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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

University of Illinois at Chicago, Chicago, Illinois, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2001; 276(11):8516-23. DOI: 10.1074/jbc.M008542200
Source: PubMed

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/EBPbeta 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 p70(S6 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/EBPbeta, but not C/EBPalpha, and that N-terminal transactivation domains in C/EBPbeta are required. Studies with Gal4 fusion proteins reveal that insulin and PKB suppress transactivation by the major activation domain in C/EBPbeta (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/EBPbeta. Mammalian two-hybrid studies indicate that insulin and PKB disrupt interactions between this region of p300 and AD II and that Ser(1834) is critical for this effect. Signaling by PKB and phosphorylation of Ser(1834) 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.

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    • "For instance, PKC-d-mediated p300 phosphorylation at serine 89 represses intrinsic acetyltransferase activity and transcriptional function (Yuan et al., 2002). In contrast, phosphorylation at serine 1835 by Akt/PKB enhances acetyltransferase activity (Huang and Chen, 2005), and also modulates p300 interaction with C/EBPb in response to insulin (Guo et al., 2001). Induction of phosphatidylinositol 3-kinase activity is associated with increased p300 stability and transcriptional activity (Chen et al., 2004). "
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    • "Glucocorticoid results in the binding of a complex of transcription factors, consisting of Foxo1, c/EBPb, and the coactivator CBP/p300, to this IRE sequence (Fig. 1B) (Ghosh et al. 2001; Guo et al. 1999, 2001; Nasrin et al. 2000). Insulin treatment results in the phosphorylation of Foxo proteins (Nasrin et al. 2000), their exclusion from the nucleus (Biggs et al. 1999; Brunet et al. 1999; Takaishi et al. 1999), and the phosphorylation of the coactivator CBP/p300 (Guo et al. 2001), leading to the dissociation of this transcription complex. Recently it has been shown that the effect of insulin on glucocorticoid-induced gene transcription can occur independent of this IRE (Gan et al. 2005). "
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    Canadian Journal of Physiology and Pharmacology 08/2006; 84(7):713-24. DOI:10.1139/y05-152 · 1.55 Impact Factor
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    • "Another report indicates that serine 1834 in p300 is phosphorylated by protein kinase B/Akt, and that phosphorylation at this site disrupts the interaction with the transcription factor C/EBPß. At the present time, one cannot distinguish whether this is due to a loss of affinity for C/EBPß or due to an increased affinity for another cellular factor that competes with C/EBPß for binding to the same region of p300 encompassing serine 1834 (Guo et al., 2001). The p42/p44 MAPKs have been found to phosphorylate CBP in vitro and enhance the potency of its transactivation domains. "
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