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A Candidate Approach Implicates the Secreted Salmonella Effector Protein SpvB in P-Body Disassembly
(2011)
P-bodies are dynamic aggregates of RNA and proteins involved in several post-transcriptional regulation processes. Pbodies have been shown to play important roles in regulating viral infection, whereas their interplay with bacterial pathogens, specifically intracellular bacteria that extensively manipulate host cell pathways, remains unknown. Here, we report that Salmonella infection induces P-body disassembly in a cell type-specific manner, and independently of previously characterized pathways such as inhibition of host cell RNA synthesis or microRNA-mediated gene silencing. We show that the Salmonella-induced P-body disassembly depends on the activation of the SPI-2 encoded type 3 secretion system, and that the secreted effector protein SpvB plays a major role in this process. P-body disruption is also induced by the related pathogen, Shigella flexneri, arguing that this might be a new mechanism by which intracellular bacterial pathogens subvert host cell function.
Bacterial glucuronidase as general marker for oncolytic virotherapy or other biological therapies
(2011)
Background: Oncolytic viral tumor therapy is an emerging field in the fight against cancer with rising numbers of clinical trials and the first clinically approved product (Adenovirus for the treatment of Head and Neck Cancer in China) in this field. Yet, until recently no general (bio)marker or reporter gene was described that could be used to evaluate successful tumor colonization and/or transgene expression in other biological therapies. Methods: Here, a bacterial glucuronidase (GusA) encoded by biological therapeutics (e.g. oncolytic viruses) was used as reporter system. Results: Using fluorogenic probes that were specifically activated by glucuronidase we could show 1) preferential activation in tumors, 2) rena l excretion of the activated fluorescent compounds and 3) reproducible detection of GusA in the serum of oncolytic vaccinia virus treated, tumor bearing mice in several tumor models. Time course studies revealed that reliable differentiation between tumor bearing and healthy mice can be done as early as 9 days post injection of the virus. Regarding the sensitivity of the newly developed assay system, we could show that a single infected tumor cell could be reliably detected in this assay. Conclusion: GusA therefore has the potential to be used as a general marker in the preclinical and clinical evaluation of (novel) biological therapies as well as being useful for the detection of rare cells such as circulating tumor cells
Despite the internet's dynamic and collaborative nature, scientists continue to produce grant proposals, lab notebooks, data files, conclusions etc. that stay in static formats or are not published online and therefore not always easily accessible to the interested public. Because of limited adoption of tools that seamlessly integrate all aspects of a research project (conception, data generation, data evaluation, peerreviewing and publishing of conclusions), much effort is later spent on reproducing or reformatting individual entities before they can be repurposed independently or as parts of articles.
We propose that workflows - performed both individually and collaboratively - could potentially become more efficient if all steps of the research cycle were coherently represented online and the underlying data were formatted, annotated and licensed for reuse. Such a system would accelerate the process of taking projects from conception to publication stages and allow for continuous updating of the data sets and their interpretation as well as their integration into other independent projects.
A major advantage of such work ows is the increased transparency, both with respect to the scientific process as to the contribution of each participant. The latter point is important from a perspective of motivation, as it enables the allocation of reputation, which creates incentives for scientists to contribute to projects. Such work ow platforms offering possibilities to fine-tune the accessibility of their content could gradually pave the path from the current static mode of research presentation into a more coherent practice of open science.
Background:
The probiotic Escherichia coli strain Nissle 1917 (EcN) has been shown to interfere in a human in vitro model with the invasion of several bacterial pathogens into epithelial cells, but the underlying molecular mechanisms are not known.
Methodology/Principal Findings:
In this study, we investigated the inhibitory effects of EcN on Salmonella Typhimurium invasion of porcine intestinal epithelial cells, focusing on EcN effects on the various stages of Salmonella infection including intracellular and extracellular Salmonella growth rates, virulence gene regulation, and adhesion. We show that EcN affects the initial Salmonella invasion steps by modulating Salmonella virulence gene regulation and Salmonella SiiE-mediated adhesion, but not extra-and intracellular Salmonella growth. However, the inhibitory activity of EcN against Salmonella invasion always correlated with EcN adhesion capacities. EcN mutants defective in the expression of F1C fimbriae and flagellae were less adherent and less inhibitory toward Salmonella invasion. Another E. coli strain expressing F1C fimbriae was also adherent to IPEC-J2 cells, and was similarly inhibitory against Salmonella invasion like EcN.
