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Pascale Cossart

Publications and source records attributed to Pascale Cossart.

At least 55 records · Page 3Linked to original sources
PubMed2004

Exploitation of host cell cytoskeleton and signalling during Listeria monocytogenes entry into mammalian cells.

Deciphering how Listeria monocytogenes exploits the host cell machinery to invade mammalian cells during infection is a key issue for the understanding how this food-borne pathogen causes a pleiotropic disease ranging from gastro-enteritis to meningitis and abortions. Using multidisciplinary approaches, essentially combining bacterial genetics and cell biology, we have identified two bacterial proteins critical for entry into target cells, InlA and InlB. Their cellular ligands have been also identified: InlA interacts with the adhesion molecule E-cadherin, while InlB interacts with the receptor for the globular head of the complement factor C1q (gC1q-R), with the hepatocyte growth factor receptor (c-Met) and with glycosaminoglycans (including heparan sulphate). The dynamic interaction between these cellular receptors and the actin cytoskeleton is currently under investigation. Several intracellular molecules have been recognized as key effectors for Listeria entry into target cells, including catenins (implicated in the connection of E-cadherin to actin) and the actin depolymerising factor/cofilin (involved in the rearrangement of the cytoskeleton in the InlB-dependent internalisation pathway). At the organism level, species specificity has been discovered concerning the interaction between InlA and E-cadherin, leading to the generation of transgenic mice expressing the human E-cadherin, in which the critical role of InlA in the crossing of the intestinal barrier has been clearly determined. Listeria appears as an instrumental model for addressing critical questions concerning both the complex process of bacterial pathogenesis and also fundamental molecular processes, such as phagocytosis.

Actins↗
PubMed2004

Exploitation of host cell cytoskeleton and signalling during Listeria monocytogenes entry into mammalian cells.

Deciphering how Listeria monocytogenes exploits the host cell machinery to invade mammalian cells during infection isa key issue for the understanding how this food-borne pathogen causes a pleiotropic disease ranging from gastro-enteritis to meningitis and abortions. Using multidisciplinary approaches, essentially combining bacterial genetics and cell biology, we have identified two bacterial proteins critical for entry into target cells, InlA and InlB. Their cellular ligands have been also identified: InlA interacts with the adhesion molecule E-cadherin, while InlB interacts with the receptor for the globular head of the complement factor Clq (gClq-R), with the hepatocyte growth factor receptor (c-Met) and with glycosaminoglycans(including heparan sulphate). The dynamic interaction between these cellular receptors and the actin cytoskeleton is currently under investigation. Several intracellular molecules have been recognized as key effectors for Listeria entry into target cells,including catenins (implicated in the connection of E-cadherin to actin) and the actin depolymerising factor/cofilin (involved in the rearrangement of the cytoskeleton in the InlB-dependent internalisation pathway). At the organism level, species specificity has been discovered concerning the interaction between InlA and E-cadherin, leading to the generation of transgenic mice expressing the human E-cadherin, in which the critical role of InlA in the crossing of the intestinal barrier has been clearly determined. Listeria appears as an instrumental model for addressing critical questions concerning both the complex process of bacterial pathogenesis and also fundamental molecular processes, such as phagocytosis.

Animals↗
PubMed2004

Bacterial invasion: a new strategy to dominate cytoskeleton plasticity.

Some bacterial pathogens enter mammalian cells by injecting, directly into the host cytosol, proteins that trigger cytoskeletal rearrangements necessary for internalization. In the February 27 issue of Molecular Cell, McGhie et al. identify mechanisms by which the Salmonella protein SipA interferes with ADF/cofilin and gelsolin function. Thus Salmonella not only triggers actin polymerization but also counteracts the major F-actin destabilizing proteins.

Actin Depolymerizing Factors↗
PubMed2004

Subversion of phosphoinositide metabolism by intracellular bacterial pathogens.

