Biomedical subjects

P Cossart

Publications and source records attributed to P Cossart.

At least 37 records · Page 2Linked to original sources

PubMed2000

gC1q-R/p32, a C1q-binding protein, is a receptor for the InlB invasion protein of Listeria monocytogenes.

InlB is a Listeria monocytogenes protein that promotes entry of the bacterium into mammalian cells by stimulating tyrosine phosphorylation of the adaptor proteins Gab1, Cbl and Shc, and activation of phosphatidyl- inositol (PI) 3-kinase. Using affinity chromatography and enzyme-linked immunosorbent assay, we demonstrate a direct interaction between InlB and the mammalian protein gC1q-R, the receptor of the globular part of the complement component C1q. Soluble C1q or anti-gC1q-R antibodies impair InlB-mediated entry. Transient transfection of GPC16 cells, which are non-permissive to InlB-mediated entry, with a plasmid-expressing human gC1q-R promotes entry of InlB-coated beads. Furthermore, several experiments indicate that membrane recruitment and activation of PI 3-kinase involve an InlB-gC1q-R interaction and that gC1q-R associates with Gab1 upon stimulation of Vero cells with InlB. Thus, gC1q-R constitutes a cellular receptor involved in InlB-mediated activation of PI 3-kinase and tyrosine phosphorylation of the adaptor protein Gab1. After E-cadherin, the receptor for internalin, gC1q-R is the second identified mammalian receptor promoting entry of L. monocytogenes into mammalian cells.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Listeria monocytogenes ActA protein interacts with phosphatidylinositol 4,5-bisphosphate in vitro.

The N-terminal region of the Listeria monocytogenes ActA protein, in conjunction with host cell factors, is sufficient for actin polymerization at the bacterial surface. Previous data suggested that ActA could protect barbed ends from capping proteins. We tested this hypothesis by actin polymerization experiments in the presence of the ActA N-terminal fragment and capping protein. ActA does not protect barbed ends from capping protein. In contrast, this polypeptide prevents PIP(2) from inhibiting the capping activity of capping protein. Gel filtration and tryptophan fluorescence experiments showed that the purified ActA N-terminal fragment binds to PIP(2) and PIP, defining phosphoinositides as novels ligands for this functional domain of ActA. Phosphoinositide binding to the N-terminal region of ActA may induce conformational changes in ActA and/or facilitate binding of other cell components, important for ActA-induced actin polymerization.

Actin Depolymerizing Factors↗

PubMed2000

Interactions between Listeria monocytogenes and host mammalian cells.

Bacterial pathogens have developed a variety of strategies to induce their own internalization into mammalian cells which are normally nonphagocytic. The Gram-positive bacterium Listeria monocytogenes enters into many cultured cell types using two bacterial surface proteins, InlA (internalin) and InlB. In both cases, entry takes place after engagement of a receptor and induction of a series of signaling events.

Animals↗

PubMed2000

A novel function of InIB from Listeria monocytogenes: activation of NF-kappaB in J774 macrophages.

Listeria monocytogenes causes a pro-inflammatory response on adhesion to macrophages. Upregulation of inflammation genes involves the transcription factor NF-kappaB. Several components of L. monocytogenes, including lipoteichoic acid (LTA), phospholipases and listeriolysin O (LLO), have since been shown to mediate NF-kappaB activation. Here, we report that purified recombinant InlB, but not internalin (InlA), is a potent activator of NF-kappaB in the mouse macrophage-like cell line J774. Expression of InlB in Listeria innocua enhances its ability to activate NF-kappaB, while deletion of InlB from L. monocytogenes marginally decreases its effect on NF-kappaB, possibly because of the presence of NF-kappaB activators such as LTA and LLO. The effect correlates with the rapid degradation of IkappaBalpha, a sustained degradation of IkappaBbeta and increases in tumour necrosis factor alpha (TNF-alpha) and interleukin (IL) 6 production, two cytokines controlled by NF-kappaB. Using a series of anti-InlB monoclonal antibodies and domains of InlB, NF-kappaB activation was shown to be dependent upon the N-terminal 213-amino-acid leucine-rich repeat (LRR) domain of InlB, recently demonstrated to be responsible for InlB-mediated L. monocytogenes invasion and phosphoinositide-3 (PI-3) kinase activation. The effect of InlB was blocked by PI-3 kinase inhibitors, indicating the involvement of PI-3 kinase in this response. This report thus illustrates that InlB not only promotes invasion, but also contributes to the macrophage pro-inflammatory response.

