Pathogen and Toxin Entry - How Pathogens and Toxins Induce and Harness Endocytotic Mechanisms

Humans have been exposed to a plethora of pathogens (bacteria, viruses) ever since. Infectious diseases are among the leading causes of death worldwide. For example, in 2011, 1.34 million people died of tuberculosis, which is caused by an infection with Mycobacterium tuberculosis. Even more died of an infection by the human immunodeficiency virus (HIV; 1.78 million) or lower respiratory tract infection (3.46 million) [1]. In addition, recurring pandemic outbreaks of the influenza A virus, as in 2009, or an epidemic outbreak of enterohemorrhagic E. coli (EHEC) in Germany in 2011, show quite plainly that pathogens in the 21th century still are a severe health problem, not only in developing countries

Chancen für eine nachhaltige Erholung: IW-Konjunkturprognose 2005

Deutschland steht an einer konjunkturellen Wegmarke. Entweder gelingt es, aus der graduellen Verbesserung der Angebotsbedingungen im Umfeld einer weiterhin stark wachsenden Weltwirtschaft auf einen nachhaltigen Erholungskurs einzuschwenken, oder es droht der Rückfall in die Stagnation. Die Chancen für eine Belebung der Inlandsnachfrage – vor allem durch eine anziehende Investitionstätigkeit – sind günstiger als in den vorangegangenen Jahren. Deshalb steht das Erholungsszenario, dem eine Eintrittswahrscheinlichkeit von 70 Prozent zugrunde liegt, im Mittelpunkt der Konjunkturprognose des Instituts der deutschen Wirtschaft Köln. Das reale Bruttoinlandsprodukt wird demnach im Jahr 2005 mit 2 Prozent leicht stärker zulegen als in diesem Jahr. Die konjunkturelle Belebung erfasst auch den Arbeitsmarkt. Im Vergleich zu diesem Jahr steigt die Anzahl der Erwerbstätigen im Jahr 2005 im Durchschnitt um 180.000 Personen an, die Anzahl der Arbeitslosen sinkt um 150.000 Personen auf gut 4,2 Millionen

Real-time monitoring of cell surface protein arrival with split luciferases

Each cell in a multicellular organism permanently adjusts the concentration of its cell surface proteins. In particular, epithelial cells tightly control the number of carriers, transporters and cell adhesion proteins at their plasma membrane. However, sensitively measuring the cell surface concentration of a particular protein of interest in live cells and in real time represents a considerable challenge. Here, we introduce a novel approach based on split luciferases, which uses one luciferase fragment as a tag on the protein of interest and the second fragment as a supplement to the extracellular medium. Once the protein of interest arrives at the cell surface, the luciferase fragments complement and generate luminescence. We compared the performance of split Gaussia luciferase and split Nanoluciferase by using a system to synchronize biosynthetic trafficking with conditional aggregation domains. The best results were achieved with split Nanoluciferase, for which luminescence increased more than 6000-fold upon recombination. Furthermore, we showed that our approach can separately detect and quantify the arrival of membrane proteins at the apical and basolateral plasma membrane in single polarized epithelial cells by detecting the luminescence signals with a microscope, thus opening novel avenues for characterizing the variations in trafficking in individual epithelial cells

Glycans in autophagy, endocytosis and lysosomal functions

Glycans have been shown to function as versatile molecular signals in cells. This prompted us to look at their roles in endocytosis, endolysosomal system and autophagy. We start by introducing the cell biological aspects of these pathways, the concept of the sugar code, and provide an overview on the role of glycans in the targeting of lysosomal proteins and in lysosomal functions. Moreover, we review evidence on the regulation of endocytosis and autophagy by glycans. Finally, we discuss the emerging concept that cytosolic exposure of luminal glycans, and their detection by endogenous lectins, provides a mechanism for the surveillance of the integrity of the endolysosomal compartments, and serves their eventual repair or disposal

Synchronizing Protein Traffic to the Primary Cilium

The primary cilium is able to maintain a specific protein composition, which is critical for its function as a signaling organelle. Here we introduce a system to synchronize biosynthetic trafficking of ciliary proteins that is based on conditional aggregation domains (CADs). This approach enables to create a wave of ciliary proteins that are transported together, which opens novel avenues for visualizing and studying ciliary import mechanisms. By using somatostatin receptor 3 (SSTR3) as model protein we studied intracellular transport and ciliary import with high temporal and spatial resolution in epithelial Madin-Darby canine kidney (MDCK) cells. This yielded the interesting discovery that SSTR3, besides being transported to the primary cilium, is also targeted to the basolateral plasma membrane. In addition, we found a similar behavior for another ciliary protein, nephrocystin-3 (NPHP3), thus suggesting a potential correlation between ciliary and basolateral trafficking. Furthermore, our CAD-based system allowed assembling a large dataset in which apical and basolateral surface SSTR3 signals could be compared to ciliary SSTR3 signals on a single cell level. This enabled to generate novel complementary evidence for the previously proposed lateral import mechanism of SSTR3 into the cilium along the plasma membrane

Pseudomonas aeruginosa lectin LecB inhibits tissue repair processes by triggering β-catenin degradation

