HNF4 and COUP-TFII interact to modulate transcription of the cholesterol 7alpha-hydroxylase gene (CYP7A1).
The gene for cholesterol 7alpha-hydroxylase (CYP7A1) contains a sequence at nt -149 to -118 that was found to play a large role in determining the overall transcriptional activity and regulation of the promoter. Hepatocyte nuclear factor 4 (HNF4) and chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) synergistically activate transcription of the CYP7A1 promoter. Transactivation of CYP7A1 by HNF4 in the human hepatoma cell line, HepG2, was enhanced by cotransfection with COUP-TFII or the basal transcription element binding protein (BTEB). HNF4 prepared from rat liver nuclear extracts bound to oligomers homologous to the nt -146 to -134 sequences in electrophoretic mobility shift assays (EMSA), which corresponded to a conserved region containing a direct repeat of hormone response elements spaced by one nucleotide (DR1). The sequences surrounding this DR1 were found to be essential for the HNF4 transactivation. In vitro-translated COUP-TFII was found to bind the adjacent sequences from nt -139 to -128 (DR0), but COUP-TFII interacted with this region at a much lower affinity than to the COUP-TFII-site at nt -72 to -57 (DR4). Mutations at nt -139 to -128 or nt -72 to -57 reduced the COUP-TFII and HNF4 synergy; however, these COUP-TFII-binding sequences were not absolutely required for the cooperative effect of HNF4 and COUP-TFII on transactivation. These results indicated that the observed transactivation was the result of protein/protein interactions facilitated by the juxtaposition of the binding elements.
Stroup
D
D
Department of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, P. O. Box 95, Rootstown, OH 44272-0095, USA.
Chiang
J Y
JY
D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051837:COUP Transcription Factor II; D051836:COUP Transcription Factors; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D017930:Genes, Reporter; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D008099:Liver / Q000378:metabolism; D008156:Luciferases / Q000235:genetics; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D011987:Receptors, Steroid; D011994:Recombinant Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051837:COUP Transcription Factor II; D051836:COUP Transcription Factors; D002790:Cholesterol 7-alpha-Hydroxylase; D017931:DNA Primers; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; D008156:Luciferases; D010750:Phosphoproteins; D011987:Receptors, Steroid; D011994:Recombinant Proteins; D014157:Transcription Factors; C403128:MLX protein, human; C497588:Nr2f2 protein, rat; C095569:NR2F2 protein, human