Lipid droplets are required for lipid mediator production and cancer cell proliferation

Lipid droplets are dynamic organelles with a central role in fatty acid metabolism. They protect cells from lipotoxicity by sequestering excess fatty acids but also provide fatty acids for metabolic reactions and signalling events. Here we show that lipid droplet turnover in cancer cells is required for production of {omega}-3 and {omega}-6 polyunsaturated fatty acid (PUFA)-derived inflammatory lipid mediators, including eicosanoids and specialised pro-resolving mediators. We show that incorporation of PUFAs into triglycerides mediated by diacylglycerol acyltransferase 1 (DGAT1), and their release by adipose triglyceride lipase (ATGL), are required for cyclooxygenase- and lipoxygenase-dependent lipid mediator production and cancer cell proliferation. The human group X secreted phospholipase A2 (hGX sPLA2) drives the delivery of membrane-derived PUFAs into lipid droplets, while ATGL promotes the incorporation of lipid droplet-derived PUFAs into phospholipids. The group IVA cytosolic PLA2 (cPLA2) acts on membrane phospholipids and complements ATGL in the regulation of PUFA trafficking between phospholipids and triglycerides. This study identifies lipid droplets as essential cellular hubs that control PUFA availability for production of lipid mediators involved in inflammation and tumorigenesis. Synopsis O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=125 SRC="FIGDIR/small/470010v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@13df1c6org.highwire.dtl.DTLVardef@1cc25c8org.highwire.dtl.DTLVardef@1c47cc0org.highwire.dtl.DTLVardef@da4508_HPS_FORMAT_FIGEXP M_FIG C_FIG This study shows that lipid droplets in cancer cells control the supply of {omega}-3 and {omega}-6 polyunsaturated fatty acids (PUFAs) for the production of lipid mediators, which in turn drive cancer cell proliferation. The esterification of PUFAs into triacylglycerols (TAGs) and their release from lipid droplets are necessary for PUFA entry into lipid mediator production pathways. O_LILipid mediator production induced by the human group X secreted phospholipase A2 (hGX sPLA2), which releases PUFAs from the plasma membrane and serum lipoproteins, depends on diacylglycerol acyltransferase 1 (DGAT1)-mediated TAG synthesis. C_LIO_LIAdipose triglyceride lipase (ATGL) liberates {omega}-3 and {omega}-6 PUFAs from TAGs and drives lipid mediator production via cyclooxygenase (COX) and lipoxygenase (LOX) pathways. C_LIO_LIATGL promotes the incorporation of lipid droplet-derived PUFAs into phospholipids, which are targeted by the group IVA cytosolic PLA2 (cPLA2), thereby selectively supplying arachidonic acid for lipid mediator production. C_LIO_LILipid droplets are required for cPLA2-induced lipid mediator production also in cells that do not depend on ATGL for the supply PUFAs into lipid mediator pathways. C_LI