title: C/EBP transcription factors regulate SREBP1c gene expression during adipogenesis.
abstract: The transcription factor SREBP1c (sterol-regulatory-element-binding protein 1c) is highly expressed in adipose tissue and plays a central role in several aspects of adipocyte development including the induction of PPARgamma (peroxisome-proliferator-activated receptor gamma), the generation of an endogenous PPARgamma ligand and the expression of several genes critical for lipid biosynthesis. Despite its significance, the regulation of SREBP1c expression during adipogenesis is not well characterized. We have noted that in several models of adipogenesis, SREBP1c expression closely mimics that of known C/EBPbeta (CCAAT/enhancer-binding protein beta) targets. Inhibition of C/EBP activity during adipogenesis by expressing either the dominant-negative C/EBPbeta LIP (liver-enriched inhibitory protein) isoform, the co-repressor ETO (eight-twenty one/MTG8) or using siRNAs (small interfering RNAs) targeting either C/EBPbeta or C/EBPdelta significantly impaired early SREBP1c induction. Furthermore, ChIP (chromatin immunoprecipitation) assays identified specific sequences in the SREBP1c promoter to which C/EBPbeta and C/EBPdelta bind in intact cells, demonstrating that these factors may directly regulate SREBP1c expression. Using cells in which C/EBPalpha expression is inhibited using shRNA (short hairpin RNA) and ChIP assays we show that C/EBPalpha replaces C/EBPbeta and C/EBPdelta as a regulator of SREBP1c expression in maturing adipocytes. These results provide novel insight into the induction of SREBP1c expression during adipogenesis. Moreover, the findings of the present study identify an important additional mechanism via which the C/EBP transcription factors may control a network of gene expression regulating adipogenesis, lipogenesis and insulin sensitivity.
authors.affiliation: University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke's Hospital, Hills Road, Cambridge CB2 0QQ, UK.
authors.forename: Victoria A
authors.initials: VA
authors.lastname: Payne
authors.forename: Wo-Shing
authors.initials: WS
authors.lastname: Au
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Lowe
authors.forename: Shaikh M
authors.initials: SM
authors.lastname: Rahman
authors.forename: Jacob E
authors.initials: JE
authors.lastname: Friedman
authors.forename: Stephen
authors.initials: S
authors.lastname: O'Rahilly
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Rochford
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D050156:Adipogenesis; D000818:Animals; D015153:Blotting, Western; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics / Q000378:metabolism; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism; D051743:CCAAT-Enhancer-Binding Protein-delta / Q000235:genetics / Q000378:metabolism; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D000075142:RUNX1 Translocation Partner 1 Protein; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D022763:CCAAT-Enhancer-Binding Protein-alpha; D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C493598:MTG8 protein, mouse; D011518:Proto-Oncogene Proteins; D000075142:RUNX1 Translocation Partner 1 Protein; C082222:RUNX1T1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D051743:CCAAT-Enhancer-Binding Protein-delta