Publications (30)172.24 Total impact
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Article: Bacterial colonization of host cells in the absence of cholesterol.
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ABSTRACT: Reports implicating important roles for cholesterol and cholesterol-rich lipid rafts in host-pathogen interactions have largely employed sterol sequestering agents and biosynthesis inhibitors. Because the pleiotropic effects of these compounds can complicate experimental interpretation, we developed a new model system to investigate cholesterol requirements in pathogen infection utilizing DHCR24(-/-) mouse embryonic fibroblasts (MEFs). DHCR24(-/-) MEFs lack the Δ24 sterol reductase required for the final enzymatic step in cholesterol biosynthesis, and consequently accumulate desmosterol into cellular membranes. Defective lipid raft function by DHCR24(-/-) MEFs adapted to growth in cholesterol-free medium was confirmed by showing deficient uptake of cholera-toxin B and impaired signaling by epidermal growth factor. Infection in the absence of cholesterol was then investigated for three intracellular bacterial pathogens: Coxiella burnetii, Salmonella enterica serovar Typhimurium, and Chlamydia trachomatis. Invasion by S. Typhimurium and C. trachomatis was unaltered in DHCR24(-/-) MEFs. In contrast, C. burnetii entry was significantly decreased in -cholesterol MEFs, and also in +cholesterol MEFs when lipid raft-associated α(V)β(3) integrin was blocked, suggesting a role for lipid rafts in C. burnetii uptake. Once internalized, all three pathogens established their respective vacuolar niches and replicated normally. However, the C. burnetii-occupied vacuole within DHCR24(-/-) MEFs lacked the CD63-postive material and multilamellar membranes typical of vacuoles formed in wild type cells, indicating cholesterol functions in trafficking of multivesicular bodies to the pathogen vacuole. These data demonstrate that cholesterol is not essential for invasion and intracellular replication by S. Typhimurium and C. trachomatis, but plays a role in C. burnetii-host cell interactions.PLoS Pathogens 01/2013; 9(1):e1003107. · 9.13 Impact Factor -
Article: Sensing of Bacterial Type IV Secretion via the Unfolded Protein Response.
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ABSTRACT: ABSTRACT Host cytokine responses to Brucella abortus infection are elicited predominantly by the deployment of a type IV secretion system (T4SS). However, the mechanism by which the T4SS elicits inflammation remains unknown. Here we show that translocation of the T4SS substrate VceC into host cells induces proinflammatory responses. Ectopically expressed VceC interacted with the endoplasmic reticulum (ER) chaperone BiP/Grp78 and localized to the ER of HeLa cells. ER localization of VceC required a transmembrane domain in its N terminus. Notably, the expression of VceC resulted in reorganization of ER structures. In macrophages, VceC was required for B. abortus-induced inflammation by induction of the unfolded protein response by a process requiring inositol-requiring transmembrane kinase/endonuclease 1. Altogether, these findings suggest that translocation of the T4SS effector VceC induces ER stress, which results in the induction of proinflammatory host cell responses during B. abortus infection. IMPORTANCE Brucella species are pathogens that require a type IV secretion system (T4SS) to survive in host cells and to maintain chronic infection. By as-yet-unknown pathways, the T4SS also elicits inflammatory responses in infected cells. Here we show that inflammation caused by the T4SS results in part from the sensing of a T4SS substrate, VceC, that localizes to the endoplasmic reticulum (ER), an intracellular site of Brucella replication. Possibly via binding of the ER chaperone BiP, VceC causes ER stress with concomitant expression of proinflammatory cytokines. Thus, induction of the unfolded protein response may represent a novel pathway by which host cells can detect pathogens deploying a T4SS.mBio 01/2013; 4(1). · 5.31 Impact Factor -
Article: Eating the strangers within: host control of intracellular bacteria via xenophagy.
