Activation of phospholipase D by E-series prostaglandins in human erythroleukemia cells.

Phospholipase D (PLD) can be activated by a variety of receptor agonists in different cell types. However, an effect of prostaglandins (PGs) on the activity of this enzyme has not been demonstrated previously. In this study, we found that PGE1 could stimulate PLD in human erythroleukemia cells, as measured by phosphatidylethanol formation, with an ED50 of 3.5 x 10(-7) M. PGE2 was also active, but other PGs including prostacyclin, PGD2 and PGF2, had no effect. PGE1 also elicited cyclic AMP production over the same concentration range that activated PLD. However, it is unlikely that cyclic AMP per se is responsible for PGE-induced PLD activation, because PLD could be substantially activated by PGE2 at concentrations (0.1-1 microM) which did not stimulate cyclic AMP production. Furthermore, no increase of phosphatidylethanol formation could be observed when cells were treated with other adenylyl cyclase-activating agents such as prostacyclin, forskolin and vasoactive intestinal peptide. In Ca+(+)-free medium, PLD activation by PGE1 and PGE2 was greatly reduced, indicating that their effect was through a Ca+(+)-dependent pathway. Pretreatment of cells with pertussis toxin abolished PGE1- and PGE2-stimulated PLD activity, implying the involvement of a G protein in the PGE-mediated signal transduction pathway. Our results not only indicate that E-series PGs may initiate some of their cellular effects through a novel pathway, activation of PLD, but also suggest that PGE-stimulated PLD activity in human erythroleukemia cells is Ca+(+)-dependent and is regulated via a pertussis toxin-sensitive G protein.