beta aggregation. Front Immunol 2023; 14:1286474. [PMID: 38035103 PMCID: PMC10687467 DOI: 10.3389/fimmu.2023.1286474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Accepted: 10/30/2023] [Indexed: 12/02/2023] Open
Abstract
Low-density lipoprotein receptor-related protein-associated protein 1 (LRPAP1), also known as receptor associated protein (RAP), is an endoplasmic reticulum (ER) chaperone and inhibitor of LDL receptor related protein 1 (LRP1) and related receptors. These receptors have dozens of physiological ligands and cell functions, but it is not known whether cells release LRPAP1 physiologically at levels that regulate these receptors and cell functions. We used mouse BV-2 and human CHME3 microglial cell lines, and found that microglia released nanomolar levels of LRPAP1 when inflammatory activated by lipopolysaccharide or when ER stressed by tunicamycin. LRPAP1 was found on the surface of live activated and non-activated microglia, and anti-LRPAP1 antibodies induced internalization. Addition of 10 nM LRPAP1 inhibited microglial phagocytosis of isolated synapses and cells, and the uptake of Aβ. LRPAP1 also inhibited Aβ aggregation in vitro. Thus, activated and stressed microglia release LRPAP1 levels that can inhibit phagocytosis, Aβ uptake and Aβ aggregation. We conclude that LRPAP1 release may regulate microglial functions and Aβ pathology, and more generally that extracellular LRPAP1 may be a physiological and pathological regulator of a wide range of cell functions.
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Affiliation(s)
| | - Guy C. Brown
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
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4
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Yadav SPS, Yu A, Zhao J, Singh J, Kakkar S, Chakraborty S, Mechref Y, Molitoris B, Wagner MC. Glycosylation of a key cubilin Asn residue results in reduced binding to albumin. J Biol Chem 2022; 298:102371. [PMID: 35970386 PMCID: PMC9485058 DOI: 10.1016/j.jbc.2022.102371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 08/09/2022] [Accepted: 08/10/2022] [Indexed: 10/28/2022] Open
Abstract
Kidney disease often manifests with an increase in proteinuria, which can result from both glomerular and/or proximal tubule injury. The proximal tubules are the major site of protein and peptide endocytosis of the glomerular filtrate, and cubilin is the proximal tubule brush border membrane glycoprotein receptor that binds filtered albumin and initiates its processing in proximal tubules. Albumin also undergoes multiple modifications depending upon the physiologic state. We previously documented that carbamylated albumin had reduced cubilin binding, but the effects of cubilin modifications on binding albumin remain unclear. Here, we investigate the cubilin-albumin binding interaction to define the impact of cubilin glycosylation and map the key glycosylation sites while also targeting specific changes in a rat model of proteinuria. We identified a key Asn residue, N1285, that when glycosylated reduced albumin binding. In addition, we found a pH-induced conformation change may contribute to ligand release. To further define the albumin-cubilin binding site, we determined the solution structure of cubilin's albumin-binding domain, CUB7,8, using small-angle X-ray scattering and molecular modeling. We combined this information with mass spectrometry crosslinking experiments of CUB7,8 and albumin that provides a model of the key amino acids required for cubilin-albumin binding. Together, our data supports an important role for glycosylation in regulating the cubilin interaction with albumin, which is altered in proteinuria and provides new insight into the binding interface necessary for the cubilin-albumin interaction.
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Affiliation(s)
- Shiv Pratap Singh Yadav
- Nephrology Division, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Aiying Yu
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA
| | - Jingfu Zhao
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA
| | - Jasdeep Singh
- Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, New Delhi, India
| | - Saloni Kakkar
- CSIR-Institute of Microbial Technology, Chandigarh, India
| | | | - Yehia Mechref
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA
| | - Bruce Molitoris
- Nephrology Division, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA; Department of Cellular & Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | - Mark C Wagner
- Nephrology Division, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA.
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5
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Role of Endocytosis Proteins in Gefitinib-Mediated EGFR Internalisation in Glioma Cells. Cells 2021; 10:cells10113258. [PMID: 34831480 PMCID: PMC8618144 DOI: 10.3390/cells10113258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Revised: 11/12/2021] [Accepted: 11/17/2021] [Indexed: 11/23/2022] Open
Abstract
EGFR (epidermal growth factor receptor), a member of the ErbB tyrosine kinase receptor family, is a clinical therapeutic target in numerous solid tumours. EGFR overexpression in glioblastoma (GBM) drives cell invasion and tumour progression. However, clinical trials were disappointing, and a molecular basis to explain these poor results is still missing. EGFR endocytosis and membrane trafficking, which tightly regulate EGFR oncosignaling, are often dysregulated in glioma. In a previous work, we showed that EGFR tyrosine kinase inhibitors, such as gefitinib, lead to enhanced EGFR endocytosis into fused early endosomes. Here, using pharmacological inhibitors, siRNA-mediated silencing, or expression of mutant proteins, we showed that dynamin 2 (DNM2), the small GTPase Rab5 and the endocytosis receptor LDL receptor-related protein 1 (LRP-1), contribute significantly to gefitinib-mediated EGFR endocytosis in glioma cells. Importantly, we showed that inhibition of DNM2 or LRP-1 also decreased glioma cell responsiveness to gefitinib during cell evasion from tumour spheroids. By highlighting the contribution of endocytosis proteins in the activity of gefitinib on glioma cells, this study suggests that endocytosis and membrane trafficking might be an attractive therapeutic target to improve GBM treatment.
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6
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Ganaie SS, Schwarz MM, McMillen CM, Price DA, Feng AX, Albe JR, Wang W, Miersch S, Orvedahl A, Cole AR, Sentmanat MF, Mishra N, Boyles DA, Koenig ZT, Kujawa MR, Demers MA, Hoehl RM, Moyle AB, Wagner ND, Stubbs SH, Cardarelli L, Teyra J, McElroy A, Gross ML, Whelan SPJ, Doench J, Cui X, Brett TJ, Sidhu SS, Virgin HW, Egawa T, Leung DW, Amarasinghe GK, Hartman AL. Lrp1 is a host entry factor for Rift Valley fever virus. Cell 2021; 184:5163-5178.e24. [PMID: 34559985 DOI: 10.1016/j.cell.2021.09.001] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2020] [Revised: 04/29/2021] [Accepted: 09/01/2021] [Indexed: 12/26/2022]
Abstract
Rift Valley fever virus (RVFV) is a zoonotic pathogen with pandemic potential. RVFV entry is mediated by the viral glycoprotein (Gn), but host entry factors remain poorly defined. Our genome-wide CRISPR screen identified low-density lipoprotein receptor-related protein 1 (mouse Lrp1/human LRP1), heat shock protein (Grp94), and receptor-associated protein (RAP) as critical host factors for RVFV infection. RVFV Gn directly binds to specific Lrp1 clusters and is glycosylation independent. Exogenous addition of murine RAP domain 3 (mRAPD3) and anti-Lrp1 antibodies neutralizes RVFV infection in taxonomically diverse cell lines. Mice treated with mRAPD3 and infected with pathogenic RVFV are protected from disease and death. A mutant mRAPD3 that binds Lrp1 weakly failed to protect from RVFV infection. Together, these data support Lrp1 as a host entry factor for RVFV infection and define a new target to limit RVFV infections.
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Affiliation(s)
- Safder S Ganaie
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Madeline M Schwarz
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Infectious Diseases and Microbiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA
| | - Cynthia M McMillen
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Infectious Diseases and Microbiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA
| | - David A Price
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Annie X Feng
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Joseph R Albe
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Wenjie Wang
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Shane Miersch
- The Donnelly Centre, University of Toronto, Toronto, ON, Canada
| | - Anthony Orvedahl
- Department of Pediatrics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Aidan R Cole
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Monica F Sentmanat
- Genome Engineering and iPSC Center (GEiC), Department of Genetics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Nawneet Mishra
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Devin A Boyles
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Zachary T Koenig
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Infectious Diseases and Microbiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA
| | - Michael R Kujawa
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Infectious Diseases and Microbiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA
| | - Matthew A Demers
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Ryan M Hoehl
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Austin B Moyle
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA
| | - Nicole D Wagner
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA
| | - Sarah H Stubbs
- Department of Microbiology, Harvard Medical School, Boston, MA, USA
| | - Lia Cardarelli
- The Donnelly Centre, University of Toronto, Toronto, ON, Canada
| | - Joan Teyra
- The Donnelly Centre, University of Toronto, Toronto, ON, Canada
| | - Anita McElroy
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Pediatrics, Division of Pediatric Infectious Disease, University of Pittsburgh, Pittsburgh, PA, USA
| | - Michael L Gross
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA
| | - Sean P J Whelan
- Department of Molecular Microbiology, Washington University in St. Louis, St. Louis, MO, USA
| | - John Doench
- Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Xiaoxia Cui
- Genome Engineering and iPSC Center (GEiC), Department of Genetics, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Tom J Brett
- Department of Medicine, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Sachdev S Sidhu
- The Donnelly Centre, University of Toronto, Toronto, ON, Canada
| | - Herbert W Virgin
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA; Current address: Vir Biotechnology, San Francisco, CA, USA
| | - Takeshi Egawa
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Daisy W Leung
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA; Department of Medicine, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - Gaya K Amarasinghe
- Department of Pathology and Immunology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA.
| | - Amy L Hartman
- Center for Vaccine Research, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Infectious Diseases and Microbiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA.
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7
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Hamad MIK, Jbara A, Rabaya O, Petrova P, Daoud S, Melliti N, Meseke M, Lutz D, Petrasch-Parwez E, Schwitalla JC, Mark MD, Herlitze S, Reiss G, Herz J, Förster E. Reelin signaling modulates GABA B receptor function in the neocortex. J Neurochem 2021; 156:589-603. [PMID: 32083308 PMCID: PMC7442713 DOI: 10.1111/jnc.14990] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Revised: 01/27/2020] [Accepted: 02/18/2020] [Indexed: 11/27/2022]
Abstract
Reelin is a protein that is best known for its role in controlling neuronal layer formation in the developing cortex. Here, we studied its role for post-natal cortical network function, which is poorly explored. To preclude early cortical migration defects caused by Reelin deficiency, we used a conditional Reelin knock-out (RelncKO ) mouse, and induced Reelin deficiency post-natally. Induced Reelin deficiency caused hyperexcitability of the neocortical network in vitro and ex vivo. Blocking Reelin binding to its receptors ApoER2 and VLDLR resulted in a similar effect. Hyperexcitability in RelncKO organotypic slice cultures could be rescued by co-culture with wild-type organotypic slice cultures. Moreover, the GABAB receptor (GABAB R) agonist baclofen failed to activate and the antagonist CGP35348 failed to block GABAB Rs in RelncKO mice. Immunolabeling of RelncKO cortical slices revealed a reduction in GABAB R1 and GABAB R2 surface expression at the plasma membrane and western blot of RelncKO cortical tissue revealed decreased phosphorylation of the GABAB R2 subunit at serine 892 and increased phosphorylation at serine 783, reflecting receptor deactivation and proteolysis. These data show a role of Reelin in controlling early network activity, by modulating GABAB R function. Cover Image for this issue: https://doi.org/10.1111/jnc.15054.
