Transcriptional activation by the orphan nuclear receptor ARP-1.
ARP-1 is a ubiquitous orphan nuclear receptor that binds to a site (site A) in the apolipoprotein AI (apoAI) liver-specific enhancer and represses its transcriptional activity in hepatoblastoma HepG2 cells. Electrophoretic mobility shift analysis of HepG2 cell nuclear extracts showed that in addition to ARP-1, site A also binds the orphan nuclear receptors Ear-2 and HNF-4. In in vitro transcription assays, Hela cell nuclear extracts which contain ARP-1 had no effect on transcription from a basal promoter linked to multiple copies of site A. However, supplementation of these extracts with excess amounts of recombinant ARP-1 resulted in significant stimulation. Supplementation of the extracts with purified polypeptides representing fusions between the ARP-1 N- or C-terminal domains and the yeast activator GAL4 DNA binding domain also stimulated transcription from a basal promoter linked to multiple GAL4 DNA binding sites. Co-immunoprecipitation assays using ARP-1-selective antibodies revealed specific physical interactions between ARP-1 and the basal transcription factor TFIIB. We conclude that ARP-1 possesses intrinsic transcription activation potential which is modulated, at least in part, by the intracellular balance of other nuclear receptors that also bind to its cognate DNA binding site.
Malik
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Department of Cardiovascular Molecular Biology, Lederle Laboratories, Pearl River, NY 10965, USA.
Karathanasis
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S
D001054:Apolipoproteins A / Q000378:metabolism*; D051837:COUP Transcription Factor II; D051836:COUP Transcription Factors; D002474:Cell-Free System; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D035581:Transcription Factor TFIIB; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation
D001054:Apolipoproteins A; D051837:COUP Transcription Factor II; D051836:COUP Transcription Factors; D004268:DNA-Binding Proteins; D011987:Receptors, Steroid; D011994:Recombinant Proteins; D035581:Transcription Factor TFIIB; D014157:Transcription Factors; C095569:NR2F2 protein, human