IDENTIFICATION OF A BILE-ACID RESPONSE ELEMENT IN THE CHOLESTEROL 7-ALPHA-HYDROXYLASE GENE CYP7A

The transcriptional activity of the cholesterol 7 alpha-hydroxylase ge ne CYP7A is repressed by bile acids. Taurine conjugates of chenodeoxyc holate and deoxycholate, but not cholate and ursodeoxycholate, inhibit ed the CYP7A promoter/luciferase reporter activity in transient transf ection assays in Hep G2 cells. A region from nucleotide (nt) -74 to -5 5 was found to mediate bile acid response. However, deletion of this b ile acid response element (BARE-I) enhanced reporter activity but did not eliminate the bile acid response. This is due to the presence of a nother BARE-II located in a conserved region between nt -149 and -128. Deletion or mutations of these sequences reduced promoter activity an d abolished bile acid repression. This BARE-II shares an identical AGT TCAAG core sequence with BARE-I. Electrophoretic mobility shift assays of BARE-I and BARE-II probes using Hep G2 nuclear extract and the par tially purified binding activity of nt -65/-54 DNA-affinity column rev ealed that the same or a similar nuclear protein might bind to both BA REs. BARE-II is the major BARE involved in the transcriptional repress ion of the CYP7A gene by hydrophobic bile acids.