The Novel Neutrophil Differentiation Marker Phosphatidylglucoside Mediates Neutrophil Apoptosis

Abstract

A new type of glycolipid, phosphatidylglucoside (PtdGlc), was identified as a component of raft-like membrane domains of the human leukemia cell line HL-60. In this study, we show that PtdGlc forms functional domains that are different from those produced by lactosylceramide (LacCer)-enriched lipid rafts. These rafts initiate neutrophil apoptosis. Neutrophils are the only type of human peripheral blood leukocyte or monocyte-derived dendritic cell to express large amounts of PtdGlc on their cell surfaces. PtdGlc was not colocalized with LacCer. Anti-PtdGlc IgM DIM21 did not induce neutrophil chemotaxis or superoxide generation, whereas anti-LacCer IgM T5A7 induced these activities. DIM21, but not T5A7, significantly induced neutrophil apoptosis. DIM21-induced apoptosis was inhibited by specific inhibitors of cysteine-containing aspartate-specific proteases (caspases)-8, -9, and -3 but not by the Src family kinase inhibitor PP1, PIP3 kinase inhibitor LY294002, NADPH oxidase inhibitor diphenyleneiodonium, superoxide dismutase, or catalase. PtdGlc was colocalized with Fas on the neutrophil plasma membrane. DIM21 and the agonist anti-Fas Ab DX2 induced the formation of large Fas-colocalized clusters of PtdGlc on the plasma membrane. Furthermore, the antagonistic anti-Fas Ab ZB4 significantly inhibited DIM21-induced neutrophil apoptosis. These results suggest that PtdGlc is specifically expressed on neutrophils and mediates apoptosis of these cells, and that the Fas-associated death signal may be involved in PtdGlc-mediated apoptosis.

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“…To this end, we used DIM21 antibody as an artificial ligand and found that adding DIM21 to cultured neural progenitor cells prepared from fetal mouse telencephalon results in the recruitment of EGF receptors into PtdGlc-rich lipid rafts, leading to the activation of EGF receptors [141]. In human neutrophils, DIM21 treatment induced Fas clustering, leading to Fas-dependent apoptotic cell death [138]. This suggests that the Fas-receptor is associated with lipid rafts composed of PtdGlc on neutrophil plasma membranes.…”

“…Differentiated CD15-positive neutrophils contain PtdGlc [137]. In these cells, PtdGlc comprises C18:0/C18:0 and C18:0/C20:0 fatty acyl chains [138].…”

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“…85) and Kina et al . 80) demonstrated that PtdGlc is highly and specifically expressed on human neutrophils. In neutrophils, DIM21 treatment induces Fas clustering, leading to Fas-dependent apoptotic cell death, 80) Moreover, these Fas clusters colocalize with PtdGlc to form large rafts.…”

“…80) demonstrated that PtdGlc is highly and specifically expressed on human neutrophils. In neutrophils, DIM21 treatment induces Fas clustering, leading to Fas-dependent apoptotic cell death, 80) Moreover, these Fas clusters colocalize with PtdGlc to form large rafts. 80) These findings underscore the importance of identifying natural PtdGlc ligands that mirror the effects of the artificial ligand DIM21.…”

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“…In mammals, ceramide is synthesized by a family of six enzymes, ceramide synthases (CerS) 1 -6, each of which uses a relatively restricted subset of fatty acyl-CoAs for N-acylation of the sphingoid long chain base [31]. 1a) [32]. These properties suggest that molecular varieties and expression patterns of GSLs reflect the functions of these cells.…”