Group IIA secretory phospholipase A(2) stimulates inducible nitric oxide synthase expression via ERK and NF-kappa B in macrophages

The mammalian group IIA secretory phospholipase A(2) (sPLA(2)) is believed to play an important role in inflammation and cell injury. The present stud y underlines the importance of group IIA sPLA(2) in the regulation of iNOS. Treatment of cells with sPLA(2) induced protein expression and mRNA accumu lation of iNOS in a dose-dependent manner. The pretreatment of cells with r ho -BPB or SCA, selective sPLA(2) inhibitors, inhibited sPLA(2)-induced iNO S expression. sPLA(2) stimulated the simultaneous activation of two classes of mitogen-activated protein kinases ERK and JNK, but did not stimulate p3 8 MAPK. PD98059, a selective MEK inhibitor, inhibited sPLA(2)-induced nitri te production and iNOS expression as well as ERK phosphorylation. In additi on, pretreatment of rho -BPB or SCA also resulted in Inhibition of sPLA(2)- induced ERK phosphorylation. The sPLA(2) signaling mechanisms involving the activation of transcription factor NF-kappaB were studied in the same cell s. That stimulation of cells with sPLA(2) caused NF-kappaB activation in a time-dependent manner was shown by the detection of NF-kappaB-specific DNA- protein binding and by I kappaB alpha degradtion. SPLA(2)-induced NF-kappaB activation was prevented in the presence of rho -BPB. Furthermore, the NF- kappaB inhibitor PDTC suppressed sPLA(2)-induced nitrite production and iNO S expression as well as I kappaB alpha degradation. The results strongly su ggest that group IIA SPLA(2) induces iNOS in macrophages and that this indu ction occurs through ERK and NF-kappaB.