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L. monocytogenes causes listeriosis, a foodborne disease that is particularly dangerous for immunocompromised individuals and fetuses. Several virulence factors of this bacterial pathogen belong to a family of leucine-rich repeat (LRR)-containing proteins called internalins. Among these, InlP is known for its role in placental infection. We report here a function of InlP in mammalian cell nucleus organization. We demonstrate that bacteria do not produce InlP under in vitro culture conditions. When ectopically expressed in human cells, InlP translocates into the nucleus and changes the morphology of nuclear speckles, which are membrane-less organelles storing splicing factors. Using yeast two-hybrid screen, immunoprecipitation and pull-down experiments, we identify the tumor suppressor and splicing factor RBM5 as a major nuclear target of InlP. InlP inhibits RBM5-induced cell death and stimulate the formation of RBM5-induced nuclear granules, where the SC35 speckle protein redistributes. Taken together, these results suggest that InlP acts as a nucleomodulin controlling compartmentalization and function of RBM5 in the nucleus and that L. monocytogenes has developed a mechanism to target the host cell splicing machinery.

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SummaryRecent studies have reported on the presence of bacterial RNA within or outside extracellular membrane vesicles, possibly as ribonucleoprotein complexes. Proteins that bind and stabilize bacterial RNAs in the extracellular environment have not been reported. Here, we show that the bacterial pathogenListeria monocytogenessecretes a small RNA binding protein that we named Zea. We show that Zea binds and stabilizes a subset ofL. monocytogenesRNAs causing their accumulation in the extracellular medium. Furthermore, Zea binds RIG-I, the vertebrate non-self-RNA innate immunity sensor and potentiates RIG-I-signaling leading to interferon β production. By performingin vivoinfection, we finally show that Zea modulatesL. monocytogenesvirulence. Together, this study reveals that bacterial extracellular RNAs and RNA binding proteins can affect the host-pathogen crosstalk.

Membrane fission is an essential cellular process by which continuous membranes split into separate parts. We have previously identified CtBP1-S/BARS (BARS) as a key component of a protein complex that is required for fission of several endomembranes, including basolateral post-Golgi transport carriers. Assembly of this complex occurs at the Golgi apparatus, where BARS binds to the phosphoinositide kinase PI4KIIIβ through a 14-3-3γ dimer, as well as to ARF and the PKD and PAK kinases. We now report that, when incorporated into this complex, BARS binds to and activates a trans-Golgi lysophosphatidic acid (LPA) acyltransferase type δ (LPAATδ) that converts LPA into phosphatidic acid (PA); and that this reaction is essential for fission of the carriers. LPA and PA have unique biophysical properties, and their interconversion might facilitate the fission process either directly or indirectly (via recruitment of proteins that bind to PA, including BARS itself)., CtBP1-S/BARS is required for fission of endomembrane compartments including the Golgi. Here the authors show that CtBP1-S/BARS activates a trans-Golgi lysophosphatidic acid acyltransferase that catalyses the production of phosphatidic acid and is required for fission of the post-Golgi carrier membrane.

Summary Mutations in mitochondrial genes impairing energy production cause mitochondrial diseases (MDs), and clinical studies have shown that MD patients are prone to bacterial infections. However, the relationship between mitochondrial (dys)function and infection remains largely unexplored, especially in epithelial cells, the first barrier to many pathogens. Here, we generate an epithelial cell model for one of the most common mitochondrial diseases, Leigh syndrome, by deleting surfeit locus protein 1 (SURF1), an assembly factor for respiratory chain complex IV. We use this genetic model and a complementary, nutrient-based approach to modulate mitochondrial respiration rates and show that impaired mitochondrial respiration favors entry of the human pathogen Listeria monocytogenes, a well-established bacterial infection model. Reversely, enhanced mitochondrial energy metabolism decreases infection efficiency. We further demonstrate that endocytic recycling is reduced in mitochondrial respiration-dependent cells, dampening L. monocytogenes infection by slowing the recycling of its host cell receptor c-Met, highlighting a previously undescribed role of mitochondrial respiration during infection., Graphical abstract, Highlights • Enhanced mitochondrial respiration decreases L. monocytogenes infection • Bacterial entry is affected by the host cell metabolism • Mitochondrial respiration restricts host cell receptor recycling and thus infection, Spier et al. show that the cellular energy metabolism affects infection of epithelial cells by L. monocytogenes. Mitochondrial respiration modulates L. monocytogenes entry by limiting endocytic recycling of receptors such as c-Met back to the plasma membrane, leading to decreased bacterial load in cells with high respiratory activity.

Mitochondrial function adapts to cellular demands and is affected by the ability of the organelle to undergo fusion and fission in response to physiological and non-physiological cues. We previously showed that infection with the human bacterial pathogenListeria monocytogeneselicits transient mitochondrial fission and a drop in mitochondrial-dependent energy production through a mechanism requiring the bacterial pore-forming toxin listeriolysin O (LLO). Here, we performed quantitative mitochondrial proteomics to search for host factors involved inL. monocytogenes-induced mitochondrial fission. We found that Mic10, a critical component of the mitochondrial contact site and cristae organizing system (MICOS) complex, is significantly enriched in mitochondria isolated from cells infected with wild-type but not with LLO-deficientL. monocytogenes. Increased mitochondrial Mic10 levels did not correlate with upregulated transcription, suggesting a post-transcriptional regulation. We showed that Mic10 is necessary forL. monocytogenes-induced mitochondrial network fragmentation, and that it contributes toL. monocytogenescellular infection independently of MICOS proteins Mic13, Mic26 and Mic27. Together,L. monocytogenesinfection allowed us to uncover a role for Mic10 in mitochondrial fission.ImportancePathogenic bacteria can target host cell organelles to take control of key cellular processes and promote their intracellular survival, growth, and persistence. Mitochondria are essential, highly dynamic organelles with pivotal roles in a wide variety of cell functions. Mitochondrial dynamics and function are intimately linked. Our previous research showed thatListeria monocytogenesinfection impairs mitochondrial function and triggers fission of the mitochondrial network at an early infection stage, in a process that is independent of the main mitochondrial fission protein Drp1. Here, we analyzed how mitochondrial proteins change in response toL. monocytogenesinfection and found that infection raises the levels of Mic10, a mitochondrial inner membrane protein involved in formation of cristae. We show that Mic10 is important forL. monocytogenes-dependent mitochondrial fission and infection of host cells. Our findings thus offer new insight into the mechanisms used byL. monocytogenesto hijack mitochondria to optimize host infection.