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ABSTRACT: Many bacterial pathogens rely on an intracellular cycle to ensure their proliferation within infected hosts, through their ability to avoid or circumvent host bactericidal pathways. Recent evidence supports an increasingly important role for the autophagy pathway in innate immune defences against intracellular pathogens, as a mechanism of capture of either cytosol-adapted or vacuolar bacteria that redirect them to the lysosomal compartment for killing. Antibacterial autophagy, also referred to as xenophagy, involves selective recognition of intracellular bacteria and their targeting to the autophagic machinery for degradation. Here we review recent advances in our molecular understanding of these processes, and in how bacteria have adapted to avoid xenophagy or even take advantage of this innate immune process.Cellular Microbiology 09/2011; 13(9):1319-27. · 5.46 Impact Factor -
Article: Coiled-coil domains enhance the membrane association of Salmonella type III effectors.
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ABSTRACT: Coiled-coil domains in eukaryotic and prokaryotic proteins contribute to diverse structural and regulatory functions. Here we have used in silico analysis to predict which proteins in the proteome of the enteric pathogen, Salmonella enterica serovar Typhimurium, harbour coiled-coil domains. We found that coiled-coil domains are especially prevalent in virulence-associated proteins, including type III effectors. Using SopB as a model coiled-coil domain type III effector, we have investigated the role of this motif in various aspects of effector function including chaperone binding, secretion and translocation, protein stability, localization and biological activity. Compared with wild-type SopB, SopB coiled-coil mutants were unstable, both inside bacteria and after translocation into host cells. In addition, the putative coiled-coil domain was required for the efficient membrane association of SopB in host cells. Since many other Salmonella effectors were predicted to contain coiled-coil domains, we also investigated the role of this motif in their intracellular targeting in mammalian cells. Mutation of the predicted coiled-coil domains in PipB2, SseJ and SopD2 also eliminated their membrane localization in mammalian cells. These findings suggest that coiled-coil domains represent a common membrane-targeting determinant for Salmonella type III effectors.Cellular Microbiology 06/2011; 13(10):1497-517. · 5.46 Impact Factor -
Article: Activation of Akt by the bacterial inositol phosphatase, SopB, is wortmannin insensitive.
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ABSTRACT: Salmonella enterica uses effector proteins translocated by a Type III Secretion System to invade epithelial cells. One of the invasion-associated effectors, SopB, is an inositol phosphatase that mediates sustained activation of the pro-survival kinase Akt in infected cells. Canonical activation of Akt involves membrane translocation and phosphorylation and is dependent on phosphatidyl inositide 3 kinase (PI3K). Here we have investigated these two distinct processes in Salmonella infected HeLa cells. Firstly, we found that SopB-dependent membrane translocation and phosphorylation of Akt are insensitive to the PI3K inhibitor wortmannin. Similarly, depletion of the PI3K regulatory subunits p85α and p85ß by RNAi had no inhibitory effect on SopB-dependent Akt phosphorylation. Nevertheless, SopB-dependent phosphorylation does depend on the Akt kinases, PDK1 and rictor-mTOR. Membrane translocation assays revealed a dependence on SopB for Akt recruitment to Salmonella ruffles and suggest that this is mediated by phosphoinositide (3,4) P(2) rather than phosphoinositide (3,4,5) P(3). Altogether these data demonstrate that Salmonella activates Akt via a wortmannin insensitive mechanism that is likely a class I PI3K-independent process that incorporates some essential elements of the canonical pathway.PLoS ONE 01/2011; 6(7):e22260. · 4.09 Impact Factor -
Article: Dissemination of invasive Salmonella via bacterial-induced extrusion of mucosal epithelia.
