Platelet activating factor‐induced apoptosis is inhibited by ectopic expression of the platelet activating factor G‐protein coupled receptor

Abstract

The pro-inflammatory lipid mediator platelet activating factor (PAF: 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) accumulates in ischemia, epilepsy, and human immunodeficiency virus-1-associated dementia and is implicated in neuronal loss. The present study was undertaken to establish a role for its G-protein coupled receptor in regulating neurotoxicity. PC12 cells do not express PAF receptor mRNA as demonstrated by northern analysis and RT-PCR. In the absence of the G-protein coupled receptor, PAF (0.1)1 lM) triggered chromatin condensation, DNA strand breaks, oligonucleosomal fragmentation, and nuclear disintegration characteristic of apoptosis. Lyso-PAF (0.001-1 lM), the immediate metabolite of PAF, did not elicit apoptotic death. Concentrations of PAF or lyso-PAF that exceeded critical micelle concentration had physicochemical effects on plasma membrane resulting in necrosis. Apoptosis but not necrosis was inhibited by the PAF antagonist BN52021 (1-100 lM) but not CV3988 (0.2-20 lM). Ectopic PAF receptor expression protected PC12 transfectants from ligand-induced apoptosis. PAF receptor-mediated protection was inhibited by CV3988 (1 lM). These data provide empirical evidence that: (i) PAF can initiate apoptosis independently of its G-protein coupled receptor; (ii) PAF signaling initiated by its G-protein coupled receptor is cytoprotective to PC12 cells; (iii) the pro-and anti-apoptotic effects of PAF on PC12 cells can be pharmacologically distinguished using two different PAF antagonists.

Platelet-Activating Factor Is Crucial in Psoralen and Ultraviolet A-Induced Immune Suppression, Inflammation, and Apoptosis

“…Abstract presented at the 67th Annual Meeting of the Society for Investigative Dermatology, May 3 to 6, 2006 Philadelphia, PA). Interestingly, however, Brewer and colleagues 39 have shown that PAF can have anti-and proapoptotic effects in cells, initiated by its G-protein-coupled receptor or occurring independently of this receptor. Furthermore, Southall and colleagues 40 have shown that the activation of the epidermal PAF receptor protected from apoptosis induced by either TNF-␣ or TNF-related apoptosis-inducing ligand and that this protective effect was inhibited by pretreatment with PAF receptor antagonists mediated by a nuclear factor-B-dependent pathway.…”

Anti-apoptotic Actions of the Platelet-activating Factor Acetylhydrolase I α2 Catalytic Subunit

“…3) PAFR-independent cell death can be inhibited by two PAF antagonists: the gingkolide BN 52021 and the fungal derivative Apoptotic PAF Signal Transduction in the Absence of PAFR-To provide mechanistic insight into how PAF transduces cell death in the absence of PAFR, we followed the internalization and metabolic fate of Bodipy fluorophore-conjugated PAF in PAF-sensitive cells (11,43). PC12 cells express all of the components of both cytosolic PAF-AH enzymes (I and II) but not plasma PAF-AH or PAFR.…”

“…Although the majority of PAF effects are understood to be transduced by its G-protein-coupled receptor (PAFR) (10), PAFR signaling has been shown to be both pro-and anti-apoptotic. Ectopic PAFR expression exacerbates cell death induced by etoposide and mitomycin C but protects cells from tumor necrosis factor ␣, TRAIL, and extracellular PAF (6,7,11,12). These opposing effects likely depend upon the relative ratio of NF-B-dependent pro-and anti-apoptotic gene products elicited in different cell types in response to the combination of an external apoptotic inducer and PAF (6).…”

“…Accumulating evidence points to additional PAF signaling pathways transduced independently of PAFR (11,(13)(14)(15)(16)(17). PAFR-negative cells undergo apoptosis when extracellular PAF concentrations reach 100 nM and necrosis when PAF levels exceed the critical micelle concentration of 3 M (11).…”

Antidiabetic Activity of Extracts from Needle, Bark, and Cone ofPicea glauca.: Organ-Specific Protection from Glucose Toxicity and Glucose Deprivation

“…PC12-AC cells, a clonal derivate (Brewer et al, 2002) of the PC12 rat adrenal pheochromocytoma cell line (American Type Culture Collection), were maintained in complete media (RPMI 1640 containing 10% horse serum and 5% newborn calf serum) under normoglucose (11 mM) conditions. Cells were seeded in 96-well plates (1.25 × 10 4 cells/well) and allowed to adhere at 37…”