title: Activation of CCAAT/enhancer-binding protein (C/EBP) alpha expression by C/EBP beta during adipogenesis requires a peroxisome proliferator-activated receptor-gamma-associated repression of HDAC1 at the C/ebp alpha gene promoter.
abstract: Studies have shown that CCAAT/enhancer-binding protein beta (C/EBP beta) can stimulate adipogenesis in noncommitted fibroblasts by activating expression of peroxisome proliferator-activated receptor-gamma (PPARgamma). Other investigations have established a role for C/EBP alpha as well as PPARgamma in orchestrating the complex program of adipogenic gene expression during terminal preadipocyte differentiation. Consequently, it is important to identify factors regulating transcription of the C/ebp alpha gene. In this study, we demonstrated that inhibition of PPARgamma activity by exposure of 3T3-L1 preadipocytes to a potent and selective PPARgamma antagonist inhibits adipogenesis but also blocks the activation of C/EBP alpha expression at the onset of differentiation. Ectopic expression of C/EBP beta in Swiss 3T3 mouse fibroblasts (Swiss-LAP cells) induces PPARgamma expression without any significant enhancement of C/EBP alpha expression. Treatment of Swiss-LAP cells with a PPARgamma agonist induces adipogenesis, which includes activation of C/EBP alpha expression. To further establish a role for PPARgamma in regulating C/EBP alpha expression, we expressed C/EBP beta in PPARgamma-deficient mouse embryo fibroblasts (MEFs). The data show that C/EBP beta is capable of inducing PPARgamma in Ppar gamma+/- MEFs, which leads to activation of adipogenesis, including C/EBP alpha expression following exposure to a PPARgamma ligand. In contrast, C/EBP beta is not able to induce C/EBP alpha expression or adipogenesis in Ppar gamma-/- MEFs. Chromatin immunoprecipitation analysis reveals that C/EBP beta is bound to the minimal promoter of the C/ebp alpha gene in association with HDAC1 in unstimulated Swiss-LAP cells. Exposure of the cells to a PPARgamma ligand dislodges HDAC1 from the proximal promoter of the C/ebp alpha gene, which involves degradation of HDAC1 in the 26 S proteasome. These data suggest that C/EBP beta activates a single unified pathway of adipogenesis involving its stimulation of PPARgamma expression, which then activates C/EBP alpha expression by dislodging HDAC1 from the promoter for degradation in the proteasome.
authors.affiliation: Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zuo
authors.forename: Li
authors.initials: L
authors.lastname: Qiang
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Farmer
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D001391:Azo Compounds / Q000494:pharmacology; D001549:Benzamides / Q000494:pharmacology; D015153:Blotting, Western; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000096:biosynthesis* / Q000235:genetics; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000096:biosynthesis* / Q000235:genetics; D002454:Cell Differentiation; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases / Q000378:metabolism*; D047468:Immunoprecipitation; D008024:Ligands; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D051379:Mice; D047495:PPAR gamma / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D012313:RNA / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D001391:Azo Compounds; D001549:Benzamides; D022763:CCAAT-Enhancer-Binding Protein-alpha; D022782:CCAAT-Enhancer-Binding Protein-beta; D008024:Ligands; D008055:Lipids; D047495:PPAR gamma; D011725:Pyridines; C458508:T 0070907; D012313:RNA; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1; D006655:Histone Deacetylases; C011049:oil red O