Insulin stimulates glucose uptake in adipose and muscle cells via translocation of the intracellular vesicles containing GLUT4. It was largely unknown whether and/or how the signaling molecules such as PI 3-kinase and Akt regulate the mechanical movements of the GLUT4-containing vesicles. Hence, this study was performed to test the hypothesis that actin and microtubules function in translocating GLUT4 vesicles. Treatments of insulin as well as endothelin-1 (ET-1), an insulin-mimicking peptide which does not act through PI 3-kinase, induced polymerization of actin without affecting the microtubular network. By mass spectrometry, the tyrosine kinase PYK2 was identified to be tyrosine phosphorylated specifically by ET-1 but not by insulin. Expression of the carboxyl-terminal fragment (CRNK) PYK2, but not wild type nor kinase-deficient PYK2 mutants, inhibited ET-1-stimulated actin polymerization while expression of all three PYK2 constructs had no effect on insulin-stimulated actin polymerization. More importantly, expression of CRNK, but not wild type nor kinase-deficient PYK2 constructs, blocked ET-1- but not insulin-stimulated GLUT4 translocation to the plasma membrane. These suggest that ET-1 and insulin stimulate actin polymerization via distinct signaling pathways, and that the actin polymerization is required for GLUT4 vesicle translocation. In order to test the possible involvement of microtubule in GLUT4 vesicle translocation, time lapse imaging of 3T3-L1 adipocytes expressing GLUT4-YFP and tubulin-CFP was performed. GLUT4-YFP vesicles move long-range bi-directionally on microtubules, which suggests the presence of molecular motors on the vesicles. Moreover, insulin increased the number of vesicle movements on microtubules without changing the velocities. Interestingly, the stimulatory action of insulin appears to be independent of PI 3-kinase activation. Conventional kinesin was identified as a highly expressed kinesin isotype in adipocytes. Notably, expression of dominant negative mutants but not wild type kinesin inhibited insulin-stimulated long-range GLUT4 vesicle movements and GLUT4 translocation to the plasma membrane in live and fixed cells, respectively. These data indicate that insulin signaling induces the movement of GLUT4 vesicles on microtubule which is mediated by conventional kinesin. Overall, the data presented here provide evidence supporting the hypothesis that actin and microtubule cytoskeletons are required for insulin to mobilize GLUT4 vesicles in adipocytes.

This thesis examines the hypothesis that human erythrocyte net sugar transport is the sum of two serial processes: sugar translocation followed by interaction of newly imported sugar with an intracellular binding complex from which sugar dissociates into the bulk cytosol. This hypothesis suggests that steady-state transport measurements in the human erythrocyte do not accurately reflect the intrinsic catalytic features of the glucose transporter and unless correctly interpreted, may lead to apparent inconsistencies in the operational behavior of the human erythrocyte sugar transport system. Our results support this proposal by demonstrating that although sugar transport measurements in human red blood cells suggest that transport is catalytically asymmetric, ligand binding measurements indicate that transport must be symmetric. In order to examine the serial compartments hypothesis, we set out to determine the following: 1) identify the component(s) of the proposed sugar binding complex, 2) determine whether cytosolic ATP levels and transporter quaternary structure affect sugar binding to the sugar binding complex, and 3) determine whether the sugar binding site(s) are located within or outside the cell. We present findings which support the hypothesis that the sugar binding complex is in fact the sugar transport protein, GLUT1. The number of sugar binding sites and the release of sugar from the GLUT1 complex are regulated by ATP and by GLUT1 quaternary structure. The sugar binding sites are located on a cytoplasmic domain of the GLUT1 complex. We show how these observations can account for the apparent complexity of erythrocyte sugar transport and its regulation by ATP.

