Pardaxin, a new pharmacological tool to stimulate the arachidonic acid cascade in PC12 cells

The effect of Pardaxin, a neurotoxin that induces neurotransmitter release from neurons, on the arachidonic acid (AA) cascade was studied in PC12 cell s. Both native and the synthetic Pardaxin selectively stimulated phospholip ase A(2) (PLA(2)) activity (measured by [H-3]AA release) in the presence as well as in the absence of extracellular calcium. Pardaxin-stimulated PLA(2 ) activity was also evident in the increased formation of lysophosphatidylc holine. Pardaxin analogs, lacking the ct-helical structure that is essentia l for insertion into the plasma membrane, were ineffective in stimulating t he AA cascade in PC12 cells. Pardaxin stimulation of PLA(2) was markedly in hibited by the nonselective PLA(2) inhibitors bromophenacyl bromide and mep acrine, by methyl arachidonyl fluorophosphonate, a dual inhibitor of calciu m-dependent cytosolic PLA(2) and the calcium-independent PLA(2) and by brom oenol lactone[(E)-6-(bromoethylene)tetrahydro-3-(1-naphthalenyl-2H-pyran-2- one], a highly specific inhibitor of calcium-independent PLA(2). After Pard axin treatment, there was increased release of AA metabolites produced by t he cyclooxygenase pathway as expressed in an 8-fold increase of PGE(2) rele ase. The release of other eicosanoids, such as 6-keto-PGF(1 alpha) and thro mboxane B-2, was also augmented. Pardaxin-induced PGE(2) release was observ ed in calcium-free medium and in the absence of any increase in cytosolic c alcium. Dexamethasone partially inhibited Pardaxin-induced PGE(2) release. This effect was reversed by the type II corticosteroid receptor antagonist RU-38486. Our results indicate that Pardaxin stimulates release of AA and e icosanoids, independently of calcium, and suggest that calcium-independent PLA(2) prays an important role in Pardaxin stimulation of the AA cascade.