Master Manipulators: An Update on
            <i>Legionella Pneumophila</i>
            Icm/Dot Translocated Substrates and their Host targets

Isaac, Dervla T.; Isberg, Ralph R.

doi:10.2217/fmb.13.162

Cited by 86 publications

(84 citation statements)

References 90 publications

(135 reference statements)

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“…Evidence in support of this model includes the results that interference with ER budding and biogenesis of vesicles involved in the ER to Golgi membrane depresses the formation of replication vacuoles (13,22,67). Furthermore, a large collection of IDTS target proteins are involved in both tethering and fusion of ER-derived vesicles to the Golgi compartment (68). There is evidence, however, that L. pneumophila may hijack ER-plasma membrane interactions or induce novel pathways to direct peripheral ER to interface directly with the plasma membrane during the early stages of vacuole formation.…”

Section: Discussionmentioning

confidence: 90%

Endoplasmic Reticulum Tubule Protein Reticulon 4 Associates with the Legionella pneumophila Vacuole and with Translocated Substrate Ceg9

et al. 2015

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Intracellular growth of Legionella pneumophila occurs in a replication vacuole constructed by host proteins that regulate vesicular traffic from the host endoplasmic reticulum (ER). This process is promoted by a combination of approximately 300 Icm/Dot translocated substrates (IDTS). One of these proteins, Ceg9, was previously identified in a screen for L. pneumophila IDTS that manipulate secretory traffic when overexpressed in yeast. Using ectopic expression of Ceg9 in mammalian cells, we demonstrate that Ceg9 interacts with isoforms of host reticulon 4 (Rtn4), a protein that regulates ER tubule formation. Binding occurs under conditions that prevent association with other known reticulon binding proteins, arguing that Ceg9 binding is stable. A tripartite complex was demonstrated among Rtn4, Ceg9, and atlastin 1, a previously characterized reticulon interacting partner. The binding of Ceg9 to Rtn4 was not due to bridging by atlastin 1 but resulted from the two interacting partners binding independently to reticulon. When Ceg9 is ectopically expressed in mammalian cells, it shows a localization pattern that is indistinguishable from that of Rtn4, perhaps due to interactions between and similar structural features of the two proteins. Consistent with Rtn4 playing a role in the formation of the Legionella-containing vacuole, it was recruited to almost 50% of the vacuoles within 20 min postinfection. Our studies suggest that L. pneumophila proteins interact with ER tubules at an early stage of replication vacuole formation. I ntravacuolar growth of intracellular pathogens involves intimate interaction with specific subsets of host cell membrane compartments (1). In the case of Chlamydia trachomatis, the association of the replication vacuole with the trans-Golgi and the endoplasmic reticulum (ER) network is a key step during the establishment of an intracellular niche (2-5). Similarly, vacuoles harboring Brucella, Salmonella, and Mycobacterium species also interface with defined membrane compartments that aid the growth of these bacteria in host cells (6-10). Failure to establish association with the appropriate organelles can have dire consequences, including loss of vacuolar membrane integrity, activation of inflammatory host cell death, and trafficking of the microorganism into degradative compartments (3,6,11,12).Legionella pneumophila is one such intravacuolar pathogen that targets specific intracellular compartments during its replication cycle (13-16). The bacterium is a pathogen of amoebae and humans. In humans, L. pneumophila's primary manifestation of virulence is Legionnaires' disease, a potentially lethal pneumonia resulting from growth of the bacteria within alveolar macrophages (17, 18). Biogenesis of the microbial replication vacuole is evolutionarily conserved from amoebae to eukaryotic cells (16,19), with the bacterium growing in an ER-encompassed compartment called the Legionella-containing vacuole (LCV) (13,15,20). The connection between the LCV and ER dynamics is well established, since the prop...

