Janus Kinase 3 Activity Is Necessary for Phosphorylation of Cytosolic Phospholipase A2 and Prostaglandin E2 Synthesis by Macrophages Infected with Francisella tularensis Live Vaccine Strain

Abstract

ABSTRACTFrancisella tularensis, the causative agent of tularemia, modulates the host immune response to gain a survival advantage within the host. One mechanism of immune evasion is the ability ofF. tularensisto induce the synthesis of the small lipid mediator prostaglandin E2 (PGE2), which alters the host T cell response making the host more susceptible toFrancisellagrowth. PGE2is synthesized by a tightly regulated biosynthetic pathway following stimulation. The synthesis of PGE2begins with the liberation of arachidonic acid (AA) from membrane phospholipids by cytosolic phospholipase A2 (cPLA2). AA is subsequently converted to the unstable intermediate PGH2by cyclooxygenase-2 (COX-2), and PGH2undergoes an isomerization reaction to generate PGE2. Our objective was to identifyF. tularensis-activated host signaling pathways that regulate the activity of the enzymes in the PGE2-biosynthetic pathway. In this study, we show that cPLA2, p38 mitogen-activated protein kinase (MAPK), and Janus kinase 3 (JAK3) signaling are necessary forF. tularensis-induced PGE2production. Inhibition of JAK3 activity reduced the phosphorylation of cPLA2and COX-2 protein levels. In addition, JAK3 regulates cPLA2phosphorylation independent of transcription. Moreover, p38 MAPK activity is required forF. tularensis-induced COX-2 protein synthesis, but not for the phosphorylation of cPLA2. This research highlights a unique signaling axis in which JAK3 and p38 MAPK regulate the activity of multiple enzymes of the PGE2-biosynthetic pathway in macrophages infected withF. tularensis.