Novel translocation responses of cytosolic phospholipase A2α fluorescent proteins

Abstract

Cytosolic phospholipase A2 (cPLA2)alpha responds to the rise in cytosolic Ca2+ ([Ca2+]i) attending cell stimulation by moving to intracellular membranes, releasing arachidonic acid (AA) from these membranes, and thereby initiating the synthesis of various lipid mediators. Under some conditions, however, cPLA2alpha translocation occurs without any corresponding changes in [Ca2+]i. The signal for such responses has not been identified. Using confocal microscopy to track fluorescent proteins fused to cPLA2alpha or cPLA2alpha's C2 domain, we find that AA mimics Ca2+ ionophores in stimulating cPLA(2)alpha translocations to the perinuclear ER and to a novel site, the lipid body. Unlike the ionophores, AA acted independently of [Ca2+](i) rises and did not translocate the proteins to the Golgi. AA's action did not involve its metabolism to eicosanoids or acylation into cellular lipids. Receptor agonists also stimulated translocations targeting lipid bodies. We propose that AA is a signal for Ca2+-independent cPLA2alpha translocation and that lipid bodies are common targets of cPLA2alpha and contributors to stimulus-induced lipid mediator synthesis.

The cationic cluster of group IVA phospholipase A2 (Lys488/Lys541/Lys543/Lys544) is involved in translocation of the enzyme to phagosomes in human macrophages

“…Most of the research carried out to date has thoroughly documented the translocation of cPLA 2 ␣ to intracellular membranes such as those of the nuclear envelope, Golgi complex, or endoplasmic reticulum ( 9 ). A few instances have been reported of translocation of cPLA 2 ␣ to cellular membranes different to those indicated above ( 20,35,36 ). This study adds to these studies by showing that the phagosomal membrane of human macrophages is also a site for cPLA 2 ␣ translocation during activation conditions.…”

Simultaneous activation of p38 and JNK by arachidonic acid stimulates the cytosolic phospholipase A2-dependent synthesis of lipid droplets in human monocytes

“…Likewise, cells depleted of cPLA 2 ␣ by RNA silencing result in the appearance of tubulo-vesicular profi les of the smooth endoplasmic reticulum, compatible with a role of cPLA 2 ␣ in regulating the structure of this organelle (11). cPLA 2 ␣ has recently been reported to translocate to LD after cell activation (24,25,63). Studies on cPLA 2 ␣ targeting to membranes have indicated that, in addition to increased Ca 2+ availability, there are other factors regulating the association of the enzyme to membranes, including the local concentration of phosphoinositides in the membrane (64,65) and the phosphorylation state of the cPLA 2 ␣ (66).…”

“…(10,(20)(21)(22). Decided amounts of arachidonic acid (AA) are present in the phospholipid monolayer surrounding the LD, and a variety of enzymes involved in AA metabolism have been demonstrated to localize in LDs (23)(24)(25)(26). One of these enzymes is the group IVA phospholipase A 2 , also known as cytosolic phospholipase A 2 ␣ (cPLA 2 ␣ ), a central enzyme for the release of AA from phospholipids (27)(28)(29)(30)(31).…”

Subcellular Localization and Role of Lipin-1 in Human Macrophages

“…AA esterified in phospholipids, and some AA-metabolizing enzymes have been localized in part to LDs, including cyclooxygenase-2, 5-and 15-lipoxygenases, and PGE 2 synthase (29). Very recently, translocation of cPLA 2 a to LDs has also been shown (35,69). This work describes lipin-1a as another lipid signaling enzyme associated to LD membranes.…”