Functional association of type IIA secretory phospholipase A, with the glycosylphosphatidylinositol-anchored heparan sulfate proteoglycan in the cyclooxygenase-2-mediated delayed prostanoid-biosynthetic pathway

An emerging body of evidence suggests that type IIA secretory phospholipase A(2) (sPLA(2)-IIA) participates in the amplification of the stimulus-induc ed cyclooxygenase (COX)-2-dependent delayed prostaglandin (PG)-biosynthetic response in several cell types. However, the biological importance of the ability of sPLA(2)-IIA to bind to heparan sulfate proteoglycan (HSPG) on ce ll surfaces has remained controversial. Here we show that glypican, a glyco sylphosphatidylinositol (GPI)-anchored HSPG, acts as a physical and functio nal adaptor for sPLA(2)-IIA. sPLA(2)-IIA-dependent PGE(2) generation by int erleukin-1-stimulated cells was markedly attenuated by treatment of the cel ls with heparin, heparinase or GPI-specific phospholipase C, which solubili zed the cell surface-associated sPLA(2)-IIA. Overexpression of glypican-1 i ncreased the association of sPLA(2)-IIA with the cell membrane, and glypica n-1 was coimmunoprecipitated by the antibody against sPLA(2)-IIA Glypican-1 overexpression led to marked augmentation of sPLA(2)-IIA-mediated arachido nic acid release, PGE(2) generation, and COX-2 induction in interleukin-1-s timulated cells, particularly when the sPLA(2)-IIA expression level was sub optimal. Immunofluorescent microscopic analyses of cytokine-stimulated cell s revealed that sPLA(2)-IIA was present in the caveolae, a microdomain in w hich GPI-anchored proteins reside, and also appeared in the perinuclear are a in proximity to COX-2. We therefore propose that a GPI-anchored HSPG glyp ican facilitates the trafficking of sPLA(2)-IIA into particular subcellular compartments, and arachidonic acid thus released from the compartments may link efficiently to the downstream COX-2-mediated PG biosynthesis.