Akt as a mediator of secretory phospholipase A2 receptor-involved inducible nitric oxide synthase expression

The induction of inducible NO synthase (iNOS) by group IIA phospholipase A(2) (PLA(2)) involves the stimulation of a novel signaling cascade. In this study, we demonstrate that group IIA PLA2 up-regulates the expression of iNOS through a novel pathway that includes M-type secretory PLA2 receptor (sPLA(2)R), phosphatidylinositol 3-kinase (PI3K), and Akt. Group IIA PLA2 Stimulated iNOS expression and promoted nitrite production in a dose- and time-dependent manner in Raw264.7 cells. Upon treating with group IIA PLA2, Akt is phosphorylated in a PI3K-dependent manner. Pretreatment with LY294002, a PI3K inhibitor, strongly suppressed group IIA PLA(2)-induced iNOS expression and PI3K/Akt activation. The promoter activity of iNOS was stimulated by group IIA PLA2, and this was suppressed by LY294002. Transfection with Akt cDNA resulted in Akt protein overexpression in Raw264.7 cells and effectively enhanced the group IIA PLA2-induced reporter activity of the iNOS promoter. M-type sPLA2R was highly expressed in Raw264.7 cells. Overexpression of M-type sPLA2R enhanced group IIA PLA(2)-induced promoter activity and iNOS protein expression, and these effects were abolished by LY294002. However, site-directed mutation in residue responsible for PLA(2) catalytic activity markedly reduced their ability to production of nitrites and expression of iNOS. These results suggest that group IIA PLA2 induces nitrite production by involving of M-type sPLA2R, which then mediates signal transduction events that lead to PI3K/Akt activation.