Differential intranuclear organization of transcription factors Sp1 and Sp3.
Sp1 and Sp3 are ubiquitously expressed mammalian transcription factors that activate or repress the expression of a variety of genes and are thought to compete for the same DNA binding site. We used indirect immunofluorescence microscopy and image deconvolution to show that Sp1 and Sp3 are organized into distinct nonoverlapping domains in human breast and ovarian cells. Domains of Sp1 and Sp3 infrequently associate with sites of transcription. Sp3 partitions with the tightly bound nuclear protein fraction of hormone responsive MCF-7 breast cancer cells, whereas only a subpopulation of Sp1 is found in that fraction. Both Sp1 and Sp3 are bound to the nuclear matrix, and the nuclear matrix-associated sites of Sp1 and Sp3 are different. Indirect immunofluorescence studies demonstrate that Sp1 and Sp3 associate with histone deacetylases 1 and 2 and with the estrogen receptor alpha, albeit at low frequencies in MCF-7 cells. Chromatin immunoprecipitation (ChIP) and re-ChIP assays revealed that although both Sp1 and Sp3 bind to the estrogen-responsive trefoil factor 1 promoter in MCF-7 cells, they do not occupy the same promoter. Our results demonstrate the different features of Sp1 and Sp3, providing further evidence that Sp3 is not a functional equivalent of Sp1.
Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Manitoba R3E 0V9, Canada.
Shihua
S
He
Jian-Min
JM
Sun
Lin
L
Li
James R
JR
Davie
D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D047628:Estrogen Receptor alpha / Q000378:metabolism; D005260:Female; D006801:Humans; D015530:Nuclear Matrix / Q000378:metabolism; D011401:Promoter Regions, Genetic; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D051705:Sp3 Transcription Factor / Q000378:metabolism*; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins / Q000235:genetics
D047628:Estrogen Receptor alpha; D016329:Sp1 Transcription Factor; C051838:TFF1 protein, human; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins; D051705:Sp3 Transcription Factor