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ABSTRACT: Salmonella enterica is an intracellular bacterial pathogen that resides and proliferates within a membrane-bound vacuole in epithelial cells of the gut and gallbladder. Although essential to disease, how Salmonella escapes from its intracellular niche and spreads to secondary cells within the same host, or to a new host, is not known. Here, we demonstrate that a subpopulation of Salmonella hyperreplicating in the cytosol of epithelial cells serves as a reservoir for dissemination. These bacteria are transcriptionally distinct from intravacuolar Salmonella. They are induced for the invasion-associated type III secretion system and possess flagella; hence, they are primed for invasion. Epithelial cells laden with these cytosolic bacteria are extruded out of the monolayer, releasing invasion-primed and -competent Salmonella into the lumen. This extrusion mechanism is morphologically similar to the process of cell shedding required for turnover of the intestinal epithelium. In contrast to the homeostatic mechanism, however, bacterial-induced extrusion is accompanied by an inflammatory cell death characterized by caspase-1 activation and the apical release of IL-18, an important cytokine regulator of gut inflammation. Although epithelial extrusion is obviously beneficial to Salmonella for completion of its life cycle, it also provides a mechanistic explanation for the mucosal inflammation that is triggered during Salmonella infection of the gastrointestinal and biliary tracts.Proceedings of the National Academy of Sciences 09/2010; 107(41):17733-8. · 9.68 Impact Factor -
Article: Induction of Salmonella pathogenicity island 1 under different growth conditions can affect Salmonella-host cell interactions in vitro.
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ABSTRACT: Salmonella invade non-phagocytic cells by inducing massive actin rearrangements, resulting in membrane ruffle formation and phagocytosis of the bacteria. This process is mediated by a cohort of effector proteins translocated into the host cell by type III secretion system 1, which is encoded by genes in the Salmonella pathogenicity island (SPI) 1 regulon. This network is precisely regulated and must be induced outside of host cells. In vitro invasive Salmonella are prepared by growth in synthetic media although the details vary. Here, we show that culture conditions affect the frequency, and therefore invasion efficiency, of SPI1-induced bacteria and also can affect the ability of Salmonella to adapt to its intracellular niche following invasion. Aerobically grown late-exponential-phase bacteria were more invasive and this was associated with a greater frequency of SPI1-induced, motile bacteria, as revealed by single-cell analysis of gene expression. Culture conditions also affected the ability of Salmonella to adapt to the intracellular environment, since they caused marked differences in intracellular replication. These findings show that induction of SPI1 under different pre-invasion growth conditions can affect the ability of Salmonella to interact with eukaryotic host cells.Microbiology 04/2010; 156(Pt 4):1120-33. · 3.06 Impact Factor -
Article: Ubiquitination of the bacterial inositol phosphatase, SopB, regulates its biological activity at the plasma membrane.
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ABSTRACT: The Salmonella type III effector, SopB, is an inositol polyphosphate phosphatase that modulates host cell phospholipids at the plasma membrane and the nascent Salmonella-containing vacuole (SCV). Translocated SopB persists for many hours after infection and is ubiquitinated but the significance of this covalent modification has not been investigated. Here we identify by mass spectrometry six lysine residues of SopB that are mono-ubiquitinated. Substitution of these six lysine residues with arginine, SopB-K(6)R, almost completely eliminated SopB ubiquitination. We found that ubiquitination does not affect SopB stability or membrane association, or SopB-dependent events in SCV biogenesis. However, two spatially and temporally distinct events are dependent on ubiquitination, downregulation of SopB activity at the plasma membrane and prolonged retention of SopB on the SCV. Activation of the mammalian pro-survival kinase Akt/PKB, a downstream target of SopB, was intensified and prolonged after infection with the SopB-K(6)R mutant. At later times, fewer SCV were decorated with SopB-K(6)R compared with SopB. Instead SopB-K(6)R was present as discrete vesicles spread diffusely throughout the cell. Altogether, our data show that ubiquitination of SopB is not related to its intracellular stability but rather regulates its enzymatic activity at the plasma membrane and intracellular localization.Cellular Microbiology 08/2009; 11(11):1652-70. · 5.46 Impact Factor -
Article: Of microbes and membranes: pathogenic subversion of host cell processes.
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ABSTRACT: A recent gathering of researchers at the EMBO conference "At the joint edge of Cellular Microbiology and Cell Biology" was aimed at melding ideas from both scientific fields to advance our understanding of infectious diseases at the cellular level. Work presented at this meeting highlighted how pathogens exploit host cell membrane processes to their advantage and also revealed fundamental signaling and trafficking mechanisms of eukaryotic cells.Cell host & microbe 01/2009; 4(6):514-8. · 13.02 Impact Factor -
Article: HilD-mediated transcriptional cross-talk between SPI-1 and SPI-2.
