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Hiriart M, Sanchez-Soto C, Diaz-Garcia CM, Castanares DT, Avitia M, Velasco M, Mas-Oliva J, Macias-Silva M, González-Villalpando C, Delgado-Coello B, Sosa-Garrocho M, Vidaltamayo R, Fuentes-Silva D. Hyperinsulinemia is Associated with Increased Soluble Insulin Receptors Release from Hepatocytes. Front Endocrinol (Lausanne) 2014; 5:95. [PMID: 24995000 PMCID: PMC4062980 DOI: 10.3389/fendo.2014.00095] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2014] [Accepted: 06/05/2014] [Indexed: 12/26/2022] Open
Abstract
It has been generally assumed that insulin circulates freely in blood. However it can also interact with plasma proteins. Insulin receptors are located in the membrane of target cells and consist of an alpha and beta subunits with a tyrosine kinase cytoplasmic domain. The ectodomain, called soluble insulin receptor (SIR) has been found elevated in patients with diabetes mellitus. We explored if insulin binds to SIRs in circulation under physiological conditions and hypothesize that this SIR may be released by hepatocytes in response to high insulin concentrations. The presence of SIR in rat and human plasmas and the culture medium of hepatocytes was explored using Western blot analysis. A purification protocol was performed to isolated SIR using affinity, gel filtration, and ion exchange chromatographies. A modified reverse hemolytic plaque assay was used to measure SIR release from cultured hepatocytes. Incubation with 1 nmol l(-1) insulin induces the release of the insulin receptor ectodomains from normal rat hepatocytes. This effect can be partially prevented by blocking protease activity. Furthermore, plasma levels of SIR were higher in a model of metabolic syndrome, where rats are hyperinsulinemic. We also found increased SIR levels in hyperinsulinemic humans. SIR may be an important regulator of the amount of free insulin in circulation. In hyperinsulinemia, the amount of this soluble receptor increases and this could lead to higher amounts of insulin bound to this receptor, rather than free insulin, which is the biologically active form of the hormone. This observation could enlighten the mechanisms of insulin resistance.
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Affiliation(s)
- Marcia Hiriart
- Departamento de Neurodesarrollo y Fisiología, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
- *Correspondence: Marcia Hiriart, Departamento de Neurodesarrollo y Fisiología, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, Circuito Ext., Coyoacan, México DF CP 04510, Mexico e-mail:
| | - Carmen Sanchez-Soto
- Departamento de Neurodesarrollo y Fisiología, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Carlos Manlio Diaz-Garcia
- Departamento de Neurodesarrollo y Fisiología, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Diana T. Castanares
- Departamento de Neurodesarrollo y Fisiología, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
- Centro Médico ABC, Mexico City, Mexico
| | - Morena Avitia
- Departamento de Neurodesarrollo y Fisiología, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
- Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Myrian Velasco
- Departamento de Neurodesarrollo y Fisiología, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Jaime Mas-Oliva
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Marina Macias-Silva
- Departamento de Biología Celular y del Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | | | - Blanca Delgado-Coello
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Marcela Sosa-Garrocho
- Departamento de Biología Celular y del Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Román Vidaltamayo
- Departamento de Neurodesarrollo y Fisiología, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
- Departamento de Ciencias Básicas, Universidad de Monterrey, Monterrey, Mexico
| | - Deyanira Fuentes-Silva
- Departamento de Biomacromoléculas, Instituto de Química, Universidad Nacional Autónoma de México, Mexico City, Mexico
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Rentería ME, Gandhi NS, Vinuesa P, Helmerhorst E, Mancera RL. A comparative structural bioinformatics analysis of the insulin receptor family ectodomain based on phylogenetic information. PLoS One 2008; 3:e3667. [PMID: 18989367 PMCID: PMC2577065 DOI: 10.1371/journal.pone.0003667] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Accepted: 10/20/2008] [Indexed: 01/01/2023] Open
Abstract
The insulin receptor (IR), the insulin-like growth factor 1 receptor (IGF1R) and the insulin receptor-related receptor (IRR) are covalently-linked homodimers made up of several structural domains. The molecular mechanism of ligand binding to the ectodomain of these receptors and the resulting activation of their tyrosine kinase domain is still not well understood. We have carried out an amino acid residue conservation analysis in order to reconstruct the phylogeny of the IR Family. We have confirmed the location of ligand binding site 1 of the IGF1R and IR. Importantly, we have also predicted the likely location of the insulin binding site 2 on the surface of the fibronectin type III domains of the IR. An evolutionary conserved surface on the second leucine-rich domain that may interact with the ligand could not be detected. We suggest a possible mechanical trigger of the activation of the IR that involves a slight 'twist' rotation of the last two fibronectin type III domains in order to face the likely location of insulin. Finally, a strong selective pressure was found amongst the IRR orthologous sequences, suggesting that this orphan receptor has a yet unknown physiological role which may be conserved from amphibians to mammals.
