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Hayes AJ, Melrose J. Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity. Biomolecules 2020; 10:E1244. [PMID: 32867198 PMCID: PMC7564073 DOI: 10.3390/biom10091244] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 08/19/2020] [Accepted: 08/23/2020] [Indexed: 02/06/2023] Open
Abstract
This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.
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Affiliation(s)
- Anthony J Hayes
- Bioimaging Research Hub, Cardiff School of Biosciences, Cardiff University, Cardiff CF10 3AX, Wales, UK
| | - James Melrose
- Raymond Purves Laboratory, Institute of Bone and Joint Research, Kolling Institute of Medical Research, Northern Sydney Local Health District, Royal North Shore Hospital, St. Leonards 2065, NSW, Australia
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney 2052, NSW, Australia
- Sydney Medical School, Northern, The University of Sydney, Faculty of Medicine and Health at Royal North Shore Hospital, St. Leonards 2065, NSW, Australia
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2
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Xu M, Stattin EL, Shaw G, Heinegård D, Sullivan G, Wilmut I, Colman A, Önnerfjord P, Khabut A, Aspberg A, Dockery P, Hardingham T, Murphy M, Barry F. Chondrocytes Derived From Mesenchymal Stromal Cells and Induced Pluripotent Cells of Patients With Familial Osteochondritis Dissecans Exhibit an Endoplasmic Reticulum Stress Response and Defective Matrix Assembly. Stem Cells Transl Med 2016; 5:1171-81. [PMID: 27388238 DOI: 10.5966/sctm.2015-0384] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 03/16/2016] [Indexed: 11/16/2022] Open
Abstract
UNLABELLED : Familial osteochondritis dissecans (FOCD) is an inherited skeletal defect characterized by the development of large cartilage lesions in multiple joints, short stature, and early onset of severe osteoarthritis. It is associated with a heterozygous mutation in the ACAN gene, resulting in a Val-Met replacement in the C-type lectin domain of aggrecan. To understand the cellular pathogenesis of this condition, we studied the chondrogenic differentiation of patient bone marrow mesenchymal stromal cells (BM-MSCs). We also looked at cartilage derived from induced pluripotent stem cells (iPSCs) generated from patient fibroblasts. Our results revealed several characteristics of the differentiated chondrocytes that help to explain the disease phenotype and susceptibility to cartilage injury. First, patient chondrogenic pellets had poor structural integrity but were rich in glycosaminoglycan. Second, it was evident that large amounts of aggrecan accumulated within the endoplasmic reticulum of chondrocytes differentiated from both BM-MSCs and iPSCs. In turn, there was a marked absence of aggrecan in the extracellular matrix. Third, it was evident that matrix synthesis and assembly were globally dysregulated. These results highlight some of the abnormal aspects of chondrogenesis in these patient cells and help to explain the underlying cellular pathology. The results suggest that FOCD is a chondrocyte aggrecanosis with associated matrix dysregulation. The work provides a new in vitro model of osteoarthritis and cartilage degeneration based on the use of iPSCs and highlights how insights into disease phenotype and pathogenesis can be uncovered by studying differentiation of patient stem cells. SIGNIFICANCE The isolation and study of patient stem cells and the development of methods for the generation of iPSCs have opened up exciting opportunities in understanding causes and exploring new treatments for major diseases. This technology was used to unravel the cellular phenotype in a severe form of inherited osteoarthritis, termed familial osteochondritis dissecans. The phenotypic abnormalities that give rise to cartilage lesions in these patients were able to be described via the generation of chondrocytes from bone marrow-derived mesenchymal stromal cells and iPSCs, illustrating the extraordinary value of these approaches in disease modeling.