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ABSTRACT: The acquisition of new genetic traits by horizontal gene transfer and their incorporation into preexisting regulatory networks have been essential events in the evolution of bacterial pathogens. An example of successful assimilation of virulence traits is Salmonella enterica, which acquired, at distinct evolutionary times, Salmonella pathogenicity island 1 (SPI-1), required for efficient invasion of the intestinal epithelium and intestinal disease, and SPI-2, essential for Salmonella replication and survival within macrophages and the progression of a systemic infection. A positive regulatory cascade mainly composed of HilD, HilA, and InvF, encoded in SPI-1, controls the expression of SPI-1 genes, whereas the two-component regulatory system SsrA/B, encoded in SPI-2, controls expression of SPI-2 genes. In this study, we report a previously undescribed transcriptional cross-talk between SPI-1 and SPI-2, where the SPI-1-encoded regulator HilD is essential for the activation of both the SPI-1 and SPI-2 regulons but at different times during the stationary phase of growth in Luria-Bertani medium. Our data indicate that HilD counteracts the H-NS-mediated repression exerted on the OmpR-dependent activation of the ssrAB operon by specifically interacting with its regulatory region. In contrast, HilD is not required for SPI-2 regulon expression under the in vitro growth conditions that are thought to resemble the intracellular environment. Our results suggest that two independent SPI-2 activation pathways evolved to take advantage of the SPI-2-encoded information at different niches and, in consequence, in response to different growth conditions.Proceedings of the National Academy of Sciences 10/2008; 105(38):14591-6. · 9.68 Impact Factor -
Article: Dynamic behavior of Salmonella-induced membrane tubules in epithelial cells.
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ABSTRACT: Salmonella Typhimurium is a facultative intracellular pathogen that causes acute gastroenteritis in man. Intracellular Salmonella survive and replicate within a modified phagosome known as the Salmonella-containing vacuole (SCV). The onset of intracellular replication is accompanied by the appearance of membrane tubules, called Salmonella-induced filaments (Sifs), extending from the SCV. Sifs are enriched in late endosomal/lysosomal membrane proteins such as lysosome-associated membrane protein 1, but their formation and ability to interact with endosomal compartments are not characterized. In this study, we use live cell imaging techniques to define the dynamics of Sif formation in infected epithelial cells. At early time-points, Sifs are simple tubules extending from the surface of SCVs. These tubules are highly dynamic and exhibit bidirectional, microtubule-dependent movement. At the distal ends of individual Sif tubules, furthest from the SCV, a distinct 'leader' domain was often observed. At later times, Sifs develop into highly complex tubular networks that extend throughout the cell and appear less dynamic than nascent Sifs; however, individual tubules continue to display bidirectional dynamics. Sifs can acquire endocytic content by fusion, indicating a sustained interaction with the endocytic pathway. Together, these results show that these Salmonella-induced tubules form a highly dynamic network that involves both microtubule-dependent motility and interactions with endosomal compartments.Traffic 10/2008; 9(12):2117-29. · 4.92 Impact Factor -
Article: Brucella intracellular replication requires trafficking through the late endosomal/lysosomal compartment.
