GLUT 1-glucose transporter protein in adult and fetal mouse lung

Investigating genetic characteristics of hepatitis B virus-associated and -non-associated hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a primary liver malignancy that mainly occurs in patients with chronic liver disease and cirrhosis. Risk factors for HCC include hepatitis B virus (HBV) infection. However, the specific role of HBV infection in HCC development is not yet completely understood. In order to reveal the effects of HBV on HCC, we compare the genes of HCC patients infected with HBV with those who are not infected.

METHODS

We encoded the genes of these two types of HCC in databases using enrichment scores of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway terms. A random forest algorithm was employed in order to distinguish these two types in the classifier, and a series of feature selection approaches was used in order to select their optimal features. Novel HBV-associated and -non-associated HCC genes were predicted, respectively, based on their optimal features in the classifier. A shortest-path algorithm was also employed in order to find all of the shortest-paths genes connecting the known related genes.

RESULTS

A total of 54 different features between HBV-associated and -non-associated HCC genes were identified. In total, 1236 and 881 novel related genes were predicted for HBV-associated and -non-associated HCC, respectively. By integrating the predicted genes and shortest path genes in their gene interaction network, we identified 679 common genes involved in the two types of HCC.

CONCLUSION

We identified the significantly different genetic features between two types of HCC. We also predicted related genes for the two types based on their specific features. Finally, we determined the common genes and features that were involved in both of these two types of HCC.

Apical and basolateral localisation of GLUT2 transporters in human lung epithelial cells

Glucose concentrations of normal human airway surface liquid are ~12.5 times lower than blood glucose concentrations indicating that glucose uptake by epithelial cells may play a role in maintaining lung glucose homeostasis. We have therefore investigated potential glucose uptake mechanisms in non-polarised and polarised H441 human airway epithelial cells and bronchial biopsies. We detected mRNA and protein for glucose transporter type 2 (GLUT2) and glucose transporter type 4 (GLUT4) in non-polarised cells but GLUT4 was not detected in the plasma membrane. In polarised cells, GLUT2 protein was detected in both apical and basolateral membranes. Furthermore, GLUT2 protein was localised to epithelial cells of human bronchial mucosa biopsies. In non-polarised H441 cells, uptake of d-glucose and deoxyglucose was similar. Uptake of both was inhibited by phloretin indicating that glucose uptake was via GLUT-mediated transport. Phloretin-sensitive transport remained the predominant route for glucose uptake across apical and basolateral membranes of polarised cells and was maximal at 5–10 mM glucose. We could not conclusively demonstrate sodium/glucose transporter-mediated transport in non-polarised or polarised cells. Our study provides the first evidence that glucose transport in human airway epithelial cells in vitro and in vivo utilises GLUT2 transporters. We speculate that these transporters could contribute to glucose uptake/homeostasis in the human airway.

The Ubiquitous Glucose Transporter GLUT-1 Is a Receptor for HTLV

The human T cell leukemia virus (HTLV) is associated with leukemia and neurological syndromes. The physiopathological effects of HTLV envelopes are unclear and the identity of the receptor, present on all vertebrate cell lines, has been elusive. We show that the receptor binding domains of both HTLV-1 and -2 envelope glycoproteins inhibit glucose transport by interacting with GLUT-1, the ubiquitous vertebrate glucose transporter. Receptor binding and HTLV envelope-driven infection are selectively inhibited when glucose transport or GLUT-1 expression are blocked by cytochalasin B or siRNAs, respectively. Furthermore, ectopic expression of GLUT-1, but not the related transporter GLUT-3, restores HTLV infection abrogated by either GLUT-1 siRNAs or interfering HTLV envelope glycoproteins. Therefore, GLUT-1 is a receptor for HTLV. Perturbations in glucose metabolism resulting from interactions of HTLV envelope glycoproteins with GLUT-1 are likely to contribute to HTLV-associated disorders.

Modulation of glucose transport in fetal rat lung: a sexual dimorphism

Male fetuses exhibit delayed lung maturation and surfactant production in comparison with female fetuses. This delay may be related to sex hormone effects: estrogen enhances and androgens delay lung development. The uptake of glucose, an important precursor for surfactant synthesis, may be differently affected by estrogen and androgens. In these studies we determined the effects of these two hormones on glucose transport (glucose uptake, glucose transporter [Glut] 1 protein, and mRNA) and hexokinase activity in lung tissue of fetal rats. On Day 20 of gestation (term = 21.5 d) lung tissue was harvested from female and male fetal rats, minced into explants, and cultured for 24 h. Basal glucose uptake, measured in the absence of sex hormones, was 37% higher (P < 0.05) in female compared with male lungs. Explants were washed and cultured for an additional 3 h or 24 h in either estradiol or dihydrotestosterone (DHT) at 0, 1, 10, or 100 nM. Twenty-four-hour treatment with estradiol in both male and female explants increase 2-deoxyglucose uptake, Glut 1 protein, and mRNA levels (P < 0.05). However, explants from male fetuses were not as responsive to estradiol treatment as were those from females (P < 0.05). Treatment for 24 h with DHT decreased 2-deoxyglucose uptake, Glut 1 protein, and mRNA levels in females and males (P < 0.05). There was no difference in response between females and males. Short-term incubation (3 h) with sex hormones had no effect on glucose uptake. However, 3-h treatment with estradiol did increase Glut 1 mRNA levels (P < 0.05). Hexokinase activity was not affected by estradiol or DHT treatment. These findings indicate that estradiol and DHT differentially regulate glucose uptake in fetal rat lung tissue. This regulation of substrate supply (glucose) by estradiol and DHT may be another mechanism for the sexual dimorphism observed in lung development and surfactant synthesis.

