Synergistic transcriptional activation by CTF/NF-I and the estrogen receptor involves stabilized interactions with a limiting target factor.
Transcription initiation at eukaryotic protein-coding gene promoters is regulated by a complex interplay of site-specific DNA-binding proteins acting synergistically or antagonistically. Here, we have analyzed the mechanisms of synergistic transcriptional activation between members of the CCAAT-binding transcription factor/nuclear factor I (CTF/NF-I) family and the estrogen receptor. By using cotransfection experiments with HeLa cells, we show that the proline-rich transcriptional activation domain of CTF-1, when fused to the GAL4 DNA-binding domain, synergizes with each of the two estrogen receptor-activating regions. Cooperative DNA binding between the GAL4-CTF-1 fusion and the estrogen receptor does not occur in vitro, and in vivo competition experiments demonstrate that both activators can be specifically inhibited by the overexpression of a proline-rich competitor, indicating that a common limiting factor is mediating their transcriptional activation functions. Furthermore, the two activators functioning synergistically are much more resistant to competition than either factor alone, suggesting that synergism between CTF-1 and the estrogen receptor is the result of a stronger tethering of the limiting target factor(s) to the two promoter-bound activators.
Martinez
E
E
Institut de Biologie Animale, Bâtiment de Biologie, Université de Lausanne, Switzerland.
Dusserre
Y
Y
Wahli
W
W
Mermod
N
N
D022762:CCAAT-Enhancer-Binding Proteins; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D006367:HeLa Cells / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008957:Models, Genetic; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D010957:Plasmids; D011392:Proline; D011401:Promoter Regions, Genetic; D011960:Receptors, Estrogen / Q000378:metabolism*; D015183:Restriction Mapping; D014157:Transcription Factors; D014158:Transcription, Genetic; D014162:Transfection; D051840:Y-Box-Binding Protein 1
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D051839:NFI Transcription Factors; C497647:NFIC protein, human; D009687:Nuclear Proteins; D011960:Receptors, Estrogen; D014157:Transcription Factors; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human; D011392:Proline; D015500:Chloramphenicol O-Acetyltransferase