Secretory phospholipase A(2) receptor-mediated activation of cytosolic phospholipase A(2) in murine bone marrow-derived mast cells

The current study examined the signal transduction steps involved in the se lective release of arachidonic acid (AA) induced by the addition of secreto ry 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 grou p IB PLA(2) to BMMC caused a transient increase in cPLA(2) activity and tra nslocation of this activity to membrane fractions. Western analyses reveale d that these changes In cPLA(2) were accompanied by a time-dependent gel sh ift of cPLA(2) induced by phosphorylation of cPLA(2) at various sites. A no ncatalytic ligand of the sPLA(2) receptor, p-amino-phenyl-alpha -D-mannopyr anoside BSA, also induced an increase In cPLA(2) activity in BMMC, sPLA(2) receptor ligands induced the phosphorylation of p44/p42 mitogen-activated p rotein kinase, Additionally, an Inhibitor of p44/p42 mitogen-activated prot ein kinase (PD98059) significantly inhibited sPLA(2)-induced cPLA(2) activa tion 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 purifi ed sPLA(2) from BMMC enhanced cPLA(2) activity and AA release. Similarly, o verexpression of mouse groups IIA or V PLA(2) in BMMC induced an increase i n AA release. These data suggest that sPLA(2) mediate the selective release of AA by binding to cell surface receptors and then inducing signal transd uction events that lead to cPLA(2) activation.