Animals↗

PubMed2000

Actin-based motility of pathogens: the Arp2/3 complex is a central player.

Bacterial actin-based motility has provided cell biologists with tools that led to the recent discovery that, in many forms of actin-based motilities, a key player is a protein complex named the Arp2/3 complex. The Arp2/3 complex is evolutionally conserved and made up of seven polypeptides involved in both actin filament nucleation and organization. Interestingly, this complex is inactive by itself and recent work has highlighted the fact that its activation is achieved differently in the different types of actin-based motilities, including the well-known examples of Listeria and Shigella motilities. Proteins of the WASP family and small G-proteins are involved in most cases. It is interesting that bacteria bypass or mimic some of the events occurring in eukaryotic systems. The Shigella protein IcsA recruits N-WASP and activates it in a Cdc42-like fashion. This activation leads to Arp2/3 complex recruitment, activation of the complex and ultimately actin polymerization and movement. The Listeria ActA protein activates Arp2/3 directly and, thus, seems to mimic proteins of the WASP family. A breakthrough in the field is the recent reconstitution of the actin-based motilities of Listeria and N-WASP-coated E. coli (IcsA) using a restricted number of purified cellular proteins including F-actin, the Arp2/3 complex, actin depolymerizing factor (ADF or cofilin) and capping protein. The movement was more effective upon addition of profilin, alpha-actinin and VASP (for Listeria). Bacterial actin-based motility is now one of the best-documented examples of the exploitation of mammalian cell machineries by bacterial pathogens.

Actin-Related Protein 2↗

PubMed2000

The invasion protein InIB from Listeria monocytogenes activates PLC-gamma1 downstream from PI 3-kinase.

Entry of the bacterial pathogen Listeria monocytogenes into non-phagocytic mammalian cells is mainly mediated by the InlB protein. Here we show that in the human epithelial cell line HEp-2, the invasion protein InlB activates sequentially a p85beta-p110 class I(A) PI 3-kinase and the phospholipase C-gamma1 (PLC-gamma1) without detectable tyrosine phosphorylation of PLC-gamma1. Purified InlB stimulates association of PLC-gamma1 with one or more tyrosine-phosphorylated proteins, followed by a transient increase in intracellular inositol 1,4,5-trisphosphate (IP3) levels and a release of intracellular Ca2+ in a PI 3-kinase-dependent manner. Infection of HEp-2 cells with wild-type L. monocytogenes bacteria also induces association of PLC-gamma1 with phosphotyrosyl proteins. This interaction is undetectable upon infection with a deltainlB mutant revealing an InlB specific signal. Interestingly, pharmacological or genetic inactivation of PLC-gamma1 does not significantly affect InlB-mediated bacterial uptake, suggesting that InlB-mediated PLC-gamma1 activation and calcium mobilization are involved in post-internalization steps.

Bacterial Proteins↗

PubMed1999

Cutting edge: paradigm revisited: antibody provides resistance to Listeria infection.

Listeriolysin O (LLO) is a secreted pore-forming toxin of the facultative intracellular bacterium Listeria monocytogenes. We assessed the ability of a murine anti-LLO mAb to affect the course of infection in mice challenged with Listeria. This mAb was previously shown to be capable of neutralizing LLO-mediated pore formation in vitro, and here we show that the passive administration of this Ab to mice before infection provides increased resistance. Mice treated with the mAb were protected from a lethal challenge with virulent Listeria and showed a significant reduction in Listeria burden during the first hours to days postinfection. These effects of the Ab were independent of host B or T cells, since treatment with the mAb provided enhanced resistance to SCID mice. The titer of anti-LLO Abs during the regular infection of mice with Listeria was found to be low to negative.

Animals↗

PubMed1999

A single amino acid in E-cadherin responsible for host specificity towards the human pathogen Listeria monocytogenes.

