The glucose transporter 4 (GLUT4) is the major insulin-responsive glucose transporter in adipose and muscle tissues. Although the early steps in the insulin signaling pathway governing translocation of GLUT4 to the plasma membrane are well understood, the final steps in this pathway are not. TUG is a protein which has been shown to affect trafficking of GLUT4 both in the basal state and in response to insulin. One protein-protein interaction between TUG and the large cytosolic loop of GLUT4 has previously been identified. Based on reports of the requirement of the GLUT4 N-terminal domain for its proper targeting to the plasma membrane, we postulated that an interaction might also exist between TUG and the N-terminal domain of GLUT4, and we tested this hypothesis using two sets of pull-down experiments. In the first set, using the N-terminal domain of GLUT4 fused with glutathione S-transferase (GST), we were able to pull TUG down from the lysates of TUG-transfected HEK 293 cells. TUG was also pulled down by the GLUT4 cytosolic loop and, to a much lesser extent, its C-terminal domain. However, there was no specific interaction between these fusion proteins and the lysates of cells transfected with a truncated form of TUG lacking its own N-terminal domain. In the second set of experiments, using a biotinylated synthetic GLUT4 N-terminal peptide, we pulled down a protein detected by an anti-TUG antibody and running at ~64 kDa, a slightly higher molecular weight than wild-type TUG. We believe that this band represents modified full-length TUG. This interaction was not seen using synthetic GLUT4 N-terminal peptide mutated at 4 amino acids previously identified as necessary for proper GLUT4 retention and insulin-responsive trafficking. We conclude that TUG interacts not only with the large cytosolic loop of GLUT4, but also with the N-terminal domain of GLUT4, and that this latter interaction can be disrupted by mutations in GLUT4 that cause defective trafficking, suggesting that this interaction is critical for GLUT4 intracellular retention and insulin-responsive GLUT4 trafficking.

Thesis (Ph. D.)--Cornell University, August, 2008. / Vita. Includes bibliographical references (leaves 164-175).

The relationship between human erythrocyte glucose transporter (GLUT1) oligomeric structure and function was studied. GLUT1 was purified from human erythrocytes in the absence (GLUT1-DTT) or the presence (GLUT1+DTT) of dithiothreitol. Chemical cross-linking studies of lipid bilayer-resident purified GLUT1 and hydrodynamic studies of cholate-solubilized GLUT1 support the view that GLUT1-DTT is a homotetramer and GLUT1+DTT is a homodimer. Parallel studies on human erythrocyte, and studies employing conformation-specific antibodies (anti-GLUT1-DTT antibodies, ∂-IgGs), indicate that erythrocyte-resident GLUT1 resembles GLUT1-DTT (a homotetramer). While the D-glucose binding capacities of GLUT1-DTT and GLUT1+DTT are indistinguishable, GLUT1-DTT presents at least two population of binding sites to D-glucose whereas GLUT1+DTT presents only one population of sugar binding sites. The cytochalasin B (CCB) binding capacity of GLUT1-DTT (0.4 sites/monomer) is one half of that of GLUT1+DTT. GLUT1-DTT and GLUT1+DTT contain 2 and 6 free sulfhydryls per monomer respectively. The subunits (monomers) of tetrameric and dimeric GLUT1 are not linked by disulfide bridges. Erythrocyte resident GLUT1 presents at least two binding sites to D-glucose and binds CCB with a molar stoichiometry of 0.55 sites per GLUT1 monomer. Following treatment with high pH plus dithiothreitol, the sugar binding capacity of erythrocyte membrane resident transporter is unaltered but the transporter now presents only one population of binding sites to D-glucose, binds CCB with molar stoichiometry of 1.3 sites per GLUT1 monomer and displays significantly reduced affinity for ∂-IgGs. These findings demonstrate that erythrocyte resident glucose transporter is GLUT1-DTT (a GLUT1 tetramer) and that GLUT1 oligomeric structure determines GLUT1 functional properties. A model which rationalizes these findings is proposed.