by Chan Ka Kui. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 104-113). / Abstracts in English and Chinese. / ABSTRACT --- p.1 / Chapter 1 --- INTRODUCTION --- p.5 / Chapter 1.1 --- Incidence rate of breast cancer in Hong Kong --- p.5 / Chapter 1.2 --- Estrogen and breast cancer --- p.6 / Chapter 1.3 --- The relation between glucose transporters and breast cancer --- p.7 / Chapter 1.4 --- Antisense oligonucleotide --- p.10 / Chapter 1.5 --- Action mechanisms of antisense oligonucleotide --- p.11 / Chapter 1.6 --- Modification of the oligonucleotide --- p.13 / Chapter 1.7 --- Length --- p.16 / Chapter 1.8 --- Sequence selection of the antisense oligonucleotide --- p.16 / Chapter 1.9 --- Delivery means in antisense oligonucleotide --- p.18 / Chapter 1.10 --- The therapeutic role of antisense oligonucleotide --- p.19 / Chapter 1.11 --- Objective of the project --- p.21 / Chapter 2 --- MATERIAL AND METHODS --- p.23 / Chapter 2.1 --- Materials --- p.23 / Chapter 2.2 --- Methods --- p.26 / Chapter 3 --- RESULTS --- p.37 / Chapter 3.1 --- The characteristics of MCF-7 and MDA-MB-231 cells --- p.37 / Chapter 3.2 --- Trend of uptake of antisense oligonucleotides in MCF-7 and MDA- MB-231 cells --- p.41 / Chapter 3.3 --- The integrity of the oligonucleotide in serum-free medium during transfection --- p.48 / Chapter 3.4 --- Detection of effects of Glut5 antisense oligonucleotides of breast tumor cells-MTT assay --- p.50 / Chapter 3.5 --- Detection of the antiproliferative effect by trypan blue exclusion assay and thymidine incorporation --- p.56 / Chapter 3.6 --- Cell cycle analysis and DNA extraction --- p.61 / Chapter 3.7 --- Suppression of Glut5 mRNA detected by RT-PCR --- p.66 / Chapter 3.8 --- Suppression of translation of Glut5 proteins as indicated by Western blotting --- p.73 / Chapter 3.9 --- Measurement of the fructose and glucose uptake in MCF-7 and MDA -MB-231 cells after antisense treatment --- p.76 / Chapter 3.10 --- Change of the phosphofructokinase-1 (PFK-1) activities in MDA- MB-231 cells --- p.82 / Chapter 3.11 --- Measurement of the change in the intracellular pH of the breast tumor cells --- p.84 / Chapter 4 --- DISCUSSION --- p.89 / Chapter 4.1 --- The insights of Glut5 antisense oligonucleotide into cancer therapy --- p.89 / Chapter 4.2 --- The uptake pattern of Glut5 antisense oligonucleotides in breast tumor cells --- p.90 / Chapter 4.3 --- Stability of antisense oligonucleotide during transfection --- p.92 / Chapter 4.4 --- Effects of Glut5 antisense oligonucleotide on MCF-7 and MDA-MB- 231cells --- p.93 / Chapter 4.5 --- Proofs of undergoing antisense action mechanism --- p.95 / Chapter 4.6 --- Physiological changes in breast tumor cells after antisense treatment --- p.97 / Chapter 5 --- CONCLUSION --- p.103 / Chapter 6 --- References --- p.104

Lam Mei Wah. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 172-181). / Abstracts in English and Chinese. / Abstract --- p.i / 論文撮要 --- p.iv / Acknowledgement --- p.vii / Table of contents --- p.viii / List of tables --- p.xi / List of figures --- p.xii / Abbreviations --- p.xvii / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- The facilitative glucose transporter family --- p.2 / Chapter 1.2 --- Overexpression of glucose transporters in tumor cells --- p.5 / Chapter 1.3 --- Antisense strategy --- p.8 / Chapter 1.3.1 --- Modifications of oligonucleotides --- p.9 / Chapter 1.3.2 --- Delivery system for oligonucleotides --- p.13 / Chapter 1.3.3 --- Factors influencing antisense activity --- p.16 / Chapter 1.3.4 --- Mechanism of action of antisense oligonucleotides --- p.17 / Chapter 1.3.5 --- Clinical trials of antisense treatment --- p.21 / Chapter 1.4 --- Objective of present study --- p.23 / Chapter Chapter 2: --- Materials and Methods --- p.24 / Chapter 2.1 --- Materials --- p.25 / Chapter 2.1.1 --- Reagents and buffers --- p.25 / Chapter 2.1.2 --- Reagents for Western blot analysis --- p.26 / Chapter 2.1.3 --- Culture medium --- p.28 / Chapter 2.1.4 --- Chemicals --- p.29 / Chapter 2.1.5 --- Culture of cells --- p.31 / Chapter 2.1.5.1 --- Differentiated Human Hepatoblastoma cell line (HepG2) --- p.31 / Chapter 2.1.5.2 --- "Multi-drug resistant hepatoma cell