Anti-CD3 and Concanavalin A-induced Human T Cell Proliferation Is Associated with an Increased Rate of Arachidonate-Phospholipid Remodeling

Abstract

In this study arachidonate-phospholipid remodeling was investigated in resting and proliferating human T lymphocytes. Lymphocytes induced to proliferate with either the mitogen concanavalin A or with anti-CD3 (OKT3) in combination with interleukin 2 (OKT3/IL-2) showed a greatly accelerated rate of [ 3 H]arachidonatephospholipid remodeling compared with resting lymphocytes or with lymphocytes stimulated with OKT3 or IL-2 alone. The concanavalin A-stimulated cells showed a 2-fold increase in the specific activity of CoAindependent transacylase compared with unstimulated cells, indicating that this enzyme is inducible. Stimulation with OKT3 resulted in greatly increased quantities of the group VI calcium-independent phospholipase A 2 but not of the quantity of group IV cytosolic phospholipase A 2 . However, group IV phospholipase A 2 became phosphorylated in OKT3-stimulated cells, as determined by decreased electrophoretic mobility. Incubation of cells with the group VI phospholipase A 2 inhibitor, bromoenol lactone, or the dual group IV/group VI phospholipase A 2 inhibitor, methyl arachidonyl fluorophosphonate, did not block arachidonate-phospholipid remodeling resting or proliferating T cells, suggesting that these phospholipases A 2 were not involved in arachidonate-phospholipid remodeling. The incubation of nonproliferating human lymphocytes with inhibitors of CoA-independent transacylase had little impact on cell survival. In contrast, OKT3/IL-2-stimulated T lymphocytes were very sensitive to apoptosis induced by CoA-independent transacylase inhibitors. Altogether these results indicate that increased arachidonate-phospholipid remodeling is associated with T cell proliferation and that CoA-independent transacylase may be a novel therapeutic target for proliferative disorders.

Group VI Phospholipases A2: Homeostatic Phospholipases with Significant Potential as Targets for Novel Therapeutics

“…As noted above, some studies suggest that apoptosis is induced due to AA accumulation, a likely outcome of iPLA 2 activity [126][127][128]138]. There is evidence that iPLA 2 is involved in acyl chain remodeling and that apoptosis ensues when this process is inhibited [72,138]. However, as the role for iPLA 2 in acyl chain remodeling appears to be limited to macrophage cell lines [17,72,74,75], this is likely not a major mechanism for iPLA 2 -mediated apoptosis.…”

“…There is evidence that iPLA 2 is involved in acyl chain remodeling and that apoptosis ensues when this process is inhibited [72,138]. However, as the role for iPLA 2 in acyl chain remodeling appears to be limited to macrophage cell lines [17,72,74,75], this is likely not a major mechanism for iPLA 2 -mediated apoptosis. Other studies suggest that apoptosis downstream of AA accumulation is mediated through the generation of ceramide [139], a proapoptic sphingolipid derived from sphingomyelin hydrolysis [140].…”

“…In addition, a recent study indicates that iPLA 2 is involved in the acyl chain remodeling that generates the tetra C18:2 species of cardiolipin that is essential for Complex IV function and mitochondrial respiration [24]. However, it must be noted that studies in variety of cells and tissues, including pancreatic islet cells, an insulinoma cell line, T cells, and most recently in macrophages of iPLA 2 -null mice suggest that the acyl chain composition of GPL does not change when iPLA 2 expression or iPLA 2 activity are modulated [17,[72][73][74][75]. Together, these studies suggest that iPLA 2 likely regulates acyl chain remodeling in a select subset of cells and tissues.…”

Spontaneous Development of Endoplasmic Reticulum Stress That Can Lead to Diabetes Mellitus Is Associated with Higher Calcium-independent Phospholipase A2 Expression

“…The iPLA 2 ␤, classified as a Group VIA isoform of iPLA 2 , is a member of a large family of PLA 2 s (27) that is cytosolic and does not require Ca 2ϩ for activity (28 -30). It is activated by ATP, is inhibited by the bromoenol lactone suicide substrate (BEL) inhibitor of iPLA 2 ␤ (31), and is recognized to have a role in signal transduction (28,(31)(32)(33)(34)(35)(36)(37)(38)(39). We found that induction of ER stress with the sarcoendoplasmic reticulum Ca 2ϩ -ATPase inhibitor thapsigargin causes INS-1 cell apoptosis that is amplified by overexpression of iPLA 2 ␤ and is inhibited by BEL (40).…”

Altered Arachidonate Distribution in Macrophages from Caveolin-1 Null Mice Leading to Reduced Eicosanoid Synthesis

“…[5,6,8,9,11,12,14, H]AA (specific activity 211 Ci/mmol) and radioactive substrates for enzyme assays were from GE Healthcare. Thin layer chromatography plates were from Scharlab (Barcelona, Spain).…”