Hepatocyte nuclear factor 4-mediated activation of rat CYP3A1 gene and its modes of modulation by apolipoprotein AI regulatory protein I and v-ErbA-related protein 3

CYP3A1 gene (P450/6 beta B) encodes testosterone 6 beta-hydroxylase (EC 1.14.14.1) in rats. The promoter region of CYP3A1 gene contains three binding sites for nuclear factors: 6 beta B-A (-105 to -86), 6 beta B-B (-139 to -118), and 6 beta B-C (-164 to -145). The 6 beta B-A site shows a high degree of similarity to a consensus sequence of the binding site of hepatocyte nuclear factor 4 (HNF-4) and also to the 6 beta A-A site on the rat CYP3A2 gene promoter region. Our previous study suggested an involvement of the 6 beta A-A site in the basal transactivation of CYP3A2 gene using HepG2 cells. In the present study, transactivation through the 6 beta B-A and 6 beta A-A sites of CYP3A1 and CYP3A2 genes has directly been shown by coexpression of HNF-4 and CYP3A1 or CYP3A2 promoter-reporter fused genes. Similar experiments further showed that nuclear factor binding at the 6 beta B-B site hampered HNF4-mediated transactivation of CYP3A1 gene. Recombinant apolipoprotein AT. regulatory protein I (ARP-1) and v-ErbA-related protein 3 (EAR-3) are shown to suppress HNF-4-mediated activation at the 6 beta B-B site without competition of HNF-4, (C) 1999 Academic Press.