1
|
Zaarur N, Meriin AB, Singh M, Goel RK, Zaia J, Kandror KV. Akt may associate with insulin-responsive vesicles via interaction with sortilin. FEBS Lett 2024; 598:390-399. [PMID: 38105115 PMCID: PMC10922807 DOI: 10.1002/1873-3468.14790] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Revised: 12/04/2023] [Accepted: 12/07/2023] [Indexed: 12/19/2023]
Abstract
Insulin-responsive vesicles (IRVs) deliver the glucose transporter Glut4 to the plasma membrane in response to activation of the insulin signaling cascade: insulin receptor-IRS-PI3 kinase-Akt-TBC1D4-Rab10. Previous studies have shown that Akt, TBC1D4, and Rab10 are compartmentalized on the IRVs. Although functionally significant, the mechanism of Akt association with the IRVs remains unknown. Using pull-down assays, immunofluorescence microscopy, and cross-linking, we have found that Akt may be recruited to the IRVs via the interaction with the juxtamembrane domain of the cytoplasmic C terminus of sortilin, a major IRV protein. Overexpression of full-length sortilin increases insulin-stimulated phosphorylation of TBC1D4 and glucose uptake in adipocytes, while overexpression of the cytoplasmic tail of sortilin has the opposite effect. Our findings demonstrate that the IRVs represent both a scaffold and a target of insulin signaling.
Collapse
Affiliation(s)
- Nava Zaarur
- Department of Biochemistry and Cell Biology, Chobanian and Avedisian School of Medicine, Boston University, Boston, MA 02118
| | - Anatoli B. Meriin
- Department of Biochemistry and Cell Biology, Chobanian and Avedisian School of Medicine, Boston University, Boston, MA 02118
| | - Maneet Singh
- Department of Biochemistry and Cell Biology, Chobanian and Avedisian School of Medicine, Boston University, Boston, MA 02118
| | - Raghuveera K. Goel
- Department of Biochemistry and Cell Biology, Chobanian and Avedisian School of Medicine, Boston University, Boston, MA 02118
- Center for Network Systems Biology, Chobanian and Avedisian School of Medicine, Boston University, Boston, MA 02118
| | - Joseph Zaia
- Department of Biochemistry and Cell Biology, Chobanian and Avedisian School of Medicine, Boston University, Boston, MA 02118
- Center for Network Systems Biology, Chobanian and Avedisian School of Medicine, Boston University, Boston, MA 02118
| | - Konstantin V. Kandror
- Department of Biochemistry and Cell Biology, Chobanian and Avedisian School of Medicine, Boston University, Boston, MA 02118
| |
Collapse
|
2
|
Lui A, Patel RS, Krause-Hauch M, Sparks RP, Patel NA. Regulation of Human Sortilin Alternative Splicing by Glucagon-like Peptide-1 (GLP1) in Adipocytes. Int J Mol Sci 2023; 24:14324. [PMID: 37762628 PMCID: PMC10531797 DOI: 10.3390/ijms241814324] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 09/13/2023] [Accepted: 09/15/2023] [Indexed: 09/29/2023] Open
Abstract
Type 2 diabetes mellitus is a chronic metabolic disease with no cure. Adipose tissue is a major site of systemic insulin resistance. Sortilin is a central component of the glucose transporter -Glut4 storage vesicles (GSV) which translocate to the plasma membrane to uptake glucose from circulation. Here, using human adipocytes we demonstrate the presence of the alternatively spliced, truncated sortilin variant (Sort_T) whose expression is significantly increased in diabetic adipose tissue. Artificial-intelligence-based modeling, molecular dynamics, intrinsically disordered region analysis, and co-immunoprecipitation demonstrated association of Sort_T with Glut4 and decreased glucose uptake in adipocytes. The results show that glucagon-like peptide-1 (GLP1) hormone decreases Sort_T. We deciphered the molecular mechanism underlying GLP1 regulation of alternative splicing of human sortilin. Using splicing minigenes and RNA-immunoprecipitation assays, the results show that GLP1 regulates Sort_T alternative splicing via the splice factor, TRA2B. We demonstrate that targeted antisense oligonucleotide morpholinos reduces Sort_T levels and improves glucose uptake in diabetic adipocytes. Thus, we demonstrate that GLP1 regulates alternative splicing of sortilin in human diabetic adipocytes.
