title: Tandem repeat of C/EBP binding sites mediates PPARgamma2 gene transcription in glucocorticoid-induced adipocyte differentiation.
abstract: Bone marrow stromal stem cells differentiate into many different types of cells including osteoblasts and adipocytes. Long-term glucocorticoid treatment decreases osteoblastic activity but increases adipocytes. We investigated the mechanism of glucocorticoid-induced PPARgamma2 transcription. Treatment of human bone marrow stromal cells with dexamethasone induced the differentiation of these cells into adipocytes as measured by oil-red O staining, and Northern blot analysis showed that dexamethasone strongly induced PPARgamma2 mRNA expression in cells cultured in adipocyte induction medium. Moreover, the mRNA of C/EBPdelta, an adipocyte-promoting transcription factor, was also induced by dexamethasone in the presence of induction medium. Gel mobility shift assays using purified GST-C/EBPdelta fusion protein showed that C/EBPdelta specifically binds to a 40-base pair DNA element from PPARgamma2 promoter, which was found to contain a tandem repeat of C/EBP binding sites. Transfection studies in mouse mesenchymal C3H10T1/2 cells showed that it is the tandem repeat of the C/EBP binding site in PPARgamma2 promoter region that regulates dexamethasone-mediated PPARgamma2 gene activation. We conclude that glucocorticoid-induced adipogenesis from bone marrow stromal cells is mediated through a reaction cascade in which dexamethasone transcriptionally activates C/EBPdelta; C/EBPdelta then binds to PPARgamma2 promoter and transactivates PPARgamma2 gene expression. This activated master regulator, in turn, initiates the adipocyte differentiation.
authors.affiliation: Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
authors.forename: X M
authors.initials: XM
authors.lastname: Shi
authors.forename: H C
authors.initials: HC
authors.lastname: Blair
authors.forename: X
authors.initials: X
authors.lastname: Yang
authors.forename: J M
authors.initials: JM
authors.lastname: McDonald
authors.forename: X
authors.initials: X
authors.lastname: Cao
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D001854:Bone Marrow Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D022762:CCAAT-Enhancer-Binding Proteins; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics*; D020080:Tandem Repeat Sequences; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D005938:Glucocorticoids; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D003907:Dexamethasone; D004247:DNA