Critical Role of a Sheath Phosphorylation Site On the Assembly and Function of an Atypical Type VI Secretion System.

The bacterial pathogen possesses a noncanonical type VI secretion system (T6SS) that is required for phagosomal escape in infected macrophages. KCl stimulation has been previously used to trigger assembly and secretion of the T6SS in culture. By differential proteomics, we found here that the amounts of the T6SS proteins remained unchanged upon KCl stimulation, suggesting involvement of post-translational modifications in T6SS assembly.

Importance of Metabolic Adaptations in Pathogenesis.

is a highly infectious Gram-negative bacterium and the causative agent of the zoonotic disease tularemia. This bacterial pathogen can infect a broad variety of animal species and can be transmitted to humans in numerous ways with various clinical outcomes. Although, possesses the capacity to infect numerous mammalian cell types, the macrophage constitutes the main intracellular niche, used for bacterial dissemination.

Role of Glycosylation/Deglycolysation Processes in Pathogenesis.

is able to invade, survive and replicate inside a variety of cell types. However, preferentially enters host macrophages where it rapidly escapes to the cytosol to avoid phagosomal stresses and to multiply to high numbers. We previously showed that human monocyte infection by LVS triggered deglycosylation of the glutamine transporter SLC1A5.

Host glycosylation pathways and the unfolded protein response contribute to the infection by Francisella.

Protein glycosylation processes play a crucial role in most physiological functions, including cell signalling, cellular differentiation and adhesion. We previously demonstrated that rapid deglycosylation of membrane proteins was specifically triggered after infection of human macrophages by the bacterial pathogen Francisella tularensis. Using a glycan processing gene microarray, we found here that Francisella infection modulated expression of numerous glycosidase and glycosyltransferase genes.

Gluconeogenesis, an essential metabolic pathway for pathogenic Francisella.

Intracellular multiplication and dissemination of the infectious bacterial pathogen Francisella tularensis implies the utilization of multiple host-derived nutrients. Here, we demonstrate that gluconeogenesis constitutes an essential metabolic pathway in Francisella pathogenesis. Indeed, inactivation of gene glpX, encoding the unique fructose 1,6-bisphosphatase of Francisella, severely impaired bacterial intracellular multiplication when cells were supplemented by gluconeogenic substrates such as glycerol or pyruvate.

The complex amino acid diet of Francisella in infected macrophages.

Francisella tularensis, the agent of the zoonotic disease tularemia, is a highly infectious bacterium for a large number of animal species and can be transmitted to humans by various means. The bacterium is able to infect a variety of cell types but replicates in mammalian hosts mainly in the cytosol of infected macrophages. In order to resist the stressful and nutrient-restricted intracellular environments, it encounters during its systemic dissemination, Francisella has developed dedicated stress resistance mechanisms and adapted its metabolic and nutritional needs.

Importance of host cell arginine uptake in Francisella phagosomal escape and ribosomal protein amounts.

Upon entry into mammalian host cells, the pathogenic bacterium Francisella must import host cell arginine to multiply actively in the host cytoplasm. We identified and functionally characterized an arginine transporter (hereafter designated ArgP) whose inactivation considerably delayed bacterial phagosomal escape and intracellular multiplication. Intramacrophagic growth of the ΔargP mutant was fully restored upon supplementation of the growth medium with excess arginine, in both F.

Importance of branched-chain amino acid utilization in Francisella intracellular adaptation.

Intracellular bacterial pathogens have adapted their metabolism to optimally utilize the nutrients available in infected host cells. We recently reported the identification of an asparagine transporter required specifically for cytosolic multiplication of Francisella. In the present work, we characterized a new member of the major super family (MSF) of transporters, involved in isoleucine uptake.

Detection of the interaction between host and bacterial proteins: eukaryotic nucleolin interacts with Francisella elongation factor Tu.

Dissecting the interaction between bacterial and host proteins is fundamental in understanding pathogenesis. It is also very helpful for exploring new therapeutic approaches, either preventive or curative. Here, we describe different techniques, which allowed us to detect new molecules involved in the binding and infection of the bacterium Francisella tularensis, on human cells.

Francisella tularensis intracellular survival: to eat or to die.

Francisella tularensis is a highly infectious facultative intracellular bacterium causing the zoonotic disease tularemia. Numerous attributes required for F. tularensis intracellular multiplication have been identified recently.

Glutamate utilization couples oxidative stress defense and the tricarboxylic acid cycle in Francisella phagosomal escape.

Intracellular bacterial pathogens have developed a variety of strategies to avoid degradation by the host innate immune defense mechanisms triggered upon phagocytocis. Upon infection of mammalian host cells, the intracellular pathogen Francisella replicates exclusively in the cytosolic compartment. Hence, its ability to escape rapidly from the phagosomal compartment is critical for its pathogenicity.

Asparagine assimilation is critical for intracellular replication and dissemination of Francisella.

In order to develop a successful infectious cycle, intracellular bacterial pathogens must be able to adapt their metabolism to optimally utilize the nutrients available in the cellular compartments and tissues where they reside. Francisella tularensis, the agent of the zoonotic disease tularaemia, is a highly infectious bacterium for a large number of animal species. This bacterium replicates in its mammalian hosts mainly in the cytosol of infected macrophages.

