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Wang M, Alabi A, Gu HM, Gill G, Zhang Z, Jarad S, Xia XD, Shen Y, Wang GQ, Zhang DW. Identification of amino acid residues in the MT-loop of MT1-MMP critical for its ability to cleave low-density lipoprotein receptor. Front Cardiovasc Med 2022; 9:917238. [PMID: 36093157 PMCID: PMC9452735 DOI: 10.3389/fcvm.2022.917238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2022] [Accepted: 08/01/2022] [Indexed: 11/13/2022] Open
Abstract
Low-density lipoprotein receptor (LDLR) mediates clearance of plasma LDL cholesterol, preventing the development of atherosclerosis. We previously demonstrated that membrane type 1-matrix metalloproteinase (MT1-MMP) cleaves LDLR and exacerbates the development of atherosclerosis. Here, we investigated determinants in LDLR and MT1-MMP that were critical for MT1-MMP-induced LDLR cleavage. We observed that deletion of various functional domains in LDLR or removal of each of the five predicted cleavage sites of MT1-MMP on LDLR did not affect MT1-MMP-induced cleavage of the receptor. Removal of the hemopexin domain or the C-terminal cytoplasmic tail of MT1-MMP also did not impair its ability to cleave LDLR. On the other hand, mutant MT1-MMP, in which the catalytic domain or the MT-loop was deleted, could not cleave LDLR. Further Ala-scanning analysis revealed an important role for Ile at position 167 of the MT-loop in MT1-MMP’s action on LDLR. Replacement of Ile167 with Ala, Thr, Glu, or Lys resulted in a marked loss of the ability to cleave LDLR, whereas mutation of Ile167 to a non-polar amino acid residue, including Leu, Val, Met, and Phe, had no effect. Therefore, our studies indicate that MT1-MMP does not require a specific cleavage site on LDLR. In contrast, an amino acid residue with a hydrophobic side chain at position 167 in the MT-loop is critical for MT1-MMP-induced LDLR cleavage.
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Affiliation(s)
- Maggie Wang
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
| | - Adekunle Alabi
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
| | - Hong-mei Gu
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
| | - Govind Gill
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
| | - Ziyang Zhang
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
| | - Suha Jarad
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
| | - Xiao-dan Xia
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
- Department of Orthopedics, The Sixth Affiliated Hospital of Guangzhou Medical University, Qingyuan People’s Hospital, Qingyuan, China
| | - Yishi Shen
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
| | - Gui-qing Wang
- Department of Orthopedics, The Sixth Affiliated Hospital of Guangzhou Medical University, Qingyuan People’s Hospital, Qingyuan, China
| | - Da-wei Zhang
- The Department of Pediatrics and Group on the Molecular Cell Biology of Lipids, Faculty of Medicine Dentistry, College of Health Sciences, University of Alberta, Edmonton, AB, Canada
- *Correspondence: Da-wei Zhang,
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Namgung J, Mizuta H, Yamaguchi Y, Nagata J, Todo T, Yilmaz O, Hiramatsu N. Knock out of a major vitellogenin receptor gene with eight ligand binding repeats in medaka (Oryzias latipes) using the CRISPR/Cas9 system. Comp Biochem Physiol A Mol Integr Physiol 2021; 257:110967. [PMID: 33895320 DOI: 10.1016/j.cbpa.2021.110967] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 04/19/2021] [Accepted: 04/19/2021] [Indexed: 11/16/2022]
Abstract
Recent studies of vitellogenesis engendered a novel model of teleost yolk formation in which multiple yolk precursors, vitellogenins (Vtgs), and their receptors (Vtgrs) interact to ensure proper yolk composition for embryonic development and larval growth. As a step toward verification of this concept, we examined the role of one candidate Vtgr, termed low-density lipoprotein receptor relative with eight ligand-binding repeat (Lr8), in the medaka, a representative teleost and established laboratory model. A homozygous lr8 knock out (lr8-KO) medaka was produced to perform reverse-genetic functional analyses. In ovaries of wild type (WT) medaka, Western blotting detected a putative Lr8 protein band at ~130 kDa, while immunohistochemistry detected the putative Lr8 signal at the periphery of the oocyte underneath the zona radiata. These signals disappeared in ovaries of the lr8-KO group. Offspring of lr8-KO medaka exhibited decreased survival rate compared to WT fish, but KO of lr8 was not 100% lethal. There was no significant difference in total yolk protein content or size of eggs between WT and lr8-KO fish. However, LC-MS/MS analyses revealed a remarkable decrease in the relative abundance of yolk proteins derived from VtgAb in lr8-KO eggs, in conjunction with a compensatory increase in proteins derived from VtgAa1. These findings strongly support the conclusion that Lr8 is an important receptor for VtgAb in medaka. The disruption of proper yolk composition by lr8-KO is possibly one cause of the low offspring survival.
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Affiliation(s)
- Jin Namgung
- Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan
| | - Hiroko Mizuta
- Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan
| | - Yo Yamaguchi
- Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan
| | - Jun Nagata
- Mariculture Fisheries Research Institute, Fisheries Research Department, Hokkaido Research Organization, 1-4-1 Masuura, Abashiri, Hokkaido 099-3119, Japan
| | - Takashi Todo
- Division of Marine Life Sciences, Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan
| | - Ozlem Yilmaz
- Institute of Marine Research, Austevoll Research Station, Storebø, Norway
| | - Naoshi Hiramatsu
- Division of Marine Life Sciences, Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan.
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3
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Alabi A, Xia XD, Gu HM, Wang F, Deng SJ, Yang N, Adijiang A, Douglas DN, Kneteman NM, Xue Y, Chen L, Qin S, Wang G, Zhang DW. Membrane type 1 matrix metalloproteinase promotes LDL receptor shedding and accelerates the development of atherosclerosis. Nat Commun 2021; 12:1889. [PMID: 33767172 PMCID: PMC7994674 DOI: 10.1038/s41467-021-22167-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Accepted: 03/02/2021] [Indexed: 01/07/2023] Open
Abstract
Plasma low-density lipoprotein (LDL) is primarily cleared by LDL receptor (LDLR). LDLR can be proteolytically cleaved to release its soluble ectodomain (sLDLR) into extracellular milieu. However, the proteinase responsible for LDLR cleavage is unknown. Here we report that membrane type 1-matrix metalloproteinase (MT1-MMP) co-immunoprecipitates and co-localizes with LDLR and promotes LDLR cleavage. Plasma sLDLR and cholesterol levels are reduced while hepatic LDLR is increased in mice lacking hepatic MT1-MMP. Opposite effects are observed when MT1-MMP is overexpressed. MT1-MMP overexpression significantly increases atherosclerotic lesions, while MT1-MMP knockdown significantly reduces cholesteryl ester accumulation in the aortas of apolipoprotein E (apoE) knockout mice. Furthermore, sLDLR is associated with apoB and apoE-containing lipoproteins in mouse and human plasma. Plasma levels of sLDLR are significantly increased in subjects with high plasma LDL cholesterol levels. Thus, we demonstrate that MT1-MMP promotes ectodomain shedding of hepatic LDLR, thereby regulating plasma cholesterol levels and the development of atherosclerosis.
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Affiliation(s)
- Adekunle Alabi
- The Department of Pediatrics and Group on the Molecular and Cell Biology of Lipids, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Xiao-Dan Xia
- The Department of Pediatrics and Group on the Molecular and Cell Biology of Lipids, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada.,Department of Orthopedics, The Sixth Affiliated Hospital of Guangzhou Medical University, Qingyuan People's Hospital, Qingyuan, China
| | - Hong-Mei Gu
- The Department of Pediatrics and Group on the Molecular and Cell Biology of Lipids, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Faqi Wang
- The Department of Pediatrics and Group on the Molecular and Cell Biology of Lipids, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Shi-Jun Deng
- The Department of Pediatrics and Group on the Molecular and Cell Biology of Lipids, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Nana Yang
- Experimental Center for Medical Research, Weifang Medical University, Weifang, China
| | - Ayinuer Adijiang
- The Department of Pediatrics and Group on the Molecular and Cell Biology of Lipids, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Donna N Douglas
- Department of Surgery, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Norman M Kneteman
- Department of Surgery, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
| | - Yazhuo Xue
- Institute of Atherosclerosis in Shandong First Medical University (Shandong Academy of Medical Sciences), Taian, China
| | - Li Chen
- Institute of Atherosclerosis in Shandong First Medical University (Shandong Academy of Medical Sciences), Taian, China
| | - Shucun Qin
- Institute of Atherosclerosis in Shandong First Medical University (Shandong Academy of Medical Sciences), Taian, China
| | - Guiqing Wang
- Department of Orthopedics, The Sixth Affiliated Hospital of Guangzhou Medical University, Qingyuan People's Hospital, Qingyuan, China
| | - Da-Wei Zhang
- The Department of Pediatrics and Group on the Molecular and Cell Biology of Lipids, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada.
