cAMP opposes the glucose-mediated induction of the L-PK gene by preventing the recruitment of a complex containing ChREBP, HNF4alpha, and CBP.
Glucose-mediated activation of the L-type pyruvate kinase (L-PK) gene is repressed by cAMP, making this an excellent model for studying the mechanism by which these contrary signals regulate gene expression. Using the 832/13 rat insulinoma cell line, we demonstrate using RNA interference and chromatin immunoprecipitation that carbohydrate response element binding protein (ChREBP), hepatic nuclear factor 4alpha (HNF4alpha), and the coactivator CREB binding protein (CBP) are required for the glucose response of the L-PK gene and are recruited to the promoter by glucose. The cAMP agonist forskolin blocked the glucose-mediated induction of the L-PK gene in a PKA-dependent manner and blocked the recruitment of ChREBP, HNF4alpha, and CBP to the L-PK promoter, while simultaneously recruiting CBP to the cAMP-inducible gene, nuclear receptor subfamily 4, group A, member 2 (NR4A2). Overexpression of CBP, but not ChREBP, reversed the cAMP repression of the L-PK gene. In addition, CBP augmented the glucose response of the L-PK promoter. We conclude that cAMP and glucose signaling converge on a complex containing ChREBP, HNF4alpha, and CBP, and that cAMP acts by disrupting this transcriptional complex assembled by glucose-derived signals.
Burke
Susan J
SJ
Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA.
Collier
J Jason
JJ
Scott
Donald K
DK
D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000378:metabolism; D050882:CREB-Binding Protein / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases; D005947:Glucose / Q000494:pharmacology*; D051557:Hepatocyte Nuclear Factor 4 / Q000378:metabolism; D046912:Multiprotein Complexes / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D021381:Protein Transport; D011770:Pyruvate Kinase / Q000235:genetics*; D051381:Rats; D015398:Signal Transduction; D014158:Transcription, Genetic; D015533:Transcriptional Activation / Q000187:drug effects*
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051557:Hepatocyte Nuclear Factor 4; C496594:Hnf4a protein, rat; C442825:Mlxipl protein, rat; D046912:Multiprotein Complexes; D000242:Cyclic AMP; D050882:CREB-Binding Protein; D011770:Pyruvate Kinase; D017868:Cyclic AMP-Dependent Protein Kinases; D005947:Glucose