Basic transcription element binding protein (BTEB) transactivates the cholesterol 7 alpha-hydroxylase gene (CYP7A)

Cholesterol 7 alpha-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 the se BAREs are highly conserved and shared a novel sequence, AGTTCAAG. To ide ntify and isolate nuclear protein factors that bind to these BAREs, we have screened a human liver cDNA expression library with oligonucleotide probes con containing the sequence from nt -149 to -127. Twenty positive clones w ere selected and purified, Partial nucleotide sequences of these clones wer e determined. Nucleotide homology search of DNA databases of the sequences of these clones revealed that sequence of one clone, G13, is identical to b asic 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 trans cription element (BTE) in BARE-II and a Spl binding site located in the nt -100/-82 region of the CYP7A promoter. Transient transfection assays have c onfirmed that BTEB was able to transactivate the CYP7A promoter/luciferase chimeric gene. (C) 1998 Academic Press.