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Interaction of low molecular weight group IIA phospholipase A₂ with apoptotic human T cells: role of heparan sulfate proteoglycans

ERIC BOILARD, SYLVAIN G. BOURGOIN, CHANTALE BERNATCHEZ, PATRICE E. POUBELLE and MARC E. SURETTE^,,1

Centre de Recherche en Rhumatologie et Immunologie, Centre de Recherche du Centre Hospitalier Universitaire de Québec, Pavillon CHUL, and Faculté de Médecine, Université Laval, Québec, Canada G1V 4G2; and
Pilot Therapeutics Inc., Charleston, South Carolina, USA

¹Correspondence: Pilot Therapeutics Inc., 2000 Daniel Island Dr., Suite 440, Charleston, SC 29492, USA. E-mail: MarcS{at}pilott.com

Human group IIA phospholipase A₂ (hIIA PLA₂) is a 14 kDa secreted enzyme associated with inflammatory diseases. A newly discovered property of hIIA PLA₂ is the binding affinity for the heparan sulfate proteoglycan (HSPG) glypican-1. In this study, the binding of hIIA PLA₂ to apoptotic human T cells was investigated. Little or no exogenous hIIA PLA₂ bound to CD3-activated T cells but significant binding was measured on activated T cells induced to undergo apoptosis by anti-CD95. Binding to early apoptotic T cells was greater than to late apoptotic cells. The addition of heparin and the hydrolysis of HSPG by heparinase III only partially inhibited hIIA PLA₂ binding to apoptotic cells, suggesting an interaction with both HSPG and other binding protein(s). Two low molecular weight HSPG were coimmunoprecipitated with hIIA PLA₂ from apoptotic T cells, but not from living cells. Treatment of CD95-stimulated T cells with hIIA PLA₂ resulted in the release of arachidonic acid but not oleic acid from cells and this release was blocked by heparin and heparinase III. Altogether, these results suggest a role for hIIA PLA₂ in the release of arachidonic acid from apoptotic cells through interactions with HSPG and its potential implication in the progression of inflammatory diseases.—Boilard, E., Bourgoin, S. G., Bernatchez, C., Poubelle, P. E., Surette, M. E. Interaction of low molecular weight group IIA phospholipase A₂ with apoptotic human T cells: role of heparan sulfate proteoglycans.

Key Words: lymphocytes • apoptosis • IIA phospholipase A₂ • heparan sulfate proteoglycan • arachidonic acid • arthritis

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