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Affiliation(s)
- Miguel E. Rentería
- Western Australian Biomedical Research Institute and School of Biomedical Sciences, Curtin University of Technology, Perth, Western Austrailia, Australia
| | - Neha S. Gandhi
- Western Australian Biomedical Research Institute and School of Biomedical Sciences, Curtin University of Technology, Perth, Western Austrailia, Australia
| | - Pablo Vinuesa
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - Erik Helmerhorst
- Western Australian Biomedical Research Institute and School of Biomedical Sciences, Curtin University of Technology, Perth, Western Austrailia, Australia
| | - Ricardo L. Mancera
- Western Australian Biomedical Research Institute and School of Biomedical Sciences, Curtin University of Technology, Perth, Western Austrailia, Australia
- School of Pharmacy, Curtin University of Technology, Perth, Western Austrailia, Australia
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3
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Sparrow LG, Gorman JJ, Strike PM, Robinson CP, McKern NM, Epa VC, Ward CW. The location and characterisation of the O-linked glycans of the human insulin receptor. Proteins 2006; 66:261-5. [PMID: 17078079 DOI: 10.1002/prot.21261] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
O-linked glycosylation is a post-translational and post-folding event involving exposed S/T residues at beta-turns or in regions with extended conformation. O-linked sites are difficult to predict from sequence analyses compared to N-linked sites. Here we compare the results of chemical analyses of isolated glycopeptides with the prediction using the neural network prediction method NetOGlyc3.1, a procedure that has been reported to correctly predict 76% of O-glycosylated residues in proteins. Using the heavily glycosylated human insulin receptor as the test protein six sites of mucin-type O-glycosylation were found at residues T744, T749, S757, S758, T759, and T763 compared to the three sites (T759 and T763- correctly, T756- incorrectly) predicted by the neural network method. These six sites occur in a 20 residue segment that begins nine residues downstream from the start of the insulin receptor beta-chain. This region which also includes N-linked glycosylation sites at N742 and N755, is predicted to lack secondary structure and is followed by residues 765-770, the known linear epitope for the monoclonal antibody 18-44.
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Affiliation(s)
- Lindsay G Sparrow
- Commonwealth Scientific and Industrial Research Organisation, Molecular and Health Technologies, Parkville, Victoria 3052, Australia
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Masnikosa R, Baricević I, Jones DR, Nedić O. Characterisation of insulin-like growth factor receptors and insulin receptors in the human placenta using lectin affinity methods. Growth Horm IGF Res 2006; 16:174-184. [PMID: 16730207 DOI: 10.1016/j.ghir.2006.04.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Insulin and insulin-like growth factor receptors (IR, IGF-IR, IGF-IIR) from human placental cell membranes were solubilised and their glycoprotein properties were studied in terms of their interaction with five lectins: wheat germ agglutinin (WGA), banana lectin (BanLec), phytohaemagglutinin (PHA), concanavalin A (Con A), and Sambucus nigra agglutinin (SNA). The pattern of binding to the immobilised lectins indicated that the glycosylation of the IGF-IR, IGF-IIR and IR differed. We found several populations of receptors in placental cell membranes, differing with respect to their oligosaccharide moieties. IGF-IIR populations bore highly branched complex type N-glycans with a very high content of oligosaccharides terminating with Sia, high-mannose type N-glycans and hybrid type N-glycans. All these glycans seemed to be attached to the same IGF-II receptor molecules. Two major glycoforms of IR were detected, one having multiple highly branched N-glycans with a low content of terminal Sia and the other, having high-mannose type glycans attached to multiple N-glycosylation sites. As for the IGF-IR, multiple glycoforms were detected, bearing complex type N-glycans with various content of Sia-terminating branches, hybrid type N-glycans or high-mannose type N-glycans. The specific binding of (125)I-IGF-II to its receptor increased in the presence of immobilised WGA and SNA, which might imply the existence of a mammalian lectin counterpart whose potential physiological significance may lie in different targeting to various membrane compartments, thereby potentially modifying their cell signalling pathways.
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Affiliation(s)
- Romana Masnikosa
- INEP-Institute for the Application of Nuclear Energy, Belgrade, Serbia and Montenegro.
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Parry S, Hadaschik D, Blancher C, Kumaran MK, Bochkina N, Morris HR, Richardson S, Aitman TJ, Gauguier D, Siddle K, Scott J, Dell A. Glycomics investigation into insulin action. Biochim Biophys Acta Gen Subj 2006; 1760:652-68. [PMID: 16473469 DOI: 10.1016/j.bbagen.2005.12.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2005] [Revised: 12/09/2005] [Accepted: 12/12/2005] [Indexed: 11/30/2022]
Abstract
Defects in glycosylation are becoming increasingly associated with a range of human diseases. In some cases, the disease is caused by the glycosylation defect, whereas in others, the aberrant glycosylation may be a consequence of the disease. The implementation of highly sensitive and rapid mass spectrometric screening strategies for profiling the glycans present in model biological systems is revealing valuable insights into disease phenotypes. In addition, glycan screening is proving useful in the analysis of knock-out mice where it is possible to assess the role of glycosyltransferases and glycosidases and what function they have at the cellular and whole organism level. In this study, we analysed the effect of insulin on the glycosylation of 3T3-L1 cells and the effect of insulin resistance on glycosylation in a mouse model. Transcription profiling of 3T3-L1 cells treated with and without insulin revealed expression changes of several glycogenes. In contrast, mass spectrometric screening analysis of the glycans from these cells revealed very similar profiles suggesting that any changes in glycosylation were most likely on specific proteins rather than a global phenomenon. A fat-fed versus carbohydrate-fed mouse insulin resistant model was analysed to test the consequences of chronic insulin resistance. Muscle and liver N-glycosylation profiles from these mice are reported.
