title: Endogenous secreted phospholipase A2 group X regulates cysteinyl leukotrienes synthesis by human eosinophils.
abstract: BACKGROUND
  Phospholipase A2s mediate the rate-limiting step in the formation of eicosanoids such as cysteinyl leukotrienes (CysLTs). Group IVA cytosolic PLA2α (cPLA2α) is thought to be the dominant PLA2 in eosinophils; however, eosinophils also have secreted PLA2 (sPLA2) activity that has not been fully defined.
  
  
  OBJECTIVE
  To examine the expression of sPLA2 group X (sPLA2-X) in eosinophils, the participation of sPLA2-X in the formation of CysLTs, and the mechanism by which sPLA2-X initiates the synthesis of CysLTs in eosinophils.
  
  
  METHODS
  Peripheral blood eosinophils were obtained from volunteers with asthma and/or allergy. A rabbit polyclonal anti-sPLA2-X antibody identified sPLA2-X by Western blot. We used confocal microscopy to colocalize the sPLA2-X to intracellular structures. An inhibitor of sPLA2-X (ROC-0929) that does not inhibit other mammalian sPLA2s, as well as inhibitors of the mitogen-activated kinase cascade (MAPK) and cPLA2α, was used to examine the mechanism of N-formyl-methionyl-leucyl-phenylalanine (fMLP)-mediated formation of CysLT.
  
  
  RESULTS
  Eosinophils express the mammalian sPLA2-X gene (PLA2G10). The sPLA2-X protein is located in the endoplasmic reticulum, golgi, and granules of eosinophils and moves to the granules and lipid bodies during fMLP-mediated activation. Selective sPLA2-X inhibition attenuated the fMLP-mediated release of arachidonic acid and CysLT formation by eosinophils. Inhibitors of p38, extracellular-signal-regulated kinases 1/2 (p44/42 MAPK), c-Jun N-terminal kinase, and cPLA2α also attenuated the fMLP-mediated formation of CysLT. The sPLA2-X inhibitor reduced the phosphorylation of p38 and extracellular-signal-regulated kinases 1/2 (p44/42 MAPK) as well as cPLA2α during cellular activation, indicating that sPLA2-X is involved in activating the MAPK cascade leading to the formation of CysLT via cPLA2α. We further demonstrate that sPLA2-X is activated before secretion from the cell during activation. Short-term priming with IL-13 and TNF/IL-1β increased the expression of PLA2G10 by eosinophils.
  
  
  CONCLUSIONS
  These results demonstrate that sPLA2-X plays a significant role in the formation of CysLTs by human eosinophils. The predominant role of the enzyme is the regulation of MAPK activation that leads to the phosphorylation of cPLA2α. The sPLA2-X protein is regulated by proteolytic cleavage, suggesting that an inflammatory environment may promote the formation of CysLTs through this mechanism. These results have important implications for the treatment of eosinophilic disorders such as asthma.
authors.affiliation: Division of Pulmonary and Critical Care, the Department of Medicine, University of Washington, Seattle, Wash. Electronic address: tealh@uw.edu.
authors.forename: Teal S
authors.initials: TS
authors.lastname: Hallstrand
authors.affiliation: Division of Pulmonary and Critical Care, the Department of Medicine, University of Washington, Seattle, Wash.
authors.forename: Ying
authors.initials: Y
authors.lastname: Lai
authors.affiliation: Molecular and Cellular Biology Program, University of Washington, Seattle, Wash.
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Hooper
authors.affiliation: Department of Chemistry, University of Washington, Seattle, Wash.
authors.forename: Rob C
authors.initials: RC
authors.lastname: Oslund
authors.affiliation: Division of Pulmonary and Critical Care, the Department of Medicine, University of Washington, Seattle, Wash.
authors.forename: William A
authors.initials: WA
authors.lastname: Altemeier
authors.affiliation: Division of Pulmonary and Critical Care, the Department of Medicine, University of Washington, Seattle, Wash.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Matute-Bello
authors.affiliation: Department of Chemistry, University of Washington, Seattle, Wash; Department of Biochemistry, University of Washington, Seattle, Wash.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Gelb
mesh_terms: D000328:Adult; D002460:Cell Line; D003545:Cysteine / Q000276:immunology*; D004804:Eosinophils / Q000276:immunology*; D005260:Female; D054509:Group X Phospholipases A2 / Q000276:immunology*; D006801:Humans; D006967:Hypersensitivity / Q000276:immunology; D015289:Leukotrienes / Q000276:immunology*; D008297:Male
chemical_list: D015289:Leukotrienes; C112381:cysteinyl-leukotriene; D054509:Group X Phospholipases A2; D003545:Cysteine
keywords: Eosinophil; allergy; asthma; leukotriene; mitogen-activated kinase; phospholipase A(2)