Francisella tularensis LVS Induction of Prostaglandin Biosynthesis by Infected Macrophages Requires Specific Host Phospholipases and

Francisella tularensis induces the synthesis of prostaglandin E2 (PGE2) by infected macrophages to alter host immune responses, thus providing a survival advantage to the bacterium.We previously demonstrated that PGE2 synthesis by F. tularensis-infected macrophages requires cytosolic phospholipase A2 (cPLA2), cyclooxygenase 2 (COX-2), andmicrosomal prostaglandin E syn-thase 1 (mPGES1). During inducible PGE2 synthesis, cPLA2 hydrolyzes arachidonic acid (AA) from cellular phospholipids to be converted to PGE2. However, in F. tularensis-infected macrophages we observed a temporal disconnect between Ser505-cPLA2 phosphorylation (a marker of activation) and PGE2 synthesis. These results suggested to us that cPLA2 is not responsible for the liberation of AA to be converted into PGE2 by F. tularensis-infected macrophages. Utilizing small-molecule inhibitors, we dem-onstrated that phospholipase D and diacylglycerol lipase were required for providing AA for PGE2 biosynthesis. cPLA2, on the other hand, was required for macrophage cytokine responses to F. tularensis. We also demonstrated for the first time that lipin-1 and PAP2a contribute to macrophage inflammation in response to F. tularensis. Our results identify both an alternative pathway for inducible PGE2 synthesis and a role for lipid-modifying enzymes in the regulation of macrophage inflammatory function. Francisella tularensis is a Gram-negative facultative intracellularbacterium and the causative agent of tularemia, a disease ca-pable of causing a high level of mortality in humans. The most severe form of the disease is pneumonic tularemia. Inhalation of as few as 10 organisms can cause disease which has a 30 % cas