Obesity and Diabetes, the major cause for morbidity and mortality in United States raises a general curiosity regarding health care expenses when talked about treating them. Every year approximately 300,000 US adults die of reasons associated to obesity and diabetes, becoming the sixth leading cause of death. The prevalence of those diagnosed with diabetes witnessed an exponential curve in the last decade and for the year 2011 about 8.3% of the population in the US has been diagnosed with diabetes and it is predicted that in the year 2030 the prevalence of diabetes is to reach 4.4% globally. Type 2 diabetes is a condition, which develops when the body no longer makes enough insulin or when the insulin so produced does not work effectively. In reaction to the increase in obesity, treatments for obesity became more common especially the pharmacological treatments. Since this treatment also required one to change their lifestyle and food habits, bariatric surgeries were considered as an option to treat obesity and diabetes. A range of surgical procedures have been used to stimulate weight loss for obese patients. These procedures resulted in weight loss by restricting the size of the stomach (Gastric Banding) or bypassing a portion of the intestine (Gastric Bypass). Roux-en-Y Gastric Bypass (RYGB) accomplishes weight loss during a combination of gastric restriction and malabsorption. Reduction of the stomach to a small gastric pouch results in feelings of satiety. The RYGB procedure has been performed regularly since the early 1980s; it was first performed laparoscopically in the early 1990s. Ileal interposition (IT) is a surgical procedure where a section of ileum is snipped and moved closer to the jejunum. It is said that the food takes just ten minutes to reach the ileum instead of an hour after this procedure. The ileum produces Glucagon like Peptide-1 (GLP-1) which helps in insulin secretion. Glucose is a key stimulator for mammals and is derived from the diet consumed, transferred from the circulation into the target cells. Glucose penetrates the eukaryotic cells through membrane associated carrier proteins, the Na+ coupled glucose transporter (SGLT-1) and the glucose transporter (GLUT). These transporters are structurally and functionally distinct. The main research question was "are the receptors involved in glucose transport across the membrane (GLUT2 and SGLT1) important for Ileal Interposition"? With experiments like real time PCR (qPCR) and immunohistochemistry (IHC), we have observed the differences in the expression of these receptors with respect to the location and organ. Ileal interposition showed a significant difference (p<0.01) compared to sham-operated rats in the expression of GLUT2 in the gluconeogenic organs. The increased GLUT2 levels in ileal interposition may explain glucose sensitivity and these data emphasize the need for GLUT2 to maintain a positive glucose homeostasis and further study on SGLT1/GLUT2 influence on gluconeogenesis.

Since the initial characterization of the human glucose transporter GLUT1, it has been observed that the presence of intracellular sugar stimulates the unidirectional rate of sugar uptake by a kinetic phenomenon known as trans-acceleration. Both GLUTs 1 and 3 catalyze transacceleration, while both GLUTs 2 and 4 do not. Although the basis for trans-acceleration is unknown, potential explanations include the requirement of a modulating cofactor, cellular context, or that the behavior is an artifact of imperfect transport measurements. This thesis examines whether trans-acceleration is a sequence-specific property intrinsic to the transporter. A method for detecting trans-acceleration in mammalian cells at physiologic temperature was developed through transport of two different glucose analogs. Homology-scanning mutagenesis was employed to exchange transmembrane domains (TMs) of GLUTs 1 and 4, and thereby test for accelerated-exchange loss- or gain-of-function. This approach was extended to GLUTs 2 and 3. The catalytic rates of these chimeric proteins were determined through transport measurements and expression measured by cell-surface biotinylation. These studies show that the sequence of putative scaffolding domain TM6 is both necessary and sufficient for trans-acceleration in scaffolds of GLUT1, GLUT2, and GLUT4. The substitution of TM6 sequence between these transporters has no effect on the turnover under exchange conditions, yet profoundly modifies turnover in the absence of intracellular sugar. We propose that the sequence-specific interaction of TM6 with other TMs structurally restrains relaxation of the empty carrier in GLUTs which catalyze trans-acceleration, and that binding of intracellular sugar affects these interactions to reduce the overall duration of the transport cycle. In addition, our model suggests that the substrate binding constant and rate of carrier relaxation are inter-dependent. In this model, the dissociation constant determined by substrate binding and dissociation rates at the endofacial sugar binding site must be larger than the equivalent constant at the exofacial site in order for trans-acceleration to occur.

