Untersuchungen zur biologischen Funktion des trimeren Autotransporter Adhäsins Ata in Acinetobacter baumannii

Acinetobacter baumannii ist ein Gram-negatives humanpathogenes Bakterium, welches für eine Vielzahl von nosokomialen Infektionen verantwortlich ist. Das in A. baumannii beschriebene Membranprotein Ata gehört zur Familie der trimeren Autotransporter Adhäsine (TAA), die in Gram-negativen Bakterien weit verbreitet sind und wichtige Virulenzfaktoren darstellen. Unter Verwendung eines markerlos generierten isogenen ata-Deletionsstammes sowie komplementierter Kontrollstämme wurde die Funktion von Ata bei der Infektion mit A. baumannii untersucht. Es wurde nachgewiesen, dass die initiale Interaktion von A. baumannii an Bestandteile der extrazellulären Matrix durch Ata vermittelt wird. Weiterhin ist die Adhäsion des Bakteriums an humane Endothel- und Epithelzellen, sowohl in vitro als auch ex vivo unter dynamischen Flussbedingungen, abhängig von Ata. Das Protein befähigt die Bakterien außerdem zu einer gesteigerten Invasionsrate in humane Zellen, die vermutlich über die Interaktion des TAAs mit β-Integrinen des Wirts gesteuert wird. Während der Infektion von humanen Endothelzellen mit A. baumannii bewirkt Ata eine zeitabhängige Induktion proinflammatorischer Zytokine wie IL-6 und IL-8. Dies führt unter anderem zu einer Ata-abhängigen Rekrutierung bzw. Aktivierung von humanen Immunzellen bzw. Hämozyten in den Larven der Großen Wachsmotte (G. mellonella). Ata stimuliert die Caspase 3- und Caspase 7-Aktivität, was zur Apoptose der Wirtszelle führt. Im in vivo-Infektionsmodell zeigt der Wildtyp-Stamm im Vergleich zum ata-Deletionsstamm eine erhöhte Pathogenität. Die in der vorliegenden Arbeit gewonnenen Daten belegen, dass das trimere Autotransporter Adhäsin Ata in A. baumannii ein wichtiger multifunktioneller Virulenzfaktor ist und somit maßgeblich zur erfolgreichen Etablierung einer Infektion von A. baumannii im menschlichen Körper beiträgt

Bridging topological and functional information in protein interaction networks by short loops profiling

Protein-protein interaction networks (PPINs) have been employed to identify potential novel interconnections between proteins as well as crucial cellular functions. In this study we identify fundamental principles of PPIN topologies by analysing network motifs of short loops, which are small cyclic interactions of between 3 and 6 proteins. We compared 30 PPINs with corresponding randomised null models and examined the occurrence of common biological functions in loops extracted from a cross-validated high-confidence dataset of 622 human protein complexes. We demonstrate that loops are an intrinsic feature of PPINs and that specific cell functions are predominantly performed by loops of different lengths. Topologically, we find that loops are strongly related to the accuracy of PPINs and define a core of interactions with high resilience. The identification of this core and the analysis of loop composition are promising tools to assess PPIN quality and to uncover possible biases from experimental detection methods. More than 96% of loops share at least one biological function, with enrichment of cellular functions related to mRNA metabolic processing and the cell cycle. Our analyses suggest that these motifs can be used in the design of targeted experiments for functional phenotype detection.This research was supported by the Biotechnology and Biological Sciences Research Council (BB/H018409/1 to AP, ACCC and FF, and BB/J016284/1 to NSBT) and by the Leukaemia & Lymphoma Research (to NSBT and FF). SSC is funded by a Leukaemia & Lymphoma Research Gordon Piller PhD Studentship

The DEAD-box helicase DDX3 supports the assembly of functional 80S ribosomes

The DEAD-box helicase DDX3 has suggested functions in innate immunity, mRNA translocation and translation, and it participates in the propagation of assorted viruses. Exploring initially the role of DDX3 in the life cycle of hepatitis C virus, we observed the protein to be involved in translation directed by different viral internal ribosomal entry sites. Extension of these studies revealed a general supportive role of DDX3 in translation initiation. DDX3 was found to interact in an RNA-independent manner with defined components of the translational pre-initiation complex and to specifically associate with newly assembling 80S ribosomes. DDX3 knock down and in vitro reconstitution experiments revealed a significant function of the protein in the formation of 80S translation initiation complexes. Our study implies that DDX3 assists the 60S subunit joining process to assemble functional 80S ribosomes

Predictive Genes in Adjacent Normal Tissue Are Preferentially Altered by sCNV during Tumorigenesis in Liver Cancer and May Rate Limiting

Background: In hepatocellular carcinoma (HCC) genes predictive of survival have been found in both adjacent normal (AN) and tumor (TU) tissues. The relationships between these two sets of predictive genes and the general process of tumorigenesis and disease progression remains unclear. Methodology/Principal Findings: Here we have investigated HCC tumorigenesis by comparing gene expression, DNA copy number variation and survival using ~250 AN and TU samples representing, respectively, the pre-cancer state, and the result of tumorigenesis. Genes that participate in tumorigenesis were defined using a gene-gene correlation meta-analysis procedure that compared AN versus TU tissues. Genes predictive of survival in AN (AN-survival genes) were found to be enriched in the differential gene-gene correlation gene set indicating that they directly participate in the process of tumorigenesis. Additionally the AN-survival genes were mostly not predictive after tumorigenesis in TU tissue and this transition was associated with and could largely be explained by the effect of somatic DNA copy number variation (sCNV) in cis and in trans. The data was consistent with the variance of AN-survival genes being rate-limiting steps in tumorigenesis and this was confirmed using a treatment that promotes HCC tumorigenesis that selectively altered AN-survival genes and genes differentially correlated between AN and TU. Conclusions/Significance: This suggests that the process of tumor evolution involves rate-limiting steps related to the background from which the tumor evolved where these were frequently predictive of clinical outcome. Additionally treatments that alter the likelihood of tumorigenesis occurring may act by altering AN-survival genes, suggesting that the process can be manipulated. Further sCNV explains a substantial fraction of tumor specific expression and may therefore be a causal driver of tumor evolution in HCC and perhaps many solid tumor types. © 2011 Lamb et al.published_or_final_versio