ROLE OF THE LIVER-ENRICHED TRANSCRIPTION FACTORS C EBP-ALPHA AND DBP IN THE EXPRESSION OF HUMAN CYP3A4 AND CYP3A7/

In the human fetal liver, CYP3A7 is expressed as early as the 13th wee k of gestation. This continues to the perinatal period when it is shar ply repressed prior to birth. Concomitantly, the expression of CYP3A4, not detectable in the fetus, sharply increases in the perinatal perio d to remain elevated throughout adulthood. The mechanisms controlling these developmental patterns of expression have not yet been elucidate d at the molecular level. The aim of the present work was to make a fu nctional analysis of the 5'-flanking regions of CYP3A4 and CYP3A7 in d ifferent cell lines, including CHO, HepG2, WRL68 and Caco-2 TC7, after cotransfection with two hepato-specific transcription factors, C/EBP alpha and DBP. Six deletions of different length of the 5'-flanking re gion of each gene, spanning from -1240 to +11 for CYP3A4 and from -115 7 to +13 for CYP3A7, were analysed by reporter gene assay. With the CY P3A4 constructs, C/EBP alpha stimulated the transcriptional activity i n CHO cells in a way that suggested the presence of at least two C/EBP alpha-responsive elements, one downstream of -55 and one upstream of this position. In CYP3A7, the proximal element exhibited comparable st imulation to the corresponding one in CYP3A4, although the more distal one appeared to respond to a much smaller extent. CYP3A4 and CYP3A7 c onstructs also responded to C/EBP alpha in HepG2 and WRL68. However, o nly CYP3A4 and not CYP3A7 was transactivated by this factor in the Cac o-2-TC7 cell line. In CHO cells, only the shortest proximal promoter d eletion of CYP3A4 (downstream of -57) responded to DBP, while neither the longer constructs nor the CYP3A7 deletions were transactivated. Al though preliminary, our results suggest that C/EBP alpha, and possibly other members of the C/EBP family, play a prominent part in the expre ssion of the CYP3A family in man, and that the two genes respond diffe rently to C/EBP alpha and DBP, two factors that exhibit a strict proli feration-dependent pattern of expression in the liver.