Journal of Lipid Research (Jan 2000)
HNF4 and COUP-TFII interact to modulate transcription of the cholesterol 7α-hydroxylase gene (CYP7A1)
Abstract
The gene for cholesterol 7α-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., and J. Y. L. Chiang. HNF4 and COUP-TFII interact to modulate transcription of the cholesterol 7α-hydroxylase gene (CYP7A1).
