Regulation Of Cyp3a4 Expression By Par Transcription Factors

CYP3A4 expression, the most abundant cytochrome P450 found in adult human liver, may be regulated in part by the proline and acidic amino acid rich (PAR) transcription factor family. Two putative PAR binding sites were identified in the proximal region of the CYP3A4 promoter, position −57 to −51 (site 1) and −33 to −27 (site 2). To test the functional significance of both sites, a reporter construct in which CYP3A4 sequences from −771 to +56 directs luciferase was used to transiently transfect HepG2 cells. Co-transfection experiments were conducted with expression vectors for each of the human PAR transcription factors. A 3.0- and 3.7-fold enhancement was observed with hepatic leukemia factor (HLF) and thyrotroph embryonic factor (TEF), respectively. No significant effect was observed with E4 binding protein 4 (E4BP4), a negatively acting member of the PAR family. In contrast, a 23.6-fold enhancement was observed with D-element binding protein (DBP) which subsequently was demonstrated to be dose-dependent. Site directed mutagenesis of the putative PAR site 1, but not site 2, significantly reduced the ability of DBP to enhance CYP3A4 promoter activity. These data suggest a role for DBP in CYP3A4 transcriptional regulation. Further, given that DBP expression is activated in the postnatal liver, these data also are consistent with this factor participating in CYP3A4 developmental regulation.