Expression of secretory phospholipase A₂ receptor in mast cells results in enhanced arachidonic acid mobilization

The goal of the current study was to determine whether the binding of secretory phospholipase A₂ (sPLA₂) to cell surface receptors is important in arachidonic acid (AA) mobilization by murine bone marrow derived mast cells (BMMC). M-type sPLA₂ receptor cDNA was subcloned into a mammalian expression vector (pCMV-5/PLA₂R™) and then utilized to transfect BMMC. Western blot analysis indicated increased expression of a 180 kDa protein within 6-12 h after transfection of BMMC. Maximum expression of the 180 kDa sPLA₂ receptor was observed at 24 h followed by a decrease in levels by 48-72 h. Stimulation of BMMC with antigen resulted in an eight-fold increase in AA release from pCMV-5/PLA₂R™ transfected cells compared to the mock-transfected controls. Maximum AA mobilization from BMMC occurred 48 h after transfection. These initial studies suggested that sPLA₂ released by antigen-stimulated mast cells induces AA release via its capacity to bind to cell surface receptors. In another set of studies, BMMC were incubated with different concentrations of sPLA₂. Cells expressing M-type SPLA₂ receptor released more AA (∼2 fold) than mock-transfected cells. Taken together, these data suggest that PLA₂ secreted by stimulated BMMC or provided from exogenous sources mediates AA release from mast cells by binding to cell surface receptors.