Role of Microtubules in Glucose Uptake by C6 Glioma Cells

Abstract

Abstract:Drugs that influence tubulin function were used to investigate the role of microtubules in hexose uptake by C6 glioma cells. In C6 cells, colchicine and vinblastine (which inhibit tubulin polymerization) inhibited radioactive ['H]2-deoxy-D-glucose uptake by about 30%". Paclitaxel (which promotes tubulin polymerization) stimulated hexose uptake by about 25%. To further demonstrate that microtubules play a role in hexose uptake, C6 cells were transfected with GLUT1 cDNA and then challenged with 100 nM paclitaxel. In GLUTI-transfected cells paclitaxel stimulated 2-deoxy-D-glucose uptake by about 35%. To study the role of tubulin in agonist-stimulated hexose uptake, the effect of colchicine on carbachol-induced uptake was next examined. Hexose uptake was increased with carbachol in concentration-dependent manner which was abolished by pretreatment with colchicine. To examine the specificity of the inhibitory effect of colchicine on G protein-mediated signal transduction pathway, the influence of colchicine on insulin (which acts via tyrosine kinase pathway) stimulation of 2-deoxy-D-glucose uptake was investigated. Hexose uptake was increased by insulin in a concentration-dependent manner which was unaffected by pretreatment with colchicine. These results suggest that microtubules are involved in basal and carbachol-stimulated glucose uptake by C6 cells.Astrocytes are non-neuronal cells. Astrocytes are stellate or star-shaped cells bearing long cytoplasmic processes. Astrocytes play structural and supporting roles in the CNS. It is estimated that astrocytes comprise 25-50% of the total volume in some brain areas. Cell bodies or processes of neurones, individual or clusters of synapses are surrounded by astrocytic processes. These relationships suggest a structural as well as a functional role for astrocytes in the CNS (Kimelberg 1995). Some of the functions of astrocytes are: guidance of neuronal migration during development, production and excretion of extracellular matrix proteins and adhesion molecules, production of neurotrophic and neurite promoting factors, cerebral angiogenesis, induction and maintenance of blood-brain barrier characteristics, neurotransmission, regulation of pH, ion concentration, osmolarity, detoxification, phagocytosis, immune functions, macromolecular translocation, and neuroendocrine functions. Among the cells in the CNS astrocytes are the only ones containing glycogen. This system is important for providing glucose for neuronal metabolism (Montgomery 1994). Rat astrocytes as well as C6 glioma cells (derived from rat tumors induced by N-nitrosomethylurea, and similar to the rat astrocytes) are well established models to study glucose metabolism (Singh et al. 1990;Wei & Yeh 1991). Although the physiological modulator of glucose uptake by brain cells is not identified, it was demonstrated that insulin and carbachol stimulated glucose uptake by astrocytes and C6 glioma cells, respectively (Singh et al.

Activation of Syntaxin 1C, an Alternative Splice Variant of HPC-1/Syntaxin 1A, by Phorbol 12-Myristate 13-Acetate (PMA) Suppresses Glucose Transport into Astroglioma Cells via the Glucose Transporter-1 (GLUT-1)

“…Second, syntaxin 1C may act on the cytoskeleton. It was demonstrated recently that components of the cytoskeleton, such as microtubules and actin filaments, are necessary for the translocation of GLUT-1 and GLUT-4 to the plasma membrane (32)(33)(34). From this viewpoint, it is interesting that syntaxin 1C possesses a tubulin binding motif in the N-terminal region.…”

“…Total RNA (20 g) isolated from native and transfected (see below) T98G cells was separated by electrophoresis in 1.0% formaldehyde-agarose denaturing gels. The EcoRI-digested 600-bp fragments of the GLUT-1 and GLUT-3 cDNA were labeled with 32 P by random priming. The GLUT-1 and GLUT-3 cDNAs were a kind gift from Dr. Shinya Nagamatsu (Kyorin University, Japan).…”

Assessing the Cytoskeletal System and its Elements in C6 Glioma Cells and Astrocytes by Atomic Force Microscopy

“…These filaments are also involved in the integration of signals transduction related to the determination of cell size and the regulation of cell migration and cell survival (Pallari and Eriksson 2006). Microtubules are involved in glucose uptake and transport, as well as the metabolism of tumor cells that is closely correlated with proliferation and hypermetabolism (Singh et al 1998;Nagamatsu et al 1996). It is necessary to understand the cytoskeletal structure and function of glioma cells to better investigate glioma invasiveness.…”

Syntaxin 1C, a soluble form of syntaxin, attenuates membrane recycling by destabilizing microtubules

“…Recently, it has been demonstrated that GLUT translocation to the PM is dependent on the cytoskeletal systems including microtubules (MTs) and actin filaments (Dransfeld et al, 2001;Singh et al, 1998;Tong et al, 2001;Wang et al, 1998). For example, drugs that influence the function of tubulin polymerization, such as vinblastine and paclitaxel, alter glucose uptake activity by GLUT1 in glioma cells (Singh et al, 1998). It has also been reported that the GLUT4 vesicular transport depends on cortical actin remodeling (Dransfeld et al, 2001;Tong et al, 2001;Wang et al, 1998) that is regulated by a direct link between SNARE proteins and the MT network (Pooley et al, 2008).…”

“…Recently, it has been demonstrated that GLUT translocation to the PM is dependent on the cytoskeletal systems including microtubules (MTs) and actin filaments (Dransfeld et al, 2001;Singh et al, 1998;Tong et al, 2001;Wang et al, 1998). For example, drugs that influence the function of tubulin polymerization, such as vinblastine and paclitaxel, alter glucose uptake activity by GLUT1 in glioma cells (Singh et al, 1998).…”