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Kim K, Goldberg IJ, Graham MJ, Sundaram M, Bertaggia E, Lee SX, Qiang L, Haeusler RA, Metzger D, Chambon P, Yao Z, Ginsberg HN, Pajvani UB. γ-Secretase Inhibition Lowers Plasma Triglyceride-Rich Lipoproteins by Stabilizing the LDL Receptor. Cell Metab 2018; 27:816-827.e4. [PMID: 29576536 PMCID: PMC5884729 DOI: 10.1016/j.cmet.2018.02.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 12/14/2017] [Accepted: 02/14/2018] [Indexed: 12/31/2022]
Abstract
Excess plasma triglycerides (TGs) are a key component of obesity-induced metabolic syndrome. We have shown that γ-secretase inhibitor (GSI) treatment improves glucose tolerance due to inhibition of hepatic Notch signaling but found additional Notch-independent reduction of plasma TG-rich lipoproteins (TRLs) in GSI-treated, as well as hepatocyte-specific, γ-secretase knockout (L-Ncst) mice, which suggested a primary effect on hepatocyte TRL uptake. Indeed, we found increased VLDL and LDL particle uptake in L-Ncst hepatocytes and Ncst-deficient hepatoma cells, in part through reduced γ-secretase-mediated low-density lipoprotein receptor (LDLR) cleavage and degradation. To exploit this novel finding, we generated a liver-selective Nicastrin ASO, which recapitulated glucose and lipid improvements of L-Ncst mice, with increased levels of hepatocyte LDLR. Collectively, these results identify the role of hepatic γ-secretase to regulate LDLR and suggest that liver-specific GSIs may simultaneously improve multiple aspects of the metabolic syndrome.
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Affiliation(s)
- KyeongJin Kim
- Department of Medicine, Columbia University, New York, NY, USA
| | - Ira J Goldberg
- Department of Medicine, New York University, New York, NY, USA
| | | | - Meenakshi Sundaram
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, ON, Canada
| | - Enrico Bertaggia
- Departments of Pathology and Cell Biology, Columbia University, New York, NY, USA
| | - Samuel X Lee
- Departments of Pathology and Cell Biology, Columbia University, New York, NY, USA
| | - Li Qiang
- Departments of Pathology and Cell Biology, Columbia University, New York, NY, USA
| | - Rebecca A Haeusler
- Departments of Pathology and Cell Biology, Columbia University, New York, NY, USA
| | | | | | - Zemin Yao
- Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, ON, Canada
| | | | - Utpal B Pajvani
- Department of Medicine, Columbia University, New York, NY, USA.
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5
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Reading BJ, Hiramatsu N, Schilling J, Molloy KT, Glassbrook N, Mizuta H, Luo W, Baltzegar DA, Williams VN, Todo T, Hara A, Sullivan CV. Lrp13 is a novel vertebrate lipoprotein receptor that binds vitellogenins in teleost fishes. J Lipid Res 2014; 55:2287-95. [PMID: 25217480 DOI: 10.1194/jlr.m050286] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Transcripts encoding a novel member of the lipoprotein receptor superfamily, termed LDL receptor-related protein (Lrp)13, were sequenced from striped bass (Morone saxatilis) and white perch (Morone americana) ovaries. Receptor proteins were purified from perch ovary membranes by protein-affinity chromatography employing an immobilized mixture of vitellogenins Aa and Ab. RT-PCR revealed lrp13 to be predominantly expressed in striped bass ovary, and in situ hybridization detected lrp13 transcripts in the ooplasm of early secondary growth oocytes. Quantitative RT-PCR confirmed peak lrp13 expression in the ovary during early secondary growth. Quantitative mass spectrometry revealed peak Lrp13 protein levels in striped bass ovary during late-vitellogenesis, and immunohistochemistry localized Lrp13 to the oolemma and zona radiata of vitellogenic oocytes. Previously unreported orthologs of lrp13 were identified in genome sequences of fishes, chicken (Gallus gallus), mouse (Mus musculus), and dog (Canis lupus familiaris). Zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus) lrp13 loci are discrete and share genomic synteny. The Lrp13 appears to function as a vitellogenin receptor and may be an important mediator of yolk formation in fishes and other oviparous vertebrates. The presence of lrp13 orthologs in mammals suggests that this lipoprotein receptor is widely distributed among vertebrates, where it may generally play a role in lipoprotein metabolism.
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Affiliation(s)
- Benjamin J Reading
- Departments of Applied Ecology North Carolina State University, Raleigh, NC
| | - Naoshi Hiramatsu
- Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan
| | - Justin Schilling
- Departments of Applied Ecology North Carolina State University, Raleigh, NC
| | - Katelyn T Molloy
- Departments of Applied Ecology North Carolina State University, Raleigh, NC
| | - Norm Glassbrook
- Genomic Sciences Laboratory, North Carolina State University, Raleigh, NC
| | - Hiroko Mizuta
- Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan
| | - Wenshu Luo
- Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan
| | | | - Valerie N Williams
- Departments of Applied Ecology North Carolina State University, Raleigh, NC
| | - Takashi Todo
- Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan
| | - Akihiko Hara
- Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan
| | - Craig V Sullivan
- Biological Sciences, North Carolina State University, Raleigh, NC Carolina AquaGyn, Raleigh, NC
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6
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Gu HM, Adijiang A, Mah M, Zhang DW. Characterization of the role of EGF-A of low density lipoprotein receptor in PCSK9 binding. J Lipid Res 2013; 54:3345-57. [PMID: 24103783 DOI: 10.1194/jlr.m041129] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Proprotein convertase subtilisin kexin-like 9 (PCSK9) promotes the degradation of low density lipoprotein receptor (LDLR) and plays an important role in regulating plasma LDL-cholesterol levels. We have shown that the epidermal growth factor precursor homology domain A (EGF-A) of the LDLR is critical for PCSK9 binding at the cell surface (pH 7.4). Here, we further characterized the role of EGF-A in binding of PCSK9 to the LDLR. We found that PCSK9 efficiently bound to the LDLR but not to other LDLR family members. Replacement of EGF-A in the very low density lipoprotein receptor (VLDLR) with EGF-A of the LDLR promoted the degradation of the mutant VLDLR induced by PCSK9. Furthermore, we found that PCSK9 bound to recombinant EGF-A in a pH-dependent manner with stronger binding at pH 6.0. We also identified amino acid residues in EGF-A of the LDLR important for PCSK9 binding. Mutations G293H, D299V, L318D, and L318H reduced PCSK9 binding to the LDLR at neutral pH without effect at pH 6.0, while mutations R329P and E332G reduced PCSK9 binding at both pH values. Thus, our findings reveal that EGF-A of the LDLR is critical for PCSK9 binding at the cell surface (neutral pH) and at the acidic endosomal environment (pH 6.0), but different determinants contribute to efficient PCSK9 binding in different pH environments.
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Affiliation(s)
- Hong-mei Gu
- Departments of Pediatrics and Biochemistry, Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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7
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Kang YL, Yochem J, Bell L, Sorensen EB, Chen L, Conner SD. Caenorhabditis elegans reveals a FxNPxY-independent low-density lipoprotein receptor internalization mechanism mediated by epsin1. Mol Biol Cell 2012; 24:308-18. [PMID: 23242996 PMCID: PMC3564534 DOI: 10.1091/mbc.e12-02-0163] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A genome-wide RNA interference screen using Caenorhabditis elegans LRP-1/megalin as a model for LDLR transport was employed to identify factors critical to LDLR uptake. We provide evidence that epsin1 promotes LDLR internalization via a FxNPxY-independent pathway. We complement C. elegans in vivo approaches with loss-of-function and biochemical analyses, using mammalian cell culture systems to evaluate epsin1’s mode of action in LDLR endocytosis. Low-density lipoprotein receptor (LDLR) internalization clears cholesterol-laden LDL particles from circulation in humans. Defects in clathrin-dependent LDLR endocytosis promote elevated serum cholesterol levels and can lead to atherosclerosis. However, our understanding of the mechanisms that control LDLR uptake remains incomplete. To identify factors critical to LDLR uptake, we pursued a genome-wide RNA interference screen using Caenorhabditis elegans LRP-1/megalin as a model for LDLR transport. In doing so, we discovered an unanticipated requirement for the clathrin-binding endocytic adaptor epsin1 in LDLR endocytosis. Epsin1 depletion reduced LDLR internalization rates in mammalian cells, similar to the reduction observed following clathrin depletion. Genetic and biochemical analyses of epsin in C. elegans and mammalian cells uncovered a requirement for the ubiquitin-interaction motif (UIM) as critical for receptor transport. As the epsin UIM promotes the internalization of some ubiquitinated receptors, we predicted LDLR ubiquitination as necessary for endocytosis. However, engineered ubiquitination-impaired LDLR mutants showed modest internalization defects that were further enhanced with epsin1 depletion, demonstrating epsin1-mediated LDLR endocytosis is independent of receptor ubiquitination. Finally, we provide evidence that epsin1-mediated LDLR uptake occurs independently of either of the two documented internalization motifs (FxNPxY or HIC) encoded within the LDLR cytoplasmic tail, indicating an additional internalization mechanism for LDLR.
