Studies on a mechanism by which cytosolic phospholipase A2 regulates the expression and function of type IIA secretory phospholipase A2

Although it has been proposed that arachidonate release by several secretory phospholipase A(2) (sPLA(2)) isozymes is modulated by cytosolic PLA(2) (cPLA(2)), the cellular component(s) that intermediates between these two signaling PLA(2)s remains unknown. Here we provide evidence that 12- or 15-lipoxygenase (12/15-LOX), which lies downstream of cPLA(2), plays a pivotal role in cytokine-induced gene expression and function of sPLA(2)-IIA. The sPLA(2)-IIA expression and associated PGE(2) generation induced by cytokines in rat fibroblastic 3Y1 cells were markedly attenuated by antioxidants that possess 12/15-LOX inhibitory activity. 3Y1 cells expressed 12/15-LOX endogenously, and forcible overexpression of 12/15-LOX in these cells greatly enhanced cytokine-induced expression of sPLA(2)-IIA, with a concomitant increase in delayed PG generation, Moreover, studies using 293 cells stably transfected with sPLA(2)-IIA revealed that stimulus-dependent hydrolysis of membrane phospholipids by sPLA(2)-IIA was enhanced by overexpression of 12/15-LOX. These results indicate that the product(s) generated by the cPLA(2)-12/15-LOX pathway following cell activation may play two roles: enhancement of sPLA(2)-IIA gene expression and membrane sensitization that leads to accelerated sPLA(2)-IIA-mediated hydrolysis.