PDX-1 mediates glucose responsiveness of GAD(67), but not GAD(65), gene transcription in islets of Langerhans.
Glucose responsiveness is a fundamental metabolic feature of pancreatic beta-cells. Glucose-regulated transcription of the insulin gene is in part mediated via the homeobox transcription factor PDX-1. Another islet protein and diabetes autoantigen, glutamic acid decarboxylase (GAD), has been shown to be subject to regulation by glycemia. We have studied the mRNA level of two isoforms of GAD, GAD(65) and GAD(67), and found that GAD(67) but not GAD(65) mRNA steady-state level is regulated by glucose. By transfection of a rat GAD(67) promoter-driven luciferase reporter gene into primary rat islet cells, we demonstrate glucose-regulated expression of the reporter gene. We show that PDX-1 is able to bind to two TAAT-boxes in the GAD(67) promoter and that functional disruption of these two PDX-1 binding elements has an additive effect in severely impairing glucose responsiveness of the GAD(67) promoter. These data strongly suggest that PDX-1 is involved in glucose-regulated expression of GAD(67).
Pedersen
Anette Amstrup
AA
Department of Diabetes Autoimmunity, Hagedorn Research Institute, Niels Steensens Vej 6, Gentofte DK-2820, Denmark.
Petersen
Helle Vestergaard
HV
Videbaek
Nicoline
N
Skak
Kresten
K
Michelsen
Birgitte Koch
BK
D000818:Animals; D001483:Base Sequence; D016384:Consensus Sequence; D017931:DNA Primers; D005947:Glucose / Q000378:metabolism*; D005968:Glutamate Decarboxylase / Q000235:genetics*; D018398:Homeodomain Proteins; D007515:Islets of Langerhans / Q000201:enzymology*; D007527:Isoenzymes / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*; D014407:Tumor Cells, Cultured
D017931:DNA Primers; D018398:Homeodomain Proteins; D007527:Isoenzymes; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; C401141:glutamate decarboxylase 2; D005947:Glucose