Fructose 2,6-bisphosphate is essential for glucose-regulated gene transcription of glucose-6-phosphatase and other ChREBP target genes in hepatocytes.
Glucose metabolism in the liver activates the transcription of various genes encoding enzymes of glycolysis and lipogenesis and also G6pc (glucose-6-phosphatase). Allosteric mechanisms involving glucose 6-phosphate or xylulose 5-phosphate and covalent modification of ChREBP (carbohydrate-response element-binding protein) have been implicated in this mechanism. However, evidence supporting an essential role for a specific metabolite or pathway in hepatocytes remains equivocal. By using diverse substrates and inhibitors and a kinase-deficient bisphosphatase-active variant of the bifunctional enzyme PFK2/FBP2 (6-phosphofructo-2-kinase-fructose-2,6-bisphosphatase), we demonstrate an essential role for fructose 2,6-bisphosphate in the induction of G6pc and other ChREBP target genes by glucose. Selective depletion of fructose 2,6-bisphosphate inhibits glucose-induced recruitment of ChREBP to the G6pc promoter and also induction of G6pc by xylitol and gluconeogenic precursors. The requirement for fructose 2,6-bisphosphate for ChREBP recruitment to the promoter does not exclude the involvement of additional metabolites acting either co-ordinately or at downstream sites. Glucose raises fructose 2,6-bisphosphate levels in hepatocytes by reversing the phosphorylation of PFK2/FBP2 at Ser32, but also independently of Ser32 dephosphorylation. This supports a role for the bifunctional enzyme as the phosphometabolite sensor and for its product, fructose 2,6-bisphosphate, as the metabolic signal for substrate-regulated ChREBP-mediated expression of G6pc and other ChREBP target genes.
Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.
Catherine
C
Arden
Susan J
SJ
Tudhope
John L
JL
Petrie
Ziad H
ZH
Al-Oanzi
Kirsty S
KS
Cullen
Alex J
AJ
Lange
Howard C
HC
Towle
Loranne
L
Agius
D021581:Active Transport, Cell Nucleus; D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D003847:Deoxyglucose / Q000494:pharmacology; D004098:Dihydroxyacetone / Q000494:pharmacology; D005635:Fructosediphosphates / Q000378:metabolism*; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D005952:Glucose-6-Phosphatase / Q000235:genetics* / Q000378:metabolism; D006019:Glycolysis; D022781:Hepatocytes / Q000201:enzymology / Q000378:metabolism*; D006595:Hexosamines / Q000378:metabolism; D008297:Male; D025481:Phosphofructokinase-2 / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D014993:Xylitol / Q000494:pharmacology
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D005635:Fructosediphosphates; D006595:Hexosamines; C442825:Mlxipl protein, rat; C027652:fructose 2,6-diphosphate; D003847:Deoxyglucose; D025481:Phosphofructokinase-2; D005952:Glucose-6-Phosphatase; D005947:Glucose; D004098:Dihydroxyacetone; D014993:Xylitol