scholarly journals Divergent Evolution of Legionella RCC1 Repeat Effectors Defines the Range of Ran GTPase Cycle Targets

mBio ◽  
2020 ◽  
Vol 11 (2) ◽  
Author(s):  
A. Leoni Swart ◽  
Bernhard Steiner ◽  
Laura Gomez-Valero ◽  
Sabina Schütz ◽  
Mandy Hannemann ◽  
...  
Keyword(s):  
Host Cell ◽  
Legionella Pneumophila ◽  
Small Gtpase ◽  
Effector Proteins ◽  
Host Cells ◽  
Divergent Evolution ◽  
Ran Gtpase ◽  
Content Type ◽  
Gtpase Cycle ◽  
Gtpase Ran

ABSTRACT Legionella pneumophila governs its interactions with host cells by secreting >300 different “effector” proteins. Some of these effectors contain eukaryotic domains such as the RCC1 (regulator of chromosome condensation 1) repeats promoting the activation of the small GTPase Ran. In this report, we reveal a conserved pattern of L. pneumophila RCC1 repeat genes, which are distributed in two main clusters of strains. Accordingly, strain Philadelphia-1 contains two RCC1 genes implicated in bacterial virulence, legG1 (Legionella eukaryotic gene 1), and ppgA, while strain Paris contains only one, pieG. The RCC1 repeat effectors localize to different cellular compartments and bind distinct components of the Ran GTPase cycle, including Ran modulators and the small GTPase itself, and yet they all promote the activation of Ran. The pieG gene spans the corresponding open reading frames of legG1 and a separate adjacent upstream gene, lpg1975. legG1 and lpg1975 are fused upon addition of a single nucleotide to encode a protein that adopts the binding specificity of PieG. Thus, a point mutation in pieG splits the gene, altering the effector target. These results indicate that divergent evolution of RCC1 repeat effectors defines the Ran GTPase cycle targets and that modulation of different components of the cycle might fine-tune Ran activation during Legionella infection. IMPORTANCE Legionella pneumophila is a ubiquitous environmental bacterium which, upon inhalation, causes a life-threatening pneumonia termed Legionnaires’ disease. The opportunistic pathogen grows in amoebae and macrophages by employing a “type IV” secretion system, which secretes more than 300 different “effector” proteins into the host cell, where they subvert pivotal processes. The function of many of these effector proteins is unknown, and their evolution has not been studied. L. pneumophila RCC1 repeat effectors target the small GTPase Ran, a molecular switch implicated in different cellular processes such as nucleocytoplasmic transport and microtubule cytoskeleton dynamics. We provide evidence that one or more RCC1 repeat genes are distributed in two main clusters of L. pneumophila strains and have divergently evolved to target different components of the Ran GTPase activation cycle at different subcellular sites. Thus, L. pneumophila employs a sophisticated strategy to subvert host cell Ran GTPase during infection.

scholarly journals Live-Cell Imaging of Phosphoinositide Dynamics and Membrane Architecture during Legionella Infection

mBio ◽  
2014 ◽  
Vol 5 (1) ◽  
Author(s):  
Stephen Weber ◽  
Maria Wagner ◽  
Hubert Hilbi
Keyword(s):  
Host Cell ◽  
Legionella Pneumophila ◽  
Live Cell Imaging ◽  
Cell Imaging ◽  
Effector Proteins ◽  
Host Cells ◽  
Wild Type ◽  
Host Cell Membrane ◽  
Content Type ◽  
Temporal And Spatial

ABSTRACTThe causative agent of Legionnaires’ disease,Legionella pneumophila, replicates in amoebae and macrophages in a distinct membrane-bound compartment, theLegionella-containing vacuole (LCV). LCV formation is governed by the bacterial Icm/Dot type IV secretion system that translocates ~300 different “effector” proteins into host cells. Some of the translocated effectors anchor to the LCV membrane via phosphoinositide (PI) lipids. Here, we use the soil amoebaDictyostelium discoideum, producing fluorescent PI probes, to analyze the LCV PI dynamics by live-cell imaging. Upon uptake of wild-type or Icm/Dot-deficientL. pneumophila, PtdIns(3,4,5)P3transiently accumulated for an average of 40 s on early phagosomes, which acquired PtdIns(3)Pwithin 1 min after uptake. Whereas phagosomes containing ΔicmTmutant bacteria remained decorated with PtdIns(3)P, more than 80% of wild-type LCVs gradually lost this PI within 2 h. The process was accompanied by a major rearrangement of PtdIns(3)P-positive membranes condensing to the cell center. PtdIns(4)Ptransiently localized to early phagosomes harboring wild-type or ΔicmT L. pneumophilaand was cleared within minutes after uptake. During the following 2 h, PtdIns(4)Psteadily accumulated only on wild-type LCVs, which maintained a discrete PtdIns(4)Pidentity spatially separated from calnexin-positive endoplasmic reticulum (ER) for at least 8 h. The separation of PtdIns(4)P-positive and ER membranes was even more pronounced for LCVs harboring ΔsidC-sdcAmutant bacteria defective for ER recruitment, without affecting initial bacterial replication in the pathogen vacuole. These findings elucidate the temporal and spatial dynamics of PI lipids implicated in LCV formation and provide insight into host cell membrane and effector protein interactions.IMPORTANCEThe environmental bacteriumLegionella pneumophilais the causative agent of Legionnaires’ pneumonia. The bacteria form in free-living amoebae and mammalian immune cells a replication-permissive compartment, theLegionella-containing vacuole (LCV). To subvert host cell processes, the bacteria secrete the amazing number of ~300 different proteins into host cells. Some of these proteins bind phosphoinositide (PI) lipids to decorate the LCV. PI lipids are crucial factors involved in host cell membrane dynamics and LCV formation. UsingDictyosteliumamoebae producing one or two distinct fluorescent probes, we elucidated the dynamic LCV PI pattern in high temporal and spatial resolution. Notably, the endocytic PI lipid PtdIns(3)Pwas slowly cleared from LCVs, thus incapacitating the host cell’s digestive machinery, while PtdIns(4)Pgradually accumulated on the LCV, enabling critical interactions with host organelles. The LCV PI pattern underlies the spatiotemporal configuration of bacterial effector proteins and therefore represents a crucial aspect of LCV formation.

scholarly journals Interaction of the Ankyrin H Core Effector of Legionella with the Host LARP7 Component of the 7SK snRNP Complex

mBio ◽  
2019 ◽  
Vol 10 (4) ◽  
Author(s):  
Juanita Von Dwingelo ◽  
Ivy Yeuk Wah Chung ◽  
Christopher T. Price ◽  
Lei Li ◽  
Snake Jones ◽  
...  
Keyword(s):  
Host Cell ◽  
Legionella Pneumophila ◽  
Effector Proteins ◽  
Host Protein ◽  
Host Cells ◽  
Transcriptional Elongation ◽  
Intracellular Growth ◽  
Pol Ii ◽  
Content Type ◽  
Small Nuclear Ribonucleoprotein

ABSTRACT Species of the Legionella genus encode at least 18,000 effector proteins that are translocated through the Dot/Icm type IVB translocation system into macrophages and protist hosts to enable intracellular growth. Eight effectors, including ankyrin H (AnkH), are common to all Legionella species. The AnkH effector is also present in Coxiella and Rickettsiella. To date, no pathogenic effectors have ever been described that directly interfere with host cell transcription. We determined that the host nuclear protein La-related protein 7 (LARP7), which is a component of the 7SK small nuclear ribonucleoprotein (snRNP) complex, interacts with AnkH in the host cell nucleus. The AnkH-LARP7 interaction partially impedes interactions of the 7SK snRNP components with LARP7, interfering with transcriptional elongation by polymerase (Pol) II. Consistent with that, our data show AnkH-dependent global reprogramming of transcription of macrophages infected by Legionella pneumophila. The crystal structure of AnkH shows that it contains four N-terminal ankyrin repeats, followed by a cysteine protease-like domain and an α-helical C-terminal domain. A substitution within the β-hairpin loop of the third ankyrin repeat results in diminishment of LARP7-AnkH interactions and phenocopies the ankH null mutant defect in intracellular growth. LARP7 knockdown partially suppresses intracellular proliferation of wild-type (WT) bacteria and increases the severity of the defect of the ΔankH mutant, indicating a role for LARP7 in permissiveness of host cells to intracellular bacterial infection. We conclude that the AnkH-LARP7 interaction impedes interaction of LARP7 with 7SK snRNP, which would block transcriptional elongation by Pol II, leading to host global transcriptional reprogramming and permissiveness to L. pneumophila. IMPORTANCE For intracellular pathogens to thrive in host cells, an environment that supports survival and replication needs to be established. L. pneumophila accomplishes this through the activity of the ∼330 effector proteins that are injected into host cells during infection. Effector functions range from hijacking host trafficking pathways to altering host cell machinery, resulting in altered cell biology and innate immunity. One such pathway is the host protein synthesis pathway. Five L. pneumophila effectors have been identified that alter host cell translation, and 2 effectors have been identified that indirectly affect host cell transcription. No pathogenic effectors have been described that directly interfere with host cell transcription. Here we show a direct interaction of the AnkH effector with a host cell transcription complex involved in transcriptional elongation. We identify a novel process by which AnkH interferes with host transcriptional elongation through interference with formation of a functional complex and show that this interference is required for pathogen proliferation.

scholarly journals Targeting of the Small GTPase Rab6A′ by the Legionella pneumophila Effector LidA

2013 ◽  
Vol 81 (6) ◽  
pp. 2226-2235 ◽  
Author(s):  
Yang Chen ◽  
Matthias P. Machner
Keyword(s):  
Legionella Pneumophila ◽  
Small Gtpase ◽  
Effector Proteins ◽  
Host Cells ◽  
Intracellular Replication ◽  
Content Type ◽  
Type Iv ◽  
Gtpase Activating Proteins ◽  
Active Pool ◽  
Cell Cytosol

ABSTRACTWhen the bacteriumLegionella pneumophila, the causative agent of Legionnaires' disease, is phagocytosed by alveolar macrophages, it delivers a large number of effector proteins through its Dot/Icm type IV secretion system into the host cell cytosol. Among those proteins is LidA, an effector that interacts with several host GTPases of the Rab family, including Rab6A′, a regulator of retrograde vesicle trafficking within eukaryotic cells. The effect of LidA on Rab6A′ function and the role of Rab6A′ forL. pneumophilagrowth within host cells has been unclear. Here, we show that LidA preferentially binds Rab6A′ in the active GTP-bound conformation. Rab6 binding occurred through the central region of LidA and followed a stoichiometry for LidA and Rab6A′ of 1:2. LidA maintained Rab6A′ in the active conformation by efficiently blocking the hydrolysis of GTP by Rab6A′, even in the presence of cellular GTPase-activating proteins, suggesting that the function of Rab6A′ must be important for efficient intracellular replication ofL. pneumophila. Accordingly, we found that production of constitutively inactive Rab6A′(T27N) but not constitutively active Rab6A′(Q72L) significantly reduced the ability ofL. pneumophilato initiate intracellular replication in human macrophages. Thus, the presence of an active pool of Rab6 within host cells early during infection is required to support efficient intracellular growth ofL. pneumophila.

scholarly journals The Legionella longbeachae Icm/Dot Substrate SidC Selectively Binds Phosphatidylinositol 4-Phosphate with Nanomolar Affinity and Promotes Pathogen Vacuole-Endoplasmic Reticulum Interactions

2014 ◽  
Vol 82 (10) ◽  
pp. 4021-4033 ◽  
Author(s):  
Stephanie Dolinsky ◽  
Ina Haneburger ◽  
Adam Cichy ◽  
Mandy Hannemann ◽  
Aymelt Itzen ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Legionella Pneumophila ◽  
Severe Pneumonia ◽  
Biological Data ◽  
Effector Proteins ◽  
Host Cells ◽  
Titration Calorimetry ◽  
Dependent Manner ◽  
Content Type ◽  
Phosphatidylinositol 4

ABSTRACTLegionellaspp. cause the severe pneumonia Legionnaires' disease. The environmental bacteria replicate intracellularly in free-living amoebae and human alveolar macrophages within a distinct, endoplasmic reticulum (ER)-derived compartment termed theLegionella-containing vacuole (LCV). LCV formation requires the bacterial Icm/Dot type IV secretion system (T4SS) that translocates into host cells a plethora of different “effector” proteins, some of which anchor to the pathogen vacuole by binding to phosphoinositide (PI) lipids. Here, we identified by unbiased pulldown assays inLegionella longbeachaelysates a 111-kDa SidC homologue as the major phosphatidylinositol 4-phosphate [PtdIns(4)P]-binding protein. The PI-binding domain was mapped to a 20-kDa P4C [PtdIns(4)Pbinding of SidC] fragment. Isothermal titration calorimetry revealed that SidC ofL. longbeachae(SidCLlo) binds PtdIns(4)Pwith aKd(dissociation constant) of 71 nM, which is 3 to 4 times lower than that of the SidC orthologue ofLegionella pneumophila(SidCLpn). Upon infection of RAW 264.7 macrophages withL. longbeachae, endogenous SidCLloor ectopically produced SidCLpnlocalized in an Icm/Dot-dependent manner to the PtdIns(4)P-positive LCVs. AnL. longbeachaeΔsidCdeletion mutant was impaired for calnexin recruitment to LCVs inDictyostelium discoideumamoebae and outcompeted by wild-type bacteria inAcanthamoeba castellanii. Calnexin recruitment was restored by SidCLloor its orthologues SidCLpnand SdcALpn. Conversely, calnexin recruitment was restored by SidCLloinL. pneumophilalackingsidCandsdcA. Together, biochemical, genetic, and cell biological data indicate that SidCLlois anL. longbeachaeeffector that binds through a P4C domain with high affinity to PtdIns(4)Pon LCVs, promotes ER recruitment to the LCV, and thus plays a role in pathogen-host interactions.

scholarly journals Dependency of Coxiella burnetii Type 4B Secretion on the Chaperone IcmS

2019 ◽  
Vol 201 (23) ◽  
Author(s):  
Charles L. Larson ◽  
Paul A. Beare ◽  
Robert A. Heinzen
Keyword(s):  
Host Cell ◽  
Coxiella Burnetii ◽  
Legionella Pneumophila ◽  
Q Fever ◽  
Secretion System ◽  
Host Cells ◽  
Growth Defect ◽  
Wild Type ◽  
Signal Sequences ◽  
Content Type

ABSTRACT Macrophage parasitism by Coxiella burnetii, the cause of human Q fever, requires the translocation of proteins with effector functions directly into the host cell cytosol via a Dot/Icm type 4B secretion system (T4BSS). Secretion by the analogous Legionella pneumophila T4BSS involves signal sequences within the C-terminal and internal domains of effector proteins. The cytoplasmic chaperone pair IcmSW promotes secretion and binds internal sites distinct from signal sequences. In the present study, we investigated requirements of C. burnetii IcmS for host cell parasitism and effector translocation. A C. burnetii icmS deletion mutant (ΔicmS) exhibited impaired replication in Vero epithelial cells, deficient formation of the Coxiella-containing vacuole, and aberrant T4BSS secretion. Three secretion phenotypes were identified from a screen of 50 Dot/Icm substrates: IcmS dependent (secreted by only wild-type bacteria), IcmS independent (secreted by both wild-type and ΔicmS bacteria), or IcmS inhibited (secreted by only ΔicmS bacteria). Secretion was assessed for N-terminal or C-terminal truncated forms of CBU0794 and CBU1525. IcmS-inhibited secretion of CBU1525 required a C-terminal secretion signal whereas IcmS-dependent secretion of CBU0794 was directed by C-terminal and internal signals. Interchange of the C-terminal 50 amino acids of CBU0794 and CBU1525 revealed that sites within the C terminus regulate IcmS dependency. Glutathione S-transferase-tagged IcmSW bound internal sequences of IcmS-dependent and -inhibited substrates. Thus, the growth defect of the C. burnetii ΔicmS strain is associated with a loss of T4BSS chaperone activity that both positively and negatively regulates effector translocation. IMPORTANCE The intracellular pathogen Coxiella burnetii employs a type 4B secretion system (T4BSS) that promotes growth by translocating effectors of eukaryotic pathways into host cells. T4BSS regulation modeled in Legionella pneumophila indicates IcmS facilitates effector translocation. Here, we characterized type 4B secretion by a Coxiella ΔicmS mutant that exhibits intracellular growth defects. T4BSS substrates demonstrated increased, equivalent, or decreased secretion by the ΔicmS mutant relative to wild-type Coxiella. Similar to the Legionella T4BSS, IcmS dependency in Coxiella was determined by C-terminal and/or internal secretion signals. However, IcmS inhibited secretion of some effectors by Coxiella that were previously shown to be translocated by Legionella. Thus, Coxiella has a unique IcmS regulatory mechanism that both positively and negatively regulates T4BSS export.

scholarly journals Differences in Host Cell Invasion and Salmonella Pathogenicity Island 1 Expression between Salmonella enterica Serovar Paratyphi A and NontyphoidalS. Typhimurium

2016 ◽  
Vol 84 (4) ◽  
pp. 1150-1165 ◽  
Author(s):  
Dana Elhadad ◽  
Prerak Desai ◽  
Guntram A. Grassl ◽  
Michael McClelland ◽  
Galia Rahav ◽  
...  
Keyword(s):  
Host Cell ◽  
Cell Invasion ◽  
Salmonella Enterica ◽  
Intestinal Inflammation ◽  
Pathogenicity Island ◽  
Effector Proteins ◽  
Host Cells ◽  
Host Cell Invasion ◽  
Content Type ◽  
Microaerobic Conditions

Active invasion into nonphagocytic host cells is central toSalmonella entericapathogenicity and dependent on multiple genes withinSalmonellapathogenicity island 1 (SPI-1). Here, we explored the invasion phenotype and the expression of SPI-1 in the typhoidal serovarS. Paratyphi A compared to that of the nontyphoidal serovarS. Typhimurium. We demonstrate that whileS. Typhimurium is equally invasive under both aerobic and microaerobic conditions,S. Paratyphi A invades only following growth under microaerobic conditions. Transcriptome sequencing (RNA-Seq), reverse transcription-PCR (RT-PCR), Western blot, and secretome analyses established thatS. Paratyphi A expresses much lower levels of SPI-1 genes and secretes lesser amounts of SPI-1 effector proteins thanS. Typhimurium, especially under aerobic growth. Bypassing the native SPI-1 regulation by inducible expression of the SPI-1 activator, HilA, considerably elevated SPI-1 gene expression, host cell invasion, disruption of epithelial integrity, and induction of proinflammatory cytokine secretion byS. Paratyphi A but not byS. Typhimurium, suggesting that SPI-1 expression is naturally downregulated inS. Paratyphi A. Using streptomycin-treated mice, we were able to establish substantial intestinal colonization byS. Paratyphi A and showed moderately higher pathology and intestinal inflammation in mice infected withS. Paratyphi A overexpressinghilA. Collectively, our results reveal unexpected differences in SPI-1 expression betweenS. Paratyphi A andS. Typhimurium, indicate thatS. Paratyphi A host cell invasion is suppressed under aerobic conditions, and suggest that lower invasion in aerobic sites and suppressed expression of immunogenic SPI-1 components contributes to the restrained inflammatory infection elicited byS. Paratyphi A.

scholarly journals LtpD Is a Novel Legionella pneumophila Effector That Binds Phosphatidylinositol 3-Phosphate and Inositol Monophosphatase IMPA1

2013 ◽  
Vol 81 (11) ◽  
pp. 4261-4270 ◽  
Author(s):  
Clare R. Harding ◽  
Corinna Mattheis ◽  
Aurélie Mousnier ◽  
Clare V. Oates ◽  
Elizabeth L. Hartland ◽  
...  
Keyword(s):  
Host Cell ◽  
Legionella Pneumophila ◽  
Galleria Mellonella ◽  
Effector Proteins ◽  
Lung Epithelial Cells ◽  
Systematic Analysis ◽  
Content Type ◽  
Bacterial Replication ◽  
Phosphatidylinositol 3

ABSTRACTThe Dot/Icm type IV secretion system (T4SS) ofLegionella pneumophilais crucial for the pathogen to survive in protozoa and cause human disease. Although more than 275 effector proteins are delivered into the host cell by the T4SS, the function of the majority is unknown. Here we have characterized the Dot/Icm effector LtpD. During infection, LtpD localized to the cytoplasmic face of the membrane of theLegionella-containing vacuole (LCV). In A549 lung epithelial cells, ectopically expressed LtpD localized to large vesicular structures that contained markers of endosomal compartments. Systematic analysis of LtpD fragments identified an internal 17-kDa fragment, LtpD471-626, which was essential for targeting ectopically expressed LtpD to vesicular structures and for the association of translocated LtpD with the LCV. LtpD471-626bound directly to phosphatidylinositol 3-phosphate [PtdIns(3)P]in vitroand colocalized with the PtdIns(3)P markers FYVE and SetA in cotransfected cells. LtpD was also found to bind the host cell enzyme inositol (myo)-1 (or 4)-monophosphatase 1, an important phosphatase involved in phosphoinositide production. Analysis of the role of LtpD in infection showed that LtpD is involved in bacterial replication in THP-1 macrophages, the larvae ofGalleria mellonella, and mouse lungs. Together, these data suggest that LtpD is a novel phosphoinositide-bindingL. pneumophilaeffector that has a role in intracellular bacterial replication.

scholarly journals A Novel Legionella Genomic Island Encodes a Copper-Responsive Regulatory System and a Single Icm/Dot Effector Protein Transcriptionally Activated by Copper

mBio ◽  
2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Marika Linsky ◽  
Yevgeniya Vitkin ◽  
Gil Segal
Keyword(s):  
Gene Transfer ◽  
Horizontal Gene Transfer ◽  
Legionella Pneumophila ◽  
Genomic Island ◽  
Regulatory System ◽  
Secretion System ◽  
Effector Proteins ◽  
Host Cells ◽  
Effector Protein ◽  
Content Type

ABSTRACT The intracellular pathogen Legionella pneumophila utilizes the Icm/Dot type IV secretion system to translocate >300 effector proteins into host cells during infection. The regulation of some of these effector-encoding genes was previously shown to be coordinated by several global regulators, including three two-component systems (TCSs) found in all the Legionella species examined. Here, we describe the first Legionella genomic island encoding a single Icm/Dot effector and a dedicated TCS, which regulates its expression. This genomic island, which we named Lci, undergoes horizontal gene transfer in the Legionella genus, and the TCS encoded from this island (LciRS) is homologous to TCSs that control the expression of various metal resistance systems found in other bacteria. We found that the L. pneumophila sensor histidine kinase LciS is specifically activated by copper via a unique, small periplasmic sensing domain. Upon activation by LciS, the response regulator LciR directly binds to a conserved regulatory element and activates the expression of the adjacently located lciE effector-encoding gene. Thus, LciR represents the first local regulator of effectors identified in L. pneumophila. Moreover, we found that the expression of the lciRS operon is repressed by the Fis1 and Fis3 regulators, leading to Fis-mediated effects on copper induction of LciE and silencing of the expression of this genomic island in the absence of copper. This island represents a novel type of effector regulation in Legionella, shedding new light on the ways by which the Legionella pathogenesis system evolves its effector repertoire and expands its activating signals. IMPORTANCE Legionella pneumophila is an intracellular human pathogen that utilizes amoebae as its environmental host. The adaptation of L. pneumophila to the intracellular environment requires coordination of expression of its multicomponent pathogenesis system, which is composed of a secretion system and effector proteins. However, the regulatory factors controlling the expression of this pathogenesis system are only partially uncovered. Here, we discovered a novel regulatory system that is activated by copper and controls the expression of a single effector protein. The genes encoding both the regulatory system and the effector protein are located on a genomic island that undergoes horizontal gene transfer within the Legionella genus. This regulator-effector genomic island represents the first reported case of local regulation of effectors in Legionella. The discovery of this regulatory mechanism is an important step forward in the understanding of how the regulatory network of effectors functions and evolves in the Legionella genus.

scholarly journals An Inside Job: Hacking into Janus Kinase/Signal Transducer and Activator of Transcription Signaling Cascades by the Intracellular Protozoan Toxoplasma gondii

2011 ◽  
Vol 80 (2) ◽  
pp. 476-482 ◽  
Author(s):  
Eric Y. Denkers ◽  
David J. Bzik ◽  
Barbara A. Fox ◽  
Barbara A. Butcher
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Secretory Protein ◽  
Effector Proteins ◽  
Janus Kinase ◽  
Host Cells ◽  
Cytokine Signaling ◽  
Signal Transducer ◽  
Content Type ◽  
Transcription 3

ABSTRACTThe intracellular protozoanToxoplasma gondiiis well known for its skill at invading and living within host cells. New discoveries are now also revealing the astounding ability of the parasite to inject effector proteins into the cytoplasm to seize control of the host cell. This review summarizes recent advances in our understanding of one such secretory protein called ROP16. This molecule is released from rhoptries into the host cell during invasion. The ROP16 molecule acts as a kinase, directly activating both signal transducer and activator of transcription 3 (STAT3) and STAT6 signaling pathways. In macrophages, an important and preferential target cell of parasite infection, the injection of ROP16 has multiple consequences, including downregulation of proinflammatory cytokine signaling and macrophage deviation to an alternatively activated phenotype.

scholarly journals Alveolar Macrophages and Neutrophils Are the Primary Reservoirs for Legionella pneumophila and Mediate Cytosolic Surveillance of Type IV Secretion

2014 ◽  
Vol 82 (10) ◽  
pp. 4325-4336 ◽  
Author(s):  
Alan M. Copenhaver ◽  
Cierra N. Casson ◽  
Hieu T. Nguyen ◽  
Thomas C. Fung ◽  
Matthew M. Duda ◽  
...  
Keyword(s):  
Immune Response ◽  
Alveolar Macrophages ◽  
Legionella Pneumophila ◽  
Pulmonary Infection ◽  
Severe Pneumonia ◽  
Effector Proteins ◽  
Type Iv Secretion ◽  
Host Cells ◽  
Content Type ◽  
Type Iv

ABSTRACTLegionella pneumophila, an intracellular pathogen responsible for the severe pneumonia Legionnaires' disease, uses itsdot/icm-encoded type IV secretion system (T4SS) to translocate effector proteins that promote its survival and replication into the host cell cytosol. However, by introducing bacterial products into the host cytosol,L. pneumophilaalso activates cytosolic immunosurveillance pathways, thereby triggering robust proinflammatory responses that mediate the control of infection. Thus, the pulmonary cell types thatL. pneumophilainfects not only may act as an intracellular niche that facilitates its pathogenesis but also may contribute to the immune response againstL. pneumophila. The identity of these host cells remains poorly understood. Here, we developed a strain ofL. pneumophilaproducing a fusion protein consisting of β-lactamase fused to the T4SS-translocated effector RalF, which allowed us to track cells injected by the T4SS. Our data reveal that alveolar macrophages and neutrophils both are the primary recipients of T4SS-translocated effectors and harbor viableL. pneumophiladuring pulmonary infection of mice. Moreover, both alveolar macrophages and neutrophils from infected mice produced tumor necrosis factor and interleukin-1α in response to T4SS-sufficient, but not T4SS-deficient,L. pneumophila. Collectively, our data suggest that alveolar macrophages and neutrophils are both an intracellular reservoir forL. pneumophilaand a source of proinflammatory cytokines that contribute to the host immune response againstL. pneumophiladuring pulmonary infection.

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