Secretory phospholipase A2 receptor-mediated activation of cytosolic phospholipase A2 in murine bone marrow-derived mast cells

The current study examined the signal transduction steps involved in the selective release of arachidonic acid (AA) induced by the addition of secretory phospholipase A(2) (sPLA(2)) isotypes to bone marrow-derived mast cells (BMMC). Overexpression of sPLA(2) receptors caused a marked increase in AA and PGD(2) release after stimulation of BMMC, implicating sPLA(2) receptors in this process, The hypothesis that the release of AA by sPLA(2) involved activation of cytosolic PLA(2) (cPLA(2)) was next tested, Addition of group IB PLA(2) to BMMC caused a transient increase in cPLA(2) activity and translocation of this activity to membrane fractions. Western analyses revealed that these changes In cPLA(2) were accompanied by a time-dependent gel shift of cPLA(2) induced by phosphorylation of cPLA(2) at various sites. A noncatalytic ligand of the sPLA(2) receptor, p-amino-phenyl-alpha -D-mannopyranoside BSA, also induced an increase In cPLA(2) activity in BMMC, sPLA(2) receptor ligands induced the phosphorylation of p44/p42 mitogen-activated protein kinase, Additionally, an Inhibitor of p44/p42 mitogen-activated protein kinase (PD98059) significantly inhibited sPLA(2)-induced cPLA(2) activation and AA release. sPLA(2) receptor ligands also increased Ras activation while an inhibitor of tyrosine phosphorylation (herbimycin) inhibited the increase in cPLA(2) activation and AA release. Addition of partially purified sPLA(2) from BMMC enhanced cPLA(2) activity and AA release. Similarly, overexpression of mouse groups IIA or V PLA(2) in BMMC induced an increase in AA release. These data suggest that sPLA(2) mediate the selective release of AA by binding to cell surface receptors and then inducing signal transduction events that lead to cPLA(2) activation.