Biology subjects

Raykov, L.

Publications and source records attributed to Raykov, L..

5 recordsLinked to original sources

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↗

bioRxiv2026

Intracellular compartmentalization shapes lipid access and metabolic fitness of mycobacteria

Intracellular mycobacteria encounter distinct metabolic environments as they transition between vacuolar and cytosolic compartments within host cells, yet how nutrient access is shaped by this compartmentalization remains poorly understood. Here, we use Mycobacterium marinum fatty acyl- CoA ligase 6 (FACL6) as a functional entry point to examine how lipid acquisition and processing are coordinated during intracellular infection. By combining host and bacterial genetic perturbations with dual RNA-sequencing and high-resolution imaging in genetically tractable amoebal infection models, and validating key phenotypes in mammalian cells, we show that lipid metabolic programs in intracellular mycobacteria are tightly linked to subcellular localization. Sterol utilization and neutral lipid storage are preferentially engaged during the intravacuolar phase, whereas cytosolic exposure is associated with reduced lipid accumulation. Deletion of facl6 disrupts this coordinated scenario, resulting in altered bacterial cell envelope architecture, premature membrane damage, defective neutral lipid storage, and reduced intracellular fitness despite enhanced cytosolic access. Together, these findings reveal that loss of FACL6 causes intrinsic defects in lipid handling and highlight how compartment-specific lipid environments shape the outcome of mycobacterial infection. TeaserLoss of FACL6 reveals how intracellular compartmentalization shapes mycobacterial lipid metabolism

cell biology↗

bioRxiv2025

Mycobacterial surface shedding drives bystander cells response during early intracellular infection

Mycobacteria possess a complex cell envelope whose outermost layer plays an underexplored role in host-pathogen interactions. Using Dictyostelium discoideum as a model host phagocyte, we show that Mycobacterium marinum rapidly sheds its envelope components, including surface proteins, carbohydrates, and virulence-associated lipids, within minutes of uptake. Shed material is actively trafficking within host endocytic pathways and disseminates to neighboring bystander cells, where it accumulates and triggers several responses. Notably, bystander cells exposed to shed material exhibit a transient delay in G1/S cell cycle progression, an activation of membrane damage-response pathways, and an enhanced resistance to subsequent mycobacterial infection. These phenotypes are recapitulated by infection-free conditioning with purified envelope extracts, demonstrating that superficial components of the envelope alone are sufficient to modulate host cell responses. Moreover, this priming effect is independent of bacterial viability or the Esx-1 secretion systems, underscoring the intrinsic immunomodulatory capacity of the envelope. Interestingly, bacteria that lose their outer layer are more frequently ubiquitinated, suggesting that host-driven stripping exposes molecules that are recognized by cytosolic sensors to mount a cell-autonomous defense. Together, our findings reveal that mycobacterial envelope shedding is a widespread, early event during intracellular infection that impacts both infected and bystander cells. These findings suggest that mycobacterial outermost envelope components can influence host cell physiology and contribute to early innate immune modulation, with implications for understanding the initial determinants of infection outcomes.

microbiology↗

bioRxiv2024

Inter-kingdom signaling by the Legionella autoinducer LAI-1 involves the antimicrobial guanylate binding protein GBP

The causative agent of Legionnaires disease, Legionella pneumophila, is an amoebae-resistant environmental bacterium, which replicates intracellularly in a distinct compartment, the "Legionella-containing vacuole" (LCV). L. pneumophila employs the -hydroxyketone compound LAI-1 (Legionella autoinducer-1) for intra-species and inter-kingdom signaling. LAI-1 promotes intracellular replication and inhibits the migration of mammalian cells and Dictyostelium discoideum. In this study, we revealed that LAI-1 and "clickable" azido-LAI-1 derivatives inhibit the migration of D. discoideum and localize to LCVs. Azido-LAI-1 colocalizes with the LCV markers calnexin, P4C, and AmtA, but not with mitochondrial or lipid droplet markers. Intriguingly, LAI-1 dependent inhibition of D. discoideum migration involves the single guanylate-binding protein (GBP), a member of the GBP family of large GTPases, which in metazoan organisms promote cell autonomous immunity. D. discoideum lacking GBP ({Delta}gnbp) allows more efficient intracellular replication of L. pneumophila, without apparently compromising LCV remodeling or integrity, and GBP-GFP localizes to the ER at LCV-ER membrane contact sites (MCS). However, the peri-LCV localization of LAI-1 and GBP is not mutually dependent. Synthetic LAI-1 inhibits the expansion/remodeling of LCVs (but not vacuoles harboring avirulent L. pneumophila) in a GBP-dependent manner. Taken together, the work shows that LAI-1 localizes to LCVs, and LAI-1-dependent inter-kingdom signaling involves D. discoideum GBP, which localizes to LCV-ER MCS and acts as an antimicrobial factor by restricting the intracellular growth of L. pneumophila. Author SummarySmall molecule inter-kingdom signaling between pathogens and host cells represents a crucial but only partly understood aspect of microbial virulence. The amoeba-resistant opportunistic pathogen Legionella pneumophila employs the compound LAI-1 (Legionella autoinducer-1) for intra-species and inter-kingdom signaling. In metazoan cells, the conserved and wide-spread family of guanylate-binding protein (GBP) large GTPases usually comprises several distinct paralogues, which are implicated in pathogen detection, inflammation, cell death pathways, and cell autonomous immunity. In the social amoeba Dictyostelium discoideum, only a single GBP gene of unknown function is present. Using approaches from organic chemistry, genetics, cell biology and infection biology, we reveal that GBP is involved in the inhibition of D. discoideum migration and pathogen vacuole expansion/remodeling by LAI-1 as well as in intracellular growth of L. pneumophila. This study provides a novel link between small molecule inter-kingdom signaling and GBP-dependent cell autonomous immunity.

microbiology↗

bioRxiv2021

The Dictyostelium discoideum E3 ubiquitin ligase TrafE coordinates endolysosomal damage response and cell-autonomous immunity to Mycobacterium marinum.

Cells are perpetually challenged by pathogens, protein aggregates or chemicals, that induce plasma membrane or endolysosomal compartments damage, recognised as severe stress and controlled downstream by the endosomal sorting complex required for transport (ESCRT) and the autophagy machineries that are recruited to damaged membranes to either repair or to remove membrane remnants. Yet little is known about the upstream endolysosomal damage response (ELDR) factors that sense damage and lead to extensive tagging of the damaged organelles with signals, such as K63-polyubiquitin, required for the recruitment of ELDR components. To explore ELDR key factors responsible for detection and marking of damaged compartments we use the professional phagocyte Dictyostelium discoideum. We found an evolutionary conserved E3-ligase, TrafE, that is robustly recruited to intracellular compartments disrupted after infection with Mycobacterium marinum or after sterile damage caused by chemical compounds. TrafE acts at the intersection of ESCRT and autophagy pathways and plays a key role in functional recruitment of the ESCRT subunits ALIX, Vps32 and Vps4 to damage sites or maturing autophagosomes. Importantly, we show that the absence of TrafE severely compromises the xenophagy restriction of bacteria as well as ESCRT-mediated and autophagy-mediated ELDR, resulting in early cell death.

microbiology↗