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Affiliation(s)
- Simon Parry
- Division of Molecular Biosciences, Imperial College, London, South Kensington, UK
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6
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Hjelm Cluff A, Malmström A, Tingåker B, David G, Ekman-Ordeberg G. Normal labor associated with changes in uterine heparan sulfate proteoglycan expression and localization. Acta Obstet Gynecol Scand 2005; 84:217-24. [PMID: 15715528 DOI: 10.1111/j.0001-6349.2005.00484.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
HYPOTHESIS Proteoglycans are well-known modulators of intercellular communication and signaling. Remodeling of the proteoglycans in the human uterus occurs throughout pregnancy, and during labor. We therefore hypothesize that heparan sulfate proteoglycans (HSPGs) play an important role in establishing normal labor. In this study HSPGs were characterized and localized in human uterine tissue. METHODS Uterine biopsies were obtained from four nonpregnant women, four women during elective cesarean section and four during emergency cesarean section. The biopsies were extracted using 4 m guanidinium hydrochloride (GuHCL). HSPGs were then purified by repeated ion-exchange chromatography on dehydroepiandrosterone (DEAE)-cellulose after digestion with chondroitinase ABC and finally precipitated with Alcian blue. HSPGs were identified by agarose gel electrophoresis and Western blotting. Controlled degradation of the heparan sulfate (HS) side-chains was performed using heparitinase or deglycosylation with trifluoromethanesulfonic acid (TFMS). The resulting core proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and visualized by Coomassie staining. HSPGs were localized in uterine tissue by immunohistochemistry. RESULTS SDS-PAGE after deglycosylation indicated the presence of multiple distinct core proteins tentatively identified as syndecans 1-4 and glypican 1. Western blots confirmed the presence of these proteoglycans and also perlecan. Immunohistochemistry revealed that the HSPGs were localized mainly in the smooth muscle with few in the extracellular matrix (ECM). Syndecan 3, the dominant proteoglycan, showed the most pronounced changes during pregnancy and labor. CONCLUSION For the first time several heparan sulfate proteoglycans have been identified and localized in the human uterus and shown to vary in expression during pregnancy and labor. Syndecan 3 had the most outstanding features in this respect.
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Affiliation(s)
- Ann Hjelm Cluff
- Department of Woman and Child Health, Division for Obstetrics and Gynecology, Karolinska Hospital, Stockholm, Sweden.
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Huang K, Xu B, Hu SQ, Chu YC, Hua QX, Qu Y, Li B, Wang S, Wang RY, Nakagawa SH, Theede AM, Whittaker J, De Meyts P, Katsoyannis PG, Weiss MA. How Insulin Binds: the B-Chain α-Helix Contacts the L1 β-Helix of the Insulin Receptor. J Mol Biol 2004; 341:529-50. [PMID: 15276842 DOI: 10.1016/j.jmb.2004.05.023] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2004] [Revised: 05/11/2004] [Accepted: 05/12/2004] [Indexed: 10/26/2022]
Abstract
Binding of insulin to the insulin receptor plays a central role in the hormonal control of metabolism. Here, we investigate possible contact sites between the receptor and the conserved non-polar surface of the B-chain. Evidence is presented that two contiguous sites in an alpha-helix, Val(B12) and Tyr(B16), contact the receptor. Chemical synthesis is exploited to obtain non-standard substitutions in an engineered monomer (DKP-insulin). Substitution of Tyr(B16) by an isosteric photo-activatable derivative (para-azido-phenylalanine) enables efficient cross-linking to the receptor. Such cross-linking is specific and maps to the L1 beta-helix of the alpha-subunit. Because substitution of Val(B12) by larger side-chains markedly impairs receptor binding, cross-linking studies at B12 were not undertaken. Structure-function relationships are instead probed by side-chains of similar or smaller volume: respective substitution of Val(B12) by alanine, threonine, and alpha-aminobutyric acid leads to activities of 1(+/-0.1)%, 13(+/-6)%, and 14(+/-5)% (relative to DKP-insulin) without disproportionate changes in negative cooperativity. NMR structures are essentially identical with native insulin. The absence of transmitted structural changes suggests that the low activities of B12 analogues reflect local perturbation of a "high-affinity" hormone-receptor contact. By contrast, because position B16 tolerates alanine substitution (relative activity 34(+/-10)%), the contribution of this neighboring interaction is smaller. Together, our results support a model in which the B-chain alpha-helix, functioning as an essential recognition element, docks against the L1 beta-helix of the insulin receptor.