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Affiliation(s)
- Mohammad I K Hamad
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
- Institute for Anatomy and Clinical Morphology, School of Medicine, Faculty of Health, Herdecke University, Witten, Witten
| | - Abdalrahim Jbara
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
| | - Obada Rabaya
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
| | - Petya Petrova
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
| | - Solieman Daoud
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
| | - Nesrine Melliti
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
| | - Maurice Meseke
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
| | - David Lutz
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
| | - Elisabeth Petrasch-Parwez
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
| | | | - Melanie D Mark
- Department of Behavioral Neuroscience, Ruhr University Bochum, Bochum, Germany
| | - Stefan Herlitze
- Department of Zoology and Neurobiology, Ruhr University Bochum, Bochum, Germany
| | - Gebhard Reiss
- Institute for Anatomy and Clinical Morphology, School of Medicine, Faculty of Health, Herdecke University, Witten, Witten
| | - Joachim Herz
- Departments of Molecular Genetics, Neuroscience, Neurology and Neurotherapeutics, Center for Translational Neurodegeneration Research, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Eckart Förster
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Medical Faculty, Bochum, Germany
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8
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Shepherd CE, Affleck AJ, Bahar AY, Carew-Jones F, Gregory G, Small DH, Halliday GM. Alzheimer's amyloid-β and tau protein accumulation is associated with decreased expression of the LDL receptor-associated protein in human brain tissue. Brain Behav 2020; 10:e01672. [PMID: 32484608 PMCID: PMC7375106 DOI: 10.1002/brb3.1672] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Revised: 04/04/2020] [Accepted: 05/04/2020] [Indexed: 11/06/2022] Open
Abstract
INTRODUCTION One of the major neuropathological features of Alzheimer's disease (AD) is the accumulation of amyloid-β (Aβ) protein in the brain. Evidence suggests that the low-density lipoprotein receptor-associated protein (RAP) binds strongly to Aβ and enhances its cellular uptake and that decreased RAP expression correlates with increased Aβ production in animal models of AD. METHODS The current study examined whether RAP levels change in AD human brain tissue and whether they are related to the amount of AD pathology. RAP and NeuN levels were determined by Western blot, while low-density lipoprotein receptor-related protein 1 (LRP1), tau and Aβ levels were determined by ELISA in the temporal cortex of 17 AD and 16 control cases. RESULTS An increase in total Aβ and insoluble and soluble tau protein was observed in AD brain tissue. In contrast, RAP levels were significantly decreased in AD brain tissue compared to controls. Correlation analysis revealed that levels of RAP correlated with both total Aβ and soluble and insoluble tau levels. Neither LRP1 nor NeuN levels were significantly altered in AD brain tissue homogenates and did not correlate with Aβ or tau protein levels. CONCLUSION Reduction in RAP may contribute to the accumulation and aggregation of Aβ in the AD brain.
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Affiliation(s)
- Claire E Shepherd
- Neuroscience Research Australia, Randwick, Sydney, NSW, Australia.,University of New South Wales, Randwick, Sydney, NSW, Australia
| | - Andrew J Affleck
- Neuroscience Research Australia, Randwick, Sydney, NSW, Australia.,University of New South Wales, Randwick, Sydney, NSW, Australia
| | - Anita Y Bahar
- Neuroscience Research Australia, Randwick, Sydney, NSW, Australia
| | - Francine Carew-Jones
- Neuroscience Research Australia, Randwick, Sydney, NSW, Australia.,University of New South Wales, Randwick, Sydney, NSW, Australia
| | - Gillian Gregory
- Neuroscience Research Australia, Randwick, Sydney, NSW, Australia
| | - David H Small
- Menzies Research Institute, University of Tasmania, Hobart, TAS, Australia
| | - Glenda M Halliday
- Neuroscience Research Australia, Randwick, Sydney, NSW, Australia.,University of New South Wales, Randwick, Sydney, NSW, Australia.,Brain and Mind Centre, University of Sydney, Sydney, NSW, Australia
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9
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Omer L, Hindi L, Militello G, Stivers KB, Tien KC, Boyd NL. Familial hypercholesterolemia class II low-density lipoprotein receptor response to statin treatment. Dis Model Mech 2020; 13:dmm042911. [PMID: 32005714 PMCID: PMC7157586 DOI: 10.1242/dmm.042911] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Accepted: 01/22/2020] [Indexed: 01/10/2023] Open
Abstract
Low-density lipoprotein (LDL) receptor (LDLR) mutations are the primary cause of familial hypercholesterolemia (FH). Class II LDLR mutations result in a misfolded LDLR retained in the endoplasmic reticulum (ER). We have developed a model of FH class II and CRISPR-corrected induced pluripotent stem cells (iPSC) capable of replicating mutant and repaired LDLR functions. We show here that iPSC and derived hepatocyte-like cells (HLC) replicate misfolded LDLR accumulation and restoration of LDLR function in CRISPR-corrected cells. It was reported that model cells overexpressing class II LDLR mutants result in endoplasmic reticulum (ER) accumulation of immature LDLR and activation of the unfolded protein response (UPR). We show here that statins induce a similar accumulation of immature LDLR that is resolved with class II correction. We also demonstrate that, although capable of UPR induction with tunicamycin treatment, unlike overexpression models, statin-treated class II iPSC and derived HLC do not induce the common UPR markers Grp78 (also known as HSPA5) or spliced XBP1 [XBP1 (S)]. Because statins are reported to inhibit UPR, we utilized lipoprotein-deficient serum (LPDS) medium, but still did not detect UPR induction at the Grp78 and XBP1 (S) levels. Our study demonstrates the recapitulation of mutant and corrected class II LDLR function and suggests that overexpression models may not accurately predict statin-mediated class II protein biology.
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Affiliation(s)
- Linda Omer
- Cardiovascular Innovation Institute, University of Louisville, Louisville, KY 40202, USA
- Department of Biochemistry and Molecular Genetics, University of Louisville, Louisville, KY 40202, USA
| | - Lubna Hindi
- Cardiovascular Innovation Institute, University of Louisville, Louisville, KY 40202, USA
- Department of Bioengineering, University of Louisville, Louisville, KY 40202, USA
| | - Giuseppe Militello
- Cardiovascular Innovation Institute, University of Louisville, Louisville, KY 40202, USA
| | - Katlin B Stivers
- Cardiovascular Innovation Institute, University of Louisville, Louisville, KY 40202, USA
- Department of Microbiology and Immunology, University of Louisville, Louisville, KY 40202, USA
| | - Kenneth C Tien
- Cardiovascular Innovation Institute, University of Louisville, Louisville, KY 40202, USA
| | - Nolan L Boyd
- Cardiovascular Innovation Institute, University of Louisville, Louisville, KY 40202, USA
- Department of Physiology, University of Louisville, Louisville, KY 40202, USA
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10
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Doenhoff MJ, Modha J, Walker AJ. Failure of in vitro-cultured schistosomes to produce eggs: how does the parasite meet its needs for host-derived cytokines such as TGF-β? Int J Parasitol 2019; 49:747-757. [PMID: 31348959 DOI: 10.1016/j.ijpara.2019.05.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 05/03/2019] [Accepted: 05/09/2019] [Indexed: 12/20/2022]
Abstract
When adult schistosome worm pairs are transferred from experimental hosts to in vitro culture they cease producing viable eggs within a few days. Female worms in unisexual infections fail to mature, and when mature adult females are separated from male partners they regress sexually. Worms cultured from the larval stage are also permanently reproductively defective. The cytokine transforming growth factor beta derived from the mammalian host is considered important in stimulating schistosome female worm maturation and maintenance of fecundity. The means by which schistosomes acquire TGF-β have not been elucidated, but direct uptake in vivo seems unlikely as the concentration of free, biologically active cytokine in host blood is very low. Here we review the complexities of schistosome development and male-female interactions, and we speculate about two possibilities on how worms obtain the TGF-β they are assumed to need: (i) worms may have mechanisms to free active cytokine from the latency-inducing complex of proteins in which it is associated, and/or (ii) they may obtain the cytokine from alpha 2-macroglobulin, a blood-borne protease inhibitor to which TGF-β can bind. These ideas are experimentally testable.
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Affiliation(s)
- Michael J Doenhoff
- School of Life Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
| | - Jay Modha
- Modha Biomedical Ltd, 9B St Cuthberts Avenue, Great Glen, Leicester LE8 9EJ, UK
| | - Anthony J Walker
- Molecular Parasitology Laboratory, School of Life Sciences Pharmacy and Chemistry, Kingston University, Kingston University, Penrhyn Road, Kingston upon Thames, Surrey KT1 2EE, UK
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11
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Li Q, Lei F, Tang Y, Pan JSC, Tong Q, Sun Y, Sheikh-Hamad D. Megalin mediates plasma membrane to mitochondria cross-talk and regulates mitochondrial metabolism. Cell Mol Life Sci 2018; 75:4021-4040. [PMID: 29916093 PMCID: PMC11105752 DOI: 10.1007/s00018-018-2847-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 05/01/2018] [Accepted: 05/28/2018] [Indexed: 01/21/2023]
Abstract
Mitochondrial intracrines are extracellular signaling proteins, targeted to the mitochondria. The pathway for mitochondrial targeting of mitochondrial intracrines and actions in the mitochondria remains unknown. Megalin/LRP2 mediates the uptake of vitamins and proteins, and is critical for clearance of amyloid-β protein from the brain. Megalin mutations underlie the pathogenesis of Donnai-Barrow and Lowe syndromes, characterized by brain defects and kidney dysfunction; megalin was not previously known to reside in the mitochondria. Here, we show megalin is present in the mitochondria and associates with mitochondrial anti-oxidant proteins SIRT3 and stanniocalcin-1 (STC1). Megalin shuttles extracellularly-applied STC1, angiotensin II and TGF-β to the mitochondria through the retrograde early endosome-to-Golgi transport pathway and Rab32. Megalin knockout in cultured cells impairs glycolytic and respiratory capacities. Thus, megalin is critical for mitochondrial biology; mitochondrial intracrine signaling is a continuum of the retrograde early endosome-to-Golgi-Rab32 pathway and defects in this pathway may underlie disease processes in many systems.
