Listeriolysin of Listeria monocytogenes forms Ca2+-permeable pores leading to intracellular Ca2+ oscillations

Abstract

Summary Listeriolysin (LLO) is a major virulence factor of Listeria monocytogenes, a Gram‐positive bacterium that can cause life‐threatening diseases. Various signalling events and cellular effects, including modulation of gene expression, are triggered by LLO through unknown mechanisms. Here, we demonstrate that LLO applied extracellularly at sublytic concentrations causes long‐lasting oscillations of the intracellular Ca2+ level of human embryonic kidney cells; resulting from a pulsed influx of extracellular Ca2+ through pores that are formed by LLO in the plasma membrane. Calcium influx does not require the activity of endogenous Ca2+ channels. LLO‐formed pores are transient and oscillate between open and closed states. Pore formation and Ca2+ oscillations were also observed after exposure of cells to native Listeria monocytogenes. Our data identify LLO as a tool used by Listeria monocytogenes to manipulate the intracellular Ca2+ level without direct contact of the bacterium with the target cell. As Ca2+ oscillations modulate cellular signalling and gene expression, our findings provide a potential molecular basis for the broad spectrum of Ca2+‐dependent cellular responses induced by LLO during Listeria infection.

Crystal structure of listeriolysin O reveals molecular details of oligomerization and pore formation

“…At sublytic concentrations, LLO facilitates the influx of Ca 2 þ from the extracellular medium into the cell or causes the release of Ca 2 þ from intracellular stores into the cytosol 37 . In either case, increased levels of cytosolic free Ca 2 þ disturb cellular Ca 2 þ homeostasis, which results in release of proinflammatory mediators, changes in cellular metabolism, reorganization of the cytoskeleton and ultimately apoptosis 38,39 .…”

“…At present, it is unknown how many LLO monomers combine to form such channels, and how they interact. Previous patch clamp studies proposed at least three LLO monomers for the formation of a functional pore 37 . We propose that LLO monomers associate on the membrane by surface charge complementarity followed by membrane insertion of their b-hairpins to form a narrow b-barrel channel.…”

Streptococcus pneumoniae Infection of Host Epithelial Cells via Polymeric Immunoglobulin Receptor Transiently Induces Calcium Release from Intracellular Stores

“…The modulation of calcium signals is a very important mechanism by which pathogenic bacteria influence host cells. Bacterial toxins such as listeriolysin O, the poreforming toxin from L. monocytogenes, has been identified as a sine qua non of calcium mobilization mediating intracellular calcium oscillations (20,(41)(42)(43). Moreover, bacteria such as C. jejuni and S. typhimurium induce, independently of toxins, calcium responses that play a role in cytoskeleton rearrangements thus facilitating their cell association or even internalization into these host cells.…”

Ca2+/calmodulin-dependent invasion of microvascular endothelial cells of human brain by Escherichia coli K1

“…An increased intracellular Ca 2+ has been implicated in mediating host cell invasion by several microorganisms, such as Salmonella typhimurium, Porphomonas gingivalis, enteropathogenic E. coli, Camphylobacter jejuni, Listeria monocytogenes, and Pseudomonas aeruginosa (Belton et al 2004;Bierne et al 2000;Dramsi and Cossart 2003;Hu et al 2005;Koschinski et al 2006;Pace et al 1993;Ratner et al 2001;Shiner et al 2006;Tran Van Nhieu et al 2004). In most cases, the [Ca 2+ ] i elevation has been attributed to the formation of calcium-permeable pores by bacterial toxins, such as hemolysin, vacuolating cytotoxin A, or listeriolysin, and the subsequent influx of extracellular Ca 2+ (Belton et al 2004;Dramsi and Cossart 2003;Koschinski et al 2006;Marlink et al 2003;Repp et al 2002;Soderblom et al 2005;Tran Van Nhieu et al 2004). Much less is known about the role of the receptorinduced [Ca 2+ ] i rise that can result from bacterial interaction with host cell surface receptor(s).…”