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Affiliation(s)
- Kun Huang
- Department of Biochemistry, Case Western Reserve School of Medicine, Cleveland OH 44106-4935, USA
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8
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Edge ASB. Deglycosylation of glycoproteins with trifluoromethanesulphonic acid: elucidation of molecular structure and function. Biochem J 2003; 376:339-50. [PMID: 12974674 PMCID: PMC1223790 DOI: 10.1042/bj20030673] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2003] [Revised: 07/29/2003] [Accepted: 09/15/2003] [Indexed: 11/17/2022]
Abstract
The alteration of proteins by post-translational modifications, including phosphorylation, sulphation, processing by proteolysis, lipid attachment and glycosylation, gives rise to a broad range of molecules that can have an identical underlying protein core. An understanding of glycosylation of proteins is important in clarifying the nature of the numerous variants observed and in determining the biological roles of these modifications. Deglycosylation with TFMS (trifluoromethanesulphonic acid) [Edge, Faltynek, Hof, Reichert, and Weber, (1981) Anal. Biochem. 118, 131-137] has been used extensively to remove carbohydrate from glycoproteins, while leaving the protein backbone intact. Glycosylated proteins from animals, plants, fungi and bacteria have been deglycosylated with TFMS, and the most extensively studied types of carbohydrate chains in mammals, the N-linked, O-linked and glycosaminoglycan chains, are all removed by this procedure. The method is based on the finding that linkages between sugars are sensitive to cleavage by TFMS, whereas the peptide bond is stable and is not broken, even with prolonged deglycosylation. The relative susceptibility of individual sugars in glycosidic linkage varies with the substituents at C-2 and the occurrence of amido and acetyl groups, but even the most stable sugars are removed under conditions that are sufficiently mild to prevent scission of peptide bonds. The post-translational modifications of proteins have been shown to be required for diverse biological functions, and selective procedures to remove these modifications play an important role in the elucidation of protein structure and function.
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Affiliation(s)
- Albert S B Edge
- Harvard Medical School and Eaton Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA.
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Hwang JB, Hernandez J, Leduc R, Frost SC. Alternative glycosylation of the insulin receptor prevents oligomerization and acquisition of insulin-dependent tyrosine kinase activity. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1499:74-84. [PMID: 11118640 DOI: 10.1016/s0167-4889(00)00109-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Glucose deprivation leads to the synthesis of an aberrantly glycosylated ('alternative') and inefficiently processed form of the insulin proreceptor in 3T3-L1 adipocytes. To further explore the effect of aberrant (rather than absent) N-linked glycosylation of the insulin receptor, we examined the relationship of processing to function. Our studies show that the alternative form of the proreceptor does not oligomerize nor does it acquire the ability to undergo insulin-sensitive autophosphorylation. This along with an interaction with the glucose-regulated stress protein GRP78/BiP implies inappropriate folding/dimerization and retention in the ER. Glucose refeeding causes the post-translational modification of the alternative form of the proreceptor to a novel 'intermediate' form which is independent of new protein synthesis. As little as 100 microM glucose (or mannose) can induce this modification. In vitro digestion of the alternative and intermediate proreceptors with SPC1/furin shows that both the alpha- and beta-subunit domains are glycosylated, albeit aberrantly. This implies that the aberrantly glycosylated proreceptor could serve as a substrate for SPC1 in a physiological setting if the receptor was able to interact with the enzyme in the appropriate compartment (i.e., the trans-Golgi network). Based on inhibitor studies, however, both the alternative and intermediate forms of the proreceptor appear to be primarily targeted to the proteasome for degradation.
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10
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Abstract
The mature insulin receptor is a cell surface heterotetrameric glycoprotein composed of two alpha- and two beta-subunits. In 3T3-L1 adipocytes as in other cell types, the receptor is synthesized as a single polypeptide consisting of uncleaved alpha- and beta-subunits, migrating as a 190-kDa glycoprotein. To examine the importance of N-linked glycosylation on insulin receptor processing, we have used glucose deprivation as a tool to alter protein glycosylation. Western blot analysis shows that glucose deprivation led to a time-dependent accumulation of an alternative proreceptor of 170 kDa in a subcellular fraction consistent with endoplasmic reticulum localization. Co-precipitation assays provide evidence that the alternative proreceptor bound GRP78, an endoplasmic reticulum molecular chaperone. N-Glycosidase F treatment shows that the alternative proreceptor contained N-linked oligosaccharides. Yet, endoglycosidase H insensitivity indicates an aberrant oligosaccharide structure. Using pulse-chase methodology, we show that the synthetic rate was similar between the normal and alternative proreceptor. However, the normal proreceptor was processed into alpha- and beta-subunits (t((1)/(2)) = 1.3 +/- 0.6 h), while the alternative proreceptor was degraded (t((1)/(2)) = 5.1 +/- 0.6 h). Upon refeeding cells that were initially deprived of glucose, the alternative proreceptor was processed to a higher molecular weight form and gained sensitivity to endoglycosidase H. This "intermediate" form of the proreceptor was also degraded, although a small fraction escaped degradation, resulting in cleavage to the alpha- and beta-subunits. These data provide evidence for the first time that glucose deprivation leads to the accumulation of an alternative proreceptor, which can be post-translationally glycosylated with the readdition of glucose inducing both accelerated degradation and maturation.
