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The intracellular parasite Toxoplasma gondii invades immune cells to spread through the circulatory system, eventually reaching the brains of humans and animals. It is not well understood how parasitized immune cells interact with blood vessel walls, a process that ultimately helps Toxoplasma colonize the brain tissue. We found that when Toxoplasma infects the cells lining the blood vessels (endothelium), these produce C-C motif chemokine ligand 5 (CCL5), a potent signaling and attractant molecule. CCL5 production was triggered by a parasite-derived secreted protein, GRA15. CCL5 activated and attracted infected immune cells. In mice, the levels of CCL5 increased quickly in the brain microvasculature after infection, helping the infected immune cells adhere to brain vessels. When the effect of CCL5 was pharmacologically blocked, fewer infected cells sequestered in the brain vessels, lowering the parasite loads. These findings reveal a mechanism through which Toxoplasma manipulates host cells to produce factors that facilitate its colonization of the brain.

The intracellular parasite Toxoplasma gondii enhances its dissemination to distant organs by hijacking infected leukocytes via a Trojan Horse mechanism. Upon infecting dendritic cells (DCs), Toxoplasma induces a hypermigratory phenotype characterized by podosome dissolution and formation of F-actin stress fibers. We previously showed that these cytoskeletal changes depend on the effector protein Toxoplasma WAVE complex-interacting protein (TgWIP) secreted from parasites to infected leukocytes. Here, we identify the host adaptor proteins non-catalytic region of tyrosine kinase adaptor protein 1 and 2 (Nck1/2) and growth factor receptor-bound protein 2 (Grb2) as direct TgWIP interactors. TgWIP mainly uses two distinct proline-rich regions (PRRs) to interact with Nck1 and Grb2. Mutating these PRRs abrogates TgWIP binding to Nck1 and Grb2 and diminishes podosome dissolution and DC hypermotility. Furthermore, we show that TgWIP directly interacts with the actin nucleation-promoting factor WAVE regulatory complex (WRC) via a WRC-interacting receptor sequence (WIRS). Disrupting this interaction also influences actin cytoskeletal remodeling and DC hypermotility. Collectively, our data reveal that TgWIP directly interacts with multiple actin regulators, including Nck1, Grb2, and the WRC, to remodel the actin cytoskeleton of the host cells, elucidating a key mechanism that Toxoplasma exploits to enhance host cell migration and dissemination.IMPORTANCEThe parasite Toxoplasma gondii spreads throughout the body by hijacking immune cells and boosting their motility. This ability depends on secreted parasite proteins that manipulate the host cell’s actin cytoskeleton. One such effector, Toxoplasma gondii WAVE-interacting protein (TgWIP), induces dramatic changes in host cell shape and movement, but how it does this has remained unclear. Here, we show that TgWIP directly interacts with multiple host actin-regulatory proteins using distinct sequence motifs. Disrupting these interactions prevents cytoskeletal remodeling and impairs parasite-induced immune cell migration. Our study reveals that Toxoplasma uses defined motifs to co-opt host signaling hubs that control cell motility. Understanding how pathogens exploit the cytoskeleton not only sheds light on host-pathogen interactions but may also reveal broader principles of cell migration relevant to immunity, cancer, and development.

Chlamydia trachomatis is a human pathogen and a prevalent agent of sexually transmitted diseases. The ability to survive and propagate within a protected intracellular niche leads directly to pathology indicative of Chlamydia -mediated disease. The reduced chlamydial genome leads to comparatively limited biosynthetic capacity, thereby necessitating parasitism of metabolites and other resources from the infected host cell. Chlamydia relies heavily on type III secreted effectors to interface with and co-opt host pathways to acquire resources. We demonstrate herein that the plasma membranes of infected cells represent a potential reservoir of resources required for optimal intracellular growth. Chlamydiae employ at least one type III secreted effector protein, translocated membrane-associated effector A (TmeA), to redirect material to the vacuole by manipulating Arp2/3-dependent actin polymerization. This pathway represents a distinct mechanism by which Chlamydia acquires resources and provides evidence for TmeA function during intracellular development.

