Requirement of glucose metabolism for regulation of glucose transporter type 2 (GLUT2) gene expression in liver

Abstract

Previous studies have shown that glucose increases the glucose transporter (GLUT2) mRNA expression in the liver in vivo and in vitro. Here we report an analysis of the effects of glucose metabolism on GLUT2 gene expression. GLUT2 mRNA accumulation by glucose was not due to stabilization of its transcript but rather was a direct effect on gene transcription. A proximal fragment of the 5' regulatory region of the mouse GLUT2 gene linked to a reporter gene was transiently transfected into liver GLUT2-expressing cells. Glucose stimulated reporter gene expression in these cells, suggesting that glucose-responsive elements were included within the proximal region of the promoter. A dose-dependent effect of glucose on GLUT2 expression was observed over 10 mM glucose irrespective of the hexokinase isozyme (glucokinase K(m) 16 mM; hexokinase I K(m) 0.01 mM) present in the cell type used. This suggests that the correlation between extracellular glucose and GLUT2 mRNA concentrations is simply a reflection of an activation of glucose metabolism. The mediators and the mechanism responsible for this response remain to be determined. In conclusion, glucose metabolism is required for the proper induction of the GLUT2 gene in the liver and this effect is transcriptionally regulated.

Role of the GLUT 2 Glucose Transporter in the Response of the L-type Pyruvate Kinase Gene to Glucose in Liver-derived Cells

“…In contrast, in GLUT 2-expressing cells, the amplitude of the glucose responsiveness of the L-PK mRNA expression was correlated with the GLUT 2 mRNA level. It should be observed that GLUT 2 mRNA accumulation is itself dependent on glucose, as previously demonstrated in hepatocytes and mhAT3F cells (3,28,29), whereas abundance of GLUT 1 mRNA was independent of glucose ( Fig. 5).…”

“…In the mhPKTf3 cell line, GLUT 1 immunofluorescence was easily detectable at the plasma membrane of the cells while no 3 A. Vandewalle, unpublished results.…”

“…Regulated by Glucose-The GLUT 2 gene is known to be regulated by glucose (3,28,29). We raised the question of whether the kinetics of glucose responsiveness of the GLUT 2 and L-PK genes were similar or different in mhAT3F cells.…”

“…mhPKTf3 previously established 3 and HepG2, were transiently transfected with L-PK CAT constructs and CMV-expression vectors for GLUT 1 or GLUT 2.…”

“…In these three glucose-sensitive tissues, glucose transport and phosphorylation are performed by various isoforms of glucose transporters and hexokinases, respectively. Glucose phosphorylation to glucose 6-phosphate, required for glucose action on the transcriptional machinery (2)(3)(4)(5)(6), is mainly mediated by hexokinase (HK) 1 II in adipocytes and by hexokinase IV (or glucokinase) in the liver and ␤ cells; expression of the glucokinase gene is constitutive in the pancreas and insulin-dependent in the liver due to the existence of two different tissue-specific alternative promoters (7). However, glucokinase is replaced by other insulin-independent hexokinase isoforms (mainly HK I) in cultured hepatoma cell lines (2,8,9).…”