title: IL-5 increases expression of 5-lipoxygenase-activating protein and translocates 5-lipoxygenase to the nucleus in human blood eosinophils.
abstract: Cysteinyl-leukotrienes are potent bronchoconstrictor mediators synthesized by the 5-lipoxygenase (5-LO) pathway. Eosinophilopoietic cytokines such as IL-5 enhance cysteinyl-leukotriene synthesis in eosinophils in vitro, mimicking changes in eosinophils from asthmatic patients, but the mechanism is unknown. We hypothesized that IL-5 induces the expression of 5-LO and/or its activating protein FLAP in eosinophils, and that this might be modulated by anti-inflammatory corticosteroids. Compared with control cultures, IL-5 increased the proportion of normal blood eosinophils immunostaining for FLAP (65 +/- 4 vs 34 +/- 4%; p < 0.0001), enhanced immunoblot levels of FLAP by 51 +/- 14% (p = 0.03), and quadrupled ionophore-stimulated leukotriene C4 synthesis from 5.7 to 20.8 ng/106 cells (p < 0.02). IL-5 effects persisted for 24 h and were abolished by cycloheximide and actinomycin D. The proportion of FLAP+ eosinophils was also increased by dexamethasone (p < 0.0001). Neither IL-5 nor dexamethasone altered 5-LO expression, but IL-5 significantly increased 5-LO immunofluorescence localizing to eosinophil nuclei. Compared with normal subjects, allergic asthmatic patients had a greater proportion of circulating FLAP+ eosinophils (46 +/- 6 vs 27 +/- 3%; p < 0.03) and a smaller IL-5-induced increase in FLAP immunoreactivity (p < 0.05). Thus, IL-5 increases FLAP expression and translocates 5-LO to the nucleus in normal blood eosinophils in vitro. This is associated with an enhanced capacity for cysteinyl-leukotriene synthesis and mimics in vivo increases in FLAP expression in eosinophils from allergic asthmatics.
authors.affiliation: University Medicine, Southampton General Hospital, United Kingdom.
authors.forename: A S
authors.initials: AS
authors.lastname: Cowburn
authors.forename: S T
authors.initials: ST
authors.lastname: Holgate
authors.forename: A P
authors.initials: AP
authors.lastname: Sampson
mesh_terms: D058927:5-Lipoxygenase-Activating Proteins; D000328:Adult; D001094:Arachidonate 5-Lipoxygenase / Q000097:blood* / Q000737:chemistry; D001249:Asthma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D001692:Biological Transport; D015153:Blotting, Western; D000001:Calcimycin / Q000494:pharmacology; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000097:blood / Q000737:chemistry; D002467:Cell Nucleus / Q000201:enzymology*; D002478:Cells, Cultured; D003545:Cysteine / Q000096:biosynthesis / Q000097:blood; D004804:Eosinophils / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D015848:Interleukin-5 / Q000097:blood / Q000502:physiology*; D007958:Leukocyte Count; D015289:Leukotrienes / Q000096:biosynthesis / Q000097:blood; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000097:blood / Q000737:chemistry; D013194:Staining and Labeling; D013347:Subcellular Fractions / Q000201:enzymology / Q000378:metabolism
chemical_list: D058927:5-Lipoxygenase-Activating Proteins; C548592:ALOX5AP protein, human; D002352:Carrier Proteins; D015848:Interleukin-5; D015289:Leukotrienes; D008565:Membrane Proteins; C112381:cysteinyl-leukotriene; D000001:Calcimycin; D001094:Arachidonate 5-Lipoxygenase; D003545:Cysteine