Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GLUT4”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32Linked to original sources
PubMed1991

Insulin-like action of catecholamines and Ca2+ to stimulate glucose transport and GLUT4 translocation in perfused rat heart.

The uptake of 2-deoxyglucose by perfused rat hearts was compared to the distribution of the insulin-regulatable glucose transporter (GLUT4) in membrane preparations from the same hearts. The hearts were treated with the alpha-adrenergic combination of epinephrine + propranolol, the beta-adrenergic agonist isoproterenol, high (8 mM) Ca2+ concentrations, insulin and the alpha adrenergic combination or insulin alone. Epinephrine (1 microM) + propranolol (10 microM), isoproterenol (10 microM), high Ca2+, insulin (1 microM) + epinephrine (1 microM) + propranolol (10 microM) and insulin (1 microM) each led to an increase in 2-deoxyglucose uptake and a shift in the recovery of the GLUT4 from a high-speed pellet membrane fraction (putatively intracellular) to a low-speed pellet membrane fraction (putatively sarcolemmal). There were significant correlations (r = -0.673, P less than 0.001) between the stimulation of 2-deoxyglucose uptake and the loss of GLUT4 from the intracellular membrane fraction, or the increase in the sarcolemmal fraction. The data provide evidence that the GLUT4 is translocated by agents that stimulate glucose transport in heart, and therefore this mechanism is not restricted to insulin.

5'-Nucleotidase↗
PubMed1996

Discrete brain areas express the insulin-responsive glucose transporter GLUT4.

Whether or not glucose utilization in the brain is insulin-dependent is still a controversial issue. We looked for the presence of the insulin-sensitive glucose transporter (GLUT4) in rat brain and obtained the following results: (1) poly(A) RNAs from the hypothalamus and anterior medulla oblongata hybridize with a cDNA probe for GLUT4; (2) reverse transcription-polymerase chain reaction (RT-PCR) on RNA from various brain nuclei detects GLUT4 transcripts; (3) immunocytochemistry, using a polyclonal antibody to GLUT4; reveals a specific immunostaining pattern, whereas both electronic microscopy and double immunofluorescence staining, using a neurofilament protein marker, indicate a neuronal localization. These results are discussed in terms of a putative neuromodulator role of insulin, via glucose utilization, in brain areas involved in the regulation of fuel metabolism.

Amino Acid Sequence↗
PubMed1994

Growth factor-induced stimulation of hexose transport in 3T3-L1 adipocytes: evidence that insulin-induced translocation of GLUT4 is independent of activation of MAP kinase.

We have examined the effect of growth factors on the rate of hexose transport in 3T3-L1 adipocytes. Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) were found to stimulate deoxyglucose transport by about 2-fold. The concentrations of EGF and PDGF which elicited half maximal responses were 100 and 350 pM, respectively. The increases in transport rate were acute effects; the stimulations were evident within minutes of exposure to growth factors. By contrast, insulin stimulated deoxyglucose transport approximately 16-fold over similar time periods. We have measured the appearance of both the insulin-responsive glucose transporter (GLUT4) and the erythrocyte-type glucose transporter (GLUT1) at the cell surface in response to insulin, EGF and PDGF. We show that both EGF and PDGF induce a 2-fold increase in GLUT1 at the cell surface, but both these growth factors were without effect on GLUT4 levels at the cell surface. In contrast, insulin induced a 13-fold increase in cell surface GLUT4. We further show that insulin, EGF and PDGF all activate MAP kinase as determined by a shift in electrophoretic mobility of this protein on SDS-PAGE. However, since the large translocation of GLUT4 to the cell surface is specific for insulin, we suggest that activation of MAP kinase is not the sole requisite for this process.

3T3 Cells↗
PubMed2005

Synip phosphorylation does not regulate insulin-stimulated GLUT4 translocation.

