Transforming growth factor-beta inhibits adipocyte differentiation by Smad3 interacting with CCAAT/enhancer-binding protein (C/EBP) and repressing C/EBP transactivation function.
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.
Choy
Lisa
L
Department of Growth and Development, Programs in Cell Biology and Developmental Biology, University of California, San Francisco, California 94143-0640, USA.
Derynck
Rik
R
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology*; D000818:Animals; D001665:Binding Sites; D019921:Biotinylation; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism*; D051743:CCAAT-Enhancer-Binding Protein-delta; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D020738:Leptin / Q000235:genetics; D050356:Lipid Metabolism; D051379:Mice; D009841:Oligonucleotides / Q000494:pharmacology; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; C497253:Cebpd protein, mouse; D004268:DNA-Binding Proteins; D020738:Leptin; D009841:Oligonucleotides; D018160:Receptors, Cytoplasmic and Nuclear; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D051901:Smad4 Protein; C490810:Smad4 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D051743:CCAAT-Enhancer-Binding Protein-delta; D012313:RNA; D005982:Glutathione Transferase