Liver glucokinase gene expression is controlled by the onecut transcription factor hepatocyte nuclear factor-6.
OBJECTIVE
Glucokinase plays a key role in glucose homeostasis and the expression of its gene is differentially regulated in pancreatic beta cells and in the liver through distinct promoters. The factors that determine the tissue-specific expression of the glucokinase gene are not known. Putative binding sites for hepatocyte nuclear factor (HNF)-6, the prototype of the ONECUT family of transcription factors, are present in the hepatic promoter of the glucokinase gene and hnf6 knockout mice are diabetic [corrected]. We hypothesized that HNF-6 controls the activity of the hepatic glucokinase promoter.


METHODS
We tested the binding of recombinant HNF-6 to DNA sequences from the mouse hepatic glucokinase promoter in vitro and the effect of HNF-6 on promoter activity in transfected cells. We investigated in vivo the role of HNF-6 in mice by examining the effect of inactivating the hnf6 gene on glucokinase gene-specific deoxyribonuclease I hypersensitive sites in liver chromatin and on liver glucokinase mRNA concentration.


RESULTS
HNF-6 bound to the hepatic promoter of the glucokinase gene and stimulated its activity. Inactivation of the hnf6 gene did not modify the pattern of deoxyribonuclease I hypersensitive sites but was associated with a decrease of liver glucokinase mRNA to half the control value.


CONCLUSIONS
Although HNF-6 is not required to open chromatin of the hepatic promoter of the glucokinase gene, it stimulates transcription of the glucokinase gene in the liver. This could partly explain the diabetes observed in hnf6 knockout mice.
Hormone and Metabolic Research Unit, Université catholique de Louvain and Institute of Cellular Pathology, Brussels, Belgium.
V J
VJ
Lannoy
J F
JF
Decaux
C E
CE
Pierreux
F P
FP
Lemaigre
G G
GG
Rousseau
D000818:Animals; D002843:Chromatin / Q000502:physiology; D003850:Deoxyribonuclease I / Q000502:physiology; D015870:Gene Expression / Q000187:drug effects; D005786:Gene Expression Regulation / Q000502:physiology*; D005941:Glucokinase / Q000235:genetics* / Q000378:metabolism; D051559:Hepatocyte Nuclear Factor 6; D018398:Homeodomain Proteins / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D008099:Liver / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000037:antagonists & inhibitors; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D014407:Tumor Cells, Cultured
D002843:Chromatin; D051559:Hepatocyte Nuclear Factor 6; D018398:Homeodomain Proteins; C496606:Onecut1 protein, mouse; C496607:Onecut1 protein, rat; D012333:RNA, Messenger; D011994:Recombinant Proteins; D015534:Trans-Activators; D005941:Glucokinase; D003850:Deoxyribonuclease I