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Affiliation(s)
- Maojia Xu
- Regenerative Medicine Institute, National University of Ireland Galway, Galway, Ireland
| | - Eva-Lena Stattin
- Department of Immunology, Genetics, and Pathology, Science for Life Laboratory, Uppsala University, Uppsala, Sweden
| | - Georgina Shaw
- Regenerative Medicine Institute, National University of Ireland Galway, Galway, Ireland
| | - Dick Heinegård
- Department of Clinical Sciences, Rheumatology, and Molecular Skeletal Biology, Lund University, Lund, Sweden
| | | | - Ian Wilmut
- Medical Research Council Centre for Regenerative Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Alan Colman
- A*STAR Institute of Medical Biology, Singapore
| | - Patrik Önnerfjord
- Department of Clinical Sciences, Rheumatology, and Molecular Skeletal Biology, Lund University, Lund, Sweden
| | - Areej Khabut
- Department of Clinical Sciences, Rheumatology, and Molecular Skeletal Biology, Lund University, Lund, Sweden
| | - Anders Aspberg
- Department of Clinical Sciences, Rheumatology, and Molecular Skeletal Biology, Lund University, Lund, Sweden
| | - Peter Dockery
- Anatomy, School of Medicine, National University of Ireland Galway, Galway, Ireland
| | - Timothy Hardingham
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences University of Manchester, Manchester, United Kingdom
| | - Mary Murphy
- Regenerative Medicine Institute, National University of Ireland Galway, Galway, Ireland
| | - Frank Barry
- Regenerative Medicine Institute, National University of Ireland Galway, Galway, Ireland
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Jowitt TA, Murdoch AD, Baldock C, Berry R, Day JM, Hardingham TE. Order within disorder: aggrecan chondroitin sulphate-attachment region provides new structural insights into protein sequences classified as disordered. Proteins 2011; 78:3317-27. [PMID: 20806220 PMCID: PMC3546398 DOI: 10.1002/prot.22839] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Structural investigation of proteins containing large stretches of sequences without predicted secondary structure is the focus of much increased attention. Here, we have produced an unglycosylated 30 kDa peptide from the chondroitin sulphate (CS)-attachment region of human aggrecan (CS-peptide), which was predicted to be intrinsically disordered and compared its structure with the adjacent aggrecan G3 domain. Biophysical analyses, including analytical ultracentrifugation, light scattering, and circular dichroism showed that the CS-peptide had an elongated and stiffened conformation in contrast to the globular G3 domain. The results suggested that it contained significant secondary structure, which was sensitive to urea, and we propose that the CS-peptide forms an elongated wormlike molecule based on a dynamic range of energetically equivalent secondary structures stabilized by hydrogen bonds. The dimensions of the structure predicted from small-angle X-ray scattering analysis were compatible with EM images of fully glycosylated aggrecan and a partly glycosylated aggrecan CS2-G3 construct. The semiordered structure identified in CS-peptide was not predicted by common structural algorithms and identified a potentially distinct class of semiordered structure within sequences currently identified as disordered. Sequence comparisons suggested some evidence for comparable structures in proteins encoded by other genes (PRG4, MUC5B, and CBP). The function of these semiordered sequences may serve to spatially position attached folded modules and/or to present polypeptides for modification, such as glycosylation, and to provide templates for the multiple pleiotropic interactions proposed for disordered proteins. Proteins 2010. © 2010 Wiley-Liss, Inc.
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Affiliation(s)
- Thomas A Jowitt
- Wellcome Trust Centre for Cell Matrix Research, University of Manchester, Manchester, M13 9PT, United Kingdom.
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4
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Miwa HE, Gerken TA, Huynh TD, Flory DM, Hering TM. Mammalian expression of full-length bovine aggrecan and link protein: formation of recombinant proteoglycan aggregates and analysis of proteolytic cleavage by ADAMTS-4 and MMP-13. Biochim Biophys Acta Gen Subj 2005; 1760:472-86. [PMID: 16427204 DOI: 10.1016/j.bbagen.2005.12.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2005] [Revised: 12/01/2005] [Accepted: 12/04/2005] [Indexed: 11/18/2022]
Abstract
Aggrecan, a large chondroitin sulfate (CS) and keratan sulfate (KS) proteoglycan, has not previously been expressed as a full-length recombinant molecule. To facilitate structure/function analysis, we have characterized recombinant bovine aggrecan (rbAgg) and link protein expressed in COS-7 cells. We demonstrate that C-terminally truncated rbAgg was not secreted. Gel filtration chromatography of rbAgg and isolated glycosaminoglycan (GAG) chains, and their susceptibility to chondroitinase ABC digestion indicate that the GAG chains are predominantly CS, which likely occupy fewer serine residues than native aggrecan. To confirm functionality, we determined that rbAgg bound hyaluronan and recombinant link protein to form proteoglycan aggregates. In addition, cleavage of rbAgg by ADAMTS-4 revealed that the p68 form of ADAMTS-4 preferentially cleaves within the CS-2 domain, whereas the p40 form only effectively cleaves within the interglobular domain (IGD). MMP-13 cleaved rbAgg within the IGD, but cleaved more rapidly at a site within the CS domains, suggesting a role in C-terminal processing of aggrecan. Our results demonstrate that recombinant aggrecan can be used for in vitro analyses of matrix protease-dependent degradation of aggrecan in the IGD and CS domains, and both recombinant aggrecan and link protein can be used to study the assembly of proteoglycan aggregates with hyaluronan.