In humans, the functional regulation of facilitative glucose transporters (GLUTs) by insulin plays a central role in the maintenance of glucose homeostasis. The insensitivity of tissues to this regulation results in diabetes mellitus, however, the underlying mechanisms remain largely unknown. To establish Caenorhabditis elegans (C. elegans) as a model system to study the mechanisms of insulin regulation of GLUTs because of the well-conserved insulin/IGF-like signaling (IIS) and many unique advantages of this organism, we functionally characterized 9 candidate genes of human GLUT homologues in C. elegans based on their sequence homologies to GLUTs. We found that FGT-1 is the only functional GLUT homologue with the ability to transport 2-deoxy-D-glucose (2DG) in Xenopus oocytes. FGT-1 mediated 2DG transport could be inhibited by the GLUT inhibitor phloretin and exhibited a Michaelis constant (Km) of 2.8 mM, which is smaller than the Km values of human GLUT1 and GLUT4. In addition to glucose, FGT-1 could also transport mannose, galactose, and fructose. Using a FGT-1::GFP fusion construct under the control of the 5 kb promoter sequence of the fgt-1a gene, FGT-1 was shown to be ubiquitously expressed in C. elegans tissues and cells, including the digestive tract, neurons, and body wall muscle. Two FGT-1 alternative splicing isoforms, FGT-1A and FGT-1B, showed similar transport activity and tissue localization. To study the function of FGT-1 and its regulation by IIS, the changes in several phenotypes that are known to be regulated by IIS were observed in FGT-1-knockdown worms or null strains in the presence or absence of IIS activity. FGT-1 knockdown resulted in fat accumulation but had no effects on dauer formation or brood size in both wild-type and daf-2 (insulin receptor) gene mutant strains. However, the function of FGT-1 in animal growth and aging was dependent on the IIS background, suggesting IIS regulation of FGT-1 function. Consistently, FGT-1 mediated glucose uptake was almost completely defective in the daf-2 and age-1 (PI3 kinase) mutants, and phloretin could only marginally inhibit 2DG uptake in these strains. This defect was only partially related to the approximately 60% decrease in FGT-1 protein levels in these mutants, suggesting the involvements of both post-transcriptional and post-translational regulatory mechanisms. We also found that OGA-1, an O-GlcNAcase, is essential for the function of FGT-1, implying possible regulation of FGT-1 function by glycosylation. In summary, our study has established C. elegans as a powerful model to study the mechanism by which insulin regulates glucose transporters and has provided insights into the mechanism of defective glucose uptake by tissues in patients with diabetes.

Tsang Po Ting. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 135-152). / Abstracts in English and Chinese. / Acknowledgements --- p.i / Abstract --- p.ii / Abstract 摘要 --- p.iv / List of Figures --- p.vi / List of Tables --- p.viii / List of Abbreviations --- p.ix / Table of Contents --- p.xii / Chapter Chapter 1: --- General Introduction --- p.1 / Chapter 1.1 --- The Role of Glucose in Biological System --- p.1 / Chapter 1.2 --- Glucose Transporter Families --- p.1 / Chapter 1.2.1 --- Na+-Dependent Glucose Transporters --- p.2 / Chapter 1.2.2 --- Facilitative Glucose Transporters --- p.3 / Chapter 1.3 --- Glucose Transporter Type1 --- p.7 / Chapter 1.3.1 --- Primary Structure of the Glutl Protein --- p.7 / Chapter 1.3.2 --- Secondary Structure --- p.8 / Chapter 1.3.3 --- Tertiary Structure --- p.8 / Chapter 1.3.4 --- Kinetics Properties --- p.11 / Chapter 1.3.5 --- Tissue Distribution --- p.12 / Chapter 1.3.6 --- Multifunctional Property --- p.13 / Chapter 1.3.7 --- Characterization of GLUT1 Gene --- p.13 / Chapter 1.3.8 --- Regulation of GLUT1 Expression --- p.14 / Chapter 1.4 --- Glucose Transporter Type 1 and the Brain --- p.16 / Chapter 