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Affiliation(s)
- J B Hwang
- Department of Biochemistry and Molecular Biology, University of Florida College of Medicine, Gainesville, Florida 32610, USA
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11
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Trujillo R, Miró F, Plana M, José M, Bollen M, Stalmans W, Itarte E. Substrates for protein kinase CK2 in insulin receptor preparations from rat liver membranes: identification of a 210-kDa protein substrate as the dimeric form of endoplasmin. Arch Biochem Biophys 1997; 344:18-28. [PMID: 9244377 DOI: 10.1006/abbi.1997.0155] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Chromatography of extracts from rat liver membranes on wheat-germ lectin-Sepharose resulted in a partial resolution of the insulin receptor from other phosphorylatable proteins. Among the latter, a protein (p210, with an apparent M(r) of 210 kDa on SDS/PAGE under nonreducing conditions) was found to be phosphorylated by protein kinase CK2 on Thr and Ser residues. Under reducing conditions p210 was resolved into two phosphopolypeptides with apparent M(r) of 95 and 105 kDa. Neither the 95-kDa nor the 105-kDa polypeptides were recognized by antibodies against the beta-subunit of the insulin receptor. Both polypeptides gave identical phosphopeptide maps after protease V8 digestion and contained the same N-terminal amino acid sequence. This sequence coincided with that of endoplasmin, and both polypeptides as well as p210 were recognized by antibodies against this protein. This shows that p210 corresponds to the dimeric form of rat liver endoplasmin. DEAE-Sepharose chromatography of p210 preparations removed most other contaminating proteins and revealed the presence of a protein kinase activity that coeluted with p210. This protein kinase possessed the properties (substrate specificity and inhibition by heparin) that are characteristic of the protein kinase CK2 enzymes. Furthermore, phosphoamino acid analysis and phosphopeptide maps of the 95/105-kDa polypeptides phosphorylated either by the endogenous protein kinase or by exogenous protein kinase CK2 gave similar results. The phosphorylation of p210/endoplasmin by protein kinase CK2 and its coelution gives support to the involvement of this protein kinase in membrane-associated processes.
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Affiliation(s)
- R Trujillo
- Departament de Bioquímica i Biologia Molecular, Facultat de Cièncias,Universitat Autònoma de Barcelona, Bellaterra, Spain
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The functions of the human insulin receptor are affected in different ways by mutation of each of the four N-glycosylation sites in the beta subunit. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32417-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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13
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Myers K, Rahi-Saund V, Davison M, Young J, Cheater A, Stern P. Isolation of a cDNA encoding 5T4 oncofetal trophoblast glycoprotein. An antigen associated with metastasis contains leucine-rich repeats. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)37110-7] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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14
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Petäjä-Repo UE. Structural characterization of the carbohydrates of the rat ovarian luteinizing hormone/chorionic gonadotropin receptor. Biochem J 1994; 298 ( Pt 2):361-6. [PMID: 8135742 PMCID: PMC1137948 DOI: 10.1042/bj2980361] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The numbers and types of oligosaccharide present on the rat ovarian luteinizing hormone (LH)/chorionic gonadotropin (CG) receptor were determined by treating radiolabelled purified receptors with glycosidases and examining the changes in electrophoretic mobility and number of radiolabelled bands on SDS/PAGE. The purified receptor was also transferred to nitrocellulose after SDS/PAGE and probed with digoxigenin-labelled lectins. The following conclusions were drawn: (1) the rat ovarian LH/CG receptor contains at least two complex-type N-linked oligosaccharide chains, of which one is biantennary and the rest multiantennary. (2) The N-linked chains terminate in either unsubstituted galactose or sialic acid linked alpha 2-3 or alpha 2-6 to the penultimate galactose. (3) The N-linked oligosaccharides also contain internal poly(N-acetyl-lactosamine) sequences and fucose-linked alpha 1-6 to the proximal N-acetylglucosamine. (4) No O-linked carbohydrate moieties are present on the receptor molecule.
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Collier E, Carpentier JL, Beitz L, Carol H, Taylor SI, Gorden P. Specific glycosylation site mutations of the insulin receptor alpha subunit impair intracellular transport. Biochemistry 1993; 32:7818-23. [PMID: 8347587 DOI: 10.1021/bi00081a029] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The insulin receptor is a transmembrane protein found on multiple cell types. This receptor is synthesized as a 190-kDa proreceptor which is cleaved to produce mature alpha and beta subunits. The proreceptor contains 18 potential sites for N-linked glycosylation: 14 on the alpha subunit and 4 on the beta subunit. The codons for asparagine in the first four sites at the amino terminus of the alpha subunit were mutated to code for glutamine. This mutant receptor cDNA was stably transfected into NIH 3T3 cells. The insulin receptor produced in these cells remained in the proreceptor form; no mature alpha and beta subunits were produced. The proreceptor was slightly smaller on SDS-PAGE gels than the wild-type proreceptor and contained four less oligosaccharide chains by tryptic peptide mapping. The carbohydrate chains on the mutant proreceptor remained endoglycosidase H sensitive. However, in the presence of brefeldin A, these oligosaccharide chains could be processed to endoglycosidase H resistant chains. By immunofluorescence, the mutant proreceptor was shown to be localized to the endoplasmic reticulum. No insulin receptors could be found on the cell-surface either with cell surface labeling with biotin or with 125I-insulin binding. Thus, glycosylation of the first four N-linked glycosylation sites of the insulin receptor is necessary for the proper processing and intracellular transport of the receptor. This is in contrast to glycosylation at the four sites on the beta subunit which appear not to be important for processing but necessary for signal transduction. Therefore, N-linked glycosylation of the insulin receptor at specific sites has multiple distinctive roles.