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Affiliation(s)
- Hazuki E Miwa
- Department of Biochemistry, Case Western Reserve University, Cleveland, OH 44106, USA
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Seo NS, Hocking AM, Höök M, McQuillan DJ. Decorin core protein secretion is regulated by N-linked oligosaccharide and glycosaminoglycan additions. J Biol Chem 2005; 280:42774-84. [PMID: 16258169 DOI: 10.1074/jbc.m511531200] [Citation(s) in RCA: 28] [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
Expression of decorin using the vaccinia virus/T7 expression system resulted in secretion of two distinct glycoforms: a proteoglycan substituted with a single chondroitin sulfate chain and N-linked oligosaccharides and a core protein glycoform substituted with N-linked glycans but without a glycosaminoglycan chain. In this report, we have addressed two distinct questions. What is the rate-limiting step in glycosaminoglycan synthesis? Is glycosylation with either N-linked oligosaccharides or glycosaminoglycan required for secretion of decorin? N-terminal sequencing of the core protein glycoform, the addition of benzyl-beta-d-xyloside, and a UDP-xylose: core protein beta-d-xylosyltransferase activity assay show that xylosylation is a rate-limiting step in chondroitin sulfate biosynthesis. Decorin can be efficiently secreted with N-linked oligosaccharides alone or with a single chondroitin sulfate chain alone; however, there is severely impaired secretion of core protein devoid of any glycosylation. A decorin core protein mutant devoid of N-linked oligosaccharide attachment sites will not be secreted by Chinese hamster ovary cells deficient in xylosyltransferase or by parental Chinese hamster ovary wild type cells if the xylosyltransferase recognition sequence is disrupted. This finding suggests that quality control mechanisms sensitive to an absence of N-linked oligosaccharides can be abrogated by interaction of the core protein with the glycosaminoglycan synthetic machinery. We propose a model of regulation of decorin secretion that has several components, including appropriate substitution with N-linked oligosaccharides and factors involved in glycosaminoglycan synthesis.
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Affiliation(s)
- Neung-Seon Seo
- Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, Texas 77030, USA.
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6
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Gupta PK, Sharma S, Walunj SS, Chaturvedi VK, Raut AA, Patial S, Rai A, Pandey KD, Saini M. Immunogenic and antigenic properties of recombinant soluble glycoprotein of rabies virus. Vet Microbiol 2005; 108:207-14. [PMID: 15916870 DOI: 10.1016/j.vetmic.2005.04.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2004] [Revised: 03/09/2005] [Accepted: 04/07/2005] [Indexed: 11/21/2022]
Abstract
Rabies virus glycoprotein is a type I transmembrane protein exposed on the surface on the mature virus particle that induces virus neutralizing antibodies. In the present study, 60 amino acid C-terminal hydrophobic anchor (transmembrane) and cytoplasmic domains of glycoprotein were deleted from full-length glycoprotein and fused with polyhistidine tag. The N-terminal viral signal peptide was also replaced with CD33 signal peptide for efficient secretion in mammalian cells. Following transfection of Madin Darby bovine kidney (MDBK) cells with plasmid encoding this soluble form of glycoprotein, polyclonal populations of stably transfected resistant cells were obtained after G418 selection. The protein was expressed as a glycosylated protein and secreted outside the cells utilizing N-terminal CD33 signal peptide. The secreted soluble glycoprotein was purified from cell culture supernatant by Ni--agarose affinity chromatography utilizing C-terminal polyhistidine tag. Like full-length glycoprotein, the expressed recombinant soluble glycoprotein was found to be immunogenic when injected in rabbits. In this study, we have assessed the potential of recombinant soluble glycoprotein as diagnostic antigen in ELISA and found that this recombinant protein can be used as diagnostic antigen in ELISA for detecting anti-glycoprotein antibodies in immunized host.
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Affiliation(s)
- Praveen K Gupta
- National Biotechnology Centre, Indian Veterinary Research Institute, Izatnagar, 243122 UP, India.
