Metabolism-independent sugar effects on gene transcription: the role of 3-O-methylglucose.
Glucose effects on cellular functions such as gene expression require, in general, glucose metabolism at least to glucose-6-phosphate (G-6-P). However, the example of thioredoxin-interacting protein (TXNIP), a glucose-regulated gene involved in the cellular redox state and pancreatic beta cell apoptosis, demonstrates that this rule may not always apply. We found that aside form glucose, the nonmetabolizable sugars 2-deoxyglucose, which is still converted to G-6-P as well as 3-O-methylglucose (3-MG), which cannot be phosphorylated by glucokinase, stimulate TXNIP expression. In contrast, incubation of INS-1 beta cells with equimolar amounts (25 mM) of l-glucose or mannitol had no effect on TXNIP expression as measured by real-time RT-PCR, eliminating the possibility of an osmotic effect. Also, glucose uptake into the cell is critical because phloretin, an inhibitor of glucose transporter 2, blunted the glucose effects. Moreover, the 3-MG effect was not restricted to a cell line and was observed in 293 cells and primary human islets. Incubation of INS-1 cells with 30mM mannoheptulose, an inhibitor of glucose metabolism, blunted all glucose-induced gene expression but left the 3-MG effects unaltered. Using transient transfection studies and deletion constructs of the human TXNIP promoter, we found that the effects of glucose and 3-MG were dependent on the same region of the TXNIP promoter containing an E-box repeat carbohydrate response element (ChoRE). Thus, these findings provide the first evidence for regulation of gene expression by 3-MG, which is independent of glucose metabolism and suggest that glucose and 3-MG regulate transcription by two distinct pathways converging at a common ChoRE.
Minn
Alexandra H
AH
Department of Medicine, University of Wisconsin, Madison, Wisconsin 53792, USA.
Couto
Francesca M
FM
Shalev
Anath
A
D019325:3-O-Methylglucose / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics; D018797:Cell Cycle Proteins; D002460:Cell Line; D006801:Humans; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism*; D007340:Insulinoma / Q000378:metabolism; D051381:Rats; D013879:Thioredoxins / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C486715:TXNIP protein, human; C493796:TXNIP protein, rat; D019325:3-O-Methylglucose; D013879:Thioredoxins