The PGE2-induced inhibition of the PLD activation pathway stimulated by fMLP in human neutrophils is mediated by PKA at the PD-Kγ level

Prostaglandin E-2 (PGE(2)), an eicosanoid that modulates inflammation, inhibits several chemoattractant-elicited functions in neutrophils such as chemotaxis, production of superoxide anions, adhesion, secretion of cytotoxic enzymes and synthesis of leukotriene B-4. We previously reported that PGE(2) inhibits the fMLP signaling pathway that leads to PLD activation through suppression of P13-K gamma activity and the decreased recruitment to membranes of PLD activation factors, PKC, Rho and Arf-GTPases. This effect is mediated via the EP2 receptors known to raise cAMP in cells. The inhibition of most fMLP-induced functional responses by PGE(2) via EP2 receptors is mediated by PKA, except the chernotactic response. We have investigated the role of PKA in the EP2-mediated inhibition of the PLD activation pathway. H-89, a selective PKA pharmacological inhibitor suppressed the inhibitory effects of PGE(2) at all stages of the PLD pathway activated by fMLP, i.e. PLD activity, translocation to membranes of PKC alpha, Rho and Arf-GTPases, calcium influx, tyrosine phosphorylation of proteins and finally translocation of p110 gamma catalytic subunit of PI3-K to membranes. However, neither PLD nor PI3-K gamma was substrate of PKA. These data provide evidence that PGE(2)-stimulated PKA activity regulates the PLD pathway stimulated by fMLP at the level of PI3-K gamma and that the inhibition of PI3-K gamma activation by PKA is a complex mechanism that remains to be completely elucidated. (C) 2007 Elsevier Inc. All rights reserved.