Effect of maternal diabetes upon fetal rat myocardial and skeletal muscle glucose transporters

We investigated the effect of streptozotocin-induced short-term maternal diabetes upon fetal rat myocardial and skeletal muscle glucose transporter Glut 1 (basal form) and Glut 4 (insulin-responsive form) protein concentrations by Western blot analysis. In the severely diabetic group (SEVERE-D, n = 17), a 3-fold increase in maternal and fetal glucose concentrations (p < 0.01) was associated with a 3-fold decline in maternal (p < 0.01) with no change in fetal insulin levels when compared with the streptozotocin-treated nondiabetic (n = 10) and vehicle-treated control (control, n = 14) groups. These changes in the SEVERE-D group when compared with controls were associated with a 30 and 65% decline, respectively, in fetal myocardial and skeletal muscle (forelimb and hind limb) Glut 1 protein concentrations. The fetal myocardium also demonstrated a 45% decline in Glut 4 protein levels. Fetal skeletal muscle Glut 4 protein, which was expressed only at very low levels in controls showed no change in SEVERE-D. Immunohistochemical analysis revealed a myocyte-plasma membrane association of Glut 1 and an intracellular Glut 4 distribution in the fetal myocardium and skeletal muscle. No Glut 1 immunoreactivity was noted in either the fetal myocardial or skeletal muscle perineural sheaths, blood vessels, or the entrapped fetal red blood cells. This subcellular localization pattern was unaltered in all three treatment groups. We conclude that maternal diabetes causing fetal hyperglycemia with normoinsulinemia suppresses fetal myocardial Glut 1 and Glut 4 and fetal skeletal muscle Glut 1. The decline in the plasma membrane associated Glut 1 concentrations may serve a protective function by reducing the glucose transport rate into fetal myocardial and skeletal muscle cells, which otherwise could be vulnerable to high circulating glucose. The in-utero maternal diabetes induced decrease in fetal myocardial intracellular-Glut 4 concentration could herald the emergence of insulin resistance.

Pretranslational regulation of two cardiac glucose transporters in rats exposed to hypobaric hypoxia

To investigate the mechanism by which cardiac glucose utilization increases during hypoxia and increased work load, we studied the effect of 2 and 14 days of hypobaric hypoxia on the expression of two subtypes of the facilitative D-glucose transporter, the GLUT-4 or "insulin-regulatable" isoform and the GLUT-1 isoform thought to mediate basal transport. Rats lose weight when exposed to hypobaric hypoxia, so fasting controls were used in the 2-day studies and pair-fed controls in the 14-day experiments. Hypobaric hypoxia (PO2 69 mmHg) resulted in right ventricular (RV), but not left ventricular (LV), hypertrophy. RV and LV GLUT-1 mRNA levels increased 2- to 3-fold after 2 days and 1.5- to 2-fold after 14 days of hypobaric hypoxia compared with both fasted rats and normal controls. RV GLUT-1 protein increased approximately 3-fold and LV GLUT-1 protein increased 1.5-fold after 14 days of hypobaric hypoxia vs. both pair-fed and normal controls. RV GLUT-4 mRNA decreased to 26% and RV GLUT-4 protein decreased to 54% of normal control levels as a result of 2 days of hypobaric hypoxia. RV GLUT-4 mRNA decreased to 64% of normal control levels with no change in RV GLUT-4 protein as a result of 2 days of fasting. We conclude that hypobaric hypoxia increases cardiac GLUT-1 expression at the pretranslational level in both ventricles. The greater increase in GLUT-1 protein on the right suggests an additive effect of pressure overload. GLUT-4 expression is reduced early in the development of RV hypertrophy.

The neonatal rabbit brain glucose transporter

The Glut 1 (Hep G2/rat brain) isoform of glucose transporter is expressed in significant amounts in adult mammalian brain. The purpose of our present study was to determine the brain cellular localization of Glut 1 during the late newborn stage of development, when brain cellular proliferation and differentiation is highly active. Employing immunohistochemistry and in-situ hybridization in 10-day-old neonatal rabbit brain sections, we undertook cellular localization of Glut 1 expression. Glut 1 protein and mRNA were mainly noted in considerable amounts within the 10-day-old brain microvasculature. Lower concentrations of Glut 1 immunoreactivity were present in certain glial cells found within the deeper cortical layers of brain. Northern blot analysis of total RNA from isolated microvasculature-enriched preparation, isolated and cultured neuronal and glial cells, whole brain and whole brain with the exclusion of microvasculature obtained from the 10-day-old, revealed the universal presence of a approximately 2.8 kb Glut 1 mRNA with the exception of the neuron-enriched cultures. We conclude that during the neonatal period, when parenchymal cellular proliferation is at a peak, Glut 1 is localized not only to the microvasculature but also to certain cells which express glial morphological characteristics. The neuronal cells either do not express Glut 1 or express minute amounts.