Insulin causes the rapid translocation of the glucose transporter GLUT4 from intracellular sites to the plasma membrane in fat and muscle cells. There is considerable evidence that the signaling to this trafficking process is downstream of the insulin-activated protein kinase Akt. One Akt substrate that connects signaling to trafficking is a 160 kDa GTPase activating protein for Rabs. Another potential connecting substrate is the protein Synip, which associates with the SNARE syntaxin4. A recent study presents evidence that Akt phosphorylates Synip on serine 99, at least in vitro, and proposes that this phosphorylation enables GLUT4 translocation by causing the dissociation of Synip from syntaxin4. In the present study we show that marked overexpression of Synip mutant S99A, which lacks this phosphorylation site, has no effect on insulin-stimulated GLUT4 translocation in 3T3-L1 adipocytes. This finding is strong evidence that phosphorylation of Synip on serine 99 is not required for GLUT4 translocation.

3T3-L1 Cells↗
PubMed2005

Calmodulin binds to the Rab GTPase activating protein required for insulin-stimulated GLUT4 translocation.

Recently, we described a 160 kDa protein with a Rab GTPase activating protein domain that is phosphorylated on multiple sites by the protein kinase Akt (designated AS160). Phosphorylation of AS160 in adipocytes is required for insulin-stimulated translocation of the glucose transporter GLUT4 to the plasma membrane. In the present study, we searched for proteins that interact with the GTPase activating protein (GAP) domain region of AS160 by the yeast two-hybrid screen. This search indicated that calmodulin bound to a small domain just amino terminal to the GAP domain of AS160, and this association has been confirmed by three other methods, including co-immunoprecipitation from lysates of adipocytes. The association was Ca ion dependent. The role of calmodulin binding to AS160 in insulin-stimulated GLUT4 translocation was examined through the generation of a point mutant of AS160 that did not bind calmodulin. This mutation did not interfere with the capacity of AS160 lacking Akt phosphorylation sites to inhibit GLUT4 translocation. Consequently, calmodulin binding is probably not required for the participation of AS160 in insulin-stimulated GLUT4 translocation.

Adipocytes↗
PubMed2006

Distribution patterns of the glucose transporters GLUT4 and GLUT1 in skeletal muscles of rats (Rattus norvegicus), pigs (Sus scrofa), cows (Bos taurus), adult goats, goat kids (Capra hircus), and camels (Camelus dromedarius).

Earlier studies demonstrated that forestomach herbivores are less insulin sensitive than monogastric omnivores. The present study was carried out to determine if different distribution patterns of the glucose transporters GLUT1 and GLUT4 may contribute to these different insulin sensitivities. Western blotting was used to measure GLUT1 and GLUT4 protein contents in oxidative (masseter, diaphragm) and glycolytic (longissimus lumborum, semitendinosus) skeletal muscle membranes of monogastric omnivores (rats and pigs), and of forestomach herbivores (cows, adult goats, goat kids, and camels). Muscles were characterized biochemically. Comparing red and white muscles, the isocitrate dehydrogenase (ICDH) activity was 1.5-15-times higher in oxidative muscles of all species, whereas lactate dehydrogenase (LDH) activity was 1.4-4.4-times higher in glycolytic muscles except in adult goats. GLUT4 levels were 1.5-6.3-times higher in oxidative muscles. GLUT1 levels were 2.2-8.3-times higher in glycolytic muscles in forestomach herbivores but not in monogastric animals. We conclude that GLUT1 may be the predominant glucose transporter in glycolytic muscles of ruminating animals. The GLUT1 distribution patterns were identical in adult and pre-ruminant goats, indicating that GLUT1 expression among these muscles is determined genetically. The high blood glucose levels of camels cited in literature may be due to an "NIDDM-like" impaired GLUT4 activity in skeletal muscle.

Animals↗
PubMed2007

Dissecting multiple steps of GLUT4 trafficking and identifying the sites of insulin action.