1.5 --- Glucose Transporter Type 1 Deficiency Syndrome (GIutlDS) --- p.19 / Chapter 1.5.1 --- Backgronnd of GIutlDS --- p.19 / Chapter 1.5.2 --- Clinical Features of GIutlDS --- p.23 / Chapter 1.5.3 --- Genotype-Phenotype Correlations --- p.24 / Chapter 1.5.4 --- Diagnosis --- p.26 / Chapter 1.5.5 --- Manage nent --- p.27 / Chapter 1.5.5.1 --- Ketogenic Diet --- p.27 / Chapter 1.6 --- Hypothesis and Objectives --- p.29 / Chapter Chapter 2: --- Biochemical and Molecular Analysis of GLUT1 in a Suspected GlutlDS Case --- p.31 / Chapter 2.1 --- Materials --- p.32 / Chapter 2.1.1 --- Clinical History of Suspected GlutlDS Patient --- p.32 / Chapter 2.1.2 --- Blood Samples --- p.32 / Chapter 2.1.3 --- Reagents and Buffers for Reverse Transcription --- p.32 / Chapter 2.1.4 --- Reagents and Buffers for TA Cloning --- p.34 / Chapter 2.1.5 --- Reagents for Genomic DNA Extraction --- p.34 / Chapter 2.1.6 --- Reagents and Buffers for Polymerase Chain Reaction (PCR) --- p.34 / Chapter 2.1.7 --- Reagents and Buffers for Agarose Gel Electrophoresis --- p.35 / Chapter 2.1.8 --- Reagents for Zero-trans 3-OMG Influx in Erythrocytes --- p.37 / Chapter 2.1.9 --- Reagents for Zero-trans 3-OMG Efflux from Erythrocytes --- p.38 / Chapter 2.1.10 --- Reagents for Erythrocytes Membrane Extraction and Detection --- p.39 / Chapter 2.2 --- Methods --- p.44 / Chapter 2.2.1 --- GLUT1 Gene Analysis --- p.44 / Chapter 2.2.2 --- Zero-trans 3-OMG Influx into Erythrocytes --- p.51 / Chapter 2.2.3 --- Zero-trans 3-OMG Efflux from Erythrocytes --- p.52 / Chapter 2.2.4 --- Glutl Protein Expression --- p.54 / Chapter 2.2.5 --- Statistics --- p.57 / Chapter 2.3 --- Results --- p.58 / Chapter 2.3.1 --- Molecular Analysis of the GLUT1 Gene of a Suspected GlutlDS Patient --- p.58 / Chapter 2.3.2 --- Functional Analysis of the GlutlDS Patient's Glutl Protein --- p.61 / Chapter 2.3.3 --- Glutl Protein Expression in the GlutlDS Patient --- p.64 / Chapter 2.4 --- Discussion --- p.66 / Chapter Chapter 3: --- Pathogenicity Studies of GLUT1 Mutations --- p.71 / Chapter 3.1 --- Materials --- p.72 / Chapter 3.1.1 --- Construction of Glutl-Encoding Vectors --- p.72 / Chapter 3.1.2 --- Cell Lire --- p.73 / Chapter 3.1.3 --- "Cell Culture Media, Buffers and Other Reagents" --- p.73 / Chapter 3.1.4 --- Cell Culture Wares --- p.75 / Chapter 3.1.5 --- Reagents for Transfection --- p.75 / Chapter 3.1.6 --- Reagents for Protein Determination and Western Blot Analysis --- p.76 / Chapter 3.1.7 --- Consumables for Confocal Microscopy --- p.77 / Chapter 3.1.8 --- Reagents and Buffers for Flow Cytometry --- p.77 / Chapter 3.1.9 --- Reagents for 2-DOG Uptake in CHO-K1 Cells --- p.77 / Chapter 3.2 --- Methods --- p.79 / Chapter 3.2.1 --- Cell Culture Methodology --- p.79 / Chapter 3.2.2 --- Construction of GLUT1 Mutants --- p.80 / Chapter 3.2.3 --- Establishment of Wild Type and Mutant Glutl Expressing Cell Lines --- p.84 / Chapter 3.2.4 --- Protein Expression Study --- p.85 / Chapter 3.2.5 --- 2-DOG Influx Assay in CHO-K1 Cells --- p.87 / Chapter 3.2.6 --- Confocal Microscopy Studies on Glutl Cellular Localization --- p.89 / Chapter 3.2.7 --- Statistics --- p.90 / Chapter 3.3 --- Results --- p.91 / Chapter 3.3.1 --- Molecular Analysis of 1034-1035Insl2 Mutation --- p.91 / Chapter 3.3.2 --- Expression of the Wild Type and Mutant GFP-Glutl Fusion Proteins --- p.92 / Chapter 3.3.3 --- Functional Analysis of the 1034-1035Insl2 Mutant --- p.95 / Chapter 3.4 --- Discussion --- p.97 / Chapter Chapter 4: --- GLUT1 Promoter Study --- p.100 / Chapter 4.1 --- Materials --- p.101 / Chapter 4.1.1 --- Construction of GLUT1 Promoter Vectors --- p.101 / Chapter 4.1.2 --- Cell Lines --- p.102 / Chapter 4.1.3 --- Cell Culture Media and Other Reagents --- p.103 / Chapter 4.1.4 --- Dual Luciferase Reporter Assay System --- p.103 / Chapter 4.2 --- Methods --- p.105 / Chapter 4.2.1 --- Bioinformatics --- p.105 / Chapter 4.2.2 --- Cell Culture --- p.105 / Chapter 4.2.3 --- Construetion of GLUT1 Promoter Vectors --- p.105 / Chapter 4.2.4 --- 5'-Deletion Analysis of GLUT1 Promoter --- p.108 / Chapter 4.2.5 --- Determination of the Activities of GLUT1 Promoter Fragments --- p.110 / Chapter 4.2.6 --- Statistics --- p.113 / Chapter 4.3 --- Results --- p.114 / Chapter 4.3.1 --- Determination of the Promoter Activity of the 5'-deletion Fragments --- p.114 / Chapter 4.3.2 --- Prediction of Transcription Factors in the 5'-deletion Fragments --- p.119 / Chapter 4.4 --- Discussion --- p.121 / Chapter Chapter 5: --- General Conclusion and Future Perspectives --- p.133 / References --- p.135

Submitted by Jean Medeiros (jeanletras@uepb.edu.br) on 2016-03-15T13:08:48Z No. of bitstreams: 1 PDF - Rafaella Bastos Leite.pdf: 1326501 bytes, checksum: 57e6fffb3bbe74433cba4f469a5b6545 (MD5) / Approved for entry into archive by Secta BC (secta.csu.bc@uepb.edu.br) on 2016-07-21T21:05:02Z (GMT) No. of bitstreams: 1 PDF - Rafaella Bastos Leite.pdf: 1326501 bytes, checksum: 57e6fffb3bbe74433cba4f469a5b6545 (MD5) / Approved for entry into archive by Secta BC (secta.csu.bc@uepb.edu.br) on 2016-07-21T21:05:12Z (GMT) No. of bitstreams: 1 PDF - Rafaella Bastos Leite.pdf: 1326501 bytes, checksum: 57e6fffb3bbe74433cba4f469a5b6545 (MD5) / Made available in DSpace on 2016-07-21T21:05:12Z (GMT). No. of bitstreams: 1 PDF - Rafaella Bastos Leite.pdf: 1326501 bytes, checksum: 57e6fffb3bbe74433cba4f469a5b6545 (MD5) Previous issue date: 2014-07-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The keratocystic odontogenic tumor (KOT) stands out among the other odontogenic lesions in view of the potentially aggressive biological behavior and its association in some cases, with the Gorlin syndrome. Some studies have suggested a more aggressive biological behavior for KOTs associated with Gorlin syndrome, compared to isolated KOTs, characterized by greater growth capacity and bone infiltration and higher tendency to recur. The present study aimed to evaluate, descriptively and comparatively, by means of immunohistochemistry, the expression of glucose transporter-1 (GLUT-1) and -3 (GLUT-3) and the angiogenic index (CD34) in isolated primary and recurrent KOTs and in KOTs associated with Gorlin syndrome. The sample was composed by 21 isolated KOTs (14 primary and 7 recurrent) and 14 KOTs associated with Gorlin syndrome. The expression of GLUTs was evaluated in the epithelial component of the lesions, establishing the percentage of immunopositive cells, according to the scores: score 0 (negative), score 1 (≤ 25% of positive cells), score 2 (26% - 50% of positive cells), score 3 (51% - 75% of positive cells), and score 4 (≥ 76% positive cells). For the angiogenic index, the microvessel count (MVC) technique was applied, quantifying the microvessels immunoreactive to anti-CD34 antibody. Regarding the median scores for immunopositivity for GLUT-1 and the angiogenic index, comparisons between groups were performed using the nonparametric Kruskal-Wallis test. For GLUT-3, the data obtained from the evaluation of epithelial expression of this protein were submitted to descriptive statistical analysis. Possible correlations between the scores of immunopositivity for GLUT-1 and angiogenic index in the lesions were evaluated using the Spearman correlation test. The level of significance was set at 5% (p <0.05). The analysis of epithelial GLUT-1 immunoreactivity revealed predominance of score 4 in isolated primary KOTs (n = 9, 64.3%) and in KOTs associated with Gorlin syndrome (n = 8; 57.1%). In isolated recurrent KOTs, it was identified a slightly higher frequency of cases with scores 4 (n = 3; 42.9%) and 2 (n = 2; 28.6%). The nonparametric Kruskal-Wallis test showed no statistically significant difference between groups (p = 0.406). Regarding the GLUT-3, all groups showed higher frequency of negative cases. The few KOTs positive for GLUT-3 were classified as