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ABSTRACT: Upon entry into mammalian cells, the intracellular pathogen Brucella abortus resides within a membrane-bound compartment, the Brucella-containing vacuole (BCV), the maturation of which is controlled by the bacterium to generate a replicative organelle derived from the endoplasmic reticulum (ER). Prior to reaching the ER, Brucella is believed to ensure its intracellular survival by inhibiting fusion of the intermediate BCV with late endosomes and lysosomes, although such BCVs are acidic and accumulate the lysosomal-associated membrane protein (LAMP-1). Here, we have further examined the nature of intermediate BCVs using confocal microscopy and live cell imaging. We show that BCVs rapidly acquire several late endocytic markers, including the guanosine triphosphatase Rab7 and its effector Rab-interacting lysosomal protein (RILP), and are accessible to fluid-phase markers either delivered to the whole endocytic pathway or preloaded to lysosomes, indicating that BCVs interact with late endosomes and lysosomes. Consistently, intermediate BCVs are acidic and display proteolytic activity up to 12 h post-infection. Expression of dominant-negative Rab7 or overexpression of RILP significantly impaired the ability of bacteria to convert their vacuole into an ER-derived organelle and replicate, indicating that BCV maturation requires interactions with functional late endosomal/lysosomal compartments. In cells expressing dominant-negative Rab7[T22N], BCVs remained acidic, yet displayed decreased fusion with lysosomes. Taken together, these results demonstrate that BCVs traffic along the endocytic pathway and fuse with lysosomes, and such fusion events are required for further maturation of BCVs into an ER-derived replicative organelle.Traffic 06/2008; 9(5):678-94. · 4.92 Impact Factor -
Article: Salmonella trafficking is defined by continuous dynamic interactions with the endolysosomal system.
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ABSTRACT: Following invasion of non-phagocytic host cells, Salmonella enterica survives and replicates within a phagosome-like compartment known as the Salmonella-containing vacuole (SCV). It is now well established that SCV biogenesis, like phagosome biogenesis, involves sequential interactions with the endocytic pathway. However, Salmonella is believed to limit these interactions and, in particular, to avoid fusion of terminal lysosomes with the SCV. In this study, we reassessed this process using a high-resolution live-cell imaging approach and found an unanticipated level of interaction between the SCV and the endocytic pathway. Direct interactions, in which late endosomal/lysosomal content was transferred to SCVs, were detected within 30 min of invasion and continued for several hours. Mechanistically, these interactions were very similar to phagosome-lysosome fusion because they were accompanied by rapid acidification of the SCV, could be blocked by chemical perturbation of microtubules or vacuolar acidification and involved the smallGTPase Rab7. In comparison with vacuoles containing internalized Escherichia coli or heat-killed Salmonella, SCVs did show some delay of fusion and acidification, although, this appeared to be independent of either type III secretion system. These results provide compelling evidence that inhibition of SCV-lysosome fusion is not the major determinant in establishment of the Salmonella replicative niche in epithelial cells.Traffic 04/2007; 8(3):212-25. · 4.92 Impact Factor -
Article: Structure-based mutagenesis of SigE verifies the importance of hydrophobic and electrostatic residues in type III chaperone function.
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ABSTRACT: Despite sharing little sequence identity, most type III chaperones display a similar homodimeric structure characterized by negative charges distributed broadly over their entire surface, interspersed with hydrophobic patches. Here we have used SigE from Salmonella as a model for class IA type III chaperones to investigate the role of these surface-exposed residues in chaperone function. SigE is essential for the stability, secretion and translocation of its cognate effector, SopB (SigD). We analysed the effect of mutating nine conserved hydrophobic and electronegative surface-exposed amino acids of SigE on SopB binding, stability, secretion and translocation. Six of these mutations affected some aspect of SigE function (Leu14, Asp20, Leu22, Leu23, Ile25 and Asp51) and three were without effect (Leu54, Glu92 and Glu99). Our results highlight that both hydrophobic and electronegative surfaces are required for the function of SigE and provide an important basis for the prediction of side-chain requirements for other chaperone-effector pairs.Molecular Microbiology 12/2006; 62(4):928-40. · 5.01 Impact Factor -
Article: The Salmonella effector protein PipB2 is a linker for kinesin-1.
