Sterol regulatory element-binding protein-1c mimics the negative effect of insulin on phosphoenolpyruvate carboxykinase (GTP) gene transcription.
We have assessed the potential role of sterol regulatory element-binding protein-1c (SREBP-1c) on the transcription of the gene for the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) (EC ) (PEPCK-C). SREBP-1c introduced into primary hepatocytes with an adenovirus vector caused a total loss of PEPCK-C mRNA and a marked induction of fatty acid synthase mRNA that directly coincided with the appearance of SREBP-1c in the hepatocytes. It also blocked the induction of PEPCK-C mRNA by cAMP and dexamethasone in these cells. In contrast, a dominant negative form of SREBP-1c (dnSREBP-1c) stimulated the accumulation of PEPCK-C mRNA in these cells. SREBP-1c completely blocked the induction of PEPCK-C gene transcription by the catalytic subunit of protein kinase A (PKA), and increasing concentrations of dnSREBP-1c reversed the negative effect of insulin on transcription from the PEPCK-C gene promoter in WT-IR cells. The more than 10-fold induction of PKA-stimulated PEPCK-C gene transcription caused by the co-activator CBP, was also blocked by SREBP-1c. In addition, dnSREBP-1c reversed the strong negative effect of E1A and NF1 on PKA-stimulated transcription from the PEPCK-C gene promoter. An analysis of the possible site of action of SREBP-1c using stepwise truncations of the PEPCK-C gene promoter indicated that the negative effect of SREBP-1c on transcription is exerted at a site between -355 and -277. We conclude that SREBP-1c is an intermediate in the action of insulin on PEPCK-C gene transcription in the liver and acts by blocking the stimulatory effect cAMP that is mediated via an interaction with cAMP-binding protein.
Chakravarty
K
K
Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4935, USA.
Leahy
P
P
Becard
D
D
Hakimi
P
P
Foretz
M
M
Ferre
P
P
Foufelle
F
F
Hanson
R W
RW
D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000502:physiology*; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D004268:DNA-Binding Proteins / Q000502:physiology*; D005260:Female; D022781:Hepatocytes / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000187:drug effects*
D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D004268:DNA-Binding Proteins; D007328:Insulin; D012333:RNA, Messenger; C497389:Srebf1 protein, rat; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D017868:Cyclic AMP-Dependent Protein Kinases; D010729:Phosphoenolpyruvate Carboxykinase (GTP)