Plasmodium falciparumGlycosylphosphatidylinositol-induced TNF-α Secretion by Macrophages Is Mediated without Membrane Insertion or Endocytosis

Abstract

The glycosylphosphatidylinositols (GPIs) of Plasmodium falciparum are believed to contribute to the pathogenesis of malaria by inducing the secretion of proinflammatory cytokines by macrophages. Previous studies have shown that P. falciparum GPIs elicit toxic immune responses by protein tyrosine kinase (PTK)-and protein kinase C (PKC)-mediated cell signaling pathways, which are activated by the carbohydrate and acyl moieties of the intact GPIs, respectively. In this study, we show that induction of TNF-␣ by P. falciparum GPIs in macrophages is mediated by the recognition of the distal fourth mannose residue. This event is critical but not sufficient for the productive cell signaling; interaction by the acylglycerol moiety of GPIs is also required. These novel interactions are coupled to previously demonstrated PTK and PKC pathways, since the specific inhibitors of these kinases effectively blocked the GPI-induced TNF-␣ production. Surprisingly, sn-2 lyso-GPIs were also able to elicit TNF-␣ secretion. Contrary to the prevailing notion, GPIs are neither inserted to the plasma membranes nor endocytosized. Thus, this study defines the GPI structural requirements and reveals a novel mechanism for the outside-in activation of cell signaling by P. falciparum GPIs in inducing proinflammatory responses.

Role of glycosylphosphatidylinositols in the activation of phospholipase A2 and the neurotoxicity of prions

“…The present data show that the GPI anchors attached to PrP c and PrP Sc stimulate PGE 2 production and induce caspase-3 activity in neurons in a similar manner to PrP peptides, the miniprion sPrP106 and prion preparations (Bate et al, 2004b). These results are consistent with reports that concentrated GPI anchors can activate some cell types; for example, GPIs activate lipogenesis in adipocytes (Frick et al, 1998) or induce cytokine production from macrophages (Vijaykumar et al, 2001). The GPIs isolated from PrP c and PrP Sc migrate with similar R f values in HPTLC and we were unable to detect any significant differences in their biological activity.…”

A Glycosylphosphatidylinositol-Based Treatment Alleviates Trypanosomiasis-Associated Immunopathology

“…Together, these GPI-triggered signal pathways induce the secretion of proinflammatory cytokines including TNF as well as IL-1 and IL-6 (55,56). Hereby the induction of TNF by plasmodium GPI in macrophages required recognition of the distal fourth mannose residue of the glycan core (57). Accordingly, interfering with this recognition can inhibit the macrophage-activating potential of the GPI moiety.…”

Alkylacylglycerolipid domain of GPI molecules of Leishmania is responsible for inhibition of PKC-mediated c-fos expression

“…Prehybridization and hybridization were carried out at 42ЊC in 50% formamide with the probes previously random-labeled with [␥-32 P] dCTP to 1 ϫ 10 8 cpm/g DNA. Membranes were then washed once in 2ϫ-SSPE (20ϫ-SSPE ϭ 175.3 g NaCl, 27.6 g NaH 2 PO 4 , by guest, on May 11, 2018 www.jlr.org Downloaded from 7.4 g EDTA, pH 7.4, volume made to 1 liter), 0.1% SDS at 42ЊC for 10 min, twice in 2ϫ-SSPE, 0.1% SDS at room temperature for 15 min, twice in 2ϫ-SSPE, 0.1% SDS at 37ЊC for 10 min, and finally in 0.1ϫ-SSPE, 0.1% SDS at 42ЊC. While still damp, membranes were autoradiographed at Ϫ70ЊC with an intensifying screen using Hyperfilm-MR.…”

“…(16:0) -sn -glycero-phosphate (alkylacyl phosphatidic acid) used in the present study were prepared by chemical synthesis as follows. The starting material isopropylidenesn -glycerol was alkylated with 1-bromooctadecane using sodium by guest, on May 11, 2018 www.jlr.org…”

“…by guest, on May 11, 2018 www.jlr.org Downloaded from this, the synthetic lipid domains were coated onto RP-18 beads by the published method (15,25) and then fed to macrophages. The efficiency of the coating procedure was assessed by using 14 C-labeled palmitic acid as control, which showed that almost 99% of the material was loaded onto the beads.…”