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ABSTRACT: Understanding the mechanisms of Salmonella virulence is an important challenge. The capacity of this intracellular bacterial pathogen to cause diseases depends on the expression of virulence factors including the second type III secretion system (TTSS-2), which is used to translocate into the eukaryotic cytosol a set of effector proteins that divert the biology of the host cell and shape the bacterial replicative niche. Yet little is known about the eukaryotic functions affected by individual Salmonella effectors. Here we report that the TTSS-2 effector PipB2 interacts with the kinesin light chain, a subunit of the kinesin-1 motor complex that drives anterograde transport along microtubules. Translocation of PipB2 is both necessary and sufficient for the recruitment of kinesin-1 to the membrane of the Salmonella-containing vacuole. In vivo, PipB2 contributes to the attenuation of Salmonella mutant strains in mice. Taken together, our data indicate that the TTSS-2-mediated fine-tuning of kinesin-1 activity associated with the bacterial vacuole is crucial for the virulence of Salmonella.Proceedings of the National Academy of Sciences 10/2006; 103(36):13497-502. · 9.68 Impact Factor -
Article: Toll-like receptor 4 contributes to colitis development but not to host defense during Citrobacter rodentium infection in mice.
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ABSTRACT: Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) are noninvasive bacterial pathogens that infect their hosts' intestinal epithelium, causing severe diarrheal disease. These infections also cause intestinal inflammation, although the mechanisms underlying the inflammatory response, as well as its potential role in host defense, are unclear. Since these bacteria are gram-negative, Toll-like receptor 4 (TLR4), the innate receptor for bacterial lipopolysaccharide may contribute to the host response; however, the role of TLR4 in the gastrointestinal tract is poorly understood, and its impact has yet to be tested against this family of enteric bacterial pathogens. Since EPEC and EHEC are human specific, we infected mice with Citrobacter rodentium, a mouse-adapted attaching and effacing (A/E) bacterium that infects colonic epithelial cells, causing colitis and epithelial hyperplasia, using a similar array of virulence proteins as EPEC and EHEC. We demonstrated that C. rodentium activates TLR4 and rapidly induced NF-kappaB nuclear translocation in host cells in a partially TLR4-dependent manner. Infection of TLR4-deficient mice revealed that TLR4-dependent responses mediate much of the inflammation and tissue pathology seen during infection, including the induction of the chemokines MIP-2 and MCP-1, as well as the recruitment of macrophages and neutrophils into the infected intestine. Surprisingly, spread of C. rodentium through the colon was delayed in TLR4-deficient mice, whereas the duration of the infection was unaffected, indicating that TLR4-mediated responses against this A/E pathogen are not host protective and are ultimately maladaptive to the host, contributing to both the morbidity and the pathology seen during infection.Infection and Immunity 06/2006; 74(5):2522-36. · 4.16 Impact Factor -
Article: The mechanism of Salmonella entry determines the vacuolar environment and intracellular gene expression.
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ABSTRACT: Macrophages are an important intracellular niche for Salmonella particularly for systemic infection. The interaction of Salmonella with these cells is mediated by two type III secretion systems (TTSS), encoded on Salmonella pathogenicity islands 1 and 2 (SPI1, SPI2), which mediate distinct phases of the pathogen-host cell interaction. The SPI1 TTSS mediates invasion whereas the SPI2 TTSS is required for intramacrophage survival. Importantly, however, Salmonella can enter macrophages by either SPI1-dependent invasion or host cell-mediated phagocytosis. Here, we investigated how the mechanism of internalization affects the intracellular environment and TTSS gene expression. Intracellular bacterial survival depended on the method of entry, because complement-opsonized and SPI1-induced Salmonella initiated replication within 8 h whereas immunoglobulin G (IgG)-opsonized and non-opsonized Salmonella were initially killed. Analysis of vacuolar pH showed that acidification of the Salmonella-containing vacuole occurred more rapidly for non-opsonized or SPI1-induced Salmonella compared with IgG-opsonized or complement-opsonized Salmonella. Finally, quantitative polymerase chain reaction was used to compare the transcriptional profiles of selected SPI1 and SPI2 regulon genes. We found that the magnitude of SPI2 gene induction depended on the mechanism of internalization. Unexpectedly, SPI1 genes, which are rapidly downregulated following SPI1-mediated invasion, were induced intracellularly following phagocytic uptake. These results reveal another level of complexity in pathogen-macrophage interactions.Traffic 02/2006; 7(1):39-51. · 4.92 Impact Factor -
Article: Cloning vectors and fluorescent proteins can significantly inhibit Salmonella enterica virulence in both epithelial cells and macrophages: implications for bacterial pathogenesis studies.