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MESH Headings
- Agenesis of Corpus Callosum/genetics
- Agenesis of Corpus Callosum/metabolism
- Agenesis of Corpus Callosum/pathology
- Amyloid beta-Peptides/genetics
- Amyloid beta-Peptides/metabolism
- Animals
- Brain/metabolism
- Brain/pathology
- Cell Membrane/genetics
- Glycoproteins/genetics
- HEK293 Cells
- Hearing Loss, Sensorineural/genetics
- Hearing Loss, Sensorineural/metabolism
- Hearing Loss, Sensorineural/pathology
- Hernias, Diaphragmatic, Congenital/genetics
- Hernias, Diaphragmatic, Congenital/metabolism
- Hernias, Diaphragmatic, Congenital/pathology
- Humans
- Low Density Lipoprotein Receptor-Related Protein-2/genetics
- Low Density Lipoprotein Receptor-Related Protein-2/metabolism
- Mice
- Mitochondria/genetics
- Mitochondria/metabolism
- Myopia/genetics
- Myopia/metabolism
- Myopia/pathology
- Oculocerebrorenal Syndrome/genetics
- Oculocerebrorenal Syndrome/metabolism
- Oculocerebrorenal Syndrome/pathology
- Proteinuria/genetics
- Proteinuria/metabolism
- Proteinuria/pathology
- RAW 264.7 Cells
- Renal Tubular Transport, Inborn Errors/genetics
- Renal Tubular Transport, Inborn Errors/metabolism
- Renal Tubular Transport, Inborn Errors/pathology
- Signal Transduction
- Sirtuin 3/genetics
- Transforming Growth Factor beta/genetics
- rab GTP-Binding Proteins/genetics
- rab GTP-Binding Proteins/metabolism
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Affiliation(s)
- Qingtian Li
- Division of Nephrology, Department of Medicine, Selzman Institute for Kidney Health, Baylor College of Medicine, One Baylor Plaza, ABBR R706, M/S BCM395, Houston, TX, 77030-3498, USA
| | - Fan Lei
- Division of Nephrology, Department of Medicine, Selzman Institute for Kidney Health, Baylor College of Medicine, One Baylor Plaza, ABBR R706, M/S BCM395, Houston, TX, 77030-3498, USA
- Renmin Hospital of Wuhan University, Wuhan, Hubei, People's Republic of China
| | - Yi Tang
- Division of Nephrology, Department of Medicine, Selzman Institute for Kidney Health, Baylor College of Medicine, One Baylor Plaza, ABBR R706, M/S BCM395, Houston, TX, 77030-3498, USA
- West China Medical Center of Sichuan University, Chengdu, Sichuan, People's Republic of China
| | - Jenny Szu-Chin Pan
- Division of Nephrology, Department of Medicine, Selzman Institute for Kidney Health, Baylor College of Medicine, One Baylor Plaza, ABBR R706, M/S BCM395, Houston, TX, 77030-3498, USA
| | - Qiang Tong
- Children's Nutrition Research Center, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Yuxiang Sun
- Department of Nutrition and Food Science (NFSC), Texas A&M University, College Station, TX, 77843, USA
| | - David Sheikh-Hamad
- Division of Nephrology, Department of Medicine, Selzman Institute for Kidney Health, Baylor College of Medicine, One Baylor Plaza, ABBR R706, M/S BCM395, Houston, TX, 77030-3498, USA.
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12
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Meseke M, Neumüller F, Brunne B, Li X, Anstötz M, Pohlkamp T, Rogalla MM, Herz J, Rune GM, Bender RA. Distal Dendritic Enrichment of HCN1 Channels in Hippocampal CA1 Is Promoted by Estrogen, but Does Not Require Reelin. eNeuro 2018; 5:ENEURO.0258-18.2018. [PMID: 30406178 PMCID: PMC6220572 DOI: 10.1523/eneuro.0258-18.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2018] [Revised: 08/20/2018] [Accepted: 08/26/2018] [Indexed: 12/28/2022] Open
Abstract
HCN1 compartmentalization in CA1 pyramidal cells, essential for hippocampal information processing, is believed to be controlled by the extracellular matrix protein Reelin. Expression of Reelin, in turn, is stimulated by 17β-estradiol (E2). In this study, we therefore tested whether E2 regulates the compartmentalization of HCN1 in CA1 via Reelin. In organotypic entorhino-hippocampal cultures, we found that E2 promotes HCN1 distal dendritic enrichment via the G protein-coupled estrogen receptor GPER1, but apparently independent of Reelin, because GST-RAP, known to reduce Reelin signaling, did not prevent E2-induced HCN1 enrichment in distal CA1. We therefore re-examined the role of Reelin for the regulation of HCN1 compartmentalization and could not detect effects of reduced Reelin signaling on HCN1 distribution in CA1, either in the (developmental) slice culture model or in tamoxifen-inducible conditional reelin knockout mice during adulthood. We conclude that for HCN1 channel compartmentalization in CA1 pyramidal cells, Reelin is not as essential as previously proposed, and E2 effects on HCN1 distribution in CA1 are mediated by mechanisms that do not involve Reelin. Because HCN1 localization was not altered at different phases of the estrous cycle, gonadally derived estradiol is unlikely to regulate HCN1 channel compartmentalization, while the pattern of immunoreactivity of aromatase, the final enzyme of estradiol synthesis, argues for a role of local hippocampal E2 synthesis.
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Affiliation(s)
- Maurice Meseke
- Institute of Neuroanatomy, University Medical Center, Hamburg 20246, Germany
| | - Florian Neumüller
- Institute of Neuroanatomy, University Medical Center, Hamburg 20246, Germany
| | - Bianka Brunne
- Institute of Structural Neurobiology, Center of Molecular Neurobiology, Hamburg 20246, Germany
| | - Xiaoyu Li
- Institute of Neuroanatomy, University Medical Center, Hamburg 20246, Germany
| | - Max Anstötz
- Institute of Neuroanatomy, University Medical Center, Hamburg 20246, Germany
| | - Theresa Pohlkamp
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Meike M. Rogalla
- Institute of Neuroanatomy, University Medical Center, Hamburg 20246, Germany
| | - Joachim Herz
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Gabriele M. Rune
- Institute of Neuroanatomy, University Medical Center, Hamburg 20246, Germany
| | - Roland A. Bender
- Institute of Neuroanatomy, University Medical Center, Hamburg 20246, Germany
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Cuchillo-Ibañez I, Balmaceda V, Mata-Balaguer T, Lopez-Font I, Sáez-Valero J. Reelin in Alzheimer’s Disease, Increased Levels but Impaired Signaling: When More is Less. J Alzheimers Dis 2016; 52:403-16. [DOI: 10.3233/jad-151193] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Inmaculada Cuchillo-Ibañez
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d’Alacant, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain
| | - Valeria Balmaceda
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d’Alacant, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain
| | - Trinidad Mata-Balaguer
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d’Alacant, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain
| | - Inmaculada Lopez-Font
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d’Alacant, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain
| | - Javier Sáez-Valero
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d’Alacant, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain
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14
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Chintala SK. Tissue and urokinase plasminogen activators instigate the degeneration of retinal ganglion cells in a mouse model of glaucoma. Exp Eye Res 2015; 143:17-27. [PMID: 26474495 DOI: 10.1016/j.exer.2015.10.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 08/25/2015] [Accepted: 10/05/2015] [Indexed: 01/16/2023]
Abstract
Elevated intraocular pressure (IOP) promotes the degeneration of retinal ganglion cells (RGCs) during the progression of Primary Open-Angle Glaucoma (POAG). However, the molecular mechanisms underpinning IOP-mediated degeneration of RGCs remain unclear. Therefore, by employing a mouse model of POAG, this study examined whether elevated IOP promotes the degeneration of RGCs by up-regulating tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA) in the retina. IOP was elevated in mouse eyes by injecting fluorescent-microbeads into the anterior chamber. Once a week, for eight weeks, IOP in mouse eyes was measured by using Tono-Pen XL. At various time periods after injecting microbeads, proteolytic activity of tPA and uPA in retinal protein extracts was determined by fibrinogen/plasminogen zymography assays. Localization of tPA and uPA, and their receptor LRP-1 (low-density receptor-related protein-1) in the retina was determined by immunohistochemistry. RGCs' degeneration was assessed by immunostaining with antibodies against Brn3a. Injection of microbeads into the anterior chamber led to a progressive elevation in IOP, increased the proteolytic activity of tPA and uPA in the retina, activated plasminogen into plasmin, and promoted a significant degeneration of RGCs. Elevated IOP up-regulated tPA and LRP-1 in RGCs, and uPA in astrocytes. At four weeks after injecting microbeads, RAP (receptor associated protein; 0.5 and 1.0 μM) or tPA-Stop (1.0 and 4.0 μM) was injected into the vitreous humor. Treatment of IOP-elevated eyes with RAP led to a significant decrease in proteolytic activity of both tPA and uPA, and a significant decrease in IOP-mediated degeneration of RGCs. Also, treatment of IOP-elevated eyes with tPA-Stop decreased the proteolytic activity of both tPA and uPA, and, in turn, significantly attenuated IOP-mediated degeneration of RGCs. Results presented in this study provide evidence that elevated IOP promotes the degeneration of RGCs by up-regulating the levels of proteolytically active tPA and uPA.
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Affiliation(s)
- Shravan K Chintala
- Laboratory of Ophthalmic Neurobiology, Eye Research Institute of Oakland University, 2200 N. Squirrel Road, 409 DHE, Rochester MI 48309, USA.
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15
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Lemarchand E, Maubert E, Haelewyn B, Ali C, Rubio M, Vivien D. Stressed neurons protect themselves by a tissue-type plasminogen activator-mediated EGFR-dependent mechanism. Cell Death Differ 2015; 23:123-31. [PMID: 26068590 DOI: 10.1038/cdd.2015.76] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Revised: 04/30/2015] [Accepted: 05/04/2015] [Indexed: 11/09/2022] Open
Abstract
In the central nervous system, tissue-type plasminogen activator (tPA) has been associated with both pro-death and prosurvival actions on neurons. In most cases, this has been related to exogenous tPA. In the present study, we addressed the influence of endogenous tPA. We first observed an increased transcription of tPA following either in vivo global brain ischemia in rats or in vitro oxygen glucose deprivation (OGD) on mice and rats hippocampal slices. Hippocampal slices from tPA-deficient mice were more sensitive to OGD than wild-type slices. Pharmacological approaches targeting the known receptors of tPA revealed that only the inhibition of phosphorylation of epidermal growth factor receptors (EGFRs) prevented the neuroprotective effect of endogenous tPA. This study shows that ischemic hippocampal neurons overproduce endogenous tPA as an intend to protect themselves from ischemic death, by a mechanism involving an activation of EGFRs. Thus, strategies contributing to promote either endogenous production of tPA or its associated EGFR-linked signaling pathway may have beneficial effects following brain injuries such as stroke.