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Day JM, Olin AI, Murdoch AD, Canfield A, Sasaki T, Timpl R, Hardingham TE, Aspberg A. Alternative splicing in the aggrecan G3 domain influences binding interactions with tenascin-C and other extracellular matrix proteins. J Biol Chem 2004; 279:12511-8. [PMID: 14722076 DOI: 10.1074/jbc.m400242200] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The proteoglycans aggrecan, versican, neurocan, and brevican bind hyaluronan through their N-terminal G1 domains, and other extracellular matrix proteins through the C-type lectin repeat in their C-terminal G3 domains. Here we identify tenascin-C as a ligand for the lectins of all these proteoglycans and map the binding site on the tenascin molecule to fibronectin type III repeats, which corresponds to the proteoglycan lectin-binding site on tenascin-R. In the G3 domain, the C-type lectin is flanked by epidermal growth factor (EGF) repeats and a complement regulatory protein-like motif. In aggrecan, these are subject to alternative splicing. To investigate if these flanking modules affect the C-type lectin ligand interactions, we produced recombinant proteins corresponding to aggrecan G3 splice variants. The G3 variant proteins containing the C-type lectin showed different affinities for various ligands, including tenascin-C, tenascin-R, fibulin-1, and fibulin-2. The presence of an EGF motif enhanced the affinity of interaction, and in particular the splice variant containing both EGF motifs had significantly higher affinity for ligands, such as tenascin-R and fibulin-2. The mRNA for this splice variant was shown by reverse transcriptase-PCR to be expressed in human chondrocytes. Our findings suggest that alternative splicing in the aggrecan G3 domain may be a mechanism for modulating interactions and extracellular matrix assembly.
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Affiliation(s)
- Joanna M Day
- The Wellcome Trust Centre for Cell Matrix Research, School of Biological Sciences, University of Manchester, Manchester M13 9PT, United Kingdom
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8
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Lee V, Chen L, Paiwand F, Cao L, Wu Y, Inman R, Adams ME, Yang BB. Cleavage of the carboxyl tail from the G3 domain of aggrecan but not versican and identification of the amino acids involved in the degradation. J Biol Chem 2002; 277:22279-88. [PMID: 11932252 DOI: 10.1074/jbc.m110227200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Aggrecan, a major structural proteoglycan in cartilage, contains three globular domains, G1, G2, and G3, as well as sequences for glycosaminoglycan modification. A large number of proteases are implicated in aggrecan cleavage in normal metabolism, aging, and arthritis. These proteases are known to cleave at the IGD, KS, and CS domains. Here we report for the first time evidence of cleavage at a novel site, the carboxyl tail of aggrecan. Results from deletion mutants of the tail indicated that the likely cleavage sites were two consensus sequences, RRLXK and RSPR, present in the aggrecan analogs of many species. This was confirmed by site-directed mutagenesis. A construct containing two G3 domains (G3G3) was also found to cleave between the G3 duplicates. When G3 tail was linked to a glycosaminoglycan-modifying sequence, it was protected from cleavage. Furin inhibitor also reduced the levels of tail cleavage. The carboxyl tails of chicken and human versican were not cleaved, despite the presence of the consensus sequence. Our studies indicate that the basic amino acids present in the tail play an important role in cleavage, and this mechanism is specific to aggrecan.
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Affiliation(s)
- Vivian Lee
- Sunnybrook & Women's College Health Sciences Centre, the Department of Laboratory Medicine and Pathobiology, University of Toronto, Ontario M4N 3M5, Canada
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9
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Wu Y, Chen L, Zheng PS, Yang BB. beta 1-Integrin-mediated glioma cell adhesion and free radical-induced apoptosis are regulated by binding to a C-terminal domain of PG-M/versican. J Biol Chem 2002; 277:12294-301. [PMID: 11805102 DOI: 10.1074/jbc.m110748200] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Integrins are cell-surface glycoproteins that mediate cell activities, including tissue morphogenesis, development, immune response, and cancer, through interaction with extracellular proteins. Here we report a novel means by which integrin signaling and functions are regulated. In pull-down assays and immunoprecipitation, beta(1)-integrin bound to the C-terminal domain of PG-M/versican, an extracellular chondroitin sulfate proteoglycan. This was confirmed by cell-surface binding assays. Binding was calcium- and manganese-dependent. Upon native gel electrophoresis, beta(1)-integrin comigrated with the C-terminal domain of PG-M/versican. The interaction of beta(1)-integrin with the C-terminal domain of PG-M/versican activated focal adhesion kinase, enhanced integrin expression, and promoted cell adhesion. As a result, cells expressing the C-terminal domain of PG-M/versican were resistant to free radical-induced apoptosis. As the PG-M/versican peptide used in this study does not contain the RGD consensus-binding motif for integrins, the mechanism of the observed binding represents an entirely new function.