Human E-cadherin promotes entry of the bacterial pathogen Listeria monocytogenes into mammalian cells by interacting with internalin (InlA), a bacterial surface protein. Here we show that mouse E-cadherin, although very similar to human E-cadherin (85% identity), is not a receptor for internalin. By a series of domain-swapping and mutagenesis experiments, we identify Pro16 of E-cadherin as a residue critical for specificity: a Pro-->Glu substitution in human E-cadherin totally abrogates interaction, whereas a Glu-->Pro substitution in mouse E-cadherin results in a complete gain of function. A correlation between cell permissivity and the nature of residue 16 in E-cadherins from several species is established. The location of this key specificity residue in a region of E-cadherin not involved in cell-cell adhesion and the stringency of the interaction demonstrated here have important consequences not only for the understanding of internalin function but also for the choice of the animal model to be used to study human listeriosis: mouse, albeit previously widely used, and rat appear as inappropriate animal models to study all aspects of human listeriosis, as opposed to guinea-pig, which now stands as a small animal of choice for future in vivo studies.

Amino Acid Sequence↗

PubMed1999

The Listeria monocytogenes protein InlB is an agonist of mammalian phosphoinositide 3-kinase.

The Gram-positive pathogen Listeria monocytogenes induces its own internalization into some non-phagocytic mammalian cells by stimulating host tyrosine phosphorylation, phosphoinositide (PI) 3-kinase activity, and rearrangements in the actin cytoskeleton. Entry into many cultured cell lines is mediated by the bacterial protein InlB. Here we investigate the role of InlB in regulating mammalian signal transduction and cytoskeletal structure. Treatment of Vero cells with purified InlB caused rapid and transient increases in the lipid products of the PI 3-kinase p85-p110, tyrosine phosphorylation of the mammalian adaptor proteins Gab1, Cbl, and Shc, and association of these proteins with p85. InlB also stimulated large scale changes in the actin cytoskeleton (membrane ruffling), which were PI 3-kinase-dependent. These results identify InlB as the first reported non-mammalian agonist of PI 3-kinase and demonstrate similarities in the signal transduction events elicited by this bacterial protein and known agonists such as epidermal growth factor.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Characterisation of a new operon encoding a Zur-like protein and an associated ABC zinc permease in Listeria monocytogenes.

Metal ions uptake is mainly studied for iron, as it has often been implicated in bacterial virulence. Although Listeria monocytogenes virulence is expected to be controlled by the iron availability, little is known about such an uptake and its regulation. We describe the analysis of the first operon involved in metal ions uptake in L. monocytogenes. Its three ORFs encode respectively (1) an ABC protein, likely implicated in zinc uptake, (2) a hydrophobic membrane protein, generally associated with ABC proteins and (3) a ferric uptake regulator-like protein, that we named zinc uptake regulator, as it shows strong homologies with the zinc uptake regulator, a regulator of the zinc homeostasis in Bacillus subtilis. The expression of this operon is regulated by the zinc concentration.

Amino Acid Sequence↗

PubMed1999

Inducible recruitment of Cdc42 or WASP to a cell-surface receptor triggers actin polymerization and filopodium formation.

BACKGROUND: Cdc42, a GTP-binding protein of the Rho family, controls actin cytoskeletal organization and helps to generate actin-based protruding structures, such as filopodia. In vitro, Cdc42 regulates actin polymerization by facilitating the creation of free barbed ends - the more rapidly growing ends of actin filaments - and subsequent elongation at these ends. The Wiskott- Aldrich syndrome protein, WASP, which has a pleckstrin-homology domain and a Cdc42/Rac-binding motif, has been implicated in cell signaling and cytoskeleton reorganization. We have investigated the consequences of local recruitment of activated Cdc42 or WASP to the plasma membrane. RESULTS: We used an activated Cdc42 protein that could be recruited to an engineered membrane receptor by adding rapamycin as a bridge, and added antibody-coupled beads to aggregate these receptors. Inducible recruitment of Cdc42 to clusters of receptors stimulated actin polymerization, resulting in the formation of membrane protrusions. Cdc42-induced protrusions were enriched in the vasodilator-stimulated phosphoprotein VASP and the focal-adhesion-associated proteins zyxin and ezrin. The Cdc42 effector WASP could also induce the formation of protrusions, albeit of different morphology. CONCLUSIONS: This is the first demonstration that the local recruitment of activated Cdc42 or its downstream effector, WASP, to a membrane receptor in whole cells is sufficient to trigger actin polymerization that results in the formation of membrane protrusions. Our data suggest that Cdc42-induced actin-based protrusions result from the local and serial recruitment of cytoskeletal proteins including zyxin, VASP, and ezrin.

