Glucose regulates its own transport in Ehrlich ascites tumour cells

Energy metabolism in tumor cells

In early studies on energy metabolism of tumor cells, it was proposed that the enhanced glycolysis was induced by a decreased oxidative phosphorylation. Since then it has been indiscriminately applied to all types of tumor cells that the ATP supply is mainly or only provided by glycolysis, without an appropriate experimental evaluation. In this review, the different genetic and biochemical mechanisms by which tumor cells achieve an enhanced glycolytic flux are analyzed. Furthermore, the proposed mechanisms that arguably lead to a decreased oxidative phosphorylation in tumor cells are discussed. As the O(2) concentration in hypoxic regions of tumors seems not to be limiting for the functioning of oxidative phosphorylation, this pathway is re-evaluated regarding oxidizable substrate utilization and its contribution to ATP supply versus glycolysis. In the tumor cell lines where the oxidative metabolism prevails over the glycolytic metabolism for ATP supply, the flux control distribution of both pathways is described. The effect of glycolytic and mitochondrial drugs on tumor energy metabolism and cellular proliferation is described and discussed. Similarly, the energy metabolic changes associated with inherent and acquired resistance to radiotherapy and chemotherapy of tumor cells, and those determined by positron emission tomography, are revised. It is proposed that energy metabolism may be an alternative therapeutic target for both hypoxic (glycolytic) and oxidative tumors.

Inhibition of cell proliferation in human breast tumor cells by antisense oligonucleotides against facilitative glucose transporter 5

In recent years, successful examples of antisense oligonucleotide (AS) therapy for genetic diseases have stimulated scientists to investigate its application on cancer diseases. AS can be used to down-regulate the mRNA and protein expression by annealing to specific region of the target mRNA which is responsible for the malignancy. Glucose transporter 5 (Glut5) is a tissue specific transporter that can be found on breast cancer tissues but not on normal breast tissues. Therefore, it is of clinical interest to investigate whether AS against Glut5 mRNA can tackle breast cancer. In this study, two cell lines, MCF-7 which is estrogen-receptor positive and MDA-MB-231 which is estrogen-receptor negative, were used to mimic breast cancer tissues at early and late stages, respectively. A 15-base sequence around the start codon of Glut5 was used. It was found that AS against Glut5 exerted anti-proliferative effect on both of these two breast tumor cell lines and seemed to exert its effect via the suppression of expression of Glut5 proteins in the cells. AS against Glut5 exhibited no effect on human hepatoma HepG2 cells which do not possess any Glut5. The results imply an alternative way in treating breast tumor as the AS against Glut5, unlike tamoxifen, takes effect on breast tumor cells via suppressing the expression of Glut5 that they specifically possess, and regardless whether the breast tumors are estrogen dependent or not.

Increases in mRNA levels of glucose transporters types 1 and 3 in Ehrlich ascites tumor cells during tumor development

A common feature of many tumors is an increase in glucose catabolism during tumor growth. We studied the mechanism of this phenomenon by using Ehrlich ascites tumor bearing mice as the animal model. We found that Ehrlich ascites tumor cells possess only glucose transporter 1 (GLUT1) and GLUT3 but not GLUT2, GLUT4, or GLUT5. The mRNA levels of GLUT1 and GLUT3 increased progressively in the tumour during development; however, there were no changes observable in mRNA levels of glucose transporters of all types in brain, liver, and heart of the host mice. These findings suggest that Ehrlich ascites tumor augments its glucose transport mechanism relative to other tissues in response to its unique growth needs.

Human tumour necrosis factor-alpha inhibits glucose transport in cultured Ehrlich ascites tumour cells

Human recombinant tumour necrosis factor-alpha (rhTNF-alpha) arrested the growth of Ehrlich ascites tumour (EAT) cells in vitro. It suppressed cellular glucose uptake and decreased the membrane density of glucose transporters as measured by glucose-reversible cytochalasin B binding. The glucose transporters' affinity for substrate was also reduced. However, rhTNF-alpha treatment exerted no effect on the phosphoribosyl pyrophosphate level in EAT cells. The role of rhTNF-alpha on the inhibition of glucose transport of tumour cells is discussed.

Yeast sugar transporters

Transport of sugars is a fundamental property of all eukaryotic cells. Of particular importance is the uptake of glucose, a preferred carbon and energy source. The rate of glucose utilization in yeast is often dictated by the activity and concentration of glucose transporters in the plasma membrane. Given the importance of transport as a site of control of glycolytic flux, the regulation of glucose transporters is necessarily complex. The molecular analysis of these transporters in Saccharomyces has revealed the existence of a multigene family of sugar carriers. Recent data have raised the question of the actual role of all of these proteins in sugar catabolism, as some appear to be lowly expressed, and point mutations of these genes may confer pleiotropic phenotypes, inconsistent with a simple role as catabolic transporters. The transporters themselves appear to be intimately involved in the process of sensing glucose, a model for which there is growing support.

13C NMR studies of glucose metabolism in human leukemic CEM-C7 and CEM-C1 cells

Glucose metabolism of human leukemic cell lines CEM-C7 and CEM-C1 was investigated in vivo by 13C NMR using 13C-labeled glucose. Exact knowledge of glucose concentration, cell count, and cell viability of the cell suspensions made it possible to analyze glucose metabolism in detail. In both cell lines aerobic glycolysis accounts for virtually all glucose consumption. The use of D-[13C2]glucose provided a simple method to measure the glucose flux through the pentose phosphate pathway as 9% (CEM-C1) and 11% (CEM-C7) of glucose channeled into glycolysis. The dexamethasone-sensitive CEM-C7 cells consume glucose at a rate about 50% higher than the dexamethasone-resistant CEM-C1 cells. It is shown that this higher consumption correlates with a larger size of the CEM-C7 cells. Therefore in CEM cells the development of drug resistance does not seem to involve related changes in cell energetics.

Intracellular phosphoribosyl diphosphate level and glucose carrier in Ehrlich ascites tumour cells during tumour growth and diabetes in tumour-bearing mice

The ability of Ehrlich ascites tumour (EAT) cells in mice to take up glucose as well as the density of glucose carriers on the cells increased progressively during the course of tumour development. Simultaneously as the rate of uptake rose, the intracellular phosphoribosyl diphosphate (PRPP) levels dropped responding to the decrease of serum glucose. Hyperglycaemia induced in the host by alloxan or streptozotocin administration increased the serum glucose concentrations and intracellular PRPP levels but decreased the density of glucose carriers of the cells, whereas insulin administration reversed this condition. The physiological significance of these observations are discussed.

Prevention by thymidine against toxicity and glucose uptake inhibition of methotrexate on cultured Ehrlich ascites tumour cells

Methotrexate (MTX) arrested cell growth and inhibited 2-deoxy-D-glucose uptake of Ehrlich ascites tumour cells in vitro. The changes of glucose concentrations in the culture media did not affect the degree of suppression of cell growth by MTX. Thymidine (dThd) protected against the toxic effect of MTX on the cells. It also prevented the inhibition effect on glucose uptake of the cells by MTX. MTX significantly suppressed the maximal uptake rate of glucose (Vmax) while addition of dThd alleviated the suppression. The half-saturation constant of the uptake (Km) remained constant.