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Affiliation(s)
- E Collier
- Diabetes Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
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16
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Desarnaud F, Marie J, Lombard C, Larguier R, Seyer R, Lorca T, Jard S, Bonnafous JC. Deglycosylation and fragmentation of purified rat liver angiotensin II receptor: application to the mapping of hormone-binding domains. Biochem J 1993; 289 ( Pt 1):289-97. [PMID: 8380988 PMCID: PMC1132163 DOI: 10.1042/bj2890289] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We report new structural data about the rat liver angiotensin II receptor, which belongs to the AT1 subclass. This receptor has been purified at analytical or semi-preparative levels by a previously described strategy involving its photolabelling with a biotinylated azido probe and selective adsorption of the covalent probe-receptor complexes to immobilized streptavidin [Marie, Seyer, Lombard, Desarnaud, Aumelas, Jard and Bonnafous (1990) Biochemistry 29, 8943-8950]. Chemical or enzymic deglycosylation of the purified receptor has shown a shift in its molecular mass from 65 kDa to 40 kDa. Fragmentation of the purified receptor was carried out with V8 protease from Staphylococcus aureus, CNBr and trypsin. It was possible to find trypsin-treatment conditions which allowed production of a 6 kDa probe-fragment complex with a satisfactory yield. Attempts to localize this small fragment (5 kDa after subtraction of the probe contribution) in the recently published rat AT1 receptor sequence are reported. As expected, this fragment is not glycosylated; moreover, its further fragmentation by CNBr induces a very slight decrease in its size. These data support the hypothesis that a receptor sequence comprising the third transmembrane domain and adjacent portions of extra- and intracellular loops is involved in photolabelling by the C-terminal azidophenylalanine of the angiotensin-derived probe. These preliminary results are discussed in terms of future prospects for the characterization of hormone-binding domains of angiotensin II receptors.
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Affiliation(s)
- F Desarnaud
- Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France
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17
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N-linked oligosaccharide chains of the insulin receptor beta subunit are essential for transmembrane signaling. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)41942-4] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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18
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Lee AW. Signal transduction by the colony-stimulating factor-1 receptor; comparison to other receptor tyrosine kinases. CURRENT TOPICS IN CELLULAR REGULATION 1992; 32:73-181. [PMID: 1318184 DOI: 10.1016/b978-0-12-152832-4.50005-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- A W Lee
- Clinical Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892
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19
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Affiliation(s)
- R Taylor
- Human Metabolism Research Centre, Department of Medicine, Medical School, Newcastle upon Tyne, UK
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20
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Hayes GR, Livingston JN, Lockwood DH. Mapping of carbohydrate sites on the human insulin receptor. Biochem Biophys Res Commun 1991; 174:735-41. [PMID: 1993068 DOI: 10.1016/0006-291x(91)91479-v] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Prior to investigating the role of individual glycosylation sites in insulin receptor function, we are mapping the sites of glycosylation in the receptor. We report here a generally applicable methodology for the isolation and identification of glycosylation sites in cell surface glycoproteins. Human insulin receptors were labeled with [3H]-sugars using a CHO cell line transfected with the human receptor cDNA. Labelled receptors were mixed with receptors purified from human placental membranes and tryptic peptides prepared. Peptides were fractionated by gel filtration chromatography to limit the number of non-glycopeptides present. Peptides were then separated by reverse phase HPLC and glycopeptides identified by scintillation counting. Using this technique we have shown the insulin receptor to be glycosylated at Asn 397 and Asn 881. This increase the known number of occupied glycosylation sites to five.
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Affiliation(s)
- G R Hayes
- University of Rochester Medical Center, NY 14642
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21
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Lyon M, Gallagher JT. Purification and partial characterization of the major cell-associated heparan sulphate proteoglycan of rat liver. Biochem J 1991; 273(Pt 2):415-22. [PMID: 1846741 PMCID: PMC1149861 DOI: 10.1042/bj2730415] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Heparan sulphate proteoglycans were solubilized from whole rat livers by homogenization and dissociative extraction with 4 M-guanidinium chloride containing Triton X-100 and proteinase inhibitors. The extract was subjected to trichloroacetic acid precipitation and the proteoglycan remained soluble. This was then purified to apparent homogeneity by a combination of (a) DEAE-Sephacel chromatography, (b) digestion with chondroitinase ABC followed by f.p.l.c. Mono Q ion-exchange chromatography, and (c) density-gradient centrifugation in CsCl and 4 M-guanidinium chloride. Approx. 1.5 mg of proteoglycan was obtained from 30 livers with an estimated recovery of 25%. The purified proteoglycan was eluted from Sepharose CL6B as an apparently single polydisperse population with a Kav. of 0.19 and displayed a molecular mass of greater than or equal to 200 kDa (relative to protein standards) by SDS/PAGE. Its heparan sulphate chains were eluted with a Kav. of 0.44 and have an estimated molecular mass of 25 kDa. Digestion of the proteoglycan with a combination of heparinases yielded core proteins of 77, 49 and 44 kDa. Deglycosylation using trifluoromethanesulphonic acid, though slightly decreasing the sizes, gave an identical pattern of core proteins. Electrophoretic detergent blotting demonstrated that all of the core proteins were hydrophobic and are probably integral plasma membrane molecules. The peptide maps generated by V8 proteinase digestion of the two major core proteins (77 and 49 kDa) were very similar, suggesting that these two core proteins are structurally related.
