The promoter for the gene encoding the catalytic subunit of rat glucose-6-phosphatase contains two distinct glucose-responsive regions.
Glucose homeostasis requires the proper expression and regulation of the catalytic subunit of glucose-6-phosphatase (G-6-Pase), which hydrolyzes glucose 6-phosphate to glucose in glucose-producing tissues. Glucose induces the expression of G-6-Pase at the transcriptional and posttranscriptional levels by unknown mechanisms. To better understand this metabolic regulation, we mapped the cis-regulatory elements conferring glucose responsiveness to the rat G-6-Pase gene promoter in glucose-responsive cell lines. The full-length (-4078/+64) promoter conferred a moderate glucose response to a reporter construct in HL1C rat hepatoma cells, which was dependent on coexpression of glucokinase. The same construct provided a robust glucose response in 832/13 INS-1 rat insulinoma cells, which are not glucogenic. Glucose also strongly increased endogenous G-6-Pase mRNA levels in 832/13 cells and in rat pancreatic islets, although the induced levels from islets were still markedly lower than in untreated primary hepatocytes. A distal promoter region was glucose responsive in 832/13 cells and contained a carbohydrate response element with two E-boxes separated by five base pairs. Carbohydrate response element-binding protein bound this region in a glucose-dependent manner in situ. A second, proximal promoter region was glucose responsive in both 832/13 and HL1C cells, with a hepatocyte nuclear factor 1 binding site and two cAMP response elements required for glucose responsiveness. Expression of dominant-negative versions of both cAMP response element-binding protein and CAAT/enhancer-binding protein blocked the glucose response of the proximal region in a dose-dependent manner. We conclude that multiple, distinct cis-regulatory promoter elements are involved in the glucose response of the rat G-6-Pase gene.
Pedersen
Kim B
KB
Department of Biochemistry and Molecular Biology, Lousiana State University Health Sciences Center, New Orleans, USA.
Zhang
Pili
P
Doumen
Chris
C
Charbonnet
Marcel
M
Lu
Danhong
D
Newgard
Christopher B
CB
Haycock
John W
JW
Lange
Alex J
AJ
Scott
Donald K
DK
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins / Q000502:physiology; D020134:Catalytic Domain; D045744:Cell Line, Tumor; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology; D017930:Genes, Reporter; D005947:Glucose / Q000494:pharmacology*; D005952:Glucose-6-Phosphatase / Q000235:genetics*; D051537:Hepatocyte Nuclear Factor 1 / Q000502:physiology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D051381:Rats; D020218:Response Elements / Q000187:drug effects*; D014162:Transfection
D022762:CCAAT-Enhancer-Binding Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D051537:Hepatocyte Nuclear Factor 1; D005952:Glucose-6-Phosphatase; D005947:Glucose