Involvement of calcium-independent phospholipase A2 in uterine stromal cell phospholipid remodelling

The role of Ca2+-independent phospholipase A2 (iPLA2) in arachidonic (AA) and docosahexaenoic (DHA) acid incorporation and phospholipid remodelling in rat uterine stromal cells (UIII cells) was studied. Incorporation of AA and DHA into UIII cell phospholipids was Ca2+-independent. Bromoenollactone (BEL), a potent inhibitor of iPLA2, reduced lysophosphatidylcholine level and AA incorporation into phospholipids by approximately 20%. DHA incorporation was not affected by BEL, indicating that the pathways for AA and DHA incorporation are partially different. In control cells, the transfer of AA occurred mainly from diacyl-glycerophosphocholine (GroPCho) to alkenylacyl-glycerophosphoethanolamine (GroPEtn) and to a lesser extent from diacyl-GroPCho to diacyl-GroPEtn. [3H]DHA was redistributed from diacyl-GroPCho and alkylacyl-GroPEtn to alkenylacyl-GroPEtn. BEL treatment inhibited completely the redistributrion of AA within diacyl-GroPCho and diacyl -GroPEtn and reduced the [3H]DHA content of diacyl-GroPEtn, indicating that a BEL-sensitive iPLA2 controls the redistribution of polyunsaturated fatty acids to diacyl-GroPEtn. In contrast the redistribution of radioactive AA and DHA to alkenylacyl-GroPEtn was almost insensitive to BEL. The analysis of substrate specificity and BEL sensitivity of iPLA2 activity indicates that UIII cells exhibit at least two isoforms of iPLA2, one of which is BEL-sensitive and quite selective of diacyl species, and another one that is insensitive to BEL and selective for alkenylacyl-GroPEtn. Taken together, these results suggest that several iPLA2 participate independently in the remodelling of UIII cell phospholipids.