Conclusions:
We propose that EcN affects Salmonella adhesion through secretory components. This mechanism appears to be common to many E. coli strains, with strong adherence being a prerequisite for an effective reduction of SiiE-mediated Salmonella adhesion.
Virotherapy using oncolytic vaccinia virus strains is one of the most promising new strategies for cancer therapy. In this study, we analyzed for the first time the therapeutic efficacy of the oncolytic vaccinia virus GLV-1h68 in two human hepatocellular carcinoma cell lines HuH7 and PLC/PRF/5 (PLC) in cell culture and in tumor xenograft models. By viral proliferation assays and cell survival tests, we demonstrated that GLV-1h68 efficiently colonized, replicated in, and did lyse these cancer cells in culture. Experiments with HuH7 and PLC xenografts have revealed that a single intravenous injection (i.v.) of mice with GLV-1h68 resulted in a significant reduction of primary tumor sizes compared to uninjected controls. In addition, replication of GLV-1h68 in tumor cells led to strong inflammatory and oncolytic effects resulting in intense infiltration of MHC class II-positive cells like neutrophils, macrophages, B cells and dendritic cells and in up-regulation of 13 pro-inflammatory cytokines. Furthermore, GLV-1h68 infection of PLC tumors inhibited the formation of hemorrhagic structures which occur naturally in PLC tumors. Interestingly, we found a strongly reduced vascular density in infected PLC tumors only, but not in the non-hemorrhagic HuH7 tumor model. These data demonstrate that the GLV-1h68 vaccinia virus may have an enormous potential for treatment of human hepatocellular carcinoma in man.
Staphylococcus aureus ist einer der häufigsten Erreger von nosokomialen Infektionen. Diese grampositiven Bakterien verursachen neben harmlosen oberflächlichen Hautinfektionen auch lebensbedrohliche Systeminfektionen. Ein großes Problem in der Therapie von S. aureus-Infektionen stellen die zunehmenden Multiresistenzen dar. Die Entwicklung neuer Antibiotika wird zukünftig wahrscheinlich nicht ausreichen, da immer wieder neue Resistenzen der Bakterien zu erwarten sind. Es besteht daher dringender Bedarf an der Entwicklung alternativer Therapieformen im Kampf gegen multiresistente Problemkeime wie S. aureus. Eine Möglichkeit besteht in der Immuntherapie, zum Beispiel durch Gewinnung von monoklonalen Antikörpern gegen geeignete Targetstrukturen von S. aureus. Ziel dieser Arbeit war es, zunächst zwei Proteine IsaA und IsaB herzustellen, um diese Proteine für Immunisierungsstudien zu nutzen. Zunächst wurde das gereinigte IsaA-Protein verwendet, um ein Kaninchen zu immunisieren. Mit den daraus gewonnenen Antikörpern wurden dann erste Tierversuche begonnen, um die Bedingungen für den therapeutischen Einatz von gegen IsaA-gerichteten Antikörpern zu ermitteln und die Wirksamkeit einer Antikörper-Behandlung zu evaluieren. Für die Herstellung der gewünschten Proteine wurden die Gensequenzen zunächst aus verschiedenen S. aureus-Stämmen mittels PCR amplifiziert und in den kommerziellen Expressionsvektor pQE30 kloniert. Die amplifizierte Gensequenz stammt aus den klinischen Stämmen 418 (IsaA) bzw. 134 (IsaB). Nach der Klonierung wurden geeignete Expressions- und Reinigungsstrategien entwickelt. Dabei wurden folgende Bedingungen als optimal für Wachstum und Überexpression herausgearbeitet: IsaA: Induktion der Überexpression mit 100 µM IPTG, 3 h Wachstum bei 37°C. IsaB: Induktion der Überexpression mit 100 µM IPTG, 4 h Wachstum bei 37°C. Es stellte sich auch heraus, dass IsaA zunächst in nur unzureichender Quantität vorhanden bzw. exprimiert worden war. Die Vermutung, dass IsaA überwiegend im Pellet in sogenannten Einschlusskörpern (inclusion bodies) eingeschlossen war, erklärte dieses Phänomen. Das Protein konnte erfolgreich aus dem Pellet isoliert werden. Die Produktion und Aufreinigung beider Proteine IsaA und IsaB unter optimierten Bedingungen ergab, dass beide Proteine nun in ausreichender Menge und Konzentration für die folgende Immunisierung und die weiteren Arbeiten vorlagen. Aus Kaninchen, die mit IsaA immunisiert wurden, konnten polyklonale Antikörper gewonnen werden, die die Grundlage für einen ersten Tierversuch mit 24 Ratten bildeten. Hierbei zeigte sich, dass die Tiere, die mit 1.000.000.000 Bakterien infiziert worden waren deutlich stärkere Infektionszeichen aufwiesen als diejenigen, die mit 100.000.000 Bakterien infiziert worden waren. Weiterhin wurde deutlich, dass die Tiere, die Serum (mit Antikörper gegen IsaA) erhalten hatten, gegenüber den Vergleichstieren mit Placebo einen deutlichen Vorteil hinsichtlich Infektionszeichen und Immunantwort hatten. Somit belegen die tierexperimentiellen Ergebnisse in dieser Arbeit erstmalig den therapeutischen Nutzen von Antikörpern gegen IsaA. IsaA ist demnach ein geeignetes Target für eine Immuntherapie gegen S. aureus.