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Affiliation(s)
- Yuan-Lin Kang
- Department of Genetics, Cell Biology, and Development and the Developmental Biology Center, University of Minnesota, Minneapolis, MN 55455, USA
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Strøm TB, Tveten K, Holla ØL, Cameron J, Berge KE, Leren TP. Characterization of residues in the cytoplasmic domain of the LDL receptor required for exit from the endoplasmic reticulum. Biochem Biophys Res Commun 2011; 415:642-5. [DOI: 10.1016/j.bbrc.2011.10.127] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Accepted: 10/27/2011] [Indexed: 10/15/2022]
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9
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Mousavi SA, Berge KE, Berg T, Leren TP. Affinity and kinetics of proprotein convertase subtilisin/kexin type 9 binding to low-density lipoprotein receptors on HepG2 cells. FEBS J 2011; 278:2938-50. [PMID: 21692990 DOI: 10.1111/j.1742-4658.2011.08219.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that regulates the number of cell surface low-density lipoprotein receptors (LDLRs) and the levels of low-density lipoprotein cholesterol in plasma. Intact cells have not previously been used to determine the characteristics of binding of PCSK9 to LDLR. Using PCSK9 iodinated by the tyramine cellobiose (TC) method ([(125)I]TC-PCSK9), we measured the affinity and kinetics of binding of PCSK9 to LDLR on HepG2 cells at 4 °C. The extent of [(125)I]TC-PCSK9 binding increased as cell surface LDLR density increased. Unlabeled wild-type and two gain-of-function mutants of PCSK9 reduced binding of [(125)I]TC-PCSK9. The Scatchard plot of the binding-inhibition curve was curvilinear, indicative of high-affinity and low-affinity sites for PCSK9 binding on HepG2 cells. Nonlinear regression analysis of the binding data also indicated that a two-site model better fitted the data. The time course of [(125)I]TC-PCSK9 binding showed two phases in the association kinetics. Dissociation of [(125)I]TC-PCSK9 also occurred in two phases. Unlabeled PCSK9 accelerated the dissociation of [(125)I]TC-PCSK9. At low pH, only one phase of dissociation was apparent. Furthermore, the dissociation of [(125)I]TC-PCSK9 under pre-equilibrium conditions was faster than under equilibrium conditions. Overall, the data suggest that PCSK9 binding to cell surface LDLR cannot be described by a simple bimolecular reaction. Possible interpretations that can account for these observations are discussed.
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Affiliation(s)
- Seyed A Mousavi
- Unit for Cardiac and Cardiovascular Genetics, Department of Medical Genetics, Oslo University Hospital Rikshospitalet, Norway
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10
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Zou P, Ting AY. Imaging LDL receptor oligomerization during endocytosis using a co-internalization assay. ACS Chem Biol 2011; 6:308-13. [PMID: 21194239 DOI: 10.1021/cb100361k] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Methods to probe receptor oligomerization are useful to understand the molecular mechanisms of receptor signaling. Here we report a fluorescence imaging method to determine receptor oligomerization state in living cells during endocytic internalization. The wild-type receptor is co-expressed with an internalization-defective mutant, and the internalization kinetics of each are independently monitored. If the receptor internalizes as an oligomer, then the wild-type and mutant isoforms will mutually influence each others' trafficking properties, causing co-internalization of the mutant or co-retention of the wild-type at the cell surface. Using this approach, we found that the low density lipoprotein (LDL) receptor internalizes as an oligomer into cells, both in the presence and absence of LDL ligand. The internalization kinetics of the wild-type receptor are not changed by LDL binding. We also found that the oligomerization domain of the LDL receptor is located in its cytoplasmic tail.
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Affiliation(s)
- Peng Zou
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Alice Y. Ting
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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11
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Abstract
The purpose of this review is to provide a better understanding for the LRP co-receptor-mediated Wnt pathway signaling. Using proteomics, we have also subdivided the LRP receptor family into six sub-families, encompassing the twelve family members. This review includes a discussion of proteins containing a cystine-knot protein motif (i.e., Sclerostin, Dan, Sostdc1, Vwf, Norrin, Pdgf, Mucin) and discusses how this motif plays a role in mediating Wnt signaling through interactions with LRP.
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12
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Abstract
Endocytosis of glycosylphosphatidylinositol (GPI)-linked proteins via a specific pathway into GPI-enriched early endosomal compartments (GEECs) has been proposed. How sorting into this pathway may take place is unclear. In this issue, Bhagatji et al. (2009. J. Cell Biol. doi:10.1083/jcb.200903102) provide an original mechanism for the sorting of lipid-anchored proteins that involves exclusion of bulky extracellular domains from clathrin-coated pits.
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Affiliation(s)
- Ben Nichols
- Medical Research Council Laboratory of Molecular Biology, Cambridge CB20QH, England, UK.
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13
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Structural requirements for PCSK9-mediated degradation of the low-density lipoprotein receptor. Proc Natl Acad Sci U S A 2008; 105:13045-50. [PMID: 18753623 DOI: 10.1073/pnas.0806312105] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that controls plasma LDL cholesterol levels by posttranslational regulation of the LDL receptor (LDLR). Previously, we showed that PCSK9 binds specifically to an EGF-like repeat (EGF-A) in LDLR and reroutes the receptor from endosomes to lysosomes rather than to the cell surface. Here, we defined the regions in LDLR and PCSK9 that are required for receptor degradation and examined the relationship between PCSK9 binding and LDLR conformation. Addition of PCSK9 to cultured hepatocytes promoted degradation of WT LDLR and of receptors lacking up to four ligand binding domains, EGF-B or the clustered O-linked sugar region. In contrast, LDLRs lacking the entire ligand binding domain or the beta-propeller domain failed to be degraded, although they bound and internalized PCSK9. Using gel filtration chromatography, we assessed the effects of PCSK9 binding on an acid-dependent conformational change that happens in the extracellular domain of the LDLR. Although PCSK9 prevented the reduction in hydrodynamic radius of the receptor that occurs at a reduced pH, the effect was not sufficient for LDLR degradation. A truncated version of PCSK9 containing the prodomain and the catalytic domain, but not the C-terminal domain, bound the receptor but did not stimulate LDLR degradation. Thus, domains in both the LDLR and PCSK9 that are not required for binding (or internalization) are essential for PCSK9-mediated degradation of the LDLR.
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14
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Makarova A, Bercury KK, Adams KW, Joyner D, Deng M, Spoelgen R, Koker M, Strickland DK, Hyman BT. The LDL receptor-related protein can form homo-dimers in neuronal cells. Neurosci Lett 2008; 442:91-5. [PMID: 18602448 DOI: 10.1016/j.neulet.2008.06.070] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2007] [Revised: 06/13/2008] [Accepted: 06/18/2008] [Indexed: 10/21/2022]
Abstract
The ability of the low density lipoprotein receptor-related protein (LRP) to form homo-dimers was studied in mouse neuroblastoma and human neuroglioma cells as well as in primary cortical cultures from adult mouse brain. Homo-dimerization of LRP light chain (LC) was shown by several methods including co-immunoprecipitation, fluorescence lifetime imaging microscopy, and bimolecular fluorescence complementation assay. The requirement of intact NPXY motifs of LRP LC for homo-dimerization was ruled out by co-immunoprecipitation assay.
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Affiliation(s)
- Alexandra Makarova
- MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA
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15
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Wang J, Zhang DW, Lei Y, Xu F, Cohen JC, Hobbs HH, Xie XS. Purification and reconstitution of sterol transfer by native mouse ABCG5 and ABCG8. Biochemistry 2008; 47:5194-204. [PMID: 18402465 DOI: 10.1021/bi800292v] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
ABCG5 (G5) and ABCG8 (G8) are ATP-binding cassette half-transporters that limit intestinal uptake and promote biliary secretion of neutral sterols. Here, we describe the purification of endogenous G5G8 from mouse liver to near homogeneity. We incorporated the native proteins into membrane vesicles and reconstituted sterol transfer. Native gel electrophoresis, density-gradient ultracentrifugation, and chemical cross-linking studies indicated that the functional native complex is a heterodimer. No higher order oligomeric forms were observed at any stage in the catalytic cycle. Sterol transfer activity by purified native G5G8 was stable, stereospecific, and selective. We also report that G5 but not G8 is S-palmitoylated and that palmitoylation is not essential for dimerization, trafficking, or biliary sterol secretion. Both G5 and G8 have short but highly conserved cytoplasmic tails. The functional roles of these C-terminal regions were examined using an in vivo functional assay.
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Affiliation(s)
- Jin Wang
- Eugene McDermott Center for Human Growth and Development, Department of Internal Medicine, and the Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8591, USA
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16
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Michaely P, Zhao Z, Li WP, Garuti R, Huang LJ, Hobbs HH, Cohen JC. Identification of a VLDL-induced, FDNPVY-independent internalization mechanism for the LDLR. EMBO J 2007; 26:3273-82. [PMID: 17581630 PMCID: PMC1933400 DOI: 10.1038/sj.emboj.7601769] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2006] [Accepted: 05/30/2007] [Indexed: 11/09/2022] Open
Abstract
The low-density lipoprotein (LDL) receptor (LDLR) binds to and internalizes lipoproteins that contain apolipoproteinB100 (apoB100) or apolipoproteinE (apoE). Internalization of the apoB100 lipoprotein ligand, LDL, requires the FDNPVY(807) sequence on the LDLR cytoplasmic domain, which binds to the endocytic machinery of coated pits. We show here that inactivation of the FDNPVY(807) sequence by mutation of Y807 to cysteine prevented the uptake of LDL; however, this mutation did not prevent LDLR-dependent uptake of the apoE lipoprotein ligand, beta-VLDL. Comparison of the surface localization of the LDLR-Y807C using LDLR-immunogold, LDL-gold and beta-VLDL-gold probes revealed enrichment of LDLR-Y807C-bound beta-VLDL in coated pits, suggesting that beta-VLDL binding promoted the internalization of the LDLR-Y807C. Consistent with this possibility, treatment with monensin, which traps internalized LDLR in endosomes, resulted in the loss of surface LDLR-Y807C only when beta-VLDL was present. Reconstitution experiments in which LDLR variants were introduced into LDLR-deficient cells showed that the HIC(818) sequence is involved in beta-VLDL uptake by the LDLR-Y807C. Together, these experiments demonstrate that the LDLR has a very low-density lipoprotein (VLDL)-induced, FDNPVY-independent internalization mechanism.