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Affiliation(s)
- E Lemarchand
- INSERM UMR-S U919 Serine Proteases and Pathophysiology of the Neurovascular Unit, Université Caen Basse Normandie, Bd Henri Becquerel, GIP Cyceron, Caen, France
| | - E Maubert
- INSERM UMR-S U919 Serine Proteases and Pathophysiology of the Neurovascular Unit, Université Caen Basse Normandie, Bd Henri Becquerel, GIP Cyceron, Caen, France
| | - B Haelewyn
- ESRP (European Stroke Research Platform), Centre Universitaire de Ressources Biologiques (CURB), Université Caen Basse Normandie, Caen, France
| | - C Ali
- INSERM UMR-S U919 Serine Proteases and Pathophysiology of the Neurovascular Unit, Université Caen Basse Normandie, Bd Henri Becquerel, GIP Cyceron, Caen, France
| | - M Rubio
- INSERM UMR-S U919 Serine Proteases and Pathophysiology of the Neurovascular Unit, Université Caen Basse Normandie, Bd Henri Becquerel, GIP Cyceron, Caen, France
| | - D Vivien
- INSERM UMR-S U919 Serine Proteases and Pathophysiology of the Neurovascular Unit, Université Caen Basse Normandie, Bd Henri Becquerel, GIP Cyceron, Caen, France
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Kurokawa S, Bellinger FP, Hill KE, Burk RF, Berry MJ. Isoform-specific binding of selenoprotein P to the β-propeller domain of apolipoprotein E receptor 2 mediates selenium supply. J Biol Chem 2014; 289:9195-207. [PMID: 24532792 DOI: 10.1074/jbc.m114.549014] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Sepp1 supplies selenium to tissues via receptor-mediated endocytosis. Mice, rats, and humans have 10 selenocysteines in Sepp1, which are incorporated via recoding of the stop codon, UGA. Four isoforms of rat Sepp1 have been identified, including full-length Sepp1 and three others, which terminate at the second, third, and seventh UGA codons. Previous studies have shown that the longer Sepp1 isoforms bind to the low density lipoprotein receptor apoER2, but the mechanism remains unclear. To identify the essential residues for apoER2 binding, an in vitro Sepp1 binding assay was developed using different Sec to Cys substituted variants of Sepp1 produced in HEK293T cells. ApoER2 was found to bind the two longest isoforms. These results suggest that Sepp1 isoforms with six or more selenocysteines are taken up by apoER2. Furthermore, the C-terminal domain of Sepp1 alone can bind to apoER2. These results indicate that apoER2 binds to the Sepp1 C-terminal domain and does not require the heparin-binding site, which is located in the N-terminal domain. Site-directed mutagenesis identified three residues of Sepp1 that are necessary for apoER2 binding. Sequential deletion of extracellular domains of apoER2 surprisingly identified the YWTD β-propeller domain as the Sepp1 binding site. Finally, we show that apoER2 missing the ligand-binding repeat region, which can result from cleavage at a furin cleavage site present in some apoER2 isoforms, can act as a receptor for Sepp1. Thus, longer isoforms of Sepp1 with high selenium content interact with a binding site distinct from the ligand-binding domain of apoER2 for selenium delivery.
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Affiliation(s)
- Suguru Kurokawa
- From the Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii 96813 and
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Abstract
Alzheimer's disease (AD) is the most prevalent form of dementia in the elderly population. Accumulation, aggregation, and deposition of amyloid-β (Aβ) peptides generated through proteolytic cleavage of amyloid precursor protein (APP) are likely initiating events in the pathogenesis of AD. While Aβ production is accelerated in familial AD, increasing evidence indicates that impaired clearance of Aβ is responsible for late-onset AD. Because Aβ is mainly generated in neurons, these cells are predicted to have the highest risk of encountering Aβ among all cell types in the brain. However, it is still unclear whether they are also involved in Aβ clearance. Here we show that receptor-mediated endocytosis in neurons by the low-density lipoprotein receptor-related protein 1 (LRP1) plays a critical role in brain Aβ clearance. LRP1 is known to be an endocytic receptor for multiple ligands including Aβ. Conditional knock-out of Lrp1 in mouse forebrain neurons leads to increased brain Aβ levels and exacerbated amyloid plaque deposition selectively in the cortex of amyloid model APP/PS1 mice without affecting Aβ production. In vivo microdialysis studies demonstrated that Aβ clearance in brain interstitial fluid is impaired in neuronal Lrp1 knock-out mice. Because the neuronal LRP1-deletion did not affect the mRNA levels of major Aβ degrading enzymes, neprilysin and insulin-degrading enzyme, the disturbed Aβ clearance is likely due to the suppression of LRP1-mediated neuronal Aβ uptake and degradation. Together, our results demonstrate that LRP1 plays an important role in receptor-mediated clearance of Aβ and indicate that neurons not only produce but also clear Aβ.
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Pehar M, Puglielli L. Lysine acetylation in the lumen of the ER: a novel and essential function under the control of the UPR. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:686-97. [PMID: 23247107 DOI: 10.1016/j.bbamcr.2012.12.004] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Revised: 12/03/2012] [Accepted: 12/05/2012] [Indexed: 01/15/2023]
Abstract
The N(ε)-amino group of lysine residues can be transiently modified by the addition of an acetyl group. Recognized functions of N(ε)-lysine acetylation include regulation of activity, molecular stabilization and conformational assembly of a protein. For more than forty years lysine acetylation was thought to occur only in the cytosol and nucleus. Targets included cytoskeletal-associated proteins as well as transcription factors, histone proteins and proteins involved in DNA recombination and repair. However, in 2007 we reported that a type I membrane protein involved in the pathogenesis of Alzheimer's disease was transiently acetylated on the ε amino group of seven lysine residues while transiting along the secretory pathway. Surprisingly, the acetylation occurred in the lumen of the endoplasmic reticulum (ER) forcing us to reconsider old paradigms. Indeed, if lysine acetylation can occur in the lumen of the ER, then all the essential biochemical elements of the reaction must be available in the lumen of the organelle. Follow-up studies revealed the existence of ER-based acetyl-CoA:lysine acetyltransferases as well as a membrane transporter that translocates acetyl-CoA from the cytosol into the ER lumen. Large-scale proteomics showed that the list of substrates of the ER-based acetylation machinery includes both transiting and resident proteins. Finally, genetic studies revealed that this machinery is tightly linked to human diseases. Here, we describe these exciting findings as well as recent biochemical and cellular advances, and discuss possible impact on both human physiology and pathology.
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Affiliation(s)
- Mariana Pehar
- Department of Medicine, University of Wisconsin-Madison, VA Medical Center, Madison, WI 53705, USA
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Novel aspects of the apolipoprotein-E receptor family: regulation and functional role of their proteolytic processing. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/s11515-011-1186-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Topology of human apolipoprotein E3 uniquely regulates its diverse biological functions. Proc Natl Acad Sci U S A 2011; 108:14813-8. [PMID: 21873229 DOI: 10.1073/pnas.1106420108] [Citation(s) in RCA: 181] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Human apolipoprotein E (apoE) is one of the major determinants in lipid transport, playing a critical role in atherosclerosis and other diseases. Binding to lipid and heparan sulfate proteoglycans (HSPG) induces apoE to adopt active conformations for binding to low-density lipoprotein receptor (LDLR) family. ApoE also interacts with beta amyloid peptide, manifests critical isoform-specific effects on Alzheimer's disease. Despite the importance of apoE in these major human diseases, the fundamental questions of how apoE adjusts its structure upon binding to regulate its diverse functions remain unsolved. We report the NMR structure of apoE3, displaying a unique topology of three structural domains. The C-terminal domain presents a large exposed hydrophobic surface that likely initiates interactions with lipids, HSPG, and beta amyloid peptides. The unique topology precisely regulates apoE tertiary structure to permit only one possible conformational adaptation upon binding and provides a double security in preventing lipid-free and partially-lipidated apoE from premature binding to apoE receptors during receptor biogenesis. This topology further ensures the optimal receptor-binding activity by the fully lipidated apoE during lipoprotein transport in circulation and in the brain. These findings provide a structural framework for understanding the structural basis of the diverse functions of this important protein in human diseases.
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Protein Quality Control, Retention, and Degradation at the Endoplasmic Reticulum. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2011; 292:197-280. [DOI: 10.1016/b978-0-12-386033-0.00005-0] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Lighthouse JK, Zhang L, Hsieh JC, Rosenquist T, Holdener BC. MESD is essential for apical localization of megalin/LRP2 in the visceral endoderm. Dev Dyn 2010; 240:577-88. [PMID: 21337463 DOI: 10.1002/dvdy.22477] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/05/2010] [Indexed: 01/22/2023] Open
Abstract
Deletion of the Mesd gene region blocks gastrulation and mesoderm differentiation in mice. MESD is a chaperone for the Wnt co-receptors: low-density lipoprotein receptor-related protein (LRP) 5 and 6 (LRP5/6). We hypothesized that loss of Wnt signaling is responsible for the polarity defects observed in Mesd-deficient embryos. However, because the Mesd-deficient embryo is considerably smaller than Lrp5/6 or Wnt3 mutants, we predicted that MESD function extends more broadly to the LRP family of receptors. Consistent with this prediction, we demonstrated that MESD function in vitro was essential for maturation of the β-propeller/EGF domain common to LRPs. To begin to understand the role of MESD in LRP maturation in vivo, we generated a targeted Mesd knockout and verified that loss of Mesd blocks WNT signaling in vivo. Mesd mutants continue to express the pluripotency markers Oct4, Nanog, and Sox2, suggesting that Wnt signaling is essential for differentiation of the epiblast. Moreover, we demonstrated that MESD was essential for the apical localization of the related LRP2 (Megalin/MEG) in the visceral endoderm, resulting in impaired endocytic function. Combined, our results provide evidence that MESD functions as a general LRP chaperone and suggest that the Mesd phenotype results from both signaling and endocytic defects resulting from misfolding of multiple LRP receptors.
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Jockheck-Clark AR, Bowers EV, Totonchy MB, Neubauer J, Pizzo SV, Nicchitta CV. Re-examination of CD91 function in GRP94 (glycoprotein 96) surface binding, uptake, and peptide cross-presentation. THE JOURNAL OF IMMUNOLOGY 2010; 185:6819-30. [PMID: 21048103 DOI: 10.4049/jimmunol.1000448] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
GRP94 (gp96)-peptide complexes can be internalized by APCs and their associated peptides cross-presented to yield activation of CD8(+) T cells. Investigations into the identity (or identities) of GRP94 surface receptors have yielded conflicting results, particularly with respect to CD91 (LRP1), which has been proposed to be essential for GRP94 recognition and uptake. To assess CD91 function in GRP94 surface binding and endocytosis, these parameters were examined in mouse embryonic fibroblast (MEF) cell lines whose expression of CD91 was either reduced via RNA interference or eliminated by genetic disruption of the CD91 locus. Reduction or loss of CD91 expression abrogated the binding and uptake of receptor-associated protein, an established CD91 ligand. Surface binding and uptake of an N-terminal domain of GRP94 (GRP94.NTD) was unaffected. GRP94.NTD surface binding was markedly suppressed after treatment of MEF cell lines with heparin, sodium chlorate, or heparinase II, demonstrating that heparin sulfate proteoglycans can function in GRP94.NTD surface binding. The role of CD91 in the cross-presentation of GRP94-associated peptides was examined in the DC2.4 dendritic cell line. In DC2.4 cells, which express CD91, GRP94.NTD-peptide cross-presentation was insensitive to the CD91 ligands receptor-associated protein or activated α(2)-macroglobulin and occurred primarily via a fluid-phase, rather than receptor-mediated, uptake pathway. These data clarify conflicting data on CD91 function in GRP94 surface binding, endocytosis, and peptide cross-presentation and identify a role for heparin sulfate proteoglycans in GRP94 surface binding.