Proteins involved in Francisella tularensis survival and replication inside macrophages.

Francisella tularensis, the etiological agent of tularemia, is a member of the γ-proteobacteria class of Gram-negative bacteria. This highly virulent bacterium can infect a large range of mammalian species and has been recognized as a human pathogen for a century. F.

Francisella tularensis regulates the expression of the amino acid transporter SLC1A5 in infected THP-1 human monocytes.

Francisella tularensis, a Gram-negative bacterium that causes the disease tularemia in a large number of animal species, is thought to reside preferentially within macrophages in vivo. F. tularensis has developed mechanisms to rapidly escape from the phagosome into the cytoplasm of infected cells, a habitat with a rich supply of nutrients, ideal for multiplication.

Identification of a putative chaperone involved in stress resistance and virulence in Francisella tularensis.

Francisella tularensis is a highly infectious bacterium causing the zoonotic disease tularemia. This facultative intracellular bacterium replicates in vivo mainly inside macrophages and therefore has developed strategies to resist this stressful environment. Here, we identified a novel genetic locus that is important for stress resistance and intracellular survival of F.

Nucleolin, a shuttle protein promoting infection of human monocytes by Francisella tularensis.

Background: Francisella tularensis is a highly virulent facultative intracellular bacterium, disseminating in vivo mainly within host mononuclear phagocytes. After entry into macrophages, F. tularensis initially resides in a phagosomal compartment, whose maturation is then arrested.

Loops and networks in control of Francisella tularensis virulence.

Francisella tularensis is a highly infectious, Gram-negative bacterium responsible for the disease tularemia in a broad variety of animals, including humans. F. tularensis intracellular multiplication occurs mainly in macrophages.

Pivotal role of the Francisella tularensis heat-shock sigma factor RpoH.

Francisella tularensis is a highly infectious pathogen that infects animals and humans to cause the disease tularemia. The primary targets of this bacterium are macrophages, in which it replicates in the cytoplasm after escaping the initial phagosomal compartment. The ability to replicate within macrophages relies on the tightly regulated expression of a series of genes.

A novel receptor - ligand pathway for entry of Francisella tularensis in monocyte-like THP-1 cells: interaction between surface nucleolin and bacterial elongation factor Tu.

Background: Francisella tularensis, the causative agent of tularemia, is one of the most infectious human bacterial pathogens. It is phagocytosed by immune cells, such as monocytes and macrophages. The precise mechanisms that initiate bacterial uptake have not yet been elucidated.

The heat-shock protein ClpB of Francisella tularensis is involved in stress tolerance and is required for multiplication in target organs of infected mice.

Intracellular bacterial pathogens generally express chaperones such as Hsp100s during multiplication in host cells, allowing them to survive potentially hostile conditions. Francisella tularensis is a highly infectious bacterium causing the zoonotic disease tularaemia. The ability of F.

Infection of human B lymphoma cells by Mycoplasma fermentans induces interaction of its elongation factor with the intracytoplasmic domain of Epstein-Barr virus receptor (gp140, EBV/C3dR, CR2, CD21).

Human cell lines are often infected by mycoplama strains. We have demonstrated that when infected by Mycoplasma fermentans, human B lymphoma cell proliferation increased strongly. These infected B cells expressed a p45 kDa protein which interacted with the intracellular domain of CD21, the EBV/C3d receptor.

RB18A enhances expression of mutant p53 protein in human cells.

RB18A (TRAP220/DRIP205) is a cofactor of transcription. We herein demonstrated that RB18A downregulated p53 and upregulated MDM2 promoters. These RB18A regulations, not modified by p53wt expression, were inhibited by mutant p53 (p53mut) expression, which directly interacts with RB18A D5 domain.

Activation of Epstein-Barr virus/C3d receptor (gp140, CR2, CD21) on human cell surface triggers pp60src and Akt-GSK3 activities upstream and downstream to PI 3-kinase, respectively.

We previously demonstrated that CR2 activation on human B lymphocyte surface specifically triggered tyrosine phosphorylation of the 95-kDa nucleolin, this leading to its binding on SH2 domains of p85 sub-unit of PI 3-kinase and to activation of this enzyme. The specificity of CR2 pathway was clearly demonstrated as neither CD19 nor BCR could induce tyrosine phosphorylation of nucleolin in normal B lymphocytes. These data led us to investigate herein additional molecular events, which were triggered by CR2 activation, upstream and downstream to PI 3-kinase activation.

RB18A regulates p53-dependent apoptosis.

We previously demonstrated that RB18A, a member of TRAP220/DRIP205/PBP family, in vivo acted as a cofactor of transcription by differently regulating p53wt transactivating activity on physiological promoters. Using p53-negative cells transfected with different constructs, we herein demonstrated that RB18A down-regulated p53wt-dependent apoptosis. This biological regulation was due to a specific diminution of p53wt protein level, as level of p53mut and GAPDH proteins was not modified.