Collapse
Affiliation(s)
- Ashley Lui
- Department of Molecular Medicine, University of South Florida, Tampa, FL 33612, USA; (A.L.); (M.K.-H.)
| | - Rekha S. Patel
- Research Service, James A. Haley Veterans Hospital, Tampa, FL 33612, USA; (R.S.P.); (R.P.S.)
| | - Meredith Krause-Hauch
- Department of Molecular Medicine, University of South Florida, Tampa, FL 33612, USA; (A.L.); (M.K.-H.)
| | - Robert P. Sparks
- Research Service, James A. Haley Veterans Hospital, Tampa, FL 33612, USA; (R.S.P.); (R.P.S.)
- Department of Medicine, Division of Gastroenterology, UMass Chan Medical School, Worcester, MA 01655, USA
| | - Niketa A. Patel
- Department of Molecular Medicine, University of South Florida, Tampa, FL 33612, USA; (A.L.); (M.K.-H.)
- Research Service, James A. Haley Veterans Hospital, Tampa, FL 33612, USA; (R.S.P.); (R.P.S.)
| |
Collapse
|
3
|
Identification of Sortilin Alternatively Spliced Variants in Mouse 3T3L1 Adipocytes. Int J Mol Sci 2021; 22:ijms22030983. [PMID: 33498179 PMCID: PMC7863940 DOI: 10.3390/ijms22030983] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 01/06/2021] [Accepted: 01/13/2021] [Indexed: 12/13/2022] Open
Abstract
Type 2 diabetes mellitus is a metabolic disorder defined by systemic insulin resistance. Insulin resistance in adipocytes, an important regulator of glucose metabolism, results in impaired glucose uptake. The trafficking protein, sortilin, regulates major glucose transporter 4 (Glut4) movement, thereby promoting glucose uptake in adipocytes. Here, we demonstrate the presence of an alternatively spliced sortilin variant (Sort17b), whose levels increase with insulin resistance in mouse 3T3L1 adipocytes. Using a splicing minigene, we show that inclusion of alternative exon 17b results in the expression of Sort17b splice variant. Bioinformatic analysis indicated a novel intrinsic disorder region (IDR) encoded by exon 17b of Sort17b. Root mean square deviation (RMSD) and root mean square fluctuation (RMSF) measurements using molecular dynamics demonstrated increased flexibility of the protein backbone within the IDR. Using protein–protein docking and co-immunoprecipitation assays, we show robust binding of Glut4 to Sort17b. Further, results demonstrate that over-expression of Sort17b correlates with reduced Glut4 translocation and decreased glucose uptake in adipocytes. The study demonstrates that insulin resistance in 3T3L1 adipocytes promotes expression of a novel sortilin splice variant with thus far unknown implications in glucose metabolism. This knowledge may be used to develop therapeutics targeting sortilin variants in the management of type 2 diabetes and metabolic syndrome.
Collapse
|
4
|
Zaarur N, Pan X, Kandror KV. Detection of Detergent-sensitive Interactions Between Membrane Proteins. J Vis Exp 2018. [PMID: 29578521 DOI: 10.3791/57179] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Our ability to explore protein-protein interactions is the key to understanding regulatory connections in the cell. However, detection of protein-protein interactions in many cases is associated with significant experimental challenges. In particular, sorting receptors interact with their protein cargo in the lumen of the membrane compartments often in a detergent-sensitive fashion, making co-immunoprecipitation of these proteins unusable. Binding of the sorting receptor sortilin to glucose transporter GLUT4 may serve as an example of weak luminal interactions between membrane proteins. Here, we describe a fast, simple, and inexpensive assay to validate the interaction between sortilin and GLUT4. For that, we have designed and chemically synthesized the myc-tagged peptide corresponding to the potential sortilin-binding epitope in the luminal part of GLUT4. Sortilin tagged with six histidines was expressed in mammalian cells, and isolated from cell lysates using Cobalt beads. Sortilin immobilized on the beads was incubated with the peptide solution at different pH values, and the eluted material was analyzed by Western blotting. This assay can be easily adapted to study other detergent-sensitive protein-protein interactions.
