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CELLULAR METABOLISM

Roles of phospholipase A₂ isoforms in swelling- and melittin-induced arachidonic acid release and taurine efflux in NIH3T3 fibroblasts

Department of Biochemistry, Institute for Molecular Biology and Physiology, Copenhagen, Denmark

Submitted 4 July 2005 ; accepted in final form 11 July 2006

Osmotic swelling of NIH3T3 mouse fibroblasts activates a bromoenol lactone (BEL)-sensitive taurine efflux, pointing to the involvement of a Ca²⁺-independent phospholipase A₂ (iPLA₂) (Lambert IH. J Membr Biol 192: 19–32, 2003). We report that taurine efflux from NIH3T3 cells was not only increased by cell swelling but also decreased by cell shrinkage. Arachidonic acid release to the cell exterior was similarly decreased by shrinkage yet not detectably increased by swelling. NIH3T3 cells were found to express cytosolic calcium-dependent cPLA₂-IVA, cPLA₂-IVB, cPLA₂-IVC, iPLA₂-VIA, iPLA₂-VIB, and secretory sPLA₂-V. Arachidonic acid release from swollen cells was partially inhibited by BEL and by the sPLA₂-inhibitor manoalide. Cell swelling elicited BEL-sensitive arachidonic acid release from the nucleus, to which iPLA₂-VIA localized. Exposure to the bee venom peptide melittin, to increase PLA₂ substrate availability, potentiated arachidonic acid release and osmolyte efflux in a volume-sensitive, 5-lipoxygenase-dependent, cyclooxygenase-independent manner. Melittin-induced arachidonic acid release was inhibited by manoalide and slightly but significantly by BEL. A BEL-sensitive, melittin-induced PLA₂ activity was also detected in lysates devoid of sPLA₂, indicating that both sPLA₂ and iPLA₂ contribute to arachidonic acid release in vivo. Swelling-induced taurine efflux was inhibited potently by BEL and partially by manoalide, whereas the reverse was true for melittin-induced taurine efflux. It is suggested that in NIH3T3 cells, swelling-induced taurine efflux is dependent at least in part on arachidonic acid release by iPLA₂ and possibly also by sPLA₂, whereas melittin-induced taurine efflux is dependent on arachidonic acid release by sPLA₂ and, to a lesser extent, iPLA₂.

osmotic stress; cell volume regulation; calcium-independent phospholipase A₂; secretory phospholipase A₂; nucleus

This article has been cited by other articles:

				M. B. Friis, K. G. Vorum, and I. H. Lambert Volume-sensitive NADPH oxidase activity and taurine efflux in NIH3T3 mouse fibroblasts Am J Physiol Cell Physiol, June 1, 2008; 294(6): C1552 - C1565. [Abstract] [Full Text] [PDF]

				K. A. Poulsen, S. F. Pedersen, M. Kolko, and I. H. Lambert Induction of group VIA phospholipase A2 activity during in vitro ischemia in C2C12 myotubes is associated with changes in the level of its splice variants Am J Physiol Cell Physiol, November 1, 2007; 293(5): C1605 - C1615. [Abstract] [Full Text] [PDF]

				I. H. Lambert Activation and inactivation of the volume-sensitive taurine leak pathway in NIH3T3 fibroblasts and Ehrlich Lettre ascites cells Am J Physiol Cell Physiol, July 1, 2007; 293(1): C390 - C400. [Abstract] [Full Text] [PDF]