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Selvais C, Gaide Chevronnay HP, Lemoine P, Dedieu S, Henriet P, Courtoy PJ, Marbaix E, Emonard H. Metalloproteinase-dependent shedding of low-density lipoprotein receptor-related protein-1 ectodomain decreases endocytic clearance of endometrial matrix metalloproteinase-2 and -9 at menstruation. Endocrinology 2009; 150:3792-9. [PMID: 19406945 DOI: 10.1210/en.2009-0015] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cyclic elimination of the endometrium functional layer through menstrual bleeding results from intense tissue breakdown by proteolytic enzymes, mainly members of the matrix metalloproteinase (MMP) family. In contrast to menstrual-restricted MMPs, e.g. interstitial collagenase (MMP-1), gelatinases A (MMP-2) and B (MMP-9) mRNAs are abundant throughout the cycle without detectable tissue degradation at proliferative and secretory phases, implying a tight posttranslational control of both gelatinases. This paper addresses the role of low-density lipoprotein receptor-related protein (LRP)-1 in the endocytic clearance of endometrial gelatinases. LRP-1 mRNA and protein were studied using RT-PCR, Western blotting, and immunolabeling. Posttranslational control of LRP-1 was analyzed in explant culture. The receptor-associated protein (RAP), used as LRP antagonist, strongly increased (pro)gelatinase accumulation in medium conditioned by endometrial explants, suggesting a role for LRP-1 in their clearance. Although LRP-1 mRNA remained constant throughout the cycle, the protein ectodomain vanished at menses. LRP-1 immunolabeling selectively disappeared in areas of extracellular matrix breakdown in menstrual samples. It also disappeared from explants cultured without estrogen and progesterone (EP) due to ectodomain shedding in the medium. The shedding was inhibited by metalloproteinase inhibitors, including a disintegrin and metalloproteinase (ADAM) inhibitor, and by tissue inhibitors of MMPs (TIMP)-3 and -2, but barely by TIMP-1, pointing to ADAM-12 as the putative sheddase. In good agreement, ADAM-12 mRNA expression was repressed by EP. In conclusion, the efficient LRP-1-mediated clearance of gelatinase activity in nonbleeding endometrium is abrogated upon EP withdrawal, due to shedding of LRP-1 ectodomain by a metalloproteinase, presumably ADAM-12, itself regulated by EP.
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Affiliation(s)
- Charlotte Selvais
- Cell Biology Unit, de Duve Institute, Université catholique de Louvain, B-1200 Brussels, Belgium
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25
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Mkrtchian S, Baryshev M, Sargsyan E, Chatzistamou I, Volakaki AA, Chaviaras N, Pafiti A, Triantafyllou A, Kiaris H. ERp29, an endoplasmic reticulum secretion factor is involved in the growth of breast tumor xenografts. Mol Carcinog 2008; 47:886-92. [DOI: 10.1002/mc.20444] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Urbanus RT, Pennings MTT, Derksen RHWM, de Groot PG. Platelet activation by dimeric beta2-glycoprotein I requires signaling via both glycoprotein Ibalpha and apolipoprotein E receptor 2'. J Thromb Haemost 2008; 6:1405-12. [PMID: 18485085 DOI: 10.1111/j.1538-7836.2008.03021.x] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Dimerization of beta(2)-glycoprotein I (beta(2)-GPI) by autoantibodies is thought to trigger the clinical manifestations observed in the antiphospholipid syndrome. Arterial thrombosis, a frequently occurring clinical manifestation of the antiphospholipid syndrome, is a process in which platelets play a crucial role. Previous work has shown that binding of dimeric beta(2)-GPI to the platelet receptors apolipoprotein E receptor 2' (ApoER2') and glycoprotein Ibalpha (GPIbalpha) mediates increased platelet activation in an in vitro thrombosis model. OBJECTIVE The individual roles of ApoER2' and GPIbalpha in mediating platelet activation by dimeric beta(2)-GPI has hitherto been unclear. In this study, we have determined the roles of either receptor in platelet activation by dimeric beta(2)-GPI. METHODS Platelet activation by dimeric beta(2)-GPI was studied under conditions of flow. Intracellular signaling induced by dimeric beta(2)-GPI was subsequently analyzed by means of sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analysis. RESULTS The increase in platelet deposition onto a fibronectin surface under conditions of flow by dimeric beta(2)-GPI was completely abolished by inhibition of the interaction of dimeric beta(2)-GPI with either GPIbalpha or ApoER2'. Upon platelet stimulation with dimeric beta(2)-GPI, GPIbalpha translocated to the cytoskeleton via the scaffold protein 14-3-3zeta. Concomitantly, ApoER2' dissociated from the adapter protein Disabled1, presumably through phosphorylation of the cytoplasmic tail. Inhibition of one process could not inhibit the other. CONCLUSION We show that dimeric beta(2)-GPI signals via two distinct pathways in platelets, both of which are required for platelet activation. Abrogation of either signal results in loss of activation.
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Affiliation(s)
- R T Urbanus
- Department of Clinical Chemistry and Haematology, University Medical Centre Utrecht, Utrecht, The Netherlands
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Li Q, Huang Y, Xiao N, Murray V, Chen J, Wang J. Real time investigation of protein folding, structure, and dynamics in living cells. Methods Cell Biol 2008; 90:287-325. [PMID: 19195556 DOI: 10.1016/s0091-679x(08)00814-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Real time investigation of protein folding, structure, and dynamics at high resolution in living cells, is the next major step in nano cell biology. However, there are a number of major hurdles that need to be overcome, such as coupled translation and folding, the intervention of chaperones and folding enzymes, translocation, export, and the targeting machinery, proteasomes and degradation signals, etc. Although some progress has been made in recent years (Royer, 2006), current technology available in the field is limited for an enhanced resolution study, and no major breakthrough has been achieved in this direction. The major challenge is to develop new approaches that permit high-resolution, direct, and accurate structural measurements of protein folding and structure, in specific compartments of living cells. In this chapter, we focus on a review of a QQ-reagent based protein transduction recently developed in our laboratory technology that may allow us to develop a high-resolution in vivo investigation of protein folding, structure, and dynamics.
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Affiliation(s)
- Qianqian Li
- Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine Detroit, Michigan 48021, USA
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28
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Saavedra L, Mohamed A, Ma V, Kar S, de Chaves EP. Internalization of beta-amyloid peptide by primary neurons in the absence of apolipoprotein E. J Biol Chem 2007; 282:35722-32. [PMID: 17911110 DOI: 10.1074/jbc.m701823200] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Extracellular accumulation of beta-amyloid peptide (Abeta) has been linked to the development of Alzheimer disease. The importance of intraneuronal Abeta has been recognized more recently. Although considerable evidence indicates that extracellular Abeta contributes to the intracellular pool of Abeta, the mechanisms involved in Abeta uptake by neurons are poorly understood. We examined the molecular mechanisms involved in Abeta-(1-42) internalization by primary neurons in the absence of apolipoprotein E. We demonstrated that Abeta-(1-42) is more efficiently internalized by axons than by cell bodies of sympathetic neurons, suggesting that Abeta-(1-42) uptake might be mediated by proteins enriched in the axons. Although the acetylcholine receptor alpha7nAChR, previously suggested to be involved in Abeta internalization, is enriched in axons, our results indicate that it does not mediate Abeta-(1-42) internalization. Moreover, receptors of the low density lipoprotein receptor family are not essential for Abeta-(1-42) uptake in the absence of apolipoprotein E because receptor-associated protein had no effect on Abeta uptake. By expressing the inactive dynamin mutant dynK44A and the clathrin hub we found that Abeta-(1-42) internalization is independent of clathrin but dependent on dynamin, which suggests an endocytic pathway involving caveolae/lipid rafts. Confocal microscopy studies showing that Abeta did not co-localize with the early endosome marker EEA1 further support a clathrin-independent mechanism. The lack of co-localization of Abeta with caveolin in intracellular vesicles and the normal uptake of Abeta by neurons that do not express caveolin indicate that Abeta does not require caveolin either. Instead partial co-localization of Abeta-(1-42) with cholera toxin subunit B and sensitivity to reduction of cellular cholesterol and sphingolipid levels suggest a caveolae-independent, raft-mediated mechanism. Understanding the molecular events involved in neuronal Abeta internalization might identify potential therapeutic targets for Alzheimer disease.
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Affiliation(s)
- Lucila Saavedra
- Department of Pharmacology, University of Alberta, Edmonton, Canada
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29
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Gong C, Wang TW, Huang HS, Parent JM. Reelin regulates neuronal progenitor migration in intact and epileptic hippocampus. J Neurosci 2007; 27:1803-11. [PMID: 17314278 PMCID: PMC6673551 DOI: 10.1523/jneurosci.3111-06.2007] [Citation(s) in RCA: 168] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Dentate granule cell (DGC) neurogenesis persists throughout life in the mammalian hippocampal dentate gyrus and increases after epileptogenic insults. The DGC layer in human and experimental mesial temporal lobe epilepsy (mTLE) often shows abnormal dispersion and the appearance of hilar-ectopic DGCs. In the pilocarpine mTLE model, hilar-ectopic DGCs arise as a result of an aberrant chain migration of neural progenitors. Reelin is a secreted migration guidance cue that persists in the adult rodent and human hippocampus. We tested the hypothesis that loss of Reelin in the epileptic dentate gyrus leads to aberrant chain migration of DGC precursors. We found that interneuron subsets typically lost in human and experimental mTLE express Reelin, and DGC progenitors express the downstream Reelin signaling molecule Disabled 1 (Dab1). Prolonged seizures decreased Reelin immunoreactivity in the adult rat dentate gyrus and increased Dab1 expression in hilar-ectopic neuroblasts. Exogenous Reelin increased detachment of chain-migrating neuroblasts in dentate gyrus explants, and blockade of Reelin signaling increased chain migration. These findings suggest that Reelin modulates DGC progenitor migration to maintain normal DGC integration in the neonatal and adult mammalian dentate gyrus. Loss of Reelin expression in the epileptic adult hippocampus, moreover, likely contributes to ectopic chain migration and aberrant integration of newborn DGCs.
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Affiliation(s)
- Chao Gong
- Department of Neurology and Program for Neuroscience, University of Michigan Medical Center, Ann Arbor, Michigan 48109
| | - Tsu-Wei Wang
- Department of Neurology and Program for Neuroscience, University of Michigan Medical Center, Ann Arbor, Michigan 48109
| | - Holly S. Huang
- Department of Neurology and Program for Neuroscience, University of Michigan Medical Center, Ann Arbor, Michigan 48109
| | - Jack M. Parent
- Department of Neurology and Program for Neuroscience, University of Michigan Medical Center, Ann Arbor, Michigan 48109
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30
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Pennings MTT, Derksen RHWM, van Lummel M, Adelmeijer J, VanHoorelbeke K, Urbanus RT, Lisman T, de Groot PG. Platelet adhesion to dimeric beta-glycoprotein I under conditions of flow is mediated by at least two receptors: glycoprotein Ibalpha and apolipoprotein E receptor 2'. J Thromb Haemost 2007; 5:369-77. [PMID: 17096706 DOI: 10.1111/j.1538-7836.2007.02310.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
BACKGROUND The major antigen implicated in the antiphospholipid syndrome is beta2-glycoprotein I (beta2GPI). Dimerized beta2GPI binds to apolipoprotein E receptor 2' (apoER2') on platelets and increases platelet adhesion to collagen under conditions of flow. AIM To investigate whether the interaction between dimerized beta2GPI and platelets is sufficiently strong to resist shear stresses. METHODS We studied the interaction of platelets with immobilized dimerized beta2GPI under conditions of flow, and further analyzed the interaction using surface plasmon resonance and solid phase immunoassays. RESULTS We found that dimerized beta2GPI supports platelet adhesion and aggregate formation under venous flow conditions. Adhesion of platelets to dimerized beta2GPI was completely inhibited by the addition of soluble forms of both apoER2' and GPIbalpha, and the addition of receptor-associated protein and the removal of GPIbalpha from the platelet surface. GPIbalpha co-precipitated with apoER2', suggesting the presence of complexes between GPIbalpha and apoER2' on platelet membranes. The interaction between GPIbalpha and dimeric beta2GPI was of intermediate affinity (Kd = 180 nM) and Zn2+, but not Ca2+-dependent. Deletion of domain V from dimeric beta2GPI strongly reduced its binding to both GPIbalpha and apoER2'. Antibodies that inhibit the binding of thrombin to GPIbalpha inhibited platelet adhesion to dimeric beta2GPI completely, while antibodies blocking the binding of von Willebrand factor to GPIbalpha had no effect. Dimeric beta2GPI showed reduced binding to low-sulfated GPIbalpha compared to the fully sulfated form. CONCLUSION We show that platelets adhere to dimeric beta2GPI under both arterial and venous shear stresses. Platelets adhere via two receptors: GPIbalpha and apoER2'. These receptors are present in a complex on the platelet surface.