The phosphatidylinositol derivative PI3P is a key second messenger that regulates multiple cellular processes, particularly membrane trafficking and autophagy. We report here that PikA, a T4SS substrate of R. rickettsii , functions as a PI-3 kinase that catalyzes the production of PI3P to promote autophagy influx. PikA achieves this by recruiting Beclin 1 through direct protein-protein interactions. The expression of the dual-specific PI phosphatase Myotubularin counteracted the effects of PikA and inhibited intracellular R . rickettsii replication. Our results reveal that the modulation of PI metabolism by a bacterial PI-3 kinase is critical for R . rickettsii virulence, and this pathway may provide potential target for the development of therapeutics against infections caused by this pathogen.

Edwardsiella piscicida causes severe hemorrhagic septicemia in marine and freshwater fish worldwide, resulting in significant economic losses for the aquaculture industry (K. Y. Leung, Q. Wang, Z. Yang, and B. A. Siame, Virulence 10:555–567, 2019, https://doi.org/10.1080/21505594.2019.1621648 ). Our previous research identified a novel type III secretion system effector, EseQ, in E. piscicida whose function remains to be elucidated. In this work, we showed that EseQ binds to tubulin and GEF-H1 and destabilizes microtubules. GEF-H1 released from microtubules activates the RhoA-ROCK-MLCII signaling pathway, leading to stress fiber formation in epithelial cells. EseQ deforms the epithelial barrier and promotes E. piscicida ’s invasion in a stress fiber-dependent manner. This work contributes to the understanding of the mechanism by which E. piscicida invades host cells.

Life-threatening systemic infections often occur due to the translocation of pathogens across the gut barrier and into the bloodstream. While the microbial and host mechanisms permitting bacterial gut translocation are well characterized, these mechanisms are still unclear for fungal pathogens such as Candida albicans , a leading cause of nosocomial fungal bloodstream infections. In this study, we dissected the cellular mechanisms of translocation of C. albicans across intestinal epithelia in vitro and identified fungal genes associated with this process. We show that fungal translocation is a dynamic process initiated by invasion and followed by cellular damage and loss of epithelial integrity. A screen of >2,000 C. albicans deletion mutants identified genes required for cellular damage of and translocation across enterocytes. Correlation analysis suggests that hypha formation, barrier damage above a minimum threshold level, and a decreased epithelial integrity are required for efficient fungal translocation. Translocation occurs predominantly via a transcellular route, which is associated with fungus-induced necrotic epithelial damage, but not apoptotic cell death. The cytolytic peptide toxin of C. albicans , candidalysin, was found to be essential for damage of enterocytes and was a key factor in subsequent fungal translocation, suggesting that transcellular translocation of C. albicans through intestinal layers is mediated by candidalysin. However, fungal invasion and low-level translocation can also occur via non-transcellular routes in a candidalysin-independent manner. This is the first study showing translocation of a human-pathogenic fungus across the intestinal barrier being mediated by a peptide toxin. IMPORTANCE Candida albicans , usually a harmless fungus colonizing human mucosae, can cause lethal bloodstream infections when it manages to translocate across the intestinal epithelium. This can result from antibiotic treatment, immune dysfunction, or intestinal damage (e.g., during surgery). However, fungal processes may also contribute. In this study, we investigated the translocation process of C. albicans using in vitro cell culture models. Translocation occurs as a stepwise process starting with invasion, followed by epithelial damage and loss of epithelial integrity. The ability to secrete candidalysin, a peptide toxin deriving from the hyphal protein Ece1, is key: C. albicans hyphae, secreting candidalysin, take advantage of a necrotic weakened epithelium to translocate through the intestinal layer. Candida albicans , usually a harmless fungus colonizing human mucosae, can cause lethal bloodstream infections when it manages to translocate across the intestinal epithelium. This can result from antibiotic treatment, immune dysfunction, or intestinal damage (e.g., during surgery). However, fungal processes may also contribute. In this study, we investigated the translocation process of C. albicans using in vitro cell culture models. Translocation occurs as a stepwise process starting with invasion, followed by epithelial damage and loss of epithelial integrity. The ability to secrete candidalysin, a peptide toxin deriving from the hyphal protein Ece1, is key: C. albicans hyphae, secreting candidalysin, take advantage of a necrotic weakened epithelium to translocate through the intestinal layer.