Phosphoinositides are short-lived lipids, whose production at specific membrane locations in the cell enables the tightly controlled recruitment or activation of diverse cellular effectors involved in processes such as cell motility or phagocytosis. Bacterial pathogens have evolved molecular mechanisms to subvert phosphoinositide metabolism in host cells, promoting (or blocking) their internalization into target tissues, and/or modifying the maturation fate of their proliferating compartments within the intracellular environment.

1-Phosphatidylinositol 4-Kinase↗
PubMed2004

Auto, a surface associated autolysin of Listeria monocytogenes required for entry into eukaryotic cells and virulence.

Listeria monocytogenes is an opportunistic food-borne human and animal pathogen. Several surface proteins expressed by this intracellular pathogen are critical for the infectious process. By in silico analysis we compared the surface protein repertories of L. monocytogenes and of the non-pathogenic species Listeria innocua and identified a gene encoding a surface protein of L. monocytogenes absent in L. innocua. This gene that we named aut encodes a protein (Auto) of 572 amino acids containing a signal sequence, a N-terminal autolysin domain and a C-terminal cell wall-anchoring domain made up of four GW modules. We show here that the aut gene is expressed independently of the virulence gene regulator PrfA and encodes a surface protein with an autolytic activity. We provide evidence that Auto is required for entry of L. monocytogenes into cultured non-phagocytic eukaryotic cells. The low invasiveness of an aut deletion mutant correlates with its reduced virulence following intravenous inoculation of mice and oral infection of guinea pigs. During infection, the autolytic activity of Auto may also be critical. Auto appears thus as a novel type of L. monocytogenes virulence factor.

Amino Acid Sequence↗
PubMed2004

New aspects regarding evolution and virulence of Listeria monocytogenes revealed by comparative genomics and DNA arrays.

Listeria monocytogenes is a food-borne bacterial pathogen that causes a wide spectrum of diseases, such as meningitis, septicemia, abortion, and gastroenteritis, in humans and animals. Among the 13 L. monocytogenes serovars described, invasive disease is mostly associated with serovar 4b strains. To investigate the genetic diversity of L. monocytogenes strains with different virulence potentials, we partially sequenced an epidemic serovar 4b strain and compared it with the complete sequence of the nonepidemic L. monocytogenes EGDe serovar 1/2a strain. We identified an unexpected genetic divergence between the two strains, as about 8% of the sequences were serovar 4b specific. These sequences included seven genes coding for surface proteins, two of which belong to the internalin family, and three genes coding for transcriptional regulators, all of which might be important in different steps of the infectious process. Based on the sequence information, we then characterized the gene content of 113 Listeria strains by using a newly designed Listeria array containing the "flexible" part of the sequenced Listeria genomes. Hybridization results showed that all of the previously identified virulence factors of L. monocytogenes were present in the 93 L. monocytogenes strains tested. However, distinct patterns of the presence or absence of other genes were identified among the different L. monocytogenes serovars and Listeria species. These results allow new insights into the evolution of L. monocytogenes, suggesting that early divergence of the ancestral L. monocytogenes serovar 1/2c strains from the serovar 1/2b strains led to two major phylogenetic lineages, one of them including the serogroup 4 strains, which branched off the serovar 1/2b ancestral lineage, leading (mostly by gene loss) to the species Listeria innocua. The identification of 30 L. monocytogenes-specific and several serovar-specific marker genes, such as three L. monocytogenes serovar 4b-specific surface protein-coding genes, should prove powerful for the rapid tracing of listeriosis outbreaks, but it also represents a fundamental basis for the functional study of virulence differences between L. monocytogenes strains.

Biological Evolution↗
PubMed2004

Sequence and binding activity of the autolysin-adhesin Ami from epidemic Listeria monocytogenes 4b.