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Affiliation(s)
- M T T Pennings
- Laboratory of Clinical Chemistry and Haematology, University Medical Centre Utrecht, Utrecht, the Netherlands
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31
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Skeldal S, Larsen JV, Pedersen KE, Petersen HH, Egelund R, Christensen A, Jensen JK, Gliemann J, Andreasen PA. Binding areas of urokinase-type plasminogen activator?plasminogen activator inhibitor-1 complex for endocytosis receptors of the low-density lipoprotein receptor family, determined by site-directed mutagenesis. FEBS J 2006; 273:5143-59. [PMID: 17042782 DOI: 10.1111/j.1742-4658.2006.05511.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Some endocytosis receptors related to the low-density lipoprotein receptor, including low-density lipoprotein receptor-related protein-1A, very-low-density lipoprotein receptor, and sorting protein-related receptor, bind protease-inhibitor complexes, including urokinase-type plasminogen activator (uPA), plasminogen activator inhibitor-1 (PAI-1), and the uPA-PAI-1 complex. The unique capacity of these receptors for high-affinity binding of many structurally unrelated ligands renders mapping of receptor-binding surfaces of serpin and serine protease ligands a special challenge. We have mapped the receptor-binding area of the uPA-PAI-1 complex by site-directed mutagenesis. Substitution of a cluster of basic residues near the 37-loop and 60-loop of uPA reduced the receptor-binding affinity of the uPA-PAI-1 complex approximately twofold. Deletion of the N-terminal growth factor domain of uPA reduced the affinity 2-4-fold, depending on the receptor, and deletion of both the growth factor domain and the kringle reduced the affinity sevenfold. The binding affinity of the uPA-PAI-1 complex to the receptors was greatly reduced by substitution of basic and hydrophobic residues in alpha-helix D and alpha-helix E of PAI-1. The localization of the implicated residues in the 3D structures of uPA and PAI-1 shows that they form a continuous receptor-binding area spanning the serpin as well as the A-chain and the serine protease domain of uPA. Our results suggest that the 10-100-fold higher affinity of the uPA-PAI-1 complex compared with the free components depends on the bonus effect of bringing the binding areas on uPA and PAI-1 together on the same binding entity.
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Affiliation(s)
- Sune Skeldal
- Department of Molecular Biology, University of Aarhus, Denmark
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32
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LaDu MJ, Stine WB, Narita M, Getz GS, Reardon CA, Bu G. Self-assembly of HEK cell-secreted ApoE particles resembles ApoE enrichment of lipoproteins as a ligand for the LDL receptor-related protein. Biochemistry 2006; 45:381-90. [PMID: 16401069 PMCID: PMC2564845 DOI: 10.1021/bi051765s] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Recent studies have shown that the lipidation and assembly state of apolipoprotein E (apoE) determine receptor recognition and amyloid-beta peptide (Abeta) binding. We previously demonstrated that apoE secreted by HEK cells stably expressing apoE3 or apoE4 (HEK-apoE) binds Abeta and inhibits Abeta-induced neurotoxicity by an isoform-specific process that requires apoE receptors. Here we characterized the structure of HEK-apoE assemblies and determined their receptor binding specificity. By chromatography, HEK-apoE elutes in high molecular mass fractions and is the size of plasma HDL, consistent with a multiprotein assembly. No lipid was associated with these apoE assemblies. Several methods for analyzing receptor binding indicate that HEK-apoE is a ligand for low-density lipoprotein (LDL) receptor-related protein (LRP) but not the LDL receptor. This suggests that self-assembly of apoE may induce a functional conformation necessary for binding to LRP. Our results indicate that, in addition to lipid content, the assembly state of apoE influences Abeta binding and receptor recognition.
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Affiliation(s)
- Mary Jo LaDu
- Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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Abstract
For most of proteins to be active, they need well-defined three-dimensional structures alone or in complex. Folding is a process through which newly synthesized proteins get to the native state. Protein folding inside cells is assisted by various chaperones and folding factors, and misfolded proteins are eliminated by the ubiquitin-proteasome degradation system to ensure high fidelity of protein expression. Under certain circumstances, misfolded proteins escape the degradation process, yielding to deposit of protein aggregates such as loop-sheet polymer and amyloid fibril. Diseases characterized by insoluble deposits of proteins have been recognized for long time and are grouped as conformational diseases. Study of protein folding mechanism is required for better understanding of the molecular pathway of such conformational diseases.
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Affiliation(s)
- Cheolju Lee
- Life Sciences Division, Korea Institute of Science and Technology, Hawolgok-dong, Seongbuk-gu, Seoul 136-791 Korea.
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Qiu S, Korwek KM, Weeber EJ. A fresh look at an ancient receptor family: emerging roles for low density lipoprotein receptors in synaptic plasticity and memory formation. Neurobiol Learn Mem 2005; 85:16-29. [PMID: 16198608 DOI: 10.1016/j.nlm.2005.08.009] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2005] [Revised: 07/30/2005] [Accepted: 08/11/2005] [Indexed: 01/11/2023]
Abstract
The well-known family of low-density lipoprotein receptors represents a collection of ancient membrane receptors that have been remarkably conserved throughout evolution. These multifunctional receptors, known to regulate cholesterol transport, are becoming increasingly interesting to the neuroscience community due to their ability to transduce a diversity of extracellular signals across the membrane in the adult CNS. Their roles in modulating synaptic plasticity and necessity in hippocampus-specific learning and memory have recently come to light. In addition, genetic, biochemical and behavioral studies have implicated these signaling systems in a number of human neurodegenerative and neuropsychiatric disorders involving loss of cognitive ability, such as Alzheimer's disease, schizophrenia and autism. This review describes the known functions of these receptors and discusses their potential role in processes of synaptic regulation and memory formation.
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Affiliation(s)
- Shenfeng Qiu
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37232-0615, USA
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35
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Pastrana DV, Hanson AJ, Knisely J, Bu G, Fitzgerald DJ. LRP1B functions as a receptor for Pseudomonas exotoxin. Biochim Biophys Acta Mol Basis Dis 2005; 1741:234-9. [PMID: 16095885 DOI: 10.1016/j.bbadis.2005.06.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2005] [Revised: 06/06/2005] [Accepted: 06/15/2005] [Indexed: 10/25/2022]
Abstract
Pseudomonas aeruginosa is an opportunistic pathogen that produces several virulence factors, among them Pseudomonas Exotoxin A (PE). Previously, low-density lipoprotein receptor-related protein 1 (LRP 1) was shown to be the primary receptor for PE. In this report, we show that a close family member, LRP 1B, can also function as a receptor.
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Affiliation(s)
- Diana V Pastrana
- Laboratory of Molecular Biology, CCR, National Cancer Institute, Bethesda, MD 20892-4263, USA
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36
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Emonard H, Bellon G, de Diesbach P, Mettlen M, Hornebeck W, Courtoy PJ. Regulation of matrix metalloproteinase (MMP) activity by the low-density lipoprotein receptor-related protein (LRP). A new function for an “old friend”. Biochimie 2005; 87:369-76. [PMID: 15781324 DOI: 10.1016/j.biochi.2004.11.013] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Accepted: 11/15/2004] [Indexed: 12/27/2022]
Abstract
Matrix metalloproteinases (MMPs) are essential contributors to a microenvironment that promotes tumour progression. During the two last decades, inhibition of MMPs has become the focus of considerable interest for cancer therapy, and numerous synthetic metalloproteinase inhibitors have been developed by the pharmaceutical industry. However, clinical trials have shown disappointing efficacy or unexpected toxicity and new targets are thus eagerly awaited. The identification of endocytic clearance of several MMPs by the low-density lipoprotein receptor-related protein (LRP) might provide insight into novel strategies for controlling MMP level during malignant processes. This review attempts to summarize recent aspects on the cellular and molecular basis of LRP-mediated endocytic disposal of MMPs.
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Affiliation(s)
- Hervé Emonard
- CNRS UMR 6198, IFR 53, Faculté de Médecine, 51, rue Cognacq Jay, 51095 Reims cedex, France.
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37
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Abstract
It has been proposed that the aggregation of nascent transmembrane segments of polytopic proteins is prevented by chaperones present in the endoplasmic reticulum membrane; now the first experimental support for this proposal has been reported.
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Affiliation(s)
- J Michael Lord
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
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38
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Wilsie LC, Chanchani S, Navaratna D, Orlando RA. Cell surface heparan sulfate proteoglycans contribute to intracellular lipid accumulation in adipocytes. Lipids Health Dis 2005; 4:2. [PMID: 15636641 PMCID: PMC545935 DOI: 10.1186/1476-511x-4-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2004] [Accepted: 01/06/2005] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND Transport of fatty acids within the cytosol of adipocytes and their subsequent assimilation into lipid droplets has been thoroughly investigated; however, the mechanism by which fatty acids are transported across the plasma membrane from the extracellular environment remains unclear. Since triacylglycerol-rich lipoproteins represent an abundant source of fatty acids for adipocyte utilization, we have investigated the expression levels of cell surface lipoprotein receptors and their functional contributions toward intracellular lipid accumulation; these include very low density lipoprotein receptor (VLDL-R), low density lipoprotein receptor-related protein (LRP), and heparan sulfate proteoglycans (HSPG). RESULTS We found that expression of these three lipoprotein receptors increased 5-fold, 2-fold, and 2.5-fold, respectively, during adipocyte differentiation. The major proteoglycans expressed by mature adipocytes are of high molecular weight (>500 kD) and contain both heparan and chondroitin sulfate moieties. Using ligand binding antagonists, we observed that HSPG, rather than VLDL-R or LRP, play a primary role in the uptake of DiI-labeled apoE-VLDL by mature adipocytes. In addition, inhibitors of HSPG maturation resulted in a significant reduction (>85%) in intracellular lipid accumulation. CONCLUSIONS These results suggest that cell surface HSPG is required for fatty acid transport across the plasma membrane of adipocytes.