score 1 (≤ 25% of positive cells), showing a low expression of this protein in the epithelial component. The mean number of microvessels was 63.80 in isolated primary KOTs, 61.11 in KOTs associated with the Gorlin syndrome, and 65.88 in isolated recurrent KOTs, without significant differences between groups (p = 0.965). The results of this study suggest that the differences in biological behavior of isolated KOTs and KOTs associated with Gorlin syndrome may not be related to the expression of GLUTs-1 and -3, or to the angiogenic index in the lesions. The high expression of GLUT-1 in KOTs suggests an important role for this protein in glucose uptake by the epithelial cells of these tumors. / O tumor odontogênico ceratocístico (TOC) se destaca entre as demais lesões odontogênicas em virtude do comportamento biológico potencialmente agressivo e por sua associação, em alguns casos, à síndrome de Gorlin. Pesquisas tem sugerido um comportamento biológico mais agressivo para os TOCs associados à síndrome de Gorlin, em comparação aos TOCs isolados, caracterizado por maior capacidade de crescimento e infiltração óssea e maior tendência a recorrência. O presente estudo se propôs a avaliar, descritiva e comparativamente, a imunoexpressão dos transportadores de glicose-1 (GLUT-1) e -3 (GLUT-3) e o índice angiogênico (CD34) em TOCs isolados primários e recorrentes e TOCs associados à síndrome de Gorlin. A amostra foi composta por 21 TOCs isolados (14 primários e 7 recorrentes) e 14 TOCs associados à síndrome de Gorlin. A expressão dos GLUTs foi avaliada no componente epitelial das lesões, estabelecendo-se o percentual de células imunopositivas, de acordo com os escores: escore 0 (negativo), escore 1 (≤ 25% das células positivas), escore 2 (26% - 50% das células positivas), escore 3 (51% - 75% das células positivas) e escore 4 (≥76% das células positivas). Para o índice angiogênico, foi empregada a técnica da contagem microvascular (MVC), quantificando-se os microvasos imunomarcados pelo anticorpo anti-CD34. Em relação às medianas para os escores de imunopositividade para GLUT-1 e para o índice angiogênico, as comparações entre os grupos foram realizadas por meio do teste não paramétrico de Kruskal-Wallis. Para o GLUT-3, os dados obtidos com a avaliação da expressão epitelial desta proteína foram submetidos apenas à análise estatística descritiva. Possíveis correlações entre os escores de imunopositividade para GLUT-1 e o índice angiogênico nas lesões foram avaliadas por meio do teste de correlação de Spearman. O nível de significância foi estabelecido em 5% (p < 0,05). A análise da imunoexpressão epitelial de GLUT-1 revelou predomínio de casos com escore 4 nos TOCs isolados primários (n = 9; 64,3%) e nos TOCs associados à síndrome de Gorlin (n = 8; 57,1%). Nos TOCs isolados recorrentes, foi identificada frequência discretamente maior para os casos com escores 4 (n = 3; 42,9%) e 2 (n = 2; 28,6%). O teste não paramétrico de Kruskal-Wallis revelou ausência de diferença estatisticamente significativa entre os grupos (p = 0,406). Em relação ao GLUT-3, todos os grupos estudados revelaram maior frequência de casos negativos. Os poucos TOCs positivos para GLUT-3 foram classificados como escore 1 (≤ 25% das células positivas), revelando uma baixa expressão desta proteína no componente epitelial. O número médio de microvasos foi de 63,80 nos TOCs isolados primários, 61,11 nos TOCs associados a síndrome de Gorlin e 65,88 nos TOCs isolados recorrentes, sem diferenças significativas entre os grupos (p = 0,965). Os resultados do presente estudo sugerem que as diferenças no comportamento biológico de TOCs isolados e TOCs associados à síndrome de Gorlin não foram relacionadas com a expressão de GLUTs-1 e -3 ou com o índice angiogênico (CD34) nas lesões. A alta expressão de GLUT-1 em TOCs sugere um importante papel para esta proteína na captação de glicose pelas células epiteliais destes tumores.