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Affiliation(s)
- Peter Michaely
- Department of Cell Biology, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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17
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Yang N, Wang X, Jiang J, Frank SJ. Role of the growth hormone (GH) receptor transmembrane domain in receptor predimerization and GH-induced activation. Mol Endocrinol 2007; 21:1642-55. [PMID: 17456794 DOI: 10.1210/me.2006-0458] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The GH receptor (GHR) mediates GH effects by activating the GHR-associated cytoplasmic tyrosine kinase, Janus kinase 2. Recent studies indicate that GHRs exist as dimers independently of GH binding. Some authors suggest that receptor predimerization is mediated by the transmembrane domain (TMD) and that GH binding initiates signaling by triggering changes in the orientation of the two GHRs within the dimer. In this study, we investigate the role of GHR TMD in GH-independent receptor dimerization and ligand-induced activation. We prepared a GHR mutant, GHR(LDLR), in which the TMD is replaced with the TMD of the human low-density lipoprotein receptor (LDLR). The resultant chimera has a TMD two residues shorter than the native GHR TMD; thus, in addition to possessing a different TMD, the altered GHR(LDLR) TMD helical register may change positions of the GHR extracellular domain (ECD) and intracellular domain relative to the TMD when compared with the wild-type (WT) receptor. When each was coexpressed with an intracellular domain-truncated GHR mutant, GHR(1-274-Myc), both WT GHR and GHR(LDLR) were specifically coprecipitated with GHR(1-274-Myc), indicating that the GHR TMD was not required for GHR heterodimerization with GHR(1-274-Myc). We further examined the contribution of the so-called "dimerization interface," a GHR ECD region that is critical for GH-induced signaling, to receptor predimerization. Coimmunoprecipitation experiments with either WT GHR, a dimerization interface mutant (GHR-H150D), or a control mutant (GHR-T147D) with GHR(1-274-Myc) showed dramatically reduced coprecipitation of GHR-H150D with GHR(1-274-Myc) when compared with WT GHR or GHR-T147K. This result suggests that, in contrast to some recent models, the dimerization interface contributes to GHR predimerization. We also compared WT GHR with GHR(LDLR) and GHR(LDLRDelta4) (a chimera in which the LDLR TMD has an internal deletion of four residues) with regard to response to GH stimulation. Although the chimeras had similar GH dose responses and time courses for signaling as WT GHR, they were markedly less sensitive to inhibition of signaling by a conformation-sensitive GHR ECD monoclonal antibody. Further, the chimeras were much less sensitive to inducible metalloprotease cleavage than was WT GHR, implying that the ECD conformations of the chimera receptors differ from WT GHR. Collectively, our data indicate that the composition and/or length of the TMD affect some aspects of GHR function, but do not affect receptor predimerization or GH-induced GHR activation. Further, they suggest that the GHR ECD-TMD is more flexible than previously thought in terms of the ability to achieve the active conformation in response to GH.
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Affiliation(s)
- Ning Yang
- Department of Cell Biology, Division of Endocrinology, Diabetes, and Metabolism, University of Alabama at Birmingham, Birmingham, Alabama 35294-0012, USA
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18
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Zhang DW, Lagace TA, Garuti R, Zhao Z, McDonald M, Horton JD, Cohen JC, Hobbs HH. Binding of proprotein convertase subtilisin/kexin type 9 to epidermal growth factor-like repeat A of low density lipoprotein receptor decreases receptor recycling and increases degradation. J Biol Chem 2007; 282:18602-18612. [PMID: 17452316 DOI: 10.1074/jbc.m702027200] [Citation(s) in RCA: 595] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes degradation of hepatic low density lipoprotein receptors (LDLR), the major route of clearance of circulating cholesterol. Gain-of-function mutations in PCSK9 cause hypercholesterolemia and premature atherosclerosis, whereas loss-of-function mutations result in hypocholesterolemia and protection from heart disease. Recombinant human PCSK9 binds the LDLR on the surface of cultured hepatocytes and promotes degradation of the receptor after internalization. Here we localized the site of binding of PCSK9 within the extracellular domain of the LDLR and determined the fate of the receptor after PCSK9 binding. Recombinant human PCSK9 interacted in a sequence-specific manner with the first epidermal growth factor-like repeat (EGF-A) in the EGF homology domain of the human LDLR. Similar binding specificity was observed between PCSK9 and purified EGF-A. Binding to EGF-A was calcium-dependent and increased dramatically with reduction in pH from 7 to 5.2. The addition of PCSK9, but not heat-inactivated PCSK9, to the medium of cultured hepatocytes resulted in redistribution of the receptor from the plasma membrane to lysosomes. These data are consistent with a model in which PCSK9 binding to EGF-A interferes with an acid-dependent conformational change required for receptor recycling. As a consequence, the LDLR is rerouted from the endosome to the lysosome where it is degraded.
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Affiliation(s)
- Da-Wei Zhang
- Departments of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Thomas A Lagace
- Departments of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Rita Garuti
- Departments of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Zhenze Zhao
- Departments of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Meghan McDonald
- Departments of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Jay D Horton
- Departments of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Jonathan C Cohen
- Departments of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390; Donald W. Reynolds Cardiovascular Clinical Research Center, University of Texas Southwestern Medical Center, Dallas, Texas 75390.
| | - Helen H Hobbs
- Departments of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390; Donald W. Reynolds Cardiovascular Clinical Research Center, University of Texas Southwestern Medical Center, Dallas, Texas 75390; Howard Hughes Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390.
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19
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Bohlooly-Y M, Bohlooly M, Olsson B, Bruder CEG, Lindén D, Sjögren K, Bjursell M, Egecioglu E, Svensson L, Brodin P, Waterton JC, Isaksson OGP, Sundler F, Ahrén B, Ohlsson C, Oscarsson J, Törnell J. Growth hormone overexpression in the central nervous system results in hyperphagia-induced obesity associated with insulin resistance and dyslipidemia. Diabetes 2005; 54:51-62. [PMID: 15616010 DOI: 10.2337/diabetes.54.1.51] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
It is well known that peripherally administered growth hormone (GH) results in decreased body fat mass. However, GH-deficient patients increase their food intake when substituted with GH, suggesting that GH also has an appetite stimulating effect. Transgenic mice with an overexpression of bovine GH in the central nervous system (CNS) were created to investigate the role of GH in CNS. This study shows that overexpression of GH in the CNS differentiates the effect of GH on body fat mass from that on appetite. The transgenic mice were not GH-deficient but were obese and showed increased food intake as well as increased hypothalamic expression of agouti-related protein and neuropeptide Y. GH also had an acute effect on food intake following intracerebroventricular injection of C57BL/6 mice. The transgenic mice were severely hyperinsulinemic and showed a marked hyperplasia of the islets of Langerhans. In addition, the transgenic mice displayed alterations in serum lipid and lipoprotein levels and hepatic gene expression. In conclusion, GH overexpression in the CNS results in hyperphagia-induced obesity indicating a dual effect of GH with a central stimulation of appetite and a peripheral lipolytic effect.
