title: Phosphoenolpyruvate carboxykinase (GTP) gene transcription and hyperglycemia are regulated by glucocorticoids in genetically obese db/db transgenic mice.
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.
authors.affiliation: Department of Nutrition, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4935, USA. jef8@po.cwru.edu
authors.forename: J E
authors.initials: JE
authors.lastname: Friedman
authors.forename: Y
authors.initials: Y
authors.lastname: Sun
authors.forename: T
authors.initials: T
authors.lastname: Ishizuka
authors.forename: C J
authors.initials: CJ
authors.lastname: Farrell
authors.forename: S E
authors.initials: SE
authors.lastname: McCormack
authors.forename: L M
authors.initials: LM
authors.lastname: Herron
authors.forename: P
authors.initials: P
authors.lastname: Hakimi
authors.forename: P
authors.initials: P
authors.lastname: Lechner
authors.forename: J S
authors.initials: JS
authors.lastname: Yun
mesh_terms: D000818:Animals; D001665:Binding Sites; D004247:DNA / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology* / Q000235:genetics*; D017930:Genes, Reporter; D005938:Glucocorticoids / Q000502:physiology*; D006727:Hormone Antagonists / Q000494:pharmacology; D006943:Hyperglycemia / Q000503:physiopathology*; D055504:Insulin Receptor Substrate Proteins; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D008822:Mice, Transgenic; D015735:Mifepristone / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics*; D010750:Phosphoproteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D005938:Glucocorticoids; D006727:Hormone Antagonists; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D015735:Mifepristone; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D010729:Phosphoenolpyruvate Carboxykinase (GTP)