Insulin-stimulated GLUT4 translocation is central to glucose homeostasis. Functional assays to distinguish individual steps in the GLUT4 translocation process are lacking, thus limiting progress toward elucidation of the underlying molecular mechanism. Here we have developed a robust method, which relies on dynamic tracking of single GLUT4 storage vesicles (GSVs) in real time, for dissecting and systematically analyzing the docking, priming, and fusion steps of GSVs with the cell surface in vivo. Using this method, we have shown that the preparation of GSVs for fusion competence after docking at the surface is a key step regulated by insulin, whereas the docking step is regulated by PI3K and its downstream effector, the Rab GAP AS160. These data show that Akt-dependent phosphorylation of AS160 is not the major regulated step in GLUT4 trafficking, implicating alternative Akt substrates or alternative signaling pathways downstream of GSV docking at the cell surface as the major regulatory node.

Adipocytes↗
PubMed2005

Sortilin is essential and sufficient for the formation of Glut4 storage vesicles in 3T3-L1 adipocytes.

Impaired translocation of the glucose transporter isoform 4 (Glut4) to the plasma membrane in fat and skeletal muscle cells may represent a primary defect in the development of type 2 diabetes mellitus. Glut4 is localized in specialized storage vesicles (GSVs), the biological nature and biogenesis of which are not known. Here, we report that GSVs are formed in differentiating 3T3-L1 adipocytes upon induction of sortilin on day 2 of differentiation. Forced expression of Glut4 prior to induction of sortilin leads to rapid degradation of the transporter, whereas overexpression of sortilin increases formation of GSVs and stimulates insulin-regulated glucose uptake. Knockdown of sortilin decreases both formation of GSVs and insulin-regulated glucose uptake. Finally, we have reconstituted functional GSVs in undifferentiated cells by double transfection of Glut4 and sortilin. Thus, sortilin is not only essential, but also sufficient for biogenesis of GSVs and acquisition of insulin responsiveness in adipose cells.

3T3-L1 Cells↗
PubMed2004

GLUT4 but not GLUT1 expression decreases early in the development of feline obesity.

The increase in obesity in people and pets has been phenomenal. As in man, obesity in pets is a risk factor for many diseases including diabetes mellitus. Recently, tissue-specific regulation of glucose metabolism in fat and muscle tissue has been identified as an important factor for insulin sensitivity and it has been hypothesized that glucose uptake into tissues is altered in obesity causing insulin resistance. The purpose of this study was to determine the expression of the glucose transporter proteins GLUT4 and GLUT1 in muscle and fat from lean and obese cats. Seventeen domestic felines were tested in the lean state and again after a 6-month period of ad libitum food intake which led to a significant increase in weight (P < 0.0001). Obese cats showed a significantly higher area under the curve (AUC) for glucose, AUC for insulin and a significant decrease in glucose percentage disappearance per min (K-value) (P = 0.013, 0.018 and 0.017, respectively) during an intravenous glucose tolerance test, but no change in baseline glucose or glycosylated hemoglobin concentrations. GLUT4 expression was decreased in biopsies of both muscle (P = 0.002) and fat (P = 0.001) in the obese animals. GLUT4 in muscle and fat significantly and negatively correlated with the insulin AUC (r2 = 0.36, P = 0.004 and r2 = 0.18, P = 0.040, respectively). GLUT1 expression showed no significant change in the obese cats in either tissue. It is concluded that the changes in GLUT4 are early derangements in obesity and occur before glucose intolerance is clinically evident.

Adipose Tissue↗
PubMed2006

Gliclazide protects 3T3L1 adipocytes against insulin resistance induced by hydrogen peroxide with restoration of GLUT4 translocation.

