Identification of a bile acid response element in the cholesterol 7 alpha-hydroxylase gene CYP7A.
The transcriptional activity of the cholesterol 7 alpha-hydroxylase gene CYP7A is repressed by bile acids. Taurine conjugates of chenodeoxycholate and deoxycholate, but not cholate and ursodeoxycholate, inhibited the CYP7A promoter/luciferase reporter activity in transient transfection assays in Hep G2 cells. A region from nucleotide (nt) -74 to -55 was found to mediate bile acid response. However, deletion of this bile acid response element (BARE-I) enhanced reporter activity but did not eliminate the bile acid response. This is due to the presence of another BARE-II located in a conserved region between nt -149 and -128. Deletion or mutations of these sequences reduced promoter activity and abolished bile acid repression. This BARE-II shares an identical AGTTCAAG core sequence with BARE-I. Electrophoretic mobility shift assays of BARE-I and BARE-II probes using Hep G2 nuclear extract and the partially purified binding activity of nt -65/-54 DNA-affinity column revealed that the same or a similar nuclear protein might bind to both BAREs. BARE-II is the major BARE involved in the transcriptional repression of the CYP7A gene by hydrophobic bile acids.
Stroup
D
D
Department of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, Rootstown 44272-0095, USA.
Crestani
M
M
Chiang
J Y
JY
D000818:Animals; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000494:pharmacology*; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005246:Feedback; D005796:Genes / Q000187:drug effects*; D017930:Genes, Reporter; D008156:Luciferases / Q000235:genetics; D051381:Rats; D014407:Tumor Cells, Cultured
D001647:Bile Acids and Salts; D004268:DNA-Binding Proteins; D008156:Luciferases; D002790:Cholesterol 7-alpha-Hydroxylase