15-lipoxygenase-2 gene regulation by its product 15-(S)-hydroxyeicosatetraenoic acid through a negative feedback mechanism that involves peroxisome proliferator-activated receptor γ

An inverse relationship exists between the expression of 15-lipoxygenase-2 (15-LOX-2) and peroxisome proliferator-activated receptor c (PPARc) in normal prostate epithelial cells (PrECs) compared with their expression in prostate carcinoma cells (PC-3). The reason for this difference, however, is unknown. We hypothesized that this inverse expression partly involves the 15-LOX-2 promoter and 15-S-hydroxyeicosatetraenoic acid (15-(S)HETE), a product of 15- LOX-2 that binds to PPARc. We identified an active steroid nuclear receptor half-site present in the 15-LOX-2 promoter fragment F-5 (-618/+177) that can interact with PPARc. After forced expression of wild-type PPARc, 15-(S)-HETE (1 mu M) decreased F-5 reporter activity in PrECs whereas forced expression of 15-LOX-2 resulted in 15-(S)-HETE production which enhanced F-5 activity in PC-3. In contrast, the expression of dominant-negative PPARc reversed the transcriptional activation of F-5 by enhancing it 202-fold in PrEC or suppressing it in PC-3; the effect in PC-3 was positively increased 150-fold in the presence of 15-(S)-HETE (1 mu M). Peroxisome proliferator-activated receptor c interacted with 15-LOX-2 promoter sequences in pulldown experiments using biotinylated 15-LOX-2 (-560/-596 bp) oligonucleotides. In gelshift analyses PPARc and orphan receptor ROR alpha were shown to interact with the F-5 fragment in PC-3 cells. These data suggest that crosstalk mechanisms exist between the 15-LOX-2 gene and PPARc to counterbalance expression and help explain the inverse relationship of these genes in normal versus cancer cells.