| Description |
Evidence has shown that COX-2 plays important roles in tumor angiogenesis. NSAIDs, cyclooxygenase inhibitors, inhibit tumor growth at least partially through their inhibition in angiogenesis. However, the underlying mechanism by which COX-2 contributes to angiogenesis is not clear. The goal of this dissertation is (a) to determine the expression and role of COX-2 in endothelial cells; (b) to evaluate the direct effect of NSAIDs on endothelial cells, and (c) to study the expression, regulation, and functional analysis of prostanoid receptors in endothelial cells. We find that confluent endothelial cells exhibit little COX-2 protein, while subconfluent or wounded endothelial cells express high levels of COX-2. This high expression of COX-2 in subconfluent or wounded cells leads to increased production of PGE2, a major COX-2 metabolite, into the surrounding media. NS-398, a COX-2 specific inhibitor, attenuates endothelial migration, and adding back PGE2 partially overcomes the reduction in cell migration. This indicates that COX-2/PGE2 contributes to endothelial migration. In addition, exogenous PGE2 up-regulates COX-2 expression in confluent endothelial cells, suggesting an amplification loop between COX-2, prostaglandins and angiogenic stimuli. The anti-tumor effect of NSAIDs can be ascribed to both cyclooxygenase-dependent and -independent components. Here, we discover that NS398 at high concentration (100 ?M) modulates stress fiber formation, focal adhesion assembling and cell-cell contact in endothelial cells. This effect is COX/PGE2-independent since 100 µM exceeds the effective concentration of NS398 that inhibits PGE2, and adding back PGE2 could not recover the effect of NS398 on endothelial cells. Since the cell cytoskeleton plays crucial roles in cell migration and angiogenesis, NS398 also can affect endothelial migration in ways that are COX-2/PGE2-independent. Prostanoids and their receptors mediate the effects of COX-2 activity in endothelial behavior. We find that endothelial cells express EP2, EP3, EN (PGE2 receptor subtypes), FP (PGF2? receptor) and TP (thromboxane A2 receptor) messages. EP2, EP4, FP and TP messages are increased by mechanically wounding the endothelial monolayer. PGE2 activates ERK and p38 signaling pathways through EP2/EP4 receptors in endothelial cells. Moreover, activation of EP2/EP4 induces COX-2 expression in a p38-dependent way, indicating the existence of a potential positive feedback loop in endothelial cells. |
