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Infection and Immunity, April 1999, p. 1770-1778, Vol. 67, No. 4
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Listeria monocytogenes Phospholipase C-Dependent Calcium Signaling Modulates Bacterial Entry into J774 Macrophage-Like Cells

Sandra J. Wadsworth, and Howard Goldfine*

Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6076

Received 8 October 1998/Returned for modification 18 November 1998/Accepted 8 December 1998

Listeria monocytogenes secretes several proteins that have been shown to contribute to virulence. Among these is listeriolysin O (LLO), a pore-forming hemolysin that is absolutely required for virulence. Two other virulence factors are phospholipases: a phosphatidylinositol-specific phospholipase C (PI-PLC [plcA]) and a broad-range PLC (plcB). Although mutations in plcA or plcB resulted in small increases in mouse 50% lethal dose (LD50), deletions in both genes resulted in a 500-fold increase in LD50. We have examined the role of these secreted proteins in host intracellular signaling in the J774 macrophage-like cell line. Measurements of cytosolic free calcium ([Ca2+]i) have revealed a rapid spike upon exposure of these cells to wild-type L. monocytogenes. This is followed by a second peak at 5 min and a third prolonged peak with a maximal [Ca2+]i of 800 to 1,000 nM. The pattern of calcium changes was greatly altered by deletion of any of the three virulence factors. An LLO mutant produced none of these elevations in [Ca2+]i; however, a transient elevation was observed whenever these bacteria entered the cell. A PI-PLC mutant produced a diminished single elevation in [Ca2+]i at 15 to 30 min. A broad-range PLC mutant produced only the first calcium spike. Studies with inhibitors suggested that the first elevation arises from influx of calcium from the extracellular medium through plasma membrane channels and that the second and third elevations come from release of Ca2+ from intracellular stores. We observed that internalization of wild-type bacteria and the broad-range PLC mutant was delayed for 5 to 10 min, but the LLO and PI-PLC mutants were internalized rapidly upon infection. Inhibitors that affected calcium signaling changed the kinetics of association of wild-type bacteria with J774 cells, the kinetics of entry, and the efficiency of escape from the primary phagosome.

* Corresponding author. Mailing address: Department of Microbiology, University of Pennsylvania School of Medicine, 301C Johnson Pavilion, Philadelphia, PA 19104-6076. Phone: (215) 898-6384. Fax: (215) 573-4856. E-mail: goldfinh{at}mail.med.upenn.edu.

Infection and Immunity, April 1999, p. 1770-1778, Vol. 67, No. 4
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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