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Affiliation(s)
- Larissa C Wilsie
- Department of Biochemistry and Molecular Biology, University of New Mexico, Health Sciences Center, 915 Camino de Salud, Albuquerque, New Mexico, 87131, USA
| | - Shree Chanchani
- Department of Biochemistry and Molecular Biology, University of New Mexico, Health Sciences Center, 915 Camino de Salud, Albuquerque, New Mexico, 87131, USA
| | - Deepti Navaratna
- Department of Biochemistry and Molecular Biology, University of New Mexico, Health Sciences Center, 915 Camino de Salud, Albuquerque, New Mexico, 87131, USA
| | - Robert A Orlando
- Department of Biochemistry and Molecular Biology, University of New Mexico, Health Sciences Center, 915 Camino de Salud, Albuquerque, New Mexico, 87131, USA
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Emonard H, Bellon G, Troeberg L, Berton A, Robinet A, Henriet P, Marbaix E, Kirkegaard K, Patthy L, Eeckhout Y, Nagase H, Hornebeck W, Courtoy PJ. Low density lipoprotein receptor-related protein mediates endocytic clearance of pro-MMP-2.TIMP-2 complex through a thrombospondin-independent mechanism. J Biol Chem 2004; 279:54944-51. [PMID: 15489233 DOI: 10.1074/jbc.m406792200] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low density lipoprotein receptor-related protein (LRP) mediates the endocytic clearance of various proteinases and proteinase.inhibitor complexes, including thrombospondin (TSP)-dependent endocytosis of matrix metalloproteinase (MMP)-2 (or gelatinase A), a key effector of extracellular matrix remodeling and cancer progression. However, the zymogen of MMP-2 (pro-MMP-2) mostly occurs in tissues as a complex with the tissue inhibitor of MMPs (TIMP-2). Here we show that clearance of the pro-MMP-2.TIMP-2 complex is also mediated by LRP, because addition of receptor-associated protein (RAP), a natural LRP ligand antagonist, inhibited endocytosis and lysosomal degradation of (125)I-pro-MMP-2.TIMP-2. Both TIMP-2 and the pro-MMP-2 collagen-binding domain independently competed for endocytosis of (125)I-pro-MMP-2.TIMP-2 complex. Surface plasmon resonance studies indicated that pro-MMP-2, TIMP-2, and pro-MMP-2.TIMP-2 directly interact with LRP in the absence of TSP. LRP-mediated endocytic clearance of (125)I-pro-MMP-2 was inhibited by anti-TSP antibodies and accelerated upon complexing with TSP-1, but these treatments had no effect on (125)I-pro-MMP-2.TIMP-2 uptake. This implies that mechanisms of clearance by LRP of pro-MMP-2 and pro-MMP-2.TIMP-2 complex are different. Interestingly, RAP did not inhibit binding of (125)I-pro-MMP-2.TIMP-2 to the cell surface. We conclude that clearance of pro-MMP-2.TIMP-2 complex is a TSP-independent two-step process, involving (i) initial binding to the cell membrane in a RAP-insensitive manner and (ii) subsequent LRP-dependent (RAP-sensitive) internalization and degradation.
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Affiliation(s)
- Hervé Emonard
- CNRS UMR 6198, IFR 53 Biomolecules, Faculty of Medicine, F-51100 Reims, France
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MacLeod JC, Sayer RJ, Lucocq JM, Hubbard MJ. ERp29, a general endoplasmic reticulum marker, is highly expressed throughout the brain. J Comp Neurol 2004; 477:29-42. [PMID: 15281078 DOI: 10.1002/cne.20222] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
ERp29 is a recently discovered resident of the endoplasmic reticulum (ER) that is abundant in brain and most other mammalian tissues. Investigations of nonneural secretory tissues have implicated ERp29 in a major role producing export proteins, but a molecular activity remains wanting for this functional orphan. Intriguingly, ERp29 appears to be heavily utilized in the cerebellum, a brain region not conventionally regarded as neurosecretory. To elucidate this functional quandary, we used immunochemical approaches to characterize the regional, cellular, and subcellular distributions of ERp29 in rat brain. Immunohistochemistry revealed ubiquitous expression in neuronal and nonneuronal cells, with a distinctive variation in somatic ERp29 levels. Highly expressing cells were found in diverse locations, implying that ERp29 is not biased towards the cerebellum functionally. Using immunolocalization data mined from the literature, a proteomic profile was developed to assess the functional significance of ERp29's characteristic expression pattern. Surprisingly, ERp29 correlated poorly with classical markers of neurosecretion, but strongly with a variety of major membrane proteins. Together with immunogold localization of ERp29 to somatic ER, these observations led to a novel hypothesis that ERp29 is involved primarily in production of endomembrane proteins rather than proteins destined for export. This study establishes ERp29 as a general ER marker for brain cells and provides a stimulating clue about ERp29's enigmatic function. ERp29 appears to have broad significance for neural pathophysiology, given its ubiquitous distribution and prominence in brain over classical ER residents like BiP and protein disulfide isomerase.
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Affiliation(s)
- Jennifer C MacLeod
- Department of Physiology, University of Otago, Dunedin 9001, New Zealand
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41
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Westergaard UB, Sørensen ES, Hermey G, Nielsen MS, Nykjaer A, Kirkegaard K, Jacobsen C, Gliemann J, Madsen P, Petersen CM. Functional organization of the sortilin Vps10p domain. J Biol Chem 2004; 279:50221-9. [PMID: 15364913 DOI: 10.1074/jbc.m408873200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A Vps10p domain makes up the entire luminal part of Sortilin, and this type of domain is the hallmark of a new family of neuronal receptors that target a variety of ligands, including neurotrophins and neuropeptides. We have shown that two structural features of the Vps10p domain, the N-terminal propeptide and the C-terminal segment of ten conserved cysteines (10CC), are key elements in the function of Sortilin. The propeptide has two functions. (i) It binds the mature part of Sortilin and prevents ligands in the biosynthetic pathway from binding to the uncleaved proreceptor, and (ii) it facilitates receptor transport in early Golgi compartments by a mechanism that does not depend on its ability to prevent ligand binding. In contrast, other Vps10p domain receptors, such as SorLA and SorCS3, do not need their propeptide for normal and swift processing. The 10CC segment constitutes an exchangeable module containing five conserved disulfide bridges, and using module-shuffling and truncations, we have shown that the 10CC segment is a major ligand-binding region in Sortilin.
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Affiliation(s)
- Uffe B Westergaard
- Institute of Medical Biochemistry, Ole Worms Allé, Building 170, University of Aarhus, Aarhus, Denmark
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42
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Barral JM, Broadley SA, Schaffar G, Hartl FU. Roles of molecular chaperones in protein misfolding diseases. Semin Cell Dev Biol 2004; 15:17-29. [PMID: 15036203 DOI: 10.1016/j.semcdb.2003.12.010] [Citation(s) in RCA: 209] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Human misfolding diseases result from the failure of proteins to reach their active state or from the accumulation of aberrantly folded proteins. The mechanisms by which molecular chaperones influence the development of these diseases is beginning to be understood. Mutations that compromise the activity of chaperones lead to several rare syndromes. In contrast, the more frequent amyloid-related neurodegenerative diseases are caused by a gain of toxic function of misfolded proteins. Toxicity in these disorders may result from an imbalance between normal chaperone capacity and production of dangerous protein species. Increased chaperone expression can suppress the neurotoxicity of these molecules, suggesting possible therapeutic strategies.
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Affiliation(s)
- José M Barral
- Department of Cellular Biochemistry, Max-Planck-Institut für Biochemie, Am Klopferspitz 18a, D-82152 Martinsried, Germany
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43
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Lisi S, Chiovato L, Pinchera A, Marcocci C, Menconi F, Morabito E, Altea MA, McCluskey RT, Marinò M. Impaired thyroglobulin (Tg) secretion by FRTL-5 cells transfected with soluble receptor associated protein (RAP): evidence for a role of RAP in the Tg biosynthetic pathway. J Endocrinol Invest 2003; 26:1105-10. [PMID: 15008249 DOI: 10.1007/bf03345258] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Secretion of thyroglobulin (Tg) by thyrocytes requires several endoplasmic reticulum (ER)-resident molecular chaperones. The receptor-associated protein (RAP), a known molecular chaperone, binds to Tg in thyroid cells shortly after biosynthesis. Here we investigated whether RAP is involved in Tg secretion by FRTL-5 cells. For this purpose, we studied Tg secretion by FRTL-5 cells transfected with a soluble RAP chimera, as a mean for interfering with endogenous RAP. We used a RAP-human IgG Fc (RAP-Ig) chimeric cDNA, which was designed in order to exclude the ER retention sequence of RAP and to allow generation of a secreted form of RAP. FRTL-5 cells were transiently transfected with the RAP-Ig cDNA or, as control, with a CD8-Ig cDNA. Media were collected at 24, 48 and 72 h after transfection. Secretion of fusion proteins and of Tg in the media was measured by ELISA. As expected, under standard culture conditions, RAP was not secreted into the media by FRTL-5 cells, even though it could be detected by Western blotting in cell extracts. In transfection experiments, fusion proteins were present in the media of FRTL-5 cells transfected with either RAP-Ig or CD8-Ig, indicating that transfection was successful. Although Tg was found in the media of FRTL-5 cells transfected with either CD8-Ig or RAP-Ig, a lower amount was found in cells transfected with RAP-Ig. Therefore, we concluded that RAP is involved in Tg secretion by FRTL-5 cells suggesting that RAP may function as a Tg molecular chaperone.
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Affiliation(s)
- S Lisi
- Department of Endocrinology, University of Pisa, Pisa, Italy
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Bovenschen N, Herz J, Grimbergen JM, Lenting PJ, Havekes LM, Mertens K, van Vlijmen BJM. Elevated plasma factor VIII in a mouse model of low-density lipoprotein receptor-related protein deficiency. Blood 2003; 101:3933-9. [PMID: 12522008 DOI: 10.1182/blood-2002-07-2081] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
It has been established that low-density lipoprotein receptor-related protein (LRP) is involved in the cellular uptake and degradation of coagulation factor VIII (FVIII) in vitro. To address the physiologic role of LRP in regulating plasma FVIII in vivo, we used cre/loxP-mediated conditional LRP- deficient mice (MX1cre(+)LRP(flox/flox)). Upon inactivation of the LRP gene, MX1cre(+)LRP(flox/flox) mice had significantly higher plasma FVIII as compared with control LRP(flox/flox) mice (3.4 and 2.0 U/mL, respectively; P <.001). Elevated plasma FVIII levels in MX1cre(+)LRP(flox/flox) mice coincided with increased plasma von Willebrand factor (VWF) (2.0 and 1.6 U/mL for MX1cre(+)LRP(flox/flox) and control LRP(flox/flox) mice, respectively; P <.05). Elevation of plasma FVIII and VWF persisted for at least 6 weeks after inactivation of the LRP gene. Upon comparing plasma FVIII and VWF in individual mice, we observed an increase of the FVIII/VWF ratio in MX1cre(+)LRP(flox/flox) mice as compared with control LRP(flox/flox) mice. Administration of either a vasopressin analog or an endotoxin resulted in increased plasma VWF, but not FVIII. In clearance experiments, MX1cre(+)LRP(flox/flox) mice displayed a 1.5-fold prolongation of FVIII mean residence time. Adenovirus-mediated overexpression of the 39-kDa receptor-associated protein (RAP) in normal mice resulted in a 3.5-fold increase of plasma FVIII. These data confirm that the regulation of plasma FVIII in vivo involves a RAP-sensitive mechanism. Surprisingly, plasma FVIII in MX1cre(+)LRP(flox/flox) mice increased 2-fold after RAP gene transfer. We propose that RAP-sensitive determinants other than hepatic LRP contribute to the regulation of plasma FVIII in vivo.