AbstractPseudomonas aeruginosa is an opportunistic pathogen that induces severe lung infections such as ventilator-associated pneumonia and acute lung injury. Under these conditions, the bacterium diminishes epithelial integrity and inhibits tissue repair mechanisms, leading to persistent infections. Understanding the involved bacterial virulence factors and their mode of action is essential for the development of new therapeutic approaches.In our study we discovered a so far unknown effect of the P. aeruginosa lectin LecB on host cell physiology. LecB alone was sufficient to attenuate migration and proliferation of human lung epithelial cells and to induce transcriptional activity of NF-κB. These effects are characteristic of impaired tissue repair. Moreover, we found a strong degradation of β-catenin, which was partially recovered by the proteasome inhibitor lactacystin. In addition, LecB induced loss of cell–cell contacts and reduced expression of the β-catenin targets c-myc and cyclin D1. Blocking of LecB binding to host cell plasma membrane receptors by soluble l-fucose prevented these changes in host cell behavior and signaling, and thereby provides a powerful strategy to suppress LecB function.Our findings suggest that P. aeruginosa employs LecB as a virulence factor to induce β-catenin degradation, which then represses processes that are directly linked to tissue recovery

Lipid Reorganization Induced by Shiga Toxin Clustering on Planar Membranes

The homopentameric B-subunit of bacterial protein Shiga toxin (STxB) binds to the glycolipid Gb3 in plasma membranes, which is the initial step for entering cells by a clathrin-independent mechanism. It has been suggested that protein clustering and lipid reorganization determine toxin uptake into cells. Here, we elucidated the molecular requirements for STxB induced Gb3 clustering and for the proposed lipid reorganization in planar membranes. The influence of binding site III of the B-subunit as well as the Gb3 lipid structure was investigated by means of high resolution methods such as fluorescence and scanning force microscopy. STxB was found to form protein clusters on homogenous 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/cholesterol/Gb3 (65∶30∶5) bilayers. In contrast, membranes composed of DOPC/cholesterol/sphingomyelin/Gb3 (40∶35∶20∶5) phase separate into a liquid ordered and liquid disordered phase. Dependent on the fatty acid composition of Gb3, STxB-Gb3 complexes organize within the liquid ordered phase upon protein binding. Our findings suggest that STxB is capable of forming a new membrane phase that is characterized by lipid compaction. The significance of this finding is discussed in the context of Shiga toxin-induced formation of endocytic membrane invaginations

Keine Rezession in Deutschland trotz hoher Unsicherheit: IW-Konjunkturprognose Herbst 2011

Das Wachstumstempo der deutschen Wirtschaft wird sich merklich verlangsamen. Eine Rezession wird trotz der Verunsicherung infolge des Wiederauflebens der Finanzmarktprobleme nicht erwartet. Das reale BIP wird im Jahr 2011 um 3 Prozent ansteigen. Im Jahr 2012 wird der deutsche Außenhandel nur noch moderat zulegen, und dies wird auch deutlich die Investitionstätigkeit der Unternehmen dämpfen. Der Konsum bleibt wegen der anhaltend guten Arbeitsmarktentwicklung eine Konjunkturstütze. Die deutsche Wirtschaft wird im Jahr 2012 nur noch um knapp 1 ¼ Prozent wachsen. Trotz der konjunkturellen Abschwächung wird es hierzulande im Jahresdurchschnitt 2012 mehr als 41 Millionen Erwerbstätige geben. Die Anzahl der registrierten Arbeitslosen wird im Jahresdurchschnitt 2012 auf rund 2,8 Millionen zurückgehen. Mit einem Defizit von knapp 7 Milliarden Euro und einer Defizitquote von ½ Prozent des BIP ist der Staatshaushalt in Deutschland im Jahr 2012 nahezu ausgeglichen

Solide Dynamik in einem risikobehafteten Umfeld: IW-Konjunkturprognose Frühjahr 2011

Die deutsche Wirtschaft hat die globale Finanzmarkt- und Wirtschaftskrise hinter sich gelassen und ist auf Rekordkurs. Das reale Bruttoinlandsprodukt wird im Jahr 2011 um gut 3 ½ Prozent und im Jahr 2012 um 2 ¼ Prozent zulegen. Dabei kommen die Wachstumsimpulse hauptsächlich aus dem Inland. Der Private Konsum expandiert vor dem Hintergrund der guten Arbeitsmarktentwicklung. Die Arbeitslosigkeit wird im Jahresdurchschnitt 2012 auf 2,6 Millionen Personen zurückgehen. Die Investitionstätigkeit findet auf breiter Ebene statt. Im Gefolge des breit angelegten und kräftigen Aufschwungs kommt auch die Konsolidierung des Staatshaushalts voran. Das Staatsdefizit wird im Jahr 2012 bei ½ Prozent des BIP liegen. Die erwartete solide Entwicklung in Deutschland ist allerdings eingebettet in ein risikobehaftetes globaes Umfeld. Es überwiegen jedoch die positiven Determinanten, sodass die Weltwirtschaft weiterhin robust bleibt

Pseudomonas aeruginosa lectin LecB impairs keratinocyte fitness by abrogating growth factor signalling

Lectins are glycan-binding proteins with no catalytic activity and ubiquitously expressed in nature. Numerous bacteria use lectins to efficiently bind to epithelia, thus facilitating tissue colonisation. Wounded skin is one of the preferred niches for Pseudomonas aeruginosa, which has developed diverse strategies to impair tissue repair processes and promote infection. Here, we analyse the effect of the P. aeruginosa fucose-binding lectin LecB on human keratinocytes and demonstrate that it triggers events in the host, upon binding to fucosylated residues on cell membrane receptors, which extend beyond its role as an adhesion molecule. We found that LecB associates with insulin-like growth factor-1 receptor and dampens its signalling, leading to the arrest of cell cycle. In addition, we describe a novel LecB-triggered mechanism to down-regulate host cell receptors by showing that LecB leads to insulin-like growth factor-1 receptor internalisation and subsequent missorting towards intracellular endosomal compartments, without receptor activation. Overall, these data highlight that LecB is a multitask virulence factor that, through subversion of several host pathways, has a profound impact on keratinocyte proliferation and survival