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20
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Michaely P, Li WP, Anderson RGW, Cohen JC, Hobbs HH. The modular adaptor protein ARH is required for low density lipoprotein (LDL) binding and internalization but not for LDL receptor clustering in coated pits. J Biol Chem 2004; 279:34023-31. [PMID: 15166224 DOI: 10.1074/jbc.m405242200] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ARH is an adaptor protein required for efficient endocytosis of low density lipoprotein (LDL) receptors (LDLRs) in selected tissues. Individuals lacking ARH (ARH-/-) have severe hypercholesterolemia due to impaired hepatic clearance of LDL. Immortalized lymphocytes, but not fibroblasts, from ARH-deficient subjects fail to internalize LDL. To further define the role of ARH in LDLR function, we compared the subcellular distribution of the LDLR in lymphocytes from normal and ARH-/- subjects. In normal lymphocytes LDLRs were predominantly located in intracellular compartments, whereas in ARH-/- cells the receptors were almost exclusively on the plasma membrane. Biochemical assays and quantification of LDLR by electron microscopy indicated that ARH-/- lymphocytes had >20-fold more LDLR on the cell surface and a approximately 27-fold excess of LDLR outside of coated pits. The accumulation of LDLR on the cell surface was not due to failure of receptors to localize in coated pits since the number of LDLRs in coated pits was similar in ARH-/- and normal cells. Despite the dramatic increase in cell surface receptors, LDL binding was only 2-fold higher in the ARH-/- lymphocytes. These findings indicate that ARH is required not only for internalization of the LDL.LDLR complex but also for efficient binding of LDL to the receptor and suggest that ARH stabilizes the associations of the receptor with LDL and with the invaginating portion of the budding pit, thereby increasing the efficiency of LDL internalization.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Adaptor Proteins, Vesicular Transport/deficiency
- Adaptor Proteins, Vesicular Transport/physiology
- Cell Line, Transformed
- Cell Membrane/chemistry
- Coated Pits, Cell-Membrane/chemistry
- Coated Pits, Cell-Membrane/metabolism
- Endocytosis
- Fluorescent Antibody Technique
- Humans
- Hypercholesterolemia/blood
- Immunohistochemistry
- Iodine Radioisotopes
- Lipoproteins, LDL/blood
- Lymphocytes/ultrastructure
- Microscopy, Electron
- Receptors, LDL/analysis
- Receptors, LDL/blood
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Affiliation(s)
- Peter Michaely
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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21
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Begg MJ, Sturrock ED, van der Westhuyzen DR. Soluble LDL-R are formed by cell surface cleavage in response to phorbol esters. ACTA ACUST UNITED AC 2004; 271:524-33. [PMID: 14728679 DOI: 10.1046/j.1432-1033.2003.03953.x] [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] [Indexed: 11/20/2022]
Abstract
A 140-kDa soluble form of the low density lipoprotein (LDL) receptor has been isolated from the culture medium of HepG2 cells and a number of other cell types. It is produced from the 160-kDa mature LDL receptor by a proteolytic cleavage, which is stimulated in the presence of 4beta-phorbol 12-myristate 13-acetate (PMA), leading to the release of a soluble fragment that constitutes the bulk of the extracellular domain of the LDL receptor. By labeling HepG2 cells with [35S]methionine and chasing in the presence of PMA, we demonstrated that up to 20% of LDL-receptors were released into the medium in a 2-h period. Simultaneously, the level of labeled cellular receptors was reduced by 30% in those cells treated with PMA compared to untreated cells, as was the total number of cell surface LDL-receptors assayed by the binding of 125I-labeled antibody to whole cells. To determine if endocytosis was required for cleavage, internalization-defective LDL-receptors were created by mutagenesis or deletion of the NPXY internalization signal, transfected into Chinese hamster ovary cells, and assayed for cleavage in the presence and absence of PMA. Cleavage was significantly greater in the case of the mutant receptors than for wild-type receptors, both in the absence and presence of PMA. Similar results were seen in human skin fibroblasts homozygous for each of the internalization-defective LDL receptor phenotypes. LDL receptor cleavage was inhibited by the hydoxamate-based inhibitor TAPI, indicating the resemblance of the LDL receptor cleavage mechanism to that of other surface released membrane proteins.
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Affiliation(s)
- Michael J Begg
- Division of Medical Biochemistry, University of Cape Town, South Africa
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22
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Sun XM, Soutar AK. The transmembrane domain and PXXP motifs of ApoE receptor 2 exclude it from carrying out clathrin-mediated endocytosis. J Biol Chem 2003; 278:19926-32. [PMID: 12621059 DOI: 10.1074/jbc.m302047200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low density lipoprotein (LDL) receptor family comprises several proteins with similar structures including the LDL receptor and apoE receptor 2 (apoER2). The human brain expresses two major splice variants of apoER2 mRNA, one of which includes an additional exon that encodes 59 residues in the cytoplasmic domain. This exon is absent from the LDL receptor and contains three proline-rich (PXXP) motifs that may allow apoER2 to function as a signal transducer. To investigate the role of this insert, we took advantage of the well characterized low density lipoprotein receptor pathway. Chimeras comprising the ectodomain and transmembrane domain of the LDL receptor fused to the cytoplasmic domain of apoER2 lacking the PXXP-containing residues are able to mediate clathrin-dependent endocytosis of LDL as effectively as cells expressing the LDL receptor but not if the PXXP insert is present in the protein. Although expressed on the cell surface, the PXXP-containing chimeric receptor is excluded from clathrin vesicles as judged by its failure to co-localize with adaptor protein-2 possibly due to interaction with intracellular adaptors or scaffolding proteins. Chimeras with the transmembrane domain of apoER2, predicted to be longer than that of the LDL receptor by several residues, fail to mediate endocytosis of LDL or to co-localize with adaptor protein-2 regardless of the presence or absence of the PXXP insert. Thus features of apoER2 that distinguish it as a signaling receptor, rather than as an endocytosis receptor like the LDL receptor, reside in or near the transmembrane domain and in the proline-rich motifs.
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Affiliation(s)
- Xi-Ming Sun
- Lipoprotein Group, Medical Research Council Clinical Sciences Centre, Imperial College Faculty of Medicine, London W12 ONN, United Kingdom
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23
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Sachais BS, Kuo A, Nassar T, Morgan J, Kariko K, Williams KJ, Feldman M, Aviram M, Shah N, Jarett L, Poncz M, Cines DB, Higazi AAR. Platelet factor 4 binds to low-density lipoprotein receptors and disrupts the endocytic machinery, resulting in retention of low-density lipoprotein on the cell surface. Blood 2002; 99:3613-22. [PMID: 11986215 DOI: 10.1182/blood.v99.10.3613] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The influence of platelets on the cellular metabolism of atherogenic lipoproteins has not been characterized in detail. Therefore, we investigated the effect of platelet factor 4 (PF4), a cationic protein released in high concentration by activated platelets, on the uptake and degradation of low-density lipoprotein (LDL) via the LDL receptor (LDL-R). LDL-R-dependent binding, internalization, and degradation of LDL by cultured cells were inhibited 50%, 80%, and 80%, respectively, on addition of PF4. PF4 bound specifically to the ligand-binding domain of recombinant soluble LDL-R (half-maximal binding 0.5 microg/mL PF4) and partially (approximately 50%) inhibited the binding of LDL. Inhibition of internalization and degradation by PF4 required the presence of cell-associated proteoglycans, primarily those rich in chondroitin sulfate. PF4 variants with impaired heparin binding lacked the capacity to inhibit LDL. PF4, soluble LDL-R, and LDL formed ternary complexes with cell-surface proteoglycans. PF4 induced the retention of LDL/LDL-R complexes on the surface of human fibroblasts in multimolecular clusters unassociated with coated pits, as assessed by immuno-electron microscopy. These studies demonstrate that PF4 inhibits the catabolism of LDL in vitro in part by competing for binding to LDL-R, by promoting interactions with cell-associated chondroitin sulfate proteoglycans, and by disrupting the normal endocytic trafficking of LDL/LDL-R complexes. Retention of LDL on cell surfaces may facilitate proatherogenic modifications and support an expanded role for platelets in the pathogenesis of atherosclerosis.
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Affiliation(s)
- Bruce S Sachais
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia 19104, USA.
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24
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Lindén D, Alsterholm M, Wennbo H, Oscarsson J. PPARα deficiency increases secretion and serum levels of apolipoprotein B-containing lipoproteins. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31509-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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25
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Jeon H, Shipley GG. Localization of the N-terminal domain of the low density lipoprotein receptor. J Biol Chem 2000; 275:30465-70. [PMID: 10889195 DOI: 10.1074/jbc.m002582200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low density lipoprotein (LDL) receptor is a transmembrane glycoprotein performing "receptor-mediated endocytosis" of cholesterol-rich lipoproteins. At the N terminus, the LDL receptor has modular cysteine-rich repeats in both the ligand binding domain and the epidermal growth factor (EGF) precursor homology domain. Each repeat contains six disulfide-bonded cysteine residues, and this structural motif has also been found in many other proteins. The bovine LDL receptor has been purified and reconstituted into egg yolk phosphatidylcholine vesicle bilayers. Using gel electrophoresis and cryoelectron microscopy (cryoEM), the ability of the reconstituted LDL receptor to bind its ligand LDL has been demonstrated. After reduction of the disulfide-bonds in the N-terminal domain of the receptor, the reduced LDL receptor was visualized using cryoEM; reduced LDL receptors showed images with a diffuse density region at the distal end of the extracellular domain. Gold labeling of the reduced cysteine residues was achieved with monomaleimido-Nanogold, and the bound Nanogold was visualized in cryoEM images of the reduced, gold-labeled receptor. Multiple gold particles were observed in the diffuse density region at the distal end of the receptor. Thus, the location of the ligand binding domain of the LDL receptor has been determined, and a model is suggested for the arrangement of the seven cysteine-rich repeats of the ligand binding domain and two EGF-like cysteine-rich repeats of the EGF precursor homology domain.
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Affiliation(s)
- H Jeon
- Departments of Biophysics and Biochemistry, Center for Advanced Biomedical Research, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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26
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Jeon H, Shipley GG. Vesicle-reconstituted low density lipoprotein receptor. Visualization by cryoelectron microscopy. J Biol Chem 2000; 275:30458-64. [PMID: 10889196 DOI: 10.1074/jbc.m002583200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low density lipoprotein (LDL) receptor is a key protein for maintaining cellular cholesterol homeostasis by binding cholesterol-rich lipoproteins through their apoB and apoE apoproteins. The LDL receptor is a transmembrane glycoprotein of M(r) approximately 115 kDa; based on its primary sequence, five distinct structural domains have been identified (Yamamoto, T., Davis, C. G., Brown, M. S., Schneider, W. J., Casey, M. L., Goldstein, J. L., and Russell, D. W. (1984) Cell 39, 27-38). As a first step toward providing a structural description of the intact LDL receptor, the receptor has been purified from bovine adrenal cortices, reconstituted into unilamellar egg yolk phosphatidylcholine vesicles, and imaged using cryoelectron microscopy (cryoEM). CryoEM has the advantage of providing images of the reconstituted LDL receptor in its frozen, fully hydrated state. LDL receptor molecules were visualized as elongated, stick-like projections from the vesicle surface with maximum dimensions approximately 120-A length by approximately 45-A width. In some of the images, a short arm (or arms) was visible at the distal end of the stick-like projections. The LDL receptor was labeled via accessible free cysteine residues, probably including that corresponding to Cys-431 of the known full-length sequence of the human LDL receptor. The accessible cysteine was demonstrated using a maleimide-biotin.streptavidin conjugate and confirmed by labeling with monomaleimido-Nanogold. Images obtained by cryoEM showed that the extracellular stick-like domain of the reconstituted LDL receptor was labeled by Nanogold. This combined cryoEM-Nanogold labeling study has provided the first low resolution structural images of the reconstituted, full-length bovine LDL receptor.
