Functional characterisation of the regulation of CAAT enhancer binding protein alpha by GSK-3 phosphorylation of Threonines 222/226
Citation:
Liu HK, Perrier S, Lipina C, Finlay D, McLauchlan H, Hastie CJ, Hundal HS, Sutherland C, Functional characterisation of the regulation of CAAT enhancer binding protein alpha by GSK-3 phosphorylation of Threonines 222/226, BMC Molecular Biology, 7, 14, 2006Download Item:
Abstract:
BACKGROUND:
Glycogen Synthase Kinase-3 (GSK3) activity is repressed following insulin treatment of cells. Pharmacological inhibition of GSK3 mimics the effect of insulin on Phosphoenolpyruvate Carboxykinase (PEPCK), Glucose-6 Phosphatase (G6Pase) and IGF binding protein-1 (IGFBP1) gene expression. CAAT/enhancer binding protein alpha (C/EBPalpha) regulates these gene promoters in liver and is phosphorylated on two residues (T222/T226) by GSK3, although the functional outcome of the phosphorylation has not been established. We aimed to establish whether CEBPalpha is a link between GSK3 and these gene promoters.
RESULTS:
C/EBPalpha represses the IGFBP1 thymine-rich insulin response element (TIRE), but mutation of T222 or T226 of C/EBPalpha to non-phosphorylatable alanines has no effect on C/EBPalpha activity in liver cells (towards the TIRE or a consensus C/EBP binding sequence). Phosphorylation of T222/T226 is decreased by GSK3 inhibition, suggesting GSK3 does phosphorylate T222/226 in intact cells. However, phosphorylation was not altered by treatment of liver cells with insulin. Meanwhile C/EBPalpha activity in 3T3 L1 preadipocytes was enhanced by mutation of T222/T226 and/or S230 to alanine residues. Finally, we demonstrate that C/EBPalpha is a very poor substrate for GSK3 in vitro and in cells.
CONCLUSION:
The work demonstrates an important role for this domain in the regulation of C/EBPalpha activity in adipocytes but not hepatocytes, however GSK3 phosphorylation of these residues does not mediate regulation of this C/EBP activity. In short, we find no evidence that C/EBPalpha activity is regulated by direct phosphorylation by GSK3.
Author's Homepage:
http://people.tcd.ie/finlaydDescription:
PUBLISHED
Author: FINLAY, DAVID
Publisher:
BioMed CentralType of material:
Journal ArticleCollections
Series/Report no:
BMC Molecular Biology;7;
14;
Availability:
Full text availableMetadata
Show full item recordLicences: