Role for RpoS but Not RelA of<i>Legionella pneumophila</i>in Modulation of Phagosome Biogenesis and Adaptation to the Phagosomal Microenvironment

Abu-Zant, Alaeddin; Asare, Rexford; Graham, James E.; Kwaik, Yousef Abu

doi:10.1128/iai.74.5.3021-3026.2006

Cited by 42 publications

(61 citation statements)

References 47 publications

(71 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has been proposed that the postexponential accumulation of ppGpp observed in L. pneumophila activates two parallel pathways (1): one controlled by S (1,38,68,109) and another in which activation of the two-component system LetAS results in a reduction in functional CsrA protein (5,6,10,39,40,62,71,72). However, previous studies have shown an overlap in the LetAS and S regulatory outcomes that suggest that the pathways might be interconnected (5,10,68,70,71).…”

Section: Discussionmentioning

confidence: 70%

“…Reduced transcription of ribosomal protein genes and tRNA genes has been linked to the postexponential accumulation of the signaling molecule ppGpp and the stringent response to limiting amino acid availability (26,79). In both L. pneumophila and E. coli, ppGpp results in S accumulation; however, the stringent response and S regulatory networks appear to be independent (1,39,81). It is interesting that with respect to amino acid biosynthetic gene transcription, the roles of ppGpp, which functions as a direct activator (81), and S , whose effect is predominantly negative (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…(91). Mutations in the rpoS gene exhibit some, but not all, icm/dot mutant intracellular multiplication phenotypes (1,38). Characterization of the phenotypes of the rpoS mutant required the use of multiple host cell types: A. castellanii was used to measure intracellular multiplication, D. discoideum was used for endocytic trafficking microscopy studies, and the J774 macrophage cell line was used to assay Icm/Dot-dependent translocation.…”

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

σ^SControls Multiple Pathways Associated with Intracellular Multiplication ofLegionella pneumophila

et al. 2009

View full text Add to dashboard Cite

Legionella pneumophila is the causative agent of the severe and potentially fatal pneumonia Legionnaires' disease. L. pneumophila is able to replicate within macrophages and protozoa by establishing a replicative compartment in a process that requires the Icm/Dot type IVB secretion system. The signals and regulatory pathways required for Legionella infection and intracellular replication are poorly understood. Mutation of the rpoS gene, which encodes S , does not affect growth in rich medium but severely decreases L. pneumophila intracellular multiplication within protozoan hosts. To gain insight into the intracellular multiplication defect of an rpoS mutant, we examined its pattern of gene expression during exponential and postexponential growth. We found that S affects distinct groups of genes that contribute to Legionella intracellular multiplication. We demonstrate that rpoS mutants have a functional Icm/Dot system yet are defective for the expression of many genes encoding Icm/Dot-translocated substrates. We also show that S affects the transcription of the cpxR and pmrA genes, which encode two-component response regulators that directly affect the transcription of Icm/Dot substrates. Our characterization of the L. pneumophila small RNA csrB homologs, rsmY and rsmZ, introduces a link between S and the posttranscriptional regulator CsrA. We analyzed the network of S -controlled genes by mutational analysis of transcriptional regulators affected by S . One of these, encoding the L. pneumophila arginine repressor homolog gene, argR, is required for maximal intracellular growth in amoebae. These data show that S is a key regulator of multiple pathways required for L. pneumophila intracellular multiplication.Legionella pneumophila is a gram-negative opportunistic human pathogen that causes the severe and potentially fatal pneumonia Legionnaires' disease (30,47,67,83). L. pneumophila's ability to replicate within human alveolar macrophages is essential for its capacity to cause disease (44-46). Transmission of L. pneumophila to the human lung occurs as a result of the inhalation of aerosolized contaminated water droplets (74), often from exposure to showers or whirlpool baths (96). Legionella species are ubiquitous in most naturally occurring and man-made aquatic systems, where the organism replicates within a variety of unicellular protozoan hosts (28,38,96). It has been suggested that the interaction of Legionella species with environmental protozoa has selected for the bacterium's evolutionary adaptation to intracellular life in mammalian cells (99).Intracellular multiplication of L. pneumophila requires a series of ordered events that disrupt normal endocytic trafficking in both macrophage and protozoan host cells. These include preventing phagolysosome fusion and the acidification of the Legionella-containing vacuole (LCV), followed by the acquisition of membrane material derived from the Golgi and endoplasmic reticulum compartments of the host (71,85,93,95). These events are dependent upon the Icm/Dot type ...

show abstract

Section: Discussionmentioning

confidence: 70%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

σ^SControls Multiple Pathways Associated with Intracellular Multiplication ofLegionella pneumophila

et al. 2009

View full text Add to dashboard Cite

show abstract

“…Because previous work has demonstrated that the bacterial Dot/Icm secretion system is required for pore formation (1,2,11,31,41,46,58,60), we investigated the requirement of Dot/Icm proteins to trigger caspase-1-dependent pore formation by using a single cell assay with GFP-expressing bacteria. Thus, pore formation assays were performed by infecting BMMs with either wild-type or ⌬dotA mutant bacteria expressing GFP.…”

Section: Resultsmentioning

confidence: 99%

Pore Formation Triggered byLegionellaspp. Is an Nlrc4 Inflammasome-Dependent Host Cell Response That Precedes Pyroptosis