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ABSTRACT: Plasmid vectors and fluorescent protein reporter systems are commonly used in the study of bacterial pathogenesis. Here we show that they can impair the ability of Salmonella enterica serovar Typhimurium to productively infect either cultured mammalian cells or mice. This has significant implications for studies that rely on these systems.Infection and Immunity 11/2005; 73(10):7027-31. · 4.16 Impact Factor -
Article: The Salmonella effector PipB2 affects late endosome/lysosome distribution to mediate Sif extension.
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ABSTRACT: After internalization into mammalian cells, the bacterial pathogen Salmonella enterica resides within a membrane-bound compartment, the Salmonella-containing vacuole (SCV). During its maturation process, the SCV interacts extensively with host cell endocytic compartments, especially late endosomes/lysosomes (LE/Lys) at later stages. These interactions are mediated by the activities of multiple bacterial and host cell proteins. Here, we show that the Salmonella type III effector PipB2 reorganizes LE/Lys compartments in mammalian cells. This activity results in the centrifugal extension of lysosomal glycoprotein-rich membrane tubules, known as Salmonella-induced filaments, away from the SCV along microtubules. Salmonella overexpressing pipB2 induce the peripheral accumulation of LE/Lys compartments, reducing the frequency of LE/Lys tubulation. Furthermore, ectopic expression of pipB2 redistributes LE/Lys, but not other cellular organelles, to the cell periphery. In coexpression studies, PipB2 can overcome the effects of dominant-active Rab7 or Rab34 on LE/Lys positioning. Deletion of a C-terminal pentapeptide motif of PipB2, LFNEF, prevents its peripheral targeting and effect on organelle positioning. The PipB2 homologue PipB does not possess this motif or the same biological activity as PipB2. Therefore, it seems that a divergence in the biological functions of these two effectors can be accounted for by sequence divergence in their C termini.Molecular Biology of the Cell 10/2005; 16(9):4108-23. · 4.94 Impact Factor -
Article: The Salmonella effector protein SopB protects epithelial cells from apoptosis by sustained activation of Akt.
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ABSTRACT: Invasion of epithelial cells by Salmonella enterica is mediated by bacterial "effector" proteins that are delivered into the host cell by a type III secretion system. Although primarily known for their roles in actin rearrangements and membrane ruffling, translocated effectors also affect host cell processes that are not directly associated with invasion. Here, we show that SopB/SigD, an effector with phosphoinositide phosphatase activity, has anti-apoptotic activity in Salmonella-infected epithelial cells. Salmonella induced the sustained activation of Akt/protein kinase B, a pro-survival kinase, in a SopB-dependent manner. Failure to activate Akt resulted in increased levels of apoptosis after infection with a sopB deletion mutant (DeltasopB). Furthermore, cells infected with wild type bacteria, but not the DeltasopB strain, were protected from camptothecin-induced cleavage of caspase-3 and subsequent apoptosis. The anti-apoptotic activity of SopB was dependent on its phosphatase activity, because a catalytically inactive mutant was unable to protect cells from the effects of camptothecin. Finally, small interfering RNA was used to demonstrate the essential role of Akt in SopB-mediated protection against apoptosis. These results provide new insights into the mechanisms of apoptosis and highlight how bacterial effectors can intercept signaling pathways to manipulate host responses.Journal of Biological Chemistry 04/2005; 280(10):9058-64. · 4.77 Impact Factor
Top co-authors
Top Journals
- Infection and Immunity (4)
- Traffic (4)
- Molecular Microbiology (3)
- Cellular Microbiology (3)
- Cellular Microbiology (3)
Institutions
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2005–2011
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National Institutes of Health
- Laboratory of Intracellular Parasites (LICP)
Bethesda, MD, USA
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2003–2011
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National Institute of Allergy and Infectious Diseases
Bethesda, MD, USA
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2000–2003
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University of British Columbia - Vancouver
- Department of Biochemistry and Molecular Biology
Vancouver, British Columbia, Canada
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