Basic Transcription Element Binding Protein (BTEB) Transactivates the Cholesterol 7α-Hydroxylase Gene (CYP7A)

Abstract

Cholesterol 7α-hydroxylase catalyzes the first and rate-limiting step in the conversion of cholesterol to bile acids in the liver. Previously, we have identified two bile acid response elements located in nt −74 to −54 (BARE-I) and −148 to −118 (BARE-II) regions. The nucleotide sequences in these BAREs are highly conserved and shared a novel sequence, AGTTCAAG. To identify and isolate nuclear protein factors that bind to these BAREs, we have screened a human liver cDNA expression library with oligonucleotide probes containing the sequence from nt −149 to −127. Twenty positive clones were selected and purified. Partial nucleotide sequences of these clones were determined. Nucleotide homology search of DNA databases of the sequences of these clones revealed that sequence of one clone, G13, is identical to basic transcription element binding protein (BTEB), a GC box-binding protein of Sp1 family transcription factors known to regulate many cytochrome P450 genes. Electrophoretic mobility shift assays have identified a basic transcription element (BTE) in BARE-II and a Sp1 binding site located in the nt −100/−82 region of theCYP7Apromoter. Transient transfection assays have confirmed that BTEB was able to transactivate theCYP7Apromoter/luciferase chimeric gene.