Ami is an autolytic amidase from Listeria monocytogenes that is targeted to the bacterial surface via its C-terminal cell wall anchoring (CWA) domain. We recently showed that the CWA domain from Ami of L. monocytogenes EGD (serovar 1/2a) (Ami 1/2a) mediated bacterial binding to mammalian cells. Here we studied the sequence and binding properties of Ami from CHUT 82337 (serovar 4b) (Ami 4b). The Ami 4b polypeptide is predicted to be 770 amino acids long (compared with the 917 amino acids of Ami 1/2a from EGD). Ami 1/2a and Ami 4b are almost identical in the N-terminal enzymatic domain (approximately 98% amino acid identity), but the sequence is poorly conserved in the C-terminal CWA domain, with only approximately 54% amino acid identity and eight GW modules in Ami 1/2a compared with six GW modules in Ami 4b. The purified Ami 4b CWA domain efficiently bound serovar 4b bacterial cells and only poorly bound serovar 1/2a bacterial cells. The Ami 4b CWA domain was also significantly less able to bind Hep-G2 human hepatocytic cells than the Ami 1/2a CWA domain. We sequenced the ami regions encoding CWA domains of reference strains belonging to the 12 L. monocytogenes serovars. The phylogenic tree constructed from the sequences yielded a binary division into group I (serovars 1/2a, 1/2b, 1/2c, 3a, 3b, 3c, and 7) and group II (serovars 4a, 4b, 4c, 4d, and 4e). This is the first direct evidence of divergence between serovars 1/2a and 4b in a gene involved in the adhesion of L. monocytogenes to mammalian cells, as well as the first demonstration of allelic polymorphism correlated with the somatic antigen in this species.

Adhesins, Bacterial↗
PubMed2004

Sortase B, a new class of sortase in Listeria monocytogenes.

Sortases are transamidases that covalently link proteins to the peptidoglycan of gram-positive bacteria. The genome of the pathogenic bacterium Listeria monocytogenes encodes two sortases genes, srtA and srtB. The srtA gene product anchors internalin and some other LPXTG-containing proteins to the listerial surface. Here, we focus on the role of the second sortase, SrtB. Whereas SrtA acts on most of the proteins in the peptidoglycan fraction, SrtB appears to target minor amounts of surface polypeptides. We identified one of the SrtB-anchored proteins as the virulence factor SvpA, a surface-exposed protein which does not contain the LPXTG motif. Therefore, as in Staphylococcus aureus, the listerial SrtB represents a second class of sortase in L. monocytogenes, involved in the attachment of a subset of proteins to the cell wall, most likely by recognizing an NXZTN sorting motif. The DeltasrtB mutant strain does not have defects in bacterial entry, growth, or motility in tissue-cultured cells and does not show attenuated virulence in mice. SrtB-mediated anchoring could therefore be required to anchor surface proteins involved in the adaptation of this microorganism to different environmental conditions.

Amino Acid Sequence↗
PubMed2004

Molecular determinants of Listeria monocytogenes virulence.

Listeria monocytogenes is the etiological agent of listeriosis, a severe human foodborne infection characterized by gastroenteritis, meningitis, encephalitis, abortions, and perinatal infections. This gram-positive bacterium is a facultative intracellular pathogen that induces its own uptake into nonphagocytic cells and spreads from cell to cell using an actin-based motility process. This review covers both well-established and recent advances in the characterization of L. monocytogenes virulence determinants and their role in the pathophysiology of listeriosis.

Bacterial Adhesion↗
PubMed2003

Identification and characterization of a phospholipase D-superfamily gene in rickettsiae.

The completion of the sequencing of the genomes of both Rickettsia conorii and R. prowazekii provides the opportunity to identify putative virulence factors within these strictly intracellular pathogens. A role for a phospholipase A(2) (PLA(2)) in rickettsial pathogenicity was hypothesized, but the corresponding gene has not been identified. We have identified a gene that encodes a putative phospholipase D (PLD) and that has been detected by Southern blotting in 11 analyzed strains of rickettsiae. The recombinant protein is dimeric and has PLD activity, as demonstrated by its capacity to release [(3)H]-choline from phosphatidyl [(3)H]-choline. This PLD is present in whole rickettsial lysates and likely is a virulence factor, because incubation of rickettsiae with an anti-PLD antibody reduced their cytotoxic activity against Vero cells. This enzyme might account for the activity previously attributed to PLA(2) and might be critical for the intracellular life of these bacteria.

