MECHANISMS THAT ACCOUNT FOR THE SELECTIVE RELEASE OF ARACHIDONIC-ACIDFROM INTACT-CELLS BY SECRETORY PHOSPHOLIPASE A(2)

The current study examined mechanisms that account for the selective r elease of arachidonic acid (AA) from cells by secretory phospholipase A(2) (sPLA(2)). Initial studies demonstrated that low concentrations o f group I and group III PLA(2) isotypes and an sPLA(2)-enriched extrac t from bone marrow-derived mast cells (BMMC) selectively released AA f rom mast cells. Much higher concentrations of group II PLA(2) were req uired to release comparable quantities of AA. Group I PLA(2) also sele ctively released AA from another mast cell line (CFTL-15) and a monocy tic cell line (THP-1). In contrast, high concentrations of group I PLA (2) were required to release fatty acids from a promyelocytic cell lin e (HL-60) and this release was not selective for AA. Binding studies r evealed that cell types (BMMC, CFTL-15 and THP-I) which selectively re leased AA also had the capacity to specifically bind group I PLA(2). H owever, group II PLA(2), which did not selectively release AA from cel ls, also did not specifically bind to these same cell types. Additiona l studies revealed that sPLA(2) binding to the mast cell receptor was attenuated after stimulation with antigen or ionophore A23187. Reverse transcriptase-polymerase chain reaction analyses indicated the presen ce of mRNA for the sPLA(2) receptor in BMMC, CFTL-15 and THP-1 and the absence of this mRNA in HL-60. Final studies demonstrated that p-amin ophenyl-alpha-D-mannopyranoside BSA, a known ligand of the sPLA(2) rec eptor, also selectively released AA from mast cells but not from HL-60 cells. These experiments indicated that receptor occupancy alone (wit hout PLA(2) activity) is sufficient to induce the release of AA from m ast cells. Together, these data reveal that specific isotypes of sPLA( 2) have the capacity to selectively release AA from certain cells by t heir capacity to bind to sPLA(2) receptors on the cell surface. (C) 19 98 Elsevier Science B.V. All rights reserved.