Collapse
Affiliation(s)
- Nava Zaarur
- Department of Biochemistry, Boston University School of Medicine;
| | - Xiang Pan
- Department of Biochemistry, Boston University School of Medicine
| | | |
Collapse
|
5
|
Boesze-Battaglia K, Walker LP, Dhingra A, Kandror K, Tang HY, Shenker BJ. Internalization of the Active Subunit of the Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin Is Dependent upon Cellugyrin (Synaptogyrin 2), a Host Cell Non-Neuronal Paralog of the Synaptic Vesicle Protein, Synaptogyrin 1. Front Cell Infect Microbiol 2017; 7:469. [PMID: 29184850 PMCID: PMC5694546 DOI: 10.3389/fcimb.2017.00469] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 10/25/2017] [Indexed: 12/17/2022] Open
Abstract
The Aggregatibacter actinomycetemcomitans cytolethal distending toxin (Cdt) is a heterotrimeric AB2 toxin capable of inducing lymphocytes, and other cell types, to undergo cell cycle arrest and apoptosis. Exposure to Cdt results in binding to the cell surface followed by internalization and translocation of the active subunit, CdtB, to intracellular compartments. These events are dependent upon toxin binding to cholesterol in the context of lipid rich membrane microdomains often referred to as lipid rafts. We now demonstrate that, in addition to binding to the plasma membrane of lymphocytes, another early and critical event initiated by Cdt is the translocation of the host cell protein, cellugyrin (synaptogyrin-2) to the same cholesterol-rich microdomains. Furthermore, we demonstrate that cellugyrin is an intracellular binding partner for CdtB as demonstrated by immunoprecipitation. Using CRISPR/cas9 gene editing we established a Jurkat cell line deficient in cellugyrin expression (JurkatCg−); these cells were capable of binding Cdt, but unable to internalize CdtB. Furthermore, JurkatCg− cells were not susceptible to Cdt-induced toxicity; these cells failed to exhibit blockade of the PI-3K signaling pathway, cell cycle arrest or cell death. We propose that cellugyrin plays a critical role in the internalization and translocation of CdtB to critical intracellular target sites. These studies provide critical new insight into the mechanism by which Cdt, and in particular, CdtB is able to induce toxicity.
Collapse
Affiliation(s)
- Kathleen Boesze-Battaglia
- Department of Biochemistry, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, United States
| | - Lisa P Walker
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, United States
| | - Anuradha Dhingra
- Department of Biochemistry, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, United States
| | - Konstantin Kandror
- Department of Biochemistry, School of Medicine, Boston University, Boston, MA, United States
| | - Hsin-Yao Tang
- Wistar Proteomics and Metabolomics Core Facility, Wistar Institute, Philadelphia, PA, United States
| | - Bruce J Shenker
- Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, United States
| |
Collapse
|
6
|
Pan X, Zaarur N, Singh M, Morin P, Kandror KV. Sortilin and retromer mediate retrograde transport of Glut4 in 3T3-L1 adipocytes. Mol Biol Cell 2017; 28:1667-1675. [PMID: 28450454 PMCID: PMC5469609 DOI: 10.1091/mbc.e16-11-0777] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Revised: 04/10/2017] [Accepted: 04/18/2017] [Indexed: 11/11/2022] Open
Abstract
Sortilin is a multiligand sorting receptor responsible for the anterograde transport of lysosomal enzymes and substrates. Here we demonstrate that sortilin is also involved in retrograde protein traffic. In cultured 3T3-L1 adipocytes, sortilin together with retromer rescues Glut4 from degradation in lysosomes and retrieves it to the TGN, where insulin--responsive vesicles are formed. Mechanistically, the luminal Vps10p domain of sortilin interacts with the first luminal loop of Glut4, and the cytoplasmic tail of sortilin binds to retromer. Ablation of the retromer does not affect insulin signaling but decreases the stability of sortilin and Glut4 and blocks their entry into the small vesicular carriers. As a result, Glut4 cannot reach the insulin-responsive compartment, and insulin-stimulated glucose uptake in adipocytes is suppressed. We suggest that sortilin- and retromer-mediated Glut4 retrieval from endosomes may represent a step in the Glut4 pathway vulnerable to the development of insulin resistance and diabetes.
