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Infection and Immunity, April 1999, p. 1770-1778, Vol. 67, No. 4
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.
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Copyright © 1999, American Society for Microbiology. All rights reserved.
Listeria monocytogenes Phospholipase
C-Dependent Calcium Signaling Modulates Bacterial Entry into J774
Macrophage-Like Cells
*
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.
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