A B-myb promoter corepressor site facilitates in vivo occupation of the adjacent E2F site by p107 x E2F and p130 x E2F complexes.
Transcription from the B-myb (MybL2 gene) promoter is strictly cell cycle-regulated by repression mediated through an E2F site during G(0)/early G(1). We report here the characterization of a corepressor site (downstream repression site (DRS)) required for this activity that is closely linked to the E2F site. Systematic mutagenesis of the DRS enabled a consensus to be derived, and it is notable that this sequence is compatible with cell cycle gene homology region sequences associated with cell cycle-dependent elements in the cyclin A, cdc2, and CDC25C promoters. The B-myb promoter is inappropriately active during G(0) in mouse embryo fibroblasts lacking the p107 and p130 pocket proteins, and we show that the ability of transfected p107 and p130 to re-impose repression on the promoter is dependent on the DRS. In contrast, transfected Rb was unable to repress the B-myb promoter. Consistent with the notion that Rb.E2F complexes are unable to bind the B-myb promoter E2F site in vivo, footprinting showed that this site is unoccupied in cells lacking p107 and p130. Chromatin immunoprecipitation assays showed a requirement for the DRS in recruiting p107 and p130 complexes to the B-myb promoter, indicating that in vivo the DRS governs the occupancy of the adjacent E2F site by transcriptional repressors.
Catchpole
Steven
S
Ludwig Institute for Cancer Research and the Section of Virology and Cell Biology, Imperial College of Science, Technology and Medicine, Faculty of Medicine, Norfolk Place, London W2 1PG, United Kingdom.
Tavner
Fiona
F
Le Cam
Laurent
L
Sardet
Claude
C
Watson
Roger J
RJ
D016475:3T3 Cells; D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D050684:E2F Transcription Factors; D004622:Embryo, Mammalian / Q000502:physiology; D005347:Fibroblasts / Q000502:physiology; D017930:Genes, Reporter; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011506:Proteins; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; C064352:MYBL2 protein, human; C499306:Mybl2 protein, mouse; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D010750:Phosphoproteins; D011506:Proteins; C493844:RBL1 protein, human; C493837:RBL2 protein, human; C489485:Rbl1 protein, mouse; C493838:Rbl2 protein, mouse; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D015534:Trans-Activators; D014157:Transcription Factors