Listeriolysin O-Mediated Calcium Influx Potentiates Entry of Listeria monocytogenes into the Human Hep-2 Epithelial Cell Line

ABSTRACT

To investigate factors which modulate the entry of Listeria monocytogenes into mammalian cells, we have analyzed the role of Ca²⁺. We show that L. monocytogenes induced Ca²⁺ transients into the human Hep-2 epithelial cell line. The nonpathogenic species L. innocua or a L. monocytogenes mutant strain defective in listeriolysin O (LLO) production was unable to induce these calcium fluxes. Addition of plasma membrane calcium channel antagonists or chelation of extracellular calcium markedly reduced L. monocytogenes entry. In contrast, chelation of host cytosolic Ca²⁺ or blockade of Ca²⁺ release from intracellular stores did not affect invasion. These results indicate that L. monocytogenes-induced mobilization of extracellular Ca²⁺ by LLO and activation of downstream Ca²⁺-dependent signaling are required for efficient cell invasion.