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 elementbinding 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.