title: C/EBPbeta cooperates with RB:E2F to implement Ras(V12)-induced cellular senescence.
abstract: In primary cells, overexpression of oncogenes such as Ras(V12) induces premature senescence rather than transformation. Senescence is an irreversible form of G1 arrest that requires the p19ARF/p53 and p16INK4a/pRB pathways and may suppress tumorigenesis in vivo. Here we show that the transcription factor C/EBPbeta is required for Ras(V12)-induced senescence. C/EBPbeta-/- mouse embryo fibroblasts (MEFs) expressing Ras(V12) continued to proliferate despite unimpaired induction of p19ARF and p53, and lacked morphological features of senescent fibroblasts. Enforced C/EBPbeta expression inhibited proliferation of wild-type MEFs and also slowed proliferation of p19Arf-/- and p53-/- cells, indicating that C/EBPbeta acts downstream or independently of p19ARF/p53 to suppress growth. C/EBPbeta was unable to inhibit proliferation of MEFs lacking all three RB family proteins or wild-type cells expressing dominant negative E2F-1 and, instead, stimulated their growth. C/EBPbeta decreased expression of several E2F target genes and was associated with their promoters in chromatin immunoprecipitation assays, suggesting that C/EBPbeta functions by repressing genes required for cell cycle progression. C/EBPbeta is therefore a novel component of the RB:E2F-dependent senescence program activated by oncogenic stress in primary cells.
authors.affiliation: Laboratory of Protein Dynamics and Signaling, NCI-Frederick, Frederick, MD 21702-1201, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Sebastian
authors.forename: Radek
authors.initials: R
authors.lastname: Malik
authors.forename: Sara
authors.initials: S
authors.lastname: Thomas
authors.forename: Julien
authors.initials: J
authors.lastname: Sage
authors.forename: Peter Frederick
authors.initials: PF
authors.lastname: Johnson
mesh_terms: D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000235:genetics; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D051379:Mice; D018345:Mice, Knockout; D011401:Promoter Regions, Genetic / Q000235:genetics; D051381:Rats; D016160:Retinoblastoma Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051742:Transcription Factor CHOP; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D025803:Tumor Suppressor Protein p14ARF / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; C417743:Cdkn2a protein, mouse; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; C497250:Ddit3 protein, mouse; C497251:Ddit3 protein, rat; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; C493755:E2f1 protein, rat; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53; D051742:Transcription Factor CHOP; D018631:ras Proteins