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Affiliation(s)
- M Lyon
- Cancer Research Campaign Department of Medical Oncology, Christie Hospital, Manchester, U.K
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22
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Taylor SI, Accili D, Cama A, Kadowaki H, Kadowaki T, Imano E, Sierra ML. Mutations in the insulin receptor gene in patients with genetic syndromes of insulin resistance. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1991; 293:197-213. [PMID: 1767731 DOI: 10.1007/978-1-4684-5949-4_19] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- S I Taylor
- Diabetes Branch, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, MD
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23
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Substitution of lysine for asparagine at position 15 in the alpha-subunit of the human insulin receptor. A mutation that impairs transport of receptors to the cell surface and decreases the affinity of insulin binding. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)30636-1] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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24
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Baculovirus-directed expression of the human insulin receptor and an insulin-binding ectodomain. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38269-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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25
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Taylor SI, Cama A, Kadowaki H, Kadowaki T, Accili D. Mutations of the human insulin receptor gene. Trends Endocrinol Metab 1990; 1:134-9. [PMID: 18411106 DOI: 10.1016/1043-2760(90)90024-w] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Mutations in the insulin receptor gene have been identified in patients with genetic forms of insulin resistance. These mutations provide insight into structure-function relationships of the insulin receptor, and also into the causes of insulin resistance in human disease.
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Affiliation(s)
- S I Taylor
- Biochemistry and Molecular Pathophysiology Section, Diabetes Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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26
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Taylor SI, Kadowaki T, Accili D, Cama A, Kadowaki H, McKeon C, Moncada V, Marcus-Samuels B, Bevins C, Ojamaa K. Mutations in the insulin receptor gene in genetic forms of insulin resistance. RECENT PROGRESS IN HORMONE RESEARCH 1990; 46:185-213; discussion 213-7. [PMID: 2177906 DOI: 10.1016/b978-0-12-571146-3.50011-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- S I Taylor
- Diabetes Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
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27
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Munshi R, Linden J. Co-purification of A1 Adenosine Receptors and Guanine Nucleotide-binding Proteins from Bovine Brain. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)63779-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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28
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An Extracellular Domain of the Insulin Receptor β-Subunit with Regulatory Function on Protein-Tyrosine Kinase. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)81838-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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29
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Waugh SM, DiBella EE, Pilch PF. Isolation of a proteolytically derived domain of the insulin receptor containing the major site of cross-linking/binding. Biochemistry 1989; 28:3448-55. [PMID: 2742847 DOI: 10.1021/bi00434a045] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Radiolabeled insulin was affinity cross-linked to purified insulin receptor with six separate bifunctional N-hydroxysuccinimide esters of different lengths. Results were qualitatively identical for each cross-linker in that insulin was predominantly cross-linked through its B chain to the receptor's alpha subunit. The maximum efficiencies of cross-linking were 10-15% for the most effective reagents, and this value was dependent upon the concentration and length of the cross-linker. In an effort to locate the cross-linking site, monoiodoinsulin was cross-linked to affinity-purified insulin receptor with disuccinimidyl suberate. Limited proteolysis of the hormone/receptor adduct with Staphylococcus aureus V8 protease, chymotrypsin, or thermolysin in an SDS-containing buffer rapidly generated a 55-kDa, insulin-labeled fragment as shown by SDS-polyacrylamide gel electrophoresis. We reported earlier that the 55-kDa chymotryptic fragment contained multiple internal disulfide bonds as evidenced by its shifting mobility on an SDS gel after dithiothreitol treatment [Boni-Schnetzler et al. (1987) J. Biol. Chem. 262, 8395-8401]. Here we show that the 55-kDa fragment is also formed by proteolysis of the receptor in the absence of prior insulin cross-linking. This fragment was prepared in amounts sufficient for sequence analysis and was purified by passage successively over gel permeation and reverse-phase HPLC columns. The sequence of the fragment's amino terminus corresponds to that of the amino terminus of the receptor's alpha subunit. This fragment also reacts with an antibody raised against a synthetic peptide corresponding to residues 242-253 of the receptor's alpha subunit.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S M Waugh
- Department of Biochemistry, School of Medicine, Boston University, Massachusetts 02118
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30
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Jokinen O, Guéant JL, Schohn H, Gräsbeck R. Lectin binding to the porcine and human ileal receptor of intrinsic factor-cobalamin. Glycoconj J 1989; 6:525-38. [PMID: 2562509 DOI: 10.1007/bf01053775] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The purified porcine receptor for the intrinsic factor-cobalamin complex bound to concanavalin A, lentil lectin and wheat germ lectin covalently coupled to Sepharose and was eluted with the corresponding soluble sugars. In contrast, human intrinsic factor bound efficiently to concanavalin A, to some extent to lentil lectin, but only slightly to wheat germ agglutinin. The binding of IF-Cbl to the receptor was inhibited when the receptor was pre-incubated with soluble wheat germ agglutinin, with an inhibition constant estimated to be 1.9 mumol/l. After transfer of the purified receptor from SDS-PAGE to Immobilon, ligand blotting of the purified receptor with iodinated lectin showed that concanavalin A and lentil lectin bound to three (75, 56 and 43 kDa) components but that wheat germ agglutinin bound only to the 75 kDa component. These results showed that the alpha subunit of the receptor could bind to wheat germ agglutinin, resulting in an inhibition of its binding with intrinsic factor. Both binding sites of intrinsic factor and of wheat germ agglutinin could be located near to each other.