Collapse
Affiliation(s)
- Xiang Pan
- Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118
| | - Nava Zaarur
- Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118
| | - Maneet Singh
- Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118
| | - Peter Morin
- Edith Nourse Rogers Memorial Veterans Hospital, Bedford, MA 01730
| | - Konstantin V Kandror
- Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118
| |
Collapse
|
7
|
Talantikite M, Berenguer M, Gonzalez T, Alessi MC, Poggi M, Peiretti F, Govers R. The first intracellular loop of GLUT4 contains a retention motif. J Cell Sci 2016; 129:2273-84. [DOI: 10.1242/jcs.183525] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Accepted: 04/20/2016] [Indexed: 01/02/2023] Open
Abstract
Glucose transporter GLUT4 plays a major role in glucose homeostasis and is efficiently retained intracellularly in adipocytes and myocytes. To simplify the analysis of its retention, various intracellular GLUT4 domains were fused individually to reporter molecules. Of the four short cytoplasmic loops of GLUT4, only the first nine-residue-long loop conferred intracellular retention of truncated forms of the transferrin receptor and CD4 in adipocytes. In contrast, the same loop of GLUT1 was without effect. The reporter molecules to which the first loop of GLUT4 was fused localized, unlike GLUT4, to the TGN, possibly explaining why these molecules did not respond to insulin. The retention induced by the GLUT4 loop was specific to adipocytes as it did not induce retention in preadipocytes. Of the SQWLGRKRA sequence that constitutes this loop, mutation of either the tryptophan or lysine residue abrogated reporter retention. Mutation of these residues individually into alanines in the full-length GLUT4 molecule resulted in a decreased retention for GLUT4-W105A. We conclude that the first intracellular loop of GLUT4 contains retention motif WLGRK, in which Trp105 plays a prominent role.
Collapse
Affiliation(s)
- Maya Talantikite
- Inserm U1062, INRA1260, Aix Marseille University, Faculty of Medicine, Marseille F-13385, France
| | - Marion Berenguer
- Inserm U895, Mediterranean Research Center for Molecular Medicine (C3M), Nice, F-06204, France
| | - Teresa Gonzalez
- Inserm U1062, INRA1260, Aix Marseille University, Faculty of Medicine, Marseille F-13385, France
| | - Marie Christine Alessi
- Inserm U1062, INRA1260, Aix Marseille University, Faculty of Medicine, Marseille F-13385, France
| | - Marjorie Poggi
- Inserm U1062, INRA1260, Aix Marseille University, Faculty of Medicine, Marseille F-13385, France
| | - Franck Peiretti
- Inserm U1062, INRA1260, Aix Marseille University, Faculty of Medicine, Marseille F-13385, France
| | - Roland Govers
- Inserm U1062, INRA1260, Aix Marseille University, Faculty of Medicine, Marseille F-13385, France
- Inserm U895, Mediterranean Research Center for Molecular Medicine (C3M), Nice, F-06204, France
| |
Collapse
|
8
|
Kioumourtzoglou D, Pryor PR, Gould GW, Bryant NJ. Alternative routes to the cell surface underpin insulin-regulated membrane trafficking of GLUT4. J Cell Sci 2015; 128:2423-9. [PMID: 26071524 PMCID: PMC4510850 DOI: 10.1242/jcs.166561] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Accepted: 05/26/2015] [Indexed: 01/12/2023] Open
Abstract
Insulin-stimulated delivery of glucose transporters (GLUT4, also known as SLC2A4) from specialized intracellular GLUT4 storage vesicles (GSVs) to the surface of fat and muscle cells is central to whole-body glucose regulation. This translocation and subsequent internalization of GLUT4 back into intracellular stores transits through numerous small membrane-bound compartments (internal GLUT4-containing vesicles; IGVs) including GSVs, but the function of these different compartments is not clear. Cellugyrin (also known as synaptogyrin-2) and sortilin define distinct populations of IGV; sortilin-positive IGVs represent GSVs, but the function of cellugyrin-containing IGVs is unknown. Here, we demonstrate a role for cellugyrin in intracellular sequestration of GLUT4 in HeLa cells and have used a proximity ligation assay to follow changes in pairwise associations between cellugyrin, sortilin, GLUT4 and membrane trafficking machinery following insulin-stimulation of 3T3-L1 adipoctyes. Our data suggest that insulin stimulates traffic from cellugyrin-containing to sortilin-containing membranes, and that cellugyrin-containing IGVs provide an insulin-sensitive reservoir to replenish GSVs following insulin-stimulated exocytosis of GLUT4. Furthermore, our data support the existence of a pathway from cellugyrin-containing membranes to the surface of 3T3-L1 adipocytes that bypasses GSVs under basal conditions, and that insulin diverts traffic away from this into GSVs.
