Abstract
GLUT1 is the predominant glucose transporter in leukemia cells, and the modulation of glucose transport activity by cytokines, oncogenes or metabolic stresses is essential for their survival and proliferation. However, the molecular mechanisms allowing to control GLUT1 trafficking and degradation are still under debate. In this study we investigated whether plasma membrane cholesterol depletion plays a role in glucose transport activity in M07e cells, a human megakaryocytic leukemia line. To this purpose, the effect of cholesterol depletion by methyl-β-cyclodextrin (MBCD) on both GLUT1 activity and trafficking was compared to that of the cytokine Stem Cell Factor (SCF). Results show that, like SCF, MBCD led to an increased glucose transport rate and caused a subcellular redistribution of GLUT1, recruiting intracellular transporter molecules to the plasma membrane. Due to the role of caveolae/lipid rafts in GLUT1 stimulation in response to many stimuli, we have also investigated the GLUT1 distribution along the fractions obtained after non ionic detergent treatment and density gradient centrifugation, which was only slightly changed upon MBCD treatment. The data suggest that MBCD exerts its action via a cholesterol-dependent mechanism that ultimately results in augmented GLUT1 translocation. Moreover, cholesterol depletion triggers GLUT1 translocation without the involvement of c-kit signalling pathway, in fact MBCD effect does not involve Akt and PLCγ phosphorylation. These data, together with the observation that the combined MBCD/SCF cell treatment caused an additive effect on glucose uptake, suggest that the action of SCF and MBCD may proceed through two distinct mechanisms, the former following a signalling pathway, and the latter possibly involving a novel cholesterol dependent mechanism.
Highlights
Malignant cells have been shown to utilize more glucose than normal cells in vitro and in vivo
We have previously shown that a growth factor such as Stem Cell Factor (SCF) activates glucose transport through a translocation of GLUT1 protein from intracellular stores to cell membrane in the human hemopoietic cell line M07e expressing only GLUT1 and that this effect can be mimicked by exogenous H2O2 in a PI3Kindependent way [6]
Recent studies have indicated that lipid rafts or lipid microdomain platforms may be implicated in signalling and membrane trafficking of a variety of cells in response to agonists or stimuli [14,15]. In light of these reports and in order to better elucidate the mechanism by which SCF activates GLUT1 translocation in M07e cells, in the present study we investigated whether plasma membrane cholesterol depletion play a role in glucose transport activity of this cell line
Summary
Malignant cells have been shown to utilize more glucose than normal cells in vitro and in vivo. These cells exhibit increased rates of glucose uptake mediated by facilitative glucose transporter (GLUT) proteins. GLUT1 is the predominant glucose transporter in hemopoietic cells, and cytokines regulate glucose uptake through modulation of GLUT1 protein levels and cell surface trafficking [3]. Maintenance of glucose transport by cytokines, oncogenes or metabolic stresses appears to be an essential feature of the survival response of hemopoietic cells. The molecular mechanisms allowing these molecules or conditions to control GLUT1 trafficking and degradation, are still under debate
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