Der Hefepilz Candida albicans gehört zu den fakultativ pathogenen Infektionserregern und ist Teil der natürlichen Mikroflora der Schleimhäute des Verdauungs- und Urogenitaltraktes der meisten gesunden Menschen. Ist das Gleichgewicht der Flora gestört, kann es zu oberflächlichen Mykosen kommen, wie z.B. der oropharyngealen Candidiasis (Mundsoor), die in der Regel durch die Gabe eines Antimykotikums in wenigen Tagen zu behandeln sind. In seltenen Fällen kann es auch zu schwerwiegenden Infektionsverläufen bis hin zu lebensbedrohlichen systemischen Mykosen kommen. Hauptsächlich immunsupprimierte Patienten, wie z.B. AIDS-Patienten oder Personen, die kürzlich einer Organ- oder Knochenmarkstransplantation unterzogen wurden, leiden häufig an oberflächlichen C. albicans-Infektionen. Insbesondere bei wiederkehrenden Infektionen ist der Pilz in der Lage, gegen das häufig verabreichte Medikament Fluconazol eine Resistenz zu entwickeln. Ein wichtiger Mechanismus dieser Resistenzentwicklung ist die Überexpression von Effluxpumpen, die das Medikament aus der Zelle heraustransportieren. Zwei Arten von Effluxpumpen, die eine Rolle in der Resistenzentwicklung in C. albicans spielen, konnten bisher identifiziert werden, die ABC (ATP binding cassette)-Transporter Cdr1 und Cdr2 sowie der MFS (major facilitator superfamily)-Transporter Mdr1. Der Zinc-Cluster Transkriptionsfaktor Mrr1 spielt eine wichtige Rolle in der Regulation der MDR1-E¬ffluxpumpe. Er kontrolliert die MDR1-Expression in Anwesenheit induzierender Substanzen und sogenannte "gain-of-function" Mutationen in MRR1 konnten als die Ursache der konstitutiven MDR1-Hochregulierung und der "Multidrug-Resistance" in C. albicans identifiziert werden. In dieser Arbeit konnte ein Ortholog zu MRR1 aus C. albicans in Candida dubliniensis, einer zu C. albicans nahe verwandten Hefe, identifiziert werden. Es wurde gezeigt, dass in den untersuchten klinischen und in vitro generierten Fluconazol-resistenten C. dubliniensis-Stämmen ebenfalls gain-of-funcion Mutationen in MRR1 die MDR1-Überexpression und eine Resistenz bewirken. Die Ergebnisse demonstrieren, dass der Transkriptionsfaktor Mrr1 eine wichtige Rolle in der Entwicklung der Resistenz in diesen humanpathogenen Pilzen spielt. Bisher ist nicht bekannt, wie der Zinc-Cluster Transkriptionsfaktor MRR1 durch induzierende Substanzen oder gain-of-function Mutationen aktiviert wird. Um zu verstehen, wie die Mrr1- Aktivität reguliert wird, wurden in dieser Arbeit durch Deletionsstudien funktionelle Domänen des Transkriptionsfaktors identifiziert. Um einen besseren Einblick in die Regulation der MDR1-vermittelten Resistenz in C. albicans zu bekommen, wurde in dieser Arbeit die gegenseitige Abhängigkeit von Mrr1 und Cap1 bzw. Upc2 in Bezug auf die MDR1-Expression untersucht. Es wurden ChIP-on-chip Analysen und Transkriptionsprofile mit aktiviertem Mrr1 durchgeführt, um direkte Targets von Mrr1 zu identifizieren. Mit der vorliegenden Arbeit wurde ein wichtiger Beitrag zum Verständnis der Entwicklung der Multidrug-Resistenz in C. albicans geleistet. E¬ffluxpumpen und deren Regulatoren stellen in der Bekämpfung von C. albicans-Infektionen ein interessantes Angriffsziel für die Entwicklung neuer Medikamente und die Weiterentwicklung bereits vorhandender Antimykotika dar.
