Regulation of prostanoid biosynthesis by human endothelial cells in angiogenesis : role of cox-2 in the intracellular and transcellular synthesis of prostanoids

Abstract

In the past several years, prostanoids have emerged as key regulators of angiogenesis in carcinoma and chronic inflammatory disease progression. In addition, recent reports have indicated that neo-angiogenesis requires an up-regulation of prostanoid biosynthetic enzymes. Thus, an induced expression of COX-2 and several tPGSs (eg. mPGES-1, TXAS) has been observed in cancer, stromal and inflammatory cells (eg. macrophages), in which the ability to synthesize prostanoids has been extensively studied. However, very little is known about the prostanoid synthesis by the vascular compartment, which plays an essential role in the angiogenic process. Therefore, in the present study, we characterize the profile of prostanoid production in endothelial cells upon treatment with proangiogenic and proinflammatory cytokines, and analyzed the expression of the endothelial terminal prostanoid synthases of PGE2, PGI2 and TXA2 in this angiogenic context. HUVEC were treated with either VEGF or IL-1β, and prostanoid contents in cell supernatants determined by enzyme-immunoassay, showing an up-regulated PGE2, PGI2 and TXA2 production. However, none concomitant upregulated expression nor enzymatic activation of the corresponding terminal prostanoid synthases was observed in endothelial cells. Our results indicate a major role of COX-2 in the biosynthesis of endothelial prostanoids. On the one hand, we have observed how the levels of prostanoids increased concomitantly to the induced expression of COX-2, on the other, this was confirmed by the fact that COX-2 silencing or selective inhibition was the only condition that significantly affected prostanoid (PGE2, PGI2, TXA2) levels in endothelial cells under both resting or stimulating conditions, thus hightlighting a preferential functional coupling of endothelial terminal prostanoid synthases to COX-2. Furthermore, COX-2 also up-regulates PGH2 production, which can be untransformed released by endothelium, and taken up and metabolized by mPGES-1 of the neighbouring tumor cells, present at the angiogenic scenario. To our knowlegde, this is the first report of eicosanoid/PGE2 production induced by the transcellular metabolism through the tumor-endothelium cross-talk during angiogenesis. A role for endothelialderived PGH2 should be considered in the design of new therapeutical approches in pathological angiogenesis.