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Affiliation(s)
- H Jeon
- Departments of Biophysics and Biochemistry, Center for Advanced Biomedical Research, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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27
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Sorci-Thomas MG, Thomas M, Curtiss L, Landrum M. Single repeat deletion in ApoA-I blocks cholesterol esterification and results in rapid catabolism of delta6 and wild-type ApoA-I in transgenic mice. J Biol Chem 2000; 275:12156-63. [PMID: 10766851 DOI: 10.1074/jbc.275.16.12156] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The deletion mutation Delta6 apolipoprotein A-I lacks residues 143-164 or repeat 6 in the mature apoA-I protein. In vitro studies show this mutation dramatically reduces the rate of lecithin:cholesterol acyltransferase (LCAT) catalyzed cholesterol esterification. The present study was initiated to investigate the effect of this mutation on in vivo high density lipoprotein (HDL) cholesterol esterification and metabolism. Transgenic mice expressing human Delta6 apoA-I (TgDelta6 +/+) were created and then crossed with apoA-I knockout mice (-/-) to generate mice expressing only human Delta6 apoA-I (TgDelta6 -/-). Human Delta6 apoA-I was associated with homogeneous sized alpha-HDL, when wild-type mouse apoA-I was present (in TgDelta6 +/+ and +/- mice). However, in the absence of endogenous mouse apoA-I, Delta6 apoA-I was found exclusively in cholesterol ester-poor HDL, and lipid-free HDL fractions. This observation coincides with the 6-fold lower cholesterol ester mass in TgDelta6 -/- mouse plasma compared with control. Structural studies show that despite the structural perturbation of a domain extending from repeat 5 to repeat 8 (137-178), Delta6 apoA-I binds to spherical unilamellar vesicles with only 2-fold less binding affinity. In summary, these data show a domain corresponding to apoA-I repeat 6 is responsible for providing an essential conformation for LCAT catalyzed generation of cholesterol esters. Deletion of apoA-I repeat 6 not only blocks normal levels of cholesterol esterification but also exerts a dominant inhibition on the ability of wild-type apoA-I to activate LCAT in vivo.
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Affiliation(s)
- M G Sorci-Thomas
- Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA.
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28
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Crottet P, Peitsch MC, Servis C, Corthésy B. Covalent homodimers of murine secretory component induced by epitope substitution unravel the capacity of the polymeric Ig receptor to dimerize noncovalently in the absence of IgA ligand. J Biol Chem 1999; 274:31445-55. [PMID: 10531346 DOI: 10.1074/jbc.274.44.31445] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recombinant secretory immunoglobulin A containing a bacterial epitope in domain I of the secretory component (SC) moiety can serve as a mucosal delivery vehicle triggering both mucosal and systemic responses (Corthésy, B., Kaufmann, M., Phalipon, A., Peitsch, M., Neutra, M. R., and Kraehenbuhl, J.-P. (1996) J. Biol. Chem. 271, 33670-33677). To load recombinant secretory IgA with multiple B and T epitopes and extend its biological functions, we selected, based on molecular modeling, five surface-exposed sites in domains II and III of murine SC. Loops predicted to be exposed at the surface of SC domains were replaced with the DYKDDDDK octapeptide (FLAG). Another two mutants were obtained with the FLAG inserted in between domains II and III or at the carboxyl terminus of SC. As shown by mass spectrometry, internal substitution of the FLAG into four of the mutants induced the formation of disulfide-linked homodimers. Three of the dimers and two of the monomers from SC mutants could be affinity-purified using an antibody to the FLAG, mapping them as candidates for insertion. FLAG-induced dimerization also occurred with the polymeric immunoglobulin receptor (pIgR) and might reflect the so-far nondemonstrated capacity of the receptor to oligomerize. By co-expressing in COS-7 cells and epithelial Caco-2 cells two pIgR constructs tagged at the carboxyl terminus with hexahistidine or FLAG, we provide the strongest evidence reported to date that the pIgR dimerizes noncovalently in the plasma membrane in the absence of polymeric IgA ligand. The implication of this finding is discussed in terms of IgA transport and specific antibody response at mucosal surfaces.
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Affiliation(s)
- P Crottet
- Institut Suisse de Recherches, Expérimentales sur le Cancer, CH-1066 Epalinges, Switzerland
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29
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Yoshida H, Yokode M, Yamamoto A, Masaki R, Murayama T, Horiuchi H, Kita T. Compensated endocytosis of LDL by hamster cells co-expressing the two distinct mutant LDL receptors defective in endocytosis and ligand binding. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)32116-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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30
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Kibbey RG, Rizo J, Gierasch LM, Anderson RG. The LDL receptor clustering motif interacts with the clathrin terminal domain in a reverse turn conformation. J Cell Biol 1998; 142:59-67. [PMID: 9660863 PMCID: PMC2133019 DOI: 10.1083/jcb.142.1.59] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/1998] [Revised: 05/29/1998] [Indexed: 02/08/2023] Open
Abstract
Previously the hexapeptide motif FXNPXY807 in the cytoplasmic tail of the LDL receptor was shown to be essential for clustering in clathrin-coated pits. We used nuclear magnetic resonance line-broadening and transferred nuclear Overhauser effect measurements to identify the molecule in the clathrin lattice that interacts with this hexapeptide, and determined the structure of the bound motif. The wild-type peptide bound in a single conformation with a reverse turn at residues NPVY. Tyr807Ser, a peptide that harbors a mutation that disrupts receptor clustering, displayed markedly reduced interactions. Clustering motif peptides interacted with clathrin cages assembled in the presence or absence of AP2, with recombinant clathrin terminal domains, but not with clathrin hubs. The identification of terminal domains as the primary site of interaction for FXNPXY807 suggests that adaptor molecules are not required for receptor-mediated endocytosis of LDL, and that at least two different tyrosine-based internalization motifs exist for clustering receptors in coated pits.
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Affiliation(s)
- R G Kibbey
- Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas, 75235, USA
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31
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Analysis of two duplications of the LDL receptor gene affectingintracellular transport, catabolism, and surface binding of the LDLreceptor. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32528-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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32
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Panzer P, Preuss U, Joberty G, Naim HY. Protein domains implicated in intracellular transport and sorting of lactase-phlorizin hydrolase. J Biol Chem 1998; 273:13861-9. [PMID: 9593732 DOI: 10.1074/jbc.273.22.13861] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The roles of various domains of intestinal lactase-phlorizin hydrolase (pro-LPH) on its folding, dimerization, and polarized sorting are investigated in deletion mutants of the ectodomain fused or not fused with the membrane-anchoring and cytoplasmic domains (MACT). Deletion of 236 amino acids immediately upstream of MACT has no effect on the folding, dimerization, transport competence, or polarized sorting of the mutant LPH1646MACT. By contrast, LPH1646, an anchorless counterpart of LPH1646MACT, is not transported beyond the ER and persists as a mannose-rich monomer during its entire life cycle. The further deletion of 87 amino acids generates a correctly folded but transport-incompetent monomeric LPH1559MACT mutant. The results strongly suggest that dimerization and transport of pro-LPH implicate a stretch of 87 amino acids in the ectodomain between LPH1646MACT and LPH1559MACT. In addition, dimerization of pro-LPH requires at least two further criteria: (i) a correctly folded ectodomain of pro-LPH and (ii) the presence of the transmembrane region. Neither of these requirements alone is sufficient for dimerization. Finally, the sorting of pro-LPH appears to be mediated by signals located between the cleavage site of pro-LPH and the LPH1646MACT mutant.
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Affiliation(s)
- P Panzer
- Protein Secretion Group, Institute of Microbiology, Heinrich Heine University of Düsseldorf, Universitätsstrasse 1, Geb. 26.12.01, D-40225 Düsseldorf, Germany
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33
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Calcium induces a conformational change in the ligand binding domain of the low density lipoprotein receptor. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)33901-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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34
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Berkhout TA, Simon HM, Patel DD, Bentzen C, Niesor E, Jackson B, Suckling KE. The novel cholesterol-lowering drug SR-12813 inhibits cholesterol synthesis via an increased degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. J Biol Chem 1996; 271:14376-82. [PMID: 8662919 DOI: 10.1074/jbc.271.24.14376] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
SR-12813 (tetra-ethyl 2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethenyl-1, 1-bisphosphonate) lowers plasma cholesterol in five species. In this paper we investigate the underlying mechanism using Hep G2 cells. SR-12813 inhibited incorporation of tritiated water into cholesterol with an IC50 of 1.2 microM but had no effect on fatty acid synthesis. Furthermore, SR-12813 reduced cellular 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity with an IC50 of 0.85 microM. The inhibition of HMG-CoA reductase activity was rapid with a T1/2 of 10 min. After a 16-h incubation with SR-12813, mRNA levels of HMG-CoA reductase and low density lipoprotein (LDL) receptor were increased. The increased expression of LDL receptor translated into a higher LDL uptake, which can explain the primary hypocholesterolemic effect of SR-12813 in vivo. Western blot analysis indicated that the amount of HMG-CoA reductase protein rapidly decreased in the presence of SR-12813. Pulse-chase experiments with [35S]methionine showed that the T1/2 of HMG-CoA reductase degradation decreased in the presence of SR-12813 from 90 to 20 min. Pre-incubation with 50 microM of lovastatin did not prevent the effects of SR-12813 on HMG-CoA reductase degradation, indicating that the compound does not need mevalonate-derived regulators for its action. It is concluded that SR-12813 inhibits cholesterol synthesis mainly by an enhanced degradation of HMG-CoA reductase.
