COX-2 Limits Prostanoid Production in Activated HUVECs and Is a Source of PGH ₂ for Transcellular Metabolism to PGE ₂ by Tumor Cells

Abstract

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 endothelialproduced 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. Key Words: angiogenesis Ⅲ endothelium Ⅲ cyclooxygenases Ⅲ prostanoids Ⅲ transcellular metabolism N umerous studies indicate that enzymes involved in the metabolism of AA and its products might contribute to tumor-induced angiogenesis. 1,2 Cyclooxygenase-2 (COX-2), which converts AA into the prostanoid precursor PGH 2 , is induced by the proangiogenic factor VEGF, released by tumor cells. Moreover, proinflammatory cytokines such as IL-1␤ and TNF␣, potent COX-2 inducers, also have proangiogenic activity. 3 COX-2 expression is elevated in tumors, and genetic inactivation or pharmacological inhibition of COX-2 reduces tumor-induced neovascularization. 4 COX-2-associated angiogenesis is thought to be mediated by derived prostanoids, such as PGE 2 , PGI 2 , and TXA 2. Strong evidence exists for a link between PGE 2 and tumor angiogenesis; and of the PGES enzymes (cPGES, mPGES-1, mPGES-2), inducible mPGES-1 appears to be critical for tumor angiogenesis. 5 Moreover, in vivo models of TXAS or PGIS overexpression indicate proangiogenic effects for TXA 2 and antiantiogenic effects for PGI 2 . 6 Despite the evidence linking prostanoids to tumor angiogenesis, their mechanism of action is poorly understood. In particular, very little is known about the possible contribution made by the regulation of endothelial terminal prostanoid synthases. PGH 2 release by endothelium has been shown in vivo and ex vivo 7,8 ; however, whether PGH 2 is transformed into final prostanoids in endothelial cells spontaneously or enzymatically is unknown.We investigated the regulation of terminal prostaglandin synthases by VEGF and IL-1␤. Our results indicate that although endothelial cel...

Interaction between head and neck squamous cell carcinoma cells and fibroblasts in the biosynthesis of PGE2

“…They also support the notion that the contribution of fi broblasts to the tumor pool of PGE 2 could be relevant. Because mPGES-1 seems to be essential for a substantial biosynthesis of PGE 2 (13)(14)(15)(16)22 ), these fi ndings also strengthen the concept that mPGES-1 may be a target for therapeutic intervention in patients with HNSCC.…”

“…Three PGES isoenzymes have been characterized: two microsomal isoforms (mPGES-1 and mPGES-2) and one cytosolic isoform (cPGES) (7). mPGES-1 is inducible by pro-infl ammatory cytokines, and it seems to be the essential PGES isoenzyme involved in PGE 2 biosynthesis under infl ammatory conditions (13)(14)(15)(16). Additionally, mPGES-1 has been reported to be over-expressed in several types of tumors (17)(18)(19)(20).…”

Cathelicidin LL-37 Induces Angiogenesis via PGE 2 –EP3 Signaling in Endothelial Cells, In Vivo Inhibition by Aspirin

“…Previous studies have attributed PGE 2 -dependent tumor angiogenesis to COX-2 expression in ECs. 2,19 Our findings, however, support an important contribution of COX-1 in ECs. COX-1 pharmacological inhibition (ASA) or silencing abrogated LL-37-induced production of PGE 2 , whereas COX-2 selective inhibition (Etoricoxib) or knockdown did not significantly affect LL-37-induced PGE 2 release (Figure 3).…”

Microvascular COX-2/mPGES-1/EP-4 axis in human abdominal aortic aneurysm

“…PGH 2 is then isomerized to PGE 2 by PGE synthases. The microsomal isoform of prostaglandin E synthase (mPGES-1) is inducible by proinfl ammatory cytokines and seems to be the main isoenzyme involved in PGE 2 biosynthesis under infl ammatory conditions (8)(9)(10)(11). COX-2/mPGES-1 is widely regarded as the major contributing enzymatic chain for PGE 2 biosynthesis under pathological conditions.…”