Activation of Host Phospholipases C and D in Macrophages after Infection withListeria monocytogenes

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Abstract
Infection of the J774 murine macrophage-derived cell line withListeria monocytogenesresults in several elevations of intracellular calcium during the first 15 min of infection. These appear to result from the actions of secreted bacterial proteins, including phosphatidylinositol-specific phospholipase C (PI-PLC), a broad-range phospholipase C, and listeriolysin O (LLO) (S. J. Wadsworth and H. Goldfine, Infect. Immun. 67:1770–1778, 1999). We have measured hydrolysis of host PI and the activation of host polyphosphoinositide-specific PLC and host phospholipase D (PLD) during infection with wild-type and mutantL. monocytogenes. Elevated hydrolysis of host PI occurred within the first 10 min of infection and was dependent on both bacterial PI-PLC and LLO, both of which were required for the earliest elevations of intracellular calcium in the host cell. A more rapid hydrolysis of host PI was observed at 30 min after infection, at the time when wild-type bacteria have been internalized. Activation of host PLC, also occurred in the first 10 min of infection but was not dependent on the presence of bacterial PI-PLC. Similar observations were made in murine bone marrow-derived macrophages. In J774 cells, activation of host PLD was observed after 20 min of infection and was dependent on bacterial LLO. Mutants in the bacterial phospholipases produced levels of PLD activation similar to those produced by the wild type. Phorbol myristate acetate (PMA) also activated host PLD, while long-term treatment with PMA resulted in loss of the ability ofL. monocytogenesto activate host PLD, suggesting an involvement of protein kinase C (PKC) in the activation of PLD. Rottlerin, an inhibitor of PKC δ in J774 cells, also inhibited the activation of PLD, but hispidin, an inhibitor of PKC βI and βII, did not. Pretreatment of J774 cells with the PLD inhibitor, 2,3-diphosphoglycerate partially inhibited escape of the bacteria from the primary phagocytic vacuole.