A bifunctional role for group IIA secreted phospholipase A2 in human rheumatoid fibroblast-like synoviocyte arachidonic acid metabolism.
Human group IIA-secreted phospholipase A(2) (sPLA(2)-IIA) is an important regulator of cytokine-mediated inflammatory responses in both in vitro and in vivo models of rheumatoid arthritis (RA). However, treatment of RA patients with sPLA(2)-IIA inhibitors shows only transient benefit. Using an activity-impaired sPLA(2)-IIA mutant protein (H48Q), we show that up-regulation of TNF-dependent PGE(2) production and cyclooxygenase-2 (COX-2) induction by exogenous sPLA(2)-IIA in RA fibroblast-like synoviocytes (FLSs) is independent of its enzyme function. Selective cytosolic phospholipase A(2)-α (cPLA(2)-α) inhibitors abrogate TNF/sPLA(2)-IIA-mediated PGE(2) production without affecting COX-2 levels, indicating arachidonic acid (AA) flux to COX-2 occurs exclusively through TNF-mediated activation of cPLA(2)-α. Nonetheless, exogenous sPLA(2)-IIA, but not H48Q, stimulates both AA mobilization from FLSs and microparticle-derived AA release that is not used for COX-2-dependent PGE(2) production. sPLA(2)-IIA-mediated AA production is inhibited by pharmacological blockade of sPLA(2)-IIA but not cPLA(2)-α. Exogenous H48Q alone, like sPLA(2)-IIA, increases COX-2 protein levels without inducing PGE(2) production. Unlike TNF, sPLA(2)-IIA alone does not rapidly mobilize NF-κB or activate phosphorylation of p38 MAPK, two key regulators of COX-2 protein expression, but does activate the ERK1/2 pathway. Thus, sPLA(2)-IIA regulates AA flux through the cPLA(2)-α/COX-2 pathway in RA FLSs by up-regulating steady state levels of these biosynthetic enzymes through an indirect mechanism, rather than direct provision of substrate to the pathway. Inhibitors that have been optimized for their potency in enzyme activity inhibition alone may not adequately block the activity-independent function of sPLA(2)-IIA.
South Western Sydney Clinical School, Sydney 2052, Australia.
Katherine J
KJ
Bryant
Matthew J
MJ
Bidgood
Pei-Wen
PW
Lei
Megan
M
Taberner
Caroline
C
Salom
Vinod
V
Kumar
Lawrence
L
Lee
W Bret
WB
Church
Brett
B
Courtenay
Brian P
BP
Smart
Michael H
MH
Gelb
Michael A
MA
Cahill
Garry G
GG
Graham
H Patrick
HP
McNeil
Kieran F
KF
Scott
D019943:Amino Acid Substitution; D000818:Animals; D016718:Arachidonic Acid / Q000235:genetics / Q000378:metabolism*; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002460:Cell Line; D051546:Cyclooxygenase 2 / Q000096:biosynthesis / Q000235:genetics; D015232:Dinoprostone / Q000096:biosynthesis / Q000235:genetics; D004285:Dogs; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D054501:Group II Phospholipases A2 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D020125:Mutation, Missense; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D013582:Synovial Fluid / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D016718:Arachidonic Acid; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D048051:p38 Mitogen-Activated Protein Kinases; D054501:Group II Phospholipases A2; D015232:Dinoprostone