Induction of cyclooxygenase-2 by secretory phospholipases A2 in nerve growth factor-stimulated rat serosal mast cells is facilitated by interaction with fibroblasts and mediated by a mechanism independent of their enzymatic functions.
Mast cells exhibit a biphasic (immediate and delayed) eicosanoid-biosynthetic response after stimulation with particular cytokines or Fc epsilonRI (high affinity receptor for IgE) cross-linking. Treatment of rat serosal connective tissue mast cells (CTMC) with nerve growth factor (NGF) induced only the delayed phase of PGD2 generation that depended on inducible cyclooxygenase-2 (COX-2), but not constitutive COX-1, even though the subcellular distributions of these isoforms were similar. Experiments using several phospholipase A2 (PLA2) isozyme-specific probes and inhibitors suggested that both constitutive cytosolic PLA2 and inducible type IIA secretory PLA2 (sPLA2) are involved in NGF-initiated, COX-2-dependent, delayed PGD2 generation in rat CTMC. A type IIA sPLA2 inhibitor, but neither cytosolic PLA2 nor COX inhibitors, reduced, while adding exogenous type IIA sPLA2 augmented, NGF-induced COX-2 expression and its attendant PGD2 generation, indicating that the sPLA2-mediated increase in delayed PGD2 generation was attributable mainly to enhanced COX-2 expression. Type IIA sPLA2 and its close relative type V sPLA2 associated with fibroblastic cell surfaces increased NGF-induced COX-2 expression more efficiently than the soluble enzymes, revealing a particular juxtacrine sPLA2 presentation route. Surprisingly, catalytically inactive type IIA sPLA2 mutants, which were incapable of promoting arachidonic acid release from cytokine-primed cells, retained the ability to enhance COX-2 expression in CTMC, indicating that the COX-2-inducing activities of sPLA2 are independent of their catalytic functions.
Tada
K
K
Department of Health Chemistry, School of Pharmaceutical Sciences, Showa University, Tokyo, Japan.
Murakami
M
M
Kambe
T
T
Kudo
I
I
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002450:Cell Communication; D002478:Cells, Cultured; D003239:Connective Tissue Cells / Q000187:drug effects / Q000201:enzymology; D051545:Cyclooxygenase 1; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000502:physiology*; D054501:Group II Phospholipases A2; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics / Q000494:pharmacology; D008407:Mast Cells / Q000187:drug effects* / Q000201:enzymology; D008563:Membrane Lipids / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D009414:Nerve Growth Factors / Q000494:pharmacology*; D010741:Phospholipases A / Q000494:pharmacology*; D054467:Phospholipases A2; D015230:Prostaglandin D2 / Q000096:biosynthesis* / Q000235:genetics; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis* / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D008563:Membrane Lipids; D008565:Membrane Proteins; D009414:Nerve Growth Factors; D016718:Arachidonic Acid; D051545:Cyclooxygenase 1; C496511:PTGS1 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; C496512:Ptgs1 protein, mouse; C496513:Ptgs1 protein, rat; D010741:Phospholipases A; D054501:Group II Phospholipases A2; D054467:Phospholipases A2; D015230:Prostaglandin D2