Transforming growth factor-beta inhibits adipocyte differentiation by Smad3 interacting with CCAAT/enhancer-binding protein (C/EBP) and repressing C/EBP transactivation function.

Department of Growth and Development, Programs in Cell Biology and Developmental Biology, University of California, San Francisco, California 94143-0640, USA.
Transforming growth factor (TGF)-beta is a potent inhibitor of adipocyte differentiation. To identify which adipocyte transcription factors might be targeted by TGF-beta, we overexpressed key adipogenic transcription factors, C/EBPbeta, C/EBPdelta, or peroxisome proliferator-activated receptor (PPAR) gamma in NIH3T3 cells and tested the ability of TGF-beta to block adipogenesis. We show that TGF-beta inhibits adipocyte differentiation driven by either C/EBPbeta or C/EBPdelta without affecting C/EBP protein expression levels, suggesting that these C/EBPs are a direct target of TGF-beta action. Because TGF-beta inhibits adipogenesis by signaling through Smad3, we examined physical and functional interactions of Smad3 and Smad4 with C/EBPbeta, C/EBPdelta, and PPARgamma2. C/EBPbeta and C/EBPdelta were found to physically interact with Smad3 and Smad4, and Smad3 cooperated with Smad4 and TGF-beta signaling to repress the transcriptional activity of C/EBPs. Thus, repression of the activity of C/EBPs by Smad3/4 at C/EBP binding sites inhibited transcription from the PPARgamma2 and leptin promoters. In contrast, PPARgamma interacted only very weakly with Smad3 and its transcriptional activity was not repressed by Smad3/4 or in response to TGF-beta. Smad3/4 did not reduce the ability of C/EBP to bind to its cognate DNA sequence, but repressed transcription by inhibiting the transactivation function of C/EBP.
Mesh Terms:
3T3 Cells, Adipocytes, Animals, Binding Sites, Biotinylation, CCAAT-Enhancer-Binding Protein-beta, CCAAT-Enhancer-Binding Protein-delta, CCAAT-Enhancer-Binding Proteins, Cell Differentiation, Cell Line, DNA-Binding Proteins, Glutathione Transferase, Leptin, Lipid Metabolism, Mice, Oligonucleotides, Plasmids, Precipitin Tests, Promoter Regions, Genetic, Protein Binding, Protein Structure, Tertiary, RNA, Receptors, Cytoplasmic and Nuclear, Smad3 Protein, Smad4 Protein, Trans-Activators, Transcription Factors, Transcription, Genetic, Transcriptional Activation, Transfection, Transforming Growth Factor beta
J. Biol. Chem. Mar. 14, 2003; 278(11);9609-19 [PUBMED:12524424]
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