title: C/EBPalpha regulation of the growth-arrest-associated gene gadd45.
abstract: CCAAT/enhancer-binding protein alpha (C/EBPalpha) is expressed in postmitotic, differentiated adipocytes and is required for adipose conversion of 3T3-L1 cells in culture. Temporal misexpression of C/EBPalpha in undifferentiated adipoblasts leads to mitotic growth arrest. We report here that growth arrest- and DNA damage-inducible gene 45 (gadd45) is preferentially expressed in differentiated 3T3-L1 adipocytes similar to phenotype-associated genes. Furthermore, C/EBPalpha transactivates a reporter plasmid containing 1.5 kb of the gadd45 promoter region. The proto-oncogene myc, which inhibits adipocyte differentiation, abrogates C/EBPalpha activation of gadd45. gadd45 is known to be a target of the tumor suppressor p53 in a G1 checkpoint activated by DNA damage. Immunoprecipitation of radiolabeled proteins with conformation-specific antibodies revealed that wild-type p53 is expressed throughout 3T3-L1 adipocyte development, including the postmitotic period characterized by the accumulation of gadd45 and C/EBPalpha. A stable 3T3-L1 subline was engineered to express a dominant negative p53, human p53(143ala). The p53(143ala) subline differentiated to adipocytes and showed appropriate developmental expression of gadd45. These findings suggest that postmitotic growth arrest is coupled to adipocyte differentiation via C/EBPalpha stimulation of growth arrest-associated and phenotype-associated genes.
authors.affiliation: Department of Biology, University of Virginia, Charlottesville, 22903, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Constance
authors.forename: J I
authors.initials: JI
authors.lastname: Morgan
authors.forename: R M
authors.initials: RM
authors.lastname: Umek
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins; D002454:Cell Differentiation; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis; D004249:DNA Damage; D017931:DNA Primers; D015342:DNA Probes; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism*; D016259:Genes, myc; D016158:Genes, p53; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D016350:Leucine Zippers; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D000097642:GADD45 Proteins
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D015500:Chloramphenicol O-Acetyltransferase; D017931:DNA Primers; D015342:DNA Probes; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D011506:Proteins; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc; D011994:Recombinant Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D000097642:GADD45 Proteins; C000715470:MAS1 protein, human