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 (P450/6βB) encodes testosterone 6β-hydroxylase (EC 1.14.14.1) in rats. The promoter region of CYP3A1 gene contains three binding sites for nuclear factors: 6βB-A (−105 to −86), 6βB-B (−139 to −118), and 6βB-C (−164 to −145). The 6βB-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 6βA-A site on the rat CYP3A2 gene promoter region. Our previous study suggested an involvement of the 6βA-A site in the basal transactivation of CYP3A2 gene using HepG2 cells. In the present study, transactivation through the 6βB-A and 6βA-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 6βB-B site hampered HNF-4-mediated transactivation of CYP3A1 gene. Recombinant apolipoprotein AI regulatory protein I (ARP-1) and v-ErbA-related protein 3 (EAR-3) are shown to suppress HNF-4-mediated activation at the 6βB-B site without competition of HNF-4.