E2F binding is required but not sufficient for repression of B-myb transcription in quiescent fibroblasts.
We have previously shown in mouse NIH3T3 fibroblasts that transcription of the B-myb gene, which encodes a transcription factor required for S phase entry, is repressed through a promoter E2F site in G0/early G1. Transcription repression at this stage of the cell cycle was correlated with binding of a specific p107/E2F complex to this site. We report here, however, that transfection of cells with the known components of this complex, p107, E2F-4 and DP-1, did not repress the B-myb promoter in cycling NIH3T3 cells, although p107 inhibited transcription transactivation by E2F-4/DP-1. To establish definitively the contribution of E2F to repression, the effects of further mutations within and surrounding the E2F site were examined. It was evident that E2F binding and repression were closely correlated, lending greater weight to the contention that E2F itself is implicated in this activity. These studies also identified a closely linked site, designated the downstream repression site (DRS), which was not required for E2F binding or transactivation but which was necessary for repression. These findings indicated that E2F-dependent repression and activation are independently regulated phenomena and suggest that repression involves additional interactions determined by the promoter context.
Bennett
J D
JD
Ludwig Institute for Cancer Research, Imperial College School of Medicine at St Mary's, London, UK.
Farlie
P G
PG
Watson
R J
RJ
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins; D002453:Cell Cycle / Q000235:genetics; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D050684:E2F Transcription Factors; D050704:E2F4 Transcription Factor; D005786:Gene Expression Regulation; D016153:Genes, Suppressor; D051379:Mice; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011506:Proteins; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D015534:Trans-Activators; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050704:E2F4 Transcription Factor; C493763:E2f4 protein, mouse; C499306:Mybl2 protein, mouse; D009687:Nuclear Proteins; D010750:Phosphoproteins; D011506:Proteins; C489485:Rbl1 protein, mouse; C493838:Rbl2 protein, mouse; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; C493736:Tfdp1 protein, mouse; D015534:Trans-Activators; D050680:Transcription Factor DP1; D014157:Transcription Factors