PHOSPHOENOLPYRUVATE CARBOXYKINASE (GTP) GENE-TRANSCRIPTION AND HYPERGLYCEMIA ARE REGULATED BY GLUCOCORTICOIDS IN GENETICALLY-OBESE DB DB TRANSGENIC MICE/

The molecular mechanisms underlying increased hepatic phosphoenolpyruv ate carboxykinase (PEPCK) gene transcription and gluconeogenesis in ty pe II diabetes are largely unknown, To examine the involvement of gluc ocorticoids and the cis-acting insulin response sequence (IRS, -416/-4 07) in the genetically obese db/db mouse model, we generated crosses b etween C57BL/KsJ-db/+ mice and transgenic mice that express -460 or -2 000 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 hom ozygosity 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 des pite severe hyperinsulinemia compared with non-diabetic non-obese tran sgenic mice, Reporter gene expression was also increased 2-fold in tra nsgenic obese diabetic db/db mice bearing a mutation in the IRS, -2000 (IRS)-hGx, compared with non-obese non-diabetic transgenic 2000(IRS)-h Gx mice. Treatment of obese diabetic db/db transgenic mice with the gl ucocorticoid receptor blocker RU 486 decreased plasma glucose by 50% a nd reduced PEPCK, GLUT2, glucose-6-phosphatase, tyrosine aminotransfer ase, CRP, and hGx reporter gene expression to levels similar to those of non-obese normoglycemic transgenic mice, Taken together, these resu lts establish that -460 bp of 5'-flanking sequence is sufficient to me diate the induction of PEPCK gene transcription in genetically obese d b/db mice during the development of hyperglycemia, The results further demonstrate that the mechanism underlying increased expression of glu coneogenic enzymes in the db/db mouse requires the action of glucocort icoids and occurs independently of factors acting through the PEPCK IR S (-416/-407) promoter binding site.