Trichomonas vaginalis , the most common non-viral sexually transmitted parasite, relies on adherence to host epithelial cells to establish infection. Our previous work highlighted the importance of N6-methyladenine (6mA) DNA methylation in the regulation of transcription and three-dimensional chromatin structure. Now, our study integrates RNA-seq, MeDIP-seq, and assay for transposase-accessible chromatin sequencing data to reveal how 6mA and chromatin accessibility modulate gene expression during T. vaginalis interaction with human host cells. We identified over 3,600 differentially expressed genes upon parasite contact with prostate cells, including pathogenesis-related genes. Moreover, we identified transcriptionally active and repressive regions flanked by 6mA that remain largely stable during the process of host interaction. We mapped genome-wide chromatin accessibility and uncovered differentially accessible regions upon host cell contact associated with a subset of genes involved in adhesion. These results suggest that local chromatin accessibility has a major role in modulating gene expression of key virulence genes during host interaction.

Candida albicans is a common fungal pathogen that causes both mucosal infections, such as thrush, and life-threatening systemic diseases. A key step in infection is the fungus invading epithelial tissues and activating the host epidermal growth factor receptor (EGFR). We discovered that C. albicans alters how EGFR is regulated by inducing its ubiquitination, a modification that leads to receptor degradation. This process depends on two major fungal virulence factors: the adhesin Als3p and Ece1p, the polypeptide that contains the candidalysin toxin. The fungus also broadly increases protein ubiquitination in oral epithelial cells. In a mouse model of oral infection, loss of EGFR in epithelial tissues reduced disease severity, suggesting that the receptor helps the fungus establish infection. These findings reveal a previously unrecognized strategy by which C. albicans manipulates protein ubiquitination and regulation in epithelial cells, offering new insights into fungal pathogenesis and potential therapeutic approaches that target host pathways.

Leishmaniasis is a disease caused by parasites, transmitted by insects, that occurs worldwide. The parasite and parasite-infected cells release extracellular vesicles (EVs), which are involved in numerous biological processes. EVs secreted by modulate the host cell and, in turn, the immune response. In this review, we focused on two particular EV-related topics: (i) EVs as carriers of virulence factors and implications in parasite biology, and (ii) the effects of -derived EVs on the host's immune response.

The opportunistic pathogen Pseudomonas aeruginosa has gained precedence over the years due to its ability to develop resistance to existing antibiotics, thereby necessitating alternative strategies to understand and combat the bacterium. Our previous work identified the interaction between the bacterial lectin LecA and its host cell glycosphingolipid receptor globotriaosylceramide (Gb3) as a crucial step for the engulfment of P. aeruginosa via the lipid zipper mechanism. In this study, we define the LecA-associated host cell membrane domain by pull-down and mass spectrometry analysis. We unraveled a predilection of LecA for binding to saturated, long fatty acyl chain-containing Gb3 species in the extracellular membrane leaflet and an induction of dynamic phosphatidylinositol (3,4,5)-trisphosphate (PIP3) clusters at the intracellular leaflet co-localizing with sites of LecA binding. We found flotillins and the GPI-anchored protein CD59 not only to be an integral part of the LecA-interacting membrane domain, but also majorly influencing bacterial invasion as depletion of either of these host cell proteins resulted in about 50% reduced invasiveness of the P. aeruginosa strain PAO1. In summary, we report that the LecA-Gb3 interaction at the extracellular leaflet induces the formation of a plasma membrane domain enriched in saturated Gb3 species, CD59, PIP3 and flotillin thereby facilitating efficient uptake of PAO1.