Feedback regulation of cyclooxygenase-2 transcription ex vivo and in vivo

Cyclooxygenase-2 (COX-2) is a rate-limiting enzyme for prostaglandin biosynthesis. Its inducible expression is regulated by complex pathways.To monitor Cox-2 transcriptional activity in vivo, we generated a knock-in mouse expressing a firefly luciferase reporter. In this study we examined, by comparing luciferase activity of Cox-2luc/+ and Cox-2luc/− cells and mice, effects of prostanoid products on Cox-2 promoter transcriptional activation. In peritoneal macrophages, luciferase induction by LPS in Cox-2luc/− cells was less than that of Cox-2luc/+ cells. However, in the presence of PGE2, induction was comparable, suggesting positive Cox-2 feedback regulation by PGE2 occurs for macrophages. In contrast, feedback modulation was not observed in TPA-induced Cox-2luc/+ and Cox-2luc/− mouse embryonic fibroblasts (MEFs). Using non-invasive in vivo imaging, we observed negative feedback regulation of Cox-2 expression during paw inflammation in living mice. Our results suggest Cox-2 expression is regulated by cell type specific feedback mechanisms, both in cultured cells and in living animals.