The Gram-negative plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) is an important model to elucidate the mechanisms involved in the interaction with the host. To gain insight into the transcriptome of the Xcv strain 85-10, we took a differential RNA sequencing (dRNA-seq) approach. Using a novel method to automatically generate comprehensive transcription start site (TSS) maps we report 1421 putative TSSs in the Xcv genome. Genes in Xcv exhibit a poorly conserved -10 promoter element and no consensus Shine-Dalgarno sequence. Moreover, 14% of all mRNAs are leaderless and 13% of them have unusually long 5'-UTRs. Northern blot analyses confirmed 16 intergenic small RNAs and seven cis-encoded antisense RNAs in Xcv. Expression of eight intergenic transcripts was controlled by HrpG and HrpX, key regulators of the Xcv type III secretion system. More detailed characterization identified sX12 as a small RNA that controls virulence of Xcv by affecting the interaction of the pathogen and its host plants. The transcriptional landscape of Xcv is unexpectedly complex, featuring abundant antisense transcripts, alternative TSSs and clade-specific small RNAs.
Background
MicroRNAs, post-transcriptional regulators of eukaryotic gene expression, are implicated in host defense against pathogens. Viruses and bacteria have evolved strategies that suppress microRNA functions, resulting in a sustainable infection. In this work we report that Helicobacter pylori, a human stomach-colonizing bacterium responsible for severe gastric inflammatory diseases and gastric cancers, downregulates an embryonic stem cell microRNA cluster in proliferating gastric epithelial cells to achieve cell cycle arrest.
Results
Using a deep sequencing approach in the AGS cell line, a widely used cell culture model to recapitulate early events of H. pylori infection of gastric mucosa, we reveal that hsa-miR-372 is the most abundant microRNA expressed in this cell line, where, together with hsa-miR-373, it promotes cell proliferation by silencing large tumor suppressor homolog 2 (LATS2) gene expression. Shortly after H. pylori infection, miR-372 and miR-373 synthesis is highly inhibited, leading to the post-transcriptional release of LATS2 expression and thus, to a cell cycle arrest at the G1/S transition. This downregulation of a specific cell-cycle-regulating microRNA is dependent on the translocation of the bacterial effector CagA into the host cells, a mechanism highly associated with the development of severe atrophic gastritis and intestinal-type gastric carcinoma.
Conclusions
These data constitute a novel example of host-pathogen interplay involving microRNAs, and unveil the couple LATS2/miR-372 and miR-373 as an unexpected mechanism in infection-induced cell cycle arrest in proliferating gastric cells, which may be relevant in inhibition of gastric epithelium renewal, a major host defense mechanism against bacterial infections.
Background:
Recent studies have shown that human ferritin can be used as a reporter of gene expression for magnetic resonance imaging (MRI). Bacteria also encode three classes of ferritin-type molecules with iron accumulation properties.
Methods and Findings:
Here, we investigated whether these bacterial ferritins can also be used as MRI reporter genes and which of the bacterial ferritins is the most suitable reporter. Bacterial ferritins were overexpressed in probiotic E. coli Nissle 1917. Cultures of these bacteria were analyzed and those generating highest MRI contrast were further investigated in tumor bearing mice. Among members of three classes of bacterial ferritin tested, bacterioferritin showed the most promise as a reporter gene. Although all three proteins accumulated similar amounts of iron when overexpressed individually, bacterioferritin showed the highest contrast change. By site-directed mutagenesis we also show that the heme iron, a unique part of the bacterioferritin molecule, is not critical for MRI contrast change. Tumor-specific induction of bacterioferritin-expression in colonized tumors resulted in contrast changes within the bacteria-colonized tumors.
Conclusions:
Our data suggest that colonization and gene expression by live vectors expressing bacterioferritin can be monitored by MRI due to contrast changes.