3',5'-cyclic adenosine monophosphate response element-binding protein and CCAAT enhancer-binding protein are dispensable for insulin inhibition of phosphoenolpyruvate carboxykinase transcription and for its synergistic induction by protein kinase A and glucocorticoids.
Phosphoenolpyruvate carboxykinase (PEPCK) transcription is induced by cAMP/protein kinase A (PKA) and glucocorticoids [dexamethasone (Dex)] and is inhibited by insulin to regulate blood glucose. Recent reports suggested that CCAAT enhancer binding protein (C/EBP) binding to the PEPCK cAMP response element (CRE) plays a role in Dex induction and that insulin-induces inhibitory forms of C/EBPbeta to inhibit transcription. Here, we assessed the roles of CRE-binding protein (CREB) and C/EBP factors in mediating hormone-regulated transcription. Neither cAMP nor insulin regulated the phosphorylation of C/EBP. Cycloheximide did not block insulin inhibition, indicating that alternate translation of C/EBPbeta is not required. Dominant-negative CREB or C/EBP blocked induction by PKA, but neither affected regulation by Dex or insulin. Tethering the activation domains of CREB or C/EBP to a CRE-->Gal4 (G4) site mediated varying extents of basal and PKA-inducible activity, but neither activation domain affected induction by Dex or inhibition by insulin. Surprisingly, synergistic induction by PKA and Dex did not require the CRE and was unaffected by dominant-negative CREB or C/EBP. PKA and Dex also synergistically induced a minimal 3 x glucocorticoid response element promoter, but inhibited Dex induction of the mouse mammary tumor virus and IGF-binding protein 1 promoters, even though PKA alone did not regulate these promoters. These results suggest that PKA modifies the activity of other factors involved in Dex induction to mediate synergistic induction or inhibition in a promoter-specific manner. Our data indicate that the roles of CREB and C/EBP are restricted to mediating PEPCK induction by PKA, and that other factors mediate PEPCK induction by Dex, synergism between PKA and Dex, and inhibition by insulin.
Yeagley
David
D
The Pennsylvania State University, College of Medicine, Department of Cellular and Molecular Physiology, C4718, 500 University Drive, Hershey, Pennsylvania 17033, USA.
Quinn
Patrick G
PG
D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology; D015536:Down-Regulation; D005938:Glucocorticoids / Q000494:pharmacology / Q000502:physiology*; D007328:Insulin / Q000494:pharmacology*; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D020218:Response Elements; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
D022762:CCAAT-Enhancer-Binding Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D005938:Glucocorticoids; D007328:Insulin; D011500:Protein Synthesis Inhibitors; D018808:Transcription Factor AP-1; D003907:Dexamethasone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D010729:Phosphoenolpyruvate Carboxykinase (GTP)