COX-2 limits prostanoid production in activated HUVECs and is a source of PGH2 for transcellular metabolism to PGE2 by tumor cells.

OBJECTIVE Inducible expression of cyclooxygenase-2 (COX-2) and terminal prostaglandin synthases (tPGS) has been mainly analyzed in tumor, stromal, and inflammatory cells, and little is known about the regulation of prostanoid biosynthesis by endothelial cells. Here we characterize the profile of prostanoids produced by activated HUVECs and analyze the expression and activities of tPGS. METHODS AND RESULTS Enzyme immunoassays indicated increased endothelial prostanoid production after proangiogenic stimulation, but without parallel upregulation of tPGS. Endothelial prostanoid production instead depended on the induction of COX-2 and was abolished by COX-2 silencing or pharmacological inhibition. COX-2 is functionally coupled to prostacyclin and thromboxane synthases in HUVECs, but these cells show no detectable PGE(2) synthase (PGES) activity. Endothelial PGE(2) production is partly mediated by nonenzymatic decomposition of COX-2-derived PGH(2), but endothelial-produced PGH(2) can also be metabolized enzymatically by microsomal PGES-1 in cocultured tumor cells. CONCLUSIONS Our findings identify a novel transcellular metabolism of PGE(2) between the endothelial and tumor compartments. Given the role of PGE(2) as a mediator of COX-2 proangiogenic effects, transcellular metabolism of endothelial-derived PGH(2) is a potential target for treatment of pathological angiogenesis.