Glycogen synthase kinase-3 regulates IGFBP-1 gene transcription through the thymine-rich insulin response element.
BACKGROUND
Hepatic expression of several gene products involved in glucose metabolism, including phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6Pase) and insulin-like growth factor binding protein-1 (IGFBP-1), is rapidly and completely inhibited by insulin. This inhibition is mediated through the regulation of a DNA element present in each of these gene promoters, that we call the Thymine-rich Insulin Response Element (TIRE). The insulin signalling pathway that results in the inhibition of these gene promoters requires the activation of phosphatidylinositol 3-kinase (PI 3-kinase). However, the molecules that connect PI 3-kinase to these gene promoters are not yet fully defined. Glycogen Synthase Kinase 3 (GSK-3) is inhibited following activation of PI 3-kinase. We have shown previously that inhibitors of GSK-3 reduce the activity of two TIRE-containing gene promoters (PEPCK and G6Pase), whose products are required for gluconeogenesis.


RESULTS
In this report we demonstrate that in H4IIE-C3 cells, four distinct classes of GSK-3 inhibitor mimic the effect of insulin on a third TIRE-containing gene, IGFBP-1. We identify the TIRE as the minimum requirement for inhibition by these agents, and demonstrate that the target of GSK-3 is unlikely to be the postulated TIRE-binding protein FOXO-1. Importantly, overexpression of GSK-3 in cells reduces the insulin regulation of TIRE activity as well as endogenous IGFBP-1 expression.


CONCLUSIONS
These results implicate GSK-3 as an intermediate in the pathway from the insulin receptor to the TIRE. Indeed, this is the first demonstration of an absolute requirement for GSK-3 inhibition in insulin regulation of gene transcription. These data support the potential use of GSK-3 inhibitors in the treatment of insulin resistant states such as Type 2 diabetes mellitus, but suggest that it will be important to identify all TIRE-containing genes to assess potential side effects of these agents.
Finlay
David
D
Department of Pathology and Neurosciences, University of Dundee, Ninewells Medical School and Hospital, Dundee, DD1 9SY United Kingdom. d.finlay@fundee.ac.uk
Patel
Satish
S
Dickson
Lorna M
LM
Shpiro
Natalia
N
Marquez
Rodolfo
R
Rhodes
Chris J
CJ
Sutherland
Calum
C
D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D045744:Cell Line, Tumor; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000502:physiology; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation / Q000187:drug effects; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000502:physiology*; D007328:Insulin / Q000502:physiology*; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000096:biosynthesis / Q000235:genetics*; D008094:Lithium / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D020218:Response Elements / Q000502:physiology*; D013941:Thymine; D015534:Trans-Activators / Q000378:metabolism; D014158:Transcription, Genetic; D051176:beta Catenin; D000071161:Forkhead Box Protein O1
D001552:Benzazepines; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D051858:Forkhead Transcription Factors; D038362:Glycogen Synthase Kinase 3; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D008094:Lithium; D009419:Nerve Tissue Proteins; D011725:Pyridines; D011743:Pyrimidines; D013941:Thymine; D015534:Trans-Activators; D051176:beta Catenin; C473711:Chir 99021; C495268:Ctnnb1 protein, rat; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1