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Affiliation(s)
- Yaojiong Wu
- Sunnybrook and Women's College Health Sciences Centre and the Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario M4N 3M5, Canada
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Chen L, Wu Y, Lee V, Kiani C, Adams ME, Yao Y, Yang BB. The folded modules of aggrecan G3 domain exert two separable functions in glycosaminoglycan modification and product secretion. J Biol Chem 2002; 277:2657-65. [PMID: 11714693 DOI: 10.1074/jbc.m101153200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Aggrecan is the major proteoglycan in the extracellular matrix of cartilage. A notable exception is nanomelic cartilage, which lacks aggrecan in its matrix. The example of nanomelia and other evidence leads us to believe that the G3 domain plays an important role in aggrecan processing, and it has indeed been confirmed that G3 allows glycosaminoglycan (GAG) chain attachment and product secretion. However, it is not clear how G3, which contains at least a carbohydrate recognition domain (CRD) and a complement binding protein (CBP) motif, plays these two functional roles. The present study was designed to dissect the mechanisms of this phenomenon and specially 1) to determine the effects of various cysteine residues in GAG modification and product secretion as well as 2) to investigate which of the two processing events is the critical step in the product processing. Our studies demonstrated that removal of the two amino-terminal cysteines in the CRD motif and the single cysteine in the amino terminus of CBP inhibited secretion of CRD and CBP. Use of the double mutant CRD construct also allowed us to observe a deviation from the usual strict coupling of GAG modification and product secretion steps. The presence of a small chondroitin sulfate fragment overcame the secretion-inhibitory effects once the small chondroitin sulfate fragment was modified by GAG.
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Affiliation(s)
- Liwen Chen
- Sunnybrook and Women's College Health Sciences Centre and Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto M4N 3M5, Canada
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Chen TL, Wang PY, Luo W, Gwon SS, Flay NW, Zheng J, Guo C, Tanzer ML, Vertel BM. Aggrecan domains expected to traffic through the exocytic pathway are misdirected to the nucleus. Exp Cell Res 2001; 263:224-35. [PMID: 11161721 DOI: 10.1006/excr.2000.5093] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In this article, we report the misdirected targeting of expressed aggrecan domains. Aggrecan, the chondroitin sulfate (CS) proteoglycan of cartilage, normally progresses through the exocytic pathway. Proteins expressed from constructs containing the putative aggrecan signal sequence (i.e., the first 23 N-terminal amino acids), specified globular (G) domains G1 and/or G3, and a segment of the CS domain were detected in the endoplasmic reticulum (ER) and Golgi complex. Although proteins expressed from constructs containing the putative signal and G3, but lacking G1, were detected to a limited extent in the secretory pathway, they primarily accumulated in nuclei. Discrete nuclear inclusions were seen when G3 was expressed. Immunoelectron microscopic characterization of the inclusions suggested the association of nuclear G3 with other proteins. When signal-free G3 constructs and those with G3 immediately following the N-terminal signal were expressed, abundant dispersed accumulations filled the nucleoplasm. The data suggest first, that signal-free and signal-containing G3 proteins enter the nucleus from the cytosol, and second, that the entry of signal-containing G3 proteins into the ER lumen is inefficient. Hsp25, Hsp70, and ubiquitin were colocalized with nuclear G3, indicating the involvement of chaperones and the degradative machinery in the formation and/or attempted disposal of the abnormal nuclear inclusions. Overall, the results focus attention on (1) intracellular protein trafficking at the ER membrane and the nuclear envelope and (2) chaperone interactions and mechanisms leading to abnormal protein deposition in the nucleus.
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Affiliation(s)
- T L Chen
- Department of Cell Biology & Anatomy, FUHS/The Chicago Medical School, North Chicago, Illinois, 60064, USA
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Kiani C, Lee V, Cao L, Chen L, Wu Y, Zhang Y, Adams ME, Yang BB. Roles of aggrecan domains in biosynthesis, modification by glycosaminoglycans and product secretion. Biochem J 2001; 354:199-207. [PMID: 11171095 PMCID: PMC1221644 DOI: 10.1042/0264-6021:3540199] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Aggrecan is a member of the chondroitin sulphate (CS) proteoglycan family, which also includes versican/PG-M, neurocan and brevican. Members of this family exhibit structural similarity: a G1 domain at the N-terminus and a G3 domain at the C-terminus, with a central sequence for modification by CS chains. A unique feature of aggrecan is the insertion of three additional domains, an inter-globular domain (IGD), a G2 domain and a keratan sulphate (KS) domain (sequence modified by KS chains), between the G1 domain and the CS domain (sequence modified by CS chains). The G1 and G3 domains have been implicated in product secretion, but G2, although structurally similar to the tandem repeats of G1, performs an unknown function. To define the functions of each aggrecan domain in product processing, we cloned and expressed these domains in various combinations in COS-7 cells. The results indicated that the G3 domain enhanced product secretion, alone or in combination with the KS or CS domain, and promoted glycosaminoglycan (GAG) chain attachment. Constructs containing the G1 domain were not secreted. Addition of a CS domain sequence to G1 reduced this inhibition, but GAG chain attachment was still decreased. The potential GAG chain attachment site in the IGD was occupied by GAGs, and IGD product was secreted efficiently. The KS domain was modified by GAG chains and secreted. Finally, the G2 domain was expressed but not secreted, and inhibited secretion of the IGD when expressed as an IGD-G2 combination.