Silveira

Zamboni

2010

Infect Immun

View full text Add to dashboard Cite

Legionella pneumophila, the etiological agent of Legionnaires disease, is known to trigger pore formation in bone marrow-derived macrophages (BMMs) by mechanisms dependent on the type IVB secretion system known as Dot/Icm. Here, we used several mutants of L. pneumophila in combination with knockout mice to assess the host and bacterial factors involved in pore formation in BMMs. We found that regardless of Dot/Icm activity, pore formation does not occur in BMMs deficient in caspase-1 and Nlrc4/Ipaf. Pore formation was temporally associated with interleukin-1␤ secretion and preceded host cell lysis and pyroptosis. Pore-forming ability was dependent on bacterial Dot/Icm but independent of several effector proteins, multiplication, and de novo protein synthesis. Flagellin, which is known to trigger the Nlrc4 inflammasome, was required for pore formation as flaA mutant bacteria failed to induce cell permeabilization. Accordingly, transfection of purified flagellin was sufficient to trigger pore formation independent of infection. By using 11 different Legionella species, we found robust pore formation in response to L. micdadei, L. bozemanii, L. gratiana, L. jordanis, and L. rubrilucens, and this trait correlated with flagellin expression by these species. Together, the results suggest that pore formation is neither L. pneumophila specific nor the result of membrane damage induced by Dot/Icm activity; instead, it is a highly coordinated host cell response dependent on host Nlrc4 and caspase-1 and on bacterial flagellin and type IV secretion system.

show abstract

“…In mouse and human primary macrophages, the rpoS mutant of L. pneumophila is trafficked to a late endosome-like or lysosomal compartment and does not replicate (3,13). Therefore, we examined the integrity of the phagosome harboring the rpoS mutant in hMDMs.…”

Section: Vol 75 2007 Escape Of Dot/icm Mutants Into the Cytoplasm 3295mentioning

confidence: 99%

Rapid Escape of thedot/icmMutants ofLegionella pneumophilainto the Cytosol of Mammalian and Protozoan Cells

et al. 2007

Self Cite

View full text Add to dashboard Cite

The Legionella pneumophila-containing phagosome evades endocytic fusion and intercepts endoplasmic reticulum (ER)-to-Golgi vesicle traffic, which is believed to be mediated by the Dot/Icm type IV secretion system. Although phagosomes harboring dot/icm mutants are thought to mature through the endosomallysosomal pathway, colocalization studies with lysosomal markers have reported contradictory results. In addition, phagosomes harboring the dot/icm mutants do not interact with endocytosed materials, which is inconsistent with maturation of the phagosomes in the endosomal-lysosomal pathway. Using multiple strategies, we show that the dot/icm mutants defective in the Dot/Icm structural apparatus are unable to maintain the integrity of their phagosomes and escape into the cytoplasm within minutes of entry into various mammalian and protozoan cells in a process independent of the type II secretion system. In contrast, mutants defective in cytoplasmic chaperones of Dot/Icm effectors and rpoS, letA/S, and letE regulatory mutants are all localized within intact phagosomes. Importantly, non-dot/icm L. pneumophila mutants whose phagosomes acquire late endosomal-lysosomal markers are all located within intact phagosomes. Using high-resolution electron microscopy, we show that phagosomes harboring the dot/icm transporter mutants do not fuse to lysosomes but are free in the cytoplasm. Inhibition of ER-to-Golgi vesicle traffic by brefeldin A does not affect the integrity of the phagosomes harboring the parental strain of L. pneumophila. We conclude that the Dot/Icm transporter is involved in maintaining the integrity of the L. pneumophila phagosome, independent of interception of ER-to-Golgi vesicle traffic, which is a novel function of type IV secretion systems.

show abstract

Role for RpoS but Not RelA ofLegionella pneumophilain Modulation of Phagosome Biogenesis and Adaptation to the Phagosomal Microenvironment

Cited by 42 publications

References 47 publications

σ^SControls Multiple Pathways Associated with Intracellular Multiplication ofLegionella pneumophila

σ^SControls Multiple Pathways Associated with Intracellular Multiplication ofLegionella pneumophila

Pore Formation Triggered byLegionellaspp. Is an Nlrc4 Inflammasome-Dependent Host Cell Response That Precedes Pyroptosis

Rapid Escape of thedot/icmMutants ofLegionella pneumophilainto the Cytosol of Mammalian and Protozoan Cells

Contact Info

Product

Resources

About

Role for RpoS but Not RelA ofLegionella pneumophilain Modulation of Phagosome Biogenesis and Adaptation to the Phagosomal Microenvironment

Cited by 42 publications

References 47 publications

σSControls Multiple Pathways Associated with Intracellular Multiplication ofLegionella pneumophila

σSControls Multiple Pathways Associated with Intracellular Multiplication ofLegionella pneumophila

Pore Formation Triggered byLegionellaspp. Is an Nlrc4 Inflammasome-Dependent Host Cell Response That Precedes Pyroptosis

Rapid Escape of thedot/icmMutants ofLegionella pneumophilainto the Cytosol of Mammalian and Protozoan Cells

Contact Info

Product

Resources

About

σ^SControls Multiple Pathways Associated with Intracellular Multiplication ofLegionella pneumophila

σ^SControls Multiple Pathways Associated with Intracellular Multiplication ofLegionella pneumophila