Amino Acid Sequence↗
PubMed2003

Comparison of the genome sequences of Listeria monocytogenes and Listeria innocua: clues for evolution and pathogenicity.

Listeria monocytogenes, an invasive opportunistic, food-borne pathogen, remains one of the leading causes of mortality from food-borne infections. The recently determined complete genome sequences of L. monocytogenes strain EGDe and of that of the closely related non-pathogenic species Listeria innocua strain CLIP11262 enhance our knowledge of the genetic basis of the virulence of L. monocytogenes and advance our understanding of the evolution of these Listeria species. Both genomes encode a high number of surface, transport and regulatory proteins. Comparison of the genome organisation revealed a perfect synteny between the two Listeria genomes. Comparison with other closely related bacteria also showed a high conservation in genome organisation among the Listeria, Staphylococcus and Bacillus group of low G+C content bacteria. Distinct G+C content of a number of strain-specific genes suggests intensive lateral gene transfer. The identification of a 55-kb locus encoding proteins with high homology to Salmonella enterica serovar Typhimurium vitamin B(12) synthesis proteins as well as those necessary for degradation of ethanolamine and propanediol further indicates acquisition of a complete metabolic pathway by horizontal gene transfer and a probable role of this locus in anaerobic growth in the host.

Anaerobiosis↗
PubMed2003

Invasion of mammalian cells by Listeria monocytogenes: functional mimicry to subvert cellular functions.

The bacterium Listeria monocytogenes has the unusual capacity to enter and to multiply in nonphagocytic cells. Bacterially induced phagocytosis is triggered mainly by the two surface proteins internalin (also called InlA) and InlB, which interact with host cell receptors and either mimic or act in place of the normal cellular ligands. Internalin interacts specifically with human E-cadherin, whereas InlB activates the tyrosine kinase receptor Met and also interacts with the ubiquitous receptor gC1qR and proteoglycans. Signals induced by crosstalk between the bacterium and the host cell allow internalization, which is a prelude to intracellular multiplication, actin-based movement and spread of the bacterium from cell to cell. Manipulating the bacterial invasion proteins offers us an unprecedented tool with which to understand the complex phenomenon of phagocytosis.

Animals↗
PubMed2003

RNA-mediated control of virulence gene expression in bacterial pathogens.

Until recently, gene expression was thought to be controlled mainly at the level of transcription initiation by repressor or activator proteins. In some cases, transcription elongation is controlled by a so-called attenuation mechanism that involves alternative base-pairing between different regions of an mRNA transcript. Recent data reveal that other mechanisms can regulate gene expression and involve RNAs that might act as antisense RNAs, sequestering molecules, or thermosensors. This review focuses on recent studies in bacterial pathogens in which a growing list of examples show that RNA can control virulence gene expression.

Bacteria↗
PubMed2003

Transcriptome analysis of Listeria monocytogenes identifies three groups of genes differently regulated by PrfA.

