Significance Entry of bacteria into host cells critically depends on their proper engulfment by the plasma membrane. So far, actin polymerization has been described as a major driving force in this process. However, our study reveals that the interaction of the bacterial surface lectin LecA with the host cell glycosphingolipid Gb3 is fully sufficient to promote engulfment of Pseudomonas aeruginosa , whereas actin polymerization is dispensable. Hence, the formation of a “lipid zipper” represents a previously unidentified mechanism of bacterial uptake and demonstrates that bacterial pathogens have evolved lipid-based invasion strategies that may function in addition to protein receptor-based ones. Furthermore, by identifying the LecA/Gb3 interaction as the major invasion-promoting factor, our study provides new targets for drugs that may prevent bacterial invasion and dissemination.

Protein trafficking in and out of the nucleus represents a key step in controlling cell fate and function. Here we report the development of a red light-inducible and far-red light-reversible synthetic system for controlling nuclear localization of proteins in mammalian cells and zebrafish. First, we synthetically reconstructed and validated the red light-dependent Arabidopsis phytochrome B nuclear import mediated by phytochrome-interacting factor 3 in a nonplant environment and support current hypotheses on the import mechanism in planta. On the basis of this principle we next regulated nuclear import and activity of target proteins by the spatiotemporal projection of light patterns. A synthetic transcription factor was translocated into the nucleus of mammalian cells and zebrafish to drive transgene expression. These data demonstrate the first in vivo application of a plant phytochrome-based optogenetic tool in vertebrates and expand the repertoire of available light-regulated molecular devices.

Pseudomonas 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.

BackgroundFruiting body lectins have been proposed to act as effector proteins in the defense of fungi against parasites and predators. The Marasmius oreades agglutinin (MOA) is a lectin from the fairy ring mushroom with specificity for Galα1-3Gal containing carbohydrates. This lectin is composed of an N-terminal carbohydrate-binding domain and a C-terminal dimerization domain. The dimerization domain of MOA shows in addition calcium-dependent cysteine protease activity, similar to the calpain family.MethodsCell detachment assay, cell viability assay, immunofluorescence, live cell imaging and Western blot using MDCKII cell line.ResultsIn this study, we demonstrate in MDCKII cells that after internalization, MOA protease activity induces profound physiological cellular responses, like cytoskeleton rearrangement, cell detachment and cell death. These changes are preceded by a decrease in FAK phosphorylation and an internalization and degradation of β1-integrin, consistent with a disruption of integrin-dependent cell adhesion signaling. Once internalized, MOA accumulates in late endosomal compartments.ConclusionOur results suggest a possible toxic mechanism of MOA, which consists of disturbing the cell adhesion and the cell viability.General significanceAfter being ingested by a predator, MOA might exert a protective role by diminishing host cell integrity.