Insulin suppresses transactivation by CAAT/Enhancer-binding proteins β (C/EBPβ). Signaling to p300/CREB-binding protein by protein kinase B disrupts interaction with the major activation domain of C/EBPβ

Shaodong Guo, Stephen B. Cichy, Xiaowei He, Qunying Yang, Maria Ragland, Asish K. Ghosh, Peter F. Johnson, Terry G. Unterman*

*Corresponding author for this work

Research output: Contribution to journalArticle

80 Scopus citations

Abstract

CAAT/enhancer-binding proteins (C/EBPs) play an important role in the regulation of gene expression in insulin-responsive tissues. We have found that a complex containing C/EBPβ interacts with an insulin response sequence in the insulin-like growth factor-binding protein-1 (IGFBP-1) gene and that a C/EBP-binding site can mediate effects of insulin on promoter activity. Here, we examined mechanisms mediating this effect of insulin. The ability of insulin to suppress promoter activity via a C/EBP-binding site is blocked by LY294002, a phosphatidylinositol 3-kinase inhibitor, but not by rapamycin, which blocks activation of p70S6 kinase. Dominant negative phosphatidylinositol 3-kinase and protein kinase B (PKB) block the effect of insulin, while activated PKB suppresses promoter function via a C/EBP-binding site, mimicking the effect of insulin. Coexpression studies indicate that insulin and PKB suppress transactivation by C/EBPβ, but not C/EBPα, and that N-terminal transactivation domains in C/EBPβ are required. Studies with Gal4 fusion proteins reveal that insulin and PKB suppress transactivation by the major activation domain in C/EBPβ (AD II), located between amino acids 31 and 83. Studies with E1A protein indicate that interaction with p300/CBP is required for transactivation by AD II and the effect of insulin and PKB. Based on a consensus sequence, we identified a PKB phosphorylation site (Ser 1834) within the region of p300/CBP known to bind C/EBPβ. Mammalian two-hybrid studies indicate that insulin and PKB disrupt interactions between this region of p300 and AD II and that Ser1834 is critical for this effect. Signaling by PKB and phosphorylation of Ser1834 may play an important role in modulating interactions between p300/CBP and transcription factors and mediate effects of insulin and related growth factors on gene expression.

Original languageEnglish (US)
Pages (from-to)8516-8523
Number of pages8
JournalJournal of Biological Chemistry
Volume276
Issue number11
DOIs
StatePublished - Mar 16 2001

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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