C/EBPalpha inhibits cell growth via direct repression of E2F-DP-mediated transcription.
Using an inducible transcription system which allows the regulated expression of C/EBP isoforms in tissue culture cells, we have found that the ectopic expression of C/EBPalpha, at a level comparable to that found in normal liver tissue, has a pronounced antimitogenic effect in mouse L cells and NIH 3T3 cells. The inhibition of cell division by C/EBPalpha in mouse cells cannot be reversed by simian virus 40 T antigen, by oncogenic ras, or by adenovirus E1a protein. When expressed in thymidine kinase-deficient L cells or 3T3 cells, C/EBPalpha is detected in a protein complex which binds to the E2F binding sites found in the promoters of the genes for E2F-1 and dihydrofolate reductase (DHFR). Bacterially expressed C/EBPalpha has no affinity for these E2F sites, but when recombinant C/EBPalpha is added to nuclear extracts from mouse fibroblasts, a new E2F binding activity appears, which contains the C/EBPalpha protein. Using an E2F-DP1-responsive promoter linked to a reporter gene, it can be shown that C/EBPalpha directly inhibits the induction of this promoter by E2F-DP1 in transient-transfection assays. Furthermore, C/EBPalpha can be shown to inhibit the S-phase induction of the E2F and DHFR promoters in permanent cell lines. These findings delineate a straightforward mechanism for C/EBPalpha-mediated cell growth arrest through repression of E2F-DP-mediated S-phase transcription.
Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
B A
BA
Slomiany
K L
KL
D'Arigo
M M
MM
Kelly
D T
DT
Kurtz
D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005786:Gene Expression Regulation; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics*; D020033:Protein Isoforms / Q000235:genetics; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
C533431:Arid4a protein, mouse; D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D009687:Nuclear Proteins; D020033:Protein Isoforms; D056465:Retinoblastoma-Binding Protein 1; C493736:Tfdp1 protein, mouse; D050680:Transcription Factor DP1; D014157:Transcription Factors