Endothelial Cell Confluence Regulates Cyclooxygenase-2 and Prostaglandin E2 Production That Modulate Motility

Huimiao Jiang,Andrew S Weyrich,Guy A Zimmerman,Thomas M Mcintyre

doi:10.1074/jbc.m406094200

Abstract

Endothelial cells line the vasculature and, after mechanical denudation during invasive procedures or cellular loss from natural causes, migrate to reestablish a confluent monolayer. We find confluent monolayers of human umbilical vein endothelial cells were quiescent and expressed low levels of cyclooxygenase-2, but expressed cyclooxygenase-2 at levels comparable with cytokine-stimulated cells when present in a subconfluent culture. Mechanically wounding endothelial cell monolayers stimulated rapid cyclooxygenase-2 expression that increased with the level of wounding. Cyclooxygenase-2 re-expression occurred throughout the culture, suggesting signaling from cells proximal to the wound to distal cells. Media from wounded monolayers stimulated cyclooxygenase-2 expression in confluent monolayers, which correlated with the level of wounding of the donor monolayer. Wounded monolayers and cells in subconfluent cultures secreted enhanced levels of prostaglandin (PG) E(2) that depended on cyclooxygenase-2 activity, and PGE(2) stimulated cyclooxygenase-2 expression in confluent endothelial cell monolayers. Cells from subconfluent monolayers migrated through filters more readily than those from confluent monolayers, and the cyclooxygenase-2-selective inhibitor NS-398 suppressed migration. Adding PGE(2) to NS-398-treated cells augmented migration. Endothelial cells also migrated into mechanically denuded areas of confluent monolayers, and this too was suppressed by NS-398. We conclude that endothelial cells not in contact with neighboring cells express cyclooxygenase-2 that results in enhanced release of PGE(2), and that this autocrine and paracrine loop enhances endothelial cell migration to cover denuded areas of the endothelium.

Highlights

Angiogenesis, the formation of new blood vessels from preexisting blood vessels, is essential for wound repair, tumor growth, and metastasis [1]
Cyclooxygenase-2 and PGE2 Production Are Regulated by Cell Contact—Inducible cyclooxygenase-2 has a key role in tumor angiogenesis [15, 20], and the prostaglandin PGE2 it produces stimulates angiogenesis [21, 22] and endothelial cell adhesion and spreading [17]
We find that individual endothelial cells not organized into a tightly confluent monolayer of cells express cyclooxygenase-2

Summary

Introduction

Angiogenesis, the formation of new blood vessels from preexisting blood vessels, is essential for wound repair, tumor growth, and metastasis [1]. NSAIDs inhibit endothelial cell spreading, migration, and angiogenesis [16], processes controlled by PGE2 [17], just as genetic ablation of cyclooxygenase-2 blocks the growth of cyclooxygenase-2-replete tumors by suppressing angiogenesis [3]. These gene-targeted animals show that it is cyclooxygenase-2 expression in the host stromal cells, including endothelium, and not by the tumor cells themselves that is critical and suggest that host autocrine and paracrine signaling has a role in tumorigenesis. Tumors express high levels of PGE2, and pharmacologic suppression of cyclooxygenase-2 activity, and not that of cyclooxygenase-1, depletes PGE2 and blocks tumorigenesis [18]. Re-expression of cyclooxygenase-2, which was down-regulated as cells formed a monolayer, results in enhanced PGE2 secretion that aids endothelial cell migration to reestablish a confluent monolayer of endothelial cells

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Conclusion