Increased oxidative stress under hyperglycemia may contribute to progressive deterioration of peripheral insulin sensitivity. In this study, we investigated whether gliclazide, a second-generation sulfonylurea, can protect 3T3L1 adipocytes from insulin resistance induced by oxidative stress, and whether gliclazide can restore insulin-stimulated glucose transporter 4 (GLUT4) translocation under oxidative stress. We incubated 3T3L1 adipocytes in hydrogen peroxide to produce oxidative stress, then administered various concentrations of gliclazide, N-acetylcystein (NAC), or glibenclamide. Cells treated with these drugs were next exposed to insulin, subsequent glucose uptake was measured, and the insulin-stimulated GLUT4 translocation was monitored in living cells. We found that hydrogen peroxide treatment alone suppressed glucose uptake by insulin stimulation to 65.9%+/-7.8% of the corresponding controls (P<.01). However, addition of 0.1 to 10 micromol/L gliclazide to hydrogen peroxide-treated cells dose-dependently restored glucose uptake, with 5 micromol/L gliclazide significantly restoring glucose uptake to 93.3+/-6.6% (P<.01) even under hydrogen peroxide. Treatment with the known anti-oxidant NAC also dose-dependently (0.1-10 mmol/L) restored insulin-induced glucose uptake in the presence of hydrogen peroxide. However, glibenclamide (0.1-10 micromol/L), another second-generation sulfonylurea, failed to improve glucose uptake. Similarly, treatment with 5 micromol/L gliclazide or 10 mmol/L NAC significantly overcome the reduction in insulin-stimulated GLUT4 translocation by hydrogen peroxide (P<.01), whereas 5 micromol/L glibenclamide did not. Therefore our data regarding gliclazide further characterize its mechanism of hypoglycemic effect: the observed improvements in insulin sensitivity and in GLUT4 translocation indicate that gliclazide counters the hydrogen peroxide-induced insulin resistance in 3T3L1 adipocytes and also would further augment the hypoglycemic effect of this drug as insulinotropic sulfonylurea.

3T3-L1 Cells↗
PubMed2006

Bridging the GAP between insulin signaling and GLUT4 translocation.

Upon binding and activating its cell-surface receptor, insulin triggers signaling cascades that regulate many cellular processes. Regarding glucose homeostasis, insulin suppresses hepatic glucose production and increases glucose transport into muscle and adipose tissues. At the cellular level, glucose uptake results from the insulin-stimulated translocation of the glucose transporter 4 (GLUT4) from intracellular storage sites to the plasma membrane. Although the signaling molecules that function proximal to the activated insulin receptor have been well characterized, it is not known how the distal insulin-signaling cascade interfaces with and mobilizes GLUT4-containing compartments. Recently, several candidate signaling molecules, including AS160, PIKfyve and synip, have been identified that might provide functional links between the insulin signaling cascade and GLUT4 compartments. Future work will focus on delineating the precise GLUT4 trafficking steps regulated by these molecules.

Animals↗
PubMed1997

Molecular mechanisms of contraction-induced translocation of GLUT4 in isolated cardiomyocytes.

Isolated adult rat ventricular cardiomyocytes were used to investigate the effects of contractile activity on 3-O-methylglucose transport on the translocation of the insulin-responsive glucose transporter GLUT4, and the possible activation of intermediates of the insulin signaling cascade. When elicited by field stimulation, contraction at 1 Hz did not significantly affect the adenosine triphosphate (ATP) content of cardiac cells, even after 60 min. At 5 Hz, a stable ATP level was observed until 15 minutes with a rapid decline at later time points. Stimulation of cardiomyocytes at 5 Hz for 5 minutes induced a 2-3 fold increase of 3-O-methylglucose transport with no additional stimulation in the presence of insulin (10[-7] M). Subcellular fractionation and immunoblotting analysis of GLUT4 distribution indicated that both contraction and insulin induced an identical increase (8-9-fold) of GLUT4 in the plasma membrane with a concomitant decrease (one third) in the microsomal fraction. Treatment of cardiomyocytes with wortmannin produced a complete inhibition of insulin- and contraction-induced glucose uptake. However, immunoprecipitation of insulin receptor substrate-1 (IRS-1) showed that the p85 regulatory subunit of phosphatidylinositol-3 kinase did not associate with IRS-1 upon contraction but with a marked stimulated association in response to insulin. These data suggest the existence of identical insulin- and contraction-recruitable GLUT4 pool. Contraction-induced signaling may use a limited part of the insulin-signaling cascade, possibly involving IRS-2. We further suggest that insulin resistance at the level of IRS-1 will not affect contraction-regulated glucose uptake by the heart.

