title: CCAAT/enhancer binding protein homologous protein (DDIT3) induces osteoblastic cell differentiation.
abstract: CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP/DDIT3), a member of the C/EBP family of transcription factors, plays a role in cell survival and differentiation. CHOP/DDIT3 binds to C/EBPs to form heterodimers that do not bind to consensus Cebp sequences, acting as a dominant-negative inhibitor. CHOP/DDIT3 blocks adipogenesis, and we postulated it could induce osteoblastogenesis. We investigated the effects of constitutive CHOP/DDIT3 overexpression in murine ST-2 stromal cells transduced with retroviral vectors. ST-2 cells differentiated toward osteoblasts, and CHOP/DDIT3 accelerated and enhanced the appearance of mineralized nodules, and the expression of osteocalcin and alkaline phosphatase mRNAs, particularly in the presence of bone morphogenetic protein-2. CHOP/DDIT3 overexpression opposed adipogenesis, and did not cause substantial changes in cell number. CHOP/DDIT3 overexpression did not modify C/EBPalpha or -beta mRNA levels but decreased C/EBPdelta after 24 d of culture. Electrophoretic mobility shift and supershift assays demonstrated that overexpression of CHOP/DDIT3 decreased the binding of C/EBPs to their consensus sequence by interacting with C/EBPalpha and -beta, confirming its dominant-negative role. In addition, CHOP/DDIT3 enhanced bone morphogenetic protein-2/Smad signaling. In conclusion, CHOP/DDIT3 enhances osteoblastic differentiation of stromal cells, in part by interacting with C/EBPalpha and -beta and also by enhancing Smad signaling.
authors.affiliation: Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105-1299, USA.
authors.forename: Renata C
authors.initials: RC
authors.lastname: Pereira
authors.forename: Anne M
authors.initials: AM
authors.lastname: Delany
authors.forename: Ernesto
authors.initials: E
authors.lastname: Canalis
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D004357:Drug Synergism; D051379:Mice; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D015675:Osteocalcin / Q000378:metabolism; D010641:Phenotype; D020033:Protein Isoforms / Q000378:metabolism; D017154:Stromal Cells / Q000166:cytology; D051742:Transcription Factor CHOP; D014157:Transcription Factors / Q000235:genetics / Q000494:pharmacology*; D014161:Transduction, Genetic; D016212:Transforming Growth Factor beta
chemical_list: C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D022762:CCAAT-Enhancer-Binding Proteins; C497250:Ddit3 protein, mouse; D020033:Protein Isoforms; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D015675:Osteocalcin; D051742:Transcription Factor CHOP; D000469:Alkaline Phosphatase