Investigation into the involvement of phospholipases A2 and MAP kinases in modulation of AA release and cell growth in A549 cells

1 We have investigated the contribution of specific PLA(2)s to eicosanoid release from A549 cells by using specific inhibitors of secretory PLA(2) (ONO-RS-82 and oleyloxyethylphosphocholine), cytosolic PLA(2) (AACOCF(3) and MAFP) and calcium-independent PLA(2) (HELSS, MAFP and PACOCF(3)). Similarly, by using specific inhibitors of p38 MAPK (SB 203580), ERK1/2 MAPK (Apigenin) and MEK1/2 (PD 98059) we have further evaluated potential pathways of AA release in this cell line. 2 ONO-RS-82 and oleyloxyethylphosphocholine had no significant effect on EGF or IL-1 beta stimulated H-3-AA or PGE(2) release or cell proliferation. AACOCF(3), HELSS, MAFP and PACOCF(3) significantly inhibited both EGF and IL-1 beta stimulated H-3-AA and PGE(2) release as well as cell proliferation. Apigenin and PD 98509 significantly inhibited both EGF and IL-1 beta stimulated H-3-AA and PGE? release and cell proliferation whereas, SE 203580 had no significant effect on EGF or IL-1 beta stimulated H-3-AA release, or cell proliferation but significantly suppressed EGF or IL-1 beta stimulated PGE, release. 3 These results confirm that the liberation of AA release, generation of PGE2 and cell proliferation is mediated largely through the actions of cPLA(2) whereas, sPLA(2) plays no significant role. We now also report a hitherto unsuspected contribution of iPLA(2) to this process and demonstrate that the stimulating action of EGF and IL-I beta in AA release and cell proliferation is mediated in part via a MEK and ERK-dependent pathway (but not through p38MAPK). We therefore propose that selective inhibitors of MEK and MARK pathways may be useful in controlling AA release, eicosanoid production and cell proliferation.