3-O-Methylglucose↗
PubMed2002

Insulin-responsive glucose transporters-GLUT8 and GLUT4 are expressed in the developing mammalian brain.

We investigated the spatial and temporal distribution of insulin-responsive facilitative glucose transporter isoforms GLUT4 and GLUT8 in the developing mouse brain. Employing Western blot analysis and specific antibodies, GLUT4 and GLUT8 peaked during the suckling phase. Immunohistochemical analysis revealed the presence of GLUT4 mainly in neurites in sensory and motor areas of cortical and subcortical structures of the brain from P7 until adulthood. In contrast, GLUT8 was found in the same anatomical structures within neurites and cell bodies. Most striking was the presence of GLUT8 in the cell bodies of the substantia nigra. We conclude that both GLUT4 and GLUT8 are present in murine brain, with highest concentrations noted during the suckling phase. These insulin-responsive isoforms may have a unique role in augmenting substrate delivery under conditions of increased demand.

Animals↗
PubMed2001

Altered Glut4 mRNA levels in specific brain areas of hyperglycemic-hyperinsulinemic rats.

The insulin sensitive glucose transporter Glut4 is expressed in neurons of the brain among which those of hypothalamic nuclei. It has been proposed that this transporter might be involved in the hypothalamic glucose-insulin sensing mechanism and thus in the nervous regulation of metabolism. In order to get further insights into its putative role, Glut4 expression was analyzed by quantitative competitive reverse transcription-polymerase chain reaction, in hypothalamic nuclei of hyperglycemic-hyperinsulinemic (HG-HI) rats, a model characterized by alteration of the autonomic nervous system activity. Glut4 mRNA content was decreased in the lateral hypothalamic area (33%) and arcuate nucleus (27%) but significantly only in the former. It was unchanged in other structures. These results are in favor of an alteration of Glut4 expression by short-term hyperglycemia and hyperinsulinemia that, in turn, could affect autonomic nervous system activity.

Animals↗
PubMed1997

Quantitative methods for measuring the insulin-regulatable glucose transporter (Glut4).

This review article describes various quantitation methods for the insulin-regulatable glucose transporter (Glut4). Several methods including reconstituted glucose transport, cytochalasin B binding assays, immunocytochemistry, immunoblots, ELISA, and the more recently developed exofacial labels are discussed. Since Glut4 translocates from an intracellular compartment to the plasma membrane in response to the action of insulin, it is of particular interest to measure Glut4 changes in the membrane fractions. Hence, the measurement of Glut4 commonly involves the isolation of cell membranes using subcellular fractionation in combination with one of the quantitation methods. The limitations of each quantitation method due to the use of subcellular fractionation are discussed in this article. As well, the advantages and disadvantages in terms of isoform specificity and technical difficulties of each method are presented.

Affinity Labels↗
PubMed2000

Modulation of GLUT4 and GLUT1 recycling by insulin in rat adipocytes: kinetic analysis based on the involvement of multiple intracellular compartments.