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Affiliation(s)
- T A Berkhout
- Department of Vascular Biology, Smithkline Beecham Pharmaceuticals, The Frythe, Welwyn, Herts. AL6 9AR, United Kingdom
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35
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Setiadi H, Disdier M, Green SA, Canfield WM, McEver RP. Residues throughout the cytoplasmic domain affect the internalization efficiency of P-selectin. J Biol Chem 1995; 270:26818-26. [PMID: 7592923 DOI: 10.1074/jbc.270.45.26818] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The cytoplasmic domains of many membrane proteins have short sequences, usually including a tyrosine or a di-leucine, that function as sorting signals. P-selectin is an adhesion receptor for leukocytes that is expressed on activated platelets and endothelial cells. Its 35-residue cytoplasmic domain contains signals for sorting into regulated secretory granules, for endocytosis, and for movement from endosomes to lysosomes. The domain has a membrane-distal sequence, YGVFTNAAF, that resembles some tyrosine-based signals. We studied the effects of deletions and mutations in the cytoplasmic tail of human P-selectin on its internalization in clathrin-coated pits of transfected Chinese hamster ovary cells. Mutations and deletions in the putative tyrosine-based motif did not clearly implicate these residues as critical components of a short internalization signal. Indeed, a construct containing a truncated 18-residue cytoplasmic domain with a single substitution (K761A/H773Stop) was internalized nearly three times as fast as wild-type P-selectin; this construct contained no di-leucine, tyrosine, or other known sorting motif. Substitution of residues throughout the cytoplasmic domain affected the internalization rate of P-selectin. Furthermore, the cytoplasmic domain of P-selectin mediated faster internalization when attached to the extracellular and transmembrane domains of the low density lipoprotein receptor than when attached to the corresponding domains of P-selectin. Thus, we were unable to identify a short internalization signal in the cytoplasmic tail of P-selectin. Residues throughout the cytoplasmic domain, and perhaps the transmembrane sequence to which the domain is attached, affect the efficiency of internalization.
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Affiliation(s)
- H Setiadi
- W. K. Warren Medical Research Institute, Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, USA
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36
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Sass C, Giroux LM, Lussier-Cacan S, Davignon J, Minnich A. Unexpected consequences of deletion of the first two repeats of the ligand-binding domain from the low density lipoprotein receptor. Evidence from a human mutation. J Biol Chem 1995; 270:25166-71. [PMID: 7559651 DOI: 10.1074/jbc.270.42.25166] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Heterozygosity for a 5-kilobase (kb) deletion of the first two ligand-binding repeats (exons 2 and 3) of the low density lipoprotein (LDL) receptor (R) gene (LDL-R delta 5kb) confers familial hypercholesterolemia (FH). The FH phenotype is unexpected based on previous site-directed mutagenesis showing that deletion of exons 2 and 3 resulted in little or no defect in LDL-R activity. In the present study, we took unique advantage of the ability to distinguish the LDL-R delta 5kb from the normal receptor on the basis of size, in order to resolve this apparent discrepancy. Fibroblasts from heterozygotes for the LDL-R delta 5kb displayed 50% of normal capacity to bind LDL and beta-VLDL, apparently due to lower receptor number. Cellular mRNA for the delta 5kb allele was at least as abundant as that for the normal allele. Immunoblotting and cell binding assays with anti-LDL-R antibody IgG-4A4 demonstrated normal synthesis and transport of the delta 5kb receptor. Ligand blotting demonstrated that the delta 5kb receptor displayed minimal or no ability to bind LDL or beta-VLDL. Thus, in contrast to transfected cell lines, in human fibroblasts, the first two cysteine rich repeats of the LDL-R appear functionally necessary. These characteristics of the LDL-R delta 5kb in human fibroblasts explain the in vivo phenotype of carriers.
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Affiliation(s)
- C Sass
- Department of Medicine, University of Montreal, Quebec, Canada
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37
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Sappington TW, Hays AR, Raikhel AS. Mosquito vitellogenin receptor: purification, developmental and biochemical characterization. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 1995; 25:807-817. [PMID: 7633468 DOI: 10.1016/0965-1748(95)00016-o] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Vitellogenin receptors (VgRs) play a critical role in egg development of oviparous animals by mediating endocytosis of the major yolk protein precursor, vitellogenin. A modification of the method for extracting the mosquito (Aedes aegypti) VgR from ovary membranes resulted in an 11-fold higher yield and 56-fold increase in relative purity of the VgR, in turn permitting purification, antibody production, and microsequencing. A Kd of 15 nM was estimated from binding assays for the enriched VgR, indicating a very high affinity for its ligand. Immunoprecipitation of [14C]VgR using anti-VgR polyclonal antibodies followed by SDS-PAGE under reducing conditions and fluorography demonstrated that the 205 kDa VgR does not consist of subunits held together with disulfide bonds. However, an immunoblot of the native VgR suggests that it exists as an approximately 390 kDa noncovalent homodimer in its native state. Immunoblot assays confirmed that the VgR is present only in ovarian tissue. A quantitative immunoassay of VgR extracts showed that VgR was present in previtellogenic ovaries on the day of emergence, increasing from 2 ng to more than 10 ng per ovary by day 5. After initiation of vitellogenesis and onset of Vg uptake, VgR quantity increased rapidly between 8 and 24 h after a blood meal, then began to decline between 24 and 36 h. Immunocytochemistry confirmed the presence of substantial amounts of the VgR in 4-day-old previtellogenic oocytes. In both previtellogenic and vitellogenic ovaries, the VgR was present only in the oocyte, primarily in the cortex.
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Affiliation(s)
- T W Sappington
- Department of Entomology, Michigan State University, East Lansing 48824, USA
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38
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Krupenko SA, Kolesnik OI, Krupenko NI, Strel'chyonok OA. Organization of the transcortin-binding domain on placental plasma membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1235:387-94. [PMID: 7756349 DOI: 10.1016/0005-2736(95)80028-e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Complex formation between transcortin (corticosteroid-binding globulin) and 20 kDa sialoglycoprotein from human syncytiotrophoblast plasma membranes (presumably a transcortin-recognizing subunit of the transcortin membrane receptor) was studied using FPLC and cross-linking with bifunctional reagents. The action of 1,5-difluoro-2,4-dinitrobenzene (DFDNB) on a solution of the purified 20 kDa sialoglycoprotein and transcortin resulted in formation of covalently linked complexes of 95 kDa and 140 kDa consisting of one transcortin molecule and either two or four molecules of the membrane sialoglycoprotein (the molecular mass of transcortin is 55 kDa). Additionally, cross-linking resulted in the appearance of a 43 kDa species which is the cross-linked dimer of the membrane protein. The dimer was also observed during chromatography on a Superose 12 column in the absence of DFDNB treatment. Treatment of intact syncytiotrophoblast membranes with DFDNB resulted in isolation of the transcortin binding protein dimer as the major portion of total pool of the protein. Formation of the transcortin complexes with two and four molecules of the membrane protein was also observed when the membranes were incubated with 125I-labeled transcortin and treated with DFDNB, but formation of the latter complexes predominated. The results obtained suggest that the recognizing and binding domain for transcortin in placental membranes is organized as dimers consisting of non-covalently linked sialoglycoprotein monomers of a 20 kDa each and that transcortin has two sites for interaction with this dimer. Apparently, binding of two dimers results in the formation of the functional form of the transcortin-receptor complex. The possible biological role of such a complex is discussed.
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Affiliation(s)
- S A Krupenko
- Institute of Biorganic Chemistry, Byelorussian Academy of Sciences, Minsk, Belarus
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39
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Patel DD, Soutar AK, Knight BL. Abnormal structure and co-operative binding of low-density lipoprotein receptors containing the Glu-80-->Lys mutation. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1255:285-92. [PMID: 7734445 DOI: 10.1016/0005-2760(94)00243-r] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The properties of low-density lipoprotein (LDL) receptors containing a Glu to Lys substitution at position 80 have been studied in fibroblasts from a homozygous familial hypercholesterolaemic subject (MB) and in monkey COS cells transfected with the mutant cDNA. Receptors containing the Glu-80-->Lys mutation were processed more slowly than the normal protein and only approx. 50% reached the surface as the mature form. Both cell types exhibited a normal concentration binding curve for beta-very-low-density lipoproteins (beta-VLDL) but an atypical, sigmoidal curve for LDL. The mature mutant receptor protein migrated abnormally slowly on SDS-PAGE under non-reducing conditions but normally under reducing conditions or after treatment with neuraminidase. It also showed an unusual ability to form dimers that were stable in detergents. Transfected normal and mutant receptors were apparently cleaved on the surface of the cells to give a product lacking the NH2-terminal portion of the protein, which was resistant to further proteolytic digestion. The results suggest that the Glu-80-->Lys substitution produces a change in the conformation of the protein, stabilized by polysaccharide chains, which results in a strong self-association of receptor molecules that affects their ability to bind LDL.