line, R-HepG2 cells" --- p.32 / Chapter 2.1.6 --- Animal Studies --- p.33 / Chapter 2.2 --- Methods --- p.34 / Chapter 2.2.1 --- In vitro studies --- p.34 / Chapter 2.2.1.1 --- Design of oligonucleotide sequence --- p.34 / Chapter 2.2.1.2 --- Transfection --- p.35 / Chapter 2.2.1.3 --- MTT assay --- p.36 / Chapter 2.2.1.4 --- Flow cytometry --- p.37 / Chapter 2.2.1.5 --- H-thymidine incorporation assay --- p.45 / Chapter 2.2.1.6 --- 2-Deoxy-D-[l-3H] glucose uptake assay --- p.46 / Chapter 2.2.1.7 --- Adenosine-5'-triphosphate (ATP) assay --- p.47 / Chapter 2.2.1.8 --- Western blot analysis --- p.50 / Chapter 2.2.2 --- In vivo studies --- p.55 / Chapter 2.2.2.1 --- Animal studies --- p.55 / Chapter (i) --- Lactate dehydrogenase (LDH) assay --- p.58 / Chapter (ii) --- Creatine kinase (CK) assay --- p.60 / Chapter (iii) --- Aspartate transaminase (AST) assay --- p.62 / Chapter (iv) --- Alanine transaminase (ALT) assay --- p.64 / Chapter Chapter 3: --- Results --- p.67 / Chapter 3.1 --- In vitro studies --- p.68 / Chapter 3.1.1 --- Characteristics of the multi-drug resistant cell line (R-HepG2) developed in our laboratory --- p.68 / Chapter 3.1.2 --- Effect of lipofectin on cell viability --- p.77 / Chapter 3.1.3 --- Cellular uptake of antisense oligonucleotide --- p.82 / Chapter 3.1.4 --- Effect of Glut 2 antisense oligonucleotides on human hepatoma HepG2 and its multidrug resistant (R-HepG2) cells by MTT assay --- p.87 / Chapter 3.1.5 --- Suppression of Glut 2 protein expression by antisense oligonucleotides as revealed by Western blot analysis --- p.96 / Chapter 3.1.6 --- Uptake of glucose in HepG2 and R-HepG2 after Glut 2 antisense treatment --- p.100 / Chapter 3.1.7 --- ATP content in HepG2 and R-HepG2 was lowered after treating the cells with antisense oligonucleotides --- p.108 / Chapter 3.1.8 --- Antisense oligonucleotides against Glut 2 exhibited antiproliferative effect on HepG2 and R-HepG2 cells --- p.117 / Chapter 3.1.9 --- Change in cell cycle pattern after antisense treatment --- p.125 / Chapter 3.1.10 --- Glut 2 antisense oligonucleotides did not induce apoptosis --- p.131 / Chapter 3.2 --- In vivo studies --- p.135 / Chapter 3.2.1 --- Effect of antisense oligonucleotides on the tumor weight in nude mice bearing HepG2 cells or R-HepG2 cells --- p.135 / Chapter 3.2.2 --- Assessment of any side effect of antisense drug done on normal tissues of nude mice --- p.139 / Chapter 3.2.2.1 --- Treatment on tumor bearing nude mice with Glut 2 antisense or sense oligonucleotides did not cause myocardial injury --- p.139 / Chapter 3.2.2.2 --- Liver injury was not detected in Glut 2 antisense or sense oligonucleotides treated tumor bearing nude mice --- p.147 / Chapter Chapter 4: --- Discussion --- p.151 / Chapter 4.1 --- In vitro study of the effect of antisense oligonucleotides against Glut 2 on HepG2 and its multi-drug resistant R-HepG2 cell lines --- p.152 / Chapter 4.1.1 --- Design of antisense oligonucleotides against Glut 2 --- p.154 / Chapter 4.1.2 --- Conditions for antisense inhibition by oligonucleotides --- p.155 / Chapter 4.1.3 --- Biological effects of antisense oligonucleotides --- p.158 / Chapter 4.2 --- In vivo study of the effect of antisense oligonucleotides against Glut 2 on HepG2 or R-HepG2 cells bearing nude mice --- p.166 / Chapter 4.2.1 --- Effect of Glut 2 antisense oligonucleotides on tumor weight --- p.167 / Chapter 4.2.2 --- In vivo side effects of oligonucleotides --- p.168 / Chapter 4.3 --- Conclusion --- p.169 / Bibliography --- p.172

Hebert and Carruthers (1992) showed that the human erythrocyte glucose transporter is an allosteric complex of four GLUT1 proteins whose structure and substrate binding properties are stabilized by reductant-sensitive noncovalent subunit interactions. The GLUT1 tetramer dissociates into dimers upon exposure to reductant but subunits are not associated via disulfide bridges. Each subunit of SDS-denatured tetrameric GLUT1 exposes only two thiols while reduced denatured GLUT1 exposes all six sulfhydryl groups. They hypothesized that glucose transporter oligomeric structure and cooperative catalytic function resulted from noncovalent subunit interactions promoted or stabilized by