Transcellular Secretion of Group V Phospholipase A2 from Epithelium Induces β2-Integrin-Mediated Adhesion and Synthesis of Leukotriene C4 in Eosinophils

Abstract

We examined the mechanism by which secretory group V phospholipase A2 (gVPLA2) secreted from stimulated epithelial cells activates eosinophil adhesion to ICAM-1 surrogate protein and secretion of leukotriene (LT)C4. Exogenous human group V PLA2 (hVPLA2) caused an increase in surface CD11b expression and focal clustering of this integrin, which corresponded to increased β2 integrin-mediated adhesion. Human IIaPLA2, a close homolog of hVPLA2, or W31A, an inactive mutant of hVPLA2, did not affect these responses. Exogenous lysophosphatidylcholine but not arachidonic acid mimicked the β2 integrin-mediated adhesion caused by hVPLA2 activation. Inhibition of hVPLA2 with MCL-3G1, a mAb against gVPLA2, or with LY311727, a global secretory phospholipase A2 (PLA2) inhibitor, attenuated the activity of hVPLA2; trifluoromethylketone, an inhibitor of cytosolic group IVA PLA2 (gIVA-PLA2), had no inhibitory effect on hVPLA2-mediated adhesion. Activation of β2 integrin-dependent adhesion by hVPLA2 did not cause ERK1/2 activation and was independent of gIVA-PLA2 phosphorylation. In other studies, eosinophils cocultured with epithelial cells were stimulated with FMLP/cytochalasin B (FMLP/B) and/or endothelin-1 (ET-1) before LTC4 assay. FMLP/B alone caused release of LTC4 from eosinophils, which was augmented by coculture with epithelial cells activated with ET-1. Addition of MCL-3G1 to cocultured cells caused ∼50% inhibition of LTC4 secretion elicited by ET-1, which was blocked further by trifluoromethylketone. Our data indicate that hVPLA2 causes focal clustering of CD11b and β2 integrin adhesion by a novel mechanism that is independent of arachidonic acid synthesis and gIVA-PLA2 activation. We also demonstrate that gVPLA2, endogenously secreted from activated epithelial cells, promotes secretion of LTC4 in cocultured eosinophils.

Multiple Roles of Phospholipase A2during Lung Infection and Inflammation

“…For this complex mechanistic process to occur in vivo, the initial group V sPLA 2 activation of neutrophils requires an alternative, nonneutrophil cell source of group V sPLA 2 , which is speculated to be provided by other inflammatory cells, such as mast cells or macrophages (57). Indeed, transcellular sPLA 2 activity for the purposes of eicosanoid generation has been reported in other studies (77,79,128). Bronchial epithelial cells produce group V sPLA 2 in response to endothelin-1, which is then capable of directly hydrolyzing eosinophil membranes to produce AA for subsequent conversion to cysteinyl LTs, such as LTC 4 .…”

“…Bronchial epithelial cells produce group V sPLA 2 in response to endothelin-1, which is then capable of directly hydrolyzing eosinophil membranes to produce AA for subsequent conversion to cysteinyl LTs, such as LTC 4 . LTC 4 s, as well as other eicosanoids, are frequently found to be enhanced in the BALF of asthmatic patients (64,77,128). Of particular note, AA release leading to LTC 4 synthesis in eosinophils was shown to occur independently of cPLA 2 , demonstrating the ability of sPLA 2 group V to directly generate AA for eicosanoid synthesis (77,79,128).…”

Group V Phospholipase A2 in Bone Marrow-derived Myeloid Cells and Bronchial Epithelial Cells Promotes Bacterial Clearance after Escherichia coli Pneumonia

“…However, increased GV sPLA 2 levels in BAL fluid may not be sufficient to kill E. coli because direct exposure of live E. coli to recombinant GV sPLA 2 had no effect on bacterial viability in vitro. As endogenous GV sPLA 2 released from stimulated epithelial cells can translocate to eosinophils and promote eosinophil adhesion to ICAM-1 and eicosanoid biosynthesis (34), it is possible that GV sPLA 2 released by myeloid cells or bronchial epithelial cells regulates bacterial clearance through paracrine regulation of inflammatory cells in the interstitial microenvironment.…”

Genes for Difference in Eosinophilic Phenotype between MES and BN.MES-Cybames Rats Are on Chromosomes 9, 5, and 1

“…In addition, treatment with an antibody against CD52 has been shown to completely deplete circulating eosinophils in renal recipients [39]. PLA2G5 induces beta 2-integrin-mediated adhesion of eosinophils [21]. Candidate genes on chromosome 9 include interleukin-17F (Il17f) and signal transducer and activator of transcription 1 (Stat1).…”

“…The Matsumoto Eosinophilia Shinshu (MES) rat strain has a genetic predisposition to develop eosinophilia [18,[20][21][22][23][24]34]. In these rats, a marked increase in peripheral blood eosinophils (>500/µl) occurs at about nine weeks of age, with eosinophilia progressing with age until the number of eosinophils eventually exceeds the level that is characteristic of human idiopathic hypereosinophilia (>1,500/µl).…”