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Affiliation(s)
- D D Patel
- Medical Research Council Clinical Sciences Centre, Royal Postgraduate Medical School, Hammersmith Hospital, London, UK
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40
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Partial duplication of the EGF precursor homology domain of the LDL-receptor protein causing familial hypercholesterolemia (FH-Salerno). J Lipid Res 1994. [DOI: 10.1016/s0022-2275(20)40083-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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41
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Jensen HK, Jensen TG, Jensen LG, Hansen PS, Kjeldsen M, Andresen BS, Nielsen V, Meinertz H, Hansen AB, Bolund L. Characterization of a disease-causing Glu119-Lys mutation in the low-density lipoprotein receptor gene in two Danish families with heterozygous familial hypercholesterolemia. Hum Mutat 1994; 4:102-13. [PMID: 7981713 DOI: 10.1002/humu.1380040203] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Mutations in the gene for the low-density lipoprotein receptor (LDL receptor) cause the autosomal dominant inherited disease familial hypercholesterolemia (FH). In 15 Danish patients with heterozygous FH we have screened exon 4 of the LDL receptor gene for point mutations and small rearrangements employing genomic DNA amplification and bidirectional solid-phase sequencing. Two subjects were found to be heterozygous for a guanine to adenine base substitution at nucleotide position 418 of the LDL receptor cDNA. This point mutation results in an amino acid change from glutamic acid to lysine at amino acid residue 119 in the third repeat of the cysteine-rich ligand binding domain of the mature LDL receptor. Disruption of LDL receptor function by the Glu119-Lys mutation was confirmed by site-directed mutagenesis and expression in COS-7 cells. By Western blotting the mutation was found to affect the processing of the LDL receptor protein. Using flow cytometric analysis of the transfected cells a decreased binding and internalization of LDL by the mutant receptor was documented. By means of a mutation-specific PCR-based assay the Glu119-Lys mutation was not detected in another 85 apparently unrelated Danish heterozygous FH patients. We identified six persons in the index families with the Glu119-Lys mutation cosegregating with the clinical syndrome of FH in these families. Furthermore, haplotype analysis revealed that the haplotype [SfaNI+, StuI+, AvaII-, (dTA)7] of the mutation carrying allele was the same in the two apparently unrelated patients. This indicates that the mutation has been inherited from a common ancestor.
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Affiliation(s)
- H K Jensen
- Center for Medical Molecular Biology, Aarhus University Hospital, Skejby Sygehus, Denmark
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42
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Sun XM, Patel DD, Webb JC, Knight BL, Fan LM, Cai HJ, Soutar AK. Familial hypercholesterolemia in China. Identification of mutations in the LDL-receptor gene that result in a receptor-negative phenotype. ARTERIOSCLEROSIS AND THROMBOSIS : A JOURNAL OF VASCULAR BIOLOGY 1994; 14:85-94. [PMID: 7903864 DOI: 10.1161/01.atv.14.1.85] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Familial hypercholesterolemia (FH), caused by many different mutations in the low-density lipoprotein (LDL)-receptor gene, invariably leads to severe premature coronary heart disease (CHD) in homozygous individuals. Heterozygous FH patients are less severely affected but are still at increased risk of CHD in most populations. Although FH homozygotes in China are affected similarly to those elsewhere, heterozygotes are not detected in the general population and obligate heterozygotes are often not hypercholesterolemic by Western standards. Mutations in the LDL-receptor genes of 10 homozygous FH patients from the Jiang-su province of China and their heterozygous parents were analyzed. These include one large and two minor deletions and eight point mutations: four are predicted to introduce a premature stop codon, five to result in a single amino acid substitution or deletion, and one to produce a protein with an abnormal cytoplasmic tail. Expression of the mutant LDL-receptor cDNAs in vitro confirmed that these mutations impaired LDL-receptor function and that several would cause a receptor-negative phenotype. Thus, the lack of clinical expression in obligate FH heterozygotes is not due to unusually "mild" mutations in the LDL-receptor gene, and other genetic or environmental factors must therefore be important in determining phenotypic expression.
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Affiliation(s)
- X M Sun
- MRC Lipoprotein Team, Hammersmith Hospital, London, UK
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43
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Chappell DA, Fry GL, Waknitz MA, Muhonen LE, Pladet MW. Low density lipoprotein receptors bind and mediate cellular catabolism of normal very low density lipoproteins in vitro. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)74418-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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44
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Feher MD, Webb JC, Patel DD, Lant AF, Mayne PD, Knight BL, Soutar AK. Cholesterol-lowering drug therapy in a patient with receptor-negative homozygous familial hypercholesterolaemia. Atherosclerosis 1993; 103:171-80. [PMID: 8292093 DOI: 10.1016/0021-9150(93)90260-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Familial hypercholesterolaemia (FH) is caused by mutations in the gene for the low density lipoprotein (LDL) receptor. It is generally believed that homozygous FH patients do not respond well to lipid-lowering drug therapy with inhibitors of 3-hydroxy-3-methylglutaryl CoA reductase because they cannot respond to an increased demand for hepatic cholesterol by up-regulation of LDL-receptor activity. In this paper we show that serum cholesterol in a homozygous FH patient with a receptor-negative LDL-receptor phenotype was reduced by 30% after treatment with simvastatin alone and by a further 11% with simvastatin in combination with probucol and nicotinic acid. The patient was a true homozygote, with two identical alleles of the LDL receptor gene in which a previously undescribed point mutation in exon 11 introduces a premature termination codon at residue 540 in the protein; the mutant protein is predicted to be truncated in the domain with homology to the epidermal growth factor precursor. Cultured cells from the patient were unable to bind, internalise or degrade LDL by the receptor pathway and there was no immunodetectable LDL receptor protein in the cells. Thus the lipid lowering effect of simvastatin in this individual must involve mechanisms other than stimulation of LDL receptors.
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Affiliation(s)
- M D Feher
- Department of Academic Therapeutics, Chelsea and Westminster Hospital, London, UK
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45
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Fourie AM, Coetzee GA, Gevers W, van der Westhuyzen DR. Low-density lipoprotein receptor point mutation results in expression of both active and inactive surface forms of the same mutant receptor. Biochemistry 1992; 31:12754-9. [PMID: 1463746 DOI: 10.1021/bi00166a007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
LDL receptors, expressed in cultured fibroblasts from patients homozygous for the FH Afrikaner-1 (FH1) mutation (Asp206 to Glu), are transported from the endoplasmic reticulum (ER) to the Golgi apparatus more slowly than in normal cells. In the present study, binding characteristics of FH1 cells for lipoprotein ligands (LDL and beta VLDL) and for receptor-specific monoclonal antibodies pointed to the existence of two surface forms of the same mutant receptor. One of these forms bound lipoproteins with normal high affinity whereas another did not. Binding studies of transfected hamster cells expressing only the mutant human gene confirmed the single-gene origin of the different forms. The existence of functionally distinct forms of the receptor protein was supported by the observation that only lipoprotein-binding receptor molecules were trapped intracellularly and degraded following ammonium chloride treatment of cells in the presence of ligand. The lipoprotein-binding receptor population was indistinguishable from normal receptors with respect to its affinity for LDL and beta VLDL, uptake and degradation of lipoprotein, and receptor recycling. Ligand blotting versus immunoblotting of receptors revealed normal-sized mutant receptors that were not recognized by lipoprotein ligand. Despite these differences, both mutant forms of the receptor were degraded at rates similar to those of normal receptors. We propose that the single amino acid substitution in this receptor interferes with the folding and/or posttranslational processing of precursor molecules in such a way that receptors adopt alternative stable structures.
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Affiliation(s)
- A M Fourie
- Department of Medical Biochemistry, University of Cape Town Medical School, South Africa
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46
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Matter K, Hunziker W, Mellman I. Basolateral sorting of LDL receptor in MDCK cells: the cytoplasmic domain contains two tyrosine-dependent targeting determinants. Cell 1992; 71:741-53. [PMID: 1423629 DOI: 10.1016/0092-8674(92)90551-m] [Citation(s) in RCA: 298] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
In MDCK cells, transport of membrane proteins to the basolateral plasma membrane has been shown to require a distinct cytoplasmic domain determinant. Although the determinant is often related to signals used for localization in clathrin-coated pits, inactivation of the coated pit domain in the human LDL receptor did not affect basolateral targeting. By expressing mutant and chimeric LDL receptors, we have now identified two independently acting signals that are individually sufficient for basolateral targeting. The two determinants mediate basolateral sorting with different efficiencies, but both contain tyrosine residues critical for activity. The first determinant was colinear with, but distinct from, the coated pit domain of the receptor. The second was found in the C-terminal region of the cytoplasmic domain of the receptor and, although tyrosine-dependent, did not mediate endocytosis. The results suggest that membrane proteins can have functionally redundant signals for basolateral transport and that a tyrosine-containing motif may be a common feature of multiple intracellular sorting events.
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Affiliation(s)
- K Matter
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510
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47
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Characterization of two new point mutations in the low density lipoprotein receptor genes of an English patient with homozygous familial hypercholesterolemia. J Lipid Res 1992. [DOI: 10.1016/s0022-2275(20)41433-6] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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