Abstract |
The molecular mechanisms underlying increased hepatic phosphoenolpyruvate carboxykinase (PEPCK) gene transcription and gluconeogenesis in type II diabetes are largely unknown. To examine the involvement of glucocorticoids and the cis-acting insulin response sequence (IRS, -416/-407) in the genetically obese db/db mouse model, we generated crosses between C57BL/KsJ-db/+ mice and transgenic mice that express -460 or -2000 base pairs of the rat PEPCK gene promoter containing an intact or mutated IRS, linked to a reporter gene. Transgenic mice expressing the intact PEPCK(460)-CRP ( C-reactive protein) transgene bred to near homozygosity at the db locus were obese, hyperinsulinemic, and developed fasting hyperglycemia (389 +/- 26 mg/100 ml) between 4 and 10 weeks of age. Levels of CRP reporter gene expression were increased 2-fold despite severe hyperinsulinemia compared with non-diabetic non-obese transgenic mice. Reporter gene expression was also increased 2-fold in transgenic obese diabetic db/db mice bearing a mutation in the IRS, -2000(IRS)-hGx, compared with non-obese non-diabetic transgenic 2000(IRS)-hGx mice. Treatment of obese diabetic db/db transgenic mice with the glucocorticoid receptor blocker RU 486 decreased plasma glucose by 50% and reduced PEPCK, GLUT2, glucose-6-phosphatase, tyrosine aminotransferase, CRP, and hGx reporter gene expression to levels similar to those of non-obese normoglycemic transgenic mice. Taken together, these results establish that -460 bp of 5'-flanking sequence is sufficient to mediate the induction of PEPCK gene transcription in genetically obese db/db mice during the development of hyperglycemia. The results further demonstrate that the mechanism underlying increased expression of gluconeogenic enzymes in the db/db mouse requires the action of glucocorticoids and occurs independently of factors acting through the PEPCK IRS (-416/-407) promoter binding site.
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Authors | J E Friedman, Y Sun, T Ishizuka, C J Farrell, S E McCormack, L M Herron, P Hakimi, P Lechner, J S Yun |
Journal | The Journal of biological chemistry
(J Biol Chem)
Vol. 272
Issue 50
Pg. 31475-81
(Dec 12 1997)
ISSN: 0021-9258 [Print] United States |
PMID | 9395482
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
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Chemical References |
- Glucocorticoids
- Hormone Antagonists
- Insulin Receptor Substrate Proteins
- Irs1 protein, mouse
- Irs1 protein, rat
- Phosphoproteins
- Mifepristone
- DNA
- Phosphatidylinositol 3-Kinases
- Receptor, Insulin
- Phosphoenolpyruvate Carboxykinase (GTP)
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Topics |
- Animals
- Binding Sites
- DNA
(metabolism)
- Diabetes Mellitus, Type 2
(enzymology, genetics)
- Genes, Reporter
- Glucocorticoids
(physiology)
- Hormone Antagonists
(pharmacology)
- Hyperglycemia
(physiopathology)
- Insulin Receptor Substrate Proteins
- Liver
(drug effects, metabolism)
- Mice
- Mice, Inbred C57BL
- Mice, Obese
- Mice, Transgenic
- Mifepristone
(pharmacology)
- Phosphatidylinositol 3-Kinases
(metabolism)
- Phosphoenolpyruvate Carboxykinase (GTP)
(genetics)
- Phosphoproteins
(metabolism)
- Promoter Regions, Genetic
- Rats
- Receptor, Insulin
(metabolism)
- Transcription, Genetic
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