PrfA is the major regulator of Listeria virulence gene expression. This protein is a member of the Crp/Fnr family of transcription regulators. To gain a deeper understanding of the PrfA regulon, we constructed a whole-genome array based on the complete genome sequence of Listeria monocytogenes strain EGDe and evaluated the expression profiles of the wild-type EGDe and a prfA-deleted mutant (EGDe Delta prfA). Both strains were grown at 37 degrees C in brain-heart infusion broth (BHI) and BHI supplemented with either activated charcoal, a compound known to enhance virulence gene expression, or cellobiose, a sugar reported to downregulate virulence gene expression in spite of full expression of PrfA. We identified three groups of genes that are regulated differently. Group I comprises, in addition to the 10 already known genes, two new genes, lmo2219 and lmo0788, both positively regulated and preceded by a putative PrfA box. Group II comprises eight negatively regulated genes: lmo0278 is preceded by a putative PrfA box, and the remaining seven genes (lmo0178-lmo0184) are organized in an operon. Group III comprises 53 genes, of which only two (lmo0596 and lmo2067) are preceded by a putative PrfA box. Charcoal addition induced upregulation of group I genes but abolished regulation by PrfA of most group III genes. In the presence of cellobiose, all the group I genes were downregulated, whereas group III genes remained fully activated. Group II genes were repressed in all conditions tested. A comparison of the expression profiles between a second L. monocytogenes strain (P14), its spontaneous mutant expressing a constitutively active PrfA variant (P14prfA*) and its corresponding prfA-deleted mutant (P14 Delta prfA) and the EGDe strain revealed interesting strain-specific differences. Sequences strongly similar to a sigma B-dependent promoter were identified upstream of 22 group III genes. These results suggest that PrfA positively regulates a core set of 12 genes preceded by a PrfA box and probably expressed from a sigma A-dependent promoter. In contrast, a second set of PrfA-regulated genes lack a PrfA box and are expressed from a sigma B-dependent promoter. This study reveals that PrfA can act as an activator or a repressor and suggests that PrfA may directly or indirectly activate different sets of genes in association with different sigma factors.

Bacterial Proteins↗
PubMed2003

Identification of Listeria monocytogenes genes involved in salt and alkaline-pH tolerance.

The capacity of Listeria monocytogenes to tolerate salt and alkaline stresses is of particular importance, as this pathogen is often exposed to such environments during food processing and food preservation. We screened a library of Tn917-lacZ insertional mutants in order to identify genes involved in salt and/or alkaline tolerance. We isolated six mutants sensitive to salt stress and 12 mutants sensitive to salt and alkaline stresses. The position of the insertion of the transposon was located in 15 of these mutants. In six mutants the transposon was inserted in intergenic regions, and in nine mutants it was inserted in genes. Most of the genes have unknown functions, but sequence comparisons indicated that they encode putative transporters.

Bacterial Proteins↗
PubMed2003

Listeriolysin O-mediated calcium influx potentiates entry of Listeria monocytogenes into the human Hep-2 epithelial cell line.

To investigate factors which modulate the entry of Listeria monocytogenes into mammalian cells, we have analyzed the role of Ca(2+). We show that L. monocytogenes induced Ca(2+) transients into the human Hep-2 epithelial cell line. The nonpathogenic species L. innocua or a L. monocytogenes mutant strain defective in listeriolysin O (LLO) production was unable to induce these calcium fluxes. Addition of plasma membrane calcium channel antagonists or chelation of extracellular calcium markedly reduced L. monocytogenes entry. In contrast, chelation of host cytosolic Ca(2+) or blockade of Ca(2+) release from intracellular stores did not affect invasion. These results indicate that L. monocytogenes-induced mobilization of extracellular Ca(2+) by LLO and activation of downstream Ca(2+)-dependent signaling are required for efficient cell invasion.

Bacterial Adhesion↗
PubMed2002

GW domains of the Listeria monocytogenes invasion protein InlB are SH3-like and mediate binding to host ligands.

InlB, a surface-localized protein of Listeria monocytogenes, induces phagocytosis in non-phagocytic mammalian cells by activating Met, a receptor tyrosine kinase. InlB also binds glycosaminoglycans and the protein gC1q-R, two additional host ligands implicated in invasion. We present the structure of InlB, revealing a highly elongated molecule with leucine-rich repeats that bind Met at one end, and GW domains that dissociably bind the bacterial surface at the other. Surprisingly, the GW domains are seen to resemble SH3 domains. Despite this, GW domains are unlikely to act as functional mimics of SH3 domains since their potential proline-binding sites are blocked or destroyed. However, we do show that the GW domains, in addition to binding glycosaminoglycans, bind gC1q-R specifically, and that this binding requires release of InlB from the bacterial surface. Dissociable attachment to the bacterial surface via the GW domains may be responsible for restricting Met activation to a small, localized area of the host cell and for coupling InlB-induced host membrane dynamics with bacterial proximity during invasion.

Amino Acid Sequence↗