Actins↗

PubMed1999

Structure of the lnlB leucine-rich repeats, a domain that triggers host cell invasion by the bacterial pathogen L. monocytogenes.

The L. monocytogenes protein lnlB activates phosphoinositide 3-kinase and induces phagocytosis in several mammalian cell types. The 1.86 A resolution X-ray crystal structure of the leucine-rich repeat domain of lnlB that is both necessary and sufficient to induce phagocytosis is presented here. The structure supports a crucial role for calcium in host cell invasion by L. monocytogenes and supplies a rationale for its function. Calciums are bound to the protein in an unusually exposed manner that suggests that the metals may act as a bridge between lnlB and mammalian cell surface receptors. The structure also identifies surfaces on the curved and elongated molecule that may constitute additional interaction sites in forming a bacterial-mammalian signaling complex.

Amino Acid Sequence↗

PubMed1999

The 213-amino-acid leucine-rich repeat region of the listeria monocytogenes InlB protein is sufficient for entry into mammalian cells, stimulation of PI 3-kinase and membrane ruffling.

The Listeria monocytogenes InlB protein is a 630-amino-acid surface protein that mediates entry of the bacterium into a wide variety of cell types, including hepatocytes, fibroblasts and epithelial cells such as Vero, HEp-2 and HeLa cells. Invasion stimulates host proteins tyrosine phosphorylation, PI 3-kinase activity and rearrangements in the actin cytoskeleton. We previously showed that InlB is sufficient for entry of InlB-coated latex beads into cells and recent results indicate that purified InlB can stimulate PI 3-kinase activity and is thus the first bacterial agonist of this lipid kinase. In this study, we identified the region of InlB responsible for entry and stimulation of signal transduction events. Eight monoclonal antibodies directed against InlB were raised and, of those, five inhibited bacterial entry. These five antibodies recognized epitopes within the leucine-rich repeat (LRR) region and/or the inter-repeat (IR) region. InlB-staphylococcal protein A (SPA) fusion proteins and recombinant InlB derivatives were generated and tested for their capacity to mediate entry into cultured mammalian cells. All the InlB derivatives that carried the amino-terminal 213-amino-acid LRR region conferred invasiveness to the normally non-invasive bacterium L. innocua or to inert latex beads and the corresponding purified polypeptides inhibited bacterial entry. In addition, the 213-amino-acid LRR region was able to stimulate PI 3-kinase activity and changes in the actin cytoskeleton (membrane ruffling). These properties were not detected with purified internalin, another invasion protein of L. monocytogenes that displays LRRs similar to those of InlB. Taken together, these results show that the first 213 amino acids of InlB are critical for its specific properties.

Animals↗

PubMed1999

PrfA, the transcriptional activator of virulence genes, is upregulated during interaction of Listeria monocytogenes with mammalian cells and in eukaryotic cell extracts.

Most virulence genes of Listeria monocytogenes are activated by the transcriptional regulator PrfA. Previous studies have shown that environmental parameters, such as temperature, pH, stress conditions and medium composition, affect the expression of PrfA and PrfA-dependent proteins. In this report, we demonstrate a threefold increase in PrfA protein synthesis during infection of mammalian cells, which correlates with the increased activity of the plcA promoter, the major prfA promoter. Increased PrfA synthesis begins when L. monocytogenes adheres to host cells. In addition, we show that the observed induction of PrfA during the interaction of L. monocytogenes with mammalian cells can be reproduced in vitro using total cell extracts. Our data suggest a role for host proteinase K-sensitive protein(s) in PrfA upregulation.

Animals↗

PubMed1999

Interaction between the protein InlB of Listeria monocytogenes and lipoteichoic acid: a novel mechanism of protein association at the surface of gram-positive bacteria.

