Independent Functioning of Cytosolic Phospholipase A2 and Phospholipase D1 in Trp-Lys-Tyr-Met-Val-D-Met-Induced Superoxide Generation in Human Monocytes

Abstract

Recently, a novel peptide (Trp-Lys-Tyr-Met-Val-D-Met, WKYMVm) has been shown to induce superoxide generation in human monocytes. The peptide stimulated phospholipase A2 (PLA2) activity in a concentration- and time-dependent manner. Superoxide generation as well as arachidonic acid (AA) release evoked by treatment with WKYMVm could be almost completely blocked by pretreatment of the cells with cytosolic PLA2 (cPLA2)-specific inhibitors. The involvement of cPLA2 in the peptide-induced AA release was further supported by translocation of cPLA2 to the nuclear membrane of monocytes incubated with WKYMVm. WKYMVm-induced phosphatidylbutanol formation was completely abolished by pretreatment with PKC inhibitors. Immunoblot showed that monocytes express phospholipase D1 (PLD1), but not PLD2. GF109203X as well as butan-1-ol inhibited peptide-induced superoxide generation in monocytes. Furthermore, the interrelationship between the two phospholipases, cPLA2 and PLD1, and upstream signaling molecules involved in WKYMVm-dependent activation was investigated. The inhibition of cPLA2 did not blunt peptide-stimulated PLD1 activation or vice versa. Intracellular Ca2+ mobilization was indispensable for the activation of PLD1 as well as cPLA2. The WKYMVm-dependent stimulation of cPLA2 activity was partially dependent on the activation of PKC and mitogen-activated protein kinase, while PKC activation, but not mitogen-activated protein kinase activation, was an essential prerequisite for stimulation of PLD1. Taken together, activation of the two phospholipases, which are absolutely required for superoxide generation, takes place through independent signaling pathways that diverge from a common pathway at a point downstream of Ca2+.

The Synthetic Peptide Trp-Lys-Tyr-Met-Val-D-Met Inhibits Human Monocyte-Derived Dendritic Cell Maturation via Formyl Peptide Receptor and Formyl Peptide Receptor-Like 2

“…Some viral chemokine homologues bind to chemokine or chemoattractant receptors, alter receptor activation properties, and inhibit the proper functioning of receptor-mediated immune responses (47). Because HIV T-20 peptide and H. pylori Hp (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) peptide are ligands of FPR and FPRL2, respectively, it appears that these pathogen-derived agonists suppress DC-mediated immune responses by activating FPR or FPRL2.…”

“…Previous studies have demonstrated that WKYMVm induces human monocytes and neutrophils to generate cellular superoxide and to undergo chemotactic migration (11)(12)(13). Three cell surface G-protein-coupled WKYMVm receptors have been identified (14 -16), namely, formyl peptide receptor (FPR), FPR-like 1 (FPRL1), and FPR-like 2 (FPRL2) (14 -16).…”

Trp-Lys-Tyr-Met-Val-Met stimulates phagocytosis via phospho-lipase D-dependent signaling in mouse dendritic cells

“…This correlates with the ligand binding analysis that showed the existence of multiple receptors for WKYMVm in the DC2.4 cells. (Milella et al, 1999;Bae et al, 2000;Melendez et al, 2001). Examination of WKYMVM effect on the PLD activation in the DC2.4 cells was carried out by using transphosphatidylation, a characteristic reaction of PLD in the presence of 0.5% normal butanol (n-butanol).…”

Selective induction of phospholipase D1 in pathogen-activated human monocytes

“…fMet-Leu-Phe (fMLP), a prototypic bacterium-derived chemotactic agonist, was shown to induce the translocation of ARF-regulated PLD activity to the plasma membrane in human neutrophils [23]. It was reported recently that fresh circulating human monocytes express detectable levels of PLD1 protein [24].…”