K ⁺ Efflux Is Required for Histone H3 Dephosphorylation by Listeria monocytogenes Listeriolysin O and Other Pore-Forming Toxins

Abstract

Chromatin modification triggered by bacteria is a newly described mechanism by which pathogens impact host transcription. Listeria monocytogenes dephosphorylates histone H3 through the action of listeriolysin O (LLO); however, the underlying mechanism is unknown. Here we show that an unrelated pore-forming toxin, Aeromonas aerolysin, also provokes H3 dephosphorylation (dePH3). As reported for aerolysin, we show that LLO and related toxins induce a pore-dependent K ؉ efflux and that this efflux is the signal required for dePH3. In addition, LLO-induced K ؉ efflux activates caspase-1. However, we demonstrate that dePH3 is unlinked to this activation. Therefore, our study unveils K ؉ efflux as an important signal leading to two independent events critical for infection, inflammasome activation and histone modification.Posttranslational modification of histone tails is a mechanism originally observed during viral infections and recently reported for several bacterial pathogens (12). Histones are essential players in eukaryotic chromatin formation, contributing to the packaging of DNA in the nucleus while retaining the properties of DNA for replication, transcription, etc. Chromatin is composed of an octameric complex of histones H2A, H2B, H3, and H4 around which DNA wraps and condenses into a nucleosome. It is now clear that modifications of N-terminal histone tails induce changes in chromatin and control access of the transcriptional machinery to promoter regions, thereby regulating gene expression. To date, a few bacteria have been shown to modulate host chromatin. However, the underlying mechanisms remain unknown (2, 12).Listeria monocytogenes is an invasive pathogen which secretes a pore-forming toxin, listeriolysin O (LLO), during infection. LLO is part of a large family of cholesterol-dependent cytolysins (CDCs), all produced by Gram-positive bacteria (4, 24). L. monocytogenes and the closely related species Listeria ivanovii are the only intracellular bacteria to produce such a toxin. However, secretion of LLO is not restricted to the intracellular compartment and can also occur outside cells (14, 28). The pores formed by CDCs are large (25 to 30 nm), and except for one member (9), CDCs have no known protein receptors, although cholesterol is a prerequisite for pore formation. LLO and other CDCs are potent signaling molecules triggering a variety of cellular responses, including mitogenactivated protein kinase and NF-B activation, Ca 2ϩ signaling, and lipid raft aggregation (28). In addition, we have shown that LLO and CDCs provoke several histone modifications (11). However, the underlying mechanisms are unknown.Aerolysin is a pore-forming toxin secreted by Aeromonas hydrophila and is distinct from CDCs. It is produced as an inactive precursor, binds to glycosylphosphatidylinositol-anchored proteins on host cell surfaces, and is proteolytically cleaved. In its mature form, the toxin heptamerizes into a circular ring which forms small pores (1 to 2 nm) permeable to ions but not to proteins (1). K ϩ efflux thr...

Role for Telomerase in Listeria monocytogenes Infection

“…K ϩ efflux leads to histone H3 dephosphorylation (20), while Ca 2ϩ influx plays a role during bacterial entry and induces mitochondrial fragmentation (13,47). To study the implication of the two ions in the decrease of hTERT levels, we prevented K ϩ efflux by incubating cells in high extracellular concentrations of KCl, while Ca 2ϩ influx was blocked by incubating cells with EGTA, a calcium chelator.…”

The arsenal of virulence factors deployed byListeria monocytogenesto promote its cell infection cycle

“…123 LLO was also shown to be critical for dephosphorylation of histone H3 and deacetylation of histone H4, during the early phase of infection, 215 through a mechanism that involves LLO-induced pore-dependent efflux of potassium ions. 216 Indeed, reduced levels of histone modifications were associated to modulation of specific host cell gene expression, suggesting that LLO-mediated genetic reprogramming of the host cell could be an additional mechanism whereby L. monocytogenes manipulates the host immune response. Since mitochondria constitute important innate immune response signaling integrators, the short-term fragmentation of these organelles, as elicited by extracellularly secreted LLO, may be another way for Listeria to interfere with host immune response-activating events to its own advantage.…”

Fluxes of Ca 2+ and K + Are Required for the Listeriolysin O-Dependent Internalization Pathway of Listeria monocytogenes

“…Variations in the intracellular concentration of K ϩ also affect host cell biology. Following host cell exposure to LLO, a decrease in the intracellular concentration of K ϩ leads to caspase-1 activation, histone H3 dephosphorylation, and the arrest of protein synthesis (28,40). In the work described here, we evaluated the roles of Ca 2ϩ and K ϩ fluxes triggered upon host cell perforation by LLO in L. monocytogenes internalization.…”

“…Indeed, LLO is released by L. monocytogenes in the extracellular environment (22,23), eliciting various host cell responses. These responses include the activation of mitogenactivated protein (MAP) kinases (24,25), the NLRP3 inflammasome (27,28), caspase-1, and NF-B (26). Extracellular LLO also decreases SUMOylation (29) and histone phosphorylation (28,30) and causes mitochondrial fragmentation (31) as well as the arrest of protein synthesis (32).…”