Activation of cytokine production by secreted phospholipase A2 in human lung macrophages expressing the M-type receptor.
Secreted phospholipases A(2) (sPLA(2)) are enzymes released in plasma and extracellular fluids during inflammatory diseases. Because human group IB and X sPLA(2)s are expressed in the lung, we examined their effects on primary human lung macrophages (HLM). Both sPLA(2)s induced TNF-alpha and IL-6 release in a concentration-dependent manner by increasing their mRNA expression. This effect was independent of their enzymatic activity because 1) the capacity of sPLA(2)s to mobilize arachidonic acid from HLM was unrelated to their ability to induce cytokine production; and 2) two catalytically inactive isoforms of group IB sPLA(2) (bromophenacyl bromide-inactivated human sPLA(2) and the H48Q mutant of the porcine sPLA(2)) were as effective as the catalytically active sPLA(2)s in inducing cytokine production. HLM expressed the M-type receptor for sPLA(2)s at both mRNA and protein levels, as determined by RT-PCR, immunoblotting, immunoprecipitation, and flow cytometry. Me-indoxam, which decreases sPLA(2) activity as well as binding to the M-type receptor, suppressed sPLA(2)-induced cytokine production. Incubation of HLM with the sPLA(2)s was associated with phosphorylation of ERK1/2, and a specific inhibitor of this pathway, PD98059, significantly reduced the production of IL-6 elicited by sPLA(2)s. In conclusion, two distinct sPLA(2)s produced in the human lung stimulate cytokine production by HLM via a mechanism that is independent of their enzymatic activity and involves activation of the ERK1/2 pathway. HLM express the M-type receptor, but its involvement in eliciting cytokine production deserves further investigation.
Granata
Francescopaolo
F
Division of Clinical Immunology and Allergy, University of Naples Federico II, Via S. Pansini 5, 80131 Naples, Italy.
Petraroli
Angelica
A
Boilard
Eric
E
Bezzine
Sofiane
S
Bollinger
James
J
Del Vecchio
Luigi
L
Gelb
Michael H
MH
Lambeau
Gerard
G
Marone
Gianni
G
Triggiani
Massimo
M
D016207:Cytokines / Q000096:biosynthesis* / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D048049:Extracellular Signal-Regulated MAP Kinases / Q000187:drug effects / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000494:pharmacology; D008168:Lung / Q000166:cytology / Q000276:immunology*; D008264:Macrophages / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D010741:Phospholipases A / Q000276:immunology* / Q000378:metabolism; D054467:Phospholipases A2; D012333:RNA, Messenger / Q000032:analysis; D011956:Receptors, Cell Surface / Q000378:metabolism*; D054507:Receptors, Phospholipase A2; D020133:Reverse Transcriptase Polymerase Chain Reaction
D016207:Cytokines; D005419:Flavonoids; D047908:Intracellular Signaling Peptides and Proteins; C516360:PLA2R1 protein, human; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D054507:Receptors, Phospholipase A2; C015482:protein kinase modulator; D048049:Extracellular Signal-Regulated MAP Kinases; D010741:Phospholipases A; D054467:Phospholipases A2; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one