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Section: Discussionmentioning

confidence: 90%

Endoplasmic Reticulum Tubule Protein Reticulon 4 Associates with the Legionella pneumophila Vacuole and with Translocated Substrate Ceg9

et al. 2015

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“…L. pneumophila secretes ϳ300 effector proteins into the host cytosol via a T4SS that it uses to manipulate the process of vacuole maturation (8,25). The identification of effector proteins that have important intracellular functions has been challenging because elimination of a single effector, or even large clusters of effectors, does not typically interfere with the ability of L. pneumophila to replicate intracellularly (13,14).…”

Section: Discussionmentioning

confidence: 99%

“…Several recent studies have increased the number of identified T4SS effectors to more than 300 (22)(23)(24)(25)(26)(27)(28). We created a plasmid library containing the majority of effector proteins expressed from a constitutive low-expression vector.…”

mentioning

confidence: 99%

Toxicity and SidJ-Mediated Suppression of Toxicity Require Distinct Regions in the SidE Family of Legionella pneumophila Effectors

Havey

Roy

2015

Infect Immun

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Intracellular bacteria use a variety of strategies to evade degradation and create a replicative niche. Legionella pneumophila is an intravacuolar pathogen that establishes a replicative niche through the secretion of more than 300 effector proteins. The function of most effectors remains to be determined. Toxicity in yeast has been used to identify functional domains and elucidate the biochemical function of effectors. A library of L. pneumophila effectors was screened using an expression plasmid that produces low levels of each protein. This screen identified the effector SdeA as a protein that confers a strong toxic phenotype that inhibits yeast replication. The toxicity of SdeA was suppressed in cells producing the effector SidJ. The effector SdeA is a member of the SidE family of L. pneumophila effector proteins. All SidE orthologs encoded by the Philadelphia isolate of Legionella pneumophila were toxic to yeast, and SidJ suppressed the toxicity of each. We identified a conserved central region in the SidE proteins that was sufficient to mediate yeast toxicity. Surprisingly, SidJ did not suppress toxicity when this central region was produced in yeast. We determined that the amino-terminal region of SidE was essential for SidJ-mediated suppression of toxicity. Thus, there is a genetic interaction that links the activity of SidJ and the amino-terminal region of SidE, which is required to modulate the toxic activity displayed by the central region of the SidE protein. This suggests a complex mechanism by which the L. pneumophila effector SidJ modulates the function of the SidE proteins after translocation into host cells.L egionella pneumophila is a Gram-negative, facultative intravacuolar pathogen that is the causative agent of Legionnaires' disease in humans (1-3). L. pneumophila is phagocytosed by host cells and creates a vacuole that supports replication by inhibiting the fusion of host endocytic vesicles and subverting the transport of secretory vesicles (4-7). The bacterially encoded Dot/Icm type IV secretion system (T4SS) is essential for the creation of this Legionella-containing vacuole (LCV) (8, 9). Proteins secreted by the T4SS, known as effectors, have been shown to both decorate the LCV and modify the location and function of host proteins, especially Rab GTPases (8,10,11). Determining the function of these effector proteins has been complicated by the observation that deletion of a single effector or groups of effectors does not typically result in a strong replication defect within host cells (12)(13)(14).The use of the yeast Saccharomyces cerevisiae as a system to study L. pneumophila effector proteins has been successful in previous studies (15)(16)(17)(18)(19). Examples include studies on the effector protein RalF, which was shown to inhibit yeast replication when overproduced, and the effector proteins YlfA and YlfB were both identified in an early yeast toxicity screen (16). Effector toxicity in yeast has also been used to study effector activities. The L. pneumophila effector AnkX is capa...

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“…Its ability to replicate inside macrophages requires the Icm/Dot type IV secretion system (T4SS), which translocates approximately 300 effector proteins into host cells. 103 A screen for regulators of icmR expression, which encodes a chaperone component of the T4SS, identified CpxR as a positive regulator. 104 CpxR bound to the icmR control region in vitro, which contains a conserved CpxRbinding sequence, and a cpxR null mutation reduced expression of an icmR-lacZ translational fusion.…”

Section: Regulation Of Pili By the Cpx Responsementioning

confidence: 99%

Regulation of bacterial virulence gene expression by cell envelope stress responses

Flores-Kim

Darwin

2014

Virulence

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Master Manipulators: An Update on Legionella Pneumophila Icm/Dot Translocated Substrates and their Host targets

Cited by 86 publications

References 90 publications

Endoplasmic Reticulum Tubule Protein Reticulon 4 Associates with the Legionella pneumophila Vacuole and with Translocated Substrate Ceg9

Endoplasmic Reticulum Tubule Protein Reticulon 4 Associates with the Legionella pneumophila Vacuole and with Translocated Substrate Ceg9

Toxicity and SidJ-Mediated Suppression of Toxicity Require Distinct Regions in the SidE Family of Legionella pneumophila Effectors

Regulation of bacterial virulence gene expression by cell envelope stress responses

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