Promoter Activity and Regulation of the CYP4F2 Leukotriene B4 ω-Hydroxylase Gene by Peroxisomal Proliferators and Retinoic Acid in HepG2 Cells

The human liver CYP4F2 gene (Accession No. AF221943) encodes a leukotriene B4 ω-hydroxylase that metabolizes leukotriene B4 (LTB4) to a less potent proinflammatory eicosanoid, 20-OH-LTB4. We sequenced a 6.7-kb genomic fragment of the human CYP4F2 gene that has the first five exons and 500 bp of the 5′-flanking region. The major transcription start site was found to be 49 bp upstream of the 3′ end of exon 1 and the ATG translation initiation codon was located in exon 2. Besides the TATA box at −39 bp and basal transcription factor binding sites, the promoter region and 412-bp intron 1 have several putative binding sites for nuclear factors that may mediate the inflammatory response and lipid homeostasis. We found two DR1 elements in the 5′ promoter, a DR2 element in intron 1, and RXR/RAR binding sites in both intron 1 and the 5′ promoter. DNase I footprinting revealed three protected sequences, with the region containing two CAATT boxes at −71 and −111 bp important in CYP4F2 gene expression. Luciferase reporter assays showed that the 500-bp upstream sequence has strong promoter activity. Transient transfection experiments identified two sites in the 5′ promoter and intron 1 that cooperate in gene transcription while exon 1 and a GC-rich region flanking exon 1 inhibit transcription. trans-Retinoic acid and 9-cis-retinoic acid stimulate promoter activity 3- and 6-fold, respectively, while cotransfection with RXRα or RAR/RXRα further enhanced activity. Peroxisome proliferators inhibit CYP4F2 gene promoter activity and cotransfection with PPARα or PPARα/RXRα can slightly attenuate this inhibition. Both saturated fatty acids and 12-hydroxydodecanoic acid (12-OH-C12) can stimulate CYP4F2 gene promoter activity. Therefore, the CYP4F2 gene is repressed by peroxisomal proliferators and induced by retinoic acid, with RAR/RXRα mediating the induction while PPARα/RXR functions neither in the repression nor in the induction by peroxisomal proliferators or retinoic acid.