Modulation of Bacterial Type III Secretion System by a Spermidine Transporter Dependent Signaling Pathway

10.1371/journal.pone.0001291PLoS ONE212

Identification of Small Molecule Inhibitors of Pseudomonas aeruginosa Exoenzyme S Using a Yeast Phenotypic Screen

Pseudomonas aeruginosa is an opportunistic human pathogen that is a key factor in the mortality of cystic fibrosis patients, and infection represents an increased threat for human health worldwide. Because resistance of Pseudomonas aeruginosa to antibiotics is increasing, new inhibitors of pharmacologically validated targets of this bacterium are needed. Here we demonstrate that a cell-based yeast phenotypic assay, combined with a large-scale inhibitor screen, identified small molecule inhibitors that can suppress the toxicity caused by heterologous expression of selected Pseudomonas aeruginosa ORFs. We identified the first small molecule inhibitor of Exoenzyme S (ExoS), a toxin involved in Type III secretion. We show that this inhibitor, exosin, modulates ExoS ADP-ribosyltransferase activity in vitro, suggesting the inhibition is direct. Moreover, exosin and two of its analogues display a significant protective effect against Pseudomonas infection in vivo. Furthermore, because the assay was performed in yeast, we were able to demonstrate that several yeast homologues of the known human ExoS targets are likely ADP-ribosylated by the toxin. For example, using an in vitro enzymatic assay, we demonstrate that yeast Ras2p is directly modified by ExoS. Lastly, by surveying a collection of yeast deletion mutants, we identified Bmh1p, a yeast homologue of the human FAS, as an ExoS cofactor, revealing that portions of the bacterial toxin mode of action are conserved from yeast to human. Taken together, our integrated cell-based, chemical-genetic approach demonstrates that such screens can augment traditional drug screening approaches and facilitate the discovery of new compounds against a broad range of human pathogens

Modified Needle-Tip PcrV Proteins Reveal Distinct Phenotypes Relevant to the Control of Type III Secretion and Intoxication by Pseudomonas aeruginosa

The type III secretion system (T3SS) is employed to deliver effector proteins to the cytosol of eukaryotic hosts by multiple species of Gram-negative bacteria, including Pseudomonas aeruginosa. Translocation of effectors is dependent on the proteins encoded by the pcrGVHpopBD operon. These proteins form a T3S translocator complex, composed of a needle-tip complex (PcrV), translocons (PopB and PopD), and chaperones (PcrG and PcrH). PcrV mediates the folding and insertion of PopB/PopD in host plasmic membranes, where assembled translocons form a translocation channel. Assembly of this complex and delivery of effectors through this machinery is tightly controlled by PcrV, yet the multifunctional aspects of this molecule have not been defined. In addition, PcrV is a protective antigen for P. aeruginosa infection as is the ortholog, LcrV, for Yersinia. We constructed PcrV derivatives containing in-frame linker insertions and site-specific mutations. The expression of these derivatives was regulated by a T3S-specific promoter in a pcrV-null mutant of PA103. Nine derivatives disrupted the regulation of effector secretion and constitutively released an effector protein into growth medium. Three of these regulatory mutants, in which the linker was inserted in the N-terminal globular domain, were competent for the translocation of a cytotoxin, ExoU, into eukaryotic host cells. We also isolated strains expressing a delayed-toxicity phenotype, which secrete translocators slowly despite the normal level of effector secretion. Most of the cytotoxic translocation-competent strains retained the protective epitope of PcrV derivatives, and Mab166 was able to protect erythrocytes during infection with these strains. The use of defined PcrV derivatives possessing distinct phenotypes may lead to a better understanding of the functional aspects of T3 needle-tip proteins and the development of therapeutic agents or vaccines targeting T3SS-mediated intoxication

Control of moderate-to-severe asthma with randomized ciclesonide doses of 160, 320 and 640 μg/day

Søren E Pedersen,1 Niyati Prasad,2 Udo-Michael Goehring,3 Henrik Andersson,4 Dirkje S Postma5 1Pediatric Research Unit, Kolding Hospital, University of Southern Denmark, Kolding, Denmark; 2Vertex, Phase IV & Global Strategy, London, UK; 3Vifor Pharma Ltd, Clinical Research & Biometrics, Glattbrugg, Switzerland; 4Swedish Social Insurance Agency, Government Offices of Sweden, Stockholm, Sweden; 5Department of Pulmonology, Griac Research Institute, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands Background: The inhaled corticosteroid (ICS) ciclesonide (Cic), controls asthma symptoms in the majority of patients at the recommended dose of 160 µg/day. However, the relationship between the level of asthma control and increasing doses of Cic is unknown. This study investigated whether long-term treatment with higher doses of Cic would further improve asthma symptoms in patients with uncontrolled asthma despite ICS use. Patients and methods: In a double-blind, randomized, parallel-group study, 367 patients were allocated to one of three treatment arms (Cic 160, 320 and 640 μg/day). After a single-blind, 3-week baseline period with Cic 160 µg/day, eligible patients were randomized to receive 52 weeks of treatment with Cic 160, 320 or 640 μg/day (double-blind period) during which forced expiratory volume in 1 second (FEV1), exacerbations and Asthma Control Questionnaire (ACQ) scores were measured. Results: Treatment with all the three doses was associated with significant improvements in ACQ scores, FEV1 and asthma symptoms (P<0.01). There were no statistically significant differences between the three doses. The results of the primary end point analysis showed a numerical improvement in the ACQ score with Cic 640 μg/day compared with Cic 160 μg/day (least square [LS] mean: -0.122; two-sided P-value: 0.30). Post hoc subgroup analyses showed that the improvement in the ACQ score with Cic 640 μg/day compared with Cic 160 μg/day was statistically significant in subjects who experience at least one exacerbation per year (LS mean: -0.586; 95% confidence interval: -1.110, -0.062, P=0.0285). Adverse events were low and consistent with the known safety profile of Cic. Conclusion: In patients with persistent, uncontrolled asthma, increasing the Cic dose from 160 to 640 µg/day provided no clear additional effect. Patients who experience more than one exacerbation per year may benefit from higher doses; however, further studies are necessary to confirm this. All Cic doses were well tolerated. Keywords: dose-response, asthma contro

Phosphorylation-independent interaction between 14-3-3 and exoenzyme S: from structure to pathogenesis

14-3-3 proteins are phosphoserine/phosphothreonine-recognizing adapter proteins that regulate the activity of a vast array of targets. There are also examples of 14-3-3 proteins binding their targets via unphosphorylated motifs. Here we present a structural and biological investigation of the phosphorylation-independent interaction between 14-3-3 and exoenzyme S (ExoS), an ADP-ribosyltransferase toxin of Pseudomonas aeruginosa. ExoS binds to 14-3-3 in a novel binding mode mostly relying on hydrophobic contacts. The 1.5 Å crystal structure is supported by cytotoxicity analysis, which reveals that substitution of the corresponding hydrophobic residues significantly weakens the ability of ExoS to modify the endogenous targets RAS/RAP1 and to induce cell death. Furthermore, mutation of key residues within the ExoS binding site for 14-3-3 impairs virulence in a mouse pneumonia model. In conclusion, we show that ExoS binds 14-3-3 in a novel reversed orientation that is primarily dependent on hydrophobic residues. This interaction is phosphorylation independent and is required for the function of ExoS