Glucocorticoids are widely used in clinical therapy. However, they cause adverse effects including insulin resistance and Type 2 diabetes, which are characterised by decreased glucose transport into the muscles and fat. How glucocorticoids inhibit glucose transport remains unclear. Insulin stimulates glucose uptake via the insulin receptor substrate (IRS)-1 / phosphoinositide-3-kinase (PI3K) / protein kinase B (AKT) pathway and promotes the redistribution of GLUT4 from intracellular storage compartments to the plasma membrane (PM). Insulin-stimulated phosphorylation of AKT substrate of 160 kDa (AS160), a Rab-GTPase activating protein is downstream of AKT and appears to be essential for exposure of GLUT4 at the PM and glucose uptake. This is mediated through the association of phosphorylated AS160 (at the key residue T642) with 14-3-3 in the cytosol. The mildly insulin-responsive GLUT1 mediates basal glucose uptake in adipocytes. It is also subject to regulated trafficking like GLUT4. This study aimed to determine the level at which glucocorticoids inhibit glucose uptake in adipocytes. Effects of the synthetic glucocorticoid dexamethasone (Dex) and the natural glucocorticoid cortisol, on GLUT1 and GLUT4 function were examined. Candidates for the glucocorticoid-mediated inhibition of GLUT1- and GLUT4-mediated glucose uptake were investigated. These were glycogen synthase kinase (GSK) 3β (an AKT substrate) for GLUT1-mediated glucose transport; and adaptor protein containing PH domain, PTB domain, and leucine zipper motif (APPL)-1 (an AKT-interacting protein) and AS160 for GLUT4-mediated glucose transport. Dex and cortisol significantly decreased basal glucose uptake by 50% (p<0.05) in SGBS and 3T3-L1 adipocytes. Similarly, insulin-stimulated glucose uptake was decreased by 50% (p<0.001 for SGBS; p<0.05 for 3T3-L1) and 30% (p<0.05 for both) at 1 nM and 100 nM insulin respectively. Similar results were observed with differentiated primary human preadipocytes and human adipose explants. Dex-mediated inhibition of basal glucose uptake was limited to insulin-sensitive cell types implying that glucocorticoids may regulate GLUTs at steps common to GLUT1 and GLUT4 trafficking. Dex-mediated reduction in glucose uptake correlated with the reduction in basal and insulin-stimulated expression of GLUT1 and GLUT4 to the PM without changes in total GLUT1/4 expression. Dex did not alter total expression or phosphorylation of proximal insulin-signalling molecules up to and including AKT but increased FOXO1 expression, and modified GSK3β-S9 phosphorylation. Dex did not alter total APPL1 expression or subcellular distribution. Dex significantly decreased 1nM-insulin stimulated AS160-T642 phosphorylation by 50% (p<0.05) in SGBS and 3T3-L1 adipocytes via the glucocorticoid repector (GR). This correlated with reduced AS160:14-3-3 interaction. Similar results were obtained for AS160-T642 basal phosphorylation. At 1nM insulin, AS160-T642 phosphorylation is maximal at sub-maximal glucose uptake, i.e. AS160 phosphorylation significantly contributes to glucose uptake. RU486 significantly prevented but did not fully abrogate the Dex-mediated reduction in glucose uptake suggesting additional Dex-induced defects. In conclusion, glucocorticoids inhibit glucose uptake at a level distal to AKT by GR-dependent mechanisms. A role for GSK3β or APPL1 in glucocorticoid-mediated inhibition of glucose uptake requires further investigations. FOXO1 represents a suitable candidate for mediating the Dex-induced defects. Of significance, perturbation in AS160-T642 phosphorylation contributes to Dex-mediated inhibition of glucose uptake. Thus, AS160 presents a novel therapeutic target in the improvement of glucocorticoid-mediated inhibition of glucose uptake.

Diss. (sammanfattning) Linköping : Linköpings universitet, 2007. / Härtill 4 uppsatser.