Biology subjects

Toinon, J.

Publications and source records attributed to Toinon, J..

3 recordsLinked to original sources

bioRxiv2026

Time-resolved transcriptomic profiling of Dictyostelium discoideum infection with Mycobacterium marinum reveals Atg9-dependent restriction via maintenance of vacuole integrity

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a major global health challenge, highlighting the need to better understand host mechanisms restricting mycobacteria infection. Mycobacterium marinum (Mm) shares key virulence mechanisms with Mtb and provides a suitable model for studying mycobacterial pathogenesis. Here, we used Dictyostelium discoideum (Dd), a genetically tractable phagocytic model with evolutionarily conserved pathways shared with mammalian macrophages, to investigate host responses to Mm infection. Time-resolved transcriptomic profiling across early, intermediate, and late stages of infection identified global infection-responsive genes, stage-specific pathways, and substantial conservation with transcriptional responses of human macrophages infected with Mtb. Autophagy and ESCRT pathways were dynamically regulated throughout infection, suggesting stage-specific roles in host defence. We focused on Atg9, an autophagy factor that was strongly induced during infection and recruited to damaged mycobacterium-containing vacuoles (MCVs). Atg9 promoted membrane damage control and maintained MCV integrity, thereby preventing premature bacteria escape to the cytosol of virulent Mm. Loss of Atg9 led to accumulation of MCV damage, accelerated escape to the cytosol, and enhanced intracellular bacteria growth, phenocopying atg1-deficient cells. Our findings further distinguish complementary host defence mechanisms acting at distinct stages of infection: Atg9-associated membrane repair, potentially involving ATG8ylation, limits vacuole damage and bacteria escape during early infection, whereas Atg9-dependent xenophagic restriction contributes to bacteria clearance at later stages. Together, these findings establish Dd as a powerful model for dissecting conserved host responses to mycobacteria and identify Atg9-dependent membrane protection as a key host resistance mechanism with potential relevance to TB pathogenesis and therapeutic intervention.

microbiology↗

bioRxiv2026

STAT transcription factors regulate host defences and vacuolar integrity during Mycobacterium marinum infection

Signal transducers and activators of transcription (STAT) are central regulators of cytokine-mediated immunity in metazoans, yet their ancestral functions prior to the emergence of interferon signalling remain poorly understood. Dictyostelium discoideum expresses four STAT-like factors that impact the intracellular fate of Mycobacterium marinum (Mm). Using dst knockout strains, we identify DstA and DstB as susceptibility factors, whereas DstC acts as a resistance factor, revealing a regulatory axis controlling the integrity of the Mm-containing vacuole (MCV). Despite the absence of canonical cytokine receptors and JAK kinases, DstA rapidly translocates to the nucleus in a damage-dependent manner, whereas DstB and DstC exhibit delayed cytosolic redistribution. DstA associates with VacA, a membrane microdomain component, regulates its transcription and accumulation at the MCV, while VacA acts as a cytoplasmic anchor that limits DstA nuclear translocation. Our findings establish STAT-like proteins as evolutionarily ancient regulators of vacuole integrity and host defence, providing new insights into the origins of STAT-mediated immune responses during mycobacterial infection.

microbiology↗

bioRxiv2022

A Legionella pneumophila effector impedes host gene silencing to promote virulence

RNA silencing is a gene silencing mechanism directed by small RNAs. Human miRNAs act as central regulators of host-bacteria interactions. However, it is unknown whether human pathogenic bacteria could impede RNA silencing to promote virulence. Here, we show that the Legionella pneumophila type IV-secreted effector LegK1 efficiently suppresses siRNA and miRNA activities in human cells. This effect depends on its known kinase activity, but also on its novel capacity, found here, to bind Argonaute (Ago) proteins. We further demonstrate that the ability of LegK1 to activate NF-{kappa}B signaling is required for RNA silencing suppression, establishing a link between effector-mediated NF-{kappa}B signaling and RNA silencing suppression. LegK1 also promotes L. pneumophila growth in both amoeba and human macrophages, supporting a role for this effector in virulence. Finally, we show that, in infected-macrophages, the latter activity relies, in part, on the genetic targeting of human Ago4. These findings indicate that a L. pneumophila effector has evolved to suppress RNA silencing to promote virulence. Significance StatementIt is now well established that mammalian viruses suppress RNAi to promote their replication in host cells. However, whether mammalian pathogenic bacteria use a similar virulence strategy remains unknown. Here, we show that the LegK1 effector from Legionella pneumophia, the causal agent of Legionnaires disease, efficiently suppresses RNAi in human cells. This effect depends on its ability to interact with Argonaute (Ago) proteins and to activate NF-{kappa}B signaling. In addition, LegK1 promotes virulence in infected-macrophages through the genetic targeting of human Ago4. Based on the lack of NF-{kappa}B-related factors in amoebae, and on the presence of canonical Ago proteins in these natural L. pneumophila hosts, we propose that the RNAi suppression activity of LegK1 represents its primary virulence function.

molecular biology↗