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Phosphocholine antagonizes listeriolysin O-induced host cell responses of Listeria monocytogenes.

BACKGROUND
Bacterial toxins disrupt plasma membrane integrity with multitudinous effects on host cells. The secreted pore-forming toxin listeriolysin O (LLO) of the intracellular pathogen Listeria monocytogenes promotes egress of the bacteria from vacuolar compartments into the host cytosol often without overt destruction of the infected cell. Intracellular LLO activity is tightly controlled by host factors including compartmental pH, redox-, proteolytic- and proteostatic-factors, and inhibited by cholesterol.


METHODS
Combining infection studies of L. monocytogenes wildtype and isogenic mutants together with biochemical studies with purified phospholipases, we investigate the effect of their enzymatic activities on LLO.


RESULTS
Here, we show that phosphocholine (ChoP), a reaction product of the phosphatidylcholine-specific phospholipase C (PC-PLC) of L. monocytogenes, is a potent inhibitor of intra- and extracellular LLO activities. Binding of ChoP to LLO is redox-independent, and leads to the inhibition of LLO-dependent induction of calcium flux, mitochondrial damage and apoptosis. ChoP also inhibits the hemolytic activities of the related cholesterol-dependent cytolysins (CDC), pneumolysin and streptolysin.


CONCLUSION
Our study uncovers a strategy used by L. monocytogenes to modulate cytotoxic LLO activity through the enzymatic activity of its PC-PLC. This mechanism appears to be widespread and also used by other CDC pore-forming toxin-producing bacteria.