intramolecular disulfide bridges. These interactions give rise to an antiparallel arrangement of substrate binding sites within the transporter complex. In the present studies, we tested aspects of this model. Specifically, we wanted 1) to understand why the native, noncovalent, homotetrameric GLUT1 complex is sensitive to reductant, 2) to determine whether the tetramer is more catalytically efficient than the dimer in situ, and 3) to test the hypothesis that it is the antiparallel arrangement of substrate binding sites between subunits that provides the transporter with its catalytic advantage. We used biochemical and molecular biological approaches to isolate specific determinants of transporter oligomeric structure and/or transport function in purified isolated transporter preparations, in intact red cells and in CHO cells. We have also examined the hypothesis that net sugar transport in the human erythrocyte is rate limited by reduced cytosolic diffusion of sugars and/or by reversible sugar association with intracellular macromolecules. Our findings support the hypothesis that each subunit of the parental glucose transporter contains a single intramolecular disulfide bridge located between cysteine residues 347 and 421. This disulfide seems to be necessary for GLUT1 tetramerization. Our findings suggest that GLUT1 N-terminal residues 1 through 199 provide contact surfaces for subunit dimerization but are insufficient for subunit tetramerization. Our studies also show that in situ disulfide disruption by cell impermeant reductants results in the loss of cooperative subunit interactions and a 3 to 15-fold reduction in the transport efficiency of the transporter. We further find that in situ GLUT1 is susceptible to exofacial proteolysis. Exofacial trypsin cleavage eliminates cooperativity between subunits but does not affect transporter oligomeric structure or transport activity. Thus catalytic efficiency does not derive directly from cooperative interactions between substrate binding sites on adjacent subunits. We have confirmed that 30MG transport in human erythrocytes is a diffusion limited process. We find that steady-state sugar uptake in red cells and K562 cells measures two processes - sugar translocation and intracellular sugar binding. We propose a model for native GLUT1 structure and function.

Hydrodynamic analysis and electron microscopy of GLUT1/lipid/detergent micelles and freeze fracture electron microscopy of GLUT1 proteoliposomes support the hypothesis that the glucose transporter is a multimeric (probably tetrameric) complex of GLUT1 proteins. Some detergents (e.g. octylglucoside) maintain the multimeric complex while other detergents (e.g. CHAPS and dodecylmaltoside) promote the dissociation of GLUT1 oligomers into smaller aggregation states (dimers or monomers). GLUT1 does not appear to exchange rapidly between protein/lipid/detergent micelles but is able to self-associate in the plane of the lipid bilayer. Quantitatively deglycosylated GLUT1 displays aberrant electrophoretic mobility, but each protein band contains full-length GLUT1 and the less mobile species, when treated with additional detergent and reductant, converts to the more mobile species. Preliminary structural analysis suggests that denaturing detergent- and thiol chemistry-related changes of α-helical content may mirror mobility shifts. Limited proteolysis of membrane-resident GLUT1 (± ligands) releases membrane-spanning α-helical domains suggesting that (i) some bilayer-resident helices are highly solvent exposed; (ii) membrane-spanning domains 1, 2, & 4 and 7, 8, & 10 are destabilized upon ligand binding; and (iii) helix packing compares well with high-resolution structures of prokaryotic transporters from the same superfamily. Results are consistent with a central, hydrophilic, translocation pathway comprised of amphipathic, membrane-spanning domains that alter associations upon ligand/substrate binding. We have resolved technical difficulties (heterogeneity, lipid/detergent removal, glycosylation, small molecule contamination) associated with GLUT1 analysis by mass spectrometry; and we map global conformational changes between sugar uptake and sugar efflux.