Hexose specificity for downregulation of HepG2/brain-type glucose transporter gene expression in L6 myocytes

Abstract

Glucose deprivation of L6 myocytes results in the upregulation of glucose transporter activity, protein and mRNA. We have investigated the downregulation of transporter gene expression by glucose and other hexoses in glucose-deprived L6 myocytes. Glucose transport activity was measured as the uptake of 3H-2-deoxyglucose. Transporter protein and mRNA were detected by immunoblot and Northern blot analysis, respectively, with probes to the rat brain glucose transporter. Glucose deprivation of myocytes, in the absence and presence of insulin, increased 3H-2-deoxyglucose uptake, transporter protein and mRNA levels. Refeeding with glucose reversed the glucose deprivation effects on transport activity and mRNA within 12 h, with half-maximal effects at 1-2 mmol/l glucose. Mannose fully substituted for glucose. Refeeding with the non-metabolisable glucose analogues 2-deoxyglucose and 3-0-methylglucose, or with glucosamine or mannitol, downregulated 3H-2-deoxyglucose uptake but had little or no effect on transporter protein and mRNA expression. In contrast, glucose-6-phosphate markedly increased 3H-2-deoxyglucose uptake but partly downregulated transporter mRNA levels, whereas galactose had a small stimulatory effect on both 3H-2-deoxyglucose uptake and transporter mRNA; neither affected transporter protein levels. The transporter mRNA level was not affected by several metabolites (pyruvate, glyceraldehyde, glycerol) and amino acids (alanine, glutamine). These findings indicate that (i) there are independent pathways for hexose regulation of transport activity, protein and mRNA and (ii) down-regulation of transporter mRNA requires metabolism beyond hexose phosphate whereas glucose uptake may be regulated by direct interaction of hexoses with the transporter.

The SLC2 (GLUT) family of membrane transporters

“…The 14 human GLUT proteins possess various substrate specificities and are involved in the transport of several hexoses in addition to myo-inositol (Uldry et al, 2001), urate (Bibert et al, 2009; Matsuo et al, 2008; So and Thorens, 2010), glucosamine (Maher and Harrison, 1990), and ascorbate (Lee et al, 2010). All of the members of the GLUT family are facilitative transporters with the exception of HMIT, which is a H+/myo-inositol symporter (Uldry et al, 2001).…”

Differential control of the functional cell surface expression and content of hexose transporter GLUT-1 by glucose and glucose metabolism in murine fibroblasts

“…The relative roles ofthese individual components have, however, not been thoroughly elucidated. Mechanistically, the long-term regulation of hexose transport by glucose has been reported to alter the synthesis [5,6,[8][9][10]18] and/or degradation [1,[4][5][6]10,11,19-21] of some glucose transporter isoforms. The molecular basis of this chronic regulation varies with species and tissue of origin [1][2][3][4][5][6][7][8][9][10][11].…”

“…In contrast, Germinario et al [13] used various glucose analogues to suggest that control of hexose transport in human fibroblasts is independent of both glucose metabolism and carrier-substrate interaction. More recently Maher and Harrison [18], using cultured L6 myocytes, in which a component of GLUT-I regulation is at the transcriptional level, have suggested that GLUT-I gene expression and hexose transport are regulated by independent pathways. In preliminary studies of the effects of various sugars and their analogues on the regulation of GLUT-I by glucose deprivation, we also found indirect evidence in support of different mechanisms regulating hexose transport and GLUT-I content in murine fibroblasts (P. Ortiz and H. C. Haspel, unpublished work).…”

Glucose deprivation and hypoxia increase the expression of the GLUT1 glucose transporter via a specific mRNA cis‐acting regulatory element

“…1995). In experimental cell culture models of BBB and peripheral tissues, a compensatory up‐regulation of the GLUT1 gene was demonstrated in glucose deprivation through a mechanism that involves GLUT1 mRNA stabilization (Maher and Harrison 1990; Boado and Pardridge 1993). The aim of the present study was to investigate the role of the stabilizing GLUT1 CAE 2181−2190 in glucose deprivation and hypoxia using rat C6 stable transfected cell lines and site‐directed deletion.…”