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Affiliation(s)
- O Jokinen
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
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31
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Krieger M, Reddy P, Kozarsky K, Kingsley D, Hobbie L, Penman M. Analysis of the synthesis, intracellular sorting, and function of glycoproteins using a mammalian cell mutant with reversible glycosylation defects. Methods Cell Biol 1989; 32:57-84. [PMID: 2691861 DOI: 10.1016/s0091-679x(08)61167-x] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- M Krieger
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139
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32
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Cheifetz S, Andres JL, Massagué J. The transforming growth factor-beta receptor type III is a membrane proteoglycan. Domain structure of the receptor. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)37487-8] [Citation(s) in RCA: 113] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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33
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Kahn CR, White MF. The insulin receptor and the molecular mechanism of insulin action. J Clin Invest 1988; 82:1151-6. [PMID: 3049671 PMCID: PMC442664 DOI: 10.1172/jci113711] [Citation(s) in RCA: 273] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Affiliation(s)
- C R Kahn
- Joslin Diabetes Center, Brigham and Women's Hospital, Boston, MA 02215
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34
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Miyazono K, Hellman U, Wernstedt C, Heldin CH. Latent high molecular weight complex of transforming growth factor beta 1. Purification from human platelets and structural characterization. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68800-3] [Citation(s) in RCA: 430] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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35
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Hart CB, Roth J, Lesniak MA. Post-translational modifications of the insulin receptor. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1988; 231:481-94. [PMID: 3046252 DOI: 10.1007/978-1-4684-9042-8_41] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- C B Hart
- Diabetes Branch, NIDDK, NIH, Bethesda, Maryland 20892
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36
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Burant CF, Treutelaar MK, Block NE, Buse MG. Structural differences between liver- and muscle-derived insulin receptors in rats. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)66876-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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37
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Abstract
A1 adenosine receptors from different tissues and species were photoaffinity labelled and then the carbohydrate content was examined by both enzymatic and chemical treatment. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the labelled membrane receptors shows that neuraminidase treatment alters the electrophoretic mobility of the receptor band indicating the presence of terminal neuraminic acids. Neuraminidase digestion does not influence the binding characteristics of the receptor. The totally deglycosylated receptor protein obtained by chemical treatment has an apparent molecular weight of 32,000.
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38
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van den Bosch R, Geuze HJ, du Maine AP, Strous GJ. Transport and metabolism of 5'-nucleotidase in a rat hepatoma cell line. EUROPEAN JOURNAL OF BIOCHEMISTRY 1986; 160:49-54. [PMID: 3021451 DOI: 10.1111/j.1432-1033.1986.tb09938.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The biosynthesis of the ectoenzyme 5'-nucleotidase in the rat hepatoma cell line H4S has been studied by pulse-labeling with [35S]methionine and subsequent immunoprecipitation of the cell lysate. 5'-Nucleotidase is a membrane glycoprotein with an apparent molecular mass on SDS-gels of 72 kDa. The enzyme is initially synthesized as a 68-kDa precursor which is converted to the mature 72-kDa form in 15-60 min (t1/2 = 25 min). The molecular mass of the unglycosylated enzyme is approximately 58 kDa. Culturing the cells in the presence of varying concentrations of tunicamycin, an inhibitor of N-glycosylation, revealed six species of 5'-nucleotidase after sodium dodecyl sulfate/polyacrylamide electrophoresis. This indicates the presence of five N-linked oligosaccharide chains accounting for the difference between the 58-kDa polypeptide backbone and the 68-kDa species. The 68-kDa precursor is susceptible to cleavage by endo-beta-N-acetylglycosaminidase H; the 72-kDa mature protein is converted to several bands upon this treatment. This result indicates that part of 5'-nucleotidase keeps one or two high-mannose or hybrid chains in the mature form, even after prolonged pulse-chase labeling. The newly synthesized mature enzyme reaches the cell surface after 20-30 min. The half-life of 5'-nucleotidase is about 30 h in H4S cells. No immunoprecipitable 5'-nucleosidase is released into the culture medium.
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39
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Burant CF, Treutelaar MK, Buse MG. Diabetes-induced functional and structural changes in insulin receptors from rat skeletal muscle. J Clin Invest 1986; 77:260-70. [PMID: 3003151 PMCID: PMC423335 DOI: 10.1172/jci112285] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The effect of diabetes on the structure and function of insulin receptors was studied in rats 7 d after streptozotocin injection, using solubilized, partially purified receptors from rat hindlimb muscles. Diabetes increased the number of insulin receptors per gram of muscle 60-70% without apparent change in insulin binding affinity. Incubation of receptors at 4 degrees C with [gamma-32P]ATP and insulin resulted in dose-dependent autophosphorylation of the beta-subunit on tyrosine residues; receptors from diabetic rats showed decreased base-line phosphorylation, as well as a decrease in autophosphorylation at maximally stimulating insulin concentrations. These receptors also showed diminished exogenous substrate kinase activity using histone H2b and angiotensin II as phosphoacceptors. The electrophoretic mobility (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) of a subpopulation of beta-subunits derived from diabetics was slightly decreased; differences in electrophoretic mobility between control- and diabetic-derived beta-subunits were enhanced by generating fragments by partial Staphylococcus aureus V8 protease digestion. Endoglycosidase-H or neuraminidase treatment increased the electrophoretic mobility of beta-subunits in both groups, but only neuraminidase appeared to decrease or abolish differences in electrophoretic mobility between controls and diabetics, suggesting that excess sialilation may account, in part, for the altered mobility of diabetic derived beta-subunits. All structural and functional alterations in insulin receptors were prevented by treating diabetic rats with insulin for 60 h. Peripheral insulin resistance associated with insulinopenic diabetes may be related to modifications in insulin receptor structure, resulting in impaired signal transmission.
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