title: CCAAT/enhancer-binding protein beta is required for mitotic clonal expansion during adipogenesis.
abstract: Hormonal induction of growth-arrested 3T3-L1 preadipocytes triggers a signaling cascade that culminates in adipogenesis. CCAATenhancer-binding protein (CEBP)beta is expressed immediately but gains DNA-binding activity only after a long lag as the cells synchronously begin mitotic clonal expansion (MCE). After MCE, a process required for adipogenesis, CEBPbeta activates expression of CEBPalpha and peroxisome proliferator-activated receptor gamma, which then transcriptionally activate genes that produce the adipocyte phenotype. When mouse embryo fibroblasts (MEFs) are subjected to the same differentiation protocol, a subset of the MEFs undergoes a similar program of events. Similar to 3T3-L1 preadipocytes, the MEFs reenter the cell cycle (as indicated by the synchronous expression of cyclin A) and undergo MCE as evidenced by the incorporation of BrdUrd into DNA and the formation of mitotic foci of cells that undergo adipogenesis. CEBPbeta is expressed immediately after induction but exhibits delayed acquisition of DNA-binding activity followed by expression of adipocyte markers and the accumulation of cytoplasmic triglyceride. MEFs from CEBPbeta(-/-) mice, however, neither undergo MCE nor differentiate into adipocytes. Forced expression of CEBPbeta (LAP) but not dominant-negative CEBPbeta (LIP) in CEBPbeta(-/-) MEFs restores MCE, expression of adipocyte markers, and the capacity to form mitotic foci of cells that undergo adipogenesis. These findings demonstrate that expression of CEBPbeta is a prerequisite for MCE in the adipocyte-differentiation program.
authors.affiliation: Department of Biological Chemistry and Pediatrics (Division of Endocrinology), Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA. qtang1@jhem.jhmi.edu
authors.forename: Qi-Qun
authors.initials: QQ
authors.lastname: Tang
authors.forename: Tamara C
authors.initials: TC
authors.lastname: Otto
authors.forename: M Daniel
authors.initials: MD
authors.lastname: Lane
mesh_terms: D016475:3T3 Cells; D000256:Adenoviridae / Q000235:genetics; D017667:Adipocytes / Q000166:cytology*; D000818:Animals; D001391:Azo Compounds / Q000494:pharmacology; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000502:physiology*; D002454:Cell Differentiation; D004396:Coloring Agents / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism; D015151:Immunoblotting; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008938:Mitosis; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D001391:Azo Compounds; D022782:CCAAT-Enhancer-Binding Protein-beta; D004396:Coloring Agents; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; C011049:oil red O