Collapse
Affiliation(s)
- Dimitrios Kioumourtzoglou
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK Department of Biology, University of York, York YO10 5DD, UK
| | - Paul R Pryor
- Department of Biology, University of York, York YO10 5DD, UK Centre for Immunology and Infection, Hull York Medical School, University of York, York YO10 5DD, UK
| | - Gwyn W Gould
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Nia J Bryant
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK Department of Biology, University of York, York YO10 5DD, UK
| |
Collapse
|
9
|
Abstract
GLUT4 is regulated by its intracellular localization. In the absence of insulin, GLUT4 is efficiently retained intracellularly within storage compartments in muscle and fat cells. Upon insulin stimulation (and contraction in muscle), GLUT4 translocates from these compartments to the cell surface where it transports glucose from the extracellular milieu into the cell. Its implication in insulin-regulated glucose uptake makes GLUT4 not only a key player in normal glucose homeostasis but also an important element in insulin resistance and type 2 diabetes. Nevertheless, how GLUT4 is retained intracellularly and how insulin acts on this retention mechanism is largely unclear. In this review, the current knowledge regarding the various molecular processes that govern GLUT4 physiology is discussed as well as the questions that remain.
Collapse
|
10
|
Huang G, Buckler-Pena D, Nauta T, Singh M, Asmar A, Shi J, Kim JY, Kandror KV. Insulin responsiveness of glucose transporter 4 in 3T3-L1 cells depends on the presence of sortilin. Mol Biol Cell 2013; 24:3115-22. [PMID: 23966466 PMCID: PMC3784384 DOI: 10.1091/mbc.e12-10-0765] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Insulin-dependent translocation of Glut4 to the plasma membrane of fat and skeletal muscle cells plays the key role in postprandial clearance of blood glucose. In undifferentiated cells, insulin responsiveness of Glut4 depends on the presence of sortilin, whereas sortilin responds to insulin regardless of Glut4 expression. Insulin-dependent translocation of glucose transporter 4 (Glut4) to the plasma membrane of fat and skeletal muscle cells plays the key role in postprandial clearance of blood glucose. Glut4 represents the major cell-specific component of the insulin-responsive vesicles (IRVs). It is not clear, however, whether the presence of Glut4 in the IRVs is essential for their ability to respond to insulin stimulation. We prepared two lines of 3T3-L1 cells with low and high expression of myc7-Glut4 and studied its translocation to the plasma membrane upon insulin stimulation, using fluorescence-assisted cell sorting and cell surface biotinylation. In undifferentiated 3T3-L1 preadipocytes, translocation of myc7-Glut4 was low regardless of its expression levels. Coexpression of sortilin increased targeting of myc7-Glut4 to the IRVs, and its insulin responsiveness rose to the maximal levels observed in fully differentiated adipocytes. Sortilin ectopically expressed in undifferentiated cells was translocated to the plasma membrane regardless of the presence or absence of myc7-Glut4. AS160/TBC1D4 is expressed at low levels in preadipocytes but is induced in differentiation and provides an additional mechanism for the intracellular retention and insulin-stimulated release of Glut4.
Collapse
Affiliation(s)
- Guanrong Huang
- Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118
| | | | | | | | | | | | | | | |
Collapse
|
11
|
Deciphering the role of GLUT4 N-glycosylation in adipocyte and muscle cell models. Biochem J 2012; 445:265-73. [DOI: 10.1042/bj20120232] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
GLUT4 (glucose transporter 4) is responsible for the insulin-induced uptake of glucose by muscle and fat cells. In non-stimulated (basal) cells, GLUT4 is retained intracellularly, whereas insulin stimulation leads to its translocation from storage compartments towards the cell surface. How GLUT4 is retained intracellularly is largely unknown. Previously, aberrant GLUT4 N-glycosylation has been linked to increased basal cell-surface levels, while N-glycosylation-deficient GLUT4 was found to be quickly degraded. As recycling and degradation of GLUT4 are positively correlated, we hypothesized that incorrect N-glycosylation of GLUT4 might reduce its intracellular retention, resulting in an increased cell-surface recycling, in increased basal cell-surface levels, and in enhanced GLUT4 degradation. In the present study, we have investigated N-glycosylation-deficient GLUT4 in detail in 3T3-L1 preadipocytes, 3T3-L1 adipocytes and L6 myoblasts. We have found no alterations in retention, insulin response, internalization or glucose transport activity. Degradation of the mutant molecule was increased, although once present at the cell surface, its degradation was identical with that of wild-type GLUT4. Our findings indicate that N-glycosylation is important for efficient trafficking of GLUT4 to its proper compartments, but once the transporter has arrived there, N-glycosylation plays no further major role in its intracellular trafficking, nor in its functional activity.
Collapse
|