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Affiliation(s)
- C Kiani
- Department of Laboratory Medicine and Pathobiology, University of Toronto, 100 College Street, Toronto M5G 1L5, Canada
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13
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Domowicz MS, Pirok EW, Novak TE, Schwartz NB. Role of the C-terminal G3 domain in sorting and secretion of aggrecan core protein and ubiquitin-mediated degradation of accumulated mutant precursors. J Biol Chem 2000; 275:35098-105. [PMID: 11063750 DOI: 10.1074/jbc.275.45.35098] [Citation(s) in RCA: 25] [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
Aggrecan is a complex multidomain macromolecule that undergoes extensive processing and post-translational modification. A thorough understanding of the events and signals that promote translocation of aggrecan through the secretory pathway is lacking. To investigate which features of the C-terminal G3 region are necessary for successful translocation of the core protein, a number of deletion constructs based on the chick aggrecan cDNA sequence were prepared and transiently expressed in COS-1 cells and the natural host, embryonic chick chondrocytes; stable cell lines were established as well. The present results clearly establish a precise requirement for that portion of the G3 C-lectin domain encoded by exon 15 for: (i) translocation from the endoplasmic reticulum (ER) to the Golgi, (ii) secretion from the cell, (iii) galactosylation of chondroitin sulfate (CS) chains, (iv) generation of Ca(+2)-dependent galactose binding ability. Furthermore, in the absence of this subdomain there is excess accumulation in the ER of expression products leading to a stress-related response involving the chaperones Grp78 and protein disulfide isomerase, followed by degradation via a ubiquitin-proteosome pathway. All of these events in the model system faithfully mimic the naturally occurring nanomelic mutant, which also elicits a ubiquitin-mediated degradation response due to the accumulation of the truncated core protein precursor. This study represents the first report of the mode of degradation of overexpressed or misfolded proteoglycans and suggests that, although proteoglycans follow different glycosylation pathways from other glycoproteins, they are monitored by an ER surveillance system similar to that which detects other misfolded proteins.
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MESH Headings
- Aggrecans
- Animals
- Biological Transport
- Blotting, Western
- COS Cells
- Calcium/metabolism
- Carrier Proteins/metabolism
- Cell Line
- Cells, Cultured
- Chick Embryo
- Chondroitin Sulfates/metabolism
- Chromatography, Affinity
- Cysteine Endopeptidases/metabolism
- Cytosol/metabolism
- DNA, Complementary/metabolism
- Electrophoresis, Polyacrylamide Gel
- Endoplasmic Reticulum/metabolism
- Endoplasmic Reticulum Chaperone BiP
- Exons
- Extracellular Matrix Proteins
- Galactose/metabolism
- Gene Deletion
- Golgi Apparatus/metabolism
- Heat-Shock Proteins
- Immunohistochemistry
- Lectins/chemistry
- Lectins, C-Type
- Molecular Chaperones/metabolism
- Multienzyme Complexes/metabolism
- Mutagenesis, Site-Directed
- Phenotype
- Plasmids/metabolism
- Precipitin Tests
- Proteasome Endopeptidase Complex
- Protein Binding
- Protein Disulfide-Isomerases/metabolism
- Protein Folding
- Protein Processing, Post-Translational
- Protein Structure, Tertiary
- Proteoglycans/chemistry
- Proteoglycans/metabolism
- Transfection
- Translocation, Genetic
- Ubiquitins/metabolism
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Affiliation(s)
- M S Domowicz
- Departments of Pediatrics and Biochemistry & Molecular Biology, Committee on Developmental Biology, The University of Chicago, Chicago, Illinois 60637, USA
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