The trafficking kinetics of GLUT4 and GLUT1 in rat epididymal adipocytes were analyzed by a four-compartment model based upon steady-state pool sizes of three intracellular fractions and one plasma membrane fraction separated and assessed under both basal and insulin-stimulated states. The steady-state compartment sizes provided relative values of the kinetic coefficients characterizing the rate of each process in the loop. Absolute values of these coefficients were obtained by matching the simulated half-times to those observed experimentally and reported in the literature for both basal and insulin-stimulated states. Our analysis revealed that insulin modulates the GLUT4 trafficking at multiple steps in the rat adipocyte, not only reducing the endocytotic rate constant 3-4-fold and increasing the exocytotic rate 8-24-fold but also increasing the two rate coefficients coupling the three intracellular compartments 2-6-fold each. Furthermore, GLUT1 was completely segregated from GLUT4 in two of the three intracellular compartments, and its steady-state distribution is consistent with a four-compartment model of GLUT1 recycling involving an insulin sensitive endocytosis step in common with the GLUT4 system, but with all other processes being insensitive to insulin.

Adipocytes↗
PubMed1999

A phosphotyrosyl mimetic peptide reverses impairment of insulin-stimulated translocation of GLUT4 caused by overexpression of PTP1B in rat adipose cells.

Biological actions of insulin are initiated by activation of the insulin receptor tyrosine kinase. Protein tyrosine phosphatases (PTPases) PTP1B and PTPalpha are known to dephosphorylate the insulin receptor and may contribute to insulin resistance in diseases such as diabetes. We previously reported that overexpression of PTP1B in rat adipose cells significantly impairs insulin-stimulated translocation of GLUT4 [Chen, H., et al. (1997) J. Biol. Chem. 272, 8026]. In the present study, we treated adipose cells with a PTPase inhibitor containing the phosphotyrosyl mimetic difluorophosphonomethyl phenylalanine (F2Pmp) to determine whether we could improve the insulin resistance caused by overexpression of PTP1B or PTPalpha. Rat adipose cells transfected by electroporation with either PTP1B or PTPalpha were treated without or with the inhibitor, and effects on insulin-stimulated translocation of a cotransfected epitope-tagged GLUT4 were studied. The IC50 of the F2Pmp-containing inhibitor is 180 nM for PTP1B and 10 mM for PTPalpha in vitro. As expected, in the absence of the inhibitor, overexpression of either PTP1B or PTPalpha caused a significant decrease in the amount of GLUT4 at the cell surface both in the absence and in the presence of insulin when compared with control cells transfected with epitope-tagged GLUT4 alone. Interestingly, the insulin resistance caused by overexpression of PTP1B (but not PTPalpha) was reversed by treating the transfected cells with the F2Pmp-containing inhibitor. Furthermore, the inhibitor blocked the insulin-stimulated association of PTP1B with the insulin receptor. We conclude that the F2Pmp-containing compound is a potent and specific inhibitor of overexpressed PTP1B that may be useful for designing rational therapies for treating insulin resistant diseases such as diabetes.

Adipocytes↗
PubMed2001

GLUT4--at the cross roads between membrane trafficking and signal transduction.

GLUT4 is a mammalian facilitative glucose transporter that is highly expressed in adipose tissue and striated muscle. In response to insulin, GLUT4 moves from intracellular storage areas to the plasma membrane, thus increasing cellular glucose uptake. While the verification of this 'translocation hypothesis' (Cushman SW, Wardzala LJ. J Biol Chem 1980;255: 4758-4762 and Suzuki K, Kono T. Proc Natl Acad Sci 1980;77: 2542-2545) has increased our understanding of insulin-regulated glucose transport, a number of fundamental questions remain unanswered. Where is GLUT4 stored within the basal cell? How does GLUT4 move to the cell surface and what mechanism does insulin employ to accelerate this process? Ultimately we require a convergence of trafficking studies with research in signal transduction. However, despite more than 30 years of intensive research we have still not reached this point. The problem is complex, involving at least two separate signal transduction pathways which feed into what appears to be a very dynamic sorting process. Below we discuss some of these complexities and highlight new data that are bringing us closer to the resolution of these questions.

Adipocytes↗