Proliferation-dependent changes in release of arachidonic acid from endothelial cells.

Abstract

Stimulation of endothelial cells resulted in release of arachidonic acid from phospholipids. The magnitude of this response decreased as the cells became confluent and the change coincided with a decrease in the percentage of cells in growth phases (G2 + M); this was not a consequence of time in culture or a factor in the growth medium. Preconfluent cells released 30% of arachidonic acid; confluent cells released only 6%. The decreasing release of arachidonic acid was demonstrated using metabolic labeling, mass measurements of arachidonic acid, and measurement of PGI2. The decrease was not due to a changing pool of arachidonic acid, and mass measurements showed no depletion of arachidonic acid. Release from each phospholipid and from each phospholipid class decreased with confluence. Conversion of confluent cells to the proliferative phenotype by mechanical wounding of the monolayer caused increased release of arachidonic acid. Potential mechanisms for these changes were investigated using assays of phospholipase activity. Phospholipase A2 activity changed in concert with the alteration in release, a consequence of changes in phosphorylation of the enzyme. The increased release of arachidonic acid from preconfluent, actively dividing cells may have important physiologic implications and may help elucidate mechanisms regulating release of arachidonic acid. (J. Clin.

The Confluence-dependent Interaction of Cytosolic Phospholipase A2-α with Annexin A1 Regulates Endothelial Cell Prostaglandin E2 Generation

“…7). This represents a novel molecular switch for the control of endothelial prostaglandin generation and accounts for earlier observations that confluent endothelial cells generate lower levels of prostaglandins compared with nonconfluent endothelial cells (14,15). In this study, we describe the Ca 2ϩ -induced association of cPLA 2 ␣ with the ER/ERGIC of nonconfluent HUVECs.…”

“…2ϩ Elevation Targets cPLA 2 ␣ to Intracellular Membranes in Subconfluent Endothelial Cells-cPLA 2 ␣ activity is greater in subconfluent endothelial cells than in quiescent, confluent endothelial cells (15,16). We have previously shown that subconfluent and confluent endothelial cells (see supplemental Fig.…”

“…cPLA 2 ␣ away from its intracellular substrate, accounting for the reduced AA release seen at endothelial cell confluence (15,16). (14,15).…”

“…(14,15). We predicted that the sequestration of cPLA 2 ␣ at confluence would be important to the control of prostaglandin generation.…”

Nuclear localisation of cytosolic phospholipase A2-α in the EA.hy.926 human endothelial cell line is proliferation dependent and modulated by phosphorylation

“…It is possible that entry into the nucleus simply provides cPLA 2-α with an additional pool of phospholipid substrate. Previous data have shown that actively growing endothelial cells are able to liberate more arachidonic acid than growth-arrested cells (Whatley et al, 1994). Thus, while endothelial cells are proliferating, for example at sites of wounds, they can produce elevated levels of prostacyclin, resulting in decreased platelet activation.…”