InlB is a Listeria monocytogenes protein that is sufficient to promote entry in a variety of mammalian cells. The last 232-amino-acid domain (Csa) of InlB has been shown to mediate attachment on the listerial surface, although its sequence does not suggest any known mechanism of association to the bacterial surface. InlB is present both on the bacterial surface and in culture supernatants. As has been recently demonstrated, both forms of InlB, soluble and surface-bound, can trigger signalling in host cells. To elucidate the specific role of each of the two forms, it was important to understand how InlB associates with the bacterial surface. Using microscopy, we find evidence that InlB is partially buried in the cell wall layer, and using fractionation experiments we demonstrate that InlB associates with the bacterial cytoplasmic membrane. Moreover, using purified lipoteichoic acid (LTA) and the three polypeptides InlB, Csa, or InlBDeltaCsa (InlB lacking the last 232 amino acids), we demonstrate that LTA is a ligand for the Csa domain of InlB. These results provide the first evidence of an interaction between lipoteichoic acids and a bacterial protein involved in adhesion and signalling, and highlight a new mechanism of protein association on the surface of Gram-positive bacteria.

Bacterial Proteins↗

PubMed1999

Cell wall teichoic acid glycosylation in Listeria monocytogenes serotype 4b requires gtcA, a novel, serogroup-specific gene.

We have identified a novel gene, gtcA, involved in the decoration of cell wall teichoic acid of Listeria monocytogenes serotype 4b with galactose and glucose. Insertional inactivation of gtcA brought about loss of reactivity with the serotype 4b-specific monoclonal antibody c74.22 and was accompanied by a complete lack of galactose and a marked reduction in the amounts of glucose on teichoic acid. Interestingly, the composition of membrane-associated lipoteichoic acid was not affected. Complementation of the mutants with the cloned gtcA in trans restored galactose and glucose on teichoic acid to wild-type levels. The complemented strains also recovered reactivity with c74.22. Within L. monocytogenes, sequences homologous to gtcA were found in all serogroup 4 isolates but not in strains of any other serotypes. In serotype 4b, gtcA appears to be the first member of a bicistronic operon which includes a gene with homology to Bacillus subtilis rpmE, encoding ribosomal protein L31. In contrast to gtcA, the latter gene appears conserved among all screened serotypes of L. monocytogenes.

Amino Acid Sequence↗

PubMed1999

A comparative study of the actin-based motilities of the pathogenic bacteria Listeria monocytogenes, Shigella flexneri and Rickettsia conorii.

Listeria monocytogenes, Shigella flexneri, and Rickettsia conorii are three bacterial pathogens that are able to polymerize actin into 'comet tail' structures and move within the cytosol of infected cells. The actin-based motilities of L. monocytogenes and S. flexneri are known to require the bacterial proteins ActA and IcsA, respectively, and several mammalian cytoskeleton proteins including the Arp2/3 complex and VASP (vasodilator-stimulated phosphoprotein) for L. monocytogenes and vinculin and N-WASP (the neural Wiskott-Aldrich syndrome protein) for S. flexneri. In contrast, little is known about the motility of R. conorii. In the present study, we have analysed the actin-based motility of this bacterium in comparison to that of L. monocytogenes and S. flexneri. Rickettsia moved at least three times more slowly than Listeria and Shigella in both infected cells and Xenopus laevis egg extracts. Decoration of actin with the S1 subfragment of myosin in infected cells showed that the comet tails of Rickettsia have a structure strikingly different from those of L. monocytogenes or S. flexneri. In Listeria and Shigella tails, actin filaments form a branching network while Rickettsia tails display longer and not cross-linked actin filaments. Immunofluorescence studies revealed that the two host proteins, VASP and (&agr;)-actinin colocalized with actin in the tails of Rickettsia but neither the Arp2/3 complex which we detected in the Shigella actin tails, nor N-WASP, were detected in Rickettsia actin tails. Taken together, these results suggest that R. conorii may use a different mechanism of actin polymerization.

Actins↗

PubMed1998

EVH1/WH1 domains of VASP and WASP proteins belong to a large family including Ran-binding domains of the RanBP1 family.

The two cytoskeletal proteins VASP and WASP and the protein Homer share a conserved domain, currently designated the WHI domain (WASP homology domain 1) or EVH1 domain (ENA/VASP homology domain 1), which could play an important role in various cellular events such as transport, folding of proteins, and signal transduction. We report here additional occurrences of this domain in Ran-binding proteins of the RanBP1 family and various others proteins, or putative proteins of eukaryotic organisms, suggesting that the EVH1/WH1 domain may be more widely used than originally thought.

Amino Acid Sequence↗