Lysophospholipids of different classes mobilize neutrophil secretory vesicles and induce redundant signaling through G2A.
Lysophosphatidylcholine has been shown to enhance neutrophil functions through a mechanism involving the G protein-coupled receptor G2A. Recent data support an indirect effect of lysophosphatidylcholine on G2A rather than direct ligand binding. These observations prompted the hypothesis that other lysophospholipids (lyso-PLs) may also signal for human neutrophil activation through G2A. To this end, 1-oleoyl-2-hydroxy-sn-glycero-3-[phospho-L-choline], but also C18:1/OH lyso-PLs bearing the phosphoserine and phosphoethanolamine head groups, presented on albumin, were shown to signal for calcium flux in a self- and cross-desensitizing manner, implicating a single receptor. Blocking Abs to G2A inhibited calcium signaling by all three lyso-PLs. Furthermore, inhibition by both pertussis toxin and U-73122 established signaling via the Galphai/phospholipase C pathway for calcium mobilization. Altered plasma membrane localization of G2A has been hypothesized to facilitate signaling. Accordingly, an increase in detectable G2A was demonstrated by 1 min after lyso-PL stimulation and was followed by visible patching of the receptor. Western blotting showed that G2A resides in the plasma membrane/secretory vesicle fraction and not in neutrophil primary, secondary, or tertiary granules. Enhanced detection of G2A induced by lyso-PLs was paralleled by enhanced detection of CD45, confirming mobilization of the labile secretory vesicle pool. Together, these data show that lyso-PLs bearing various head groups redundantly mobilize G2A latent within secretory vesicles and result in G2A receptor/Galphai/phospholipase C signaling for calcium flux in neutrophils.
Frasch
S Courtney
SC
Department of Pediatrics, Division of Cell Biology, National Jewish Medical and Research Center, Denver, CO 80206, USA.
Zemski-Berry
Karin
K
Murphy
Robert C
RC
Borregaard
Niels
N
Henson
Peter M
PM
Bratton
Donna L
DL
D020013:Calcium Signaling / Q000276:immunology*; D018797:Cell Cycle Proteins / Q000502:physiology*; D002478:Cells, Cultured; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D006801:Humans; D008246:Lysophospholipids / Q000097:blood* / Q000145:classification* / Q000502:physiology; D018375:Neutrophil Activation / Q000276:immunology*; D009504:Neutrophils / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000502:physiology*; D022142:Secretory Vesicles / Q000276:immunology / Q000378:metabolism*; D010738:Type C Phospholipases / Q000502:physiology
D018797:Cell Cycle Proteins; C115270:G2A receptor; D008246:Lysophospholipids; D043562:Receptors, G-Protein-Coupled; D010738:Type C Phospholipases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go