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Affiliation(s)
- Niels Bovenschen
- Department of Plasma Proteins, Sanquin Research at CLB, Amsterdam, The Netherlands
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Wilsie LC, Orlando RA. The low density lipoprotein receptor-related protein complexes with cell surface heparan sulfate proteoglycans to regulate proteoglycan-mediated lipoprotein catabolism. J Biol Chem 2003; 278:15758-64. [PMID: 12598530 DOI: 10.1074/jbc.m208786200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
It has been proposed that clearance of cholesterol-enriched very low density lipoprotein (VLDL) particles occurs through a multistep process beginning with their initial binding to cell-surface heparan sulfate proteoglycans (HSPG), followed by their uptake into cells by a receptor-mediated process that utilizes members of the low density lipoprotein receptor (LDLR) family, including the low density lipoprotein receptor-related protein (LRP). We have further explored the relationship between HSPG binding of VLDL and its subsequent internalization by focusing on the LRP pathway using a cell line deficient in LDLR. In this study, we show that LRP and HSPG are part of a co-immunoprecipitable complex at the cell surface demonstrating a novel association for these two cell surface receptors. Cell surface binding assays show that this complex can be disrupted by an LRP-specific ligand binding antagonist, which in turn leads to increased VLDL binding and degradation. The increase in VLDL binding results from an increase in the availability of HSPG sites as treatment with heparinase or competitors of glycosaminoglycan chain addition eliminated the augmented binding. From these results we propose a model whereby LRP regulates the availability of VLDL binding sites at the cell surface by complexing with HSPG. Once HSPG dissociates from LRP, it is then able to bind and internalize VLDL independent of LRP endocytic activity. We conclude that HSPG and LRP together participate in VLDL clearance by means of a synergistic relationship.
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Affiliation(s)
- Larissa C Wilsie
- Department of Biochemistry and Molecular Biology, Health Sciences Center, University of New Mexico, Albuquerque, NM 87131-0001, USA
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Kasravi FB, Welch WJ, Peters-Lideu CA, Weisgraber KH, Harris HW. Induction of cytokine tolerance in rodent hepatocytes by chylomicron-bound LPS is low-density lipoprotein receptor dependent. Shock 2003; 19:157-62. [PMID: 12578125 DOI: 10.1097/00024382-200302000-00012] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
We examined the role of lipoprotein receptors in mediating chylomicron-bound lipopolysaccharide (CM-LPS)-induced cytokine tolerance in rodent hepatocytes. We found that 2 h of pretreatment with CM-LPS (5 mg TG/mL) was sufficient to induce cytokine tolerance, as measured by decreased nitric oxide (NO) production by hepatocytes (20% of the Control group, P < 0.03). Tolerance was evident as early as 2 h after pretreatment and disappeared after 40 h. Furthermore, we evaluated the roles of the low-density lipoprotein (LDL) receptor (LDLR) and LDL receptor-related protein (LRP) in the induction of cytokine tolerance in hepatocytes. Biochemical inhibition of the receptors or use of hepatocytes from LDLR-deficient mice revealed that functional LDLR was necessary for the induction of tolerance. However, by increasing the pretreatment time, the LRP compensated for the absence of the LDLR in induction of cytokine tolerance. In conclusion, CM-LPS-mediated induction of cytokine tolerance to proinflammatory cytokines is a time- and dose-dependent process that requires functional lipoprotein receptors. These findings underscore an interrelationship between TG-rich lipoprotein metabolism and innate immunity.
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Affiliation(s)
- F Behzad Kasravi
- University of California at San Francisco Surgical Research Laboratory at San Francisco General Hospital, University of California, San Francisco, California 94110, USA
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Van Hoof D, Rodenburg KW, Van der Horst DJ. Insect lipoprotein follows a transferrin-like recycling pathway that is mediated by the insect LDL receptor homologue. J Cell Sci 2002; 115:4001-12. [PMID: 12356906 DOI: 10.1242/jcs.00113] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The lipoprotein of insects, high-density lipophorin (HDLp), is homologous to that of mammalian low-density lipoprotein (LDL) with respect to its apolipoprotein structure. Moreover, an endocytic receptor for HDLp has been identified (insect lipophorin receptor, iLR) that is homologus to the LDL receptor. We transfected LDL-receptor-expressing CHO cells with iLR cDNA to study the endocytic uptake and intracellular pathways of LDL and HDLp simultaneously. Our studies provide evidence that these mammalian and insect lipoproteins follow distinct intracellular routes after receptor-mediated endocytosis. Multicolour imaging and immunofluorescence was used to visualize the intracellular trafficking of fluorescently labeled ligands in these cells. Upon internalization, which can be completely inhibited by human receptor-associated protein (RAP), mammalian and insect lipoproteins share endocytic vesicles. Subsequently, however, HDLp evacuates the LDL-containing endosomes. In contrast to LDL, which is completely degraded in lysosomes after dissociating from its receptor, both HDLp and iLR converge in a nonlysosomal juxtanuclear compartment. Colocalization studies with transferrin identified this organelle as the endocytic recycling compartment via which iron-depleted transferrin exits the cell. Fluorescently labeled RAP is also transported to this recycling organelle upon receptor-mediated endocytosis by iLR. Internalized HDLp eventually exits the cell via the recycling compartment, a process that can be blocked by monensin, and is re-secreted with a t(1/2) of approximately 13 minutes. From these observations, we conclude that HDLp is the first non-exchangeable apolipoprotein-containing lipoprotein that follows a transferrin-like recycling pathway despite the similarities between mammalian and insect lipoproteins and their receptors.
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Affiliation(s)
- Dennis Van Hoof
- Department of Biochemical Physiology and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
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Demeule M, Poirier J, Jodoin J, Bertrand Y, Desrosiers RR, Dagenais C, Nguyen T, Lanthier J, Gabathuler R, Kennard M, Jefferies WA, Karkan D, Tsai S, Fenart L, Cecchelli R, Béliveau R. High transcytosis of melanotransferrin (P97) across the blood-brain barrier. J Neurochem 2002; 83:924-33. [PMID: 12421365 DOI: 10.1046/j.1471-4159.2002.01201.x] [Citation(s) in RCA: 164] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The blood-brain barrier (BBB) performs a neuroprotective function by tightly controlling access to the brain; consequently it also impedes access of proteins as well as pharmacological agents to cerebral tissues. We demonstrate here that recombinant human melanotransferrin (P97) is highly accumulated into the mouse brain following intravenous injection and in situ brain perfusion. Moreover, P97 transcytosis across bovine brain capillary endothelial cell (BBCEC) monolayers is at least 14-fold higher than that of holo-transferrin, with no apparent intra-endothelial degradation. This high transcytosis of P97 was not related to changes in the BBCEC monolayer integrity. In addition, the transendothelial transport of P97 was sensitive to temperature and was both concentration- and conformation-dependent, suggesting that the transport of P97 is due to receptor-mediated endocytosis. In spite of the high degree of sequence identity between P97 and transferrin, a different receptor than the one for transferrin is involved in P97 transendothelial transport. A member of the low-density lipoprotein receptor protein family, likely LRP, seems to be involved in P97 transendothelial transport. The brain accumulation, high rate of P97 transcytosis and its very low level in the blood suggest that P97 could be advantageously employed as a new delivery system to target drugs directly to the brain.
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Affiliation(s)
- Michel Demeule
- Laboratoire de Médecine Moléculaire, Département de Chimie-Biochimie, Université du Québec à Montréal-Hôpital Sainte-Justine, Montréal, Québec, Canada
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Laurent-Matha V, Lucas A, Huttler S, Sandhoff K, Garcia M, Rochefort H. Procathepsin D interacts with prosaposin in cancer cells but its internalization is not mediated by LDL receptor-related protein. Exp Cell Res 2002; 277:210-9. [PMID: 12083803 DOI: 10.1006/excr.2002.5556] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The cell surface binding, endocytosis, and lysosomal routing of procathepsin D (procath-D) in cancer cells are mostly independent of the mannose-6-phosphate (M6P) receptors. In an attempt to define the receptor involved, we intracellularly cross-linked procath-D with a 68-kDa protein that we identified with specific antibodies as prosaposin in human breast and ovarian cancer cell lines. In cancer cells, this protein-protein interaction was resistant to ammonium chloride or M6P treatment, indicating that it was independent of the M6P receptors. A similar interaction also occurred in the breast cancer cell culture medium between the secreted prosaposin and procath-D. Since these two precursors can be endocytosed, we then determined whether they were interacting with the same cell surface receptor. In fibroblasts, we confirmed that the endocytosis of these two proteins was different since it was generally mediated by the M6P receptors for procath-D and mostly by LRP (LDL receptor-related protein) for prosaposin. In breast cancer cells, prosaposin endocytosis was not detected, in contrast to procath-D endocytosis, suggesting that the majority of procath-D is not internalized as a complex with prosaposin. Moreover, RAP (receptor-associated protein), a ligand inhibiting LRP-mediated endocytosis, prevented internalization of prosaposin in 49-F rat fibroblasts, but did not affect procath-D M6P-independent internalization in MDA-MB231 cells. We conclude that in breast cancer cells, even though procath-D interacts intracellularly and extracellarly with prosaposin, it is endocytosed independent of prosaposin by a receptor different from the M6P receptors and the LRP.
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Affiliation(s)
- Valérie Laurent-Matha
- INSERM Endocrinologie Moléculaire et Cellulaire des Cancers (U540), University of Montpellier 1, 60, rue de Navacelles, France
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Gillian-Daniel DL, Bates PW, Tebon A, Attie AD. Endoplasmic reticulum localization of the low density lipoprotein receptor mediates presecretory degradation of apolipoprotein B. Proc Natl Acad Sci U S A 2002; 99:4337-42. [PMID: 11904390 PMCID: PMC123649 DOI: 10.1073/pnas.072557199] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mutations in the low density lipoprotein (LDL) receptor (LDLR) cause hypercholesterolemia because of inefficient LDL clearance from the circulation. In addition, there is a paradoxical oversecretion of the metabolic precursor of LDL, very low density lipoprotein (VLDL). We recently demonstrated that the LDLR mediates pre-secretory degradation of the major VLDL protein, apolipoprotein B (apoB). Kinetic studies suggested that the degradation process is initiated in the secretory pathway. Here, we evaluated the ability of several LDLR variants that are stalled within the secretory pathway to regulate apoB secretion. Both a naturally occurring mutant LDLR and an LDLR consisting of only the ligand-binding domains and a C-terminal endoplasmic reticulum (ER) retention sequence were localized to the ER and not at the cell surface. In the presence of either of the ER-localized LDLRs, apoB secretion was essentially abolished. When the ligand-binding domain of the truncated receptor was mutated the receptor was unable to block apoB secretion, indicating that the inhibition of apoB secretion depends on the ability of the LDLR to bind to its ligand. These findings establish LDLR-mediated pre-secretory apoB degradation as a pathway distinct from reuptake of nascent lipoproteins at the cell surface. The LDLR provides an example of a receptor that modulates export of its ligand from the ER.
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