Different Functional Aspects of the Group II Subfamily (Types IIA and V) and Type X Secretory Phospholipase A2s in Regulating Arachidonic Acid Release and Prostaglandin Generation

Abstract

We have recently reported that members of the heparin-binding group II subfamily of secretory PLA 2 s (sPLA 2 s) (types IIA and V), when transfected into 293 cells, released [ 3 H]arachidonic acid (AA) preferentially in response to interleukin-1 (IL-1) and acted as "signaling" PLA 2 s that were functionally coupled with prostaglandin biosynthesis. Here we show that these group II subfamily sPLA 2 s and the type X sPLA 2 behave in a different manner, the former being more efficiently coupled with the prostaglandin-biosynthetic pathway than the latter, in 293 transfectants. Type X sPLA 2 , which bound only minimally to cell surface proteoglycans, augmented the release of both [ 3 H]AA and [ 3 H]oleic acid in the presence of serum but not IL-1. Both types IIA and V sPLA 2 , the AA released by which was efficiently converted to prostaglandin E 2 , markedly augmented IL-1-induced expression of cyclooxygenase (COX)-2 in a heparin-sensitive fashion, whereas type X sPLA 2 lacked the ability to augment COX-2 expression, thereby exhibiting the poor prostaglandin E 2 -biosynthetic response unless either of the COX isozymes was forcibly introduced into type X sPLA 2 -expressing cells. Implication of phospholipid scramblase, an enzyme responsible for the perturbation of plasma membrane asymmetry, revealed that the scramblase-transfected cells became more sensitive to types IIA and V, but not X, sPLA 2 , releasing both [ 3 H]AA and [ 3 H]oleic acid in an IL-1-independent manner. Thus, although phospholipid scramblase-mediated alteration in plasma membrane asymmetry actually led to the increased cellular susceptibility to the group II subfamily of sPLA 2 s, several lines of evidence suggest that it does not entirely mimic their actions on cells after IL-1 signaling. Interestingly, coexpression of type IIA or V, but not X, sPLA 2 and phospholipid scramblase resulted in a marked reduction in cell growth, revealing an unexplored antiproliferative aspect of particular classes of sPLA 2 .

Inhibition of arachidonic acid metabolism and its implication on cell proliferation and tumour-angiogenesis

“…PLA 2 , however, is the only phospholipase that seems to be able to release free AA directly in a single-step reaction, by hydrolysing an ester bond at the sn-2 position of phospholipids [8], which is why it features as the main phospholipase of interest in most literature in connection with AA metabolism. Mammalian cells contain several isoforms of the enzyme PLA 2 [ 9 ], which receive their stimulatory signals from a vast range of inflammatory signals, cytokines, growth factors and hormones.…”

Cross-talk between Cytosolic Phospholipase A2α (cPLA2α) and Secretory Phospholipase A2 (sPLA2) in Hydrogen Peroxide-induced Arachidonic Acid Release in Murine Mesangial Cells

“…Several other activation mechanisms have been proposed to account for sPLA 2 interactions with cells. Membrane pertubation by phospholipid scramblase has been proposed to contribute to sensitization of cells toward the action of sPLA 2 (68). Other studies have demonstrated that cPLA 2 ␣ is required for group IIa or V PLA 2 s to act properly (26,67,69,70).…”

Arachidonic Acid Release from Mammalian Cells Transfected with Human Groups IIA and X Secreted Phospholipase A2 Occurs Predominantly during the Secretory Process and with the Involvement of Cytosolic Phospholipase A2-α

“…These observations raise the possibility that the site of fatty acid release by hGIIA is within intracellular vesicles. In contrast, the non-heparan sulfate-binding hGX is thought to act on the extracellular face of the plasma membrane of HEK293 cells and does not accumulate in intracellular domains (18). It is not yet known whether there is a biochemical connection between IL-1␤-induced arachidonate release and intracellular action of hGIIA.…”

“…hGX is not a highly basic protein and accumulates in the extracellular medium when transfected in HEK293 cells (18). Whereas serum stimulates arachidonate release from both hGIIA-and hGX-transfected HEK293 cells, only the former cells show an additional increase in fatty acid release if the pro-inflammatory cytokine interleukin-1␤ (IL-1␤) is added along with serum (18). The biochemical basis for this cytokine effect is not known.…”

“…This sPLA 2 is highly basic and is thought to bind to the anionic heparan sulfate chains of cell surface glypican (21), a GPI-linked proteoglycan. hGX is not a highly basic protein and accumulates in the extracellular medium when transfected in HEK293 cells (18). Whereas serum stimulates arachidonate release from both hGIIA-and hGX-transfected HEK293 cells, only the former cells show an additional increase in fatty acid release if the pro-inflammatory cytokine interleukin-1␤ (IL-1␤) is added along with serum (18).…”